Coupled effects of wind‐storms and drought on tree mortality across 115 forest stands from the Western Alps and the Jura mountains

Damage due to wind‐storms and droughts is increasing in many temperate forests, yet little is known about the long‐term roles of these key climatic factors in forest dynamics and in the carbon budget. The objective of this study was to estimate individual and coupled effects of droughts and wind‐storms on adult tree mortality across a 31‐year period in 115 managed, mixed coniferous forest stands from the Western Alps and the Jura mountains. For each stand, yearly mortality was inferred from management records, yearly drought from interpolated fields of monthly temperature, precipitation and soil water holding capacity, and wind‐storms from interpolated fields of daily maximum wind speed. We performed a thorough model selection based on a leave‐one‐out cross‐validation of the time series. We compared different critical wind speeds (CWSs) for damage, wind‐storm, and stand variables and statistical models. We found that a model including stand characteristics, drought, and storm strength using a CWS of 25 ms^?1 performed the best across most stands. Using this best model, we found that drought increased damage risk only in the most southerly forests, and its effect is generally maintained for up to 2 years. Storm strength increased damage risk in all forests in a relatively uniform way. In some stands, we found positive interaction between drought and storm strength most likely because drought weakens trees, and they became more prone to stem breakage under wind‐loading. In other stands, we found negative interaction between drought and storm strength, where excessive rain likely leads to soil water saturation making trees more susceptible to overturning in a wind‐storm. Our results stress that temporal data are essential to make valid inferences about ecological impacts of disturbance events, and that making inferences about disturbance agents separately can be of limited validity. Under projected future climatic conditions, the direction and strength of these ecological interactions could also change.     

Altered resource availability and the population dynamics of tree species in Amazonian secondary forests

Despite research demonstrating that water and nutrient availability exert strong effects on multiple ecosystem processes in tropical forests, little is known about the effect of these factors on the demography and population dynamics of tropical trees. Over the course of 5 years, we monitored two common Amazonian secondary forest species—Lacistema pubescens and Myrcia sylvatica—in dry-season irrigation, litter-removal and control plots. We then evaluated the effects of altered water and nutrient availability on population demography and dynamics using matrix models and life table response experiments. Our results show that despite prolonged experimental manipulation of water and nutrient availability, there were nearly no consistent and unidirectional treatment effects on the demography of either species. The patterns and significance of observed treatment effects were largely dependent on cross-year variability not related to rainfall patterns, and disappeared once we pooled data across years. Furthermore, most of these transient treatment effects had little effect on population growth rates. Our results suggest that despite major experimental manipulations of water and nutrient availability—factors considered critical to the ecology of tropical pioneer tree species—autogenic light limitation appears to be the primary regulator of tree demography at early/mid successional stages. Indeed, the effects of light availability may completely override those of other factors thought to influence the successional development of Amazonian secondary forests.     

The Effects of Established Trees on Woody Regeneration during Secondary Succession in Tropical Dry Forests

Understanding the mechanisms controlling secondary succession in tropical dry forests is important for the conservation and restoration of this highly threatened biome. Canopy‐forming trees in tropical forests strongly influence later stages of succession through their effect on woody plant regeneration. In dry forests, this may be complex given the seasonal interplay of water and light limitations. We reviewed observational and experimental studies to assess (1) the relative importance of positive and negative effects of established trees on regeneration; (2) the mechanisms underlying these effects; and (3) to test the ‘stress gradient hypothesis’ in successional tropical dry forests. The effects of established trees on seed dispersal, seed survival, and seed germination—either through direct changes to moisture and temperature regimes or mediated by seed dispersers and predators—are mainly positive. The balance between positive and negative effects on seedling establishment is more complex and depends on the season and leaf phenology of both trees and seedlings. Seedling survival is generally enhanced by established trees mitigating dry conditions. Established trees have counteracting effects on water and light availability that influence seedling growth. The probability of a positive effect of established trees on seedling survival decreases with increased rainfall, which supports the stress gradient hypothesis. Priorities for future research are experiments to test for facilitation and competition and their underlying mechanisms, long‐term studies evaluating how these effects change with ontogeny, and studies focusing on the species‐specificity of interactions.     

