Dispersal limitation drives successional pathways in Central Siberian forests under current and intensified fire regimes

Fire is a primary driver of boreal forest dynamics. Intensifying fire regimes due to climate change may cause a shift in boreal forest composition toward reduced dominance of conifers and greater abundance of deciduous hardwoods, with potential biogeochemical and biophysical feedbacks to regional and global climate. This shift has already been observed in some North American boreal forests and has been attributed to changes in site conditions. However, it is unknown if the mechanisms controlling fire‐induced changes in deciduous hardwood cover are similar among different boreal forests, which differ in the ecological traits of the dominant tree species. To better understand the consequences of intensifying fire regimes in boreal forests, we studied postfire regeneration in five burns in the Central Siberian dark taiga, a vast but poorly studied boreal region. We combined field measurements, dendrochronological analysis, and seed‐source maps derived from high‐resolution satellite images to quantify the importance of site conditions (e.g., organic layer depth) vs. seed availability in shaping postfire regeneration. We show that dispersal limitation of evergreen conifers was the main factor determining postfire regeneration composition and density. Site conditions had significant but weaker effects. We used information on postfire regeneration to develop a classification scheme for successional pathways, representing the dominance of deciduous hardwoods vs. evergreen conifers at different successional stages. We estimated the spatial distribution of different successional pathways under alternative fire regime scenarios. Under intensified fire regimes, dispersal limitation of evergreen conifers is predicted to become more severe, primarily due to reduced abundance of surviving seed sources within burned areas. Increased dispersal limitation of evergreen conifers, in turn, is predicted to increase the prevalence of successional pathways dominated by deciduous hardwoods. The likely fire‐induced shift toward greater deciduous hardwood cover may affect climate–vegetation feedbacks via surface albedo, Bowen ratio, and carbon cycling.     

论季雨林的水平地带性

季雨林是受制于湿度因子的经度地带性植被类型,它是随着湿度条件的下降由热带雨林向热带疏林过渡的居间类型,而不是受制于温度因子的纬度地带性植被类型,不是随着温度条件的下降由热带雨林向亚热带常绿阔叶林过渡的居间类型。我国南亚热带的榕树群系、黄桐群系,以及热带北缘的青皮群系均不应是季雨林,前二者是典型的南亚热带低地常绿阔叶林或南亚热带雨林,后者则是热带雨林的一分类群。     

The ecology and distribution of lichens in tropical deciduous and evergreen forests of northern Thailand

During three years of research on epiphytic lichen communities as indicators of environmental change in northern Thailand plots were set up in a range of forest types between 400 and 1600 m in 1991/2 and revisited in 1993. Other areas were visited in 1993 and collections made in a wider range of geographical, altitudinal and vegetation conditions in Thailand. From this data factors influencing the distribution of lichens in a monsoon climate are outlined and characteristic components of the lichen flora given at family, generic and where possible specific level. Dominant taxa of the montane forests include hygrophilous macrolichens of the 'Lobarion' that are also a characteristic component of old growth fagaceous forests in Europe, whereas the evergreen forests are dominated by moisture-dependent crustose taxa with a trentepohlioid photobiont, and the deciduous dipterocarp forests by often brightly coloured xerophytic lichens with a trebouxioid photobiont. Taxa are proposed as indicators of forest type including those that are indicators of old-growth forests and of disturbance. Quantitative recording of selected taxa at genus and species level is suggested to estimate rates of change in monsoon forests in southeast Asia.     

Contrasting patterns of phylogenetic diversity across climatic zones of Western Ghats: A biodiversity hotspot in peninsular India

