Mapping species density of trees,shrubs and vines in a tropical forest,using field measurements,satellite multiespectral imagery and spatial interpolation

We estimated the number of species in a tropical forest landscape in Quintana Roo, Mexico, based on the relationship between reflectance values of satellite imagery and field measurements of plant species density (mean number of species per plot). Total species density as well as that of tree, shrub and vine species were identified from 141 sampling quadrats (16543 individuals sampled). Spatial prediction of plant diversity was performed using universal kriging. This approach considered the linear relationship between plant species density and reflectance values of Thematic Mapper™, as well as the spatial dependence of the observations. We explored the linear relationships between spectral properties of TM bands and the species density of trees, shrubs and vines, using regression analysis. We employed Akaike Information Criterion (AIC) to select a set of candidate models. Based on Akaike weights, we calculated model-averaged parameters. Linear regression between number of species and reflectance values of TM bands yielded regression residuals. We used variogram analysis to analyze the spatial structure of these residuals. Results show that accounting for spatial autocorrelation in the residual variation improved model R² from 0.57 to 0.66 for number of all species, from 0.58 to 0.65 for number of tree species, from 0.26 to 0.41 for number of shrub species and from 0.13 to 0.17 for species density of vines. The empirical models we developed can be used to predict landscape-level species density in the Yucatan Peninsula, helping to guide and evaluate management and conservation strategies.     

西双版纳热带山地雨林群落乔木树种多样性研究

根据块样地资料对西双版纳热带山地雨林树种多样性特征进行了分析.结果表明,在2 500m²的样地上,随着起测胸径递增,各样地乔木个体数和树种丰富度均表现为依次递减;低海拔带上(850～1000 m)的山地雨林(1、2号样地)的各指数值无一定变化规律,较高海拔带上(1200～2000 m)的山地雨林(3～6号样地)的Shannon-Wiener指数和Simpson指数均表现为依次递减,而Pielou均匀度指数则呈依次递增的趋势.较高海拔带上的山地雨林在较小乔木起测胸径(≥2 cm、≥5 cm、≥10 cm)的树种丰富度、多样性和均匀度指数均要明显大于低海拔带上的山地雨林,而两者在较大乔木起测胸径(≥20 cm、≥30 cm、≥50 cm)的各指数值无明显差异.随着取样面积的递增,各样地树种丰富度、多样性和均匀度指数在取样面积递增到2 000m²处均已趋于平缓.     

古尔班通古特沙漠南部植物多样性及群落分类

采用分层取样的方法,以1000m2/样地为最小观测面积,对古尔班通古特沙漠南部61样地植物多样性进行了调查。发现92个物种,隶属于22科71属,单种科、单种属多,区系优势现象明显。草本植物占总物种数的81.5%,短命植物占43.5%,对物种丰富度和盖度的空间变化起决定作用。属的区系成分分析表明地中海、西亚至中亚分布型成分占大多数,具有典型的地中海旱生植物区系分布特征。总物种数,草本物种数,短命植物物种数与纬度显著负相关,与经度和海拔显著正相关。从南到北,总盖度、草本盖度和短命植物的盖度显著下降,灌木的盖度则增加,从西到东,总盖度、草本盖度和短命植物的盖度显著增加,而灌木的盖度则减少。采用多元回归树(Multivariate regression trees,MRT)方法,根据纬度、土壤pH值和海拔,将61样地分为4个群落。结合降水在古尔班通古特沙漠由西到东,由南到北梯度变化所导致的物种多样性的变化,推测如果未来降水持续增加,古尔班通古特沙漠草本植物的优势将更加明显。     

Seedling assemblages and the alternative successional pathways experienced by Atlantic forest fragments

Background: Habitat loss and fragmentation have been argued to drastically alter the composition of tree assemblages inhabiting small forest fragments but the successional trajectory experienced by such edge-affected habitats remains controversial.

Aims: Here we examine whether small fragments (3.4–91.2 ha) support seedling assemblages more similar to those in 10–70-year-old secondary forests than to those in mature forests, in order to infer to what extent fragments move toward early successional systems.

Methods: Using 59 0.1-ha plots distributed in a fragmented landscape of Brazilian Atlantic forest, we evaluated species richness and functional and taxonomic composition of seedling assemblages in 20 small forest fragments, 19 stands of secondary forest and 20 stands of mature forests in the interior of an exceptionally large fragment (ca. 3500 ha).