Disturbance regime changes the trait distribution,phylogenetic structure and community assembly of tropical rain forests

A rapidly increasing effort to merge functional community ecology and phylogenetic biology has increased our understanding of community assembly. However, studies using both phylogenetic‐ and trait‐based methods have been mainly conducted in old‐growth forests, with fewer studies in human‐disturbed communities, which play an increasingly important role in providing ecosystem services as primary forests are degraded. We used data from 18 1‐ha plots in tropical old‐growth forests and secondary forests with different disturbance histories (logging and shifting cultivation) and vegetation types (tropical lowland and montane forests) on Hainan Island, southern China. The distributions of 11 functional traits were compared among these six forest types. We used a null model approach to assess the effects of disturbance regimes on variation in response and effect traits and community phylogenetic structure across different stem sizes (saplings, treelets, and adult trees) and spatial scales (10–50 m). We found significant differences in the distribution of functional traits in highly disturbed lowland sites versus other forest types. Many individuals in highly disturbed lowland sites were deciduous, spiny, with non‐fleshy fruits and seeds dispersed passively or by wind, and low SLA. The response traits of coexisting species were clustered in all sites except for highly disturbed lowland sites where evenness was evident. There were different distributions of effect traits for saplings and treelets among different forest types but adult trees showed stronger clustering of trait values with increasing spatial scale among all forest types. Phylogenetic clustering predominated across all size classes and spatial scales in the highly disturbed lowland sites, and evenness in other forest types. High disturbance can lead to abiotic filtering, generating a community dominated by closely related species with disturbance‐adapted traits, where biotic interactions play a relatively minor role. In lightly disturbed and old growth forests, multiple processes simultaneously drive the community assembly, but biotic processes dominate at the fine scale.     

Tree diversity reduces herbivory by forest insects

Biodiversity loss from plant communities is often acknowledged to affect primary production but little is known about effects on herbivores. We conducted a meta-analysis of a worldwide data set of 119 studies to compare herbivory in single-species and mixed forests. This showed a significant reduction of herbivory in more diverse forests but this varied with the host specificity of insects. In diverse forests, herbivory by oligophagous species was virtually always reduced, whereas the response of polyphagous species was variable. Further analyses revealed that the composition of tree mixtures may be more important than species richness per se because diversity effects on herbivory were greater when mixed forests comprised taxonomically more distant tree species, and when the proportion of non-host trees was greater than that of host trees. These findings provide new support for the role of biodiversity in ecosystem functioning across trophic levels.     

Carbon dioxide and the uneasy interactions of trees and savannah grasses

Savannahs are a mixture of trees and grasses often occurring as alternate states to closed forests. Savannah fires are frequent where grass productivity is high in the wet season. Fires help maintain grassy vegetation where the climate is suitable for woodlands or forests. Saplings in savannahs are particularly vulnerable to topkill of above-ground biomass. Larger trees are more fire-resistant and suffer little damage when burnt. Recruitment to large mature tree size classes depends on sapling growth rates to fire-resistant sizes and the time between fires. Carbon dioxide (CO(2)) can influence the growth rate of juvenile plants, thereby affecting tree recruitment and the conversion of open savannahs to woodlands. Trees have increased in many savannahs throughout the world, whereas some humid savannahs are being invaded by forests. CO(2) has been implicated in this woody increase but attribution to global drivers has been controversial where changes in grazing and fire have also occurred. We report on diverse tests of the magnitude of CO(2) effects on both ancient and modern ecosystems with a particular focus on African savannahs. Large increases in trees of mesic savannahs in the region cannot easily be explained by land use change but are consistent with experimental and simulation studies of CO(2) effects. Changes in arid savannahs seem less obviously linked to CO(2) effects and may be driven more by overgrazing. Large-scale shifts in the tree-grass balance in the past and the future need to be better understood. They not only have major impacts on the ecology of grassy ecosystems but also on Earth-atmosphere linkages and the global carbon cycle in ways that are still being discovered.     

