Cumulative patterns of fire and harvest disturbance: Comparing case studies from Russia and Canada

Written by:

Jocelyne Laflamme, MFC 2019 University of Toronto, Graduate Department of Forestry

Advisors:

Justina Ray Wildlife Conservation Society Canada

University of Toronto, Graduate Department of Forestry

Brendan Rogers, Woods Hole Research Centre

Abstract As fires become more frequent due to climate change, and the footprint of timber

harvesting continues, the cumulative effects of multiple disturbances will become more prevalent across the boreal forest. While emerging literature highlights the ecological consequences of these interactions, such as threatening biodiversity, watershed health and regeneration, there remains little information on their geographic scale. The purpose of this study is to quantify the cumulative impacts of fire and harvest disturbance in two study regions (Saskatchewan, Canada, and Angara, Russia), including both their additive and compounding effects. Study regions were chosen based on high rates of disturbance from harvest and fire, relative to their respective countries. While data were available for harvest and fire in Saskatchewan, and for harvest in Angara, fire polygons needed to be digitized by hand for Angara. To do so, I used a MODIS burned area product to guide the search for fires, and derived the difference Normalized Burned Ratio from Landsat imagery to trace fire perimeters. Of the total study areas, 8% of Saskatchewan and 22% of Angara were impacted by fire, harvest or both, while 0.26% and 2.67%, respectively, were impacted by successive disturbances between 2001-2017. Harvesting increased the total area disturbed by 26% and the areas successively disturbed by 73% in Saskatchewan, and by 14% and 30%, respectively, in Angara. The compounding impacts of successive disturbances may be mitigated by re-evaluating priority regions for firefighting or reducing the flammability of regenerating stands. However, landscape level approaches will be necessary to address the additive impacts of harvest and fire, such as setting maximum disturbance thresholds.

Introduction Boreal forests are increasingly recognized for their globally significant role in

carbon storage and climate regulation (Bradshaw and Warkentin, 2015). The boreal forest is broadly defined as regions north of 50° N latitude with trees at least 5 m tall and a canopy cover greater than 10% (Burton et al. 2010), although shorter trees in the northern boreal may necessitate a lower height threshold (e.g., Montesano et al., 2016). The biome accounts for approximately 32% of global forest cover (Achard et al., 2006) and stores roughly two-thirds of all global forest carbon, the majority of which is stored within thick organic soil layers (Pan et al. 2011; Bradshaw and Warkentin, 2015). These forests provide a myriad of additional ecosystem services such as surface freshwater storage and regulation (Schindler 2001), habitat and biodiversity, air quality, food security, as well as non-timber forest products and recreation (Ruckstuhl et al., 2007). Further, the boreal zone contains almost 50% of the world’s remaining intact forest landscapes (Potapov et al., 2017) and 30% of the planet’s primary forests (FAO 2005). Compared to fragmented and secondary forests, intact forests provide disproportionate benefits for climate regulation, conservation of biodiversity, human health and cultural values (Watson et al., 2018). However, anthropogenic pressures, exacerbated by evolving disturbance regimes caused by climate change, may compromise the ability of the boreal forest to provide these ecosystem services in the future (Gauthier et al., 2015).

Large-scale disturbances are natural phenomena across the boreal landscape and have played a critical role in shaping the forests of today (Burton et al., 2010). Forest fires are a prominent natural disturbance in the boreal forest and can affect up to 10 - 15 million hectares per year (Flannigan et al., 2009). Fire dynamics are primarily driven by weather and ignition sources, as well as fuel volume, structure, and moisture (Hély et al., 2001). With the climate warming two times faster in the boreal region compared to the global average (Soja et al., 2007), and the mean annual temperature having already increased by 1.5° C at these latitudes (Stocker et al., 2013), the impacts of climate change on fire regimes are now evident. Fires are burning an increasing proportion of the boreal forest each year, and at greater intensities (Kasischke and Turetsky, 2006; Ponomarev et al., 2016). These changes are caused by warming surface temperatures (Gillett, 2004), drying conditions (Flannigan et al., 2005), and an increasing number of lightning ignitions (Veraverbeke et al., 2017). The current fire regime has exceeded the natural limits of disturbances from the past 10,000 years (Kelly et al., 2013), and threaten the carbon storage, biodiversity and other ecosystem services provided by the boreal forest (Gauthier et al., 2015).

In southern boreal forests, timber extraction is another prominent agent of disturbance, with over two-thirds of the global boreal forest currently considered to be under management (Gauthier et al., 2015). An estimated 28% has been logged at least once (Burton et al., 2003), with 300 million m3 harvested annually, primarily through

clear-cut, even-aged silvicultural techniques (Burton et al., 2010). The coniferous species that dominate the landscape are used for the production of softwood lumber, pulp and paper (Burton et al., 2003). A cold climate and short growing season contribute to longer harvest rotation periods of 60-100 years (Burton et al., 2010). Therefore, most harvesting today takes place in primary forests rather than in previously harvested stands (Kuuluvainen and Gauthier, 2018), and the frontier of the forest industry continues to progress northwards into intact landscapes (Boucher et al., 2017). For example, a case study from Quebec found that the concentration of logging activities moved from the 49th to the 51st parallel between 1960 and 2010 (Boucher et al., 2017); however, there are economic restraints on how far northward the industry can expand. Regardless, the timber industry substantially alters the forest ecosystem, and even for those jurisdictions, particularly in North America, that have recently designed harvest methods with the intention to emulate fire disturbance, significant differences between managed and unmanaged ecosystems persist (Cyr et al., 2009; Kuuluvainen, 2009). For example, the additional anthropogenic disturbance in the landscape has shifted the age class structure towards a higher prevalence of younger stands (Cyr et al, 2009). Further, harvesting reduces structural diversity and important habitat features such as dead wood (Siitonen 2001). These and other differences can negatively impact biodiversity, the provision of ecosystem services, and resilience of the boreal forest to other disturbances (Bengtsson et al., 2003; Drapeau et al., 2009; Rist and Moen, 2013).

The combined area of boreal forest in Canada and Russia make up 89% of the global total extent (Wulder et al., 2007). Thus, investigating the impacts of disturbances in the boreal forest of both countries can provide a thorough understanding of the threats to the current state of this ecosystem. In both Canada and Russia, clear-cutting is the most prominent method for harvest in the boreal forests (Burton et al., 2003). In both regions, over 90% of forested land is public (Whiteman et al., 2015), and the government issues leases to private companies who then harvest the land, abiding by regional policies (Bernier et al., 2017). The policies differ between countries in both requirements for sustainable management, as well as levels of enforcement (Tittler et al., 2001; Papilla, 2012). Since the collapse of the Soviet Union, multiple shifts in the structure of governance paired with cuts to funding for forest management departments have substantially hindered Russia’s ability to ensure the sustainable management of their forests (Papilla, 2012). Additional differences in fire regimes also exist across the two continents (de Groot et al., 2013; Rogers et al., 2015). While fires in Russia tend to be more frequent, they also tend to be lower-severity surface fire, with low to moderate tree mortality (Rogers et al., 2015). In contrast, fires across boreal North America are typically high-severity crown fires and stand-replacing (Rogers et al., 2015). However, under the influence of climate change, high-intensity crown fires are becoming increasingly common in Russia (Shvidenko and Schepaschenko, 2013).

