Alterations following a fire in a forest community of Alto Rio Xingu

This study records the consequences of fire upon the soil and structure of the Amazonian Forest of Gaucha do Norte, Mato Grosso state, Brazil (13degrees12'S and 53degrees20'W). For this, the number of individuals sampled in 1 ha of the forest, during a phytosociological survey completed 2 days before the accidental fire, was compared with the survivors recorded afterwards in the reinventory of the area taken 2 days and 10 months after the fire. For the surveys, the area of 1 ha was subdivided into 50 plots of 10 m x 20 m, and all the individuals with circumference at breast height (CBH) greater than or equal to 15 cm were sampled. Chemical analysis of the 30 soil samples collected 2 days before the fire were compared with those obtained 15 days and 1 year after the fire. It was seen that, soon after the fire, there was a significant increase in the nutrient levels in the soil, an increase in the pH and a decrease in the aluminum toxicity. However, after 1 year, losses by lixiviation resulted in a nutrient reserve in the soil of less than that before the fire. The tree mortality was extremely high (23.98%), particularly amongst the younger individuals of the population (93.68% of the total of deaths in the period). There was no significant reduction in the forest richness analyzed: 60% of the species had reduced populations after the fire, but just four species were locally extinct. Results, however, demonstrated a role for fire in the selection of resistant species or those adapted to fires, since some species demonstrated a greater tolerance to the fire than others. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Forest ecology ; the forest environment, the forest community and the forest itself.

Includes bibliography.

Phosphorus fertilisation and large legume species affect jarrah forest restoration after bauxite mining

Re-establishing nutrient-cycling is often a key goal of mine-site restoration. This goal can be achieved by applying fertilisers (particularly P) in combination with seeding N-fixing legumes. However, the effect of this strategy on other key restoration goals such as the establishment and growth of non-leguminous species has received little attention. We investigated the effects of P-application rates either singly, or in combination with seeding seven large understorey legume species, on jarrah forest restoration after bauxite mining. Five years after P application and seeding, legume species richness, density and cover were higher in the legume-seeded treatment. However, the increased establishment of legumes did not lead to increased soil N. Increasing P-application rates from 0 to 80 kg P ha−1 did not affect legume species richness, but significantly reduced legume density and increased legume cover: cover was maximal (∼50%) where 80 kg P ha−1 had been applied with large legume seeds. Increasing P-application had no effect on species richness of non-legume species, but increased the density of weeds and native ephemerals. Cover of non-legume species decreased with increasing P-application rates and was lower in plots where large legumes had been seeded compared with non-seeded plots. There was a significant legume × P interaction on weed and ephemeral density: at 80 kg P ha−1 the decline in density of these groups was greatest where legumes were seeded. In addition, the decline in cover for non-legume species with increasing P was greatest when legumes were seeded. Applying 20 kg P ha−1 significantly increased tree growth compared with tree growth in unfertilised plots, but growth was not increased further at 80 kg ha−1 and tree growth was not affected by seeding large legumes. Taken together, these data indicate that 80 kg ha−1 P-fertiliser in combination with (seeding) large legumes maximised vegetation cover at five years but could be suboptimal for re-establishing a jarrah forest community that, like unmined forest, contains a diverse community of slow-growing re-sprouter species. The species richness and cover of non-legume understorey species, especially the resprouters, was highest in plots that received either 0 or 20 kg ha−1 P and where large legumes had not been seeded. Therefore, our findings suggest that moderation of P-fertiliser and legumes could be the best strategy to fulfil the multiple restoration goals of establishing vegetation cover, while at the same time maximising tree growth and species richness of restored forest.

Forest destructuring as revealed by the temporal dynamics of fundamental species - Case study of Santa Genebra Forest in Brazil

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Unraveling the drivers of community dissimilarity and species extinction in fragmented landscapes

