Comment on "Global resilience of tropical forest and savanna to critical transitions"

Hirota et al. (Reports, 14 October 2011, p. 232) used spatial data to show that grasslands, savannas, and forests represent opposing stable states. Reanalyzing their data and drawing from temporal studies, we argue that spatial analyses underestimate the bistability of grasslands and savannas due to limitations of substituting space for time. We propose that temporal and spatial data are needed to predict critical transitions between grasslands and savannas.     

Restoration of degraded tropical forest landscapes

The current scale of deforestation in tropical regions and the large areas of degraded lands now present underscore the urgent need for interventions to restore biodiversity, ecological functioning, and the supply of goods and ecological services previously used by poor rural communities. Traditional timber plantations have supplied some goods but have made only minor contributions to fulfilling most of these other objectives. New approaches to reforestation are now emerging, with potential for both overcoming forest degradation and addressing rural poverty.     

The global extent and determinants of savanna and forest as alternative biome states

Theoretically, fire-tree cover feedbacks can maintain savanna and forest as alternative stable states. However, the global extent of fire-driven discontinuities in tree cover is unknown, especially accounting for seasonality and soils. We use tree cover, climate, fire, and soils data sets to show that tree cover is globally discontinuous. Climate influences tree cover globally but, at intermediate rainfall (1000 to 2500 millimeters) with mild seasonality (less than 7 months), tree cover is bimodal, and only fire differentiates between savanna and forest. These may be alternative states over large areas, including parts of Amazonia and the Congo. Changes in biome distributions, whether at the cost of savanna (due to fragmentation) or forest (due to climate), will be neither smooth nor easily reversible.     

Population density of tropical forest frogs: relation to retreat sites

The forest frog Eleutherodactylus coqui defends specific sites for retreats and nests in the Luquillo Forest, Puerto Rico. The hypothesis that shortages of nest and retreat sites limit population size was tested by placing 100 bamboo frog houses in plots measuring 100 square meters in areas of high frog density. These new sites were readily adopted by adult frogs. After one year, experimental plots had significantly more nests and frogs of all sizes than did control plots.     

Phase transitions, critical phenomena, and instabilities

Transformations among many of the diverse states of matter arise from microscopic interactions involving very many (approximately 10(23)) constituent particles and result in dramatic changes in macroscopic properties. The values of some physical parameters vanish, while others approach infinity. These changes and their evolution are strikingly similar in systems as apparently different as liquids, magnets, superconductors, ferroelectrics, and liquid crystals, which suggests that there is an underlying unity to phase transition phenomena. The basis and extent of this unity are reviewed for many-body systems in equilibrium, and analogies with instability phenomena in systems far from equilibrium (such as lasers, fluid flows, and avalanche electronic devices) are pointed out.     

Genetic consequences of tropical second-growth forest regeneration

Secondary forests are more extensive than old-growth forests in many tropical regions, yet the genetic composition of colonizing populations is poorly understood. We analyzed the parentage of a founder population of 130 individuals of the canopy palm Iriartea deltoidea in a 24-year-old second-growth forest in lowland Costa Rica. Among 66 trees in adjacent old-growth forest, only two individuals contributed 56% of the genes in founders. Second-growth trees had lower genetic diversity and larger patches of similar genotypes than old-growth trees. Recovery of genetic diversity of populations in tropical second-growth forests may take many generations and will require continued dispersal from genetically diverse source populations.     

热带森林植被冠层CO2储存项的估算方法研究

评价植被冠层CO2储存项有助于提高森林-大气层面净生态系统CO2交换量(FNEE)的估算精度.基于西双版纳热带季节雨林2年完整的涡度相关系统和CO2廓线的同步观测资料,详细分析涡度相关法(Fs-EC)和廓线法(Fs-PM)CO2储存项估算结果和变化趋势.结果表明:1)廓线法CO2储存项年平均日变化曲线相比涡度相关法能更...     

