老撾Phou Khao Khoauy國家公園樹木分布特征*

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老撾Phou Khao Khoauy國家公園樹木分布特征*

Manichanh Satdichanh1,2,3,Jrme Millet4,Andreas Heinimann5,6,

Khamseng Nanthavong3,Rhett D.Harrison7,8

(1.中國科學(xué)院西雙版納熱帶植物園，云南勐臘666303；2.中國科學(xué)院大學(xué)，北京100049；

3.老撾國立大學(xué)林學(xué)院，老撾;4.Fdration des Conservatoires botaniques nationaux，法國；

5.瑞士發(fā)展與環(huán)境中心,瑞士；6.伯爾尼大學(xué)地理研究所，瑞士；7.世界混農(nóng)林中心東亞和中亞區(qū)域辦公室，云南昆明650204；

8.中國科學(xué)院東亞植物多樣性與生物地理重點(diǎn)實(shí)驗(yàn)室，云南 昆明650204)

摘要：本研究在老撾Phou Khao Khoauy國家公園(在萬象東北方向40 km)的兩種森林類型取樣，以此研究決定樹種分布的因素。本研究在海拔為300～450 m地區(qū)共設(shè)置了11個50 m×50 m樣地，并測量了所有胸徑大于10 cm的樹木。調(diào)查樣地按森林類型(混合落葉林，以山毛櫸科為主，干常綠林)分層隨機(jī)選取，共鑒定47個科，70個屬，123個種。在每個樣地的兩個位置收集土壤樣品，每個樣品在兩個深度分別為0～10 cm和10～20 cm處采集，并進(jìn)行基本土壤參數(shù)分析(pH值，有機(jī)質(zhì)OM，氮N和磷P，氧化鉀K2O，顆粒大小以及質(zhì)地)。通過聚類分析對植物群落進(jìn)行標(biāo)識，使用NMDS分類法及非參數(shù)檢驗(yàn)法研究土壤對植物分布的影響，揭示了老撾Phou Khao Khoauy國家公園內(nèi)樹種組成與土壤條件的關(guān)系。

關(guān)鍵詞：植物分布；老撾；土壤；植物群落；物種組成；熱帶雨林

Plant community ecology is determined by both biotic and abiotic factors[1～2].Species occurrence in the given plant community is not accidental but a response to climatic factors,soil conditions,species interactions and biogeography.Gradients in soil variables,water pH and other abiotic factors are strongly correlated to species distributions at both small and large scales[3～4].For example,at a global scale,plant distribution is strongly influenced by climate,topography and soil[5].At landscape scales,the soil conditions and altitude are the most important environmental variables determining plant distributions and influencing the structure of forest communities[6～8].

The vegetation types in Indo-China have been divided into two basic categories based on elevation,phenology,rainfall patterns,species dominance,floristic relationships and soil types.The first category is tropical rain forest,which includes wet-evergreen forest,dry-evergreen forest,freshwater swamp forest and evergreen montane forest.The second category is deciduous forest,which includes mixed deciduous forest and deciduous dipterocarp forest.Laos is situated on the northern edge of the tropics in Asia and supports a diversity of forest types,including both deciduous and evergreen forests.Deciduous forests mainly occur in lowland areas of southern Laos from 100 m to 800 m in elevation.Evergreen forests in Laos include rain forest,dry evergreen dipterocarp forest (a mixture of deciduous and evergreen species) and mixed coniferous forest[13～16].Mixed coniferous forest occurs at higher elevations of up to 2 000 m.However,other evergreen forest types and deciduous forest types in Laos may be distributed in very close proximity.Moreover,species often occur in both forest types[17～18].In particular,mixed deciduous forest and dry evergreen dipterocarp forest overlap in many species but vary in the proportion of evergreen versus deciduous species.The factors determining the distribution of forest types at local scales are still poorly understood.Moreover,most previous work delineating forest categories has been based on qualitative assessments.

The forests in Phou Khao Khoauy National Park (PKK) have been disturbed in the past by logging,infrastructure construction and human activities.Previous studies found that the floristic composition of PKK was significantly associated with altitude and soil conditions[19～20].However,the disturbance of native forests in PKK had lead to the existence of pioneer deciduous and evergreen vegetation.The aim of our study was to understand the factors determining the distribution of plant species in PKK.We were particularly interested to investigate whether previous suggestions that different forest types sometimes exist in close proximity are supported by a quantitative approach to assessing ecological communities.Our results are an important basis to understanding the drivers of plant distribution at landscape scales within Laos,where basic information on forest ecology is still lacking.

