High Mortality for Rare Species Following Hurricane Disturbance in the Southern Yucatán

Hurricanes are an important part of the natural disturbance regime of the Yucatán Peninsula with the potential to alter forest structure and composition, yet investigations of species‐level responses to severe winds are limited in this region. The effect of a category 5 hurricane (Hurricane Dean, 21 August 2007) on dry tropical forests across the southern Yucatán was examined with respect to tree damage, mortality, and sprouting. Damage was assessed 9–11 mo following the hurricane in 92 (500 m²) plots stratified by wind speed and normalized difference vegetation index (NDVI) change classes over a 25,000 km² study area. We investigated the relative importance of biotic (i.e., species, size, and wood density) and abiotic (i.e., wind speed) factors to better explain patterns of damage. Overall mortality was low (3.9%), however, mortality of less common species (8.5%) was elevated more than fourfold above that of 28 common species (1.8%), indicating immediate selective consequences for community composition. Species varied in the degree and type of damage experienced, with susceptibility increasing with tree diameter and height. Wood density influenced damage patterns only in areas where a critical threshold in storm intensity was exceeded (wind speeds ≥210 km/h). Although overall, damage severity increased with wind speed, common coastal species were more resistant to damage than species distributed farther inland. Our findings suggest that selective pressure exerted by frequent hurricane disturbance has, and will, continue to impact the floristic composition of forests on the Yucatán Peninsula, favoring certain wind‐resistant species. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Forest damage and recovery from catastrophic wind

The literature on the effects of catastrophic wind disturbance (windstorms, gales, cyclones, hurricanes, tornadoes) on forest vegetation is reviewed to examine factors controlling the severity of damage and the dynamics of recovery. Wind damage has been quantified in a variety of ways that lead to differing conclusions regarding severity of disturbance. Measuring damage as structural loss (percent stems damaged) and as compositional loss (percent stems dead) is suggested as a standard for quantifying severity. Catastrophic wind produces a range of gaps from the size caused by individual treefalls to much larger areas. The spatial pattern of damage is influenced by both biotic and abiotic factors. Biotic factors that influence severity of damage include stem size, species, stand conditions (canopy structure, density), and the presence of pathogens. Abiotic factors that influence severity of damage include the intensity of the wind, previous disturbance, topography, and soil characteristics. Recovery from catastrophic wind disturbance follows one of four paths: regrowth, recruitment, release, or repression. The path of recovery for a given site is controlled both by the severity of disturbance and by environmental gradients of resources. Recovery is influenced also by frequency of wind disturbance, which varies across geographical regions. To develop robust theories regarding catastrophic wind disturbance, the relative roles of different abiotic and biotic factors in controlling the patterns of severity of damage must be determined. These patterns of severity and environmental gradients must then be tied to long-term dynamics of recovery.     

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。     

The abundance,distribution and structural characteristics of tree‐holes in Nothofagus forest,New Zealand

Tree‐holes provide an important microhabitat that is used for feeding, roosting and breeding by numerous species around the world. Yet despite their ecological importance for many of New Zealand's endangered species, few studies have investigated the abundance or distribution of tree‐holes in native forests. We used complementary ground and climbed tree surveys to determine the abundance, distribution and characteristics of tree‐holes in undisturbed Nothofagus forest in the Lewis Pass, New Zealand. We found that hole‐bearing trees were surprisingly abundant compared with many other studies, including Australian Eucalyptus species and American beech. In fact, we estimated as many as 3906 tree‐holes per hectare, of which 963 holes per hectare were potentially large enough to provide roost sites for hole‐nesting bats in New Zealand, while only eight holes per hectare were potentially suitable for specialist hole‐nesting birds. This was of great interest as primary cavity‐excavating animals are absent from New Zealand forests, compared with North America and Australia. Moreover, tree‐hole formation in New Zealand is likely to be dominated by abiotic processes, such as branch breakage from windstorms and snow damage. As has been found in many other studies, tree‐holes were not uniformly distributed throughout the forest. Tree‐holes were significantly more abundant on the least abundant tree species, Nothofagus fusca, than on either N. menziesii or N. solandri. In addition to tree species, tree size was also an important factor influencing the structural characteristics of tree‐holes and their abundance in this forest. Moreover, these trends were not fully evident without climbed tree surveys. Our results revealed that ground‐based surveys consistently underestimated the number of tree‐holes present on Nothofagus trees, and illustrate the importance of using climbed inspections where possible in tree‐hole surveys. We compare our results with other studies overseas and discuss how these are linked to the biotic and abiotic processes involved in tree‐hole formation. We consider the potential implications of our findings for New Zealand's hole‐dwelling fauna and how stand dynamics and past and future forest management practices will influence the structural characteristics of tree‐holes and their abundance in remnant forest throughout New Zealand.     

