Pollination efficiency of wild bees and hoverflies provided to oilseed rape

• 1 Declining numbers in honeybees and various wild bee species pose a threat to global pollination services. The identification and quantification of the pollination service provided by different taxa within the pollinator guild is a prerequisite for the successful establishment of nature conservation and crop management regimes.
• 2 Wild bees and hoverflies are considered to be valuable pollinators in agricultural and natural systems. Although some information on pollination efficiency of individual pollinator species is available, comparative studies of both taxa at different densities are rare. In the present study, the efficiency of the solitary mason bee Osmia rufa and two hoverfly species (Eristalis tenax and Episyrphus balteatus) as pollinators of oilseed rape Brassica napus was examined in a standardized caged plant breeding regime. Honeybee Apis mellifera colonies were used as a reference pollinator taxon.
• 3 Yield parameters responded differently to pollinator density and identity. Fruit set and number of seeds per pod increased with increasing pollinator density, although these were stronger in the mason bee than the hoverfly treatment. Weight per 1000 seeds did not respond to any pollinator treatment, indicating that seed quality was not affected. Oilseed rape yield in the highest tested densities of both pollinator taxa resulted in yield values close to the efficiency of small honeybee colonies.
• 4 Hoverflies required approximately five‐fold densities of the red mason bees to reach a similar fruit set and yield. Thus, mason bees are more efficient in plant breeding and managed pollination systems. Both natural pollinator taxa, however, are of potential value in open and closed crop production systems.

     

Movement patterns of selected insect groups between natural forest,open land and rubber plantation in a tropical landscape (southern Yunnan,SW China)

In many regions of tropical Asia, the expansion of rubber monoculture plantations is conducted by replacement of natural forest areas and strongly affects biodiversity and movement patterns of wild species, including insects. Against this background, we conducted a study on selected insect groups (longhorn beetles, bark beetles, wild bees and hoverflies) along transects between rainforest patches, open uncultivated land and rubber plantation habitats in a region of Xishuangbanna (southern Yunnan, China), with the objectives to identify (a) movement directions and patterns of selected insect groups based on their abundances in modified Malaise traps in the different habitats, and (b) the role of remaining natural rainforest patches and rubber plantations, respectively, for insect diversity maintenance and conservation. The highest total numbers of species and individuals of bark beetles, longhorn beetles and wild bees were recorded from the natural forest edge compared to open land and rubber plantation edge. This result clearly indicates that the natural forest plays an important role in maintenance of these three insect groups. However, the highest number of hoverfly species and individuals was recorded from the open land sites, indicating the most relevant habitat type for this group of species. Overall, the lowest species and individual numbers were recorded from the rubber plantation edge, indicating the unsuitability of this habitat type for all insect groups considered. The distribution of species and individuals in the opposite trap sides along the transect indicates that longhorn beetles, bark beetles and wild bees show not only movements from the forest to the surrounding habitats, but also return back after encountering the unsuitable rubber plantation habitat. Bark beetle composition showed the relatively highest similarity between all trap sites and opposite trap sides among the insect groups considered, indicating a higher movement activity than the other groups. The four insect groups considered in this study show different movement modes between the forest, open land and rubber plantation, which are not the same for all taxa. Except for hoverflies, the natural forest was found to be the most important habitat for the maintenance of species diversity in the different land use types of the study area.     

Fruiting patterns of macrofungi in tropical and temperate land use types in Yunnan Province,China