Communities in fragmented landscapes are often assumed to be structured by species extinction due to habitat loss, which has led to extensive use of the species-area relationship (SAR) in fragmentation studies. However, the use of the SAR presupposes that habitat loss leads species to extinction but does not allow for extinction to be offset by colonization of disturbed-habitat specialists. Moreover, the use of SAR assumes that species richness is a good proxy of community changes in fragmented landscapes. Here, we assessed how communities dwelling in fragmented landscapes are influenced by habitat loss at multiple scales; then we estimated the ability of models ruled by SAR and by species turnover in successfully predicting changes in community composition, and asked whether species richness is indeed an informative community metric. To address these issues, we used a data set consisting of 140 bird species sampled in 65 patches, from six landscapes with different proportions of forest cover in the Atlantic Forest of Brazil. We compared empirical patterns against simulations of over 8 million communities structured by different magnitudes of the power-law SAR and with species-specific rules to assign species to sites. Empirical results showed that, while bird community composition was strongly influenced by habitat loss at the patch and landscape scale, species richness remained largely unaffected. Modeling results revealed that the compositional changes observed in the Atlantic Forest bird metacommunity were only matched by models with either unrealistic magnitudes of the SAR or by models ruled by species turnover, akin to what would be observed along natural gradients. We show that, in the presence of such compositional turnover, species richness is poorly correlated with species extinction, and z values of the SAR strongly underestimate the effects of habitat loss. We suggest that the observed compositional changes are driven by each species reaching its individual extinction threshold: either a threshold of forest cover for species that disappear with habitat loss, or of matrix cover for species that benefit from habitat loss.

Plurality of tree species responses to drought perturbation in Bornean tropical rain forest

Drought perturbation driven by the El Niño Southern Oscillation (ENSO) is a principal stochastic variable determining the dynamics of lowland rain forest in S.E. Asia. Mortality, recruitment and stem growth rates at Danum in Sabah (Malaysian Borneo) were recorded in two 4-ha plots (trees ≥ 10 cm gbh) for two periods, 1986–1996 and 1996–2001. Mortality and growth were also recorded in a sample of subplots for small trees (10 to <50 cm gbh) in two sub-periods, 1996–1999 and 1999–2001. Dynamics variables were employed to build indices of drought response for each of the 34 most abundant plot-level species (22 at the subplot level), these being interval-weighted percentage changes between periods and sub-periods. A significant yet complex effect of the strong 1997/1998 drought at the forest community level was shown by randomization procedures followed by multiple hypothesis testing. Despite a general resistance of the forest to drought, large and significant differences in short-term responses were apparent for several species. Using a diagrammatic form of stability analysis, different species showed immediate or lagged effects, high or low degrees of resilience or even oscillatory dynamics. In the context of the local topographic gradient, species’ responses define the newly termed perturbation response niche. The largest responses, particularly for recruitment and growth, were among the small trees, many of which are members of understorey taxa. The results bring with them a novel approach to understanding community dynamics: the kaleidoscopic complexity of idiosyncratic responses to stochastic perturbations suggests that plurality, rather than neutrality, of responses may be essential to understanding these tropical forests. The basis to the various responses lies with the mechanisms of tree-soil water relations which are physiologically predictable: the timing and intensity of the next drought, however, is not. To date, environmental stochasticity has been insufficiently incorporated into models of tropical forest dynamics, a step that might considerably improve the reality of theories about these globally important ecosystems.

Predicting Forest Responses to Changing Environmental Conditions

Forests change with changes in their environment based on the physiological responses of individual trees. These short-term reactions have cumulative impacts on long-term demographic performance. For a tree in a forest community, success depends on biomass growth to capture above- and belowground resources and reproductive output to establish future generations. Here we examine aspects of how forests respond to changes in moisture and light availability and how these responses are related to tree demography and physiology.

First we address the long-term pattern of tree decline before death and its connection with drought. Increasing drought stress and chronic morbidity could have pervasive impacts on forest composition in many regions. We use long-term, whole-stand inventory data from southeastern U.S. forests to show that trees exposed to drought experience multiyear declines in growth prior to mortality. Following a severe, multiyear drought, 72% of trees that did not recover their pre-drought growth rates died within 10 years. This pattern was mediated by local moisture availability. As an index of morbidity prior to death, we calculated the difference in cumulative growth after drought relative to surviving conspecifics. The strength of drought-induced morbidity varied among species and was correlated with species drought tolerance.

Next, we investigate differences among tree species in reproductive output relative to biomass growth with changes in light availability. Previous studies reach conflicting conclusions about the constraints on reproductive allocation relative to growth and how they vary through time, across species, and between environments. We test the hypothesis that canopy exposure to light, a critical resource, limits reproductive allocation by comparing long-term relationships between reproduction and growth for trees from 21 species in forests throughout the southeastern U.S. We found that species had divergent responses to light availability, with shade-intolerant species experiencing an alleviation of trade-offs between growth and reproduction at high light. Shade-tolerant species showed no changes in reproductive output across light environments.