飓风和台风对沿海地区森林生态系统的影响

飓风和台风是影响热带和温带沿海区域的主要灾害性气候之一,飓风和台风对于森林生态系统的影响是生态学关注的课题。综述了飓风和台风登陆对于森林生态系统树木和林分的危害影响形式及主要影响因素,着重举例阐述了树种和森林类型是影响台风危害程度的一个重要因素。分析了目前国际上开展的关于飓风和台风登陆对于森林生态系统碳、氮循环的影响,结果表明飓风、台风干扰导致的森林凋落物输入量、凋落物分解速率以及森林碳储存量动态变化较为复杂,与森林类型、林分空间位置以及台风过后的时间段密切相关。飓风引起的森林受损的恢复途径和机理与树冠受损严重程度直接相关,并受到光和水分条件的影响,及时的开花、结果以及充足的土壤种子库对森林植被恢复具有促进作用。在景观和区域尺度量化飓风和台风对沿海地区森林生态系统的影响也日益引起关注,在这方面,整合气象数据、遥感数据和地面调查的模型模拟方法起到重要的作用。今后应加强对于我国东南沿海地区森林生态系统遭受台风影响损失的生态监测和长期定位研究,加强关于台风对于不同森林生态系统类型和不同树种的危害形式和危害程度的研究,以及台风对于森林生态系统碳、氮循环影响的研究,弥补我国在以上领域的空白。     

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.     

Disturbances in deciduous temperate forest ecosystems of the northern hemisphere: their effects on both recent and future forest development

Disturbances in forests can kill mature trees, but also create the conditions necessary for the establishment of new tree cohorts and create micro-habitats for new plant and animal species, thereby increasing the species diversity compared to undisturbed stands. We review the types and intensities of disturbances on forests in three regions of the temperate zone of the northern hemisphere: northeastern North America, Central Europe, and East Asia. We focus on (1) the ways in which disturbances affect forest stand development; (2) the differences among the three areas in this regard; (3) the consequences for future forest management. In both northeastern North America and East Asia, hurricanes and typhoons represent the major mode of natural disturbance, while in Central Europe winter windstorms occur after deciduous trees have lost their leaves. Tornadoes can have even greater destructive power (but affect relatively narrow strips of land), and the more severe of these mainly occur in North America. The general disturbance patch system therefore is relatively large in northeastern North America, small in Central Europe, and of intermediate size in temperate East Asia. In addition to wholly natural disturbance factors, human commerce and globalization have enabled new disturbance types by introducing pests and diseases from one region to another. In North America especially, several of the most important foundation species in temperate forests are strongly affected, so that not just the species composition but also the whole forest structure is changing fundamentally. In all three areas in the past the change in land use by growing human populations strongly affected the structure as well as the species composition of forests. Nearly all the recent forest stands of the temperate zone had been used in the past in a particular way, and many of today’s forests had previously been converted into agricultural land. Finally climate change is superimposing itself on forest development worldwide. Nevertheless, climate change is not a new phenomenon, so forest ecosystems in all time periods have been exposed to changing climatic conditions and have had to adapt. Each forest stand therefore represents a unique recent expression of the interaction of environmental conditions and plant species, a “snapshot” of the relevant abiotic and biotic factors, including human impact.     