As area burned increases due to climate change (Kasischke and Turetsky, 2006), and industrial logging continues to impact the landscape (Kuuluvainen and Gauthier, 2018), the combined effects of these two disturbances will become increasingly important to consider in a management context. While the forests of today have evolved to withstand historical regimes of natural disturbance, the cumulative impacts of disturbance can pose a substantial threat (Trumbore et al., 2015). For example, woodland caribou (Rangifer tarandus caribou) are dependent on large areas of mature forests (Lesmerises et al., 2013), and therefore the additive impacts of fire and harvest across the landscape can have substantial impacts on population persistence (Wittmer et al., 2007). Canada’s federal recovery strategy even defines a maximum disturbance threshold of 35% within population ranges (Environment Canada, 2012). Quantifying the total area disturbed (anthropogenic plus fire) across the landscape (< 40 years old) is therefore important for understanding the degree of their impacts across the landscape, and implications for sensitive wildlife.

With the increasing prevalence of fire across the landscape and continued timber extraction, a greater proportion of the landscape will experience both fire and harvest, with reduced time intervals between disturbances. Krawchuk and Cumming (2009) found that across central-eastern Alberta, fire initiation increased in regions disturbed by harvest, with an opposite effect in those disturbed by fire, suggesting harvest might increase the probability of fire. Further, large piles of slash in cutblocks after harvest dry more quickly than they would if sheltered by a canopy, which can lead to a greater probability of subsequent burning by increasing the fire hazard of the landscape (Kukavskaya et al., 2013). Harvest and fire can also overlap deliberately, when valuable timber areas are burned, and the forests are salvage logged in an attempt to alleviate the economic losses (Nappi et al., 2004). In Russia, anecdotal evidence suggests fires may be intentionally set in undisturbed forest to allow salvage logging, which has lower stumpage fees (Goldammer, 2003). However, additional studies on the spatial relationships between harvest and fire are necessary to validate these claims. If harvest does indeed increase the probability of fire, this implies timber extraction not only impacts the forest directly harvested but also jeopardizes surrounding forest due to the impacts of fire.

Regardless of being intentional or by chance, successive disturbances within short time intervals can have compounding effects, potentially perturbing the ecosystem outside its natural range of variability and catalyzing a shift to an alternative stable state (Turner, 2010). In Canada and Alaska, recurring fires after short intervals promote the regeneration of deciduous species, shifting the dominance from previously coniferous stands to deciduous-dominated (Johnstone and Chapin, 2006; Johnstone et al., 2016). In the boreal forests of Quebec, subsequent burning of harvested stands have converted spruce-dominated forests to parkland vegetated primarily by lichens and shrubs, while this effect was not observed in regions affected by only harvest or fire

(Payette and Delwaide, 2003). Despite differences in historic fire regimes, similar phenomena have been reported in the Russian boreal forest, where postharvest fires have resulted in a transformation from forest to steppe ecosystems due to inadequate regeneration (Kukavskaya et al., 2016). These ecosystem-level shifts have inevitable implications for carbon balances, biodiversity, and the provision of ecosystem services (Turner, 2010), yet the extent to which such successive disturbances occur across the landscape has yet to be investigated.

The purpose of this paper is to evaluate the cumulative impacts of fire and harvest disturbances across the boreal forests of Canada and Russia using one case study in each, to understand the geographic scale of their ecological effects and develop a baseline to be referenced to determine whether these interactions increase in prevalence into the future. The specific objectives are to quantify and compare (1) the independent and additive area disturbed by fire and harvest; (2) the area affected by multiple successive disturbances and determine their sequences; and (3) investigate and compare the spatial relationships between harvest and fire in each region.

Methods

Study Regions I selected a case study region from each country to investigate the independent and cumulative patterns of harvest and fire across the boreal forest landscapes in Russia and Canada (Figure 1). To do so I selected regions that experience high disturbance rates and have available data. In Canada, Saskatchewan has the highest relative rate of forest cover loss in the country (GFW 2018). In Russia, Angara was identified by Achard et al., (2006) as a hotspot for forest cover change in a study spanning Eurasia.

The dominant drivers of disturbance in Saskatchewan and Angara are fire and harvest (Achard et al., 2006; GFW, 2018). The Saskatchewan study region was further narrowed to the Boreal Plains, where most commercial harvesting occurs. Both study regions occur near the southern end of the boreal forest and experience continental climates (Kukavskaya et al., 2013; Environment Canada, 2018). Saskatchewan forests are typically dominated by black spruce (Picea mariana) and jack pine (Pinus banksiana), with smaller proportions of larch (Larix laricina), paper birch (Betula papyrifera), and trembling aspen (Populus tremuloides). The mean annual air temperature for the region is 0.2° C, with 468 mm of precipitation annually (Environment Canada, 2018). The Angara region exists in the southern boreal forest and straddles the Angara river, located within Krasnoyarsk krai, Central Siberia. The region consists of upland, hilly terrain on either side of the river, and is dominated by the Scots pine (Pinus sylvestris), with a smaller proportion of spruce (Picea sp.) and larch (Larix gmelinii, L. sibrica) (Kukavskaya et al., 2013). Annual precipitation is slightly less than

Saskatchewan, at 360 mm, and average temperatures are 0.2° C (Kukavskaya et al., 2013). Figure 1. The global distribution of the boreal forest biome (Potapov et al. 2008; Brandt, 2009), and the location of the two case studies outline in red, Saskatchewan (left) and Angara (right).

Data Collection I calculated the extent of the cumulative impacts of fire and timber harvest using annual spatial polygon layers of the two disturbances across the study regions from 2001-2017 (Figure 2). I retrieved Saskatchewan fire data from the National Burned Area Composite created by the Canadian Forest Service National Fire Database (CFS 2019), and the province’s Ministry of Environment Forest Service provided harvest polygons. The Sukachev Institute of Forests provided the harvest polygons for Angara, and only included clear-cut regions as they were created using satellite imagery. I then used ArcMap to manually digitize the fire polygons for the Angara region, using spatial imagery downloaded from Google Earth Engine. The MODIS burned area product (Giglio et al., 2015) was used to locate areas where fires may have occurred. Then, to provide better resolution, I calculated the normalized burn ratio (NBR) and differenced normalized burn ratio (dNBR) using 30 m x 30 m Landsat imagery. I then exported the

NBR, dNBR, and true colour images from Google Earth Engine, and used this to identify and trace fires across the landscape, guided by the MODIS burned area product fire locations.

Figure 2. The total area disturbed by fire and timber harvest from 2001-2017 in the boreal forests of Saskatchewan, Canada (left) and Angara, Russia (right).

Additive Impacts To analyze the data spatially, I imported the polygons from ArcMap into RStudio. In order to accurately calculate areas, I projected the data using the Canada Albers Equal Area Conic and Albers Equal Area Russia projections for Saskatchewan and Angara, respectively. I calculated the average size and frequency of fires and harvest blocks across each study region and determined whether size, frequency, and the annual area affected by the different disturbances differed significantly between Saskatchewan and Angara, using t-tests, and Wilcoxon tests dependent on whether the data met assumptions regarding normal distribution and homogeneity of variances.

Successive Disturbances To determine the compounding impacts of harvest and fire, I calculated the area

of overlap of the two types of disturbance, and where fires burned the same area in multiple years. I determined the total area impacted by harvest, fire, and both disturbances, as well as the sequence of which disturbance occurred first. As the data were annual, I could not determine the sequence of disturbances when both fire and harvest occurred in the same year.

kilometers kilometers

Spatial Relationships I then changed the projections to the Azimuthal Equidistant Projection centered

on each study area to ensure distances were accurately calculated while I investigated whether harvest and fire were spatially correlated in either study region. I calculated the distance from the centroid of each fire polygon to the closest harvest cutblock in the previous five years. Finally, I divided the number of fires within every kilometer by the total area within that distance of the cutblocks to determine the number of fires per 100 000 hectares at each distance range.

