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Demography, Phenology, and Factors Inf luencing Reproduction of the Rare Wildflower

Spalding’s Catchfly (Silene spaldingi i ) on the Zumwalt Prair ie

R.V. Taylor1, J. Dingeldein, and H. Schmalz

Final Report (March 2012)

Abstract

Spalding’s catchfly (Silene spaldingii S. Watson) is a long-lived perennial forb that is threatened by the loss of native grassland habitat throughout the Pacific Northwest. We studied a small population of catchfly plants on the Nature Conservancy’s Zumwalt Prairie Preserve in northeastern Oregon to understand key demographic parameters, timing of key life history states, and factors affecting reproductive success. We marked 100 individual plants and monitored them weekly across the growing season to obtain data on growth form, dates of emergence, flowering and fruiting, reproductive output, as well as prevalence of insect predation and ungulate browse. We found that a substantial and highly variable fraction of Spalding’s catchfly plants remained dormant each season. Plants that did emerge began leafing out in late May or early June and first flowering was observed by 16 July. Most emergent plants were reproductive and single-stemmed, though vegetative (i.e., sterile) plants were also common. Over three-quarters of emergent plants were affected by insect predation, ungulate browse, or other herbivory. Insect predators that destroy the ovaries of Spalding’s catchfly were found on nearly half of all plants. Few plants produced seed – less than one fifth of plants which produced buds went on to produce mature fruits. When plants did succeed in producing fruits, production was low with an average of only three fruits per plant. During 5 years of study we observed 11 seedling rosettes and documented the death of 16 plants. We recommend that land managers address excessive herbivory by elk and investigate the role that fire may play in regulating insect herbivory. Future monitoring of Spalding’s catchfly, incorporating measures of ungulate herbivory, insect predation, and mature fruit production is also recommended.

Introduction

Spalding’s catchfly (Silene spaldingii S. Watson) is a long-lived perennial wildflower that was

once abundant in the prairies of the inland Pacific Northwest. Population numbers have declined

due to conversion of grassland habitat to agricultural use (U.S. Fish and Wildlife Service 2007).

Spalding’s catchfly was listed as a threatened species under the U.S. Endangered Species Act

in 2001 (US. Fish and Widlife Service 2007). In northeastern Oregon, several significant

populations of Spalding’s catchfly persist in the grasslands of the Zumwalt Prairie with a large

population (>40,000 individuals) occurring on The Nature Conservancy’s Zumwalt Prairie

1 NE Oregon Regional Ecologist, The Nature Conservancy, 906 S River St, Enterprise, OR

97828 ([email protected]).

Taylor et al. Spalding’s catchfly demography

p. 2 The Nature Conservancy (March 2012)

Preserve (ZPP; Jansen and Taylor 2010; Figure 1). Larger populations are generally more

secure and less prone to extirpation than those that are smaller (Shaffer 1981), thus the sheer

abundance of Spalding’s catchfly on the Preserve confers some confidence regarding the

viability of this population. Long-term population viability, however, is contingent on many other

factors (Flather et al. 2011). Ultimately, long-term survival of the Spalding’s catchfly population

on the Zumwalt Prairie depends on recruiting a sufficient number of new individuals (i.e.,

seedlings) to replace plants which die from natural or other causes.

The Nature Conservancy initiated a monitoring program to detect long-term trends in the

abundance of Spalding’s catchfly on the ZPP in 2005 (Taylor et al. 2008, Jansen and Taylor

2009, 2010). Determining long-term trends in this species is challenging for several reasons.

First, Spalding’s catchfly is long lived and recruitment is episodic, thus changes in population

numbers may occur very gradually (Lesica 1997, Lesica and Crone 2007). Second, unlike most

perennial herbs, individuals of Spalding’s catchfly do not produce aboveground structures in

some years, remaining dormant throughout the growing season—a trait known as “prolonged

dormancy” (Lesica and Steele 1994). In long-term study in Montana, dormancy varied greatly

from year to year, with an average dormancy rate of 30% (Lesica and Crone 2007). Dormancy

rates measured at other sites, however, have been much lower. For example, in Hells Canyon

in Oregon, dormancy rates averaged <10% over 7 years of study (Hill and Gray 2006). Finally,

less conspicuous vegetative plants as well as rapidly senescent rosettes may evade detection.

All of these traits make it difficult to assess trends by simply counting plants each year (Lesica

and Steele 1994, Lesica 2008). An understanding of the prevalence of dormancy and how it

varies from year to year is essential in interpreting population monitoring data (Lesica and Rudd

2012).

The factors controlling the population dynamics of Spalding’s catchfly are poorly understood.

Population declines are proximally a consequence of a decrease in reproductive output or an

increase in mortality, both of which, ultimately, could be caused by many factors. For example,

Spalding’s catchfly relies on the pollination services provided by bumble bees (Bombus spp.)

without which seed viability and seedling growth are greatly reduced (Lesica 1993, Lesica and

Heidel 1996). Other possible causes decreased reproductive output may include grazing and

predation of floral structures by insects (US. Fish and Widlife Service 2007). Production of a

sufficient quantity of viable seeds, while necessary, is not sufficient for adequate levels of

recruitment. Low rates of seedling establishment, growth or survival may also drive population

declines. Changes in in fire regime (Lesica 1999), competition with invasive species (Huenneke

and Thomson 1995), and soil disturbance resulting from various land uses have all been

suggested as factors which may impede recruitment (US. Fish and Widlife Service 2007).

