Gap dynamics in climaxFagus crenata forests

Gap characteristics and gap regeneration were studied in several climaxFagus crenata forests in Japan. 278 gaps were observed. Gaps covered 12% of the total land area of 20.05 ha. Gap density was 13.9 gaps per ha and, mean gap size was 92.0 m². Smaller gaps were much more frequent than larger ones. Gaps larger than 400 m² were rare. Most gaps were created by the death of single trees. Canopy trees died more often standing or with broken trunks than by uprooting, although uprooted trees were relatively abundant in the site with poor soil drainage and in the site on upper slope. Differences of gap regeneration behaviour were recognized among tree species.F. crenata regenerates in gaps from saplings recruited before gap creation and can replace not only its own gaps but also gaps of other species. Most species other thanF. crenata andMagnolia obovata could not regenerate in their own gaps. More successful regeneration ofF. crenata may occur in gaps smaller than 200 m², althought it regenerated in a wide range of gap size. However, increased relative density ofF. crenata in the canopy layer seems to prevent its successful regeneration. Gap regeneration of other species did not clearly depend on a species-specific gap size.     

阔叶红松林林隙结构与树种多样性关系研究

对阔叶红松林林隙与林下不同层次树种多样性进行比较,探讨林隙大小及发育阶段与树种多样性间的关系.结果表明,林隙与林下树种多样性存在显著差异（P<0.01）.与林下相比,林隙更新层树种多样性、丰富度和均匀度增大,生态优势度减小（P<0.01）;演替层树种多样性、丰富度和均匀度减小,生态优势度增大（P<0.0001）.林隙中不同层次树种多样性随着林隙大小呈现出相反的变化趋势.长白山阔叶红松林林隙演替层树种多样性和丰富度总体上呈单峰形变化,中等大小林隙（100～250 m²）中树种多样性和丰富度较高,生态优势度较小.而更新层树种多样性和均匀度在≥250 m²和<100 m²的林隙中最大,在200～250 m²的林隙中最小;生态优势度在200～250 m²的林隙中达到最大.更新层和演替层树种对林隙面积大小反应不同,有利于更新层幼苗建立的林隙面积并不是演替层幼树发育和成活的最适面积;随林隙年龄的增加,更新层和演替层树种多样性在不同层次上呈互补关系.     

Uncertainty in the detection of disturbance spatial patterns in temperate forests

The use of individual-based models in the study of the spatial patterns of disturbances has opened new horizons in forest ecosystem research. However, no studies so far have addressed (i) the uncertainty in geostatistical modelling of the spatial relationships in dendrochronological data, (ii) the number of increment cores necessary to study disturbance spatial patterns, and (iii) the choice of an appropriate geostatistical model in relation to disturbance regime. In addressing these issues, we hope to contribute to advances in research methodology as well as to improve interpretations and generalizations from case studies.We used data from the beech-dominated Žofínský Prales forest reserve (Czech Republic), where we cored 3020 trees on 74 ha. Block bootstrap and geostatistics were applied to the data, which covered five decades with highly different disturbance histories. This allowed us to assess the general behavior of various mathematical models. Uncertainty in the spatial patterns and stability of the models was measured as the length of the 95% confidence interval (CI) of model parameters.According to Akaike Information Criterion (AIC), the spherical model fitted best at the range of ca. 20 m, while the exponential model was best at the range of ca. 60 m. However, the best fitting models were not always the most stable. The stability of models grew significantly with sample size. At <500 cores the spherical model was the most stable, while the Gaussian model was very unstable at <300 cores. The pure nugget model produced the most precise nugget estimate. The choice of model should thus be based on the expected spatial relations of the forest ecosystem under study. Sill was the most stable parameter, with an error of ±6–20% for ≥1110 core series. By contrast, practical range was the most sensitive, with an error of at least ±59%. The estimation of the spatial pattern of severe disturbances was more precise than that of fine-scale disturbances.The results suggest that with a sample size of 1000–1400 cores and a properly chosen model, one reaches a certain precision in estimation that does not increase significantly with growing sample size. It appears that in temperate old-growth forests controlled by fine-scale disturbances, it is necessary to have at least 500 cores to estimate sill, nugget and relative nugget, while to estimate practical range at least 1000 cores are needed. When choosing the best model, the stability of the model should be considered together with the value of AIC. Our results indicate the general limits of disturbance spatial pattern studies using dendrochronological and geostatistical methods, which can be only partially overcome by sample size or sampling design.     