Results Additive Impacts

The total area of the study regions was 17.8 Mha and 13.9 Mha for Saskatchewan and Angara, respectively, of which 1.5 Mha (8%) and 3.1 Mha (22%) was affected by fire or harvest between 2001 and 2017 (Table 1). Fire was the primary disturbance agent, accounting for 80% and 90% of the total disturbed area. Mean fire size was more than twice as large in Angara compared to Saskatchewan (3030 ± 535 ha and 6333 ± 990 ha, respectively; p = 0.005), yet frequency was not significantly different between case studies (p=0.57), leading to substantially greater annual burned area (p = 0.02) in Angara relative to Saskatchewan. Harvesting showed an opposite trend, as cutblocks in Saskatchewan were almost twice as large as those in Angara (47 ha and 27 ha, respectively; p<0.0001). However, the annual number of cutblocks was greater in Angara than Saskatchewan (6 333 and 3 030 ha, respectively; p=0.005), resulting in relatively equal annual harvested area (23 296 ha and 18153 ha, respectively; p=0.43). In Angara, annual rates of disturbance were 0.17% year-1 for harvest, and 1.18% for fire, thus harvesting resulted in a 14% increase in the annual area disturbed relative to fire alone. In the Saskatchewan study region, harvesting affected an average of 0.10% year-1, and fire an average of 0.39% year-1, thus harvesting increased annual area disturbed by 26%.

Successive Disturbances Multiple successive disturbances were 10 times more likely in Angara (373 224 ha, 3%) relative to Saskatchewan (47 487 ha, 0.3%; Table 2). Successive fire events were much more prevalent in Angara, affecting 288 527 ha (2.1% of study area), compared to areas disturbed by both fire and harvest (84 697 ha, 0.6% of study area), but the addition of harvest increased the total area impacted by successive disturbances by 30%. In Saskatchewan, multiple fire events affected a similar area as successive harvest and fire events (27 429 ha, 0.15% of study area, and 20 058 ha, 0.11%, respectively), thus harvest increased the total area disturbed successively by 73%. The maximum number of successive fire events within the 17-year study period was three for Saskatchewan, while in Angara some areas burned up to five times.

However, most areas affected by multiple fires in both Angara and Saskatchewan burned only twice (73% and 99% of area affected by multiple fire events, respectively). The occurrence of fire after harvesting increased in likelihood with time after fire in Saskatchewan, while in Angara it dropped substantially after 10 years. Table 1. The mean (± standard error) size, frequency, and area disturbed, as well as cumulative impacted area of fire and harvest in the Saskatchewan (Canada) and Angara (Russia) study areas. The values are compared statistically between the two study regions.

Table 2. The area affected by multiple successive harvest and fire disturbances in the Saskatchewan, Canada and Angara, Russia study areas.

Spatial Relationships In both Angara and Saskatchewan, fire frequency was higher closer to cutblocks (Figure 3). Fire frequency was six times greater within the first kilometer from harvest compared to a baseline of 10-25 kilometers from harvest in both Saskatchewan and Angara. In Angara, 18%, 33% and 55% of fires occurred within two, five and 10 km from the nearest cutblock, and in Saskatchewan, these figures were 7%, 17% and 32%, respectively.

Figure 3. The relationship between fire frequency (per 100 000 hectares) and distance from the nearest harvest cutblock in the previous five years for Saskatchewan, Canada (left) and Angara, Russia (right).

Discussion The purpose of this study was to quantify the total area affected by fire and

harvest between 2001-2017 in the Saskatchewan and Angara study regions. Fire was a more prevalent disturbance than timber harvest in both Saskatchewan and Angara, accounting for the majority of total area disturbed and area disturbed multiple times. Harvest resulted in a greater increase in both the total area disturbed and the area disturbed multiple times in Saskatchewan compared to Angara, and therefore has a larger relative influence. However, the geographic scale of the cumulative impacts of harvest and fire were greater in Angara compared to Saskatchewan, with additive impacts affecting three times more, and compounding impacts affecting ten times more of the former study region. The cumulative ecological effects of these disturbances will likely be of correspondingly greater magnitude.

Additive Impacts The additive impacts of fire and harvest were greater in Angara relative to

Saskatchewan, yet the relative increase in disturbed area caused by the addition of harvest to the study area were moderate in both regions compared to the results from a study in central Quebec, where harvesting was found to increase annual area disturbed by 74% between 1940 and 2009 (Boucher et al., 2017). However, Boucher et al. (2017) only included forested area, rather than total area, which may have increased the proportional results since only forests are harvested yet other ecosystem types can burn, and all ecosystem types were included in this study. The differences between continents may be explained in part by the variation in fire frequency across regions, as a substantially larger portion of Angara burns annually (1.18% year-1) compared to Saskatchewan (0.17% year-1) and Quebec (0.34% year-1; Boucher et al., 2017). This supports nation-wide trends in annual burned area, as across Russia an average of 1.89% of forested area burns per year compared to 0.56% in Canada (de Groot et al., 2013). The low values from this study compared to others is likely caused by calculating the proportion burned with the total study area rather than exclusively the forested area.

The spatial relationship between harvest and fire suggests that harvest may not only increase additive disturbed area directly, but also indirectly through its correlation with fire frequency. Saskatchewan’s State of the Forest Report (Ministry of Environment, 2019) states, based on anecdotal evidence, that the creation of roads leads to increased recreational use of surrounding forests. The heightened accessibility of forests after the creation of roads for harvest likely explains the increased fire frequency in close proximity to harvested stands (Kukavskaya et al., 2013). In the boreal plains of Saskatchewan, 65% of fire ignitions were anthropogenic (Parisien et al., 2004), and in Russia, 86% are estimated to be human-caused (Shvidenko and Nilsson, 2000). In Canada, despite the large proportion of anthropogenic ignitions, they account for only a small proportion of total burned area (Stocks et al., 2002). In contrast, fires ignited within harvests in Siberia spread into surrounding primary forests and can burn up to 12 times more area than what was initially logged (Ponomarev, 2008). Regardless of the cause, increased fire ignition near harvesting means that logging affects the additive area disturbed not only directly, where timber is harvested, but also indirectly, by increasing the probability of fire disturbance in the surrounding forest.

Compounding Impacts

Repeat fire events were the most prominent combination of successive disturbance events in both Saskatchewan and Angara, with the majority of these events involving two successive fires, yet the maximum number of recurrent fires was much higher in Angara (up to five times). These results are similar to those from the nearby region of Zaibakal, where 69% of repeatedly disturbed forests burned only twice, with some regions burning up to six times over a 20-year study period (Kukavskaya et al.,

2016). The results from Saskatchewan are also quite similar to other regions from the same continent, such as the southern boreal forests of Quebec, where repeated fires on the same region occurred a maximum of three times and represented a very small portion of total burned area (Heon et al., 2014).

Characteristic differences in fire severity between continents help explain why repeated burns are more prevalent in the Angara case study compared to Saskatchewan. The high-intensity, stand-replacing fires characteristic of North American boreal forests (Wooster and Zhang, 2004; Rogers et al., 2015) can consume up to 40% of surface fuels (Amiro et al., 2008), resulting in fuel-dependent limitations for subsequent fires (Heon et al., 2014). In Russia, fires are typically lower-intensity surface fires (Wooster and Zhang, 2004; Rogers et al., 2015), which reduce surface fuel loads by only 15-20% and may not result in tree mortality (Kukavskaya et al., 2016). The remaining organic materials provide fuel for successive fires, creating a higher probability that a forest burned once will burn again in the next decade (Kukavskaya et al., 2016). Dominant tree species within the forest can also affect the likelihood of burning repeatedly. For example Kukavskaya et al., (2016) found that pine stands were more likely to burn multiple times than larch dominated stands. However, higher-intensity and crown fires are becoming more common through Siberia as the fire regime responds to changing climate (Ivanova et al., 2010). Therefore, although this may lead to fuel-mediated fire limitation, fires may also increase in severity.