Bats limit arthropods and herbivory in a tropical forest

Previous exclosure studies measuring the top-down control of arthropod abundance and herbivory combined the effects of birds and bats. We experimentally partitioned bird predation from bat predation in a lowland tropical forest in Panama and measured the direct effects (arthropod abundance) and indirect effects (herbivory). The exclusion of birds and bats each directly increased arthropod abundance on plants: Bird-exclosed plants contained 65% more, and bat-exclosed plants 153% more, arthropods than controls. Birds and bats also indirectly increased herbivory: Bird-exclosed plants suffered 67% more, and bat-exclosed plants 209% more, herbivory than controls. We conclude that bats have dramatic ecological effects that were previously overlooked.     

Tritium movement in soil of tropical rain forest

Tritiated water applied to the surface of soil in a tropical rain forest was found in free water of the litter and top 18 centimeters of soil as long as 7 months after the application. Plant roots, even in the high-rainfall environment of a tropical rain forest, therefore are exposed to tritiated water for considerable periods of time after release.     

海南热带雨林沟谷植物群落区系地理研究

海南岛热带沟谷雨林物种丰富,分别在霸王岭和黎母山的5 000 m2样地调查中,发现树种703株,两地共有树种36科,其中樟科、夹竹桃科、大戟科、楝科、山矾科和桃金娘科等共有科占有的树种数量超过60％,表明两个样地相似度较高;霸王岭和黎母山沟谷雨林群落树种都以热带分布型为优,霸王岭沟谷雨林热带科成分占85.4％,热带属成分占78.5％,黎母山沟谷雨林热带科成分占88.9％,属成分占92.6％,黎母山沟谷雨林热带科属成分比霸王岭均高,反映了较强的热带性质.     

Species loss and aboveground carbon storage in a tropical forest

Tropical forest biodiversity is declining, but the resulting effects on key ecosystem services, such as carbon storage and sequestration, remain unknown. We assessed the influence of the loss of tropical tree species on carbon storage by simulating 18 possible extinction scenarios within a well-studied 50-hectare tropical forest plot in Panama, which contains 227 tree species. Among extinction scenarios, aboveground carbon stocks varied by more than 600%, and biological insurance varied by more than 400%. These results indicate that future carbon storage in tropical forests will be influenced strongly by future species composition.     

热带果树在云南热区农林复合生态农业技术中的应用

根据云南热区的自然资源概况,探讨热带果树在本区农林复合生态农业技术中的应用.     

昆明城区大学校园与公园绿地植物组成研究

目的以种间关系原理为基础,探究河南鸡公山落叶阔叶林中藤本植物是否对林冠下其他物种的生存产生抑制或促进的效应,为理解林冠下的种间关系和共存机制提供指导。方法林冠下藤本及非藤本植物的Shannon-Wiener指数及密度采用样方法进行调查,土壤温湿度采用土壤温湿度监测仪测定。结果该地区落叶阔叶林林冠下总物种及非藤本植物Shannon-Wiener指数随着藤本植物密度的增加而显著下降,林冠下非藤本植物的Shannon-Wiener指数变异受到物种总密度、距离最近树的胸径和土壤温度的综合调节。林冠下非藤本植物的密度随着藤本植物密度的增加而下降,非藤本植物的密度受到物种总密度、土壤温度和距离最近树的胸径大小的影响。结论中国华中地区落叶阔叶林中的藤本植物对林冠下非藤本植物的Shannon-Wiener指数产生显著抑制效应,同时显著降低了个体的数量,这主要归因于藤本植物较强的扩散和生存能力及其对环境资源较强的占据能力,本研究对于提高森林生态系统中物种多样性及共存机制有重要参考价值。     

Global correlations in tropical tree species richness and abundance reject neutrality

Patterns of species richness and relative abundance at some scales cannot be distinguished from predictions of null models, including zero-sum neutral models of population change and random speciation-extinction models of evolutionary diversification. Both models predict that species richness or population abundance produced by independent iterations of the same processes in different regions should be uncorrelated. We find instead that the number of species and individuals in families of trees in forest plots are strongly correlated across Southeast Asia, Africa, and tropical America. These correlations imply that deterministic processes influenced by evolutionarily conservative family-level traits constrain the number of confamilial tree species and individuals that can be supported in regional species pools and local assemblages in humid tropical forests.     