Despite the important contribution of fungi to forest health, biomass turnover and carbon cycling, little is known about the factors that influence fungal phenology. Therefore, in order to further our understanding on how macrofungal fruiting patterns change along a gradient from temperate to tropical climate zones, we investigated the phenological patterns of macrofungal fruiting at five sites along a combined altitudinal and latitudinal gradient in SW China and NW Laos, ranging from temperate to tropical climates. Observations were conducted in the dominant land use types at these study sites: mixed forest (all sites), coniferous forest (temperate sites) and grassland (temperate sites). In total, 2866 specimens were collected, belonging to 791 morpho species, 162 genera, and 71 families. At the site level, the fruiting of ectomycorrhizal (EcMF) and saprotrophic fungi (SapF) occurred at the same time among all land use types. The fruiting season of fungi in the tropical sites began earlier and ended later compared to that of fungi in the temperate sites, which we attribute mainly to the higher temperature and more abundant rainfall of the tropical areas. EcMF taxa richness in temperate forests (both coniferous and mixed forest) showed a distinct peak at the end of the rainy season in August and September, while no significant peak was observed for SapF taxa richness. Neither functional fungal groups showed significant seasonal fluctuations in tropical areas. The temporal turnover of fungal fruiting significantly increased with the shift from tropical to temperate forests along the elevation gradient. In the grasslands, macrofungal abundance was less than 22% of that of corresponding forest sites, and taxa richness was 42% of that of corresponding forest sites. Fungal fruiting showed no significant fluctuations across the rainy season. This work represents a case study carried out over one year, and further measurements will be needed to test if these results hold true in the longer term.     

Trunk structural traits explain habitat use of a tree-dwelling spider (Selenopidae) in a tropical forest

Habitat selection by spiders may be strongly influenced by biotic, climatic, and physical factors. However, it has been shown that the selection of habitats by generalist predators (like spiders) is regulated more by the physical structure of the habitat than by prey availability. Yet, the preferences of spiders in relation to plants or plant traits remain poorly explored. In a remnant of the Atlantic forest in Brazil, the spider Selenops cocheleti is frequently detected on the trunks of plants from the Myrtaceae family. Here, we investigated quantitatively and experimentally whether the colonization of trees by S. cocheleti is related to plant species or the presence of specific structures on trunks. We found that S. cocheleti preferentially occurred on plants of the family Myrtaceae. This spider was also strongly associated with trees that have smooth trunks and/or exfoliating bark. Non-Myrtaceae plants that were occupied by this species have exfoliating bark (e.g., Piptadenia gonoacantha) or deep fissures on the trunk (e.g., the exotic species Pinus elliottii). Our results indicate that the selection of host plants by S. cocheleti is not species-specific, but based on the structural characteristics of plants. Trunks with exfoliating bark may benefit spiders by providing shelter against predators and harsh climatic conditions. Smooth surfaces might allow rapid movements, facilitating both attacks on preys and escape from predators. Our study emphasizes the importance of the physical structure of the habitat on spider's distribution. Future studies investigating how specific plant characteristics influence prey acquisition and predator avoidance would improve our understanding of habitat selection by these animals.     

Evaluating next‐generation sequencing (NGS) methods for routine monitoring of wild bees: Metabarcoding,mitogenomics or NGS barcoding

Implementing cost‐effective monitoring programs for wild bees remains challenging due to the high costs of sampling and specimen identification. To reduce costs, next‐generation sequencing (NGS)‐based methods have lately been suggested as alternatives to morphology‐based identifications. To provide a comprehensive presentation of the advantages and weaknesses of different NGS‐based identification methods, we assessed three of the most promising ones, namely metabarcoding, mitogenomics and NGS barcoding. Using a regular monitoring data set (723 specimens identified using morphology), we found that NGS barcoding performed best for both species presence/absence and abundance data, producing only few false positives (3.4%) and no false negatives. In contrast, the proportion of false positives and false negatives was higher using metabarcoding and mitogenomics. Although strong correlations were found between biomass and read numbers, abundance estimates significantly skewed the communities' composition in these two techniques. NGS barcoding recovered the same ecological patterns as morphology. Ecological conclusions based on metabarcoding and mitogenomics were similar to those based on morphology when using presence/absence data, but different when using abundance data. In terms of workload and cost, we show that metabarcoding and NGS barcoding can compete with morphology, but not mitogenomics which was consistently more expensive. Based on these results, we advocate that NGS barcoding is currently the seemliest NGS method for monitoring of wild bees. Furthermore, this method has the advantage of potentially linking DNA sequences with preserved voucher specimens, which enable morphological re‐examination and will thus produce verifiable records which can be fed into faunistic databases.     

