tion of surface rubble layer in each quadrat， and Fig．28 indicates particle−size distribution of the fine−grained layer in each quadrat． Table 11 shows environments and floristic composition of the alpine plant communities in each quadrat． The influence of particle−size distribution of surface rubble layer and thickness and particle・size distribution of fine−grained layer on vegetation was examined on every slope with roughly the same vegetation coverage．
Bare ground
Plants cannot grow because the matrix of fine−grained materials flows out owing to the large size of rubble particles on the block slope． In an aplite block slope（Plot A），
debris more than 20 cm on the long axis account for 80％of all surface rubble， and no Plants grow without the matrix．
The slope of plot M is covered by aplite rubble with varying diameters， and the rubble layer is underlain by a layer of small particle（φ3−4：17．5％，φabove 4：22．7％）
with high water content by weight（15．1％）． The small−size particles makes the overlying rubbles unstable and gives the fine−grained layer a high water content，
causing frost action．
The slope of Plot L is covered by biotite−granite rubble；the particle・size of the fine−grained layer（φ 一5−−1：55．3％）is bigger than those of other slopes， and the water retentivity is low（the water content by weight is the lowest（3．3％）of all slopes）． This low water content of soil brings shortage of water for plants．
Slol）θs with z／egeんztion co verage ρ／ 1−5 ％
Debris（pink granite， aplite， silexite）on the slope of Plot F is composed of finer rubble（surface rubble of O．2−1 cm in long axis：58％of all rubble，1−5 cm：30％）
than those of other slopes， and the thickness of the fine・grained layer is over 30 cm．
Patterned ground is also formed near this plot． The slope of Plot E is covered by finer rubble（surface rubble of O．2−1 cm in long axis：57％of all rubble；that of 1−5 cm：23 ％）than those of other slopes， and the thickness of the fine−grained layer is over 30 cm． Plants growing on the slopes of Plots F and E are restricted to two to
董oO
Ocm
30
30
A
■
B
」
Particle5
C D
humus
・ｱ・
鰹 整多 臼o智26
K
0 50 100％
A
C D E
F G H
J K L
M
N
o P
Particle−size O．2−1cm 1−5cm 5−10cm 10−20cm＞20（m Fig．27 Particle−size distribution of surface rubble layer at each plot in the Northern Japan Alps
駕0 3
20 10
／0−5cm
D瓢
／
F
0−4cm
．《＞4cm
願 o 一一口
一9
冒響
一■ 一ドー P 響 ロ！
％30
20 10
H
・・一E＞4cm
lノ ／0層4cm
％30
20 10
K
＞2cm／0−2cm
）一．
艶0 3
20 10
M
一4−3−2−101234φ 一4−3−2−101234φ 一4−3−2−101234￠
Fig．28 Particle−size distribution of fine−grained layer at each plot in the Northern Japan Alps
four species， Dicentra peregn na， Viola crassa， and so forth． This means that these slopes are too unstable for growing many plants． The small particle−size of the surface rubble and the thick fine−grained layer presumably make the land surface unstable in these slopes． The patterned ground disturbs the growing of plants．
Surface rubble（aplite）of the slope of Plot O is mainly composed of granules and pebbles（rubble of O．2−1 cm in long axis：30％，1−50 cm：30％）． The particle−size of the fine−grained layer is big（φ 一4−−3：24．1 ％，φ 一3−−2：21．5 ％）， and thus the water retentivity is low． Growing plants were limited to five species， S彪1伽勿 nipPonica， 『レ acc in iu〃z uliginosu〃z var． alpinu〃z， and the like， because of the land−
surface instability and low water retentivity．
Table 11 Environments and fioristic composition of the alpine plant communities at each Plot in the
Northem
Japan AlpsPlot
A
BC D
E FG H
1 JK
LM N 0
PGradient of slope 27° 24° 28° 26° 25° 14° 17° 17° 34° 23° 28° 28° 25° 32° 33° 33°
Exposure N90°W N80°W N80°W N80°W N60°W N50°W N80°W N70°W N60°W N50°W N50°W N60°W N50°W N60°WN60°W N60°W Lithology（1）
Ap Ap Ap
Gryl̀p
Gryl
̀p
Gry2
̀p，S Gry2
̀p
Gryl
̀p
Gry1 Gry1 Gry1 Gry1
Ap Ap
fry1
Ap Ap
Thickness of surface 一 一 一 1＜ 1＜ 1＜ 3＜ 3＜ ．5＜ 1＜ 1＜ 1く 3＜ 一 ？ ？ rubble（㎝）
％1ichen coverage 80一 80一 80一 40 20 0 10 30 20 5 20 ？ 0一 70一 ？ ？
on exposed block 90 90 90 20 80
Fine・grained layer （2） 一 （＋） （＋） 十 十 十 十 十 十 十 十 十 十 （＋） 十 十 Thickness of fine・ 一 一 一 30＜ 30＜ 30〈 30〈 30＜ ＜20 30＜ 10一 30＜ ＜20 一 ？ ？
grained layer （cm） 30
Water content a（3） 一 一 一 16．1 9．9 3．2 11．8 14．6 11．1 9．9 15．8 3．3 15．1 一 ？ 4．1
by
weight（％〉 b 一 一 一 5．3 10．9 4．5 5．6
Color of a 一 一 一 br o−br o−br o−br d−br br o−brdo−bo−br du．r 一 9−0 9−0 fine−grained
