natural disturbance in northern japanese mixed …...conifer–hardwood mixed forests in northern...
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Natural disturbance in northern Japanese mixed forests
Uryu Experimental Forest
plan to visit on 16 JUN
In natural mixed forests in Hokkaido, the annual mortality of overstory trees has
frequently been less than 1% in basal area (Kubota 2000; Yoshida et al. 2006).
Nevertheless, extreme mortality occasionally results from strong winds. Such a large
disturbance can destroy stand structure; alternatively, it can contribute to sporadic
regeneration of several tree species in mixed stands. Together with canopy gap
formation, the supply of fallen logs and tip-up mounds is recognized as a significant
process through offering seedlings a favorable establishment condition.
The M3 Catchment (3.5 ha), located in Uryu Experimental Forest (UREF), Hokkaido
University (44°21’44” N, 142°15’55” E) is designated as an experimental catchment to
examine the forest stand dynamics and its functional relationships with biogeochemical
processes.
The east half (left side) is densely dominated by conifer species, besides the west half (right
side) is gappy with more broadleaved components.
The forest understory is almost exclusively dominated by dwarf bamboo (Sasa
senanensis) except for some riparian zones.
In September 2004, a severe typhoon
struck Hokkaido Island. The maximum
wind speeds were recorded as greater
than 30-m s-1, causing wind-induced
damage of 13.3 % of basal area in this
stand.
Regeneration on tree-fall-oriented structures
Fallen logs and tip-up mounds are recognized as significant establishment microsites
for seedling establishments. This is particularly important for forests in this region where
dwarf bamboos are exclusively dominate the understory. However, considerable
variations are existed in the seedling density among fallen logs and among tip-up
mounds. To examine the causes of the variation, we are conducting seedling census in
this stand.
(Noguchi & Yoshida 2004)
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Figure. Seedling densities (except for current year seedlings) in relation to relative height of quadrats from the ground surface at the end of third growing season. The average and sd (in parentheses) are shown respectively for mound (blue) and for pit (red).
Abies sachalinensis
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Betula platyphylla
0.96 (4.1)3.17 (6.7)
1.92 (6.0)2.87 (6.3)
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3
0 50 100
Picea glehnii 1.91 (6.6)5.63 (11.7)
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lativ
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eig
ht f
rom
gro
un
d su
rfa
ce (
m)
Seedling density (/m2)
-2
-1
0
1
2
3
0 50 100
Figure. Seedling densities (except for current year seedlings) in relation to relative height of quadrats from the ground surface at the end of third growing season. The average and sd (in parentheses) are shown respectively for mound (blue) and for pit (red).
Abies sachalinensis
-2
-1
0
1
2
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0 50 100
Betula platyphylla
0.96 (4.1)3.17 (6.7)
1.92 (6.0)2.87 (6.3)
-2
-1
0
1
2
3
0 50 100
Picea glehnii 1.91 (6.6)5.63 (11.7)
Re
lativ
e h
eig
ht f
rom
gro
un
d su
rfa
ce (
m)
Seedling density (/m2)
Figure. Seedling densities (except for current year seedlings) in relation to relative height of quadrats from the ground surface at the end of third growing season. The average and sd (in parentheses) are shown respectively for mound (blue) and for pit (red).
Abies sachalinensis
-2
-1
0
1
2
3
0 50 100
Betula platyphylla
0.96 (4.1)3.17 (6.7)
-2
-1
0
1
2
3
0 50 100
Betula platyphylla
0.96 (4.1)3.17 (6.7)
1.92 (6.0)2.87 (6.3)
-2
-1
0
1
2
3
0 50 100
Picea glehnii 1.91 (6.6)5.63 (11.7)
-2
-1
0
1
2
3
0 50 100
Picea glehnii 1.91 (6.6)5.63 (11.7)
Re
lativ
e h
eig
ht f
rom
gro
un
d su
rfa
ce (
m)
Seedling density (/m2)
(Harada et al. unpublished)
Forests in Dorokawa basin
Uryu Experimental Forest
plan to visit on 16 JUN
The Dorokawa basin is located at north of the Lake Shumarinai. The size of the basin is
ca.4000ha, consisting of ca. 700 ha of flat area (wetland) and the surrounding
mountainous area. The flat area includes marshland, riparian broadleaved forests and
Picea glehnii forests. Mountainous area is largely dominated by conifer-broadleaved
mixed forests, the main components of which are Abies sacharinensis and Picea glehnii
in conifer, and Quercus mongolica, Tilia japonica, Acer mono, Betula ermanii, Betula
platypgylla, Kalopanax pictus and Phellodendron amurense in broadleaved species.
