The spatial pattern and canopy- understory association of trees in a cool temperate, mixed forest in western Japan Nobuhiro Akashi

Introduction 針広混交林：北半球に広く分布 様々なサイズのパッチを形成 その要因も様々 – 土壌と地形 (soil and topography) – 攪乱履歴 (disturbance history) – 種間競争 (competitive interaction) Natural mixed forests which consist of evergreen conifers and deciduous hardwood species are widely dispersed throughout the northern hemisphere. Most species formed patches, although the causes of patch formation were variable.

Study aims 針広混交林の樹種ごとの空間分布パターンの把握 分布パターン形成の要因の考察 – 種特性はあるのか、林冠木と下層木で分布パターン は異なるのか To determine the spatial patterns of species over various spatial scales in a mixed forest. To examines the causes of the spatial patterns of conifer and hardwood species.

Study site 紀伊山地の大台ケ原 (Ohdaigahara, in the Yoshino Kumano National Park, Kii Peninsula, western Japan) 天然林 ( 人為攪乱履歴なし )(primary forest with no artificial disturbance) 標高 (elevation):1400~1500m 年平均気温 (mean annual temperature):6.4 ℃ 年間降水量 (annual precipitation):4734mm 下層植生 (forest floor): スズタケ (Sasamorpha borealis)

Methods Line intersect sampling method – usually applied to herbaceous vegetation

belt transectline transect

Eight parallel line transects were established ranging from 100 m to 400 m in length, at 50 m intervals. Merit: 比較的簡単に広範囲の分布構造を知ることができる Trees in a large area can be more easily sampled and spatial patterns detected. Demerit: 小さな個体ほど検出されにくい Smaller individuals are more difficult to identify than bigger individuals.

一本のトランゼクトを分割し、セクションごとに被度を 調べる 分割する長さを変えることで、様々な空間スケールの分 布パターンを把握できる（今回は 12.5,25,50,100,200 ごと に分割） Dividing the line transects into sections of various length, the various scale of patterns can be analyzed. Divided into sections 12.5,25,50,100, and 200 m long in this study.

対象：樹高 1.3 m 以上 林冠木 (15 m<) と下層木 (<15 m) を区別 ギャップ : トランゼクト上に林冠木の樹冠がない部分 Trees taller than 1.3 m and whose crown projection intersected the line transect were identified and the location of each crown projection over the transect was recorded. Trees more than 15 m tall were defined as canopy trees, less than 15 m as understory trees. Parts of lines without any cover by canopy tree were defined as canopy gaps.

Slope inclination 地形の指標 各トランゼクトを 10m のセクションに分割 してそれぞれで測定 indicator of topography Each line transect was divided into 10 m sections, and an average inclination for each section was obtained.

Results

Species composition 27 tree species were observed(4 conifers 23 deciduous broad-leaved) ブナ ウラジロモミ ヒノキ オオイタヤメイゲツ コハウチワカエデ ミズナラ ミズメ

Spatial distribution of species

Morisita’s index 空間の個体の分布状態を示す指標 通常平面上で用いられるが、ここでは線上に修正 Index to examine the spatial patterns of the different species. Originally based on the number of individuals in each quadrat. Iδ(index of dispersion) 1: ランダム (random) >1: 集中 (clumped) Cδ(index of inter-specific association) 1: 同調 (closely associated) 0: ランダム (random)

Iδ q: the number of sections of a certain size P i : relative coverage of a species at section I p-: the mean coverage of the species Iδ(s)/Iδ(2s)=the ratio of the index on length of section s and 2s: a clump size of spatial distribution is detected as s with a peak of this

Cδ p xi,p yi : the relative coverage of species x and y at section I p x -,p y -: the mean coverage of species x and y

Iδ F. crenata canopy: random understory: slightly clumped A. homolepis canopy: clumped understory: random C. obtusa canopy & understory: clumped in large size

Cδ ヒノキ : 大サイズの排他的 なパッチを形成 ブナ、ウラジロモミ : 同調して分布 C. obtusa: formed large and exclusive clumps F. crenata & A. homolepis: closely associated

relative coverage of understory trees in canopy gaps 51 canopy gaps were counted(15.8% of the line transect in total) F. crenata ：ギャップ依存的に更新 (gap dependence) A. homolepis ：耐陰性高い (shade tolerant)

To detect more fine-scale association... The contact sampling method 隣り合ってる木を樹種ごとに数えていく target contact neighbor

Lateral canopy tree association 同じ樹種が隣り合いやすい Most of species showed a significantly aggregated distribution.

Vertical association between understory and canopy layer ウラジロモミ下層木 : ブナ下に多い、ウラジロモミ下、 ギャップ下に少ない ヒノキ：下層木と林冠木が同所的に分布 Understory A. homolepis : positive association with canopy F. crenata and negative association with conspecific canopy trees and gaps. C. obtusa : positive association between understory and canopy.

Distribution patterns in relation to topography As inclination increase… relative coverage of ブナ (F. crena) : decrease ヒノキ (C. obtusa) : increase gaps : increase

Discussion

C. obtusa 大きくて (size:100m~ ) 排他的パッチを形成 急傾斜地に分布 → 大規模攪乱後定着？ （付近には地すべり地形がみられた） The distribution of C. obtusa was restricted to steep slopes, and the species was found in larger clumps than other species. →Established following landslides or other such large scale catastrophic events. Several landslide scars of the scale of several hundreds of m2 were observed in the study area.

F. crenata, A. homolepis 同所的に分布 (scale : 50~100m) ブナがウラジロモミに置き換わっている (contact scale) ウラジロモミ：下層でランダム分布 → 林冠木は集中 → ブナ林のギャップを利用して林冠まで成長する？ Occurred in the same habitat(scale : 50~100m), where F. crenata tended to be replaced by A. homolepis(contact scale). The distribution of A. homolepis was random in the understory but clumped in the canopy. →Occupies canopy gaps in the understory created by broad- leaved species.

reciprocal replacement? 相互置換的更新 (reciprocal replacement) under broad- leaved canopy conifers recruit under conifer canopy conifers don't recruit broad-leaved species recruit in gaps 針葉樹の次には広葉樹が、広葉樹 の次には針葉樹が更新しやすい 北半球の針広混交林で数例報 告 複数樹種共存の仕組み？ 大台ケ原では成り立つのか？ Conifer species and broad-leaved species replace each other. We can find some reports about it in the northern hemisphere. Hypotheses used to explain the coexistence of tree species. conifer canopy tree make gap frequently?

Remained question The effect of ササ (dwarf bamboo) – 一斉枯死 (synchronous death) シカの増加 (increasing Sika deer)