Coupling effects of altitude and human disturbance on landscape and plant diversity in the vicinity of mountain villages of Beijing, China

Villages represent the source of human disturbance in mountain regions, but how they alter surrounding landscapes and further affect plant diversity distribution along altitudinal gradient is still not well documented. Although the unimodal pattern along latitudinal gradient and the hypothesis of immediate disturbance (IDH) have been supported in many studies, their coupling effects on plant diversity distribution have been given less attention. In this paper, the coupling effects surrounding mountain villages were detected: (1) altitude determined the mountain landscape at regional scale, while human disturbance altered landscape fragmentation and diversity at local scale surrounding villages. (2) With the reducing human disturbance away from villages, plant diversity decreased, then increased, and finally decreased in different land uses. The plant diversity of shrubs reached the lowest. With the increasing altitude, plant diversity of the forest represented the unimodal trend, but other land use types had different properties. (3) The mechanism of the coupling effects is that the combination of topographic and soil factors determines plant diversity distribution at both landscape and plant community levels surrounding villages.     

Altitude effects on spatial components of vascular plant diversity in a subarctic mountain tundra

Environmental gradients are caused by gradual changes in abiotic factors, which affect species abundances and distributions, and are important for the spatial distribution of biodiversity. One prominent environmental gradient is the altitude gradient. Understanding ecological processes associated with altitude gradients may help us to understand the possible effects climate change could have on species communities. We quantified vegetation cover, species richness, species evenness, beta diversity, and spatial patterns of community structure of vascular plants along altitude gradients in a subarctic mountain tundra in northern Sweden. Vascular plant cover and plant species richness showed unimodal relationships with altitude. However, species evenness did not change with altitude, suggesting that no individual species became dominant when species richness declined. Beta diversity also showed a unimodal relationship with altitude, but only for an intermediate spatial scale of 1 km. A lack of relationships with altitude for either patch or landscape scales suggests that any altitude effects on plant spatial heterogeneity occurred on scales larger than individual patches but were not effective across the whole landscape. We observed both nested and modular patterns of community structures, but only the modular patterns corresponded with altitude. Our observations point to biotic regulations of plant communities at high altitudes, but we found both scale dependencies and inconsistent magnitude of the effects of altitude on different diversity components. We urge for further studies evaluating how different factors influence plant communities in high altitude and high latitude environments, as well as studies identifying scale and context dependencies in any such influences.     

景观组成、结构和梯度格局对植物多样性的影响

植物多样性作为生物多样性研究的主要内容,一直以来受到广泛关注。近20年来,随着景观生态学的兴起和地理信息技术的发展,景观生态学与岛屿生物地理学、异质种群理论相结合,在植物多样性的保护和利用研究中得到运用。本文就在这3个理论的基础上,简述了景观组成(斑块、廊道、基质)、景观结构(斑块面积、边缘、隔离程度)和梯度格局(海拔、演替、土壤养分、干扰)对植物多样性的影响,强调了地理信息技术应用的重要性和景观层次上进行植物多样性研究的必要性。因此,在多个尺度上共同研究多个影响因子对植物多样性的复合作用,利于进一步揭示植物多样性的变化过程及其机制,有利于植物多样性的保护和利用。     

西藏岗巴拉山土壤细菌多样性海拔分布格局及其驱动因子

高原山地是对全球气候变化最为敏感的脆弱生态系统之一,研究高原山地土壤细菌群落沿海拔变化特征,对于揭示受气候变化和人为干扰的山地微生物群落结构和功能有十分重要的科学意义。研究以西藏岗巴拉山作为研究对象,运用Illumina MiSeq高通量测序技术,基于精细样方尺度分析了岗巴拉山沿海拔梯度土壤细菌群落组成和多样性的变化特征及其驱动因子。结果表明：岗巴拉山土壤细菌共包含36门125纲307目477科838属1878种,将12个海拔带分为高中低3组（低海拔从3800-4100 m、中海拔从4200-4500 m、高海拔从4600-4900 m）,中海拔总分类操作单元（OTU）数最多,特有OTU数最少,土壤细菌群落丰富度随海拔升高呈单峰趋势,但其特异性随海拔呈U型分布格局。岗巴拉山土壤细菌群落中的优势菌门是放线菌门、酸杆菌门、变形菌门、绿弯菌门、疣微菌门和芽单胞菌门等,土壤细菌群落Shannon多样性指数随海拔升高而逐渐减小,而Simpson多样性指数在高海拔最高,Chao指数随海拔升高呈单峰变化趋势。主坐标分析（PCoA）表明土壤细菌群落结构在不同海拔梯度上存在显著差异,且低海拔土壤细菌群落组内也存在显著差异。冗余分析（RDA）表明海拔、pH、总氮、总磷和有机碳对土壤细菌群落结构有显著影响,与环境因子相关性分析表明海拔、pH、总氮、总磷和有机碳与土壤细菌群落结构显著相关,曼特尔检验表明pH和海拔是影响土壤细菌群落的关键因素。岗巴拉山土壤细菌多样性沿海拔梯度呈单调下降趋势,pH是影响土壤细菌群落沿海拔变化特征的关键环境因子,总氮、总磷和有机碳也是影响土壤细菌群落的重要环境因子。     