The current woody volume of the basin is estimated to be 120m3 ha-1, in which ca. 70%
of the volume is broadleaved trees. Non-wooded land covered densely with dwarf
bamboos occupied ca.40% in area of the basin, mainly in high altitude or steep slope
area. Such area had been considerably expanded by the major typhoon in 1954.
Picea glehnii preserved forest on wetland
Picea glehnii occur in conifer- broadleaved mixed forest, while they often develop pure
stands on relatively infertile conditions (e.g. wetland or serpentinous soil area). The
preserved forest located along the Dorokawa river shows typical stand structure grown
on wetland with acidic peat soil. We established study plot of 0.5 ha in 1992, and are
measuring trees with dbh > 5cm. The canopy of the stand consists of Picea glehnii with
Betula platyphylla as a scarce associate. The dbh-class distribution shows L-shape,
indicating stable size structure. Establishment of trees primarily depends on fallen logs
or mounds. Changes in stand structure seemed to be minor with low recruitment and
mortality (0.005 and 0.003 ha-1 year-1, respectively), suggesting slow changes in
structure without major disturbances.
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DBH-class (cm)
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Establishment process
A phytolith analysis suggested that Picea glehnii colonized the wetland c.a. one
thousand years ago. Regarding the relatively long life-span of this species (several
hundred years), the current individuals seems to be in earlier generations.
Published work:
Kawano T et al (2007) Holocene phytolith record at Picea glehnii stands on the
Dorokawa mire in northern Hokkaido, Japan. The Quaternary Research 46: 413-426
Phytolith analysis was applied to clarify a
vegetation history at Picea gluhnii stands on the
Dorokowa mire, northern Hokkaido. Phytolith
assemblages from surface samples and Holocene
deposits from the mire are used to clarify the
stand-scare vegetation history, with special focus
on the dynamics of Gramineae, which includes
dwarf bamboo, and the establishment of P. gluhnii
stands on the mire. The phytolith records during
the early-Holocene (ca. 12,000 to 10,000 cal BP)
indicate the distribution of Pooideae-dominated
vegetation, which reflects the cool climate.
Phragmites (reed) dominated vegetation from the
early to mid-Holocene (ca, 10,000 to 5,000 cal BP)
suggests wet conditions like low-moor. The reed
was replaced by dwarf bamboo at ca. 5,000 cal BP,
although the distribution of dwarf bamboo was scattered. At ca. 1,500 cal BP, dwarf bamboo
increased abruptly and has been sustained to the present. Also, Pinaceae type phytoliths began
to occur continuously at ca. 1,000 cal BP. Taking into account the relationship between modern
vegetation and modern phytolith assemblages on the mire, the occurrence of the Pinaceae type
phytoliths from the sediment samples indicates the existence of P. glehnii in the study sites. On
the basis of these results, P. glehnii stands with dense undergrowth of dwarf bamboo would have
been established in the study sites on the mire by, ca. 1,000 cal BP at least.
Selection harvesting in mixed stands
After 1950s, most of the stands in the mountainous area have been repeatedly logged
with single tree selection manner. We set up long-term study plots to monitor the
consequences of the management. Logging may cause further increase in Sasa (dwarf
bamboo) cover, as well as decrease in fallen logs on which particular species preferably
regenerate. Sustainable logging system may need lower cutting rate with site
preparation for seedling establishment.