撃≠凾?秩i4） b 一 口 一 o−br br 一bl o−br 一br
Number of species （5） 0 ■ 曽 7 4 2 7 7 12 8 11 0 0 一 5 7
Vegetation coverage 0 一 一 13 3 1 10 18 70 10 35 0 0 一 5 14
（％）
Coverage of each species％
悔6α ηゴ〃御 κ1ゴ遷掬OSπ〃z var．
ゆ勿鷹 5 十 2
ノ1κ OZ6Sαφ 7ZZ￠S 30 1
伍砂θπ8づαゆゆ0痂6α 20 8 2
var．0∂00α彪
Pb云θη ゴ1勉〃2αお％・ 5 3 6 1 2 5 2
η￠〃7π8
7セガ6」4 σππ彪欝 1
G6η蹟z㎜σ頓吻 1 1
0κツ≠70ρ誌ノ砂oη20α● 2 5 5 2 5
ル1勿％α7蕗αみ0η406〃∫ゑS 3 2 2 十 2
S陀1勉万αηψρ0η20αo 3 2
cα伽η蜘伽獺π伽 qo砺o彫ssα
11
十 十
十1 12 11 2十 42
十
11
Dゴ6θη mρθ劉㎎弼〃α ﾆs ％ωo魂πα var．
十2 1 十
十 2 2
十2
5 十
ψ伽
ω7召κs彪η〃2 加 十 2 1 1 3Lz62〃ゐz σ〃θπδ6卿疹 cεS6加吻S毎0α岬 ∫OSα
十 十 十 十 1
十 3
月π麗sρ襯吻 （6） ＊ ＊ ＊
（1） Ap：Aplite， Gry1： Biotite・granite， Gry2： P°
mk
granite， S： Silexite（2）
（3）
（4）
民り4U））
（（
十：developed，（十）： partially developed，一：absent a：upPer layer， b：lower layer
br：brown， o−br：01ive・brown， d−br：dark brown， do−b：dark olive−brown， du．y−br：dull yellowish−brown， g−o：grayish・olive， br−b1：brownish−black
Vascular plant
＊：present
SloPes with vegetat加coverage of 6−20％
The debris of Plot J is biotite−granite， that of Plot G is pink granite with aplite， and that of Plots D and H are biotite・granite and aplite． Surface rubble O．2−1 cm in the long axis accounts for 80％（Plot J），44％（G），57％（D）， and 37％（H）of all rubble， and that in 1−5 cm accounts for 15％（J），30％（G），20％（D）， and 24％（H），
and thus these four slopes are covered by fine rubble． The fine−grained layer is divided into two horizons in Plots D and H， and the particle・size of the lower layer is bigger than that of the upper layer；water content by weight of the lower layer is lower than that of the upper layer． Averages of particle−size and water content by weight of upper layer and lower layer in these plots are similar to the values of Plots Jand G・Thickness of the fine−grained layer is over 30 cm on all slopes of Plots J， G，
D，and H．
Growing species on these four slopes resemble each other and are restricted to
seven to eight species， P（）ten tilla 〃ldtSu〃zurae， （り比ツtropdS ／tZponica， レTio lz cr zssa，
Ca〃zpan〃lz dusyantha， Festuca oz／ina var． alpinごz， Lu2ula wahlenbergii， and so on，
because of land−surface instability． Growing species on the slopes of Plots J， G， D， and H（vegetation coverage：10−20％）without Dt centra peregn na are more numerous than those of Plots E， F， and O（vegetation coverage：1−5％）， with 1万centra peregn na and
四〇勉crassa as dominant species．
On the slope of Plot P， rubble with long・axis of intermediate length（1−20 cm）
occupies 92％of all surface rubble（aplite）． The fine−grained layer consists of relatively coarse materials（φ一4−−1：61．1％）；and thus the water retentivity is low， and water content by weight is 4ユ％． （］arex s彪％侃伽 and Descha吻s勿 caespitosa grow on this slope．
SloPes with vegetation coverage ov〃20％
The slopes of Plots K and I are covered by biotite−granite rubble ranging from small to large． Large debris is weathered to a fairly deep leve1． Thickness of the surface rubble layer is only l cm at parts of the two slopes． Fine−grained layers of the two slopes are composed of intermediate particle−size materials（φ一2−−1：upper layer
（to 2 cm in deepness）of Plot K（72．3％），10wer layer of Plot K（64．4％）， Plot I
（76．3％））．Although thickness of the fine・grained layer is over 30 cm in all slopes with vegetation coverage of 6−20％， it is only 10−30 cm in Plot K and below 20 cm
in Plot I．
Eleven or twelve species， Vacciniu〃z uliginos〃〃z var． alpinu〃z，∠レ6如％s alpinzcs，
DiaPensta吻・nica var・・b・vata，動勧撒matSum〃rae，（初云伽αalgida，伽t・・PdS
勿》onica，〃inuartin hond∂ensdS，αz〃ゆan〃lz dasyantha， Violz 6燃sα， and Festzeca ozノゴ％α var．α砂ina，（）arex stenantha grow in these slopes， and the vegetation coverage is high．
Block sloPe Pa吻1砂o・vered by Pinzas Pu〃z吻
Slopes of Plot B and C are covered by aplite rubble， and the slope of Plot N is covered by aplite and biotite・granite rubble． Surface rubble over 20 cm on the long axis accounts for 90％（Plot B），100％（C）， and 77％（N）of all rubble． Surface rubble over 10 cm makes up 100％of all rubble in three plots． Plants are restrained from growing by outflow of matrix because there are large size gaps among rubbles． Dwarf shrubs such as Vacciniu〃z〃iginosu〃z var． alpinu〃z and／lrct∂ms
alpinus grow partially on the slope of Plot C． Surface rubbles are weathered to deep inside on these three slopes． On a bare l）10ck slope（Plot A）， weathering crust is thin，
