Canopy tree mortality depends on the proportion of crown exposed to sunlight,but this effect varies with species' wood density

Understanding what drives changes in tree mortality as well as the covariates influencing trees' response is a research priority to predict forest responses to global change. Here, we combined drone photogrammetry and ground-based data to assess the influence of crown exposure to light (relative to total crown area), growth deviations (relative to conspecifics), tree size, and species' wood density (as a surrogate for light-demanding and shade-tolerant life-history strategies) on the mortality of 984 canopy trees in an Amazon terra firme forest. Trees with lower wood density were less prone to die when their proportion of crown was more exposed to sunlight, but this relationship with relative crown exposure weakened and slightly reversed as wood density increased. Trees growing less than their species average had higher mortality, especially when the species' wood density decreased. The role of wood density in determining the survival of canopy trees under varying light conditions indicates differential responses of light-demanding versus shade-tolerant species. Our results highlight the importance of accounting for life-history strategies, via plant functional types, in vegetation dynamic models aiming to predict forest demography under a rapidly changing climate. Abstract in Spanish is available with online material.     

达维台风对海南尖峰岭热带山地雨林群落的影响

 海南岛地处我国台风的频发地带, 台风是影响海南岛热带雨林的一个重要的自然干扰因子。该文对2005年达维台风前后海南尖峰岭热带山地雨林天然次生林2 600 m²固定样地的物种组成、胸高断面积、植株数目、风倒木的影响因子、物种多样性、生物量变化及碳储量归还进行比较分析。结果显示, 台风后森林内产生大量的风倒木、断枝和落叶, 导致群落郁闭度减少、透光性增强, 并产生大量的林窗。台风后群落的组成结构发生显著变化, 受损株数达514株(占总株数26.1%); 其中风倒木比例较大, 达206株(占总株数10.5%)。方差分析结果显示, 受台风影响产生的风倒木与未明显受损树木的胸径面积、树高和木材密度均无显著差异; 但与树种组成有较紧密的关联, 对乔木层、幼树层和下木层造成的损害存在种类上的明显差异。台风产生的损害可以分为直接性损害和间接性损害两种: 1)直接性损害主要作用于乔木层, 造成大径级植株严重受损; 部分树种重要值降低, 变成伴生种, 或者次优势种和原有优势种成为共同优势种; 2)间接性损害主要通过风倒木作用于幼树层和下木层, 产生的倒木、断枝和落叶压倒其它植株, 表现为小面积范围内的个体死亡, 甚至有种类消失; 部分优势种的个体数减少较多, 但占该种群所有个体数目的比例较小。乔木层的Shannon-Wiener和Simpson多样性指数均略有下降, 而幼树层和下木层均略有上升, 但3个林层均表现为不同程度的种类消失和一些种类的个体数目减少。此次台风还造成该样地至少占台风前总生物量10.42%的生物量归还给林地, 并对森林生态系统碳循环产生重大影响。     

Asymptotic height as a predictor of growth and allometric characteristics in malaysian rain forest trees

The growth and physiological characteristics of canopy trees are expected to differ systematically from those of understory trees on the basis of size-dependent aspects of biomechanics, resource availability, and life history. Although such differences have previously been noted, there has been relatively little effort to quantify these in terms of interspecific allometric relationships. Asymptotic maximal height (H_max) is advocated as a measure of the size of dicotyledonous woody plants for this purpose. Height diameter (H–D) relationships in 38 species within six genera of Malaysian rain forest trees are well described by an asymptotic model, and thus provide a basis for estimating H_max using static observational data. Three important aspects of tree growth strategies are shown to be predictable on the basis of these values: average tree growth rates are positively related to H_max, while wood density and the initial allometric slope of (species-specific) H–D relationships are negatively related to H_max. These patterns may be explained by an association of low light levels with slow growth and high density wood in understory species; the latter property may in turn allow for relatively high allometric slopes of H–D relationships in saplings of small-statured species. Analyses that control for phylogenetic differences provide evidence that such interspecific allometric patterns are the product of convergent evolution. These results are consistent with the idea that much ecological variation within species-rich taxa of southeast Asian rain forest trees is related to differentiation along a vertical axis of tree size.     