Published work: Noguchi M & Yoshida T (2003) Tree regeneration in partially cut
conifer–hardwood mixed forests in northern Japan: roles of establishment substrate and
dwarf bamboo. Forest Ecology and Management 190: 335-344
We assessed the relationship of the regeneration (seedling and sapling) densities of seven
representative tall-tree species to the past partial cutting and current stand structure. We also
determined if differences in tree regeneration were associated to establishment substrates
(coarse woody debris (CWD) and root throws) and understory inhibitor vegetation (the dwarf
bamboo species: Sasa senanensis). The study was conducted in 17 conifer–hardwood mixed
stands in a heavy snowfall region in Hokkaido, northern Japan. The results suggest that stand
structure, rather than logging intensity, is the primary factor influencing regeneration densities.
Total conifer basal area was positively correlated with the regeneration density of individual tree
species, including two conifers and three hardwoods. These patterns differ from those observed
in old-growth stands in the region. A negative correlation between total conifer basal area and
dwarf bamboo coverage suggests that the presence of dense conifer canopies causes an
increase in regeneration density of tall-tree species by preventing domination of dwarf bamboo.
Picea glehnii, a species that depends for its establishment strongly on CWD, has lower seedling
and sapling density in stands with higher logging intensity. This seems to be a result of the
decrease in the volume of CWD with increasing logging intensity in these stands. We suggest
that both reducing logging intensity and retaining overstory conifers should be considered to
develop a sustainable silvicultural system in this region. Providing sufficient CWD and root
throws may also be important to ensure natural regeneration of tree species that require these as
an establishment substrate.
Stand structure and dynamics of an oak (Quercus
crispula)-dominated mixed primeval stand
Uryu Experimental Forest
visit (possibly)
In northern Hokkaido, mixed stands are frequently dominated by Quercus
crispula. In this type of a stand, we maintain a 1-ha-scale tree census since 1982
to observe its stand dynamics. Quercus crispula share 67 % of basal area with
low density of small trees, and Abies sachalinensis, Acer mono and Acer
japonicum dominate the sub-canopy and sapling layer. Dwarf bamboo (Sasa
senanensis) is densly established in understory.
Published work:
Takahashi et al. (2003) Stand structure and dynamics during a 16-year period in a
sub-boreal conifer–hardwood mixed forest, northern Japan. Forest Ecology and
Management 174: 39-50
The stand structure and regeneration dynamics of trees >2.0 m in trunk height were
studied during 1982–1998 in a 1 ha plot in a sub-boreal conifer–hardwood mixed forest,
northern Japan, with a dense dwarf bamboo in the understory. Total density was low in
1982 (651 trees/ha), as compared with other forests in Japan. Quercus crispula was
dominant in the upper canopy layer but their saplings were rare, while Acer mono, Acer
japonicum and Abies sachalinensis were dominant in the sub-canopy and understory
layers with many saplings. Mortality of each species was quite low during the census
period (average 0.57% per year), and there was no clear difference among the four
species. The age structure of Q. crispula was bell-shaped with a peak at ca. 200 years,
while that of the other three species was weakly reverse-J-shaped or a rough plateau. In
addition, no recruits growing over a height of 2 m were observed during the census
period in Q. crispula, but many recruits of the other species were observed. These
suggest that Q. crispula depended on episodic disturbances for the persistence of its
population. Recruits of the three species except for Q. crispula did not concentrate in
canopy gaps probably because of the dense dwarf bamboo cover there. They showed a
negative spatial association with their own canopy trees, but a positive association with
canopy trees of Q. crispula. Most of the crowns of the three species (A. sachalinensis
and the two Acer spp.) were lower than that of overtopping Q. crispula. These spatial
associations between recruits and canopy trees brought about the competitive effect of
Q. crispula on the growth rates of other species and that of itself. However, the low
mortality of trees taller than 2 m indicates that intra- and interspecific competition was
not strong as a structuring force of the tree community. Our long-term study suggests
that factors affecting recruitment (disturbances and dwarf bamboo in the forest floor) are
more important for species coexistence than intra- and interspecific competition
between trees taller than 2 m.
