Stem growth and canopy dynamics in a world-wide range of Fagus forests

Abstract. Forests dominated by Fagus (beech) occur widely in the Northern Hemisphere. Tree species dominant together with beech vary in tolerance of understorey conditions. They are deciduous broad-leaved, evergreen broad-leaved or evergreen coniferous. The frequency and intensity of events that reduce the forest canopy cover are important determinants of the ratio of beech to other species in the canopy. For trees in the understorey and the canopy, stem diameter growth rate is determined by light regime and growing space which in turn are determined by canopy cover. We evaluated increase in stem diameter growth rate as an indicator of sudden reductions in canopy cover and canopy dynamics. We used tree-ring chronologies and calculated an index of growth rate increase (GI) to compare the canopy dynamics of 11 natural beech forests. Per site, the annual average value of GI poorly reflected the effects of dry or cool summers, and it clearly reflected events like tornados and hurricanes that removed substantial canopy cover. Among groups of sites average values of GI were significantly different. In the sites with a lower level of average GI, the establishment of the more shade tolerant tree and shrub species in the understorey was favoured, and subcanopy layers became more dense. On the other hand, higher levels of average GI allowed for more light demanding tree species to reach the canopy.     

Shoot growth phenology of co-existing evergreen and deciduous species in an oak forest

Shoot growth phenology was compared for the saplings of evergreen and deciduous woody species sharing the same microsite. Growth initiation occurred earlier in evergreens (among co-stratal species) while deciduous species completed their growth earlier. Shoot growth rate was significantly greater (P<0.01) for deciduous trees than evergreen trees. The amount of shoot elongations and shoot diameter was also significantly greater (P<0.01) for deciduous trees than evergreens. On the other hand, among shrubs the amount of shoot elongation and shoot diameter was greater for evergreens but the rate of elongation and diameter was more or less similar for both. The duration of shoot elongation and shoot diameter was significantly longer in evergreens than the deciduous species. Leaf packing (number of leaves per shoot) was significantly more dense in evergreen trees (P<0.01) than in deciduous tree species. Leaf packing was more dense in evergreen than deciduous shrubs but the difference was not significant. Leaf area (per individual leaf) at full expansion was significantly greater (P<0.01) in deciduous species. Leaf dry mass and specific leaf mass in the initial stage was significantly greater for evergreen species than for deciduous species. The number of buds/10 cm of shoot was higher in evergreens. However, the per cent mortality was also higher in them.     

金佛山方竹对亮叶水青冈幼树种群数量结构的影响

为探索贵州省宽阔水保护区亮叶水青冈(Fagus lucida)种群的更新维持机制,采用样方法研究金佛山方竹(Chimonobambusa utilis)对亮叶水青冈种群数量结构的影响。结果表明,较高的金佛山方竹密度降低了亮叶水青冈种群数量,亮叶水青冈株数随径级和高度级增加都呈现递减趋势;金佛山方竹密度增加有利于亮叶水青冈小径级向中径级个体的转化,而方竹密度减少则有利于中径级向大径级个体的转化;金佛山方竹密度增大降低了亮叶水青冈种群平均胸径,但增加了平均高度。这表明金佛山方竹能够影响亮叶水青冈个体数量和形态建成,亮叶水青冈通过降低胸径和增加高度来适应竹丛环境。     

Intraspecific variability of specific leaf area fosters the persistence of understorey specialists across a light availability gradient

• Forest understorey plants are sensitive to light availability, and different species groups can respond differently to changing light conditions. A plant trait tightly linked to light capture is specific leaf area (SLA). Studies considering the relative role of within‐ and among‐species SLA variation across different species groups (e.g. specialists and generalists) are rarely implemented in temperate forest understories varying in their maturity.
• We examined community‐level SLA patterns of beech forest understories along a light availability gradient, and for habitat specialists and generalists separately. We then disentangled and quantified the contribution of intraspecific trait variability and interspecific trait differences in shaping SLA patterns.
• We revealed that the increase in community‐level SLA with decreasing light availability was primarily driven by beech forest specialists (and, to a lesser extent, by forest generalists), and this pattern was mainly determined by specialists’ high intraspecific variability. Community‐level SLA was therefore formed by different responses at different organizational levels, i.e. within and among species, and for separate species groups.
• This study provides insights into factors shaping the shade tolerance strategy in beech forest understorey plants; specialists persistence under putative less favourable conditions (i.e. high irradiation) may be fostered by their ability to adjust their light capture strategies intraspecifically.

