Long-Term Impacts of Fuelwood Extraction on a Tropical Montane Cloud Forest

Fuelwood extracted from natural forests serves as a principal energy source in rural regions of many tropical countries. Although fuelwood extraction (even low intensities) might strongly impact the structure and species composition of natural forests, long-term studies remain scarce. Here, we estimate the potential long-term impacts (over several hundred years) of such repeated harvesting of single trees on tropical montane cloud forest in central Veracruz, Mexico, by applying a process-based forest growth model. We simulate a wide range of possible harvesting scenarios differing in wood volume harvested and preferred tree species and sizes, and use a set of indicators to compare their impacts on forest size structure and community composition. Results showed that the overall impact on forest structure and community composition increased linearly with the amount of harvested wood volume. Even at low levels of harvesting, forest size structure became more homogeneous in the long term because large old trees disappeared from the forest, but these changes might take decades or even centuries. Although recruitment of harvested species benefited from harvesting, species composition shifted to tree species that are not used for fuelwood. Our results demonstrate that fuelwood extraction can have marked long-term impacts on tropical montane cloud forests. The results also offer the possibility to support the design of management strategies for the natural species-rich forests that achieve a balance between economic needs and ecological goals of the stakeholders. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Forest carbon in lowland Papua New Guinea: Local variation and the importance of small trees

Efforts to incentivize the reduction of carbon emissions from deforestation and forest degradation require accurate carbon accounting. The extensive tropical forest of Papua New Guinea (PNG) is a target for such efforts and yet local carbon estimates are few. Previous estimates, based on models of neotropical vegetation applied to PNG forest plots, did not consider such factors as the unique species composition of New Guinea vegetation, local variation in forest biomass, or the contribution of small trees. We analysed all trees >1 cm in diameter at breast height (DBH) in Melanesia's largest forest plot (Wanang) to assess local spatial variation and the role of small trees in carbon storage. Above‐ground living biomass (AGLB) of trees averaged 210.72 Mg ha^?1 at Wanang. Carbon storage at Wanang was somewhat lower than in other lowland tropical forests, whereas local variation among 1‐ha subplots and the contribution of small trees to total AGLB were substantially higher. We speculate that these differences may be attributed to the dynamics of Wanang forest where erosion of a recently uplifted and unstable terrain appears to be a major source of natural disturbance. These findings emphasize the need for locally calibrated forest carbon estimates if accurate landscape level valuation and monetization of carbon is to be achieved. Such estimates aim to situate PNG forests in the global carbon context and provide baseline information needed to improve the accuracy of PNG carbon monitoring schemes.     

Land use types influenced avian assemblage structure in a forest–agriculture landscape in Ghana

The conservation of biodiversity within tropical forest regions does not lie only in the maintenance of natural forest areas, but on conservation strategies directed toward agricultural land types within which they are embedded. This study investigated variations in bird assemblages of different functional groups of forest‐dependent birds in three agricultural land types, relative to distance from the interior of 34 tropical forest patches of varying sizes. Point counts were used to sample birds at each study site visited. Data from counts were used to estimate species richness, species evenness, and Simpson's diversity of birds. Mean species richness, evenness, and diversity were modeled as responses and as a function of agricultural land type, distance from the forest interior and three site‐scale vegetation covariates (density of large trees, fruiting trees, and patch size) using generalized linear mixed‐effect models. Mean observed species richness of birds varied significantly within habitat types. Mean observed species richness was highest in forest interior sites while sites located in farm centers recorded the lowest mean species richness. Species richness of forest specialists was strongly influenced by the type of agricultural land use. Fallow lands, density of large trees, and patch size strongly positively influenced forest specialists. Insectivorous and frugivorous birds were more species‐rich in fallow lands while monoculture plantations favored nectarivorous birds. Our results suggest that poor agricultural practices can lead to population declines of forest‐dependent birds particularly specialist species. Conservation actions should include proper land use management that ensures heterogeneity through retention of native tree species on farms in tropical forest‐agriculture landscapes.     