This study attempts to understand the biogeographic history of the Western Ghats forests by investigating decoupling between phylogenetic and taxonomic diversity. We specifically test whether the deciduous forests have been recently established, whether the southern region was a refuge, and whether the deciduous and evergreen forest species have disparate evolutionary histories. We used species composition data from 23 forest types along the Western Ghats for all woody angiosperms above 10‐cm diameter at breast height. Forests were broadly grouped as either evergreen or deciduous. Mean phylogenetic distances corrected for species richness and mean phylogenetic beta diversity corrected for shared species were assessed using z‐scores from null distributions. Null distributions were generated by randomizing the species relationships on the phylogeny. We found that all evergreen forests showed a greater phylogenetic diversity as compared with null expectations. Deciduous forests showed the inverse pattern. Within the evergreen belt, there was a decreasing phylogenetic diversity from south to north, as predicted by the southern refuge hypothesis. The phylogenetic beta diversity across evergreen–deciduous forests was lesser than the null expectation, whereas it was much higher across forests within the evergreen belt. This study provides the first phylogenetic evidence for the antiquity of evergreen forests as well as the southern refuge hypothesis in the Western Ghats. The deciduous forests species have shared evolutionary histories with the evergreen forest species, suggesting multiple shifts between evergreen and deciduous states through the lineages. Conversely, the evergreen species exhibited a disparate evolutionary history across these forests, possibly owing to sharper ecological or climatic gradients.     

Landscape dynamics in Mediterranean oak forests under global change: understanding the role of anthropogenic and environmental drivers across forest types

The Mediterranean region is projected to be extremely vulnerable to global change, which will affect the distribution of typical forest types such as native oak forests. However, our understanding of Mediterranean oak forest responses to future conditions is still very limited by the lack of knowledge on oak forest dynamics and species‐specific responses to multiple drivers. We compared the long‐term (1966–2006) forest persistence and land cover change among evergreen (cork oak and holm oak) and deciduous oak forests and evaluated the importance of anthropogenic and environmental drivers on observed changes for Portugal. We used National Forest Inventories to quantify the changes in oak forests and explored the drivers of change using multinomial logistic regression analysis and an information theoretical approach. We found distinct trends among oak forest types, reflecting the differences in oak economic value, protection status and management schemes: cork oak forests were the most persistent (62%), changing mostly to pines and eucalypt; holm oak forests were less persistent (53.2%), changing mostly to agriculture; and deciduous oak forests were the least persistent (45.7%), changing mostly to shrublands. Drivers of change had distinct importance across oak forest types, but drivers from anthropogenic origin (wildfires, population density, and land accessibility) were always among the most important. Climatic extremes were also important predictors of oak forest changes, namely extreme temperatures for evergreen oak forests and deficit of precipitation for deciduous oak forests. Our results indicate that under increasing human pressure and forecasted climate change, evergreen oak forests will continue declining and deciduous oak forests will be replaced by forests dominated by more xeric species. In the long run, multiple disturbances may change competitive dominance from oak forests to pyrophytic shrublands. A better understanding of forest dynamics and the inclusion of anthropogenic drivers on models of vegetation change will improve predicting the future of Mediterranean oak forests.     

Regional‐scale directional changes in abundance of tree species along a temperature gradient in Japan

Climate changes are assumed to shift the ranges of tree species and forest biomes. Such range shifts result from changes in abundances of tree species or functional types. Owing to global warming, the abundance of a tree species or functional type is expected to increase near the colder edge of its range and decrease near the warmer edge. This study examined directional changes in abundance and demographic parameters of forest trees along a temperature gradient, as well as a successional gradient, in Japan. Changes in the relative abundance of each of four functional types (evergreen broad‐leaved, deciduous broad‐leaved, evergreen temperate conifer, and evergreen boreal conifer) and the demography of each species (recruitment rate, mortality, and population growth rate) were analyzed in 39 permanent forest plots across the Japanese archipelago. Directional changes in the relative abundance of functional types were detected along the temperature gradient. Relative abundance of evergreen broad‐leaved trees increased near their colder range boundaries, especially in secondary forests, coinciding with the decrease in deciduous broad‐leaved trees. Similarly, relative abundance of deciduous broad‐leaved trees increased near their colder range boundaries, coinciding with the decrease in boreal conifers. These functional‐type‐level changes were mainly due to higher recruitment rates and partly to the lower mortality of individual species at colder sites. This is the first report to show that tree species abundances in temperate forests are changing directionally along a temperature gradient, which might be due to current or past climate changes as well as recovery from past disturbances.     