Increases in mortality rates of Spalding’s catchfly could result from a variety of factors including

drought, excessive browsing, or disease (US. Fish and Widlife Service 2007). Thus, information

on rates of mortality and recruitment, along with key factors that regulate these processes is

essential in formulating effective management strategies for this species.

Study objectives

Our objectives for this study were to: 1) estimate rates of dormancy, mortality, fruit production,

and seedling recruitment for Spalding’s catchfly on the ZPP; and (2) assess levels of predation



by insects and mammals. For this purpose we established six study plots on the Zumwalt Prairie

Preserve and visited them weekly throughout the growing seasons of 2006-2011. We

documented the growth and fate of all catchfly plants within the plots, from emergence to

senescence. Because our study required us to examine plants weekly and monitor their growth,

we also recorded data on phenology (i.e., timing of critical life-cycle events) including dates of

emergence, flowering, and senescence. We report here on the results of this study.

Methods

Study Area

The study was conducted at the Zumwalt Prairie Preserve (ZPP, lat. 45º 3’ N, long. 116º 6’ W)

located in Wallowa County in northeastern Oregon (Figure 1a, b). The 13,269-ha preserve is

owned and managed by The Nature Conservancy (TNC) and lies in the southwestern portion of

the Pacific Northwest Bunchgrass Prairie (Tisdale 1982). At 1,060-1,680 m elevation, the

preserve is dominated by native bunchgrasses, including Idaho fescue (Festuca idahoensis

Elmer), Sandberg bluegrass (Poa secunda J. Presl), prairie Junegrass (Koeleria macrantha

[Ledeb.] Schult.), and bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve).

Spalding’s catchfly occurs across the prairie uplands that make up the bulk of the western

portion of the preserve; the population size has been estimated at > 40,000 plants which occur

across 166 ha of prairie uplands (Figure 1b; Jansen and Taylor 2010). The study took place in

Harsin pasture, an area known to have a high abundance of Spalding’s catchfly (Figure 1c). The

study area has not been grazed by cattle (Bos taurus) since 2004 and has not experienced wild-

or prescribed-fire in recent history (>15 year). For this study we established six permanently

marked 2 m radius circular plots (12.6 m2). Plot locations were chosen subjectively (non-

randomly), each < 25 m distant of all others, and were approximately 50 m from a road to

provide ease of access.

The study area experiences cold winters and warm summers. Average daily minimum

temperatures in December and January, the two coldest months were -9° and -7° C respectively

(Zumwalt Weather Station, unpublished data, 2005-2011). In July and August, the warmest

months, average daily maximum temperatures were 26° and 25° C, respectively. Average

annual precipitation was approximately 36 cm, the bulk of which falls in two periods: May-June

and October-November (Hansen et al. 2010). Over the course of the study, precipitation during

the growing season (May-Aug) averaged 15.9 cm, with the summers of 2009 and 2010

receiving relatively high amounts of rain (22 and 23 cm respectively), and the summer of 2007

the lowest (9 cm). During the other two years of the study (’08 and ’11), precipitation was slightly

below the 5-year average (13 cm). Average daily growing season temperature was 13° C from

2007-11. The warmest year was 2007 (15 ° C) and the coolest years were 2010-11 (12° C).

Field Data Collection

From May-September in the years 2007-2011 we tracked the emergence, growth, flowering,

fruiting, and predation of all Spalding’s catchfly stems within the six study plots. Any non-rosette

stems within 20 cm of each other (measured at the soil surface) were assumed to belong to the

same plant (hereafter “putative genet”, or PG). Upon discovery, each PG was marked by

placing a steel nail in the ground approximately 5 cm from one of its stems to facilitate its



relocation during subsequent visits. Rosettes were always considered to be distinct PGs (as

defined by Lesica and Crone 2007). The location of each PG was mapped by measuring its

distance and azimuth in relation to the plot’s center stake thus allowing us to make repeated

measures throughout the season. After emergence each stem was observed weekly until it

either senesced or could no longer be located. Nails were left in the ground from one season to

the next to facilitate location of early emerging stems (e.g., rosettes) and to avoid excessive soil

disturbance.

Growth Form, Phenology, and Predation

Weekly observations of growth form and

phenological phase (i.e., phenophase) were

made for each stem of each PG following

the methods of Lesica and Crone (2007)

with minor modifications (Box 1; Figure 2).

Because a stem may exhibit multiple

phenophases simultaneously, we recorded

only the most advanced phenophase for

each stem on each visit. For stems in the

dFr and S phenophases we also counted

the number of dehiscent fruits. The

maximum number of dehiscent fruits

observed for a stem across all observations

within a year was used as an estimate of

the total reproductive output for that stem.

The phenophase of a PG was determined

by scaling up stem level data; a PG was

assigned the phenophase of its most

phenologically advanced stem (Box 1) with

one exception: a PG was considered

senesced only when all of its constituent

stems had succumbed to the S

phenophase.