Results: Small fragments presented the least species-rich seedling assemblages (17.2 ± 5.7 species), followed by secondary (22.5 ± 5.3), and mature forest (28.4 ± 5.3). Small fragments had seedling assemblages with functional and taxonomic composition more similar to those in secondary than in mature forest. Small fragments had a greater relative richness and abundance of pioneer trees (ca. 40% more), vertebrate-dispersed (6–25%), and those bearing medium-sized seeds (30–70%), while large-seeded species and individuals were reduced (>50% decrement) in comparison to seedling assemblages in mature forest.

Conclusions: By comparing seedlings across a wide range of successional habitats we offer evidence that small forest fragments are experiencing an alternative successional pathway towards an early-successional system with reduced plant diversity.     

Relationships between landscape patterns and species richness of trees,shrubs and vines in a tropical forest

The present study aims to identify and characterize the relationships among landscape structure and plant diversity in a tropical landscape forest in Quintana Roo, Mexico. Total species richness as well as that of trees, shrubs and vines species were identified from 141 sampling quadrats (16,543 individuals sampled). Based on vegetation classes obtained from multi-spectral satellite image classification, I constructed plant diversity maps of the landscape under study using stratified kriging. I calculated the mean number of species in individual patches as the average values of kriging estimates inside of each patch. I then explored the relationships between landscape pattern metrics and the species richness of trees, shrubs and vines, as well as all groups combined using regression analysis. I employed Akaike Information Criterion (AIC) to select a set of candidate models. Based on akaike weights, I calculated model-averaged parameters. Results show that plant diversity of the patches depends on both the quality of the surrounding habitats and the proximity of surrounding patches (i.e., patch isolation).     

热带森林树种多度和丰富度空间分布特征研究

用巴拿马50 hm2森林动态监测样地内直径≥1 cm的树种资料,分析了该样地树种多度(个体数)和丰富度(物种数)及其方差和变异系数在6个取样尺度(5 m×5 m,10 m×10 m,20 m×20 m,25 m×25 m,50 m×50 m,100 m×100 m)的变化规律.结果显示:(1)由于多度的可加性,不同取样尺度在样地内树种多度的变化表现出一致性;随取样尺度的增加,多度方差呈线性增加,而变异系数呈线性减小.(2)丰富度随取样尺度的变化较为复杂,随取样尺度的增加,丰富度方差呈非线性变化,在取样尺度为25 m×25 m时方差最大;变异系数随取样尺度的增加而呈线性减小.研究表明,大尺度的多度值可以由小尺度的多度值通过外推法估计,而丰富度却不能,在生物多样性的保护和管理中不能简单地从一个取样尺度的生物丰富度推测另一个取样尺度丰富度.     

A central Amazonian terra firme forest. I. High tree species richness on poor soils

Tree size, density, and species richness were established for three one-hectare plots of terra firme forest in central Amazonian Brazil. In the three hectares, 1916 individual trees with DBH 10 cm were sampled. A total of 58 families, 181 genera, and 513 species were determined. Hectare A had 285 species, 138 genera, and 47 families; hectare B 280 species, 123 genera, and 48 families; and hectare C 280 species, 125 genera, and 44 families. Comparably high species richness in Amazonia has heretofore only been reported from western Amazonia. This dispels the idea that high species richness can only develop in areas with rich soils and relatively high rainfall. It is suggested that such high species richness is the result of a combination of habitat heterogeneity and geological history. These high diversity forests, because they occur on nutrient poor soils, can be protected with little or no impact on development in the region because the soils are essentially useless for agriculture and for supporting long-term cattle pasture.     

Tree diversity in sacred groves of the Jaintia hills in Meghalaya, northeast India

Biodiversity of woody species was investigated in Ialong and Raliangsacred groves of the Jaintia hills in Meghalaya, northeast India. These grovesrepresent the climax subtropical broad-leaved forest of the area. A total of 738individuals belonging to 82 species, 59 genera and 39 families was identified ina 0.5 ha plot of the Ialong sacred grove, whereas the same area in theRaliang sacred grove had 469 individuals of 80 species, 62 genera and 41families. About 32% species were common to both groves. Lauraceae, with10–17 species, was the dominant family. The canopy and subcanopy stratawere respectively composed of 28 and 33% of the total tree species in theforest. The number of species as well as stem density were greater for the treesof lower dbh (5–15 cm) class compared to the higher (> 66cm) dbh class. The majority of the species showed a contagiousdistribution pattern and low frequency. The basal area varied from 57.4 to 71.4m² ha^–1. Species richness within theforest varied from 3 to 15 per 100 m² in Ialong and 3 to 12 per 100m² in Raliang. The dominance–distribution curves showed highequitability and low dominance in both groves.     