3．3mm on average． Weathering degree of a block covered by Pinz｛s pumila is higher than that of exposed block． The percentage at which lichen covers rubble is 80−90％
in Plots B and C and 70−80％in Plot N；thus these three slopes are stable．
Fine・grained layers are formed to only l cm thickness on blocks；bare slopes have no fine・grained layer． A source of supply of debris hardly exists at present because Pinzts pu〃zゴ伽covers the ridge lines above these slopes． Debris produced in the past，
possibly during the last glacial period， is accumulated・
4．Discussion
Based on the results obtained by this study， the availability of hypothetical model shown in Fig．5 will be examined and the role of each environmental factor in the vegetation pattern under various conditions will be discussed in this chapter．
Relationship between landforms and vegetation
・Although there are studies examining landforms as factors affecting vegetation pattern（Komarkova and Webber，1978；Haase，1987）， they have regarded landforms as vessels influencing snow depth and moisture conditions and do not mention sufficiently the relationship between landforms classified by genesis and vegetation．
（1）Shape and situations of landform：
In this study，1andforms were considered a fundamental factor that governs vegetation pattern through shape and direction of slope， and the relationship between landforms and vegetation pattem was analyzed．
Asignificant relationship exists between landforms， time of snow release， and vegetation． The conspicuous relationship between landforms and time of snow release can be explained by the fact that the time of snow release on each landform is determined by the inherent shape（convex−concave）and situation（direction of slope）
of the landform because the place where each landform has emerged i6 approximately determined． Situation（direction of slope）of the landform is generally important in a straight slope and shape is significant in convex and concave slopes for their influence on time of snow−release and vegetation．
Convex landforms such as moraines and roches moutonn6es are occupied by Pinus pumila scrub and deciduous broad−1eaved forest because of early・melting snow， and concave landforms such as nivation hollows and linear depressions are covered by alpine snow−bed community and alpine fell・field community plants owing to late・
melting snow．
On a straight slope， the south−facing slope and the windward slope are dominated by alpine fe11・field community and Pinzes pumila scrub because of early・melting snow， and the north−facing slope and the leeward slope are covered by alpine snow・bed community and alpine herbaceous plant community owing to latemelting snow．
Woody plants such as dwarf shrubs and shrubs generally tend to grow on sites with
earlier−melting snow than herbaceous plants．
（2）Genesis of landforms and geomorphic processes：
The relationship between landforms， surface materials， and vegetation is also influenced by geomorphic processes． Classifying landforms by their origin can explain more clearly the relationship between landforms and vegetation．
On talus cone， debris・flow fan， and other depositional landforms， a fine−grained layer is developed． These sites are dominated by communities composed of herbaceous plants such as alpine herbaceous plant community， alpine tall herbaceous plant community， and alpine snow・bed community， because herbaceous plants use water stored in the fine・grained layer． Because the rates of frost creep and gelifluction in soil are controlled by water conditions（Benedict，1970；Washburn，1973）， the land surface becomes unstable when water content of soil becomes high． However，
Koizumi（1979a）has pointed out that plants grow in sites with fine−grained layers even if there is a great deal of surface movement on wind−blown slopes， and that plants hardly grow in sites without the fine−grained layer even if there is little movement．
He explains this by pointing out that a fine−grained layer is needed in order for plants to absorb water and nutrients．