天山南坡高寒草地海拔梯度上的植物多样性变化格局

山地气候随海拔梯度变化使山地成为研究生物多样性的热点区域。在天山南坡巴音布鲁克高寒草地,对不同海拔梯度下的物种多样性进行了研究。结果表明共调查样地9个,出现植物34种,分属17科29属;物种丰富度随海拔升高呈明显的偏峰格局,在海拔3060m的天山羽衣草(Alchemilla tianschanica)草甸,物种组成最为丰富,出现植物17种,分属12科17属;Shannon-Wiener指数的变化范围为2.02~2.40,最小值出现在海拔2760m以紫花针茅(Stipa purpurea)为优势种的高寒草原,峰值则出现在3060m的天山羽衣草草甸,Shannon-Wiener指数随海拔梯度的变化趋势与物种丰富度基本相同,呈明显的偏峰格局;随海拔升高,Cody指数表现出明显的单峰格局;Shannon-Wiener指数与生长季温度存在显著负相关,而与生长季湿度和土壤含水量存在显著正相关。     

新疆天山南坡中段种子植物区系垂直分布格局分析

对植物多样性垂直分布格局及其维持机制的研究可以有效揭示植物物种多样性分布特征及其环境影响因子。本文通过野外调查、查阅标本并结合相关文献资料,对天山南坡中段种子植物区系沿海拔梯度的分布格局进行了系统研究。结果显示,在大区域尺度上,科属种的物种丰富度随海拔升高均呈先增加后减少的趋势,且最高值出现在中低海拔1900~2000 m处;不同生活型植物沿海拔梯度的变化格局有所不同,其中,乔木、一年生草本、藤本及寄生植物表现出随海拔升高物种丰富度逐渐降低的趋势,灌木、多年生草本及二年生草本植物物种丰富度则呈先增加后减少的变化趋势;从植物区系地理成分来看,世界分布所占的比重沿海拔梯度升高呈先增加后减少的趋势;温带地理成分所占的比重沿海拔梯度升高呈缓慢上升趋势;古地中海地理成分所占的比重沿海拔梯度升高呈先增加后减少然后再增加的变化趋势;热带地理成分所占的比重沿海拔升高呈逐渐下降的趋势;东亚地理成分所占的比重沿海拔梯度升高呈先增加后减少然后再增加的变化趋势。对该分布格局与当地干旱的气候条件及海拔梯度上热量和水分条件的变化相适应。     

Influence of urbanization on riparian forest diversity and structure in the Georgia Piedmont, US

Riparian forests are increasingly threatened by urban expansion and land use change worldwide. This study examined the relationships between landscape characteristics and woody plant diversity, structure, and composition of small order riparian corridors along an urban-rural land use gradient in the Georgia Piedmont, US. Riparian plant diversity, structure, and composition were related to landscape metrics and land use. Species richness was negatively associated with impervious surfaces and landscape diversity, and positively associated with forest cover and largest forest patch index. Shannon species diversity was strongly related to the biomass of non-native species, especially for the regeneration layer. Urban sites were characterized by high richness of non-native and pioneer species. Developing sites were dominated by the non-native shrub, Ligustrum sinense Lour., and several native overstory trees, mainly Acer negundo L. While agricultural and managed forest sites were composed of ubiquitous species, unmanaged forest sites had a structurally distinct midstory indicative of reduced disturbance. Urban and agricultural land uses showed decreased native stem densities and signs of overstory tree regeneration failure. Results from this study highlight the impact of the surrounding landscape matrix upon riparian forest plant diversity and structure.     