Dynamics of forests with Araucariaceae in the western Pacific

Abstract. Several species of Araucaria and Agathis (Araucariaceae) occur as canopy emergents in rain forests of the western pacific region, often representing major components of total stand biomass. New data from permanent forest plots (and other published work) for three species (Araucaria hunsteinii from New Guinea, A. laubenfelsii from New Caledonia, and Agathis australis from New Zealand) are used to test the validity of the temporal stand replacement model proposed by Ogden (1985) and Ogden & Stewart (1995) to explain the structural and compositional properties of New Zealand rain forests containing the conifer Agathis australis. Here we propose the model as a general one which explains the stand dynamics of rain forests with Araucariaceae across a range of sites and species in the western Pacific. Forest stands representing putative stages in the model were examined for changes through time in species recruitment, growth and survivorship, and stand richness, density and basal area. Support for the model was found on the basis of: 1. Evidence for a phase of massive conifer recruitment following landscape-scale disturbances (e.g. by fire at the Huapai site, New Zealand for Agathis australis); 2. Increasing species richness of angiosperm trees in the pole stage of forest stand development (i.e. as the initial cohort of conifers reach tree size; >10 cm DBH); 3. A high turnover rate for angiosperms (<100 yr), and low turnover for conifers (≥ 100 yr) in the pole stage, but similar turnover rates for both components (50–100 yr) as forests enter the mature to senescent phase for the initial conifer cohort; 4. Very low rates of recruitment for conifers within mature stands, and projected forest compositions which show increasing dominance by angiosperm tree species; 5. A low probability of conifer recruitment in large canopy gaps created by conifer tree falls during the initial cohort senescent phase, which could produce a second generation low density stand in the absence of landscape scale disturbance; 6. Evidence that each of the three species examined required open canopy conditions (canopy openness > 10 %) for successful recruitment. The evidence presented here supports the temporal stand replacement model, but more long-term supporting data are needed, especially for the phase immediately following landscape level disturbance.     

A preliminary study of changes in forest stratification along environmental gradients in Southeast Asia

Changes in forest stratification along environmental gradients in Southeast Asian forests were studied, by applying Quantification Method I to the records of tree height inventories and environmental conditions in 29 study forest stands. To stratify individual trees into subpopulations in a stand, an empirical and graphical method was used. After stratifying all the component individuals of the stand into subpopulations, the number of subpopulations per stand and mean tree height per subpopulation were calculated and adopted as indices of forest stratification. Of the two indices, the latter index changed linearly with respect to the maximum tree height in the stand. Hence, the number of subpopulations and the maximum tree height as a substitute for mean tree height per subpopulation were biotic dependent variables in the application of Quantification Method I, while abiotic independent variables were the following six categorized environmental factors: the number of wet months with over 100 mm month⁻¹ rainfall in a year, occurrence of fog, mean annual temperature, magnesium accumulation in mineral soil, soil water drainage, and forest fire. It was concluded that these biotic and abiotic variables were the components of multivariate regression models, which successfully explained the development of forest stratification in terms of habitat conditions.     

台风对森林的影响

台风通过树枝折断、吹落叶果、产生倒木和折干等许多途径影响林分结构和动态。森林受害程度随树种、林龄、森林类型、树高和地形而异。高密度的森林通常具有较差的根系和较大的树高/胸径比值,在台风袭击下,往往具有较高的受损和死亡的风险。台风疏开郁闭的林冠层,促进了先锋树种的大量增加、生长和成熟,形成的林隙也为个体更新提供了机会。强风造成了土壤基质的多样化,从而促进了实生苗和幼树的更新和生物多样性的增加。台风也通过改变粗木质残体,枯枝落叶层,地洞和土墩,以及繁殖可用性来影响生物多样性。台风产生的粗死木和枯枝落叶使森林的碳储量迅速归还土壤,并影响土壤的养分分布。台风减少了动物的食物供应和恶化栖息地的环境,减少鸟的数量,促进昆虫扩散。受害森林给害虫滋生提供了场所。今后的研究热点是受台风干扰森林的长期监测,不同森林土壤的有机碳贮藏,土壤和养分流失规律,台风和其他自然灾害的交叉影响,改进数学模型以准确预测台风损害。     