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。     

鼎湖山马尾松林植物养分积累动态及其对人为干扰的响应

 通过处理（根据当地习惯收割凋落物和林下层植物）和保护（无任何人为干扰）样地的比较试验,在10年时间里（1990～2000年）研究了鼎湖山生物圈保护区马尾松 (Pinus massoniana) 林群落植物养分积累动态及其对人为干扰的响应,在此基础上深入和较系统地分析讨论了不同的经营措施对马尾松林可持续性的影响,为我国目前大面积的退化马尾松林恢复和马尾松林可持续性管理提供理论依据。结果表明：1990～1995年,5年时间里由于人为干扰活动而直接从处理样地取走的各元素养分量,在林下层为（kg·hm－2）：132.72 (N)、4.72 (P)、63.32 (K)、23.51 (Ca)和7.00 (Mg),在地表凋落物为（kg·hm－2）：48.93 (N)、1.85 (P)、17.28 (K)、19.25 (Ca)和2.92 (Mg)。1990～2000年,保护样地林下层和地表凋落物各元素养分贮量分别以39%～41%和37%～38%的年平均增长速率逐年提高,至1995年达到高峰,之后各元素贮量在林下层和地表凋落物均以14%的年平均速率下降。在处理样地,1990～1995年期间各元素贮量在林下层年平均积累速率为17%,之后（1995～2000年期间）则为26%;与此同时,各元素贮量在地表凋落物年平均积累速率为22%～23%,之后（1995～2000年期间）则为28%。在整个试验过程,马尾松林乔木层养分元素总贮量随时间而增加,但其增加的速率随时间和样地不同而异。1990～1995年,保护样地乔木层养分元素总贮量增加了34.9%～38.1%,较处理样地（收获林下层和凋落物）总贮量增加的百分比（29.3%～33.5%）高。然而,1995～2000年,保护样地乔木层养分元素总贮量增加的百分比为26.3%～28.9%,较处理样地（1995～2000年也停止人为干扰）总贮量增加的百分比（28.8%～32.1%）低。可见,1990～1995年,人为干扰活动导致处理样地马尾松林乔木层养分元素年平均积累量降低约1.58%～1.72%,即年平均增长量约减少0.12～2.39 kg·hm－2（2.39 (N)、0.12 (P)、0.77 (K)、1.98 (Ca)、0.29 (Mg)）,这些量约相当于每年通过林下层和凋落物收割活动而直接从林地中取走的养分总量的6%～19%。正是由于长期以来受收割林下层和凋落物这种人为干扰的影响,鼎湖山马尾松林乔木层养分贮量较低。这种利用方式不仅直接从林地中取走大量的养分而且还对林地肥力产生间接的负面影响,其结果使该退化林地不能恢复或继续退化。作者建议的森林利用方法代替目前收割林下层和凋落物方式,既可以满足当地居民燃料的需求还有利于马尾松林的自然恢复。     

Tropical seasonal forests in monsson Asia: With emphasis on continental southeast Asia

This paper is intended to provide a brief review of the tropical seasonal forest, one type of the tropical moist forests in monsoon Asia. It will also focus on and summarise issues of current concern in relation to their depletion and global environmental issues. Tropical moist forests occur in the rainy tropical and monsoon tropical climate types. The tropical moist evergreen forest or the tropical rain forest, which account for two-thirds of the tropical moist forests are rich in biodiversity and contain valuable tropical hardwood. The tropical moist deciduous forest or the tropical seasonal forest which lie along the fringes of tropical rain forest, are less complex than the tropical rain forest and have more distinct wet and dry periods. Broadleaved deciduous trees of the genera Tectona, Shorea, and Dipterocarpus are predominantly in this forest type. Currently estimates have found that more than 17 million hectares of forest mainly tropical moist forests are being lost each year. There is a widespread recognition that agriculture and the burning of tropical moist forests contribute to global warming but to a much lesser extent than the combustion of fossil fuels and industrial activities in the developed world.     