Wood mechanics, allometry, and life-history variation in a tropical rain forest tree community

Wood density plays a central role in the life-history variation of trees, and has important consequences for mechanical properties of wood, stem and branches, and tree architecture. Wood density, modulus of rupture, modulus of elasticity, and safety factors for buckling and bending were determined for saplings of 30 Bolivian rain forest tree species, and related to two important life-history axes: juvenile light demand and maximum adult stature. Wood density was strongly positively related to wood strength and stiffness. Species safety factor for buckling was positively related to wood density and stiffness, but tree architecture (height : diameter ratio) was the strongest determinant of mechanical safety. Shade-tolerant species had dense and tough wood to enhance survival in the understorey, whereas pioneer species had low-density wood and low safety margins to enhance growth in gaps. Pioneer and shade-tolerant species showed opposite relationships between species traits and adult stature. Light demand and adult stature affect wood properties, tree architecture and plant performance in different ways, contributing to the coexistence of rain forest species.     

冰雪灾害对森林的影响

冰雪灾害是一种常见的自然灾害,往往对森林造成很大破坏。随着冰在树冠上不断积累,产生的压力逐渐增大,最后超过该部位最大弯曲力矩时林木会受到伤害。受害程度与林分的多种特征,如树种组成和林分密度及林木的多种特征,如胸径、树高、树干尖削度、叶片表面积、树冠对称性、根系、林龄等有密切关系。影响冰雪灾害的外部因素有地形因子和土壤因子,包括海拔、坡度、坡向、坡位和土壤类型、土壤厚度、土壤水分含量。冰雪灾害对林下光照、土壤、凋落物、真菌和森林动物产生影响。冰雪灾害后的林下光照对树种更新、森林动态和恢复具有重要意义。研究冰雪灾害对天然林的影响,长期监测冰雪灾害后的森林动态、林下植物的光环境、森林的养分循环、土壤以及森林动物,特别是土壤微生物的变化,加强森林的防灾管理是今后该领域的研究方向。     

Plant growth-form alters the relationship between foliar morphology and species shade-tolerance ranking in temperate woody taxa

Variation in leaf size (area per leaf) and leaf dry weight per area (LWA) in relation to species shade- and drought-tolerance, characterised by Ellenberg's light (ELD) and water demand (EWD) values, respectively, were examined in 60 temperate woody taxa at constant relative irradiance. LWA was independent of plant size, but leaf size increased with total plant height at constant ELD. Canopy position also affected leaf morphology: leaves from the upper crown third had higher LWA and were larger than leaves from the lower third. Leaf size and LWA were negatively correlated, and leaf size decreased and LWA increased with decreasing species shade-tolerance. Mean LWA was similar for trees and shrubs, but trees had larger leaves than shrubs. Furthermore, all relationships were altered by plant growth-form: none of the qualitative tendencies was significant for trees. This implies the considerably lower plasticity of foliar parameters in trees than those in shrubs. Accordingly, shade-tolerance of trees, having relatively constant leaf structure, may be most affected by the variability in biomass partitioning and crown geometry which influence foliage distribution and spacing and finally determine canopy light absorptance. Alteration of leaf form and investment pattern for construction of unit foliar surface area which change the efficiency of light interception per unit biomass investment in leaves, is a competitive strategy inherent to shrubs. EWD as well as wood anatomy did not control LWA and leaf size, though there was a trend of ring-porous tree species to be more shade-tolerant than diffuse-porous trees. Since ring-porous species are more vulnerable to cavitation than diffuse-porous species, they may be constrained to environments where irradiances and consequently evaporative demand is lower.     