Spontaneous restoration of epiphytic lichen biota in managed forests planted on habitats typical for temperate deciduous forest

The study examines the changes of epiphytic lichen diversity in differently aged stands developing after clear cutting and pine planting on fertile habitats typical for deciduous forests. The study was conducted within one large complex consisting of pine, mixed pine-hornbeam and typical old oak-linden-hornbeam forests in northern Poland. Epiphytic lichens were recorded in 50 study plots randomly selected within 5 forest stand classes of a different structure and age, ranging from 80 to over 220 years. Altogether 143 lichen species were recorded, of which only 41 were entirely nonspecific, and were occurring in all the studied forest stand classes. Significant differences in lichen species richness between stand classes were found and the number of species increases with the forest age. Lichen species composition also differs and its changes progress towards restoration of lichen biota typical for deciduous forest consistent with the habitat. The age of the forest has the most significant effect on the biodiversity of lichen biota. Microhabitat space provided by oaks is highly desirable since it greatly enriches lichen biota in forests. Phorophyte specificity of particular lichens were assessed. Hornbeam and oak have the greatest number of species mostly confined to them and constitute a main refuge for lichens with a high conservation value. The changes of lichen biota are basically parallel with the changes of the forest stand structure. The selection of some parts within managed pine forests that should not be assigned for cutting in the future can be a simple procedure which helps to restore and preserve forest biodiversity.     

亚热带常绿阔叶林和暖温带落叶阔叶林叶片热值比较研究

植物干重热值(GCV)是衡量植物生命活动及组成成分的重要指标之一,反映了植物光合作用中固定太阳辐射的能力。利用氧弹量热仪测定了亚热带和暖温带两个典型森林生态系统常见的276种常见植物叶片的干重热值,探讨了亚热带和暖温带植物热值分布特征,以及不同生活型、乔木类型间植物热值的变化规律。实验结果发现:亚热带常绿阔叶林和暖温带落叶阔叶林叶片热值的平均值分别为17.83 k J/g(n=191)和17.21k J/g(n=85),整体表现为亚热带植物暖温带植物。不同地带性植被的植物叶片热值在不同生活型间表现出相似的规律,其中亚热带常绿阔叶林表现为:乔木(19.09 k J/g)灌木(17.87 k J/g)草本(16.65 k J/g);暖温带落叶阔叶林表现为:乔木(18.41 k J/g)灌木(17.94 k J/g)草本(16.53 k J/g);不同乔木类型间均呈现常绿乔木落叶乔木、针叶乔木阔叶乔木的趋势。落叶阔叶乔木表现为亚热带暖温带,而常绿针叶乔木则呈现亚热带暖温带的趋势。此外,我们对于两个分布区域内的4种针叶树种叶片热值进行了比较,发现华北落叶松(19.32 k J/g,暖温带)杉木(19.40 k J/g,亚热带)马尾松(19.82 k J/g,亚热带)油松(20.95 k J/g,暖温带)。亚热带常绿阔叶林和暖温带落叶阔叶林植物热值的特征及其变化规律,为森林生态系统的能量流动提供了理论基础。     

AN ECOLOGICAL COMPARISON OF UPLAND DECIDUOUS AND EVERGREEN FORESTS OF CENTRAL TEXAS

Scrub evergreen forests cover most of the cedar breaks region of the Edwards Plateau of central Texas; however, limited strips of deciduous forests are found on north-facing slopes just below the limestone caprock. Dominant species occurring in the deciduous forests in descending order of importance include Quercus texana, Q. glaucoides, Juniperus ashei, Diospyros texana, Prunus serotina, Aesculus pavia, Juglans nigra, and Fraxinus texensis. Nineteen woody species were found in the deciduous forests. Forty-eight percent of the species were exclusive to the deciduous forest community. The deciduous forests had a statistically greater number of species/stand and a higher density. The deciduous species found in the strip forests had combined relative density, dominance and importance values of 59, 93 and 72%, respectively. Dominants in the evergreen forest were J. ashei and D. texana, which had relative density, dominance, and importance values totaling 90, 97 and 93%, respectively. Total dominance was the same for both communities; however, J. ashei dominance was 20 times higher in the evergreen forests. Soils of the deciduous forests were significantly deeper and rockier. Also, these soils had higher organic contents and water retention capacities. The potential field capacity (PFC) was 3.47 times higher for the deciduous forest soils resulting in a 2.36-fold increase in the water availability index (WAI). Factors regulating distribution and composition of the deciduous forest communities appear to be insolation and PFC, resulting in part from differences in topographic position.     