     

A comparison of 12 tree species of Amazonian caatinga using growth rates in gaps and understorey, and allometric relationships

1. The relative growth rate of saplings of 12 species from an oligotrophic lowland rain forest were measured in treefall gaps and understorey. Mean relative height growth ( R _H) within treefall gaps was found to be slowest for tall-tree species with branched saplings, intermediate for subcanopy trees and fastest for tall-tree species with unbranched saplings. Most species had similar R _H within the understorey. R _H values were not related to leaf mass per unit area (LMA) or foliar N concentrations.
2. Allometric relationships between the total leaf area (TLA) and height were dependent upon light conditions; in general saplings of a given height had a greater TLA in treefall gaps than in understorey. The species with the largest estimated TLA values in gaps tended to have the greatest R _H values in gaps; no such trend emerged in the understorey. The values of the allometric coefficients were not related to foliar properties.
3. The relationship between stem diameter and height was only weakly dependent on light conditions and the relationship between the growth rates in these dimensions was also weak. The lack of plasticity may reflect the fact that the height–diameter relationship has little bearing on a sapling's tolerance of shade.
4. One way of accommodating the dependence of allometry upon irradiance is to add R _H as a covariate. We derive a relationship between growth rates from this resource-dependent allometric equation and show that it reasonably describes measurements taken in the caatinga forest.     

Natural disturbance and tree species coexistence in an old-growth beech - dwarf bamboo forest,southwestern Japan

Abstract. The structure and composition of a cool-temperate old-growth beech (Fagus crenata) - dwarf bamboo (Sasa spp.) forest, partially affected by landslide disturbance, in the Daisen Forest Reserve of southwestern Japan, were investigated in relation to forest floor and canopy conditions. All stems ≥ 4 cm DBH were mapped on a 4-ha plot and analyses were made of population structure, spatial distribution and spatial association of major tree species. The dominant species, F. crenata, which had the maximum DBH among the species present, had the highest stem density. However, for other species, larger-sized species had lower stem density with few smaller stems or saplings, while smaller-sized species had higher stem density with many smaller stems or saplings. Canopy trees of F. crenata were distributed randomly in the plot, while its stems in the other layers and all other species were distributed patchily. Small patches represent gap-phase regeneration. Larger patches correlate with landslide disturbance, difference in soil age, or the presence/absence of Sasa. Cluster analysis for spatial associations among species and stems in the different layers revealed that the forest community consists of several groups. One main group was formed on sites not covered with Sasa. This group contained a successional subgroup (from Betula grossa to Acer mono and/or F. crenata) initiated by landslide disturbance and a subgroup of tree species that avoid Sasa. Another group was formed on sites with mature soils covered largely with Sasa. This contained associations of canopy trees of F. crenata and smaller-sized tree species such as Acanthopanax sciadophylloides and Acer japonicum. It is found that the community of this old-growth beech forest is largely organized by natural disturbance and heterogeneous conditions of the forest floor (difference in soil age and presence/absence of Sasa). The existence of these different factors and the different responses of species to them largely contribute to the maintenance of tree species diversity in this forest.; Keywords: Cluster analysis; Fagus crenata; Forest dynamics; Gap; Landslide; Spatial pattern.     

Light environment and tree strategies in a Bolivian tropical moist forest: an evaluation of the light partitioning hypothesis

Light partitioning is thought to contribute to the coexistence of rain forest tree species. This study evaluates the three premises underlying the light partitioning hypothesis; 1) there is a gradient in light availability at the forest floor, 2) tree species show a differential distribution with respect to light, and 3) there is a trade-off in species performance that explains their different positions along the light gradient. To address these premises, we studied the light environment, growth, and survival of saplings of ten non-pioneer tree species in a Bolivian moist forest. Light availability in the understorey was relatively high, with a mean canopy openness of 3.5% and a mean direct site factor of 6.8%. Saplings of two light demanding species occurred at significantly higher light levels than the shade tolerant species. The proportion of saplings in low-light conditions was negatively correlated with the successional position of the species. Light-demanding species were characterised by a low share of their saplings in low-light conditions, a high sapling mortality, a fast height growth and a strong growth response to light. These data show that all three premises for light partitioning are met. There is a clear gradient in shade-tolerance within the group of non-pioneer species leading to a tight packing of species along the small range of light environments found in the understorey. This revised version was published online in August 2006 with corrections to the Cover Date.     