1Materials and methods

1.1Study area and data collection

PKK is one of eighteen sites in Laos that were designated as protected areas in 1993.PKK (18°14’～18°32’N;102°38’～ 102°59’E) is a mountain range about 40 km northeast of Vientiane at its closest point.It encompasses an area of around 2 000 km2and covers three provinces including Vientiane province,Vientiane Prefecture and Borlikhamxay province.The forest types found within PKK correspond to the mixed deciduous forest (dominated by Fabaceae),dry evergreen dipterocarp forest and monodominant coniferous forest (mainly Pinaceae),at higher elevation[19].Elevation varies from ≤100 m to nearly 1 700m.Average rainfall in the rainy season (May-October) is 3 369 mm,while on average only 265 mm of rainfalls from November-April.

Data were collected from 11 permanent forest plots located on the eastern side of PKK.These plots covered mixed deciduous forest (five plots) and dry evergreen forest(six plots) only,and the elevation of the plots ranged from 300～450 m.These permanent forest plots were established by the Institude Recherche pour le Developpement (IRD)-France and Faculty of Forestry (FOF) National University of Lao (NUoL) in 2009[19].Each plot is 0.25 ha (50 m × 50 m).After stratifying by forest type,the location of plots was randomly assigned.All individual trees with a diameter-at-breast-height (DBH) ≥10 cm were enumerated.Trees with DBH ≥10 cm were chose because “the ecological sorting and soil performance on plant appears to affect trees of all size classes without inducing a shift in the diameter distribution[21]”.Tree DBH,height,and position were recorded and the species identified.Herbarium specimens were collected and deposited at the National Herbarium of Laos,NUoL Faculty of Forestry herbarium and NUoL Faculty of Science herbarium.From the 11 permanent plots a total of 1 221 individual trees,including 47 families,70 genera and 123 species were enumerated.

Soil sample collection and analyses were conducted by the Sud Expert Plantes Initiative Project[19].In each plot,two soil samples were collected from two locations across the diagonal of each plot using a soil auger;each sample was collected at two depths,between 0～10 cm and 10～20 cm depth.Soils were analyzed at the soil analysis laboratory of the National Agriculture and Forestry Research Institute (NAFRI) in Vientiane,Lao PDR.The soil samples were analyzed for pH,organic matter (OM),nitrogen (N) and phosphorus (P),potassium oxide (K2O),particle size and texture.

1.2Data analysis

All analyses were implemented in R v.3.1.3[22].We used the data collected from each plot to create a plot vs.species matrix of species abundance.Multivariate analyses were applied on this matrix.The difference in species composition across plots was quantified using Sorenson similarity index (similarity distance) based on abundance data.After that,we used hierarchical agglomerative clustering to assign groups,using the complete linkage method for group identification.To test the statistical significant of clusters we used simprof function in clustsig package in R[23].To examine the hierarchical classification and analyze the relationship between environmental variables and plant distributions in the given communities,we used non-metric multidimensional scaling (NMDS) using vegan package in R.The NMDS procedure was based on the default parameters in R,which included Bray-Curtis dissimilarity index (abundance based) and a maximum of 100 starts in search of stable solution.The soil parameters were log transformed (log10) to approximate a normal distribution for each parameter.The results of the NMDS analysis and log transformed soil parameters were used to examine the relationship between plant distribution and environmental parameters using the post-hoc non-parametric function envfit in the vegan package,based on 999 permutations.

2Results

2.1Species composition

Our cluster analysis classified plant communities in our study site into three groups.Group I covered four plots and was mainly dominated byGonocaryumsp.(13 %),Lagerstroemiacalyculata(10 %),Horsfieldiaaamygdalina(10 %),Diospyrossp.2 (6 %) andCanthiumglabrum(5 %).Group II covered three plots and was dominated byHorsfieldiaamygdalina(21 %),Hopeaferrea(10 %),Gonocaryumsp.(6 %) andXanthophyllumflavescens(5 %).Group III covered four plots and dominated byHopeaferrea(20 %),Horsfieldiaamygdalina(13 %),Alphonseagaudichaudiana(9 %) andCratoxylumcochinchinense(7 %).The relative dominance values of the top 20 species in the plant communities were as follows;Group I ranged from 0.35～16.14,Group II ranged from 0.03～10.63 and Group III ranged from 0.12～23.62 (Table 1).However,Groups II and III were not significantly different using 0.05 as the probability of a Type I error.The NMDS ordination of plant communities also represented these groups (r=0.98,stress=0.04) (Figure 1).