Lattice geometry, gap formation and scale invariance in forests

The geometry of the lattice used in ecological modeling is important because of the local nature of ecological interactions. The latter can generate complex behavior such as criticality (scale-invariance). In this work, we implement two slightly different forest disturbance models on three lattices, each with square, triangular and hexagonal symmetry, in order to study the effect of geometry. We calculate the density distribution of gaps in a forest and find bumps in the distribution at sizes that depend on lattice geometry. Similar bumps were observed in real data but remained unexplainable. We suggest that these bumps provide information about the geometry and scale of ecological interactions. We also found an effect of geometry on the conditions under which criticality appears in model forests. These conditions appear to be more biologically realistic, and also linked to the likelihood of local disturbance propagation. The scaling exponent of the gap-size distribution, however, was found to be independent of both model and geometry, a hallmark of universality.     

Shade tolerance and regeneration of some tree species of a tropical rain forest in Western Kenya

Shadetolerance and regeneration of some heavily exploited timber species(Uvariopsis congensis, Antiaris toxicaria, Funtumia africana,Prunus africana and Aningeria altissima)were studied in two adjacent sites in Kakamega tropical rain forest. The twosites have been subjected to different logging intensities. Within one of thesites, relatively intact areas were compared with adjoining more disturbedones.Seedling presence or absence in mature forest phase, sapling proportions in gapand the mature phase and diameter distributions were used to classify thespecies into shade tolerance groups. Results indicate that except forUvariopsis, the species are non-pioneer lightdemanders and could fit into three shade tolerance groups: A groupresembling pioneers but with seedling in shade, a mid-tolerant group andone showing a high shade tolerance. Amount of regeneration and disturbance wererelated: regeneration being higher in the more disturbed site except forUvariopsis. The intersite differences were mirrored whendisturbed and adjoining more intact areas within one of the sites werecompared.Species more abundant in the disturbed site also generally scored low in shadetolerance. However, the mid-tolerant Funtumia andnot Prunus or Aningeria that hadlowershade tolerance scores, dominated regeneration in the disturbed forest parts.The shade tolerance data suggest that Uvariopsis, Funtumiaand Antiaris could be amenable to natural forestmanagement. For Prunus and Aningeria,artificial regeneration in buffer plantations around the natural forest may beabetter option.     

Subcanopy gaps in temperate and tropical forests

Abstract We present a model of gaps in the vertical structure of forest vegetation. The traditional model of a forest gap assumes the existence of a ‘hole’ in the uppermost canopy layer, often extending down to near the ground. The present model extends the concept to gaps at any level, including those in lower layers below an intact canopy or subcanopy. It assumes that gaps at any level represent spaces with unused resources, especially favourable for plant growth and survival. Evidence from temperate and tropical forests indicates that gaps in the subcanopy and understorey layers below intact canopies are common, and that plants have higher growth rates in them than in non-gap sites. We also extend this model to below-ground gaps in the root zone.     

Structural characteristics and canopy dynamics of Tsuga canadensis in forests of the southern Appalachian Mountains, USA

Tsuga canadensis (L.) Carr. forests of the southern Appalachian Mountains are currently facing imminent decline induced by a nonnative insect pest, the hemlock woolly adelgid (Adelges tsugae Annand). To effectively manage these forest systems now and in the future, land managers need baseline data on forest structure and dynamics prior to large-scale Tsuga canadensis mortality. Most of our knowledge concerning the dynamics of Tsuga canadensis forests comes from more northern locations such as the Great Lakes region and New England and, therefore, may not pertain to the ecological systems found within the southern Appalachian Mountains. We examined the structure and canopy dynamics of four Tsuga canadensis forest stands within the Cataloochee watershed, in the far eastern part of Great Smoky Mountains National Park (GSMNP). We characterized the environmental settings and vertical forest layers, as well as the diameter and age-structures of each Tsuga canadensis forest stand. These environmental and structural data showed that there were indeed differences between forest stands with and without successful Tsuga canadensis regeneration. The two forest stands exhibiting successful Tsuga canadensis regeneration were located above 1,000 m in elevation on well-drained, moderately steep slopes and had the greatest canopy openness. Structural data from these two forest stands indicated a history of more continuous Tsuga canadensis regeneration. We also constructed disturbance chronologies detailing the history of canopy response to disturbance events and related these to Tsuga canadensis regeneration within each forest stand. Student t-tests adjusted for unequal variances indicated significant differences in the number of release events per tree between forest stands with and without successful Tsuga canadensis regeneration. While forest stands with successful Tsuga canadensis regeneration were more frequently disturbed by minor to major canopy disturbances, events of moderate intensity were found to be most significant in terms of regeneration. These data will be of value to land managers maintaining stands of Tsuga canadensis where treatment for hemlock woolly adelgid infestation has been successful. In areas where treatment is impractical or unsuccessful, land managers will be able to use these data to restore Tsuga canadensis forests after the wave of hemlock woolly adelgid induced mortality has passed. As of August 2008, Joshua A. Kincaid will be a member of the Environmental Studies program at Shenandoah University in Winchester, Virginia, USA     