We also recorded, by stem, any signs of

insect predation or ungulate browsing. A stem was considered to have been predated by insects

if there was any evidence that a bud, flower, or immature fruit had been significantly damaged

by an insect. Indicators of insect predation were: presence of an insect or larvae, chewed holes

in any part of the reproductive growth, and presence of frass in or adjacent to floral receptacles

(Figure 3). We did not track insect damage to stems or leaves. A stem was considered browsed

by ungulates if it was severed and had chew marks indicative of cattle, elk (Cervus elaphus) or

mule deer (Odocoileus hemionus) herbivory. The predation status of a PG on given date was

determined by scaling up the stem level data. A PG was considered depredated by insects or

browsed if any of its component stems exhibited signs of depredation.

Box 1. Growth forms and phenological stages of Spalding’s

catchfly plants observed during weekly visits to the study

plots (ordered from least to most advanced).

Dormant (D) – a plant which produces no above ground

structures. These are not observed in the field but are

inferred from observations in prior and subsequent years.

Non-reproductive

Rosette (rV) – a vegetative (i.e., non-reproductive) plant

that does not elongate into nodes and internodes.

Multi-nodal vegetative (mnV) – a plant that elongates into

nodes and internodes but lacks reproductive structures

(buds, flowers, fruits) on any of its stems.

Reproductive

Bud (B) – a multi-nodal plant having at least one unopened

flower.

Flowering (Fl) – a multi-nodal plant having at least one

flowering stem, i.e., a stem having at least open flower.

Immature fruiting (iFr) – a multi-nodal plant with at least

one stem having at least one immature (i.e., “green”) fruit.

Dehiscent fruiting (dFr) – a multi-nodal plant having at least

one mature fruit (i.e., a dried open capsule with reflexed

teeth).

Senescent (S) –a plant whose stems and leaves have

completely dried and turned brown.



Demography: Dormancy, Recruitment, and Mortality

Analysis of inter-annual demographic transitions required that we: (1) estimate how many actual

genets (hereafter “plants”) occurred within the plots across the entire 5 year study period; (2)

determine a spatial location for each plant; and (3) assign each field observation of a PG and its

constituent stems to a plant.

We first mapped all PGs observed within plots using the field-recorded azimuth and distance to

plot center using a Geographic Information System (GIS, ArcMap 9.2) and overlaid PG locations

for all 5 years of our study (Figure 4). We then used the ArcMap buffer tool to determine which

PGs, observed in different years, were within 20 cm of each other. We provisionally assigned

those PGs (and their constituent stems) to the same plant. The geographic location of each

plant was determined by averaging the X and Y coordinates of the PGs belonging to it. Rosettes

were always considered distinct from non-rV PGs, regardless of proximity (Lesica and Crone

2007). A PG > 20 cm from any other PG was generally treated as a distinct plant unless strong

evidence existed for its inclusion in another plant. For example, in a few cases, a non-rV plant

appeared where none had been observed for 3 years and this coincided with disappearance of

another PG that had occurred nearby for the previous 3 years. In this case we assessed

whether errors in field mapping of the PG could have resulted in our overestimating the spatial

separation of that PG from others. In cases where the assignment of a PG to a plant was not

possible due to conflicting evidence, we removed it from our demographic analysis (n=25).

Using this procedure we identified a total of 100 distinct plants. The greatest distance between

any single-year PG location and the GIS-derived location of the plant to which it was assigned

was 26 cm; only 8 were >15 cm.

The growth form attained by a plant in a

given year was determined by scaling up

observations made of the stems belonging

to the PG corresponding to that plant. We

set the growth form to be equal to that of

the most advanced phenophase observed

for any stem. Four growth forms were

recognized: D, Rv, mnV, and reproductive

(B, Fl, iFr, and dFr; Box 1). For example, in

2007 plant P17 consisted of three stems:

one stem emerged as mnV and later

disappeared; a second stem emerged,

produced buds, was browsed and lost all

reproductive parts and then senesced; a

third stem emerged, flowered, and

eventually produced dehiscent fruits. Plant P17 would thus be classified as having attained the

Reproductive growth. Transitions from one growth form to another and rules for assessing

mortality and recruitment were determined using rules described in Box 2. Estimates of

dormancy and mortality are sensitive to assumptions made regarding the number of years in

which plants can remain dormant. Based on previous work we assumed that dormancy lasted 1-

3 years (Lesica 1997, Lesica and Crone 2007).

Box 2. Rules used to determine demographic transitions

1. Rosettes were always presumed to be seedlings

(Lesica and Crone 2007).

2. A non-rosette plant (mnV, B, Fl, iFr, dFr) in a location

where no plant had been observed in the previous 1-2

years was considered to have been dormant in the

preceding years.

3. If a plant was observed one year but not in the

following 3 consecutive years it was assumed to be

deceased (Lesica 1997), unless an observation was

made of a non-rV plant in the same location in the

fourth year. In this case the plant was assumed to

have been dormant for 3 years.



Statistical Analyses

As this was primarily a descriptive study, statistical analysis was limited to descriptive statistics.