Architecture of Iberian canopy tree species in relation to wood density,shade tolerance and climate

Tree architecture has important consequences for tree performance as it determines resource capture, mechanical stability and dominance over competitors. We analyzed architectural relationships between stem and crown dimensions for 13 dominant Iberian canopy tree species belonging to the Pinaceae (six Pinus species) and Fagaceae (six Quercus species and Fagus sylvatica) and related these architectural traits to wood density, shade tolerance and climatic factors. Fagaceae had, compared with Pinaceae, denser wood, saplings with wider crowns and adults with larger maximal crown size but smaller maximal height. In combination, these traits enhance light acquisition and persistence in shaded environments; thus, contributing to their shade tolerance. Pinaceae species, in contrast, had low-density wood, allocate more resources to the formation of the central trunk rather than to branches and attained taller maximal heights, allowing them to grow rapidly in height and compete for light following disturbances; thus, contributing to their high light requirements. Wood density had a strong relationship with tree architecture, with dense-wooded species having smaller maximum height and wider crowns, probably because of cheaper expansion costs for producing biomechanically stable branches. Species from arid environments had shorter stems and shallower crowns for a given stem diameter, probably to reduce hydraulic path length and assure water transport. Wood density is an important correlate of variation in tree architecture between species and the two dominant families, with potentially large implications for their resource foraging strategies and successional dynamics.     

Modeling the vertical foliage distribution of an individual <Emphasis Type="Italic">Castanopsis cuspidata</Emphasis> (Thunb.) Schottky,a dominant broad-leaved tree in Japanese warm-temperate forest

The vertical foliage distribution of Castanopsis cuspidata (Thunb.) Schottky was examined in trees of various sizes to clarify its variation in relation to tree size and the light environment in a stand. As indices of these parameters, we analyzed crown social position (CSP: percent of stand height) and specific leaf area (SLA). The vertical foliage distribution of trees was expressed by a Weibull function. The variation in the vertical foliage distribution of C. cuspidata could be categorized into three types using crown social position and light environment. In the first type, leaves were concentrated to the top 20% of the tree; such trees are canopy trees that can receive full sunlight. The second type had a large relative crown depth and an asymmetric distribution with the maximum foliage located near the top of the tree; such trees are suppressed trees whose crowns do not receive sufficient light. The third type had a large relative crown depth and a symmetric distribution; such trees occur in high light environments, although their crowns are in the understory layer. The differences in the vertical foliage distribution are related to the strategies used to capture light. Multiple regression analysis showed that CSP and SLA at the top layer of the tree explained successive changes in the vertical foliage distribution. These results will contribute to scaling-up the vertical foliage distribution to the community level in pure stands of C. cuspidata using an individual-based model.     

蒙古栎次生林的生长更新与林下植被多样性对林分密度的响应

以辽宁省抚顺市清源县蒙古栎天然次生林为对象,在2018年对6块面积为0.1 hm²的蒙古栎样地进行疏伐,并于2020年调查样地内植被的生长情况,研究疏伐后形成的600(低密度)、720(中密度)、900株·hm^-2(高密度)3种密度对林木生长、林下实生苗更新与林下植被多样性的影响。结果表明: 由于疏伐后间隔年份较短,不同密度下树高、胸径无显著差异。但低密度下林冠对称指数显著高于高密度,表明树冠生长对于林分密度的响应比树干生长更迅速。中密度下实生更新苗数量最多,且相同苗高的实生苗地径显著高于其他两个密度,中密度下实生苗更新与幼苗生长都好于高、低密度。林中共有植物70种,隶属于41科67属,其中木本植物蒙古栎、胡枝子与草本植物山罗花、三叶委陵菜占优势地位。灌木层与草本层的优势度指数、均匀度指数和多样性指数在中密度下表现最佳,表明该立地条件下林分密度保持在720株·hm^-2时更有助于辽东山区蒙古栎次生林的可持续发展。     