Determinants of tree survival at local scale in a sub-tropical forest

Tree survival is a critical driver of stand dynamics, influencing forest structure and composition. Many local-scale drivers (tree size, abiotic and biotic factors) have been proposed as being important in explaining patterns of tree survival, but their contributions are still unknown. We examined the relative importance of these local drivers on tree survival using generalized linear mixed models in an old-growth sub-tropical forest in south China at three levels (community, guild, and species). Among the variables tested, tree size was typically the most important driver of tree survival, followed by abiotic and then biotic variables. Tree size has a strongly positive effect on tree survival for small trees (10–30 cm dbh) and shade-tolerant tree species. Of the abiotic factors tested, elevation tended to be more important in affecting tree survival than other topographic variables. Abiotic factors generally influenced survival of species with relatively high abundances, for individuals in smaller size classes and for mid-tolerant species. Among biotic factors, we found that the mortality of tree species was not driven by density- and frequency-dependent effects in this sub-tropical forest, as indicated by the results of both total basal area of neighbors and the proportion of conspecific neighbors in our study. We conclude that the relative importance of variables driving patterns of tree survival varied greatly among tree size classes, species guilds, shade tolerance, density, and abundance classes in this sub-tropical forest. These results also provide critical information for future studies of forest dynamics and offer insight into forest management in this region.     

森林的风/雪灾害研究综述

风／雪灾害不仪极大影响木材生产,同时对森林生态系统的稳定性也造成很大影响。森林风／雪危害的主要类型有树干弯曲、干(冠)折、掘根以及后续危害等;其发生主要依赖于气象条件、立地因子、树木和林分特征及其之间的相互作用。其中．林木尖削度(胸径／树高)和林分结构特征(树种、组成、密度等)是控制树木和林分对风／雪荷载抵抗的主要特征量。因此．通过造林、调整林分结构．加强林分管理如间伐、施肥等措施一直是用来减少林木的风／雪灾害的主要措施。另外．林木或林分发生风／雪害的模型分析研究也取得了很大进展,但由于森林风／雪害受诸如地形、天气等多种因素影响、目前所建立的模型系统在实际应用中普适性较芹。通过综述以往研究结果认为：在气象和立地条件难以控制的情况下．通过改变可控因子林分结构来减少森林风／雪害是可行的。因此．研究如何加强森林经营管理,尤其是不同形式的间伐技术和不同处理的造林措施与风／雪灾害发生的关系、如何增加林木和林分抵抗风／雪灾害的能力等是今后该研究领域的重点和难点。与此同时．应加强风／雪灾害危险率评估研究．进而对森林进行风／雪灾害危险率管理;并注重对受灾前后林地内生态效应的研究,以便为灾后的森林经营管理和调控提供坚实的理论依据。     

Tree and stand-scale factors affecting richness and composition of epiphytic bryophytes and lichens in deciduous woodland key habitats

Conservation and sustainable forestry are essential in a multi-functional landscape. In this respect, ecological studies on epiphytes are needed to determine abiotic and biotic factors associated with high diversity. The aim of the present study was to evaluate relative sensitivity of conservation targets (epiphytic bryophytes and lichens) in relation to contrasting environmental variables (tree species, tree diameter at breast height, bark crevice depth, pH, tree inclination, pH, forest stand age, area and type) in boreo-nemoral forests. The study was conducted in Latvian 34 woodland key habitat (WKH) boreo-nemoral forest stands. Generalized linear mixed models and canonical correspondence analysis showed that tree species and tree bark pH were the most important variables explaining epiphytic bryophyte and lichen composition and richness (total, Red-listed, WKH indicator species). Forest stand level factors, such as stand size and habitat type, had only minor influence on epiphytic species composition and richness. The results of the present study indicate a need to maintain the diversity of tree species and large trees, particularly Acer platanoides, Carpinus betulus, Fraxinus excelsior, Populus tremula, Tilia cordata, Ulmus glabra and Ulmus laevis in conservation of epiphytic bryophyte and lichen communities in the future.     

Climate change induces multiple risks to boreal forests and forestry in Finland: A literature review

Climate change induces multiple abiotic and biotic risks to forests and forestry. Risks in different spatial and temporal scales must be considered to ensure preconditions for sustainable multifunctional management of forests for different ecosystem services. For this purpose, the present review article summarizes the most recent findings on major abiotic and biotic risks to boreal forests in Finland under the current and changing climate, with the focus on windstorms, heavy snow loading, drought and forest fires and major insect pests and pathogens of trees. In general, the forest growth is projected to increase mainly in northern Finland. In the south, the growing conditions may become suboptimal, particularly for Norway spruce. Although the wind climate does not change remarkably, wind damage risk will increase especially in the south, because of the shortening of the soil frost period. The risk of snow damage is anticipated to increase in the north and decrease in the south. Increasing drought in summer will boost the risk of large‐scale forest fires. Also, the warmer climate increases the risk of bark beetle outbreaks and the wood decay by Heterobasidion root rot in coniferous forests. The probability of detrimental cascading events, such as those caused by a large‐scale wind damage followed by a widespread bark beetle outbreak, will increase remarkably in the future. Therefore, the simultaneous consideration of the biotic and abiotic risks is essential.     