The area affected by both harvest and fire within the study period was four times higher in Angara compared to Saskatchewan. Salvage logging likely accounts for the areas harvested after fire events, which made up 3% of all harvested area in Saskatchewan and 8% in Angara. Salvage logging may be more prevalent in Angara compared to Saskatchewan due to the reduced stumpage fees for salvage logging in Russia, therefore incentivising this type of logging (Goldammer, 2003). Almost all salvage logging in Saskatchewan occurred within five years, which is likely attributed to provincial policy that requires any salvage logging to occur within two years of the initial disturbance (Government of Saskatchewan, 2017). The high mortality rates of Saskatchewan’s crown fires mean that the dead trees quickly begin to rot, losing commercial value if not harvested promptly (Government of Saskatchewan, 2017). In contrast, high survival after surface fires in Angara reduces the chances of rotting, such that the time between fire and salvage logging does not need to be constrained.

Post-harvest fires affected four times more of the total harvested area in Angara than Saskatchewan, and the relatively high frequency of post-harvest burning is common across southern Siberia (Kukavskaya et al., 2016). For example, in the nearby region of Zabaikal, 50% of harvested stand that were artificially regenerated through planting ended up burning between 2008 and 2015 (Kukavskaya et al., 2016). Illegal logging is prevalent across Russia and is estimated to account for at least 20% of timber harvested in the Russian Far East and Siberia (World Bank, 2011). Anecdotal

evidence suggests that forests may be intentionally burned after harvest to conceal illegal overharvesting, which may explain, in part, the prevalence of post-harvest fires in this study region (Goldammer, 2003). Another possible contributing factor is the large quantity of slash left on site (up to 135 t ha-). Slash loads are typically 180 - 800% greater than fuel loads in unlogged stands and quickly dry with no canopy to shelter them from the sun, increasing fire hazard (Kukavsakay et al., 2013). In Saskatchewan, provincial policy requires slash to be burned, mulched, spread across the site, or a combination of these techniques, within two years of harvest to reduce fire hazard (Government of Saskatchewan, 2017). These compulsory slash management techniques may explain why the probability of burning increases with time since fire in Saskatchewan and provide an example of how post-harvest burning could be mitigated in Angara.

Ecological Effects of Cumulative Disturbance

The addition of harvest to a landscape already exposed to prevalent natural disturbances can substantially shift the landscape-level forest structure (Cyr et al., 2009). Increased disturbance progressively shifts the age class structure of the forest, proliferating the abundance of young stands, with forest stands over 100 years old becoming increasingly rare (Cyr et al. 2009; Boucher et al., 2014). The influence of industrial logging on this shift is more pronounced than that of fire because the latter is stochastic, thus impacting forests of a wide age range (Van Wagner, 1978), whereas harvesting exclusively targets mature stands of high biomass (Boucher et al., 2017). A case study from western Quebec, for example, found that 47% of the landscape was comprised of young stands (under 40 years old) after the introduction of industrial logging, while this figure rarely exceeded 30-38% under the natural disturbance regime (Cyr et al., 2009). Similar results have been found in northern Sweden, where the prevalence of stands 0-50 years old was eight times greater in 2003 relative to pre-industrial times (Hellberg et al., 2009). Thus, this phenomenon appears to be common across the boreal forest.

The increasing prevalence of young stands across the boreal forest landscape could have significant consequences for wildlife (Berg et al., 1994), although current knowledge of biodiversity dependent on old stands within the boreal forest remains limited (Cyr et al., 2009). However, the near-exclusion of old growth stands within the boreal forests of Fennoscandia due to intensive forestry practices provides a cautionary example (Berg et al., 1994). An evaluation in the 1990s found that over half of the IUCN red-listed species were under threat due to the increasing scarcity of old growth stands caused by wide-spread intensive forestry practices (Berg et al., 1994). For example, Marikainen et al. (2000) reported that 78% of saproxylic beetles had greater abundance in old growth stands, even compared to mature managed stands, likely due to their dependence on dead wood abundance. Epiphytic lichens, dependent on large, old

branches, are six times less abundant by mass in managed stands compared to older, natural ones (Esseen et al., 1996). Caribou, a wide-ranging species requiring requiring large areas of mature forests, experience greater rates of predation in disturbed forests with increased habitat suitability to other ungulate prey (Courtois et al., 2007; Festa-Bianchat et al., 2011). In 2002, due to declining population trends across Canada, woodland caribou were listed as threatened (COSEWIC, 2002), providing an example of how the cumulative impacts of fire and harvest disturbances across the landscape can threaten biodiversity.

In addition to the effects of cumulative disturbance on age structure and biodiversity, watershed health can also be compromised (Zhang and Wei, 2012). Forest disturbance by both fire and harvest impacts watershed hydrology by altering evapotranspiration, infiltration and water flow (Putz et al., 2003). The removal or dieback of trees increases streamflow by reducing both evapotranspiration and interception of rainfall (Putz et al., 2003). The disruption of soils can lead to soil erosion, with sediment exports up to seven times higher after fire (Prepas et al. 2003), and over 1900 times greater after harvest (Kreutzweiser and Capell, 2001). Furthermore, fire and harvest disturbance increase mobile nitrogen (Lamontagne et al., 2000) and phosphorous (Carignan et al,. 2000) within the soils, which in turn impacts aquatic systems downstream (Putz et al., 2003). For example, nitrogen and phosphorus concentrations in lakes of the Boreal Plains are closely associated with the production of toxins by cyanobacteria and phytoplankton abundance (Prepas et al., 2001; Putz et al., 2003). These changes can lead to irreversible damage to the watershed and affect the provision of ecosystem services from the aquatic systems (Zhang and Wei, 2012). In smaller watersheds, disturbance of roughly 20% of the landscape can result in such hydrological effects, while this threshold is more variable in larger systems (Zhang and Wei, 2012). Ultimately, the cumulative area disturbed, over periods of 10-20 years, drives the magnitude of resulting effects on the watershed (Putz et al., 2003).

While the additive disturbed area has important implications for age class structure, wildlife and hydrology, compounding effects of successive disturbances can completely shift the ecosystem to an alternative stable state (Turner, 2010). The impacts of successive disturbances are dependent on the time between them (Turner, 2010), as newly established trees must reach sexual maturity before the second disturbance event in order to adequately re-establish (Johnstone and Chapin, 2006). While trees in the boreal forest are adapted to return intervals of the historic fire regime and typical rotation ages of industrial forestry are suited to facilitate regeneration, successive events of fire and harvest over short time periods can be detrimental to the stand’s regenerative capacity (Johnstone and Chapin, 2006; Kukavskaya et al., 2013). The time period of this study was 17 years, representing the maximum possible time between successive disturbance events reported, and Johnstone and Chapin (2006) found that recurrent disturbances up to 30 years apart can substantially impact

regeneration. Therefore, the forest regions affected by multiple disturbances within the time period of this study are likely at risk of inadequate regeneration, and a potential shift to a different ecosystem state. In Angara, regions affected by multiple disturbances are quite substantial, affecting almost as much area as harvest.