Tree allometry and improved estimation of carbon stocks and balance in tropical forests

Tropical forests hold large stores of carbon, yet uncertainty remains regarding their quantitative contribution to the global carbon cycle. One approach to quantifying carbon biomass stores consists in inferring changes from long-term forest inventory plots. Regression models are used to convert inventory data into an estimate of aboveground biomass (AGB). We provide a critical reassessment of the quality and the robustness of these models across tropical forest types, using a large dataset of 2,410 trees ≥ 5 cm diameter, directly harvested in 27 study sites across the tropics. Proportional relationships between aboveground biomass and the product of wood density, trunk cross-sectional area, and total height are constructed. We also develop a regression model involving wood density and stem diameter only. Our models were tested for secondary and old-growth forests, for dry, moist and wet forests, for lowland and montane forests, and for mangrove forests. The most important predictors of AGB of a tree were, in decreasing order of importance, its trunk diameter, wood specific gravity, total height, and forest type (dry, moist, or wet). Overestimates prevailed, giving a bias of 0.5–6.5% when errors were averaged across all stands. Our regression models can be used reliably to predict aboveground tree biomass across a broad range of tropical forests. Because they are based on an unprecedented dataset, these models should improve the quality of tropical biomass estimates, and bring consensus about the contribution of the tropical forest biome and tropical deforestation to the global carbon cycle. Electronic Supplementary Material Supplementary material is available for this article at     

Long-term growth decline in Toona ciliata in a moist tropical forest in Bangladesh: Impact of global warming

Tropical forests are carbon rich ecosystems and small changes in tropical forest tree growth substantially influence the global carbon cycle. Forest monitoring studies report inconsistent growth changes in tropical forest trees over the past decades. Most of the studies highlighted changes in the forest level carbon gain, neglecting the species-specific growth changes which ultimately determine community-level responses. Tree-ring analysis can provide historical data on species-specific tree growth with annual resolution. Such studies are inadequate in Bangladesh, which is one of the most climate sensitive regions in the tropics. In this study, we investigated long-term growth rates of Toona ciliata in a moist tropical forest of Bangladesh by using tree-ring analysis. We sampled 50 trees of varying size, obtained increment cores from these trees and measured tree-ring width. Analyses of growth patterns revealed size-dependent growth increments. After correcting for the effect of tree size on tree growth (ontogenetic changes) by two different methods we found declining growth rates in T. ciliata from 1960 to 2013. Standardized ring-width index (RWI) was strongly negatively correlated with annual mean and maximum temperatures suggesting that rising temperature might cause the observed growth decline in T. ciliata. Assuming that global temperatures will rise at the current rate, the observed growth decline is assumed to continue. The analysis of stable carbon and oxygen isotopes may reveal more insight on the physiological response of this species to future climatic changes.     

中国西南地区热带森林演替序列碳动态

热带森林的破坏是全球性问题,我国西双版纳森林覆盖率受砍伐、火烧和短期耕种丢荒后,面积不断减少,取而代之的是大面积的不同演替状态的次生林。次生林演替过程中的碳储量和碳平衡的变化目前还鲜有研究,为了进一步揭示我国西南地区热带森林演替对于碳蓄积的影响,并制定更科学的热带森林经营管理措施,以结构复杂、生物多样和生物量巨大的热带森林为研究对象,并利用3个热带次生林的样地的实测数据,探讨了不同演替状态的热带次生林的碳储量变化,以及森林的净碳蓄积,死亡碳损失和更新碳增长等碳动态规律,分析表明:(1)在森林的演替过程中,森林的胸径分布频度从近正态分布逐渐向小径级的偏态分布发展,也就是随着演替的进展,小径级林木所占的比例越来越高。(2)热带次生林在森林固碳方面发挥着不可忽略的作用。(3)小的干扰,会波及森林的碳动态;大的干扰,如火灾和砍伐,将导致森林的次生演替,对森林的碳动态产生不可逆转的改变。(4)干旱事件是影响凋落物的季节和年间动态的原因,也是短时间尺度上影响碳平衡的一个重要因子。(5)不论原生林还是次生林,大树在生态系统碳动态方面皆扮演着重要的角色,因此本研究推荐注重大树的研究。     