陆地植物群落物种多样性维持机制

从空间尺度和特定生物区系两个尺度对物种多样性的维持机制进行了综述.在大的空间尺度,简述了引起物种多样性存在差异的物理和自然因子的作用,包括植物群落的历史和年龄、梯度变化(纬度梯度、水分梯度、海拔梯度、土壤养分梯度)、面积效应和隔离程度;针对特定生物区系,从生物因素(生产力、种间关系、林隙动态)和非生物因素(演替、干扰及空间异质性、人类活动)方面论述其与物种多样性之间的关系.     

秦岭山地天然次生林群落MRT数量分类、CCA排序及多样性垂直格局

采用多元回归树(MRT)对秦岭山地天然次生林群落进行数量分类,采用典范对应分析(CCA)进行排序,分析了秦岭山地天然次生林群落物种多样性沿海拔梯度的变化规律。结果表明:(1) 275个样方共有种子植物195种,隶属61科128属。乔、灌、草3个层次物种多样性变化沿海拔梯度的变化趋势基本一致,呈单峰模型;(2)经交叉验证认为秦岭山地天然次生林群落可分为2类,Ⅰ冬瓜杨(Populus purdomii)+陇东海棠(Malus kansuensis)+蛇莓(Duchesnea indica)群落,Ⅱ锐齿槲栎(Quercus aliena var. acuteserrata)+黄栌(Cotinus coggygria)+茜草(Rubia cordifolia)群落;(3) CCA排序结果揭示了群落生境的分布范围,反映出生态轴的排序意义,较好地反映秦岭山地天然次生林群落与环境因子的关系,其结果表明,海拔、坡向、凋落层厚度和干扰情况4个变量对该地区次生林群落的分布有较大的影响。     

Plant species and growth form richness along altitudinal gradients in the southwest Ethiopian highlands

Questions: Do growth forms and vascular plant richness follow similar patterns along an altitudinal gradient? What are the driving mechanisms that structure richness patterns at the landscape scale? Location: Southwest Ethiopian highlands. Methods: Floristic and environmental data were collected from 74 plots, each covering 400 m². The plots were distributed along altitudinal gradients. Boosted regression trees were used to derive the patterns of richness distribution along altitudinal gradients. Results: Total vascular plant richness did not show any strong response to altitude. Contrasting patterns of richness were observed for several growth forms. Woody, graminoid and climber species richness showed a unimodal structure. However, each of these morphological groups had a peak of richness at different altitudes: graminoid species attained maximum importance at a lower elevations, followed by climbers and finally woody species at higher elevations. Fern species richness increased monotonically towards higher altitudes, but herbaceous richness had a dented structure at mid‐altitudes. Soil sand fraction, silt, slope and organic matter were found to contribute a considerable amount of the predicted variance of richness for total vascular plants and growth forms. Main Conclusions: Hump‐shaped species richness patterns were observed for several growth forms. A mid‐altitudinal richness peak was the result of a combination of climate‐related water–energy dynamics, species–area relationships and local environmental factors, which have direct effects on plant physiological performance. However, altitude represents the composite gradient of several environmental variables that were interrelated. Thus, considering multiple gradients would provide a better picture of richness and the potential mechanisms responsible for the distribution of biodiversity in high‐mountain regions of the tropics.     

Natives and non‐natives plants show different responses to elevation and disturbance on the tropical high Andes of Ecuador

The aim was to assess patterns of plant diversity in response to elevation and disturbance in a tropical mountain. The study area was located in north‐central portion of the Eastern Cordillera of the Ecuadorian Andes, on a road from 1,150 m a.s.l. (Osayacu) to 4,000 (Papallacta). Along a mountain road spanning a wide altitudinal gradient, at 20 elevations we sampled three plots: one at the roadside and two perpendicular to the roadside. The relationship between elevation and species richness was assessed using linear and quadratic regressions, the effect of disturbance on species richness was determined by ANCOVA and a t test with parameters obtained from quadratic equations. Similarity of species composition among the roadside and sites distant was evaluated with the Chao‐Jaccard and classic Jaccard similarity indices, the distribution of non‐native species according to their origin were analyzed with linear and quadratic regression. The native species showed a linearly monotonic decrease with elevation, whereas non‐natives showed a quadratic distribution. Disturbed areas had the greatest number of non‐native species and lower native species richness, showing also a high floristic similarity; less disturbed areas showed the opposite. The non‐native species of temperate origin were more numerous and showed unimodal elevational distribution, while species of tropical origin were few and decreased linearly with elevation. We conclude that in a tropical highland mountain range, native and non‐native plant species respond differently to elevation: native species exhibit a monotonically linear decrease, and non‐native species show a unimodal trend. Disturbance positively affects non‐native species showing higher richness and fewer species turnover. In addition, the non‐native species are located along of the elevational gradient in relation to their biogeographic origin.     