广东南岭天然常绿阔叶林林下光环境对林下幼树功能性状的影响

光环境与幼树功能性状的关系对天然林的更新与演替具有重要的生态学意义。以广东南岭区域天然常绿阔叶林下不同林龄(幼龄林,中龄林,老龄林)的森林群落为研究对象,通过监测冠层结构、林下光照数据和林下幼树功能性状等指标,研究林龄梯度下其冠层结构与林下光环境之间的关系,以及林下幼树功能性状对光环境的响应。结果表明:(1)中龄林叶面积指数显著高于幼龄林和老龄林(P<0.05),随着林龄的增长,林冠开度和透光率逐渐下降,林龄梯度下透光率、R/FR(红光/远红光比值)、Bw/Rw(宽带蓝光/宽带红光比值)差异极显著(P<0.001);(2)天然常绿阔叶林中透光率与光质之间极显著相关(P<0.001),R/FR随着透光率的增加而增加,Bw/Rw随着透光率的增加而减少。(3)林下幼树功能性状在光环境之间差异显著(P<0.05),老龄林林下幼树叶片氮含量显著高于幼龄林,而叶片重叠率显著低于幼龄林;(4)在本试验地中,R/FR和Bw/Rw的变化对林下幼树的高径比和光合作用并无显著影响,光强对同种植物不同光环境下最大净光合速率的影响较大。总体而言,林龄梯度冠层结构和光环境的差异能在一定程度...     

Growth,morphology and leaf characteristics after simulated herbivory in Chinese subtropical evergreen saplings

Growth, morphology and leaf characteristics were assessed in late spring following simulated autumnal defoliation in second-year saplings of three Chinese subtropical evergreen tree species.Castanopsis fargesii showed strong compensatory growth in terms of plant biomass after removal of both 50 and 75% of leaf biomass and slight compensatory growth after 90% defoliation. DefoliatedC. fargesii saplings had more leaves per unit shoot length than non-defoliated saplings. New leaves on defoliated plants were smaller and had higher per area nitrogen content than new leaves on non-defoliated plants.Pinus massoniana andElaeocarpus japonicus showed strong and no compensatory growth, respectively, after 50% defoliation. The strong compensatory growth inP. massoniana andC. fargesii may partly explain why these species predominate in the early and late successional phases of evergreen broad-leaved forests     

Variation of plant diversity in a temperate unmanaged forest in northern Spain: behind the environmental and spatial explanation

The persistence of seedlings in the forest understorey is of major importance for the maintenance and regeneration of canopy trees in several forested ecosystems. In the present study, we examine the small-scale spatial pattern of a mixed beech and oak seedling–sapling bank in two areas of an unmanaged temperate deciduous forest with different environmental conditions. We used environmental, biotic and spatial variables to establish the main factors that explain the spatial pattern of these seedling–sapling banks at different scales. The stand structure in both areas was similar, but while in plot A beech dominated the canopy, plot B was dominated by oaks. In both areas, established beech individuals showed a clear reverse J-shaped distribution, whereas established oaks showed a unimodal distribution with only a few young individuals. Seedlings of beech and oak were distributed in aggregates, whereas beech saplings had a random distribution. At broader scales, the abundance of seedlings and saplings is affected by the environment as well as by inter-species competition, while at finer scales the spatial pattern is mainly influenced by stochastic processes, probably related to seed predation and establishment. The structure of the seedling–sapling bank indicates an advantage of beech over oak as far as regeneration is concerned. Beech seedlings and saplings tolerate the stress induced by the canopy and the understorey and persist for many years, while oak seedlings decline in a few years. Therefore, if current conditions persist, after canopy opening beech seedlings and saplings can grow rapidly into the canopy and the stands will move towards beech dominance.     