Tree species diversity of tropical forest vegetation in Xishuangbanna, SW China

Tree species diversity of four tropical forest vegetation types was investigated in Xishuangbanna, southwestern China. These are: tropical seasonal rain forest, tropical montane rain forest, evergreen broad-leaved forest and monsoon forest over limestone. A total of 17 samples were taken and four species diversity indices were calculated: Shannon-Wiener's H, the complement of Simpson's index, d, Fisher's and evenness index E. The results reveal the long-tailed rank/abundance diagrams of these forests. However, this feature is greatly reduced in the samples of monsoon forest over limestone. Tropical seasonal rain forest shows the highest tree species diversity of all four vegetation types. Owing to the variation of microenvironment, diversity values within the same vegetation type vary between the samples from different patches. The tree species diversity of single-dominant rain forest is not significantly lower than that of mixed rain forest, because the dominant species of some single-dominant rain forests are principally in the emergent layer. This is composed of sparse and huge trees of one species and, consequently, creates a unique canopy architecture and more heterogeneous microenvironments for the more diversified species composition under the emergent layer. The occurrence of tree species with small population sizes, particularly of species represented by only one individual, is highly correlated with the tree species diversity of the local forest vegetation. They are crucial elements in the richness of local biodiversity.     

热带季节雨林和人工橡胶林林冠截留雾水的比较研究

利用 4a( 1 999～ 2 0 0 2 )的雾水截留观测资料 ,对西双版纳热带季节雨林和人工橡胶林林冠截留雾水进行了研究。热带季节雨林和人工橡胶林全年由林冠截留的雾水分别达 89.4± 1 3.5 mm和 1 8.6± 2 .5 mm(平均值±标准差 ) (雾季各占 62 .9%± 4.8%和 91 .9%± 6.3% ) ,分别占全年降水量的 4.9%± 1 .7%和1 .1 %± 0 .2 %。年雾水截留量与年降雨量呈负相关关系。月雾水截留量与月均最低气温呈显著的负相关 ,与月均相对湿度、月均 0∶ 0 0～ 1 0∶ 0 0风速呈显著的正相关。热带季节雨林全年 68%± 5 %、人工橡胶林40 %± 4%的有雾天气里可以收集到雾水 (分别为 0 .38± 0 .2 7mm/ d和 0 .2 4± 0 .1 2 mm/ d) ,且日雾水截留量与气温和风速呈显著的相关 ,即 :气温越低、风速越大 ,日雾水截留量越多。对本地区热带季节雨林生态系统的健康生长和维持而言 ,雾及雾水极大的弥补了降雨量的不足 ,雾的这种作用在降雨量少的年份似乎更为重要     

Diversity of tropical forest landscape types in Hainan Island, China

A novel landscape classification system was proposed in this study based on landscape ecological theory and the differentiation in climate, topography, soil, vegetation and land use mode. Five basic units (zone, tract, province, region and type) and two assistant units (sub and group) were used in this system. The tropical forest landscape in Hainan Island was regarded as a landscape province, belonging to global tropical forest landscape zone, Asiatic (oriental) tropical forest landscape tract and Chinese tropical forest landscape subtract. Based on the grade system of region, sub-region, type-group and type, this landscape province (Hainan Island) is divided into 6 landscape regions (east moist forest landscape, west semi-arid forest landscape, central-south mountainous forest landscape, tropical evergreen needle-leaved forest landscape, tropical bamboo landscape and tropical plantation landscape), 11 tropical forest landscape sub-regions represented by tropical lowland valley rain forest landscape, 26 tropical forest landscape-type groups represented by tropical lowland valley Dipterocarpaceae forest landscape, and 54 forest landscape types (FLT) represented by lowland valley Vatica mangachapoi forest. Generally, this classification system represents the landscape diversity of the tropical forest in Hainan Island. Further studies are needed to better understand the landscape diversity of Hainan Island.     