Wind damage and response in New Zealand forests: a review

The literature on wind damage in New Zealand forests is reviewed to investigate how abiotic and biotic factors influence damage severity, damage type, and forest recovery. Winds that damage forests tend to result from extra-tropical depressions or from topographically enhanced westerly air flows. Severe wind damage can occur when wind speeds exceed c. 0 km/hr, although investigating the relationship between damage and wind speeds is difficult, as gusts, for which speed is usually unrecorded, are important. Damage is often quantified by estimates of area affected, with some authors detailing the size and species of damaged trees within a given area. Key abiotic factors that influence damage patterns are topographical position, edaphic conditions, and disturbance history. Important biotic factors are tree height, tree health, position of the tree within the stand, and species. Damage type (uprooting or breakage) is primarily controlled by canopy position and rooting depth. Forest responses to wind damage include sprouting, recruitment, release, and suppression, with the dominant mode of forest recovery being strongly influenced by the severity of damage, and the species composition of the stand. As noted in international literature on wind damage, a lack of consistent methods, combined with poor species and spatial coverage, makes identifying general trends difficult. Investigating the role of wind damage in New Zealand forests has focused to date on Nothofagus forests and plantations of exotic trees and few studies have investigated long term dynamics following wind disturbance events.     

Big‐sized trees overrule remaining trees' attributes and species richness as determinants of aboveground biomass in tropical forests

Large‐diameter, tall‐stature, and big‐crown trees are the main stand structures of forests, generally contributing a large fraction of aboveground biomass, and hence play an important role in climate change mitigation strategies. Here, we hypothesized that the effects of large‐diameter, tall‐stature, and big‐crown trees overrule the effects of species richness and remaining trees attributes on aboveground biomass in tropical forests (i.e., we term the “big‐sized trees hypothesis”). Specifically, we assessed the importance of: (a) the “top 1% big‐sized trees effect” relative to species richness; (b) the “99% remaining trees effect” relative to species richness; and (c) the “top 1% big‐sized trees effect” relative to the “99% remaining trees effect” and species richness on aboveground biomass. Using environmental factor and forest inventory datasets from 712 tropical forest plots in Hainan Island of southern China, we tested several structural equation models for disentangling the relative effects of big‐sized trees, remaining trees attributes, and species richness on aboveground biomass, while considering for the full (indirect effects only) and partial (direct and indirect effects) mediation effects of climatic and soil conditions, as well as interactions between species richness and trees attributes. We found that top 1% big‐sized trees attributes strongly increased aboveground biomass (i.e., explained 55%–70% of the accounted variation) compared to species richness (2%–18%) and 99% remaining trees attributes (6%–10%). In addition, species richness increased aboveground biomass indirectly via increasing big‐sized trees but via decreasing remaining trees. Hence, we show that the “big‐sized trees effect” overrides the effects of remaining trees attributes and species richness on aboveground biomass in tropical forests. This study also indicates that big‐sized trees may be more susceptible to atmospheric drought. We argue that the effects of big‐sized trees on species richness and aboveground biomass should be tested for better understanding of the ecological mechanisms underlying forest functioning.     

台风“布拉万”对东北近天然落叶松云冷杉试验林的影响

台风是重要的森林干扰因子之一,会对森林生态系统的结构和功能产生较大的影响。2012年的台风"布拉万"对我国东北地区局部森林造成了严重的破坏。以受灾最重的吉林省汪清林业局的近天然落叶松云冷杉林为对象,采用方差分析和相关分析方法,研究林分结构和地形条件对林木株数损伤率的影响。结果表明:(1)林木损伤类型可分为折断、连根拔起、搭挂、压弯4种,其中连根拔起为最主要的损伤类型,占总损伤株数的52%,台风灾害造成的林木株数损伤率平均为14.09%。(2)径级大小对林木株数损伤率的影响显著。损伤主要发生于径级较小林分处,径级越大,其株数损伤率越小。(3)林木株数损伤率随林分密度的增加有减小的趋势,但在统计学上它们的关系不显著。(4)不同树种间的林木株数损伤率差异显著,落叶松、冷杉等针叶树种损伤株数最多。(5)林分的树种多样性指数与林木株数损伤率无显著的相关性。(6)海拔、坡度和坡位对林木株数损伤率的影响不显著,但坡向的影响显著,东北坡向林分的林木株数损伤率最大。研究结果可以为灾后森林恢复和减少风灾影响的森林培育措施提供依据。     