海南岛热带森林景观类型多样性

依据景观生态学原理,按地貌、气候、土壤、植被和土地利用方式的分异,以带、域、省、区、类型为5个基本单位及亚、组等为辅助单位,组建海南岛热带森林景观类型分类体系。把海南岛热带森林景观作为省级单位,它隶属于全球热带林景观带、亚洲（东方）热带林景观域、中国热带林景观亚域,其下划分为东部潮湿森林景观、西部半干旱森林景观、中南部山地森林景观、热带常绿针叶林景观、热带竹林景观和热带人工林景观6个森林景观区;以热带低地沟谷热带雨林为代表的11个森林景观亚区;以热带低地沟谷龙脑香森林景观为代表的26个森林景观类型组;以热带低地沟谷青皮林为代表的54个森林景观类型。海南岛热带森林景观类型分类体系较全面地表达了海南岛热带森林景观类型多样性。     

Long‐term change within a Neotropical forest: assessing differential functional and floristic responses to disturbance and drought

Disentangling the relative roles of biotic and abiotic forces influencing forest structure, function, and local community composition continues to be an important goal in ecology. Here, utilizing two forest surveys 20‐year apart from a Central American dry tropical forest, we assess the relative role of past disturbance and local climatic change in the form of increased drought in driving forest dynamics. We observe: (i) a net decrease in the number of trees; (ii) a decrease in total forest biomass by 7.7 Mg ha^?1 but when calculated on subquadrat basis the biomass per unit area did not change indicating scale sensitivity of forest biomass measures; (iii) that the decrease in the number of stems occurred mainly in the smallest sizes, and in more moist and evergreen habitats; (iv) that there has been an increase in the proportion of trees that are deciduous, compound leaved and are canopy species, and a concomitant reduction in trees that are evergreen, simple‐leaved, and understory species. These changes are opposite to predictions based on recovery from disturbance, and have resulted in (v) a uniform multivariate shift from a more mesic to a more xeric forest. Together, our results show that over relatively short time scales, community composition and the functional dominance may be more responsive to climate change than recovery to past disturbances. Our findings point to the importance of assessing proportional changes in forest composition and not just changes in absolute numbers. Our findings are also consistent with the hypothesis that tropical tree species exhibit differential sensitivity to changes in precipitation. Predicted future decreases in rainfall may result in quick differential shifts in forest function, physiognomy, and species composition. Quantifying proportional functional composition offers a basis for a predictive framework for how the structure, and diversity of tropical forests will respond to global change.     

云南热带、亚热带山地灌草丛植被特点及利用途径

灌草丛植被在云南的热带、亚热带山地广泛分布。这一植被类型主要由热带(或起源于热带)的禾草所组成,形成一个很明显的禾草草层,其上散生少数乔、灌木。现已分出5个植被亚型,12个群系和17个群丛。5个植被亚型是：热性灌草丛、干热性灌草丛、暖热性灌草丛、暖温性灌草丛和温凉性灌草丛。其中干热性灌草丛可认为是“半热带草原”或“次生热带草原”。在长期演替中,5个灌草丛可分别向5个最后的气候顶极演替。在开发利用上,山地坡度大于20˚者可发展林业,小于20˚者可发展畜牧业及其他种植业。在已划定的自然保护区(或点)内,必须严格保护,并可开展一些重要科研工作。     

西双版纳青梅林的群落学研究

本文对分布在西双版纳勐腊县南部以龙脑香科植物版纳青梅为标志树种的热带森林作了群落学分析,认为它具有热带雨林的结构和基本特征,在性质上属于热带季节雨林。由于分布海拔偏高和生境特殊,它的上层乔木几乎常绿,在外貌上与望天树林和本地区典型的季节雨林有一定差异,在区系组成上向山地雨林过渡,它表现为一种季节雨林向山地雨林过渡的类型,同时也是一种热带北缘地区季节雨林的海拔极限类型。     