论滇南西双版纳的森林植被分类

本文基于多年研究成果的总结,对西双版纳森林植被的分类、主要植被类型及其特征进行了系统归纳,并讨论了它们与世界类似热带森林植被的关系。以群落的生态外貌与结构、种类组成和生境特征相结合作为植被分类的原则和依据,可以将西双版纳的热带森林植被分类为热带雨林、热带季节性湿润林、热带季雨林和热带山地常绿阔叶林四个主要的植被型,包括有至少二十个群系。热带雨林包括热带季节雨林和热带山地(低山)雨林二个植被亚型。热带季节雨林具有与赤道低地热带雨林几乎一样的群落结构和生态外貌特征,是亚洲热带雨林的一个类型,但由于发生在季风热带北缘纬度和海拔的极限条件下,受到季节性干旱和热量不足的影响,在其林冠层中有一定比例的落叶树种存在,大高位芽植物和附生植物较逊色而藤本植物和在叶级谱上的小叶型植物更丰富,这些特征又有别于赤道低地的热带雨林。热带山地雨林是热带雨林的山地亚型,是该地区热带山地较湿润生境的一种森林类型,它在植物区系组成和生态外貌特征上类似于热带亚洲的低山雨林,隶属于广义热带雨林植被型下的低山雨林亚型。热带季节性湿润林分布在石灰岩山坡中、上部,在群落外貌上类似热带山地常绿阔叶林但在植物区系组成上与后者不同,它是石灰岩山地垂直带上的一种植被类型。热带季雨林是分布在该地区开阔河谷盆地及河岸受季风影响强烈的生境的一种热带落叶森林,是介于热带雨林与萨王纳之间的植被类型。热带山地常绿阔叶林(季风常绿阔叶林)是西双版纳的主要山地植被类型,它分布在热带季节雨林带之上偏干的山地生境。它在植物区系组成上不同于该地区的热带季节雨林,在生态外貌特征上亦不同于热带山地雨林,是发育在受地区性季风气候强烈影响的热带山地的一种森林植被类型。     

Tree species identity and interactions with neighbors determine nutrient leaching in model tropical forests

An ecosystem containing a mixture of species that differ in phenology, morphology, and physiology might be expected to resist leaching of soil nutrients to a greater extent than one composed of a single species. We tested the effects of species identity and plant-life-form richness on nutrient leaching at a lowland tropical site where deep infiltration averages >2 m year(-1). Three indigenous tree species with contrasting leafing phenologies (evergreen, dry-season deciduous, and wet-season deciduous) were grown in monoculture and together with two other life-forms with which they commonly occur in tropical forests: a palm and a giant, perennial herb. To calculate nutrient leaching over an 11-year period, concentrations of nutrients in soil water were multiplied by drainage rates estimated from a water balance. The effect of plant-life-form richness on retention differed according to tree species identity and nutrient. Nitrate retention was greater in polycultures of the dry-season deciduous tree species (mean of 7.4 kg ha(-1) year(-1) of NO(3)-N lost compared to 12.7 in monoculture), and calcium and magnesium retention were greater in polycultures of the evergreen and wet-season deciduous tree species. Complementary use of light led to intensification of soil exploitation by roots, the main agent responsible for enhanced nutrient retention in some polycultures. Other mechanisms included differences in nutrient demand among species, and avoidance of catastrophic failure due to episodic weather events or pest outbreaks. Even unrealistically simple multi-life-form mimics of tropical forest can safeguard a site's nutrient capital if careful attention is paid to species' characteristics and temporal changes in interspecific interactions.     