神山森林文化传统的生态伦理学意义

在云南山地民族的传统文化里 ,对绿的图腾和对树的崇拜无处不在 ,神山森林传统已经成为一种生态文化传统 ,几乎所有的民族都会在自己居住的村寨附近选一片葱绿茂密的山林作为自己的风水林或水源林 ,有的甚至作为神山森林顶礼膜拜 ,严禁任何人砍伐和破坏。村寨和神山上的参天古树也往往成为神树和村寨的标记加以崇拜和保护。我们把山地民族这种文化传统称为神山森林文化传统。这是一种朴素的生态伦理观 ,体现一种敬畏生命的生态伦理学 ,有着深刻的自然保护意义。1　神山森林文化的生态学内涵及生态学意义文化 ,是人类对环境的一种社会生态适…     

Testing metabolic ecology theory for allometric scaling of tree size, growth and mortality in tropical forests

The theory of metabolic ecology predicts specific relationships among tree stem diameter, biomass, height, growth and mortality. As demographic rates are important to estimates of carbon fluxes in forests, this theory might offer important insights into the global carbon budget, and deserves careful assessment. We assembled data from 10 old-growth tropical forests encompassing censuses of 367 ha and > 1.7 million trees to test the theory's predictions. We also developed a set of alternative predictions that retained some assumptions of metabolic ecology while also considering how availability of a key limiting resource, light, changes with tree size. Our results show that there are no universal scaling relationships of growth or mortality with size among trees in tropical forests. Observed patterns were consistent with our alternative model in the one site where we had the data necessary to evaluate it, and were inconsistent with the predictions of metabolic ecology in all forests.     

Chimpanzee oil-palm use in southern Cantanhez National Park, Guinea-Bissau

Cantanhez National Park in southern Guinea-Bissau is a mosaic of forest, mangrove, savanna, and agricultural fields, with a high prevalence of oil-palm trees (Elaeis guineensis). It hosts many different animal species, including the chimpanzee (Pan troglodytes verus). Very little is known about the ecology of chimpanzees inhabiting this area. The main aims of this study were to evaluate chimpanzee nesting behavior, define trends of habitat use, and estimate chimpanzee density in four separate forests by applying the marked nest counts methodology. From the 287 new nests counted, 92% were built in oil-palm trees with a significantly higher frequency of nests in the forest edge than in forest cores. Differences in nest detection rates were observed in the four monitored forests, with two forests being more important for chimpanzee's nesting demands. The number of nests documented in the forests seemed to be correlated with the frequency of other signs of chimpanzee activity. Although chimpanzees selected nests on the forest edge, they were most frequently observed in forest core areas. Constraints associated with estimating chimpanzee density through oil-palm nest counting are discussed.     

Mechanical stability of trees under static loads

Wind affects the structure and functioning of a forest ecosystem continuously and may cause significant economic loss in managed forests by reducing the yield of recoverable timber, increasing the cost of unscheduled thinning and clear-cuttings, and creating problems in forestry planning. Furthermore, broken and uprooted trees within the forest are subject to insect attack and may provide a suitable breeding substrate, endangering the remaining trees. Therefore, an improved understanding of the processes behind the occurrence of wind-induced damage is of interest to many forest ecologists, but may also help managers of forest resources to make appropriate management decisions related to risk management. Using fundamental physics, empirical experiments, and mechanistic model-based approaches in interaction, we can study the susceptibility of tree stands to wind damage as affected by the wind and site and tree/stand characteristics and management. Such studies are not possible based on statistical approaches alone, which are not able to define the causal links between tree parameters and susceptibility to wind damage. The aim of this paper is to review the recent work done related to tree-pulling and wind tunnel experiments and mechanistic modeling approaches to increase our understanding of the mechanical stability of trees under static loading.     