Tree dispersion, abundance, and diversity in a tropical dry forest

Patterns of tree abundance and dispersion in a tropical deciduous (dry) forest are summarized. The generalization that tropical trees have spaced adults did not hold. All species were either clumped or randomly dispersed, with rare species more clumped than common species. Breeding system was unrelated to species abundance or dispersion, but clumping was related to mode of seed dispersal. Juvenile densities decreased approximately exponentially away from adults. Rare species gave evidence of poor reproductive performance compared with their performance when common in nearby forests. Patterns of relative species abundance in the dry forest are compared with patterns in other forests, and are explained by a simple stochastic model based on random-walk immigration and extinction set in motion by periodic community disturbance.     

Reproductive dominance of pasture trees in a fragmented tropical forest mosaic

Tropical forest fragmentation threatens biodiversity, yet basic information on population responses for major groups such as plants is lacking. Hypervariable genetic markers were used to reconstruct a population-level pedigree in fragmented tropical forest for the tree Symphonia globulifera. Though seedlings occurred only in remnant forest, the pedigree showed that most seedlings had been produced by sequentially fewer adults in pasture, creating a genetic bottleneck. The pedigree also implicated shifts in the foraging of animals that disperse pollen and seed in a secondary constriction of the bottleneck. These results suggest that tropical conservation strategies should anticipate complex, cryptic responses to fragmentation.     

海南霸王岭热带山地雨林树木苗期构筑型研究

为了解热带山地雨林主要树种苗期构筑型特征 ,笔者综合考虑树种在热带山地雨林群落中的重要性、林窗更新进程中的作用及苗圃出苗情况后 ,2 0 0 2年 7— 8月在海南霸王岭自然保护区东二保护站苗圃选择了热带山地雨林中 2 0种主要树木的幼苗 ,分不同苗龄进行了构筑型特征系统观测 .对苗龄≤ 3个月和 3个月 <苗龄≤ 12个月的幼苗 ,采用了不同的指标体系进行研究 .对比了幼苗的构筑型特征 ,并讨论了构筑型与生态对策、群落结构的关系 .结果表明 :大多数热带树木幼苗萌发方式为子叶出土、子叶叶状对生 ;初生叶多为互生 ,其次为对生、轮生 ;分枝角度中 30°和 6 0°居多 ,其次为 4 5°、75°;幼苗枝下高与树高之间符合指数函数关系 ,而树高与基径之间符合幂函数关系 ;Rauh型、Massart型树木通常采取K对策 ,Leeuwenberg型、Attims型树木通常采取r对策 ,Roux型采取r对策或K对策 ,Aubreville型的生态对策在二者之间 .     

西双版纳热带林生长动态模型及可持续经营模拟

为研究中国热带森林的可持续经营方式,在中国西南西双版纳的山地雨林中设置了12块固定观测样地,并在定期观测数据基础上估计林分生长量、林木进界率与径阶保留率等.据此建立林分自然生长的径级分布模型,择伐作业对保留木影响的损伤模型,采伐后由于林窗效应对林木生长影响的经验模型,进界生长模型等热带森林生长动态数学模型并估计了林分初始状态、林分动态转移因子等参数.以森林经营实践的内在逻辑和关键过程为基础设计了森林生长和经营模拟系统的框架概念,应用面向对象的方法设计系统的各个独立程序模块,用VBA 语言与EXCEL结合开发了系统应用软件.应用本模拟系统对西双版纳热带林的择伐经营模式作了所有可能参数组合的模拟经营实验,提出了热带林区国营林场和村寨集体林最适宜的可持续经营指标和标准.     

Biomass of tropical forests: a new estimate based on forest volumes

Recent assessments of areas of different tropical forest types and their corresponding stand volumes were used to calculate the biomass densities and total biomass of tropical forests. Total biomass was estimated at 205 x 10(9) tons, and weighted biomass densities for undisturbed closed and open broadleaf forests were 176 and 61 tons per hectare, respectively. These values are considerably lower than those previously reported and raise questions about the role of the terrestrial biota in the global carbon budget.