Tab.1　Relative dominance of the top 20 species of each plant community group at PKK.Group I ranged from 0.35～16.14,

Fig.1　　NMDS ordination of tree distributions in PKK

Fig.2　　The NMDS ordination of plant communities and

2.2Plant distribution across soil gradients

The NMDS axes explained 73 % of the total variance in species composition(stress=0.04,r=0.98) (Figure 2).The first NMDS axis had positive correlation with sand was negatively correlated with P,K2O,clay and silt.NMDS axis 2 had a positive correlation with sand and silt while P,clay and K2O were strongly negatively correlated with this axis.However,as expected following the cluster analyses,the plant communities of Group II overlapped with Group III (Figure 2).The environmental fitted vector test found that P (p = 0.021),K2O (p = 0.029),sand (0.007) and clay (0.008),but not silt (p = 0.091) were significantly associated with variation in plant community composition.These results suggest that plant communities are sorting out along a gradient from sandy soil with low P and K2O to clay soil with higher P and K2O.

3Discussion

Our results suggest that the tree distribution in the mixed deciduous and dry evergreen dipterocarp forests at PKK is strongly determined by soil gradients.The ordination analysis showed that the distribution of plant species in the given communities was significantly correlated with P,K2O,and the proportion of sand or clay particles.This suggests that these environmental factors played the key role in determining plant distribution in PKK.

Previous studies elsewhere have reported similar results on the relationship of plant distribution and soil gradients.For example,Chahoukietal[24]found that the distribution of vegetation in Poshtkouh Rangelands,Iran was correlated with the soil texture,soil salinity and other characteristics,respectively.They also found that soil texture controlled plant distribution through its effect on soil moisture availability,ventilation and distribution of the roots.Many studies on tropical soil nutrients also showed that phosphorus is an important limiting factor and assumed to limit the productivity in lowland tropical forest[25～29].Intensive logging was conducted in PKK until 1993 and currently PKK still experiencing disturbance.Logging and other disturbance factors may have contributed to the changes in the species composition and soil chemical characters at out site.

Our cluster analysis demonstrated that it is possible to identify a significant turnover in forest composition among plots located at a similar elevation and in close proximity with one another.Nevertheless,theses analyses also showed that many species were shared among the groups identified.Our results are consistent with other studies on forest types in Laos[13,17,18],and confirmed that different forest types in Laos occur in very close proximity but that a number of plant species may be shared among forest types.Differences in forest associations occurring at the same elevation appear to be driven by variation in soil conditions.

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Tree distribution in Phou Khao Khoauy National Park,Laos

Manichanh Satdichanh1,2,3,Jrme Millet4,Andreas Heinimann5,6,

Khamseng Nanthavong3,Rhett D.Harrison7,8

(1.Xishuangbanna Tropical Botanical Garden,Chinese Academy of Sciences,Mengla Yunnan 666303,P.R.China;

2.University of the Chinese Academy of Sciences,Beijing 100049,P.R.China;3.Faculty of Forestry Science,National University of Laos;

University of Bern,Switzerland;7.World Agroforestry Centre,East & Central Asia Regional Office,Kunming Yunnan 650204,P.R.China;

8.Key Laboratory of for Plant Diversity and Biogeography of East Asia,Kunming Institute of Botany,

Chinese Academy of Sciences,Kunming Yunnan 650204,China)

Abstract:To investigate the factors determining tree species distribution,forests sampling at Phou Khao Khoauy National Park (PKK),40 km NE of Vientiane in central Laos was conducted.Eleven 0.25 (50 m×50 m) samples were set up between 300～450 m elevation and all trees ≥10 cm were enumerated.Plot locations were randomly assigned after stratifying by forest type (mixed deciduous forest,dominated by Fagaceae,and dry evergreen diperocarp forest) and 47 families,70 genera and 123 species were identified.Soil samples were collected from two locations,each sample was collected at two depths,between 0～10 cm and 10～20 cm depth and they were analyzed for getting basic soil parameters [pH,organic matter (OM),nitrogen (N) and phosphorus (P),potassium oxide (K2O),particle size and texture].By cluster analysis for plant community group identification,and by non-metric multidimensional scaling (NMDS) and a post-hoc non-parametric tests for examine the influence of soil parameters on plant distribution,this study found that in Laos,which located on the northern edge of the tropics,substantial turnover in tree species composition sometimes occurs over short distances,although tree species may be shared among forest types.Moreover,turnover in species composition appears to be associated with soil conditions.

Key words:plant distribution;Laos;soil;plant community;species composition;tropical forest

中圖分類號：S 718.5

文獻(xiàn)標(biāo)識碼：A

文章編號：1672-8246(2015)06-0094-06

收稿日期：*2015-07-10Corresponding author：Manichanh Satdichanh, chanh199@gmail.com