Intraspecific sequence variation of chloroplast DNA among the component species of deciduous broad-leaved forests in Japan

To select appropriate plant materials for a phylogeography of deciduous broad-leaved forests in Japan, we surveyed intraspecific chloroplast DNA variation in 34 species found in these forests. A relatively large number of intraspecific cpDNA variations were detected in ten species: Carpinus japonica (nucleotide diversity π=0.00083), C. laxiflora (π=0.00221), Magnolia obovata (π=0.00134), Lindera triloba (π=0.00255), L. obtusiloba (π=0.00289), Pourthiaea villosa var. leavis (π=0.00263), Acer japonicum (π=0.00170), A. micranthum (π=0.00237), Euonymus oxyphyllus (π=0.00322) and Styrax obassia (π=0.00100).     

Influence of physiological phenology on the seasonal pattern of ecosystem respiration in deciduous forests

Understanding the environmental and biotic drivers of respiration at the ecosystem level is a prerequisite to further improve scenarios of the global carbon cycle. In this study we investigated the relevance of physiological phenology, defined as seasonal changes in plant physiological properties, for explaining the temporal dynamics of ecosystem respiration (R_ECO) in deciduous forests. Previous studies showed that empirical R_ECO models can be substantially improved by considering the biotic dependency of R_ECO on the short‐term productivity (e.g., daily gross primary production, GPP) in addition to the well‐known environmental controls of temperature and water availability. Here, we use a model‐data integration approach to investigate the added value of physiological phenology, represented by the first temporal derivative of GPP, or alternatively of the fraction of absorbed photosynthetically active radiation, for modeling R_ECO at 19 deciduous broadleaved forests in the FLUXNET La Thuile database. The new data‐oriented semiempirical model leads to an 8% decrease in root mean square error (RMSE) and a 6% increase in the modeling efficiency (EF) of modeled R_ECO when compared to a version of the model that does not consider the physiological phenology. The reduction of the model‐observation bias occurred mainly at the monthly time scale, and in spring and summer, while a smaller reduction was observed at the annual time scale. The proposed approach did not improve the model performance at several sites, and we identified as potential causes the plant canopy heterogeneity and the use of air temperature as a driver of ecosystem respiration instead of soil temperature. However, in the majority of sites the model‐error remained unchanged regardless of the driving temperature. Overall, our results point toward the potential for improving current approaches for modeling R_ECO in deciduous forests by including the phenological cycle of the canopy.     

长白山红松阔叶林林冠空隙特征的研究

将林冠空隙干扰作为红松阔叶林动态维持的重要因素,对长白山红松阔叶林林 冠空隙的形成方式、出现频度、分布格局、结构及林冠空隙内形成本的数量、年龄分布、种 群特征等进行了系统分析．结果表明．长白山阔叶红松林多数林冠空隙由双形成本形成, 每个林冠空隙拥有的形成木为２．４４株;林冠空隙形成的速率为０．９２个ｈｍ２·ａ－１,林冠空 隙干扰的间隔期（周转期）为７５１ａ;扩展林冠空隙面积大多在１００～６００ ｍ２之间,其中以 ４００～５００ ｍ２所占比例最大．冠空隙在５０～３５０ ｍ２之间,其中以２００～２５０ ｍ２所占比例最 大;每个形成本所形成的扩展林冠空隙平均面积为 １４１ ８２ ｍ２,形成的冠空隙面积平均为 ６７．６３ ｍ２．     

Population dynamics of coniferous and broad-leaved trees in a Japanese temperate mixed forest