Given that the above patterns depend on the maintenance of transpiration, we next developed an approach for predicting whole-tree water use from sap flux observations. Accurately scaling these observations to tree- or stand-levels requires accounting for variation in sap flux between wood types and with depth into the tree. We compared different models with sap flux data to test the hypotheses that radial sap flux profiles differ by wood type and tree size. We show that radial variation in sap flux is dependent on wood type but independent of tree size for a range of temperate trees. The best-fitting model predicted out-of-sample sap flux observations and independent estimates of sapwood area with small errors, suggesting robustness in new settings. We outline a method for predicting whole-tree water use with this model and include computer code for simple implementation in other studies.

Finally, we estimated tree water balances during drought with a statistical time-series analysis. Moisture limitation in forest stands comes predominantly from water use by the trees themselves, a drought-stand feedback. We show that drought impacts on tree fitness and forest composition can be predicted by tracking the moisture reservoir available to each tree in a mass balance. We apply this model to multiple seasonal droughts in a temperate forest with measurements of tree water use to demonstrate how species and size differences modulate moisture availability across landscapes. As trees deplete their soil moisture reservoir during droughts, a transpiration deficit develops, leading to reduced biomass growth and reproductive output.

This dissertation draws connections between the physiological condition of individual trees and their behavior in crowded, diverse, and continually-changing forest stands. The analyses take advantage of growing data sets on both the physiology and demography of trees as well as novel statistical techniques that allow us to link these observations to realistic quantitative models. The results can be used to scale up tree measurements to entire stands and address questions about the future composition of forests and the land’s balance of water and carbon.

Linking ecological condition and the soundscape in fragmented Australian forests

Natural landscapes are increasingly subjected to anthropogenic pressure and fragmentation resulting in reduced ecological condition. In this study we examined the relationship between ecological condition and the soundscape in fragmented forest remnants of south-east Queensland, Australia. The region is noted for its high biodiversity value and increased pressure associated with habitat fragmentation and urbanisation. Ten sites defined by a distinct open eucalypt forest community dominated by spotted gum (Corymbia citriodora ssp. variegata) were stratified based on patch size and patch connectivity. Each site underwent a series of detailed vegetation condition and landscape assessments, together with bird surveys and acoustic analysis using relative soundscape power. Univariate and multivariate analyses indicated that the measurement of relative soundscape power reflects ecological condition and bird species richness, and is dependent on the extent of landscape fragmentation. We conclude that acoustic monitoring technologies provide a cost effective tool for measuring ecological condition, especially in conjunction with established field observations and recordings.

中国暖温带森林群落多样性若干问题的研究

中国暖温带落叶阔叶林区维管植物共158科，931属，近4000种（含亚种，变种和变型），种子植物l3l科，877属，3770余种。暖温带植物区系有很强的温带性质，各类温带成分共548属，而各类热带成分仅226属，热带成分与温带成分(R/T)的比率为0．31。运用TWINSPAN和DCA对全国34个植物区系进行了数量分类排序，结果反映了一个地区的植物区系性质主要取决于其所在地的地理位置，同时也受山地海拔高度的强烈影响这一植物区系的基本特征。 根据暖温带森林植物的特点，修订了Raunkiear生活型系统。暖温带森林植物以地面芽植物(H)占较大的优势，占暖温带全部种类的33.9%;其次是地下芽(G)植物，占l 9.7%;全部高位芽植物占27.5%，绝大部分为落叶阔叶高位芽植物。主要由这些生活型组成的暖温带植物生活型总谱基本反映了暖温带夏季温暖多雨、冬季寒冷干旱的中纬度地区地面芽植物群落气候特征。 暖温带森林植被类型主要有7个植被亚型，约50个群系。辽东栎群落是典型的地带性森林群落。应用TWINSPAN和DCA程序将68块暖温带部分地区辽东栎群落样地和83块北京山区辽东栎群落样地分别划分为1 5个和14个群落类型。用物种丰富度指数、Simpson指数、多样性奇测法、Shannon-Wiene r指数、Pielou均匀度指数，Heip均匀度指数、AIatalo均匀度指数等常用的多样性测度方法，分别对暖温带和北京山区辽东栎群落的多样性进行了测度，结果发现，多样性作为一个整体与DCA第1轴有很大的相关关系：暖温带辽东栎群落多样性指数与DCA第1轴的复相关系数为0.7左右，北京山区较高，为0.8左右。多样性的空间特征为：随海拔的升高和纬度的降低，多样性指数呈上升趋势，反映了水热条件在辽东栎水平分布范围内、人类活动和水分因子在辽东栎垂直分布范围内对群落多样性的影响;不同群落之间多样性指数由低到高的顺序为：灌丛、辽东栎萌生丛、辽东栎林、辽东栎纯林、混交林，符合群落演替过程中多样性的动态规律。 对秦岭主峰太白山海拔1400-1600m之间植被类型和物种多样性进行了研究，在划分的1 5种群落类型中，以位于海拔1500-2300m之间的落叶阅叶混交林和栎类混交林的群落多样性最高，在海拔2300-3600m之间，群落多样性趋于单调下降，反映了热量的不足在这一海拔高度范围成为多样性的主要限制因子。