Leaf flushing during the dry season: the paradox of Asian monsoon forests

Aim Most deciduous species of dry monsoon forests in Thailand and India form new leaves 1–2 months before the first monsoon rains, during the hottest and driest part of the year around the spring equinox. Here we identify the proximate causes of this characteristic and counterintuitive ‘spring‐flushing’ of monsoon forest trees. Location Trees of 20 species were observed in semi‐deciduous dry monsoon forests of northern Thailand with a 5–6‐month‐long severe dry season and annual rainfall of 800–1500 mm. They were growing on dry ridges (dipterocarp–oak forest) or in moist gullies (mixed deciduous–evergreen forest) at 680–750 m altitude near Chiang Mai and in a dry lowland stand of Shorea siamensis in Uthai Thani province. Methods Two novel methods were developed to analyse temporal and spatial variation in vegetative dry‐season phenology indicative of differences in root access to subsoil water reserves. Results Evergreen and leaf exchanging species at cool, moist sites leafed soon after partial leaf shedding in January–February. Drought‐resistant dipterocarp species were evergreen at moist sites, deciduous at dry sites, and trees leafed soon after leaf shedding whenever subsoil water was available. Synchronous spring flushing of deciduous species around the spring equinox, as induced by increasing daylength, was common in Thailand's dipterocarp–oak forest and appears to be prevalent in Indian dry monsoon forests of the Deccan peninsula with its deep, water‐storing soils. Main conclusions In all observed species leafing during the dry season relied on subsoil water reserves, which buffer trees against prolonged climatic drought. Implicitly, rainfall periodicity, i.e. climate, is not the principal determinant of vegetative tree phenology. The establishment of new foliage before the summer rains is likely to optimize photosynthetic gain in dry monsoon forests with a relatively short, wet growing season.     

中国东北森林生长演替模拟模型及其在全球变化研究中的应用

 NEWCOP模型是一个新的适于模拟东北森林的种类组成动态的林窗类计算机模拟模型,它通过模拟在每一个林分斑块上的每株树木的更新、生长和死亡的全过程来反映森林群落的中长期生长和演替动态。由于 NEWCOP模型是一个由气候变量驱动的生态系统模型,故可用于评价气候变化对东北森林生长和演替的影响。在东北大兴安岭、小兴安岭和长白山地区对NEWCOP模型进行了验证和校准。沿环境梯度对NEWCOP模型的数字模拟实验表明：它能准确地再现顶极森林中树种组成及其在东北地区的垂直分布规律和水平分布规律;能准确地再现大兴安岭、小兴安岭和长白山的主要类型森林的生长和演替规律;在一定的场合NEWCOP还可反映林分的径级结构;NEWCOP模型还具有对现有森林的跟踪模拟能力。应用NEWCOP模型评估了东北森林生态系统对可能气候变化的敏感性。在GFDL 2×CO2和GISS 2×CO2气候变化情景下,东北森林的种类组成将发生很大变化,落叶阔叶树将取代目前长白山、小兴安岭的红松(Pinus koraiensis)和大兴安岭的兴安落叶松(Larix gmelinii)成为东北森林主要树种,而针叶树将在地带性森林中占很小的比重,阔叶树中蒙古栎(Quercus mongolica)将是最重要的树种,它将成为小兴安岭和大兴安岭最主要树种;东北地区适于森林生长的区域将大幅度减少,这些变化主要发生在气候变化过渡期。东北森林对不同的气候变化情景有不同响应。但是,总的趋势是未来东北森林中落叶阔叶树的比重将大幅度增加。这些结论对在全球气候变化背景下,我国东北合理地选择造林树种和制定现有森林的保护经营策略具有一定参考价值。     

Richness of Lichen Species,Especially of Threatened Ones,Is Promoted by Management Methods Furthering Stand Continuity

Lichens are a key component of forest biodiversity. However, a comprehensive study analyzing lichen species richness in relation to several management types, extending over different regions and forest stages and including information on site conditions is missing for temperate European forests. In three German regions (Schwäbische Alb, Hainich-Dün, Schorfheide-Chorin), the so-called Biodiversity Exploratories, we studied lichen species richness in 631 forest plots of 400 m² comprising different management types (unmanaged, selection cutting, deciduous and coniferous age-class forests resulting from clear cutting or shelterwood logging), various stand ages, and site conditions, typical for large parts of temperate Europe. We analyzed how lichen species richness responds to management and habitat variables (standing biomass, cover of deadwood, cover of rocks). We found strong regional differences with highest lichen species richness in the Schwäbische Alb, probably driven by regional differences in former air pollution, and in precipitation and habitat variables. Overall, unmanaged forests harbored 22% more threatened lichen species than managed age-class forests. In general, total, corticolous, and threatened lichen species richness did not differ among management types of deciduous forests. However, in the Schwäbische-Alb region, deciduous forests had 61% more lichen species than coniferous forests and they had 279% more threatened and 76% more corticolous lichen species. Old deciduous age classes were richer in corticolous lichen species than young ones, while old coniferous age-classes were poorer than young ones. Overall, our findings highlight the importance of stand continuity for conservation. To increase total and threatened lichen species richness we suggest (1) conserving unmanaged forests, (2) promoting silvicultural methods assuring stand continuity, (3) conserving old trees in managed forests, (4) promoting stands of native deciduous tree species instead of coniferous plantations, and (5) increasing the amount of deadwood in forests.     