Distribution of alien vs. native plant species in roadside communities along an altitudinal gradient in Tenerife and Gran Canaria (Canary Islands)

Roadside plant communities were studied along two roads following an altitudinal gradient in Gran Canaria and Tenerife (Canary Islands). Our aim was to investigate variation in plant species richness, particularly of the alien flora, along a gradient from coastal shrubland to summit vegetation (1950 m a.s.l. in Gran Canaria, 2300 m in Tenerife) in relation to variation in habitat factors (altitude, habitat structure, roadside disturbance, distance to urban nuclei). We compared different species groups that were classified in terms of their biogeographical status, origin and life form. Altitude was the most important factor determining species richness and composition along both roadside transects. Alien plants showed a unimodal distribution pattern along the altitudinal gradient, with less species and lower abundance at low and high altitudes, and highest abundance at intermediate altitude. Alien plant species were also relatively more frequent near urban centres. The number of native and alien species was significantly positively correlated along the altitudinal gradient. Both alien and native, non-endemic species showed differences in their distribution along the altitudinal gradient according to their biogeographical affinities and climatic tolerances. Despite considerable differences in species pools these patterns were consistent among the two islands. Environmental (abiotic) stress is proposed as a primary, altitude-related factor acting as a filter against most alien plants at coastal and high-mountain altitudes. A higher frequency or intensity of disturbance at intermediate altitudes may be a further causal factor promoting alien plants in this zone. Future management efforts to control alien plants along roads should, therefore, concentrate on intermediate altitudinal zones of the higher Canary Islands.     

Finding spatial regularity in mosaic landscapes: two methods integrated

Two methods were employed to find spatial regularity in a complicated mountain landscape of Beijing, China on the basis of functional and structural affinities. The first approach applied Affinity Analysis based on species composition to landscape. The mosaic diversity of the landscape was 3.5298>3, which means the study landscape is complex and controlled by multiple environmental gradients. These landscape types were divided into 3 parts according to the mean affinity values of 0.2143 and 0.7857 (0.5±1 SD). Modal sites are the central types of the landscape, which include a zonal broad-leaved forest of the region and a conifer plantation replacing the former. Outliers are found in the highest altitude and the lowest, both have few species in common with the above two modal types. The remaining landscape types are intermediate sites, which are transitional between modals and outliers, broadly distributed throughout mountain environments. Neighbor types have more species in common than those more widely separated, which probably distributed adjacently in space or in similar quality habitat. The other method employed is the new TWINSPAN analysis by substituting spatial neighboring data of landscape types for species composition data. It clearly divided the landscape types into three groups, i.e., subalpine, middle and low mountain groups, which were correlated with altitude, as well as influenced by human disturbance. The new TWINSPAN classification method is more reliable in finding spatial gradient of patchy landscapes than affinity analysis; however, affinity analysis is useful in finding species diversity pattern and the importance of landscape types in a region. Integrating advantages of the two methods could supply complete and reliable information on how landscape types are distributed in space, which environmental gradient dominates the spatial distribution of the landscape types, as well as where important and unusual types are located.     

Species Diversity and Altitudinal Gradient Patterns of Evergreen Broad leaved Forest in MeihuashanNational Natural Reserve,Fujian Province