The growth and survival of coniferous and broad-leaved trees were followed over a 5-yr period in a temperate old-growth mixed forest in Japan, and dynamic features of the forest were studied in relation to the life history of the dominants, the coniferous Abies homolepis and the broad-leaved Fagus crenata. During this period, the gap formation rate was 31m² ha^?1yr^?1, the mortality of trees > 2m high was 1.7%/yr, and the rate of loss in basal area 1.4%/yr. These values were much higher than the recruitment, 0.3%/yr, and the total growth of surviving and new trees, 0.6%/yr, owing to the inhibition of regeneration by understorey dwarf bamboo (Sasa borealis). A transition matrix model based on DBH size classes predicts that the basal area of the forest will decrease by 14% in 50 yr, but that the DBH distribution of trees > 10 cm diameter will change little. Equilibrium DBH distributions assuming recruitment being equal to mortality, were quite different between broad-leaved and coniferous trees, reflecting different survivorship curves of the two dominants. The composition and structure of the forest may change depending on the pattern and frequency of disturbances, or episodic events, notably the synchronous death of Sasa borealis.     

The boreal forests of north-eastern Eurasia

The distribution, diversity and structure of boreal forests of monsoon Asia are reviewed. The boreal zone is circumscribed by the isotherms of 15°C and 45°C of Kira's Warmth Index (WI) and includes the territory of the Amur basin, the seashores of the Sea of Okhotsk, Kamchatka, Sakhalin and the Kuril islands. Boreal forests also occur on the mountains of Hokkaido, Honshu, Korea and NE China. The oceanic sectors of the boreal zone are composed mainly of birch forests, the marine sectors of spruce-fir forests and the continental sectors of larch and pine forests. The upper limit of the boreal forests ascends from the lowest level in the North to ca. 1500 m a.s.l. in the South of the zone, and reaches above 2500 m in the mountains of the temperate zone. In the boreal zone the secondary forests are common. They form after fires and cutting. Volcanism is an essential factor in the forest dynamics in the oceanic part of the region. It is suggested that as a result of global warming one may expect a strong alteration in vegetation pattern, especially in the northern and mountain areas.Paper presented at the International Symposium on Global Change Impacts on Terrestrial Ecosystems in Monsoon Asia (TEMA) Waseda University, Tokyo, 4–6 September 1993.     

Diversity of understory plants in undisturbed and disturbed tropical lowland forests of Little Andaman Island, India

Species richness and density of understory plants were investigated in eight 1 ha plots, distributed one each in undisturbed and disturbed tropical evergreen, semi-evergreen, deciduous and littoral forests of Little Andaman island, India, which falls under one of the eight hottest hotspots of Biodiversity in the world viz. the Indo-Burma. One hundred 1 m⁻² quadrats were established in each 1 ha plot, in which all the understory plants (that include herbs, undershrubs, shrubs and herbaceous climbers) were enumerated. The total density of understory plants was 6,812 individuals (851 ha⁻¹) and species richness was 108 species, representing 104 genera and 50 families. Across the four forest types and eight study plots, the species richness ranged from 10 to 39 species ha⁻¹. All the disturbed sites harbored greater number of species than their undisturbed counterparts. Herbs dominated by species (63%) and density (4,259 individuals). The grass Eragrostis tenella (1,860 individuals; IVI 40), the invasive climber Mikania cordata (803; IVI 20) and the shrub Anaxagorea luzonensis (481; IVI 17.5) were the most abundant species. Poaceae, Asteraceae, Acanthaceae, Orchidaceae and Euphorbiaceae constituted the species-rich families represented by 6 species each. The species-area curves attained an asymptote at 0.8 ha level except in sites DD and DL, indicating 1 ha plot is not sufficient to capture all the understory species in disturbed forests. The alien weeds formed about one-fourth of the species richness (31 species; 28%) and density (1,926 individuals; 28.3%) in the study sites, indicating the extent of weed invasion and the attention required for effective conservation of the native biodiversity of the fragile island forest ecosystem.     

Fine-grain pattern in Southern Cape plateau forests

Abstract. Regeneration levels, size class distributions and a nearest neighbour technique were used to describe apreliminary dynamics frameworkfortheplateauforests. Taken over a large area, most of the canopy dominants have a negative exponential distribution of stems > 10 cm dbh per size class. In small (0.04 ha) plots, if present as more than one stem, most species are present as both canopy (> 25 cm dbh) and understorey (10–15 cm dbh) individuals. The canopy dominants maintain their rank in the bank of advance regeneration (> 5 cm height < 10 cm dbh). However, relative numbers of all regeneration of most canopy individuals are not strongly correlated with canopy closure or local abundance of conspecific adults. The mean area of nearest neighbour polygons of canopy individuals around saplings of the more common species are small. In conclusion, most species appearto be shade tolerant and locally persistent conferring a fine grain on this forest. We support recent questioning of universality of the gaps/non gaps paradigm.     