Convex landforms， from big ones like moraines or roches moutonnees to small ones of less than one meter high， are occupied by dwarf shrub heath such as Phyllod∂ce αleutica． On these convex landforms， the fine−grained layer is undeveloped because fine materials tend to be washed out， and water and nutrient are apt to be carried off．
In sites like this， disintegration of the fallen leaves and litter by microbes is restrained and humus acid acidifies soil， and thus more oligotrophic soil is produced（Saito，1977，
P．209）．
Fossil periglacial smooth slopes， blockstreams， and depressions such as linear depressions， nivation hollows， landslide scars and so forth are covered broadly by big blocks． These sites are bare owing to Iack of fine materials in one case and are covered by Pinzts pumila scrub with a thin fine−grained Iayer in another case．
Because woody plants have large superficial areas above the ground， water retained on leaves and other parts of plant body by rain and fog can be used by the plants themselves． Thick raw humus is piled on the land surface because the rate of decomposition of woody plants is slow． This raw humus restrains water in the soil from evaporating depending on the capillary phenomena． Therefore， the woody plants are supplied with water sufficiently even if fine−grained layers are undeveloped．
Relati・nship between time・f sn・w release， gmwing peri・d・f Plants， s。il moisture， stability of land surface， and vegetation
Previous studies（Ishizuka，1948；Billings and Bliss，1959；Bock，1976；Yamanaka，
1979；Ostler et al．，1982）about the relationship between time of snow release and vegetation considered time of snow release an important factor for vegetation pattern，
but they were limited to research on sites with late・melting snow．
The surveys in this study at sites with various times of snow release show that influence of time of snow release on vegetation was different among sites with late−melting snow（July−September）， sites with early−melting snow（before mid−June），
and sites with intermediate time of snow release． In sites with late・melting snow，
communities are distributed resulting from the degree to which growing periods of plants are limited， These communities are characterized by small−sized plants（2−20 cm in height）because plants must grow in a short period of time． The soil is immature and oligotrophic． The thickness of the fine・grained layer is 20−30 cm in many cases． Surface materials are apt to move and land surface is unstable because many habitats are on steep slopes．
Sites with earlymelting snow are wind・blown slopes， and they are dry in response to early melting of snow． Frost action is extensive and land surface is unstable in these sites． Communities are distributed depending on degree of dryness and instability， and are dominated by drought resistant and chianophobe plants． The soil is immature and oligotrophic． Thickness of the fine・grained layer with fine gravels is less than 20 cm．
Sites where time of snow release strongly controls the distribution of communities are sites with late・melting snow， and it is not very important in sites with intermediate time of snow release．
Relationship between soil moisture and vegetation
Although time of snow release is considered an important factor controlling vegetation pattern， various communities are often distributed in sites with definite time of snow release， In sites with intermediate time of snow release， soil moisture is considered an important factor controlling vegetation pattern．
Sites with intermediate time of snow release are seldom dry and thus these sites are divided into hydric sites and mesic sites．
In hydric sites（available moisture，15−40％；water content by weight，150−500％），
the communities are distributed depending on degree of moisture． In sites like this， the fine−grained layer is 40−100 cm thick and peat and／or clayey soil is produced． Air ratio of the soil is low because of its hydric condition， and it is hard for roots of plants to absorb oxygen from soils；thus communities dominated by plants with developed aerenchyma（graminoid， Fauha crtSta−galli， and so on）and small−sized herbs（2−20 cm in height）（P7i°〃zz6勉cuneiわlin， and the like）are distributed at these sites．
Wet sites like this are often distributed in the Northem Japan Alps with much snow cover， but less than those of the Daisetsu Mountains which are occupied by a broad・scale lava plateau． In the Southern Japan Alps with little snow cover and steep slopes， wet sites are limited in number and scale．