How liana loads alter tree allometry in tropical forests

Intense competition with lianas (wood climbers) can limit tree growth, reproduction, and survival. However, the negative effects of liana loads on tree allometry have not yet been addressed. We investigated the hypothesis that liana loading on tree crown alters tree’s allometry, expressed through slenderness (height–diameter ratio). The relationship between trunk slenderness and percentage of tree crown covered by lianas was investigated for 12 tree species from 10 fragments of the Semideciduous Seasonal Forest in Southeastern Brazil. We also tested whether the relationship between slenderness and wood density differ between trees without lianas and trees heavily infested. Liana loads significantly altered tree allometry by decreasing slenderness, even when lianas covered less than 25% of tree crown. Heavy-wood species decreased their trunk slenderness in a greater ratio than light-wood species. Our findings indicate that liana infestation shifts tree allometry, and these effects are stronger on heavy-wood tree species.     

Correlating Stem Biomechanical Properties of Hawaiian Canopy Trees with Hurricane Wind Damage1

Hawaiian forests are subject to the effects of periodic hurricane conditions. Hurricane Iniki struck the island of Kauai, Hawaii on September 11, 1992 with winds exceeding 200 km/h and caused defoliation, felling of trees by snapping and uprooting, and standing tree mortality due excessive limb and leaf loss. The purpose of this study was to evaluate if measured wood mechanical characteristics could be correlated with stem failure of trees under windstorm conditions. A field survey indicated that post-hurricane stem condition (snapped, uprooted, or standing) differed among five common canopy species and was significantly correlated with stem apparent elastic modulus (relative flexibility). Species that tended to snap had significantly higher apparent elastic moduli than those that remained standing or were uprooted. Wood density and stem diameter were not significantly related to stem failure mode. Native trees had a higher percentage per species of standing individuals but also had increased uprooting. Nonnative tree species were more often snapped and fewer were standing after the hurricane. The higher incidence of stem failure for introduced canopy trees may increase the spread of alien understory species following wind disturbance events. These relationships provide a simple means to predict relative differences in stem failure due to high wind conditions and should be considered in planning reforestation efforts on the Hawaiian Islands.     

Allometric relationships for Eucalyptus nitens (Deane and Maiden) Maiden plantations

Allometric relationships between stem, leaf area and crown dimensions were determined for Eucalyptus nitens (Deane and Maiden) Maiden using 81 trees sampled from 13 post-canopy closure sites and 34 trees sampled from 6 pre-canopy closure sites. These sites differed in site quality, stand age, fertiliser treatment, stand density and levels of weed infestation. Overall, tree age ranged from 2 to 13 years, tree height from 1.4 to 26.1 m and diameter at breast height from 0.6 to 38.7 cm. Pre-canopy closure trees exhibited site-specific relationships which were to some extent confounded with tree age. However, post-canopy closure trees had relationships which were independent of site, age and silvicultural treatments. Strong relationships between structural components were found for both stem and crown. Stem diameter at breast height was non-linearly related to tree height and crown length. Stem sapwood area (breast height or crown base) could be predicted from stem cross-sectional area. For post-canopy closure trees, a functional relationship between sapwood area (breast height and crown base) and leaf area was site-independent. The lack of specificity in terms of both site and management techniques enables these relationships to be applied generally to E. nitens plantations in Tasmania.     

Crown allometries are less responsive than stem allometry to tree size and habitat variations in an Indian monsoon forest

While theoretical allometric models postulate universal scaling exponents, empirical relationships between tree dimensions show marked variability that reflects changes in the biomass allocation pattern. As growth of the various tree compartments may be controlled by different functions, it is hypothesized that they may respond differently to factors of variation, resulting in variable tree morphologies and potentially in trade-offs between allometric relationships. We explore the variability of tree stem and crown allometries using a dataset of 1,729 trees located in an undisturbed wet evergreen forest of the Western Ghats, India. We specifically test whether species adult stature, terrain slope, tree size and crown light exposure affect the relationships between stem diameter and stem height (stem allometry), and between stem diameter and crown width, crown area and crown volume (crown allometries). Results show that both stem and crown allometries are subject to variations in relation to both endogenous (tree size, species adult stature) and exogenous (terrain slope, crown light exposure) factors. Stem allometry appears to be more affected by these factors than are crown allometries, including the stem diameter–crown volume relationship, which proved to be particularly stable. Our results support the idea that height is a prevailing adjustment factor for a tree facing variable growth (notably light) conditions, while stem diameter–crown volume allometry responds more to internal metabolic constraints. We ultimately discuss the various sources of variability in the stem and crown allometries of tropical trees that likely play an important role in forest community dynamics.     