Diversity of tropical forest landscape types in Hainan Island, China

A novel landscape classification system was proposed in this study based on landscape ecological theory and the differentiation in climate, topography, soil, vegetation and land use mode. Five basic units (zone, tract, province, region and type) and two assistant units (sub and group) were used in this system. The tropical forest landscape in Hainan Island was regarded as a landscape province, belonging to global tropical forest landscape zone, Asiatic (oriental) tropical forest landscape tract and Chinese tropical forest landscape subtract. Based on the grade system of region, sub-region, type-group and type, this landscape province (Hainan Island) is divided into 6 landscape regions (east moist forest landscape, west semi-arid forest landscape, central-south mountainous forest landscape, tropical evergreen needle-leaved forest landscape, tropical bamboo landscape and tropical plantation landscape), 11 tropical forest landscape sub-regions represented by tropical lowland valley rain forest landscape, 26 tropical forest landscape-type groups represented by tropical lowland valley Dipterocarpaceae forest landscape, and 54 forest landscape types (FLT) represented by lowland valley Vatica mangachapoi forest. Generally, this classification system represents the landscape diversity of the tropical forest in Hainan Island. Further studies are needed to better understand the landscape diversity of Hainan Island.     

Comparative responses of termite functional and taxonomic diversity to land‐use change

1. While it is clear that land‐use change significantly impacts the taxonomic dimension of soil biodiversity, how the functional dimension responds to land‐use change is less well understood. 2. This study examined how the transformation of primary forests into rubber tree monocultures impacts individual termite species and how this change is reflected in termite taxonomic and functional α‐diversity (within site) and β‐diversity (among sites). 3. Overall, individual species responded strongly to land‐use change, whereby only 11 of the 27 species found were able to tolerate both habitats. These differences caused a 27% reduction in termite taxonomic richness and reduced taxonomic β‐diversity in rubber plantations compared with primary forests. The study also revealed that the forest conversion led to a shift in some termite species with smaller body size, shorter legs and smaller mandibular traits. Primary forests exhibited higher functional richness and functional β‐diversity of termite species, indicating that functional traits of termite species in rubber plantations are more evenly distributed. 4. The present study suggests that forest conversion does not merely decrease taxonomic diversity of termites, but also exerts functional trait filtering within some termite species. The results affirm the need for biodiversity assessments that combine taxonomic and functional indicators when monitoring the impact of land‐use change.     

西双版纳热带季节雨林的树种组成和群落结构动态

研究了西双版纳热带季节雨林1 hm2(hectare)动态监测样地1993年与2007年之间树种组成和群落结构的变化。对样地中胸径≥5 cm的乔木进行了每木调查。目前其树种组成的热带分布科、属所占比例分别为91%和94%,具有较高比例的热带植物区系性质。在1993年与2007年两次调查之间,树种数量由145种增至179种,仅有1到2个个体的稀有树种所占比例从54%降为51.1%。从森林的垂直结构来看,A、B、C三层的个体死亡率分别为12.8%、12.9%和19.0%,各层树木的增长率分别为-8.5%、-1.4%和44.8%。与此相对应,C层小径级的树木所占比例有较大提高。虽然小径级的树木在种类和数量上比例增大,但个体数量和种类组成相对稳定的A、B层优势树种变化不大,维持了群落结构的稳定性。14 a间,群落中新增加的具有先锋性质的树种不超过5个。1993年时,A、B两层尚有先锋树种存在,2007年已经从A、B两层中退出。因此,从14 a间树种组成和群落结构的变化来看,虽然具有树木的死亡和增补,但其物种成分和群落结构的总体格局没有明显的变化,处于动态平衡过程中。     

The use of habitat and time by lizards in a tropical deciduous forest in western Mexico

Ecological studies on seasonally dry tropical forest herpetofauna are scarce and those focused on interspecific relations of lizards in this endangered ecosystem are even fewer. This study evaluates general and seasonal patterns in time and habitat use among four lizard species (Anolis nebulosus, Sceloporus melanorhinus, S. utiformis, and Urosaurus bicarinatus) in a protected area of dry tropical forest in western Mexico. Data were gathered by visual surveys along 12 linear parallel transects located in an undisturbed habitat. Anolis nebulosus showed a bimodal pattern in daily activity whereas the other species exhibited unimodal patterns of activity. Seasonality only affected the general activity patterns of S. melanorhinus and U. bicarinatus. With the exception of A. nebulosus and S. melanorhinus, statistical differences were found for all pairwise comparisons of general and seasonal patterns of habitat use. The use of leaf‐litter and low perches in arboreal species was higher during the dry season, probably in response to higher food availability in these habitats. As expected, environmental seasonality affects both activity time and habitat use by lizards. Results suggest greater differences in habitat use than in time of activity among species. The data also indicate complementary use of time and space by these lizard species: species showing similar activity patterns exhibit greater differences in their habitat use. Predation could be an important factor affecting the use of habitat and time by the four lizard species.