In China, evergreen broad leaved forests (EBLFs) is one of the most important vegetation types which was widly distributed in subtropical area, and it plays a very important role in the global biological diversity and natural environment conservation also. In order to reveal species diversity and altitudinal gradient patterns of evergreen broad leaved forest in Meihuashan National Natural Reserve, Fujian Province. Five altitude transects were set up at a vertical interval of 200m between 375m and 1300m above sea level in the EBLFs distribution areas, and twenty four quadrats(14400m2) had been surveyed. Species richness(S), species richness index (dGl), Simpson index (D), Shannon Wiener index (H′), Pielou evenness index (J) had been used for analysis of species diversity and altitudinal gradient pattern of EBLFs. The average value of S, dGl, H′,J and D were 64.42, 10.75, 5.75, 3.50, 0.58 respectively. The difference of community species diversity index(S, dGl, D, H′, and J) was extremely significant between transects, and the altitudinal gradient patterns of species diversity presented the unimodal variable trend, with a peak in the mid altitude(700m-900m). The species richness and Shannon Wiener index of different layer were ranked as shrub layer (include young tree and the plants between layers)>arbor layer>herb layer. The species richness of tree and shrub layer, and Shannon Wiener index of tree layer were significantly different between at transects, and trends of altitude gradient was similar to community. The Shannon Wiener index of shrub layer and herb layer, and the species richness of herb layer did not change significantly along elevation gradient. Therefore, plant species diversity distribution pattern presented a unimodal variable trend along an elevation gradient, and supported “mid domain model” in EBLFs of Meihuashan National Nature Reserve.     

Biomass and diversity of dry alpine plant communities along altitudinal gradients in the Himalayas

A non-linear relationship between phytodiversity and altitude has widely been reported, but the relationship between phytomass and altitude remains little understood. We examined the phytomass and diversity of vascular plants along altitudinal gradients on the dry alpine rangelands of Ladakh, western Himalaya. We used generalized linear and generalized additive models to assess the relationship between these vegetation parameters and altitude. We found a hump-shaped relationship between aboveground phytomass and altitude. We suspect that this is engendered by low rainfall and trampling/excessive grazing at lower slopes by domestic livestock, and low temperature and low nutrient levels at higher slopes. We also found a unimodal relationship between plant species-richness and altitude at a single mountain as well as at the scale of entire Ladakh. The species-richness at the single mountain peaked between 5,000 and 5,200 m, while it peaked between 3,500 and 4,000 m at entire Ladakh level. Perhaps biotic factors such as grazing and precipitation are, respectively, important in generating this pattern at the single mountain and entire Ladakh.     

基于移动窗口法的豫西山地丘陵地区景观异质性分析

研究典型区域景观异质性过程中,对特征尺度的判断尤为重要。基于3S技术,以豫西山地丘陵地区巩义市为研究区域,在分析其景观组分与结构的基础上,采用半变异函数和移动窗口相结合的方法,确定研究景观异质性的特征尺度,并在特征尺度下选取西北—东南方向和东北—西南方向两条样线,分析研究区不同干扰背景下景观异质性的空间特征。结果表明:豫西巩义地区总体上以旱地、建设用地、水浇地、草地和有林地景观类型为主,其中旱地所占比例最大(30.9%),沟渠所占比例最小(0.1%);根据特征尺度分析确定研究区巩义市景观异质性的合适尺度为1000 m;在特征尺度下,研究区景观破碎化以河谷平原和丘陵为主的巩义东部偏南区域最高,以人为干扰较少的南部低山有林地区最低,景观多样性分布特征则呈现4个聚集中心,分别为北部河谷平原农业区、城市建成区、南部低山区和东南丘陵区;不同干扰背景下,巩义地区景观异质性根据城市化程度呈现以市区为中心向外辐射发展的特征,同时受海拔高度因素影响较大,即在海拔200 m以下区域景观受人为干扰强烈,海拔200—500 m丘陵区域受海拔因子和人为干扰因子共同作用,海拔500 m以上区域海拔因子起主导作用。研究结果可为豫西山地丘陵地区及同类地区景观异质性的研究尺度、景观格局优化和土地的有效管理提供依据。     