Patterns of Trunk Diameter, Tree Height and Crown Depth in Crowded Abies Stands

The size structure of trees in crowded, even-aged Abies (fir)stands of ‘Shimagare’ or ‘wave-regenerated’sub-alpine forests is analyzed. Tree-height distributions showconsistently smaller variation and less positive skewness thanthe distributions of trunk diameter and crown depth (tree heightminus height of the lowest branch). This difference is associatedwith changes in the relationships between trunk diameter, treeheight and crown depth as stands age. These, in turn, resultfrom self-pruning of the lower foliage crown due to competitionfor light in crowded stands. Abies, diameter-height curve, competition, size distribution, stand development, tree geometry, wave-regeneration     

Insights into intraspecific wood density variation and its relationship to growth,height and elevation in a treeline species

• The wood economics spectrum provides a general framework for interspecific trait–trait coordination across wide environmental gradients. Whether global patterns are mirrored within species constitutes a poorly explored subject. In this study, I first determined whether wood density co‐varies together with elevation, tree growth and height at the within‐species level. Second, I determined the variation of wood density in different stem parts (trunk, branch and twigs).
• In situ trunk sapwood, trunk heartwood, branch and twig densities, in addition to stem growth rates and tree height were determined in adult trees of Nothofagus pumilio at four elevations in five locations spanning 18° of latitude. Mixed effects models were fitted to test relationships among variables.
• The variation in wood density reported in this study was narrow (ca. 0.4–0.6 g cm^?3) relative to global density variation (ca. 0.3–1.0 g cm^?3). There was no significant relationship between stem growth rates and wood density. Furthermore, the elevation gradient did not alter the wood density of any stem part. Trunk sapwood density was negatively related to tree height. Twig density was higher than branch and trunk densities. Trunk heartwood density was always significantly higher than sapwood density.
• Negative across‐species trends found in the growth–wood density relationship may not emerge as the aggregate of parallel intraspecific patterns. Actually, trees with contrasting growth rates show similar wood density values. Tree height, which is tightly related to elevation, showed a negative relationship with sapwood density.

     

Relationship between tree size and insect assemblages associated with Anadenanthera macrocarpa

This study analyzed the effects of tree size, and correlated architectural tree characteristics, on the assemblages of ants and insect herbivores associated with Anadenanthera macrocarpa (Mimosaceae). The latter is a myrmecophilous tree species from the Atlantic rainforest in south-eastern Brazil. Ants and insect herbivores were collected in 30 individuals of A. macrocarpa , ranging from young individuals (>3 m in height) to emergent trees (up to 40 m). Tree height was a strong indicator of other tree characteristics, including trunk diameter, crown height, crown volume, and number of bifurcations. Ants were collected using arboreal pitfall traps and beating, while insect herbivores with beating only. There was a significant increase in both abundance and species richness of ants and insect herbivores with an increase in tree height. In addition, tree height had a significant effect on the species composition of ants and insect herbivores. Assemblages of both taxa showed a nested organization pattern. The species found in small- and medium-sized trees, in general, consisted of a subset of the species found in the crowns and branches of larger, canopy or emergent trees. Thus, in A. macrocarpa , there was not a replacement of insect species with plant ontogeny. This finding is at variance with those conducted in tropical evergreen forests and which show a clear stratification between the understory and canopy insect faunas. Additional studies are needed to explain these contrasting patterns, but it is possible that differences in microclimate are involved. As the forest we studied is semi-deciduous, microclimatic gradients between the understory and the canopy habitat are probably less severe than in an evergreen forest, thus resulting in a lower turnover of species.     