Los estudios ecológicos de la herpetofauna de los bosques tropicales secos son escasos y aquellos enfocados a las relaciones ínterespecíficas en lagartijas de este ecosistema fuertemente amenazado son aún más raros. Este estudio evalúa el uso del tiempo y del hábitat de cuatro especies de lagartijas (Anolis nebulosus, Sceloporus melanorhinus, S. utiformis y, Urosaurus bicarinatus) en un área protegida en el occidente de México al comparar los patrones generales y estacionales. La información se obtuvo basándose en 12 transectos visuales ubicados en bosque intacto. Anolis nebulosus registró un patrón bimodal de actividad diaria mientras que en el resto fue unimodal, pero aparentemente, la estacionalidad solo afecto los patrones generales de S. melanorhinus y U. bicarinatus. A excepción de A. nebulosus y S. melanorhinus, todas las comparaciones intraespecificas de los patrones generales y estacionales del uso del hábitat mostraron diferencias estadísticamente significativas. El uso de la hojarasca y perchas mas bajas, en las especies arborícolas, fue mayor durante la época de sequía probablemente en respuesta a una mayor disponibilidad de alimento en esos hábitats durante ese tiempo. Como se esperaba, la estacionalidad puede afectar el uso del tiempo y hábitat en lagartijas. Los resultados sugieren la posibilidad de un mayor uso diferencial del hábitat que del tiempo y la ocurrencia de un uso complementario de ellos: las especies con patrones de actividad más similares difieren más en su uso del hábitat. La depredación puede tener un efecto importante en el uso del tiempo y hábitat de estas especies de lagartijas.     

土壤湿度对中国南部热带森林土壤甲烷吸收的影响

森林土壤是一个重要的大气甲烷的汇。然而,相较于寒带和温带,在热带尤其是东南亚地区,森林土壤甲烷通量的观测较少,这限制了目前对热带森林土壤甲烷通量与环境因子之间关系的认识,也给热带森林土壤甲烷汇的估算带来了一定的不确定性。在中国海南省吊罗山国家森林公园的热带森林土壤,采用激光光谱法测量了2016年9月至2018年9月逐月的土壤甲烷通量,并分析了其与周围环境因子的关系。结果表明：研究区土壤是甲烷的汇,山顶样地的年平均吸收量为0.95 kg CH₄-C hm^-2 a^-1,山脚样地的年平均吸收量为1.93 kg CH₄-C hm^-2 a^-1。干季(11月—次年4月)的甲烷吸收通量明显高于湿季(5—10月),占到全年甲烷吸收的68%。山顶样地年平均土壤湿度为19.2%,年内的波动较小(2.8%)。而山脚样地的年平均湿度相对较低,为12.7%,且年内波动大(5.4%)。土壤湿度是控制甲烷吸收最主要的环境因子,可以解释月际甲烷吸收变化的76%,甲烷吸收通量与土壤温度的相...     

Ecological and biogeographical studies on the tropical rain forest of south Yunnan,SW China with a special reference to its relation with rain forests of tropical Asia