青藏高原高寒草甸物种多样性的海拔梯度分布格局及对地上生物量的影响

植物物种多样性在海拔梯度上的变化规律以及物种多样性与生产力的关系是生态学研究的热点, 至今还没有得出一般性规律。本文以青海省海南藏族自治州贵德县的拉脊山(36°21′ N, 101°27′ E, 海拔3,389-3,876 m)和果洛藏族自治州的玛沁县军牧场山体(34°22′ N, 100°30′ E, 海拔4,121-4,268 m)为研究对象, 对植物高度、盖度、地上生物量和物种多样性随海拔高度的变化进行调查和统计分析, 以探讨青藏高原高寒草甸的物种多样性和地上生物量在海拔梯度上的变化规律及两者的关系。结果表明: (1)两条山体样带上地上生物量与物种多样性随海拔的变化规律一致: 随着海拔的升高, 地上生物量线性降低; Shannon-Wiener指数、Simpson指数和物种丰富度都呈单峰曲线, 在中间海拔最大, 而Pielou指数随海拔的升高线性增加。结合目前针对青藏高原高寒草甸的研究数据, 发现物种丰富度随海拔高度的变化均呈单峰曲线, 说明随着海拔的升高物种多样性先升高后降低可能是青藏高原物种多样性分布的普遍规律。(2)地上生物量与物种多样性的关系在两条山体样带上表现一致: 地上生物量随Shannon- Wiener指数、Simpson指数和Pielou指数的升高而线性降低, 但与物种丰富度不相关。综合两条山体样带所有样方数据, 发现地上生物量与Shannon-Wiener指数、Simpson指数不相关, 而随物种丰富度的升高线性增加。结合目前在青藏高原的相关研究数据, 发现地上生物量与物种丰富度呈S型曲线(logistic model)。     

Vegetation heterogeneity and diversity in flat and mountain landscapes of Patagonia (Argentina)

Abstract. We studied floristic and diversity patterns and their environmental controls in two landscapes of contrasting topography in the Patagonian steppe. The analyses were focused on the effects of water availability gradients and landscape configuration on plant species distribution and coexistence. Floristic variation was investigated using Correspondence Analysis. The relationship between floristic and environmental variation was analyzed using Canonical Correspondence Analysis and correlation tests. We explored diversity patterns by relating spatial distance to floristic dissimilarities. The floristic gradient was determined by shrub and grass species and was related to precipitation in the flat area, and to precipitation, elevation and potential radiation in the mountain area. Site species richness increased with water availability in both areas. Mean site species richness and species turnover in space was higher in the mountain than in the flat area. Landscape species richness and floristic gradients were more concentrated in the mountain than in the flat area. In contrast to shrubs and grasses, forb species distributions were uncoordinated and probably independent of any environmental gradient. Our results suggest (1) that landscape configuration affects species composition and diversity through its direct effect on abiotic environmental heterogeneity, and (2) that the environmental controls of the community composition vary depending on the plant functional type considered.     

河北坝上草原东沟植物群落生态梯度的数量分析

运用DCCA排序轴分类,将河北坝上草原东沟的植物群落划分为8类,效果较好．排序图表达了植物群落的环境梯度、结构梯度和人为干扰．第1轴反映了群落在海拔和坡度方面的空间梯度,第2轴反映了群落的坡向分异格局,两轴综合反映了群落沿水分梯度的空间分异．群落的层片构成和各层片物种组成也表现出相应的空间分布格局．白桦局限在阴坡高海拔陡峭处．阴坡灌木与草本层片优势种分别为金露梅与细叶苔草,阳坡则为蒿类和冰草．阳坡群落各层片优势种还存在海拔和坡度分布格局．另外,放牧、耕作和伐树等人为干扰对群落时空分布也有显著影响．一般来说,生境条件较好的群落,人为干扰较严重．     

Contrasting relationships between species diversity and genetic diversity in natural and disturbed forest tree communities

? This study aimed to reveal species-genetic diversity correlations (SGDCs) and their underlying mechanisms in natural and disturbed forests. ? A community survey and molecular analyses were carried out to compare species diversity (SD), the genetic diversity of the dominant tree species Euptelea pleiospermum (GD), the altitudinal patterns of SD and GD, SGDC, genetic differentiation (F(ST) ), community divergence (F(ST) -C), effective population size (N(e) ), and recent migration rate between mountain riparian forests along the Yandu (natural) and Nan (disturbed) rivers. ? In natural forests, both SD and GD showed a unimodal altitudinal pattern and GD was positively correlated with SD, whereas a unimodal pattern and positive SGDC were not found in the disturbed forests. SD and F(ST) at the natural sites were higher than those at the disturbed sites. However, there were no significant differences in GD, F(ST) -C, N(e) or recent migration rate between the natural and disturbed sites. ? A correlation between the patterns of SD and GD along a geographical gradient (e.g. altitude) is an important driver of positive SGDC. The absence of positive SGDC in the disturbed forests may result from reduced SD but unaffected GD, indicating nonparallel changes in SD and GD. This study furthermore cautions against generalizations about changes in SD and GD following disturbance.