Local-scale drivers of tree survival in a temperate forest

Tree survival plays a central role in forest ecosystems. Although many factors such as tree size, abiotic and biotic neighborhoods have been proposed as being important in explaining patterns of tree survival, their contributions are still subject to debate. We used generalized linear mixed models to examine the relative importance of tree size, local abiotic conditions and the density and identity of neighbors on tree survival in an old-growth temperate forest in northeastern China at three levels (community, guild and species). Tree size and both abiotic and biotic neighborhood variables influenced tree survival under current forest conditions, but their relative importance varied dramatically within and among the community, guild and species levels. Of the variables tested, tree size was typically the most important predictor of tree survival, followed by biotic and then abiotic variables. The effect of tree size on survival varied from strongly positive for small trees (1-20 cm dbh) and medium trees (20-40 cm dbh), to slightly negative for large trees (>40 cm dbh). Among the biotic factors, we found strong evidence for negative density and frequency dependence in this temperate forest, as indicated by negative effects of both total basal area of neighbors and the frequency of conspecific neighbors. Among the abiotic factors tested, soil nutrients tended to be more important in affecting tree survival than topographic variables. Abiotic factors generally influenced survival for species with relatively high abundance, for individuals in smaller size classes and for shade-tolerant species. Our study demonstrates that the relative importance of variables driving patterns of tree survival differs greatly among size classes, species guilds and abundance classes in temperate forest, which can further understanding of forest dynamics and offer important insights into forest management.     

Tree species richness and turnover throughout New Zealand forests

Abstract. Patterns of mortality, recruitment, and forest turnover were investigated using permanent plot data from temperate forests in 14 localities throughout New Zealand. Tree mortality and recruitment rates were calculated from tagged trees ≥ 10 cm diameter at 1.4 m on individual 400 m² plots, and turnover rates were calculated as the mean of mortality and recruitment rates. Turnover rates (1.4% per year) were very similar to those recorded for tropical forests (i.e. 1.5% per year). As was shown in tropical forests, we also found significant relationships between forest turnover and species richness. In New Zealand forests there was also a decrease in species richness and turnover rates with increasing latitude. Although species richness is well known to decline with latitude, our study provides support for a possible link between seasonality and disturbance with tree turnover and species diversity. While tree mortality and recruitment rates were approximately in balance at some localities, in others there were imbalances between mortality and recruitment rates.     

Minireviews: Neighborhood Effects, Disturbance Severity, and Community Stability in Forests

A theoretical framework and conceptual model for temporal stability of forest tree-species composition was developed based on a synthesis of existing studies. The model pertains primarily to time periods of several tree lifetimes (several hundred to a few thousand years) at the neighborhood and stand spatial scales (0.01–10 ha), although a few extensions to the landscape scale are also made. The cusp catastrophe was chosen to illustrate compositional dynamics at the stand level for jack pine, northern hardwood, and white pine forests in the Great Lakes Region of the United States and for tropical rainforests in the northern Amazon basin. The models feature a response surface (degree of dominance by late-successional species) that depends on two variables: type of neighborhood effects of the dominant tree species and severity of disturbances. Neighborhood effects are processes that affect the chance of a species replacing itself at the time of disturbance (they can be positive, neutral, or negative) and are of two types: overstory–undestory effects, such as the presence of advanced reproduction; and disturbance-activated effects, such as serotinous seed rain. Disturbance severity is the proportion of trees killed during a disturbance. Interactions between neighborhood effects and disturbance severity can lead to either punctuated stability (dramatic but infrequent change in composition, in those forests dominated by species with positive neighborhood effects) or succession (continuous change, in those forests dominated by species with neutral-negative neighborhood effects). We propose that neighborhood effects are a major organizing factor in forest dynamics that provide a link across spatial scales between individual trees and disturbance/patch dynamics at the stand and landscape scales. Received 23 June 1998; accepted 16 December 1998.     