Plants, as determined by the GIS analysis described above, were also the basis of all analyses

of phenology, fruit production, browse by ungulates, and insect predation. Stem level data was

scaled up to plants as follows. The phenophase of a plant on a given date was set to the most

advanced phenophase observed on any of its component stems on that date. For a given date,

a plant was considered to have been browsed or depredated by insects if any of its component

stems had been browsed or depredated. The total number of mature fruits produced by a plant

was set to the sum of the maximum number of fruits observed on each of its component stems.

For each plant we determined the first and last dates for which each phenophase was observed

within each year and averaged these across years to determine average phenology. Rates of

browse and insect predation were determined by dividing the total number of emergent (i.e.,

non-dormant) plants which emerged in a given year by the number affected by each type of

predation in that year.

Results and Discussion

Phenology and Growth Forms

We observed a total of 299 stems belonging to 100 distinct Spalding’s catchfly plants across 84

weeks over the course of the five years of our study. The average date of emergence of non-rV

plants was 24 May (± 6 days SD; min =16 May 2008; Figure 5); first buds were observed 5 Jul

(± 7 days; min = 25 Jun 2009 ) and the first open flowers were observed 16 July (SD = 11; min =

28 June 2007; Figure 5). Seedling rosettes emerged approximately 10 days later non-rV plants,

though sample sizes were small and difficulties in detecting rosettes may have precluded them

from being noted at the earliest opportunity. The average date of peak flowering, that is, the day

on which the greatest number of Fl plants was observed, was 25 July (± 8 days). Reproductive

plants continued to flower and fruit for 4-7 weeks. The average number of days for which the B,

Fl and iFr phenophases were observed were 42 (± 10 SD) , 29 (± 10), and 35 (± 16) days,

respectively. The first mature fruits were observed 14 Aug (± 4 days; min = 8 Aug 2007). Fl and

iFr phenophases occurred earlier in the year in 2007, which was relatively warm and dry; than in

the two cooler/wetter years (2010, 2011) of the study. The typical growing season for Spalding’s

catchfly, calculated as the average number of days from first emergence to last senescence

was 118 days (± 23 days; Appendix 1).

Each year we observed reproductive (B, Fl, iFr, dFr) and mnV growth forms but rV growth forms

(i.e., seedlings) were observed in only 4 of the 5 years. Reproductive plants comprised the

majority (61%) of non-dormant plants whereas sterile, non-rosette plants (mnV) were the

second most common growth form (32%; Figure 6). The relative abundance of mnV plants

varied from year to year with the highest fraction observed in 2011. Non-rV plants were

predominantly single stemmed (81%) while those with two or three stems made up 17% and 1%

of our observations, respectively. A single plant had four stems which was the maximum

number of stems observed.

Non-rosette plants senesced as early as 10 June and in a typical year 50% of plants had

senesced by 3 August (Figure 5; Appendix 1). Rosettes senesced earlier; the average date of



senescence was 14 July (± 13 days). Because rosettes and senesced plants are difficult to

detect in the field, our findings suggests that field surveys conducted for the purpose of

monitoring population trends of Spalding’s catchfly on ZPP, which are performed during the

period of peak flowering, likely miss a substantial fraction of plants. This bias has been noted by

others and should be considered in the planning and interpretation of future monitoring efforts

(Hill and Gray 2006, Lesica and Rudd 2012).

Flowering and Fruit Production

Seventeen of the 100 plants produced mature fruits during our study. Of those, 15 succeeded in

doing so only once while 2 plants did so in 2 of the 5 years. Within a year only 15% (±7% SD) of

reproductive plants advanced to the dFr phenophase (Appendix 2). Reproductive failure

occurred at several key stages in catchfly’s life cycle: 28 ± 6% produced buds but failed to

flower; 30% ± 18% flowered but failed to fruit; and 26 ± 9% produced immature fruits but never

produced seeds. A total of 54 mature fruits were produced over the 5 year period. The number

of fruits produced by dFr plants was highly skewed: 69% produced only 1 or 2 mature fruits, and

the maximum number of fruits produced was 8. Fruit production also varied greatly across

years: the lowest fruit production (3) was observed in 2007, a relatively warm/dry year, while the

highest (21) was in 2011, which was much cooler with high rainfall. Transitions from the B to Fl,

Fl to iFr, and iFr to dFr phenophases took 16 (± 4 SD), 11 (± 4), and 18 (± 4) days, respectively

(Figure 5; Appendix 1). The low rates of mature production are likely a consequence of high

rates of ungulate browse and predation of flowers and fruits by insects (see section Insect

Predation and Ungulate Browse).

Dormancy, Mortality, and Recruitment

Plants often transitioned from one growth form to another across years (Figure 7; Appendix 3).

Transitions from D to a reproductive plant (16%) and vice-versa (11%) were most common.

Dormant plants were more likely to reemerge as reproductive plants (64%) than as mnV plants

(36%). Reproductive plants were twice as likely to attain a reproductive growth form the

following year than revert to the mnV form; mnV plants, however, were equally likely to re-

emerge as reproductive or mnV forms.

Of the 100 plants considered in our demographic analyses, an average of 58% (± 14% SD) of

plants emerged in a given year while 42% (± 14%) remained dormant (Figure 6; Appendix 2).