黄土高原植被演替不同阶段植物系数的变化与适应性评价

用4年长期定位试验资料,利用植物系数、蒸散量、土壤含水量和土壤水分对植物的有效性等指标,研究了黄土高原植被群落不同演替阶段(草本群落→灌木群落→早期森林群落→顶级群落)的耗水特性与生态适应性。结果表明:不同演替阶段,群落实际蒸散量主要受降水控制,群落间差异不显著(P>0.05);土壤含水量是早期森林群落明显高于其它群落,草本群落明显高于灌木群落(P<0.05);植物系数是灌木群落>草本群落>乔木群落,而顶级群落大于早期森林群落;土壤水分对植物的有效性是早期森林和顶级群落明显高于草本和灌木群落(P<0.05)。因此,进行植被建设不但要考虑植物系数还要考虑土壤水分对不同植物的有效性。

采伐对长白山阔叶红松林乔木群落的影响

采伐方式和强度对长白山阔叶红松林中乔木群落的结构和动态有着重要的影响，进而影响到森林的更新、森林生态系统演替以及森林生态系统中各成员之间关系。本文选取受不同采伐方式以及强度干扰的阔叶红松林群落为研究对象，通过野外调查、种群空间格局统计分析讨论了不同采伐方式和强度干扰后阔叶红松林乔木群落的变化。为合理利用天然阔叶红松林，保护阔叶红松林生物多样性提供理论支持。 主要研究结果：（1）随着采伐强度的增加，原始阔叶红松林中的优势乔木树种的重要值减少而先锋物种如白桦等的重要值增加。（2）在采伐30年后，次生阔叶红松林乔木群落的生物多样性指数与原始林中没有显著差异。（3）采伐使乔木的种群空间分布格局发生变化，当种群密度较小时（<100株/ha），种群的空间格局倾向于随机分布，当种群密度较大时在小于30m尺度内呈现出聚集分布而在大于30m尺度上表现为随机分布。（4）阔叶红松林中乔木竞争强度在中低强度择伐后变化最小，而在皆伐后变化最大。（5）无论采伐方式与强度如何，红松的胸径与其竞争指数都严格服从幂函数关系。随着采伐强度的增加，来自红松种内的竞争压力逐渐减小，红松幼树数量占种群数量的比例逐渐升高。（6）采伐对阔叶红松林群落中乔木的更新和群落的演替有着明显的影响。采伐强度越大，红松、紫椴、水曲柳等乔木树种的更新数量就越多，与之相反，白桦幼树的数量随采伐强度的增加而减少。

长白山次生林群落动态及其生态恢复

该文结合中国天然林保护工程的新形势和森林可持续发展的要求，运用林学、群落生态学、恢复生态学、生物多样性保护等原理和方法，以长白山区广泛分布于中低海拔的次生林为研究对象，通过大量的野外调查、室内分析和资料收集，针对实际深入研究和评价了在自然恢复和人为抚育管理模式下次生林的动态及其过程的一些重点问题，进而揭示了在不同管理模式下次生林群落组成、结构、物种多样性、种群分布格局、种间联结等演变规律及其对森林稳定性的贡献和维持机理，丰富和补充了阔叶红松林的系统研究内容，为林区森林的发展提供了模式和依据.