Palm species richness,abundance and diversity in the Yucatan Peninsula,in a neotropical context

Species richness, abundance and diversity patterns in palm communities in the Yucatan Peninsula were compared at three sites with different forest types (semi‐deciduous, semi‐evergreen and evergreen), as well as different precipitation, geomorphology and soil depth. All individual palms, including seedlings, juveniles and adults, were identified and counted in forty‐five (0.25 ha) transects. A total of 46 000 individual palms belonging to 11 species from nine genera and two subfamilies were recorded. Palm richness, diversity and abundance were highest in the evergreen forest. Species from the subfamily Coryphoideae dominated the semi‐deciduous and semi‐evergreen forests while species from the subfamily Arecoideae dominated the evergreen forest. Seven species were found only in the evergreen forest. Chamaedorea seifrizii and Sabal yapa were found in all three forest types, while Thrinax radiata was found in the semi‐deciduous and semi‐ evergreen forests and Cocothrinax readii only in the semi‐evergreen forest. Compared to other neotropical palm communities, the richness and diversity in the Yucatan Peninsula are lower than in the western Amazon basin. Although palm richness and diversity on the Yucatan Peninsula were positively associated with precipitation, other variables, in particular soil depth and fertility as well as habitat heterogeneity (microtopography and canopy cover), need to be considered to better understand the observed patterns.     

Factors limiting the distribution of deciduous broadleaved trees in warm-temperate mountainous riparian forests

We examined differences in the responses of deciduous and evergreen broadleaved trees to fluvial disturbance and light environment near a river-facing forest edge in order to identify the factors limiting the distribution of deciduous trees, which are important components of warm-temperate mountainous riparian forests. Deciduous trees tended to be distributed on lower terraces of less than 2-m relative elevation from the water level, which corresponded with sites suffering from strong bank erosion due to high flood frequency. On the other hand, evergreen trees showed an opposite trend of distribution, indicating that high flood frequency associated with strong erosion-dominated soil disturbances might be a constraint for their establishment and/or survival. Furthermore, crowns of deciduous trees tended to be in the canopy layer at the forest edge, with fewer individuals observed beneath the canopy of evergreen trees, even at the forest edge. In contrast, evergreen trees were concentrated in the understory of the forest interior. These observations suggested that the light environment is the predominant factor affecting the establishment and survival of deciduous trees in warm-temperate mountainous riparian forests; however, the river-facing forest edge beneath the evergreen canopy is not a suitable habitat for deciduous trees. We concluded that erosion-dominated soil disturbance on lower terraces provides suitable habitats for deciduous trees by facilitating their reaching the canopy layer by limiting the establishment and/or survival of evergreen trees.

     