Tree killing by Ips typographus (Coleoptera: Scolytidae) at stand edges with and without colonized felled spruce trees

Abstract 1 To maintain biodiversity in managed spruce forests in Sweden more wind‐felled trees must be retained. However, there is concern among forest owners that this may result in higher tree mortality caused by the spruce bark beetle, Ips typographus (L.) (Col. Scolytidae). 2 To simulate wind‐felled trees, living spruce trees were cut at spruce stand edges bordering fresh clear‐cuttings. Treatments comprised edges with zero, one or five cut trees colonized by I. typographus. Edges with naturally wind‐felled trees colonized by I. typographus were also included in the analyses. 3 During the two following summers, the number of trees killed by I. typographus did not differ between edges with and without felled trees, or between edges with one or five felled trees. 4 Within edges with felled trees, there were more killed trees close to the felled trees than at other parts of the edges. Thus, felled trees provided focal points for attacks within edges. 5 It is concluded that small numbers of wind‐felled trees colonized by I. typographus may be left near spruce stand edges without increasing the risk of beetle‐induced tree mortality.     

A comprehensive synthesis of liana removal experiments in tropical forests

Lianas are a quintessential feature of tropical forests and are often perceived as being poorly studied. However, liana removal studies may be one of the most common experimental manipulations in tropical forest ecology. In this review, we synthesize data from 64 tropical liana removal experiments conducted over the past 90 yr. We explore the direction and magnitude of the effects of lianas on tree establishment, growth, survival, reproduction, biomass accretion, and plant and animal diversity in ecological and forestry studies. We discuss the geographical biases of liana removal studies and compare the various methods used to manipulate lianas. Overall, we found that lianas have a clear negative effect on trees, and trees benefitted from removing lianas in nearly every study across all forest types. Liana cutting significantly increased light and water availability, and trees responded with vastly greater reproduction, growth, survival, and biomass accumulation compared to controls where lianas were present. Removing lianas during logging significantly reduced damage of future merchantable trees and improved timber production. Our review demonstrates that lianas have an unequivocally detrimental effect on every metric of tree performance measured, regardless of forest type, forest age, or geographic location. However, lianas also appear to have a positive contribution to overall forest plant diversity and to different animal groups. Therefore, managing lianas reduces logging damage and improves timber production; however, the removal lianas may also have a negative effect on the faunal community, which could ultimately harm the plant community.     

The mechanical stability of the world’s tallest broadleaf trees

The factors that limit the maximum height of trees, whether ecophysiological or mechanical, are the subject of longstanding debate. Here, we examine the role of mechanical stability in limiting tree height and focus on trees from the tallest tropical forests on Earth, in Sabah, Malaysian Borneo, including the recently discovered tallest tropical tree, a 100.8 m Shorea faguetiana named Menara. We use terrestrial laser scans, in situ strain gauge data and finite element simulations, to map the architecture of tall tropical trees and monitor their response to wind loading. We demonstrate that a tree's risk of breaking due to gravity or self‐weight decreases with tree height and is much more strongly affected by tree architecture than by material properties. In contrast, wind damage risk increases with tree height despite the larger diameters of tall trees, resulting in a U‐shaped curve of mechanical risk with tree height. Our results suggest that the relative rarity of extreme wind speeds in north Borneo may be the reason it is home to the tallest trees in the tropics. Abstract in MALAY is available with online material.     