Studies from across the globe have shown that repeated fires in forest ecosystems can have profound ecological impacts (Cheng et al., 2013, Johnstone et al., 2013, Kukavskaya et al., 2016). Successive fires can reduce both nitrogen and carbon stocks within the ecosystem by up to 68% and 84%, respectively (Cheng et al., 2013). In Alaska and central Canada, short return intervals between fire events facilitate the regeneration of deciduously dominated stands in previously coniferous forests (Johnstone and Chapin, 2004; Johnstone et al., 2016). Successive burns in central Siberia can reduce organic matter on the forest floor and within the soil by 90-98%, leaving few nutrients to support regeneration (Kukavskaya et al., 2016). In the absence of adequate regeneration in repeatedly burned sites of Zabaikal, forested landscapes have shifted to steppe or grassland ecosystems (Kukavskaya et al., 2016). Forests are more susceptible to these observed ecosystem shifts in both North America and Russia on dry sites, whereas stands with high moisture are more robust to these changes (Johnstone and Chapin, 2004; Kukavskaya et al., 2016). Both the intensity and frequency of fires will affect the impact of these disturbances on regeneration and are expected to increase with climate change (Johnstone et al., 2016), yet further research will be necessary to understand at what point the stability of the forest ecosystem is put at risk.

The compounding effects of fire and harvest on the same forest stand have ecological consequences similar to those of repeated fires (Kukavskaya et al., 2013; Boucher et al., 2017). Kuvaskaya et al. (2013) found that in southern Siberia, sites disturbed by both logging and fire had 75 to 97% less regeneration compared to those that experienced only one of the two disturbances, often converting drier sites from forest to grassland. Boucher et al. (2017) found that in Quebec, forested areas impacted by either repeated fires or successive fire and logging regenerated as sparse, low-density forests. In addition to the consequences for regeneration, post-harvest burning can actually result in greater emissions than fires in unlogged stands (Kukavskaya et al., 2013). In Siberia, large quantities of slash left after harvest can results in 5-6 times greater carbon emissions compared the fires in unharvested forests (Kukavskaya et al., 2013). Dieleman et al. (under review) also found that harvesting impacted combustion rates of subsequent fires, exceeding those of fire-origin stands after 10 years. Therefore, the occurrence of successive fire and harvest events should be minimized to mitigate carbon emissions and impacts on ecosystem stability.

The results from this study found that both the additive and compounding impacts of harvest and fire are more prevalent in Angara than Saskatchewan, and therefore may pose greater ecological risks. For example, the area affected by

successive disturbances in Angara was almost equivalent to the total area harvested during the same time period, and thus represents a substantial portion of the forest that may experience inadequate levels of regeneration.

Management Implications The increasing size, frequency and severity of fires throughout the boreal forest will have substantial implications for forest management, if the ecological integrity and ecosystem services of these forests are to be preserved. While sustainable forest management historically focused exclusively on the constant supply of timber, the definition now includes the full range of services forests provide (Toman and Ashton, 1996). The expected increases in cumulative area disturbed threaten both biodiversity (Berg et al, 1994) and watershed health (Zhang and Wei, 2012), while increased compounding impacts of disturbance threaten the stability of the forest state itself (Kukavskaya et al., 2013; Boucher et al., 2017). Therefore, it’s becoming increasingly important for forest managers to consider the interactions of harvest and fire, and modify their practices to ensure sustainability.

Fire Management Forest managers can mitigate the cumulative and compounding effects of

disturbances through fire suppression or modifying harvest practices. Both Canada and Russia have long histories of forest fire management, but their efficacy will likely become compromised in the next several decades in the face of a changing climate (Flannigan et al., 2009). While Russia had the largest national system of fire management in the 1990s (Stocks and Connard, 2000), the collapse of the Soviet Union resulted in substantial reductions in funding and restructuring of forest management responsibilities have left them ultimately dysfunctional (Goldammer, 2003). Canadian provinces are recognized internationally for their fire management efforts, but resources will become increasingly constrained with lengthier and more intensive fire seasons (Flannigan et al., 2009). Currently, fire management agencies efficiently extinguish 97% of fires under 200 ha, while the 3% that escape initial attack account for 97% of burned area (Stocks et al., 2002). Wotton et al., (2005) found that the frequency of fires escaping initial attack will have a greater proportional increase than that of fire frequency alone, exposing the inability of their current strategy to manage future fire regimes. Further, funding and other resources would have to increase by 100-125% to maintain current efficacy of fire suppression (Wotton and Stocks, 2006). While fire management agencies may not be successful in preventing predicted increases in burned area, they may be able to reduce the compounding impacts of harvest and fire by prioritizing areas that have recently been disturbed. These areas have previously been assumed to be fire breaks, as young stands have historically been unlikely to burn (Johnstone et al., 2016). However, younger forests are burning more frequently due to

the changes in fire regimes (Johnstone et al., 2016), and prioritizing these regions in regard to fire suppression could reduce the geographic scale of regions experiencing diminished regeneration.

Stand-Level Recommendations

The compounding impacts of successive disturbance on regeneration will likely have the greatest implications for forest management, as adequate forest renewal is essential for sustainability. In both Saskatchewan and Angara, the company that harvests the forest is responsible for its regeneration (Forest Code of the Russian Federation, 2006; Government of Saskatchewan, 2016). Therefore, post-harvest burning that requires subsequent artificial regeneration for sufficient renewal for sufficient renewal, would be the financial responsibility of forest industry. The increased prevalence of such regions and their associated financial costs will encourage forest managers to find strategies that prevent these successive disturbances or ameliorate their impacts on regeneration.

Controlling the extent of salvage logging after fires is the most direct way to reduce the area of land impacted by both fire and harvest. Although salvage logging may be necessary to ameliorate economic losses caused by fires, certain measures can be taken to reduce their ecological impact, such as deliberately protecting regions of high regeneration, and retaining live trees to maintain a seed source (Cooke et al., 2019). In regard to regions that burn after harvest, there are several management strategies that may reduce the flammability of regenerating stands. Especially in Angara, where large quantities of slash are currently left on site after harvest, spreading, burning, and/or mulching this excess wood, as mandated in Saskatchewan, would likely reduce fire probability (Kukavskaya et al., 2013). Another management alternative for reducing fire probability after harvest is by facilitating the growth of deciduous species within coniferous stands (Astrup et al., 2018). Coniferous regeneration is facilitated across Canada through artificial regeneration, with pesticides such as glyphosate commonly used to suppress competing deciduous species; yet, coniferous dominated forest are 3-5 times more likely to burn than deciduous stands (Bernier et al., 2016). Girardin et al. (2015) estimated that increasing deciduous cover across the southern boreal forests by even 0.2% could mitigate predicted increases in burned area. Artificial regeneration already takes place in both Saskatchewan (Government of Saskatchewan, 2016) and southern Siberia (Kukavskaya et al., 2013), so increased deciduous cover could be achieved by planting stands of mixed species.

Landscape-Level Recommendations

While some compounding impacts of harvest and fire can be addressed at the stand-level, ensuring sustainability will also require a landscape-level approach. Limiting the cumulative area affected by disturbance to a certain threshold is one method of

restricting the impacts on biodiversity and watershed health. For example, Environment Canada (2012) suggests a maximum cumulative disturbance threshold of 35% (forests and burned areas < 40 years) in its identification of critical habitat for boreal caribou. There is also substantial literature investigating disturbance thresholds to safeguard watershed health, often referred to as equivalent clearcut area (Zhang and Wei, 2012). Saskatchewan’s Ministry of Environment mentions and monitors equivalent clearcut area in relation to forest management, based on this literature (Government of Saskatchewan, 2019). However, disturbance thresholds for watershed management exists at the scale of specific watersheds, while those for caribou conservation would require larger, landscape level approaches. As these issues become more prominent with heightened fire regimes, it will be increasingly important to integrate cumulative disturbance thresholds at different scales. In addition, forest management agencies will have to alter their management practices based on these thresholds, rather than simply monitoring, to effectively mitigate ecological impacts. However, despite broad acceptance of ecological limits, scientifically-derived thresholds remain unknown in many cases (Zhang and Wei, 2012).