Variability in solar radiation and temperature explains observed patterns and trends in tree growth rates across four tropical forests

The response of tropical forests to global climate variability and change remains poorly understood. Results from long-term studies of permanent forest plots have reported different, and in some cases opposing trends in tropical forest dynamics. In this study, we examined changes in tree growth rates at four long-term permanent tropical forest research plots in relation to variation in solar radiation, temperature and precipitation. Temporal variation in the stand-level growth rates measured at five-year intervals was found to be positively correlated with variation in incoming solar radiation and negatively related to temporal variation in night-time temperatures. Taken alone, neither solar radiation variability nor the effects of night-time temperatures can account for the observed temporal variation in tree growth rates across sites, but when considered together, these two climate variables account for most of the observed temporal variability in tree growth rates. Further analysis indicates that the stand-level response is primarily driven by the responses of smaller-sized trees (less than 20 cm in diameter). The combined temperature and radiation responses identified in this study provide a potential explanation for the conflicting patterns in tree growth rates found in previous studies.     

Forest harvesting decisions: the economics of household forest owners in the presence of in situ benefits

Within the even-aged forestry management regime, the length of the rotation period determines the age class structure of a forest area. In many countries harvesting decisions are made by households that own forest land. This paper discusses how different type of values can be included in a model that aims to explain the household forest owners' harvesting decisions. The model suggests that the in situ or amenity preferences make the forest rotation problem considerably more complex than in the classical rotation models based on maximum sustainable yield or maximization of timber revenues. This extended model is able to explain several empirical findings on harvesting behavior and prices of forest land. The model and its features are compared to certain ecological views on renewable resource management.     

森林退化/衰退的研究与实践

森林退化可以理解为森林面积减少、结构丧失、质量降低、功能下降;森林衰退则是森林退化的一种形式,指森林（树木）在生长发育过程中出现的生理机能下降、生长发育滞缓、生产力降低甚至死亡,以及地力衰退等状态.国内外研究表明,森林采伐/毁林是造成森林面积减少的最主要原因,有关森林采伐/毁林引起的森林退化研究主要集中在森林退化的后果、国家/国际政策的影响、加强全球性合作以及寻求解决途径等方面.森林衰退原因可归纳为：工、农业污染,自然胁迫/致衰因子,林分动态发生变化,森林衰退病或生态病,人工纯林以及纯林连栽导致的地力、生产力衰退等.中国的森林退化/衰退现状与世界各地森林退化基本一致,但由于历史原因,中国森林退化又有其自身特点：近一个世纪的强烈人为干扰,使大部分原始天然林退化为次生林;中国拥有世界上最多的人工林,且多数人工林均具有质量差、功能低等衰退特征.本文在综述森林退化/衰退研究与实践基础上,提出中国现代森林退化/衰退的的主要原因,给出中国森林退化/衰退的基本对策.     

A climate change‐induced threat to the ecological resilience of a subtropical monsoon evergreen broad‐leaved forest in Southern China

Recent studies have suggested that tropical forests may not be resilient against climate change in the long term, primarily owing to predicted reductions in rainfall and forest productivity, increased tree mortality, and declining forest biomass carbon sinks. These changes will be caused by drought‐induced water stress and ecosystem disturbances. Several recent studies have reported that climate change has increased tree mortality in temperate and boreal forests, or both mortality and recruitment rates in tropical forests. However, no study has yet examined these changes in the subtropical forests that account for the majority of China's forested land. In this study, we describe how the monsoon evergreen broad‐leaved forest has responded to global warming and drought stress using 32 years of data from forest observation plots. Due to an imbalance in mortality and recruitment, and changes in diameter growth rates between larger and smaller trees and among different functional groups, the average DBH of trees and forest biomass have decreased. Sap flow measurements also showed that larger trees were more stressed than smaller trees by the warming and drying environment. As a result, the monsoon evergreen broad‐leaved forest community is undergoing a transition from a forest dominated by a cohort of fewer and larger individuals to a forest dominated by a cohort of more and smaller individuals, with a different species composition, suggesting that subtropical forests are threatened by their lack of resilience against long‐term climate change.     