Growth of Fagus sylvatica saplings in an old-growth forest as affected by soil and light conditions

Abstract. Studies were conducted on 41 five yr-old common beech (Fagus sylvatica) saplings collected in an old-growth beech wood (Fontainebleau forest, biological reserve of La Tillaie, France), under varying humus and light conditions, following gypsy moth (Lymantria dispar) caterpillar injuries. Aerial and subterranean parts of each sapling were described by means of 34 parameters and environmental conditions at the microsite, where each sapling was excavated, were characterized by 23 parameters. The development of beech saplings is strongly affected by microsite conditions. An increase in sapling size was associated with darkness of the A-horizon, typical of zones with poor mineralization of organic matter. Light conditions were more important in influencing the development of the root system than that of the aerial parts. Rooting depth was shallower and rate of mycorrhiza development by the black ascomycete Cenococcum geophilum was lower in microsites receiving incident light during the morning than in those never receiving incident light during this period. Results are discussed in the frame of survival of young beech individuals in varying environmental conditions, when submitted to competition by other vegetation and adverse climate conditions.     

Tree seed germination and seedling establishment in treefall gaps and understorey in a subtropical forest of northeast India

Abstract Seed germination, and survival and growth of seedlings of four dominant tree species, Quercus dealbata, Quercus griffithii, Quercus glauca and Schima khasiana were studied in the treefall gaps and forest understorey of an undisturbed mature-phase humid subtropical broadleaved forest in northeast India. Three important microenvironmental factors namely photosynthetically active radiation (PAR), soil moisture and litter depth, were also measured in the forest understorey and gaps and correlated with seedling mortality. Seed germination of S. khasiana was significantly higher in the treefall gaps than in the understorey; among the tree species studied, it had the highest germination. Quercus seedlings were abundant in the understorey and small gaps, while S. khasiana seedlings were more numerous in the large gaps. The survivorship curves for the seedling populations revealed that the three Quercus species survived better in the understorey, while S. khasiana did so in the gaps. PAR and soil moisture were positively correlated with tree seedling mortality, which occurred mainly during the winter months. The Quercus seedlings grew better in the forest understorey and small gaps and S. khasiana seedlings in the large gaps. The differential performance of the tree seedlings to the conditions prevailing in the understorey and gaps of two sizes indicates that different species were adapted to different light environments depending upon their optimum requirements. This could be an effective mechanism for promoting species coexistence in the forest community.     

The physiological advantage of an ecological filter species, <Emphasis Type="Italic">Indocalamus longiauritus</Emphasis>, over co-occurring <Emphasis Type="Italic">Fagus lucida</Emphasis> and <Emphasis Type="Italic">Castanopsis lamontii</Emphasis> seedlings

Indocalamus longiauritus (a dwarf bamboo) dominates forest understory and functions as an ecological filter to hinder the regeneration of canopy tree species in many temperate forests. However, the physiological mechanism underlying the function of ecological filters is not clear. In this study, we measured leaf-level carbon capture ability and use efficiency of the dwarf bamboo and the co-existing Fagus lucida (beech) and Castanopsis lamontii (chinkapin) seedlings in forest understory and small gaps in a beech–chinkapin mixed forest in the summer of 2005. The results indicated that I. longiauritus exhibited greater carbon capture ability, as indexed by light-saturated photosynthetic rate (P _max), maximal carboxylation rate, maximal electron transport rate and carboxylation efficiency, than the co-occurring F. lucida and C. lamontii seedlings in both forest understory and small gaps. Higher carbon capture ability in I. longiauritus was related to its greater partition of absorbed light energy to photochemistry. I. longiauritus had higher photosynthetic nitrogen use efficiency than F. lucida and C. lamontii seedlings in both light environments. However, water use efficiency (WUE) in I. longiauritus was higher than F. lucida but lower than C. lamontii. This intermediate WUE in I. longiauritus was related to its intermediate light-saturated stomatal conductance. In addition, I. longiauritus reduced metabolic cost by increasing the ratio of P _max to respiration rate, leading to increased net carbon balance. On the other hand, F. lucida and C. lamontii seedlings had greater plasticity of carbon capture ability and leaf structural traits, which might facilitate colonization of gaps and realization of natural regeneration in these species.     