Three-quarters of dormancy events lasted 1 year and 20% were of 2 year duration. We

observed two instances of plants remaining dormant for 3 years. Only 8 plants were observed

as emergent in all 5 years of the study. The fraction of dormant vs. emergent plants varied

greatly from year to year and was approximately congruent to measures of density derived from

counts done across the entire population of the Zumwalt Prairie Preserve. That is, the high

dormancy rates we observed in 2007 and 2010 correspond with the lowest measures of density

observed in that broader scale study (Jansen and Taylor 2010), suggesting that the factors

controlling dormancy of Spalding’s catchfly operate at the scale of the population rather than the

patch. Similar to the population of Spalding’s catchfly studied by Lesica and Crone (2007), the

current year’s weather does not appear to influence dormancy in the catchfly population of the

Zumwalt Preserve. The two years of highest dormancy (2007 and 2010) had nearly opposite

weather during the growing season, the former having the warmest and driest conditions of any



year of the study and the latter being the coldest and wettest. The high rate of dormancy we

observed in 2010 is also consistent with their finding that dormancy is more likely the year

following a wet summer. Likewise, the low rates of dormancy in 2011 might be explained by the

high number of dormant plants the previous year (Lesica and Crone 2007).

We estimated that 16 of the 100 plants we observed died during our study with the majority of

those last observed in 2008 (Figure 6; Appendix 2). Mortality estimates are very limited from this

study due to its short duration. We could confidently assess mortality only for plants which were

observed as non-dormant in 2007 and/or 2008, as our criterion for death ( > 2 years with no

emergence) could not be applied to plants observed in the last 3 years of the study. Any plant

which emerged after 2008 and was not observed subsequently was assumed to be dormant but

this method of determining dormancy may include some plants that will not reemerge. Annual

survivorship estimates were 96% and 84% in 2007 and 2008, respectively, which are similar to

than the approximately 90% rate reported by Lesica (1997).

In most years seedlings were uncommon; a total of 18 were observed over 5 years. Consistent

with the findings of Lesica and Crone (2007) the abundance of rV plants was highly variable

across years. No rosettes were observed in 2007 and a maximum of 11 were observed in 2011.

Annual recruitment – calculated as the average number of rV plants divided by the number of

non-rV plants – at 5% (± 5% SD). Although our estimate of the total number of recruits slightly

exceeds our estimate of deaths, it is important to note that we could estimate mortality only for

the 2007-8 and 2008-9 periods. Some plants that we categorized as dormant in 2010 and 2011

will likely not reemerge and would, with continued observation, eventually be reclassified as

mortalities. Thus, we believe that the small population studied here probably declined slightly

across the 2007-11 period.

Insect Predation and Ungulate Browse

Predation by ungulates, insects, or other agents (i.e., plants were found pulled up or could not

be located) was observed on an average of 76% (± 5% SD) of emergent plants each year

(Table 1). Insect damage to reproductive structures affected 47% (± 18%) of all emergent plants

annually. Plants in the B phenophase were most susceptible to insect herbivory (56% of

observations). The most common insect predator we observed was the larvae of Oregon gem

moth (Noctuidae: Heliothis oregonica) which we identified by rearing a moth through

metamorphosis into adult form (Figure 3). Several moth species are known to be common

predators of other Silene species and some may also serve as pollinators (Kephart et al. 2006).

Insect predators and evidence of their damage were found on plants at different phenological

stages but was most commonly observed on plants having unopened buds, open flowers and

immature fruits. Predation on catchfly flowers and fruits by larvae virtually always destroys the

affected flower (RV Taylor and J Dingeldein, pers. obs.). Thus the high rates of predation by

these insects have important consequences for the Zumwalt population. Insect predation has

been shown in other studies to decrease overall reproductive success of other plant species

with consequences for population viability (Vickery 2002). Insect herbivory rates were

substantially lower in 2011 (21%) compared to other years so it may be that in certain years low

moth abundance provides an opportunity for catchfly plants to produce ample numbers of

mature fruits. Although insect predation on the flowers and fruits of Spalding’s catchfly by moth



larvae has been noted previously (US. Fish and Widlife Service 2007, Youtie 2009), this is the

first measure of the prevalence of this phenomenon.

Ungulate browse was observed on an average of 32% of plants (± 15% SD) and 18% (± 15%

SD) of plants had at least one stem pulled from the ground or otherwise disappeared prior to

senescence (Table 1). The study area is excluded from cattle grazing, mule deer numbers are

low, and elk scat was frequently observed in the plots (J Dingeldein, pers. obs.). We thus

suspect that elk are the primary cause of the browsing and pulling of plants. Browsing may be

one cause for low fruit production in this population of Spalding’s catchfly. It should be noted

that the rate of browsing was higher in the last two years of the study than in the initial three and

that elk numbers in the area increased sharply over the course of our study; numbers increased

from 1400 to 3500 individuals over the 5 years of this study (Oregon Department of Fish and

Wildlife, unpublished data). Browsing of Spalding’s catchfly by cattle has been identified as a

possible threat for populations occurring where livestock are pastured (US. Fish and Widlife

Service 2007). However, a study of browse rates in areas having different cattle stocking rates

found little evidence that cattle consume significant numbers of this species (Cullen and Taylor

2010).