Abstract. Ecological and biogeographic analyses of the tropical rain forest in south Yunnan were made using data from seventeen sample plots and floristic inventories of about 1000 species of seed plants. The rain forest is shown to be a type of true tropical rain forest because it has almost the same profile, physiognomic characteristics, species richness per unit area, numbers of individuals in each tree species and diameter classes of trees as classic lowland tropical rain forests. As the area is at the northern margin of monsoonal tropics, the rain forest differs from equatorial lowland rain forests in having some deciduous trees in the canopy layer, fewer megaphanaerophytes and epiphytes but more species of lianas as well as more species of microphylls. In its floristic composition, about 80% of total families. 94% of total genera and more than 90% of total species are tropical, of which about 38% of genera and 74% of species are tropical Asian. Furthermore, the rain forest has not only almost the same families and genera, but also the same families rank in the top ten both in species richness and in dominance of stems, as lowland forests in southeast Asia. It is indisputable that the flora of the rain forest is part of the tropical Asian flora. However, most of the tropical families and genera have their northern limits in south Yunnan and most have their centre of species diversity in Malesia. More strictly tropical families and genera have relatively lower species richness and importance compared with lowland rain forests in tropical southeast Asia. Thus, the flora also shows characteristics of being at the margin of the tropics. Based mainly on physiognomy and floristic composition the tropical rain forest of Yunnan is classified into two types, i.e. seasonal rain forest and wet seasonal rain forest, the latter is further divided into two subtypes, i.e. mixed rain forest and dipterocarp rain forest. From analysis of geographic elements it is also shown that the tropical rain forest of Yunnan occurs at a geographical nexus with its flora coming mainly from four sources, i.e. Malesia, south Himalayas, Indochina and China.     

Impact of rubber plantation on carabid beetle communities and species distribution in a changing tropical landscape (southern Yunnan, China)

Carabid beetles (Coleoptera: Carabidae) have widely been used to assess biodiversity values of different habitats in cultivated landscapes, but rarely in the humid tropics. This study aimed to investigate effects of land use change on the carabid assemblages in a tributary valley of the Mekong River in tropical southern Yunnan, China. The study area includes habitats of traditional land use systems (rice production and shifting cultivation successions) and was dominated by natural forests until about 30?years ago. Since then, large areas of forest have been, and still are, successively transformed into commercial rubber monoculture plantations. In total, 102 species of Carabidae (including Cicindelinae) were recorded from 13 sites over different seasons, using pitfall traps, Malaise traps and aerial collectors in trees. Cluster analysis and indicator species analysis showed that three types of habitat (rice field fallows, early natural successions and natural forest) possess a degree of uniqueness in species composition. Non-metric multidimensional scaling revealed that the environmental factors explaining 80% of the total variation in carabid assemblage composition are the degree of vegetational openness of a habitat and its plant species diversity. Rice field fallows had significantly higher numbers of species and individuals than any other type of habitat and are probably dominated by species originating from other regions. Carabid assemblages of young rubber plantations (5 and 8?years) were quantitatively similar to those of forests, but without species of significant indicator value. With increasing plantation age (20 and 40?years), the number of carabid species decreased. Increasing age and a further spatial expansion of rubber plantations at the expense of forest areas will have negative impacts on the native forest carabid assemblages with strongest effects on forest specialists and rare species.     

Interannual and seasonal variations of energy and water vapor fluxes above a tropical seasonal rain forest in Xishuangbanna, SW China

The values and variation characteristics of energy components, their relationship with net radiation and the characteristics of water balance in the forest were analyzed, based on the observation data of energy fluxes, meteorological parameters and biomass in a tropical seasonal rain forest in Xishuangbanna from January 2003 to December 2004. The results show that annual net radiation was 3516.4 MJ/(m² · a) and 3516.6 MJ/(m² · a) in 2003 and 2004, respectively, of which 46% and 44% were used in latent heat flux, and 12% and 11% were lost as sensible heat flux. Annual mean canopy surface conductance was 10.3 mm/s and 10.0 mm/s in 2003 and 2004, respectively. Moreover, canopy surface conductance was lower in dry-hot seasons than in fog-cool and rainy seasons. Canopy surface conductance correlated significantly and positively with leaf area index, but negatively with water vapor pressure deficit. In general, canopy surface conductance was not affected directly by soil water content, but highly depended on soil moisture status when soil water content was below 0.15 m³/m³. Annual total evapotranspiration of this forest ecosystem in dry seasons was lower than that in rainy seasons, which was considered as one of the most important reasons that tropical seasonal rain forest could survive and flourish in Xishuangbanna at limit of water and heat.     