滇南热带季雨林的一些问题讨论

通过分析云南南部的水、热条件及植被分布,讨论了季雨林植被类型及其特征,认为云南南部的季雨林是介于热带雨林与萨王纳之间的,在干季基本上是落叶的一种森林植被类型,符合Schimper (1903)定义的热带季雨林植被,并考虑它是一种生态学意义上的经向地带性植被,与该地区的纬向地带性植被热带季节雨林一起共同构成云南南部的水平地带性植被。在云南南部的石灰岩山坡分布的过去被认为是季雨林的森林植被,尽管也受到季节性干旱的影响而不同程度地具有落叶成分,但它在群落外貌上与典型的季雨林不相同,在植物区系组成上也明显不同于该地区非石灰岩山地的季风常绿阔叶林,在分布上亦是在石灰岩低山沟谷的热带季节性雨林水平地带性植被带之上,根据其生态外貌、植物区系组成和生境特点,我们建议用“热带季节性湿润林”来称呼这类石灰岩山地森林类型,在性质上属东南亚热带北缘石灰岩山地垂直带上的一种植被类型。     

Forest turnover rates follow global and regional patterns of productivity

Using a global database, we found that forest turnover rates (the average of tree mortality and recruitment rates) parallel broad-scale patterns of net primary productivity. First, forest turnover was higher in tropical than in temperate forests. Second, as recently demonstrated by others, Amazonian forest turnover was higher on fertile than infertile soils. Third, within temperate latitudes, turnover was highest in angiosperm forests, intermediate in mixed forests, and lowest in gymnosperm forests. Finally, within a single forest physiognomic type, turnover declined sharply with elevation (hence with temperature). These patterns of turnover in populations of trees are broadly similar to the patterns of turnover in populations of plant organs (leaves and roots) found in other studies. Our findings suggest a link between forest mass balance and the population dynamics of trees, and have implications for understanding and predicting the effects of environmental changes on forest structure and terrestrial carbon dynamics.     

Trade‐offs between carbon stocks and timber recovery in tropical forests are mediated by logging intensity

Forest degradation accounts for ~70% of total carbon losses from tropical forests. Substantial emissions are from selective logging, a land‐use activity that decreases forest carbon density. To maintain carbon values in selectively logged forests, climate change mitigation policies and government agencies promote the adoption of reduced‐impact logging (RIL) practices. However, whether RIL will maintain both carbon and timber values in managed tropical forests over time remains uncertain. In this study, we quantify the recovery of timber stocks and aboveground carbon at an experimental site where forests were subjected to different intensities of RIL (4, 8, and 16 trees/ha). Our census data span 20 years postlogging and 17 years after the liberation of future crop trees from competition in a tropical forest on the Guiana Shield, a globally important forest carbon reservoir. We model recovery of timber and carbon with a breakpoint regression that allowed us to capture elevated tree mortality immediately after logging. Recovery rates of timber and carbon were governed by the presence of residual trees (i.e., trees that persisted through the first harvest). The liberation treatment stimulated faster recovery of timber albeit at a carbon cost. Model results suggest a threshold logging intensity beyond which forests managed for timber and carbon derive few benefits from RIL, with recruitment and residual growth not sufficient to offset losses. Inclusion of the breakpoint at which carbon and timber gains outpaced postlogging mortality led to high predictive accuracy, including out‐of‐sample R² values >90%, and enabled inference on demographic changes postlogging. Our modeling framework is broadly applicable to studies that aim to quantify impacts of logging on forest recovery. Overall, we demonstrate that initial mortality drives variation in recovery rates, that the second harvest depends on old growth wood, and that timber intensification lowers carbon stocks.