Different responses to shade of evergreen and deciduous oak seedlings and the effect of acorn size

An evergreen oak species, Cyclobalanopsis multinervis, and a deciduous oak species, Quercus aliena var. acuteserrata were grown from acorns under two light levels (full sunlight and shade at about 18 % of full sunlight, simulating the light intensities in forest clearings and gaps, respectively) for one growing season. Three hypotheses were tested: (i) the deciduous species grows faster than the evergreen species in forest gaps and clearings; (ii) the deciduous species responds more strongly in terms of growth and morphology to variation in light climate than the evergreen species; and (iii) seedling size is positively correlated to acorn size. The results showed: (i) at both light levels, the deciduous seedlings gained significantly more growth in biomass and height than the evergreen seedlings; (ii) both species produced significantly more biomass in full sunlight than in shade, without showing any significant difference in height between treatments. Increase in light intensity improved the growth of the deciduous seedlings more strongly; (iii) at a similar age, the deciduous seedlings showed a greater response in leaf morphology and biomass allocation to variation in light levels, but when compared at a similar size, biomass allocation patterns did not differ significantly between species; (iv) bigger acorns tended to produce larger seedlings, larger leaf sizes and more leaf area, between and within species. These differences demonstrate that the deciduous species is gap-dependent and has the advantage over the evergreen species in forest gaps and clearings.     

Sexual vs. vegetative reproduction in relation to forest dynamics in the understorey shrub,Hydrangea paniculata (Saxifragaceae)

In the forest understorey, shrubs usually reproduce vegetatively rather than sexually, but the relative contribution of these two reproductive modes may vary with temporal changes in environmental conditions (e.g., light, substrates of forest floor) that are closely related to forest dynamics. To evaluate the occasional changes in reproductive modes of the clonal understorey shrub Hydrangea paniculata, the reproductive characteristics (i.e., flowering, seedling establishment, vegetative propagation, reproductive size and age) were investigated in four different developmental stages in a Japanese beech forest (early gap, EG; late gap, LG; building, BU; mature, MA). Flowering individuals occurred only in EG and LG, and a much greater number of seedlings was observed in both EG and LG than in BU and MA, mainly because canopy gaps provided sufficient light for flowering and suitable substrates (fallen trees and exposed mineral-soil) for seedling establishment. The flowering individuals originated from plants that had persisted in the shaded understorey until gap formation. In contrast to sexual reproduction, clonal fragmentation increased with forest development in the order LG, EG, BU, MA. This is because, in later stages of forest dynamics (BU and MA), large individuals, some of which had previously flowered in gap stages, were layered on the forest floor and subsequently produced a substantial number of clonal fragments by separation of the buried branches from the main stems which had decayed. This resulted in a large number of clonal fragments originating from a single mother plant. These results suggest that the reproductive modes of H. paniculata is strongly influenced by the changes in environmental conditions with respect to the dynamics of canopy trees. Reproduction from seed in gap stages, despite their short period, provide new genets in established populations, whereas vegetative propagation via fragmentation in closed-canopy stages enhance the stability of the population until the next disturbance.     

森林光环境对4种乔木幼树光合和光谱反射特性的影响

在林窗、林缘、林下3种自然光环境下,对吉林蛟河阔叶红松林常见树种拧筋槭、白牛槭、色木槭和红松的光合和光谱特性进行对比研究,以期从生理生态角度探讨它们对自然光环境的适应能力和响应机制。结果表明：4种乔木幼树叶片的光饱和点(LSP)和光补偿点(LCP)随着生长环境光强的下降而减小,林下各树种幼树LSP和LCP显著低于林窗内幼树(P<0.05);除白牛槭外林下其他树种最大净光合效率(P_nmax)均显著小于林窗内幼树(P<0.05);不同树种幼树表观量子效率(AQY)和暗呼吸速率(R_d)随光环境的变化并没有出现明显的变化规律,各环境间差异较小。除白牛槭外,其他树种幼树叶绿素归一化指数(Chl NDI)随环境光强的减少而增大,林下树种的光化学反射指数(PRI)普遍高于光条件更好环境下树种,说明林下幼树叶片叶绿素含量和光合速率大于其他光环境;各树种植物叶片水分指数(WI)在不同光环境之间存在显著差异,环境光强越大植物叶片WI越小,植物叶片水分浓度越小。林缘下3种槭属幼树结构不敏感植被光谱指数(SIPI)显著小于其他光环境(P<0.05)...     