Some forest management strategies may directly address the cumulative impacts of harvest and fire on age class structure and resulting implications for wildlife (Cyr et al., 2009). Burton et al., (1999) suggest using longer rotations and partial cutting to maintain natural age class distributions of the boreal forest, as this would facilitate the dynamics of natural succession, and enhance seral diversity. Partial cutting (Burton et al., 1999) and other smaller-scale silvicultural methods could help retain structural characteristics common in old growth forests, such as snags, large trees, and dead wood (Bergeron et al., 2004), reducing the additive effects of harvesting as burned area increases. Partial harvests have additional benefits relative to clearcuts, as they are less likely to produce sediment runoff, reducing the impact of the disturbance on watershed health (Kreutzweiser and Capell, 2001). Finally, limiting overall harvest and strategically planning roads based on ecological sustainability principles can protect a portion of the forest from the impacts of harvest on forest structure (Burton et al., 1999; Bergeron et al., 2004; Cyr et al., 2009). For example, roads are the primary contributor to increased sediment runoff post-harvest and strategically planning their location to avoid crossing main water channels can reduce the impacts of cumulative disturbances on the health of aquatic systems (Kreutzweiser and Capell, 2001). Cyr et al., (2009) suggested that, in order for the age structure of boreal forests to return to natural variation, these strategies should be applied to at least 40% of the landscape.

Conclusion The purpose of this study was to quantify the area of land impacted by the

cumulative and compounding effects of fire and investigate spatial interactions between the two disturbances. Determining the geographic scale of these impacts is important

for assessing the magnitude of their effects on wildlife, watershed health, and regeneration, as well as providing a baseline to evaluate whether the increase in prevalence over time. The interactions between harvest and fire between 2001 and 2017 were more prevalent in Angara compared to Saskatchewan, but country or biome-wide assessments would be required to determine whether these trends can be generalized across the two countries. Further research could also focus on broader timescales to investigate whether the geographic extent of these interactions have increased over time.

Literature Cited Achard, F., Mollicone, D., Stibig, H. J., Aksenov, D., Laestadius, L., Li, Z., ... &

Yaroshenko, A. (2006). Areas of rapid forest-cover change in boreal Eurasia. Forest Ecology and Management, 237(1-3), 322-334.

Amiro, B. D., Cantin, A., Flannigan, M. D., & De Groot, W. J. (2009). Future emissions from Canadian boreal forest fires. Canadian Journal of Forest Research, 39(2), 383-395.

Astrup, R., Bernier, P. Y., Genet, H., Lutz, D. A., & Bright, R. M. (2018). A sensible climate solution for the boreal forest. Nature Climate Change, 8(1), 11.

Bengtsson, J., Angelstam, P., Elmqvist, T., Emanuelsson, U., Folke, C., Ihse, M., ... & Nyström, M. (2003). Reserves, resilience and dynamic landscapes. AMBIO: A Journal of the Human Environment, 32(6), 389-397.

Berg, Å., Ehnström, B., Gustafsson, L., Hallingbäck, T., Jonsell, M., & Weslien, J. (1994). Threatened plant, animal, and fungus species in Swedish forests: distribution and habitat associations. Conservation biology, 8(3), 718-731.

Bergeron, Y., Flannigan, M., Gauthier, S., Leduc, A., & Lefort, P. (2004). Past, current and future fire frequency in the Canadian boreal forest: implications for sustainable forest management. AMBIO: A Journal of the Human Environment, 33(6), 356-361.

Bernier, P., Gauthier, S., Jean, P. O., Manka, F., Boulanger, Y., Beaudoin, A., & Guindon, L. (2016). Mapping local effects of forest properties on fire risk across Canada. Forests, 7(8), 157.

Bernier, P., Astrup, R., Bright, R., Genet, H., Hurmekoski, E., Kraxner, F., ... & Kurz, W. (2017). How can the circumboreal forest contribute to mitigating climate change? Workshop Meeting Report, International Boreal Forest Research Association. Haparanda, Sweden.

Boucher, Y., Grondin, P., & Auger, I. (2014). Land use history (1840–2005) and physiography as determinants of southern boreal forests. Landscape ecology, 29(3), 437-450.

Boucher, Y., Perrault-Hébert, M., Fournier, R., Drapeau, P., & Auger, I. (2017). Cumulative patterns of logging and fire (1940–2009): consequences on the structure of the eastern Canadian boreal forest. Landscape ecology, 32(2), 361-375.

Bradshaw, C. J., & Warkentin, I. G. (2015). Global estimates of boreal forest carbon stocks and flux. Global and Planetary Change, 128, 24-30.

Brandt, J. P. (2009). The extent of the North American boreal zone. Environmental Reviews, 17, 101-161.

Burton, P. J., Kneeshaw, D. D., & Coates, K. D. (1999). Managing forest harvesting to maintain old growth in boreal and sub-boreal forests. The Forestry Chronicle, 75(4), 623-631.

Burton, P. J., Messier, C., Weetman, G. F., Prepas, E. E., Adamowicz, W. L., & Tittler, R. (2003). The current state of boreal forestry and the drive for change. Towards sustainable management of the boreal forest, 1-40.

Burton, P. J., Bergeron, Y., Bogdanski, B. E., Juday, G. P., Kuuluvainen, T., McAfee, B. J., ... & Gauthier, S. (2010). Sustainability of boreal forests and forestry in a

changing environment (Vol. 25, pp. 249-282). IUFRO (International Union of Forestry Research Organizations) Secretariat.

Canadian Forest Service (CFS). 2019. Canadian National Fire Database – Agency Fire Data. Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre. Edmonton, Alberta. http://cwfis.cfs.nrcan.gc.ca/en_CA/nfdb.

Carignan, R., D'Arcy, P., & Lamontagne, S. (2000). Comparative impacts of fire and forest harvesting on water quality in Boreal Shield lakes. Canadian Journal of Fisheries and Aquatic Sciences, 57(S2), 105-117.

Cheng, C. H., Chen, Y. S., Huang, Y. H., Chiou, C. R., Lin, C. C., & Menyailo, O. V. (2013). Effects of repeated fires on ecosystem C and N stocks along a fire induced forest/grassland gradient. Journal of Geophysical Research: Biogeosciences, 118(1), 215-225.

Cooke, H. A., Morissette, J., Cobb, T., and Reid, D. (2019). Fire and Insects: Managing Naturally Disturbed Forests to Conserve Ecological Values. Wildlife Conservation Society Canada Conservation Report No. 12. Toronto, Ontario, Canada.

COSEWIC. (2002). COSEWIC assessment and update status report on the woodland caribou Rangifer tarandus caribou in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa.

Courtois, R., Ouellet, J. P., Breton, L., Gingras, A., & Dussault, C. (2007). Effects of forest disturbance on density, space use, and mortality of woodland caribou. Ecoscience, 14(4), 491-498.

Cyr, D., Gauthier, S., Bergeron, Y., & Carcaillet, C. (2009). Forest management is driving the eastern North American boreal forest outside its natural range of variability. Frontiers in Ecology and the Environment, 7(10), 519-524.

de Groot, W. J., Cantin, A. S., Flannigan, M. D., Soja, A. J., Gowman, L. M., & Newbery, A. (2013). A comparison of Canadian and Russian boreal forest fire regimes. Forest Ecology and Management, 294, 23-34.

Drapeau, P., Nappi, A., Imbeau, L., & Saint-Germain, M. (2009). Standing deadwood for keystone bird species in the eastern boreal forest: managing for snag dynamics. The Forestry Chronicle, 85(2), 227-234.

Ecosystem Status and Trends Report (ESTR) Secretariat. (2014). Boreal Plains Ecozone: Evidence for Key Findings Summary. Canadian Biodiversity: Ecosystem Status and Trends 2010, Evidence for Key Findings Summary Report No. 12. Canadian Councils of Resource Ministers. Ottawa, ON.