中国4种典型森林中常见乔木叶片的非结构性碳水化合物研究

植物叶片的非结构性碳水化合物(non-structural carbohydrates,NSC)不仅为植物的代谢过程提供重要能量,还能一定程度上反映植物对外界环境的适应策略。以温带针阔混交林(长白山)、温带阔叶林(东灵山)、亚热带常绿阔叶林(神农架)和热带雨林(尖峰岭)4种森林类型的树种为研究对象,利用蒽酮比色法测定了163种常见乔木叶片可溶性糖、淀粉和NSC(可溶性糖+淀粉)含量,探讨了不同森林类型植物叶片NSC的差异及其地带性变化规律。结果显示：（1）从森林类型上看,植物叶片NSC含量从北到南递减,即温带针阔混交林(170.79 mg/g)>温带阔叶林(100.27 mg/g)>亚热带常绿阔叶林(91.24 mg/g)>热带雨林(80.13 mg/g)。（2）从生活型上看,无论是落叶树还是阔叶树,其叶片可溶性糖、淀粉和NSC含量均表现为：温带针阔混交林>温带阔叶林>亚热带常绿阔叶林>热带雨林;北方森林叶片可溶性糖、淀粉和NSC含量均表现为落叶树种>常绿树种,或阔叶树种>针叶树种。（3）森林植物叶片NSC含量、可溶性糖与淀粉含量比值与年均温和年均降水量均呈显著负相关。研究表明,森林植物叶片可溶性糖、淀粉和NSC含量以及可溶性糖与淀粉含量比值均具有明显的从北到南递减的地带性规律;其NSC含量以及可溶性糖与淀粉含量比值与温度和水分均呈显著负相关的变化规律可能是植物对外界环境适应的重要机制之一。该研究结果不仅为阐明中国主要森林树种碳代谢和生长适应对策提供了数据基础,而且为理解区域尺度森林植被对未来气候变化的响应机理提供新的视角。     

Test of Fox's assembly rule for functional groups in lemur communities in Madagascar

This paper examines to what extent an assembly rule designed by Fox for small terrestrial mammal communities is also applicable to communities of arboreal lemurs in Madagascar. This approach extends the testing of Fox's assembly rule to a new biogeographic region and a different phylogenetic radiation. The rule operates on a functional rather than on the taxonomic level. It specifies that: "There is a much higher probability that each species entering a community will be drawn from a different functional group, until each group is represented before the cycle repeats" (Fox, 1987: 201). This rule was tested with lemur communities from 14 sites in evergreen rain forests and nine sites in dry deciduous forests of Madagascar. Lemur species were assigned to one of three different functional groups based on dietary preferences: omnivores, frugivores, folivores. The rule applies almost perfectly to extant lemur communities in evergreen rain forest. Present communities in dry deciduous forests are not ordered as perfectly as communities of the rain forest sites, but they also deviate from random assembly as generated by the null model. Including extinct species of the dry forest ecosystem indicates that the at present unfavoured composition of the lemur community has been derived from a favoured state through extinction of the large folivorous and frugivorous lemur species. In the lemur communities of the eastern Malagasy rain forest, the assembly went through at least four, and in the Holocene dry forest ecosystem through even five, cycles without failing. This assigns considerable significance to the underlying mechanisms (most likely interspecific competition) and indicates that they are still effective in the forests of Madagascar. The dry deciduous forests might have been subject to recent natural and anthropogenic changes which interfere with the operation of these deterministic processes.     

Impact of a drier Early-Mid-Holocene climate upon Amazonian forests

This paper uses a palaeoecological approach to examine the impact of drier climatic conditions of the Early-Mid-Holocene (ca 8000-4000 years ago) upon Amazonia's forests and their fire regimes. Palaeovegetation (pollen data) and palaeofire (charcoal) records are synthesized from 20 sites within the present tropical forest biome, and the underlying causes of any emergent patterns or changes are explored by reference to independent palaeoclimate data and present-day patterns of precipitation, forest cover and fire activity across Amazonia. During the Early-Mid-Holocene, Andean cloud forest taxa were replaced by lowland tree taxa as the cloud base rose while lowland ecotonal areas, which are presently covered by evergreen rainforest, were instead dominated by savannahs and/or semi-deciduous dry forests. Elsewhere in the Amazon Basin there is considerable spatial and temporal variation in patterns of vegetation disturbance and fire, which probably reflects the complex heterogeneous patterns in precipitation and seasonality across the basin, and the interactions between climate change, drought- and fire susceptibility of the forests, and Palaeo-Indian land use. Our analysis shows that the forest biome in most parts of Amazonia appears to have been remarkably resilient to climatic conditions significantly drier than those of today, despite widespread evidence of forest burning. Only in ecotonal areas is there evidence of biome replacement in the Holocene. From this palaeoecological perspective, we argue against the Amazon forest 'dieback' scenario simulated for the future.