Conclusions and Management Implications

Spalding’s catchfly has a complex life history that includes periods of prolonged dormancy

(Lesica 1997, Lesica and Crone 2007). Our study confirms that a significant fraction of catchfly

plants on the Zumwalt Prairie are dormant each year which complicates the task of assessing

population trends for this species (Lesica and Steele 1994) and should be taken into

consideration in designing future monitoring efforts (Lesica and Rudd 2012). Specifically, we

believe it is necessary to either (1) estimate dormancy for each year based on random plot

locations and adjust observed values to account for the fact that only plants which emerged

could be counted; or (2) mark plants at fixed plot locations and merge observations across

years to estimate the total number of plants alive within a fixed (e.g., 3 year) multi-year period.

The Spalding’s catchfly population we observed for this study experiences very high rates of

ungulate predation and insect predation of flowers and fruits. High rates of predation coupled

with low seed production and viability result in low reproductive output that may be ultimately

affect the viability of the Spalding’s catchfly population on the ZPP. Of particular concern is the

recent increase in the elk population of the Zumwalt Prairie area. Predation by ungulates nearly

always results in total reproductive failure as the flowers or developing fruits are consumed.

Given the current population of approximately 3500 elk, it is likely that Spalding’s catchfly

populations currently experience unprecedented levels of wild ungulate herbivory in this area.

We encourage land managers to continue to explore opportunities to decrease the numbers of

elk in the area with the expectation that this would yield benefits for Spalding’s catchfly.

It is difficult to speculate as to the cause of the high insect predation levels that we observed on

Spalding’s catchfly plants on the ZPP compared to other locations, thus we can offer no specific

management advice to abate this potential threat. Rather, we encourage further investigation

into this phenomenon. One specific avenue of research might investigate the fire ecology of

Spalding’s catchfly with relation to insect herbivory. Inhabiting an area that experienced frequent

fire for millennia, Spalding’s catchfly has been shown to tolerate fire and to have increased



recruitment success following burning (Lesica 1999). Furthermore, insect predation on

grassland wildlfowers has been shown in other studies to be influenced by fire. Vickery (2002)

found that populations of northern blazing star (Liatris scariosa var.novaeangliae) which were

excluded from fire had high rates of predation by moth larvae and virtually no reproduction.

Sites where prescribed fire was implemented temporarily reduced seed predation from

approximately 90% to 16% in the year following the burn (Vickery 2002). We believe that

research into the role that fire may play in insect predation of Spalding’s catchfly should be a

high priority.

Even when Spalding’s catchfly does succeed in producing seed, the quality of seed may be low.

A study of germination rates of seeds collected from the Zumwalt population found that only 9%

of seeds germinated (Taylor and DeBano 2012). Using our data on fruit production along with

estimates of seed production and seed viability, we estimate that each Spalding’s catchfly plant

produces on average approximately 1 viable seed per plant per year. The cause of low

germination rates is not known, but pollination limitation is one possibility (Gonzales et al. in

review). Managing for an abundance of pollinator insect species is one way to reduce the

likelihood that low seed viability leads to declines in Spalding’s catchfly populations.

The demographic analysis of Spalding’s catchfly in this study is insufficient for a robust

estimation of population viability. The relatively short duration of this study, high variation in the

production of seedling rosettes, and periods of prolonged dormancy all conspire to diminish the

accuracy and precision of our estimates of recruitment and mortality, which are essential for

robust population modeling (Menges 2000). Furthermore, it may be that the small patch of

plants studied here is not representative of the greater population of Spalding’s catchfly on the

ZPP. Rather than continuing the demographic studies of Spalding’s catchfly, we recommend

instead that a carefully designed population monitoring program track trends in the numbers of

this plant into the foreseeable future. Monitoring should include some measure of fruit

production, insect predation, and ungulate herbivory, the factors which were identified by this

study as posing the greatest threat to the Spalding’s catchfly population on ZPP. Should

declines become apparent through long-term monitoring, the knowledge gained through this

study should be used to formulate future research priorities to understand and address the

causes.

Acknowledgements

The US Fish and Wildlife service supported this work through a grant to RVT (Agreement #

F10AC00090). We thank Peter Lesica for his pioneering work on the study of Silene spaldingii

upon which this study rests heavily. Dana Ross deserves a round of applause for his assistance

in identifying the catchfly predator Heliothis oregana (Noctuidae) and Vincent Jansen lent a

strong and solid hand in our GIS analysis of plant locations. Finally, we thank the members of

The Nature Conservancy for their support of conservation science at the Zumwalt Prairie and

beyond.



References

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Grazed and Un-grazed Areas of the Zumwalt Prairie Preserve. The Nature Conservancy,

Enterprise, OR.

Flather, C. H., G. D. Hayward, S. R. Beissinger, and P. A. Stephens. 2011. Minimum viable populations:

is there a "magic number" for conservation practitioners? Trends in Ecology & Evolution 26:307-

316.

Gonzales, N., S. J. DeBano, C. Kimoto, R. V. Taylor, and C. Tubbesing. in review. Native bees

associated with isolated aspen stands in Pacific Northwest Bunchgrass Prairie. Northwest

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Hansen, J. D., V. S. Jansen, and R. V. Taylor. 2010. Zumwalt Weather and Climate Annual Report (2006-

2009). The Nature Conservancy, Enterprise, OR.