Environment Canada. (2012). Canadian Climate Normals 1981-2010 Station Data. http://climate.weather.gc.ca/climate_normals/results_1981_2010_e.html?stnID=3381&amp;autofwd=1#normals-data

Esseen, P. A., Renhorn, K. E., & Pettersson, R. B. (1996). Epiphytic lichen biomass in managed and old-growth boreal forests: effect of branch quality. Ecological Applications, 6(1), 228-238.

Festa-Bianchet, M., Ray, J. C., Boutin, S., Côté, S. D., & Gunn, A. (2011). Conservation of caribou (Rangifer tarandus) in Canada: an uncertain future. Canadian journal of zoology, 89(5), 419-434.

Flannigan, M. D., Logan, K. A., Amiro, B. D., Skinner, W. R., & Stocks, B. J. (2005). Future area burned in Canada. Climatic change, 72(1-2), 1-16.

Flannigan, M., Stocks, B., Turetsky, M., & Wotton, M. (2009). Impacts of climate change

on fire activity and fire management in the circumboreal forest. Global change biology, 15(3), 549-560.

Food and Agriculture Organization of the United Nations (FAO). (2005). Global Forest Resources Assessment. Forestry Department, Food and Agriculture Organization of the United Nations. Rome, Italy.

Gauthier, S., Bernier, P., Kuuluvainen, T., Shvidenko, A. Z., & Schepaschenko, D. G.

(2015). Boreal forest health and global change. Science, 349(6250), 819-822. Giglio, L., Justice, C., Boschetti, L., Roy, D. (2015). MCD64A1 MODIS/Terra+Aqua

Burned Area Monthly L3 Global 500m SIN Grid V006 [Data set]. NASA EOSDIS Land Processes DAAC. Accessed 2020-01-07 from https://doi.org/10.5067/MODIS/MCD64A1.006

Gillett, N. P., Weaver, A. J., Zwiers, F. W., & Flannigan, M. D. (2004). Detecting the effect of climate change on Canadian forest fires. Geophysical Research Letters, 31(18).

Girardin, M. P., & Terrier, A. (2015). Mitigating risks of future wildfires by management of the forest composition: an analysis of the offsetting potential through boreal Canada. Climatic Change, 130(4), 587-601.

Global Forest Watch. (2018). World Resources Institute. www.globalforestwatch.org. Goldammer, J. G., Sukhinin, A., & Csiszar, I. (2003). The current fire situation in the

Russian Federation: implications for enhancing international and regional cooperation in the UN framework and the global programs on fire monitoring and assessment. Int. Forest Fire News, 32, 13-42.

Government of Saskatchewan. (2017). Forest Management Planning Standard, Saskatchewan Environmental Code (pp. 37 - 40). Regina, Saskatchewan.

Hellberg, E., Josefsson, T., & Östlund, L. (2009). The transformation of a Norway spruce dominated landscape since pre-industrial times in northern Sweden: the influence of modern forest management on forest structure. Silva Fennica, 43(5), 783-797.

Hély, C., Flannigan, M., Bergeron, Y., & McRae, D. (2001). Role of vegetation and weather on fire behavior in the Canadian mixedwood boreal forest using two fire behavior prediction systems. Canadian journal of forest research, 31(3), 430-441.

Ivanova, G. A., Ivanov, V. A., Kukavskaya, E. A., & Soja, A. J. (2010). The frequency of forest fires in Scots pine stands of Tuva, Russia. Environmental Research Letters, 5(1), 015002.

James, A. R., & Stuart-Smith, A. K. (2000). Distribution of caribou and wolves in relation to linear corridors. The Journal of Wildlife Management, 154-159.

Johnstone, J. F., & Chapin, F. S. (2006). Fire interval effects on successional trajectory in boreal forests of northwest Canada. Ecosystems, 9(2), 268-277.

Johnstone, J. F., Allen, C. D., Franklin, J. F., Frelich, L. E., Harvey, B. J., Higuera, P. E., ... & Schoennagel, T. (2016). Changing disturbance regimes, ecological memory, and forest resilience. Frontiers in Ecology and the Environment, 14(7), 369-378.

Kasischke, E. S., & Bruhwiler, L. P. (2002). Emissions of carbon dioxide, carbon monoxide, and methane from boreal forest fires in 1998. Journal of Geophysical Research: Atmospheres, 107(D1), FFR-2.

Kasischke, E. S., & Turetsky, M. R. (2006). Recent changes in the fire regime across

the North American boreal region—Spatial and temporal patterns of burning across Canada and Alaska. Geophysical research letters, 33(9).

Kelly, R., Chipman, M. L., Higuera, P. E., Stefanova, I., Brubaker, L. B., & Hu, F. S. (2013). Recent burning of boreal forests exceeds fire regime limits of the past 10,000 years. Proceedings of the National Academy of Sciences, 110(32), 13055-13060.

Krawchuk, M. A., & Cumming, S. G. (2009). Disturbance history affects lightning fire initiation in the mixedwood boreal forest: observations and simulations. Forest Ecology and Management, 257(7), 1613-1622.

Kreutzweiser, D. P., & Capell, S. S. (2001). Fine sediment deposition in streams after selective forest harvesting without riparian buffers. Canadian Journal of Forest Research, 31(12), 2134-2142.

Kukavskaya, E. A., Buryak, L. V., Ivanova, G. A., Conard, S. G., Kalenskaya, O. P., Zhila, S. V., & McRae, D. J. (2013). Influence of logging on the effects of wildfire in Siberia. Environmental Research Letters, 8(4), 045034.

Kukavskaya, E. A., Buryak, L. V., Shvetsov, E. G., Conard, S. G., & Kalenskaya, O. P. (2016). The impact of increasing fire frequency on forest transformations in southern Siberia. Forest ecology and management, 382, 225-235.

Kuuluvainen, T. (2009). Forest management and biodiversity conservation based on natural ecosystem dynamics in northern Europe: the complexity challenge. AMBIO: A Journal of the Human Environment, 38(6), 309-316.

Kuuluvainen, T., & Gauthier, S. (2018). Young and old forest in the boreal: critical stages of ecosystem dynamics and management under global change. Forest Ecosystems, 5(1), 26.

Lamontagne, S., Carignan, R., D'Arcy, P., Prairie, Y. T., & Paré, D. (2000). Element export in runoff from eastern Canadian Boreal Shield drainage basins following forest harvesting and wildfires. Canadian Journal of Fisheries and Aquatic Sciences, 57(S2), 118-128.

Lesmerises, R., Ouellet, J. P., Dussault, C., & St-Laurent, M. H. (2013). The influence of landscape matrix on isolated patch use by wide-ranging animals: conservation lessons for woodland caribou. Ecology and evolution, 3(9), 2880-2891.

Martikainen, P., Siitonen, J., Punttila, P., Kaila, L., & Rauh, J. (2000). Species richness of Coleoptera in mature managed and old-growth boreal forests in southern Finland. Biological conservation, 94(2), 199-209.

Ministry of Environment. (2019). State of the Forests Report. Government of Saskatchewan, Regina, Saskatchewan.

Montesano, P., Neigh, C., Sexton, J., Feng, M., Channan, S., Ranson, K., & Townshend, J. (2016). Calibration and validation of Landsat tree cover in the taiga− tundra ecotone. Remote Sensing, 8(7), 551.

Nappi, A., Drapeau, P., & Savard, J. P. (2004). Salvage logging after wildfire in the boreal forest: is it becoming a hot issue for wildlife?. The Forestry Chronicle, 80(1), 67-74.

Pan, Y., Birdsey, R.A., Fang, J., Houghton, R., Kauppi, P.E., Kurz, W.A., Phillips, O.L., Shvidenko, A., Lewis, S.L., Canadell, J.G. and Ciais, P., (2011). A large and persistent carbon sink in the world’s forests. Science, 333(6045), pp.988-993.

