不同植物类群物种丰富度垂直格局分形特征的比较

植物生态学报2005,29(6)901~909Acta Phytoecologica Sinica不同植物类群物种丰富度垂直格局分形特征的比较任海保1张林艳2马克平1*(1中国科学院植物研究所植被数量生态学重点实验室,北京100093)(2南京大学国际地球系统科学研究所,南京210093)摘要格局和过程一直是生态学的核心问题,该文应用/非布朗运动随机分形0模型,在北京东灵山远离人为干扰地区的阴坡设置了两条宽2m的样带,描述和比较了暖温带落叶阔叶林区乔木、灌木、草本以及总的植物物种丰富度在不同尺度上沿海拔梯度变异特征,以及相关的生态过程。

研究结果表明:1)直接梯度法刻画了植物物种丰富度在海拔梯度上的总体变化趋势,并不能从中获得更多的信息。

/非布朗运动随机分形0模型揭示了不同尺度上物种丰富度的空间变化并能和生态过程相联系,研究表明该模型适合对乔木、灌木和草本植物物种丰富度的垂直梯度格局特征进行描述,但对总的植物物种丰富度有一定的局限性。

2)乔木物种丰富度在海拔梯度上的变化主要受两种生态过程的控制,小尺度上分形维数接近于2,主要受独立的不具有长程相关的生态过程控制,呈近随机分布;大尺度上分形维数接近于1,主要受自相关范围大、具有长程关联特性的生态过程控制,随海拔上升呈近似单调下降的趋势。

灌木和草本物种丰富度在海拔梯度上的变化主要受3种生态过程的控制,小尺度和大尺度上的特征与乔木相似;但在中等尺度上,分形维数接近于1.5,它们以近似布朗运动的形式变化。

虽然乔木和灌木物种丰富度在海拔梯度上变化的尺度范围相似,但决定它们的主要生态过程完全不同,或相同的生态过程以截然不同的方式作用于两种不同的植物类群。

总的植物物种丰富度在整个尺度范围内呈现标度不变性,这可能是由于决定其变化的生态过程作用尺度紧密相关,也可能因为该文研究范围的局限性。

关键词生物多样性丰富度分形维数尺度垂直格局生态过程COMPARISON OF FRACTAL CHARACTERISTICS OF SPECIES RICHNESS PATTERNS BETWEEN DIFFERENT PLANT TAXONOMIC GROUPSALONG AN ALTITUDINAL GRADIENTREN Hai_Bao1Z HA NG Lin_Yan2and M A Ke_Ping1*(1Labo ratory o f Quantitative V egetation Ecology,Ins titute o f B otany,C hine se A cadem y o f Sc ie nce s,B ei jing100093,Chi na)(2Inte rnational Ins titute o f Earth Syste m Sc ie nce,Nanjing U niversity,Nanjing210093,C hina) Abstract Using non_brown fractal model,this study w as tailored to quantify and compare the variations of species richness of trees,shrubs,herbs and total plants along altitudinal gradients and characterize the domi2 nating ecological processes that determined the varia tions.T w o transects w ere sampled far a way from any anthropogenic disturbances along the shady slopes of the Dongling M ountains,Beijing,China.B oth transects were continuous and2m wide,and every individual tree and shrub w as recorded in each transect.Discrete quadrats of1m@1m were located along transect A and B for estimation of herb species richness along the altitudinal gradients.The bevel interval between the quadrats w as10m and25m,respectively.In the present study,transect A and B w ere combined into one transec t AB,and40m was selected as optimal quadrat length along the altitudinal gradients for measuring plant species richness patterns.Species richness in each quadrat was calculated by a program w ritten in Matlab6.0.Firstly,direct gradient analysis was used to describe the overall trends in species richness of trees, shrubs,herbs and total plants with changes in altitude,and the non_brown fractal model was used to more ac2 curately detect their variations at various scales along the gradient.The model assumed that each class of eco2 logical processes affecting the distribution of a variable could be represented by an independent spatial random function.Generally,ecological phenomena were determined not by a single ecological process but by multiple ones.These processes acted on ec ological patterns at their ow n spatial scales.In the non_brow n fractal model,收稿日期:2004212221接受日期:2005207207基金项目:国家自然科学基金项目项目(39893360、39770131和39970136)本研究得到北京森林生态系统定位站全体工作人员,特别是茅世森和宋凤山两位老师的大力支持,米湘成博士为本文编写了计算程序,谨向他们致以诚挚的谢意*通讯作者Author for correspondence E_mail:makp@bri m.ac.c nthe spatial random func tions w ere nested within a larger range of spatial scales.The relative contribution of spatial random f unctions to the spatial variation of a variable was indicated by a weighting parameter that had to be greater than or equal to z ero.In this paper,w e reached the f ollowing results and c onclusions.Firstly,the direct gradient method de2 scribed the general trends of trees,shrubs,herbs and total plants along the altitudinal gradient but w as unable to provide more detail about altitudinal variations of species richness.The non_brow n fractal model uncovered altitudinal variations in species richness of trees,shrubs and herbs at various scales and related them to ecolog2 ical processes.The sharp changes in the double_log variograms suggested that the non_bro wn fractal model w as advisable f or charac teriz ing the altitudinal patterns in species richness of trees,shrubs and herbs at various scales but not appropriate for explaining the variation of total plant species richness,because there w as no ob2 vious sharp change in its double_log variogram.Sec ondly,for trees,the double_log variogram w as divided into two scale ranges(0-245m and245-570m),with a fractal dimension of1.83and1.10,respectively,im2 plying that changes in tree species richness was nearly random at small scales(0-245m)and nearly linear at large scales(245-570m)along the altitudinal gradients.This suggested that altitudinal variations in tree species richness w ere dominated by short_range processes at small scales and by long_range processes at large scales.Thirdly,for shrubs and herbs,the double_log variograms exhibited three sections(0-101m,125-298m and325-570m),and the fractal dimensions were1.78and1.97,1.56and1.43,and1.08and1. 25,respectively.The results indicated that,like trees,species richness of shrubs and herbs were distributed randomly at small scales and c hanged in a more linear fashion at large scales although variations in herb species richness was less heterogeneous than shrub species richness at large scales.These results also indicated that species richness of shrubs and herbs changed approximately like brown movement at middle scales.The results also suggested tha t altitudinal variations in species richness of shrubs and herbs w ere dominated by three eco2 logical processes,short_range ecological processes at small scales,long_rang ecological processes at large scales,and brow n f ractal processes at middle scales.Interestingly,comparisons of the variations in species richness of shrubs and herbs found that shrubs and herbs presented the same scale ranges in spatial variation in species richness buu displayed contrary trends in species richness along the altitudinal gradient,i.e.shrub species richness decreased with increasing elevation whereas herb species richness peaked at mid_high eleva2 tion.These patterns suggest that although the scales at w hich the main processes affected patterns in species richness were the same,the processes w ere c omple tely different,or the processes w ere similar but the respons2 es of shrubs and herbs to the ecological processes were different.Finally,total plant species richness did not show any obvious pattern along the altitude gradient and maintained a constant fractal dimension across all scales,perhaps because the processes defining the pa tterns of total plant species richness had similar weights and acted over closely related scales.Key words Altitudinal patterns,Biodiversity,Ecological processes,Fractal dimension,Scale,Species rich2 ness当今世界人类面临着严重的生态环境危机,现存于地球上的生物以前所未有的速度灭绝(Pimm et al.,2001)。