Hill, J. and K. Gray. 2006. Population dynamics of Spalding’s silene (Silene spaldingii Wats.) in Canyon

Grasslands at the Garden Creek Ranch, Craig Mountain, Idaho. Unpublished report prepared

May.

Huenneke, L. F. and J. K. Thomson. 1995. Potential interference between a threatened endemic thistle

and an invasive nonnative plant. Conservation Biology 9:416-425.

Jansen, V. S. and R. V. Taylor. 2009. Mapping and monitoring Spalding's Catchfly (Silene spaldingii) on

the Zumwalt Prairie Preserve (2006-2009). The Nature Conservancy, Enterprise, OR.

Jansen, V. S. and R. V. Taylor. 2010. Mapping and monitoring Spalding's Catchfly (Silene spaldingii) on

the Zumwalt Prairie Preserve (2006-2010). The Nature Conservancy, Enterprise, OR.

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predation by moths on Silene and allied Caryophyllaceae: evaluating a model system to study the

evolution of mutualisms. New Phytologist 169:667-680.

Lesica, P. 1993. Loss of fitness resulting from pollinator exclusion in Silene spaldingii (Caryophyllaceae).

Madrono 40:193-201.

Lesica, P. 1997. Demography of the endangered plant, Silene spaldingii (Caryophyllaceae) in northwest

Montana. Madrono 44:347-358.

Lesica, P. 1999. Effects of fire on the demography of the endangered, geophytic herb Silene spaldingii

(Caryophyllaceae). American Journal of Botany 86:996.

Lesica, P. 2008. Detection error associated with observing Silene spaldingii at four sites in Montana and

Washington. Unpublished report, U.S. Fish and Wildlife Service, Boise, ID.

Lesica, P. and E. Crone. 2007. Causes and consequences of prolonged dormancy for an iteroparous

geophyte, Silene spaldingii. Journal of Ecology 95:1360-1369.

Lesica, P. and B. Heidel. 1996. Pollination biology of Silene spaldingii. Unpublished report, Montana

Natural Heritage Program, Helena, MT.

Lesica, P. and N. Rudd. 2012. Guidelines for Monitoring Trend of Silene Spaldingii Populations in Key

Conservation Areas. The Nature Conservancy, Portland, OR.

Lesica, P. and B. Steele. 1994. Prolonged dormancy in vascular plants and implications for monitoring

studies. Natural Areas Journal 14:209-212.

Menges, E. S. 2000. Population viability analyses in plants: challenges and opportunities. Trends in

Ecology & Evolution 15:51-56.

Shaffer, M. L. 1981. Minimum population sizes for species conservation. BioScience:131-134.



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Tables

Table 1. Predation on Spalding’s catchfly plants by insects and ungulates and other agents (i.e.,

pulled). The number of plants affected by each type of predation along with the fraction of

emergent plants affected is provided. Averages are shown for all years.

2007 2008 2009 2010 2011 Avg ± SD

Insect, Browsed, or Pulled

# plants affected 28 39 36 26 45 34.8 ± 7.9

% emergent 80% 74% 84% 72% 71% 76.2% ±

5.4%

Insect damage

# plants affected 20 31 28 15 13 21.4 ± 7.9

% emergent 57% 58% 65% 42% 21% 48.6% ± 17.8%

Browsed

# plants affected 4 11 12 15 31 14.6 ± 10.0

% emergent 11% 21% 28% 42% 49% 30.2% ± 15.3%

Pulled

# plants affected 10 9 17 1 4 8.2 ± 6.1

% emergent 29% 17% 40% 3% 6% 18.8% ± 15.3%



Figures

Figure 1. (a) The Zumwalt Prairie (red) is a large remnant of the once extensive Pacific

Northwest Bunchgrass biome. (b) Within the Zumwalt Prairie, a large population of Spalding’s

catchfly (Silene spaldingii; red points) occurs on The Nature Conservancy’s Zumwalt Prairie

Preserve (bright green). (c) The locaiton of the 6, 2m radius plots used for this study (triangle).



Figure 2. Three growth forms of Silene spaldingii: rosette, multi-nodal vegetative, and flowering

(clockwise from top left).



Figure 3 . A common insect predator of Silene spaldingii, the larvae of the noctuid moth

Heliothis oregonica is often observed feeding on the immature ovaries and stamens of catchfly

plants on the Zumwalt Prairie. Shown here is the larvae (left) and the adult moth (right).

Figure 4 . Spatial locations of Spalding’s catchfly plants observed in one plot over 5 years of

study. Triangles indicate locations of putative genets observed weekly in the field; gray circles

are plant locations determined by mapping multiple years of observations in a Geographic

Information System. Triangles of the same color indicate putative genets that were determined

to belong to the same plant.



Figure 5 . Phenology of Spalding’s catchfly on the Zumwalt Prairie Preserve (2006-11). Red

ovals indicate the mean first observed date of a phenophase across all years and blue

rectangles indicate the mean of the last observation of that phase. Bars indicate 95%

confidence intervals.

100 150 200 250 300

Senesce

dFr

iFr

Fl

Bud

Emerge

May Jun Jul Aug Sep Oct Apr



Figure 6 . Number of dormant and emergent (reproductive, vegetative, and rosette seedlings)

Spalding’s catchfly plants observed each year of the study. The height of each bar represents

the total estimated population size for that year. The number above each bar indicates the

number of plants estimated to have died between that and the prior year (available only for

2008-9).