The vertical foliage distributions of six understory tree species in a Chamaecyparis obtusa Endl. forest

Summary The relationships between the amounts of foliage and heights of trees were studied for the dominant understory tree species, including three evergreen and three deciduous species, in a secondary forest of Chamaecyparis obtusa Endl. The relationships showed two phases: leaf increasing and stationary phases. In the leaf-increasing phase, the height growth allowed these species to expand the canopy by increasing the number of leaves. In the stationary phase, the number of leaves was relatively constant number irrespective of tree height from 160 to 400 cm. The number of leaves in the stationary phase represents the maximum number of leaves that can be supported by trees under shady conditions. From the analyses of vertical distributions of leaves in six species, mono- and multi-layer foliage distributions were detected. Two evergreen species, Eurya japonica and Cleyera japonica, showed multi-layer foliage distributions, whereas three deciduous species, Lyonia ovalifolia, Rhododendron reticulatum and Vaccinium hirtum, and one evergreen species, Pieris japonica, showed mono-layer foliage distributions. The relationships between the weights of non-photosynthetic and photosynthetic organs of the six species were examined. The proportion of non-photosynthetic organs increased with tree height. The understory species attained the stationary phase and were maintained by minimizing their investment in non-photosynthetic organs, i.e. their height growth was arrested by the shady conditions under the crown trees.     

Plant functional traits explain interspecific differences in immediate cyclone damage to trees of an endangered rainforest community in north Queensland

Abstract Cyclones cause profound immediate impacts on tropical rainforest trees, including defoliation, limb loss, snapping of stems and uprooting. Some studies have shown that plant functional traits such as tree size, buttress roots and wood density are correlated with these forms of cyclone damage. On 20 March 2006, Severe Tropical Cyclone Larry crossed the north Queensland coast and proceeded inland across the Atherton Tablelands, impacting the critically endangered Mabi Type 5b rainforest. We investigated the effects of Cyclone Larry on common tree species by categorizing damage to trees as uprooted, snapped, limbs damaged (light, moderate, severe) or upright and estimating levels of defoliation. Damage was then related to functional traits including tree size, presence of buttress roots, wood density, and leaf size and strength. Levels of damage differed between species. Tree size (diameter at breast height) and the presence of buttress roots were not related to damage levels. Wood density was significantly negatively correlated to proportion of trees with snapped stems and significantly positively correlated with the proportion of trees upright with no or light limb damage. Levels of defoliation were significantly related to leaf strength (specific leaf area – SLA) and to leaf width, but not other components of leaf size (area or length) or petiole length. Species with high wood density and low SLA (e.g. Argyrodendron spp.) were found to have high cyclone resistance, the ability to resist damage, while species with low wood density and high SLA (e.g. Dendrocnide photinophylla) exhibited low resistance. However, traits related to low resistance are also those linked to rapid growth and high cyclone resilience, the ability to recover from damage, so it is unlikely that the Mabi forest will experience long‐term changes in floristic composition following Cyclone Larry.     

尾叶桉人工林种群密度的研究

探讨了5.6年生尾叶桉种群密度与冠幅、胸径、树高、立木单株材积、林分蓄积量、木材性质及保存率等的作用规律和相关模型.结果表明,密度对胸径、立木单株材积、冠幅及枝下高的影响达到极显著水平;对蓄积量、木材纤维宽度的影响达显著水平;对树高、木材气干密度和木材纤维长度虽有一定的影响,但不显著.其中,密度与蓄积量、枝下高、木材纤维宽度呈正相关关系;而与胸径、立木单株材积、冠幅呈负相关关系.此外,尾叶桉具有较宽的合理密度范围;作为短周期浆纸林,其最佳密度应确定为2000株·hm_-2.