Pappila, M. (2016). Russian forest regulation and the integration of sustainable forest management. In The Changing Governance of Renewable Natural Resources in Northwest Russia (pp. 73-94). Routledge.

Parisien, M.-A., Hirsch, K.G., Lavoie, S.G., Todd, J.B., Kafka, V. (2004). Saskatchewan fire regime analysis. Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Alberta. Information Report NOR-X-394. 49p.

Payette, S.,& Delwaide, A. (2003). Shift of conifer boreal forest to lichen–heath parkland caused by successive stand disturbances. Ecosystems, 6(6), 540-550.

Ponomarev, E.I. (2008).Geographic conditionality of wildfires and estimation of damages of forests. Les ́ne Prace Badawcze, 69, 109–115.

Ponomarev, E., Kharuk, V., & Ranson, K. (2016). Wildfires dynamics in Siberian larch forests. Forests, 7(6), 125.

Potapov P., Hansen M.C., Stehman S.V., Loveland T.R., Pittman K. 2008. Combining MODIS and Landsat imagery to estimate and map boreal forest cover loss. Remote Sensing of Environment, 112(9), 3708-3719.

Potapov, P., Hansen, M. C., Laestadius, L., Turubanova, S., Yaroshenko, A., Thies, C., ... & Esipova, E. (2017). The last frontiers of wilderness: Tracking loss of intact forest landscapes from 2000 to 2013. Science Advances, 3(1), e1600821.

Prepas, E. E., Pinel-Alloul, B., Planas, D., Méthot, G., Paquet, S., & Reedyk, S. (2001). Forest harvest impacts on water quality and aquatic biota on the Boreal Plain: introduction to the TROLS lake program. Canadian Journal of Fisheries and Aquatic Sciences, 58(2), 421-436.

Putz, G., Burke, J. M., Smith, D. W., Chanasyk, D. S., Prepas, E. E., & Mapfumo, E. (2003). Modelling the effects of boreal forest landscape management upon streamflow and water quality: Basic concepts and considerations. Journal of Environmental Engineering and Science, 2(S1), S87-S101.

Rist, L., & Moen, J. (2013). Sustainability in forest management and a new role for resilience thinking. Forest Ecology and Management, 310, 416-427.

Rogers, B. M., Soja, A. J., Goulden, M. L., & Randerson, J. T. (2015). Influence of tree species on continental differences in boreal fires and climate feedbacks. Nature Geoscience, 8(3), 228.

Ruckstuhl K.E, Johnson E.A and Miyanishi K. 2007. Introduction. The boreal forest and global change. Philosophical Transactions of the Royal Society, 363(1501), 2243-2247.

Schindler, D. W. (2001). The cumulative effects of climate warming and other human stresses on Canadian freshwaters in the new millennium. Canadian Journal of Fisheries and Aquatic Sciences, 58(1), 18-29.

Shvidenko, A. Z., & Nilsson, S. (2000). Extent, distribution, and ecological role of fire in Russian forests. In Fire, climate change, and carbon cycling in the boreal forest (pp. 132-150). Springer, New York, NY.

Shvidenko, A. Z., & Schepaschenko, D. G. (2013). Climate change and wildfires in Russia. Contemporary Problems of Ecology, 6(7), 683-692.

Siitonen, J. (2001). Forest management, coarse woody debris and saproxylic organisms: Fennoscandian boreal forests as an example. Ecological bulletins, 11-41.

Soja, A. J., Tchebakova, N. M., French, N. H., Flannigan, M. D., Shugart, H. H., Stocks, B. J., ... & Stackhouse Jr, P. W. (2007). Climate-induced boreal forest change: predictions versus current observations. Global and Planetary Change, 56(3-4), 274-296.

Stocker, T.F., Qin, D., Plattner, G.-K., Tignor, M.M.B., Allen, S.K., Boschung, J., Nauels, A., Xia, Y., Bex, V., Midgley, P.M., (2013). Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Climate Change 2013: The Physical Sciences Basis. Intergovernmental Panel on Climate Change, Cambridge, UK.

Stocks, B. J., & Conard, S. G. (2000). Forest fire research in North America and Russia: building on past accomplishments to address current and future needs. In Forests and Society: The Role of Research, XXI IUFRO World Congress, Kuala Lumpur, Malaysia (pp. 7-12).

Stocks, B. J., Mason, J. A., Todd, J. B., Bosch, E. M., Wotton, B. M., Amiro, B. D., ... & Skinner, W. R. (2002). Large forest fires in Canada, 1959–1997. Journal of Geophysical Research: Atmospheres, 107(D1), FFR-5.

Tittler, R., Messier, C., & Burton, P. J. (2001). Hierarchical forest management planning and sustainable forest management in the boreal forest. The Forestry Chronicle, 77(6), 998-1005.

Toman, M. A., & Ashton, P. M. S. (1996). Sustainable forest ecosystems and management: a review article. Forest Science, 42(3), 366-377.

Trumbore, S., Brando, P., & Hartmann, H. (2015). Forest health and global change. Science, 349(6250), 814-818.

Turner, M. G. (2010). Disturbance and landscape dynamics in a changing world. Ecology, 91(10), 2833-2849.

Urquizo, N., Bastedo, J., Brydges, T., and Shear, H. 2000. Ecological assessment of the Boreal Shield Ecozone. Environment Canada Rep. ISBN-662-28679-0.

Veraverbeke, S., Rogers, B. M., Goulden, M. L., Jandt, R. R., Miller, C. E., Wiggins, E. B., & Randerson, J. T. (2017). Lightning as a major driver of recent large fire years in North American boreal forests. Nature Climate Change, 7(7), 529.

Watson, J. E., Evans, T., Venter, O., Williams, B., Tulloch, A., Stewart, C., ... & McAlpine, C. (2018). The exceptional value of intact forest ecosystems. Nature ecology & evolution, 2(4), 599.

Whiteman, A., Wickramasinghe, A., & Piña, L. (2015). Global trends in forest ownership, public income and expenditure on forestry and forestry employment. Forest Ecology and Management, 352, 99-108.

Wittmer, H. U., McLellan, B. N., Serrouya, R., & Apps, C. D. (2007). Changes in landscape composition influence the decline of a threatened woodland caribou population. Journal of animal ecology, 76(3), 568-579.

Wooster, M. J., & Zhang, Y. H. (2004). Boreal forest fires burn less intensely in Russia than in North America. Geophysical Research Letters, 31(20).

World Bank. (2011). Sovershenstvovaniye Pravoprimeneniya I Upravleniya v Lesnom Sektore Rossiyskoy Federatsii. Uchebnoye Posobije [Improvement of Law Enforcement and Forest Sector Management of the Russian Federation]. Work Book: Moscow, Russia.

Wotton, M., Logan, K., & McAlpine, R. (2005). Climate change and the future fire

environment in Ontario: fire occurrence and fire management impacts. Climate Change Research Report-Ontario Forest Research Institute, (CCRR-01).

Wotton, B. M., & Stocks, B. J. (2006). Fire management in Canada: vulnerability and risk trends. Canadian Wildland Fire Strategy: Background Synthesis, Analysis, and Perspectives’.(Eds K Hirsch, P Fuglem) pp, 49-55.

Wulder, M. A., Campbell, C., White, J. C., Flannigan, M., & Campbell, I. D. (2007). National circumstances in the international circumboreal community. The Forestry Chronicle, 83(4), 539-556.

Zhang, M., & Wei, X. (2012). The effects of cumulative forest disturbance on streamflow in a large watershed in the central interior of British Columbia, Canada. Hydrology and earth system sciences, 16(7), 2021-2034.