辽东山区天然次生林雪／风灾害成因及分析

对2003年春发生在辽东山区的森林雪/风灾害的成因、过程、受灾情况、造成的危害、与林分结构特征的关系以及对未来次生林生态系统的影响等进行了调查分析。结果表明,雪/风的发生是在一个大的降水天气过程基础上,由于气温的异常变化形成的,受灾严重区多分布于海拔高、坡度大,林型比较单一的桦树、柞树、色树、胡桃树和杨树等林分,林分密度和受灾率及土层厚度和受害株数均呈显著的线性负相关;受灾数量与径级和树高分别呈指数负相关和指数正相关,同时探讨了雪/风害对天然次生林生态系统内病虫害发生、林下植被、生境因子和建群种变化产生的可能影响。     

Simulation of moss and tree dynamics in the boreal forests of interior Alaska

We used a simulation model of forest dynamics to examine the ecological significance of the complex interactions among site conditions, tree growth, and the development of a thick forest floor moss layer found in many boreal forests. To examine the effect of site conditions on moss growth and forest dynamics, we simulated the dynamics of several different forest sites in the uplands of interior Alaska. Then we used a cold, wet permafrost site to examine the ecological consequences of direct moss and tree interactions. Our analyses revealed a tightly coupled system in which forest succession was highly sensitive to the interactions among site conditions, mosses, and trees. The effect of mosses on the soil thermal regime was a particularly important feedback. Direct interactions between mosses and trees that affected the development of a thick forest floor layer were also important. In particular, shading of moss by trees, reduced tree regeneration on moss-covered soils, and reduced moss growth with open forest canopies were also important determinants of forest succession. These complex feedbacks ensure that an ecosystem approach is needed to understand the ecology of boreal forests.     

Causes of spatial patterns of dead trees in forest fragments in Illinois

Natural disturbances introduce spatial heterogeneity into forests by causing non-random mortality of trees. We examined whether wind was the primary cause of spatial patterns of dead trees at fragment- and individual tree-levels in three fragments of temperate deciduous forests in Illinois, USA. Dead trees and wind-caused types of mortality were expected to be higher at forest edges, on windward aspects, in poorly-drained soils, and adjacent to existing canopy gaps. The extent of wind-related mortality was determined by comparing spatial and temporal patterns of dead trees, as well as characteristics of trees downed by single windstorms versus all dead trees. At the fragment-level, we used randomly located quadrats of 25×25 m to sample edge and interior areas of Trelease Woods, Brownfield Woods, and Hart Woods in 1995-1996 and again in 1999-2000. We noted type of mortality (standing dead, snapped-off, or uprooted trees), and measured DBH ( 10 cm) and direction of fall of each dead tree. The same measures were made for trees felled by two single storms in 1994. At the individual tree-level, domino effects were evaluated by comparing openness surrounding target treefalls vs. an equal sample size of living trees. The study provided limited evidence that wind caused spatial patterns of dead trees. Instead, spatial patterns of dead trees in the fragments accumulated from domino effects at the individual tree-level in two of the three fragments. Dead trees were more associated with preexisting gaps. Contrary to our predictions at the fragment-level, the frequency of dead trees was not greater at edges, on windward aspects, or in poorly drained soils. This study demonstrated the complexity of spatial patterns of dead trees in forest fragments. The significant domino effects indicated that the occurrence of dead trees was not random, but determined by previous disturbances.     

兴安落叶松老龄林落叶松林木死亡格局以及倒木对更新的影响

对兴安落叶松老龄林落叶松林木死亡格局和死亡木对更新的影响进行了研究 .结果表明 ,丛桦落叶松林和杜香落叶松林的枯立木以中径木占多数 ,赤杨落叶松林主要为中、大径木 ,草类落叶松林主要是中、小径木 .落叶松枯立木主要因火烧、受压和老死而形成 .丛桦落叶松林和赤杨落叶松林掘根倒木较多 .杜香落叶松林和草类落叶松林的倒木以风折为主 .地形、山体走向和盛行风向对树倒方向影响很大 .丛桦落叶松林倒木方向杂乱 ,赤杨落叶松林林木均向东倒下 ,杜香落叶松林和草类落叶松林的掘根木分别向南、东北方倒下 ,两者的风折木倒向随机性较大 .草类落叶松和赤杨落叶松老龄林内 ,倒木更新为 1 8和 40株·m- 2 ,远远高于矿物土基质上 2株·m- 2 的水平 .丛桦落叶松林内倒木和林地上更新均相当好 ,约为 2 8株·m- 2 .杜香落叶松林倒木更新效果不突出 .