| Context: Anthropogenic land use change is a main driver of biodiversity decline worldwide.Anthropogenic land use often modifies biotic and abiotic conditions of an ecosystem,potentially impacting ecological processes such as environmental filtering,dispersal and species interactions.As a result,land use change may also impact the spatial distributions of species,communities,or biodiversity,beyond the quantity of biodiversity.Spatial disarrangements of biodiversity may have consequences for ecological processes,functions and delivery of services,so that detailed understanding of land use change-associated spatial disarrangements of biodiversity is essential for informed ecological management.Therefore,in my thesis,we first conducted a metaanalysis of empirical literature to assess the state of knowledge and to identify potential knowledge gaps related land use/disturbance and spatial patterns of biodiversity.We found that land use change/habitat disturbances generally reduce the spatial autocorrelation in species diversity on average by 15.5% and reduce its range(the distance up to which autocorrelation prevails)by 21.4%,in part,due to disturbancedriven changes in environmental conditions,dispersal,species interactions,or a combination of these processes.However,there remains substantial knowledge gap regarding the effects of land use change on spatial patterns of biodiversity especially functional diversity in forest ecosystems.Moreover,whether the impacts of forest conversion on spatial patterns of species and functional diversity vary the scale of observations remain largely unclear.Questions: In my empirical study,we aimed to describe how forest conversion may affect the spatial patterns of plant species and functional diversity,and whether the observed impacts vary with the scale of observation.I consequently aimed to address the following three questions:(i)What is the effect of forest conversion on the spatial patterns of species diversity?(ii)What is the effect of forest conversion on the spatial patterns of functional diversity?(iii)Does the effect of forest conversion on the spatial patterns of species and functional diversity vary with spatial scale(cf.spatial grain)?Methods:The study was carried out at Tiantong National Forest Park,located in Ningbo,Zhejiang province,southeast China(29° 48’N,121°47’E,650 m altitude,349 square hectare area).Tiantong National Forest Park offers an ideal setting for present study because:(i)it offers regional forest-conversion types(e.g.mature intact forests,shrub land and plantation forests),(ii)it is large enough to sample for different spatial scales(e.g.1 m × 1 m,10 m × 10 m and 20 m × 20 m).Four sites(N=4)for each type of forest(mature intact forests,shrub land and plantation forests)were sampled,and one 100 m long and 20 m wide(100 m × 20 m)transect was established in each site,resulted in a total of 12 transects(N=12).Each transect was first divided into five continuous plots of 20 m × 20 m,and each of these 20 m × 20 m plots(N=5)was then further divided into four plots of 10 m × 10 m.In parallel,we also established 100 1 m × 1 m continuous plots along the edge of transect.This divisions resulted in a total of 100 spatially adjacent plots of 1m × 1m,20 spatially adjacent plots of 10 m × 10 m and five spatially adjacent plots of 20 m × 20 m per transect or per site.I defined small scale,medium scale and large scale for 1 m × 1 m plot,10 m × 10 m plot and 20 m × 20 m plot,respectively.In each 1 m × 1 m,10 m × 10 m,or 20 m × 20 m plot,all woody(trees and shrubs)and non-woody(herbs,ferns and grasses)species were identified up to species level and their abundance was recorded.At the same time,we sampled species trait values for five leaf traits(LMA = leaf mass per area,LT = leaf thickness,SLA = specific leaf area,LDMC = leaf dry matter content and LS = leaf succulence).We selected four indices for species diversity(abundance,species richness,species evenness and Shannon-diversity),and six indices for functional diversity(Rao’s Q and five CWM of leaf traits).We used Moran’s spatial correlogram for quantifying the spatial patterns of species and functional diversity.We also decomposed the overall spatial autocorrelation(i.e.,autocorrelation in the first lag)of species and functional diversity into unique positive spatial autocorrelation and negative spatial autocorrelation components.To examine whether the overall spatial autocorrelation,positive spatial autocorrelation and negative spatial autocorrelation of species and functional diversity various along forest conversion gradient and different spatial scales,we used a mixed model analysis of variance and checked the residuals for normality and homogeneity of variance,and Tukey test was used to show exact significant differences along forest conversion gradient or in different spatial scales.Result:(1)Across the types of forest conversion,all measured indices of species diversity namely abundance,richness,evenness and Shannon-diversity were positively spatially autocorrelated both at small and medium scales,but not at large scale.Spatial ranges of abundance,species richness and species evenness were lower in plantation forests compared to mature intact forests.Spatial range of abundance,species richness and Shannon-diversity were larger for small scale compared to large scale.The overall spatial autocorrelation in species diversity did not change significantly along forest conversion gradient;however,it varied with the scale of observation.Both overall and positive spatial autocorrelation in Shannon-diversity decreased with increasing the scale of observation.(2)Rao’s Q was positively spatially autocorrelated along forest conversion gradient among spatial scales,except for the large scale in mature intact forests.Spatial range of Rao’s Q was lower in plantation forests compared to mature intact forests,whereas it showed non-consistent pattern in different spatial scales.Both overall and positive spatial autocorrelation in Rao’s Q varied substantially among forest conversion gradient,and spatial scales,whereas unique negative spatial autocorrelation in Rao’s Q only differed along forest conversion gradient.(3)For CWM of leaf traits,all indices were positively spatially autocorrelated along forest conversion gradient for both small and medium scales,but not for large scale.Spatial range of different indices of CWM of leaf traits responded differently along a forest conversion gradient.Spatial range of CWM of LT and SLA were lower in plantation forests compared to mature intact forests;however,spatial range of CWM of LDMC was higher in plantation forests.Interestingly,spatial range of CWM of LMA and LS in mature intact forests versus plantation forests showed non-consistent result regarding its dependence on spatial scale.Only overall and positive spatial autocorrelation in CWM of LMA various along forest conversion gradient,with lower autocorrelation values in plantation forests compared to mature intact forests.All indices of CWM of leaf traits showed higher overall and positive spatial autocorrelation in small than large scale.Conclusions: Forest conversion had a significant effect on the spatial patterns of functional diversity,with a decline in the overall and positive spatial autocorrelation in Rao’s Q.However,I did not detect the effects of forest conversion on the spatial patterns of species diversity.No doubt,a majority of the overall and positive spatial autocorrelation in species and functional diversity was higher in small scale than in large scale.Our study highlights the importance of quantifying the overall spatial autocorrelation intensity to unique positive spatial autocorrelation and unique negative spatial autocorrelation components,and called a need for linking spatial pattern of exact environmental factors to spatial biodiversity patterns as well.More importantly,our study offered a new sight to explore the diver and dynamic behind spatial patterns of plant species and functional diversity to disturbance,hence may have important implications for both spatial ecological theory and applications in subtropical forest management and conservation. |
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