Assessing biotic and abiotic effects on forest productivity in three temperate forests

1. It is well understood that biotic and abiotic variables influence forest productivity. However, in regard to temperate forests, the relative contributions of the aforementioned drivers to biomass demographic processes (i.e., the growth rates of the survivors and recruits) have not received a great deal of attention. Thus, this study focused on the identification of the relative influencing effects of biotic and abiotic variables in the demographic biomass processes of temperate forests.
2. This study was conducted in the Changbai Mountain Nature Reserve, in northeastern China. Based on the observational data collected from three 5.2‐hectare forest plots, the annual above‐ground biomass (AGB) increment (productivity) of the surviving trees, recruits, and the total tree community (survivors + recruits) were estimated. Then, the changes in the forest productivity in response to biotic variables (including species diversity, structural diversity, and density variables) along with abiotic variables (including topographic and soil variables) were evaluated using linear mixed‐effect models.
3. This study determined that the biotic variables regulated the variabilities in productivity. Density variables were the most critical drivers of the annual AGB increments of the surviving trees and total tree community. Structural diversity enhanced the annual AGB increments of the recruits, but diminished the annual AGB increments of the surviving trees and the total tree community. Species diversity and abiotic variables did not have impacts on the productivity in the examined forest plots.
4. The results highlighted the important roles of forest density and structural diversity in the biomass demographic processes of temperate forests. The surviving and recruit trees were found to respond differently to the biotic variables, which suggested that the asymmetric competition had shaped the productivity dynamics in forests. Therefore, the findings emphasized the need to consider the demographic processes of forest productivity to better understand the functions of forests.

     

Modelling the influence of predicted future climate change on the risk of wind damage within New Zealand's planted forests

Wind is the major abiotic disturbance in New Zealand's planted forests, but little is known about how the risk of wind damage may be affected by future climate change. We linked a mechanistic wind damage model (ForestGALES) to an empirical growth model for radiata pine (Pinus radiata D. Don) and a process‐based growth model (cenw ) to predict the risk of wind damage under different future emissions scenarios and assumptions about the future wind climate. The cenw model was used to estimate site productivity for constant CO₂ concentration at 1990 values and for assumed increases in CO₂ concentration from current values to those expected during 2040 and 2090 under the B1 (low), A1B (mid‐range) and A2 (high) emission scenarios. Stand development was modelled for different levels of site productivity, contrasting silvicultural regimes and sites across New Zealand. The risk of wind damage was predicted for each regime and emission scenario combination using the ForestGALES model. The sensitivity to changes in the intensity of the future wind climate was also examined. Results showed that increased tree growth rates under the different emissions scenarios had the greatest impact on the risk of wind damage. The increase in risk was greatest for stands growing at high stand density under the A2 emissions scenario with increased CO₂ concentration. The increased productivity under this scenario resulted in increased tree height, without a corresponding increase in diameter, leading to more slender trees that were predicted to be at greater risk from wind damage. The risk of wind damage was further increased by the modest increases in the extreme wind climate that are predicted to occur. These results have implications for the development of silvicultural regimes that are resilient to climate change and also indicate that future productivity gains may be offset by greater losses from disturbances.     

Factors influencing brushtail possum (

Damage by introduced brushtail possums (Trichosurus vulpecula) to Pinus radiata trees was assessed in 41 compartments of a commercial forestry plantation on the Coromandel Peninsula, New Zealand. All the trees assessed were less than 3 years old. Possum damage in the compartments was low (median prevalence 3.3%) but highly variable (range 0?30%). Eight of 37 measured habitat factors differed significantly (P < 0.05) between the sites with damaged and undamaged trees. The best predictor of mean damage was stand age, but this explained only 21% of the variation in damage among compartments. Including both stand age and New Zealand bracken (Pteridium esculentum) cover improved the model significantly and explained 36% of variation in damage. Damage was apparently unrelated to compartment size, distance from the compartment boundary, and possum den-site availability. Surprisingly, the relationship between browse damage and a trap-catch index of possum abundance was weakly negative (r_S = −0.53, P = 0.05). The dense understorey associated with young pine stands tends to increase possum damage to associated P. radiata trees, but the possums in such stands may be less mobile at ground level and thus less easily trapped. Assessment of stand age and understorey characteristics, together with visual inspection for early signs of damage, is likely to be more cost-effective than possum surveys for identifying forest compartments at risk from possum browse.