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Quercus crispula
Abies sachalinensis
Acer mono
Acer japonicum
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Quercus crispula
Abies sachalinensis
Acer mono
Acer japonicum
Regeneration management in non-wooded area Uryu Experimental Forest
plan to visit on 22 OCT
Dwarf bamboos are acknowledged as key to the structure and dynamics of Japanese
forests, since they are widely distributed and often form exclusively dense undergrowth
in many forests. Several researchers have reported the negative effects of dwarf
bamboo undergrowth on the density of tree seedlings (Hiura et al. 1996; Nagaike et al.
1999) and on understory plant species diversity. Sasa kurilensis, a larger species with
height 2-3m, is more likely to dominate in higher altitude area with making larger
monospecific community than S. senanensis, a smaller species with height 1-2m.
Dense growth of both two species inhibits the establishment of other plant species, and
harvesting often result in enhancement of their growth rather than tree regeneration
(Noguchi and Yoshida 2005). Therefore, elimination of dwarf bamboos is a main issue
for enhancing tree regeneration as well as maintaining species diversity in this region.
Because dwarf bamboos can produce new shoot from their root stocks, cutting of
aboveground stems is generally insufficient.
Scarification is conducted widely in northern Japan to get rid of understory dwarf
bamboo species before replacement with tree species. Natural regenerating is applied
in area with sufficient mother trees, and it generally results in establishment of a pure
Betula stand in this region. The major plantation species is Picea glehnii. In the Uryu
Experimental Forest, the other plantation species include Abies, Fraxinus, Kalopanax
(by root burying), and Quercus (by sowing). Some of treated sites are designated as
standard plots for monitoring recovery of woody vegetation for a long period.
Published work: Yoshida T et al (2005) Factors influencing early vegetation
establishment following soil scarification in a mixed forest in northern Japan. Canadian
Journal of Forest Research 35: 175-188
Scarification is widely conducted in northern Japan to
remove understory dwarf bamboo species in degraded
forests for replacement with tree species. To explore
ways to enhance species diversity and restoration of
mixed forest at the treated site, we clarified the
mechanisms that lead to compositional heterogeneity
of plant species. We evaluated the relative importance
of environmental factors (scarification properties, soil
properties, light conditions, litter cover, and presence of
canopy trees) for the demography of tall tree species
(emergence, mortality, and growth) and whole
vegetation structure (species diversity and composition) over the two growing seasons
immediately following scarification. Of tall tree species, Betula spp. were dominant (60% in total
density), followed by Abies sachalinensis (Fr. Schm.) Masters, Acer mono Maxim., and
Phellodendron amurense Rupr. Light intensity was an important factor, having mostly negative
effects on the demography of these species. Soil factors (e.g., nitrogen content, moisture)
affected the demography mainly of shade-intolerant or hygrophilous species. In general, extreme
environmental conditions led to the dominance of grasses, forbs, and lianas rather than tall trees.
Maintenance of canopy cover, which limits light and supplies seeds as well as litter, proved to be
most important in promoting plant species diversification on the scarification site.
Published work: Nagai M & Yoshida T (2006) Variation in understory structure and
plant species diversity influenced by silvicultural treatments among 21- to 26-year-old
Picea glehnii plantations. Journal of Forest Research 11: 1-10
We investigated effects of silvicultural treatments (planting and subsequent treatments) on
understory structure and plant species diversity in managed Picea glehnii plantations (21–26
years old) in northern Japan. We evaluated the importance of each treatment (machinery site
preparation, planting, weeding, and thinning) in 19 plantations, with considerable variation
among treatments overall. The understory had 98 vascular plant species; the most dominant
species was a dwarf bamboo Sasa senanensis, followed by tree species Abies sachalinensis
and Betula ermanii. Multiple regression analyses showed that thinning negatively influenced
plant species diversity. Planting density showed a strong positive correlation with density of
seedlings (height <20cm), but few independent variables were correlated with density of saplings
(height ≥20cm and diameter at breast height <1cm). The negative effect of thinning and the
positive effect of planting density seem to be related to the existence or reinitiation of dense
cover of Sasa senanensis. We present possible mechanisms of response to treatments to
generalize the results. We then suggest ways to improve current treatments to meet the goals of
wood production and biodiversity conservation in the region.