Root respiration and its importance for the carbon balance of beech saplings (Fagus sylvatica L.) in a montane beech forest

Root respiration of 10-year-old beech saplings (Fagus sylvatica L.) grown in the understorey (UND) and in a natural gap (GAP) of a mature beech forest in the Solling mountains, FRG, was investigated from April until December, 1990. Respiration rates of fine, medium and coarse roots were measured in situ by a PC-controlled cuvette system. Fine root respiration rates were in the range of 0.5–9.8 nmol CO₂ gDW^–1 s^–1 at both sites, but respiration rates of UND saplings were higher, compared to those of GAP saplings. The dependence of respiratory activity on soil temperature proved to be highly significant (p<0.001) for both plots, following a quasi-Arrhenius type curve. Fine root respiration rates of UND saplings were highly significantly, negatively correlated with the water content of the attached organic material, whereas respiration rates of GAP saplings did not show such a correlation. Further, a significant correlation (p<0.01) between mycorrhizal biomass and respiration rate was detected at the UND site, but not at the GAP site. Medium and coarse root respiration rates were very similar and no significant differences between the two sites were detected. Maximum respiration rates of 3.1 nmol CO₂ gDW^–1 s^–1 were reached in the middle of July. Due to low light intensities in the under storey, daily net CO₂ assimilation rates of UND saplings were much smaller than those of GAP saplings. At both sites, net CO₂ assimilation rates varied more than respiration rates and thus the carbon balance of beech saplings was more affected by the rate of carbon fixation than by the rate of respiratory carbon loss.     

Construction and maintenance costs of mediterranean-climate evergreen and deciduous leaves I. Growth and CO2 exchange analysis

Summary Gas exchange and leaf growth analysis were used in conjunction to determine leaf-construction and maintenance costs in three co-occurring shrubs of the california chaparral, one evergreen, Heteromeles arbutifolia, and two drougth deciduous species, Lepechinia calycina, and Diplacus aurantiacus. The construction costs per unit of leaf weight were similar among the three species and very close to values reported for other evergreens but considerably higher than leaf construction costs for other deciduous or herbaceous plants. Maintenance costs per unit of leaf weight were significantly greater in one deciduous species, L. calycina, than in the evergreen. Maintenance costs for all species were in the range reported for herbaceous species and considerably above those reported for other evergreens.     

Global meta-analysis shows that relationships of leaf mass per area with species shade tolerance depend on leaf habit and ontogeny

It was predicted that relationships of leaf mass per area (LMA) with juvenile shade tolerance will depend on leaf habit, and on whether species are compared at a common age as young seedlings, or at a common size as saplings. A meta-analysis of 47 comparative studies (372 species) was used to test predictions, and the effect of light environment on this relationship. The LMA of evergreens was positively correlated with shade tolerance, irrespective of ontogeny or light environment. The LMA of young seedlings (相似文献   

Factors influencing the distribution and growth of dwarf bamboo, <Emphasis Type="Italic">Fargesia nitida</Emphasis>, in a subalpine forest in Wolong Nature Reserve,southwest China

Dwarf bamboos impose intense resource competition in subalpine coniferous forests, and their exclusive densities have crucial impacts on tree regeneration and understory species diversity. We studied the factors influencing the distribution and growth of dwarf bamboo, Fargesia nitida, in a subalpine forest in southwest China. TWINSPAN, based on an attribute matrix, could divide the subalpine forest into 11 sub-associations, and more clearly reflected ecological functional features of the subalpine forest than analysis based on a species matrix. TWINSPAN was also generally consistent with DCA ordination based on the attribute matrix. DCA and DCCA ordination showed relationships between the distribution of F. nitida population and environment factor. The first DCCA axis showed topography and disturbance gradients (except fallen trees and broken branches); the second DCCA axis showed canopy density and composition gradients. Stepwise multiple regression analyses showed that distribution (culm density and coverage) of F. nitida decreased significantly with landslide and slope aspect, and increased significantly with soil status. The light condition had positive effects on growth and size of bamboo. A stable environment in the northern slope and more broadleaved species dominating in canopy would increase the dwarf bamboo biomass. Thus, the disturbance regimes, the slope aspect and the BA of evergreen conifer trees can provide useful guidelines for the control and management of F. nitida populations, and in helping to understand the succession and regeneration of subalpine forest in this region.