0

10

20

30

40

50

60

70

80

90

2007 2008 2009 2010 2011

Nu

mb

er

of

Pla

nts

Dormant

Reproductive

Vegetative

Recruits



Figure 7. Inter-annual demographic and growth form transitions of Spalding’s catchfly on the Zumwalt Prairie Preserve (2007-11).

The weight of each arrow is proportional to the number of individual plants that underwent the indicated transition. For abbreviations

see Box 1.



Appendices

Appendix 1 – Average dates of first and last observations of growth forms and phenophases for Spalding’s catchfly plants on the Zumwalt Prairie Preserve (2007-11). See Box 1 for abbreviations.

mnV B Fl iFr dFr S

Yr First Last First Last First Last First Last First Last First Last

2007 31-May 28-Jun 4-Jul 1-Aug 28-Jun 25-Jul 18-Jul 16-Aug 8-Aug 16-Aug 10-Jul 22-Aug

2008 16-May 15-Aug 4-Jul 22-Aug 18-Jul 29-Aug 1-Aug 22-Aug 15-Aug 4-Sep 18-Jul 12-Sep

2009 21-May 18-Jun 25-Jun 13-Aug 16-Jul 19-Aug 23-Jul 9-Sep 13-Aug 24-Sep 11-Jun 30-Sep

2010 28-May 8-Jul 8-Jul 26-Aug 22-Jul 19-Aug 29-Jul 23-Sep 19-Aug 29-Sep 3-Jun 20-Oct

2011 25-May 28-Jul 14-Jul 18-Aug 28-Jul 11-Aug 4-Aug 25-Aug 18-Aug 1-Sep 14-Jul 14-Sep

Avg 24-May 13-Jul 5-Jul 16-Aug 16-Jul 14-Aug 27-Jul 31-Aug 14-Aug 8-Sep 29-Jun 19-Sep


p.20 The Nature Conservancy (March 2012)

Appendix 2 – Growth forms, dormancy, recruitment and mortality

For each year the table below provides the number of plants of each growth form (see Box 1)

and maximum phenophase observed each year. Estimates of the number of deaths and

recruitment by year are also shown.

2007

2008

2009

2010

2011 Avg ± SD

Emergent 35

53

43

36

63 46 ± 11.9

Non-reproductive 17

14

8

11

45 19 ± 14.9

rV 0

2

1

4

11 4 ± 4.4

mnV 17

12

7

7

34 15 ± 11.2

Reproductive 18

39

35

25

18 27 ± 9.7

B 5

7

11

8

6 7 ± 2.3

Fl 7

22

8

5

2 9 ± 7.7

iFr 4

6

13

6

6 7 ± 3.5

dFr 2

4

3

6

4 4 ± 1.5

Dormant 48

29

27

38

22 33 ± 10.3

Mortality - 3 - 13 - NA - NA

4 ± 6.2

Recruits + 2 + 1 + 4 + 11

5 ± 4.5

Total Plants 83

81

58

78

96 79 ± 13.7

% Emerged 42%

65%

74%

46%

66% %59 ± %13.8

% Dormant 58%

35%

26%

54%

34% %41 ± %13.8



Appendix 3 – Year to year transition probabilities (2007-11)

(a) Number of plants

Yrs 1->2 1->D 1->M 2->2 2->3 2->D 2->M 3->2 3->3 3->D 3->M D->2 D->3 D->D Total

2007-08 0 0 0 4 5 6 2 1 13 3 1 7 21 19 82

2008-09 0 0 2 1 6 2 3 5 19 7 8 1 10 17 81

2009-10 0 1 0 3 2 2 0 2 12 21 0 4 10 12 69

2010-11 1 3 0 5 1 1 0 13 8 4 0 15 9 13 73

Total 1 4 2 13 14 11 5 21 52 35 9 27 50 61 305

(b) Frequency

Yrs 1->2 1->D 1->M 2->2 2->3 2->D 2->M 3->2 3->3 3->D 3->M D->2 D->3 D->D Total

2007-08 0% 0% 0% 5% 6% 7% 2% 1% 16% 4% 1% 9% 26% 23% 100%

2008-09 0% 0% 2% 1% 7% 2% 4% 6% 23% 9% 10% 1% 12% 21% 100%

2009-10 0% 1% 0% 4% 3% 3% 0% 3% 17% 30% 0% 6% 14% 17% 100%

2010-11 1% 4% 0% 7% 1% 1% 0% 18% 11% 5% 0% 21% 12% 18% 100%

Total 0% 1% 1% 4% 5% 4% 2% 7% 17% 11% 3% 9% 16% 20% 100%

(c) Matrix

From

D mnV rV Reproductive

To

D 20.0% 3.6% 1.3% 11%

rV 0.0% 0.0% 0.0% 0.0%

mnV 8.9% 4.3% 0.3% 7%

Reproductive 16.4% 4.6% 0.0% 17%

M 0.0% 2% 1% 3%

M = Mortality; 1 = rV; 2 = mnV; 3 = B, Fl, iFr, dFr; See Box 1 for more information.

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