西双版纳热带季节雨林水热通量

利用西双版纳热带季节雨林2003和2004年常规气象、生物量以及水热通量观测资料,对该林地两年内各能量分量的数值大小和变化规律、能量分配以及水量平衡特征等进行了分析研究。结果表明,2003和2004年净辐射总量分别为3516.4MJ/(m.2a)和3516.6MJ/(m.2a)。在能量分配过程中潜热通量占优势,2003年和2004年的总量分别是相应年份净辐射总量的46%和44%,显热通量则分别只有12%和11%。2003年和2004年林冠传导率均值分别为10.3mm/s和10.0mm/s,其中干热季期间的林冠传导率明显低于雾凉季和雨季。林冠传导率与叶面积指数和空气饱和水汽压差值之间分别呈极显著的正、负线性相关关系;它基本上不受土壤含水量的影响,只是当长期无雨或雨量很小导致土壤含水量低于0.15m3/m3时,林冠传导率才与土壤含水量间存在极显著的相关关系。西双版纳热带雨林2003和2004年的蒸散量分别是663mm和634mm,受浓雾和林冠传导率的综合影响,该森林生态系统干季蒸散量低于雨季,这是西双版纳热带季节雨林能够在水热极限条件下生存并良好发育的重要原因。     

Interannual and seasonal variations of energy and water vapor fluxes above a tropical seasonal rain forest in Xishuangbanna, SW China

The values and variation characteristics of energy components, their relationship with net radiation and the characteristics of water balance in the forest were analyzed, based on the observation data of energy fluxes, meteorological parameters and biomass in a tropical seasonal rain forest in Xishuangbanna from January 2003 to December 2004. The results show that annual net radiation was 3516.4 MJ/(m² · a) and 3516.6 MJ/(m² · a) in 2003 and 2004, respectively, of which 46% and 44% were used in latent heat flux, and 12% and 11% were lost as sensible heat flux. Annual mean canopy surface conductance was 10.3 mm/s and 10.0 mm/s in 2003 and 2004, respectively. Moreover, canopy surface conductance was lower in dry-hot seasons than in fog-cool and rainy seasons. Canopy surface conductance correlated significantly and positively with leaf area index, but negatively with water vapor pressure deficit. In general, canopy surface conductance was not affected directly by soil water content, but highly depended on soil moisture status when soil water content was below 0.15 m³/m³. Annual total evapotranspiration of this forest ecosystem in dry seasons was lower than that in rainy seasons, which was considered as one of the most important reasons that tropical seasonal rain forest could survive and flourish in Xishuangbanna at limit of water and heat.     

Bird richness and composition along an agricultural gradient in New Guinea: The influence of land use,habitat heterogeneity and proximity to intact forest

Abstract We examined variation in bird species richness, abundance and guild composition along an agricultural gradient in New Guinea, and looked for any additive influence of habitat heterogeneity on these variables. The study was based on a grid of survey plots, six plots wide and 24 plots long with the long axis running from a settlement 2.4 km through active and abandoned agricultural plots towards a large area of forest. Each circular survey plot (25 m radius) was assigned to a broad habitat type, ten habitat measures taken, and birds counted for 1 h in each plot. Principal component analysis (PCA) habitat axis 1 described an axis of decreasing forest alteration (larger trees, greater tree densities, fuller canopy) that was positively correlated with distance from the settlement. Bird richness and abundance were highest at intermediate disturbance levels (plots with mid‐range axis 1 scores). Proportions of insectivores and frugivores increased with decreasing forest alteration, while proportions of nectarivores decreased. We calculated three measures of habitat heterogeneity by comparing each plot's PCA score to those of eight neighbouring plots (50–110 m away). These measures reflected how different the plot was to its neighbours, how variable the habitat was around the plot, and the degree to which the plot bordered less disturbed forest. We related these measures to plot bird variable scores independently, and to residuals following regressions of bird scores against PCA scores. Heterogeneity measures had no significant influence on abundance or richness measures, but there were greater proportions of frugivores in plots showing a given degree of habitat alteration if they bordered more pristine habitat. While we readily identified differences in bird communities along the agricultural gradient, the influences of habitat heterogeneity were not striking for birds at this fine scale.