natural disturbance in northern japanese mixed …...conifer–hardwood mixed forests in northern...

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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Picea glehnii 1.91 (6.6)5.63 (11.7)

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Seedling density (/m2)

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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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Picea glehnii 1.91 (6.6)5.63 (11.7)

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Abies sachalinensis

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Betula platyphylla

0.96 (4.1)3.17 (6.7)

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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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Picea glehnii 1.91 (6.6)5.63 (11.7)

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Picea glehnii 1.91 (6.6)5.63 (11.7)

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rom

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rfa

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(Harada et al. unpublished)

Forests in Dorokawa basin


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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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


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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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.

natural disturbance in northern japanese mixed …...conifer–hardwood mixed forests in northern...

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