In mesic sites（available moisture，10−30％；water content by weight， c．100−
150％），alpine herbaceous plant commmity（10−30 cm in height， vegetation coverage：
80−100％，ノlnemone narcdSsznora community， Tro llizts物吻磁η％s−Ranunculzts 8α腐 var． nipponicus community， and so forth）dominated by tall plants and with high vegetation coverage， makes alpine meadow landscape referred to as Ohanabatalee ． The growing area of alpine herbaceous plant community is larger， like those of Pinzcs 加駕磁scrub and Stzsa leuri lensdS community， than those of other communities．
Thickness of the fine・grained layer is intermediate（40−60 cm in average）， and soil textures are silty loam or silty clay loam in many cases． Tro〃伽 n ederinnas−
Ranunculzesαα廊var． nipPonicus community occurs in a wetter habitat・
Alpine herbaceous plant community（alpine tall herbaceous plant community）occurs on a stable slope with intermediate time of snow release（early June−mid−July；late May−1ate June in the Southem Japan Alps）and mesic condition（available moisture，10
−30％；water content by weight， c．100−150％）．
In the southern part of the Daisetsu Mountains， snow release is generally late because of heavy snowfall． Therefore， the snow lies on the leeward steep slopes and depressions until August or September． On the gentle slopes of the plateau， the period of snowmelt is mostly intermediate（early June−mid−July）， and drought rarely occurs．
Except in some moors and bogs（hydric）and on some ridges（xeric）， mesic moisture condition persists during a growing season that Iasts from June to August．
In the southern part of the Daisetsu Mountains， the lava plateau with a gently sloping surface is widespread above the forest limit， which is located around 1，600 m in altitude． This enables alpine herbaceous plant communities to occupy larger areas in this part of the Daisetsu Mountains than in any other mountains in Japan．
Although the habitats of alpine herbaceous plant community are sites with interme・
diate time of snow release and mesic moisture conditions in the Daisetsu Mountains and the Northern Japan Alps， they correspond to leeward concave slopes and depressions on ridges with late−melting snow in the Southern Japan Alps which become dry in mid−summer owing to little snow cover；the time of snow release of these sites is from late May to late June（Fig．29）． Therefore， the area occupied by alpine herbaceous plant community is narrow in the Southern Japan Alps（Figs．4and 24）．
In the Northem Japan Alps， distribution of both communities and environments is midway between the Daisetsu Mountains and the Southern Japan Alps．
Relationship between stability of land surface and vegetation
Although sites with intermediate time of snow release are generally stable， both sites with early−melting snow and sites with late−melting snow are unstable． In particular，
the sites with early−melting snow are unstable because of active frost action．
The Research Group for Alpine Geomorphology（1978）， Koizumi（1979a， b，1980a， b，
1982），and Koizumi and Tamura（1985）mentioned that distribution of communities on wind・blown slopes is influenced by modes and movements of materials（gravel）of the land surface． They considered that the particle size of rubble constituting the land surface（surface・rubble layer） and the existence of a fine−grained layer control movement of the land surface， and that the production of surface materials is governed by bed・rock lithology．
However， the difference in particle−size of rubble is caused by mode of rock breakdown even in the same lithology， and the thickness and particle−size distribution as well as the existence of a fine−grained layer presumably affect strongly the stability of land surface and distribution of communities．
Aslope covered by fine rubble is unstable and shows low vegetation coverage because needle ice creep and solifluction tend to occur（Research Group for Alpine Geomorphology，1978；So㎞a et al．，1979；Iwata，1983）． Sites occupied by large rubble are stable and have high vegetation coverage， but sites covered by very large rubble are bare or are dominated by Pinus pumila because herbaceous plants are