The link between international trade and the global distribution of invasive alien species

Invasive alien species (IAS) exact large biodiversity and economic costs and are a significant component of human-induced, global environmental change. Previous studies looking at the variation in alien species across regions have been limited geographically or taxonomically or have not considered economics. We used a global invasive species database to regress IAS per-country on a suite of socioeconomic, ecological, and biogeographical variables. We varied the countries included in the regression tree analyses, in order to explore whether certain outliers were biasing the results, and in most of the cases, merchandise imports was the most important explanatory variable. The greater the degree of international trade, the higher the number of IAS. We also found a positive relationship between species richness and the number of invasives, in accord with other investigations at large spatial scales. Island status (overall), country area, latitude, continental position (New World versus Old World) or other measures of human disturbance (e.g., GDP per capita, population density) were not found to be important determinants of a country’s degree of biological invasion, contrary to previous studies. Our findings also provide support to the idea that more resources for combating IAS should be directed at the introduction stage and that novel trade instruments need to be explored to account for this environmental externality.

Diversity,composition, and structure of tropical dry forests in Central America

Tropical dry forests have been reduced to less than 0.1% of their original expanse on the Pacific side of Central America and are considered by some to be the most endangered ecosystem in the lowland tropics. Plots 1000 m² were established in seven tropical dry forests in Costa Rica and Nicaragua in order to compare levels of species richness to other Neotropical dry forest sites and to identify environmental variables associated with species richness and abundance. A total of 204 species and 1484 individuals 2.5 cm were encountered. Santa Rosa National Park was the richest site with the highest family (33), genera (69), and species (75) diversity of all sites. Species richness and forest structure were significantly different between sites. Fabaceae was the dominant tree and shrub family at most sites, but no species was repeatably dominant based on number of stems in all fragments of tropical dry forest. Central American dry forests had similar species richness when compared to other Neotropical forests. There was no correlation between forest cover within reserves, or precipitation and plant species richness. There was a significant correlation between anthropogenic disturbance (intensity and frequency of fire, wood collection, grazing) and total species richness, tree and shrub species richness, and liana abundance. These results suggest controlling levels on anthropogenic disturbance within reserves should be a high priority for resource managers in Central America. Further research in forest fragments which examine individual and a combination of disturbance agents would help clarify the importance of anthropogenic disturbance on species richness and abundance.     

Structure,composition and species diversity in an altitude-substrate matrix of rain forest tree communities on Mount Kinabalu,Borneo

We studied forest structure, composition and tree species diversity of eight plots in an environmental matrix of four altitudes (700, 1700, 2700 and 3100 m) and two types of geological substrates (ultrabasic and non-ultrabasic rocks) on Mount Kinabalu, Borneo. On both substrate series, forest stature, mean leaf area and tree species diversity (both 4.8 cm and 10 cm diameter at breast height [dbh]) decreased with altitude. The two forests on the different substrate series were similar at 700 m in structure, generic and familial composition and tree species diversity, but became dissimilar with increasing altitude. The decline in stature with altitude was steeper on the ultrabasic substrates than on the non-ultrabasic substrates, and tree species diversity was generally lower on ultrabasic substrates than on non-ultrabasic substrates at 1700 m. The forests on non-ultrabasic substrates at higher altitudes and those on ultrabasic substrates at the lower altitudes were similar in dbh versus tree height allometry, mean leaf area, and generic and familial composition at 1700 m. These contrasting patterns in forest structure and composition between the two substrate series suggested that altitudinal change was compressed on the ultrabasic substrates compared to the non-ultrabasic substrates. Tree species diversity was correlated with maximum tree height and estimated aboveground biomass, but was not with basal area, among the eight study sites. We suggest that forests with higher tree species diversity are characterized by greater biomass allocation to height growth relative to trunk diameter growth under more productive environment than forests with lower tree species diversity.