Structure and dynamics of subalpine forests in the Wang Lang Natural Reserve, Sichuan, China

Population structure (size, age, spatial patterns) and radial growth patterns are used to analyze regeneration patterns of Abies faxoniana, Betula albosinensis, Betula utilis, Larix potaninii, Picea purpurea, and Sabina saltuaria and reconstruct disturbance history in 8 subalpine forest stands in Wang Lang Natural Reserve, Sichuan, China. In old-growth stands tree regeneration occurs in tree-fall gaps whereby A. faxoniana, Betula sp., P. purpurea, and S. saltuaria persist at stand scales by gap-phase regeneration. Clump sizes of young populations are similar to canopy gap sizes but clumps sizes vary among species. Young Betula patches are larger than those of A. faxoniana suggesting that gap-partitioning by size contributes to species coexistence in mixed stands. Picea purpurea and S. saltuaria are longer lived than A. faxoniana which may compensate for lower recruitment and prevent their replacement by A. faxoniana. Tree regeneration and community structure are also influenced by the understory bamboo Fargesia denudata. Seedlings, saplings, and shrub density all decline with an increase in bamboo cover. Species that regenerate in old-growth forest also regenerate after flooding as do species that establish only on bare substrates (i.e. Larix potaninii, Prunus sp.). Structural and compositional patterns in Wang Lang forests are a reflection of disturbance history, canopy species life history attributes such as dispersal ability, shade tolerance, growth rates, and longevity, and competition of trees and shrubs with understory bamboos.     

Comparison of the effects of canopy and understory nitrogen addition on xylem growth of two dominant species in a warm temperate forest,China

Understanding the effect of increasing atmospheric nitrogen (N) deposition on xylem growth of trees is critical to predict tree growth and carbon sequestration under global change. Canopy N addition (CAN) is generally believed to realistically simulate atmospheric N deposition on terrestrial ecosystems given it takes all processes of N deposition from forest canopy to belowground into account. However, whether CAN is more effective in reflecting the effect of atmospheric N deposition on xylem growth of trees than understory N addition (UAN) has been rarely reported. To address the question, we conducted a CAN vs. UAN experimental study to weekly monitor xylem growth of two dominant broadleaf species (Quercus acutissima Carruth. and Quercus variabilis Blume) in a warm temperate forest of China during 2014–2015. Weekly xylem increment during the two years was measured. Mixed-effects models were used to quantify the effects of N addition on xylem growth and detect the differences among treatments. We found that CAN of 50 kg N ha⁻¹ yr⁻¹ plays a more significant role in promoting xylem growth of Q. acutissima than UAN of 50 kg N ha⁻¹ yr⁻¹, and significantly enhanced the formation of differentiating xylem (zones of radial enlarging and wall-thickening cells) of Q. acutissima in the early growing season (April-June) and the rate of xylem increment, but no significant difference in xylem increment of Q. variabilis was detected between CAN50 and UAN50. This is the first study to quantitatively demonstrate that previous UAN studies may have underestimated the effects of atmospheric N deposition on tree growth by ignoring the N interception through forest canopy. Furthermore, our study also suggested a species-specific response of xylem growth to N addition. Under a certain amount of atmospheric N deposition in the future, the xylem increment of Q. acutissima may be superior to that of Q. variabilis.     

Slow understory redevelopment after clearcutting in high mountain forests

Besides natural tree regeneration itself, the development of the forest understory community is highly indicative of the ecological recovery of forest stands post-harvesting, and therefore of the sustainability of forest management. High mountain forests might show particularly slow recovery of the understory plant community because of harsh environmental conditions. We compared understory community richness and composition among three age classes of forest stands in the subalpine Engelmann Spruce–Subalpine Fir zone in the interior of British Columbia, Canada. Species composition was found to differ significantly between mature stands (>110 years old and never harvested) and both recent clearcuts (5–8 years old) and the oldest clearcuts present in the study area (second growth: 24–28 years old). A non-metric multidimensional scaling (NMDS) ordination revealed no unidirectional return of species composition in harvested stands towards that of mature forest; indeed, plots in recent clearcuts and second growth stands were similar to one another and clearly separated from the mature stands. Indicator Species Analysis revealed that moss species were particularly indicative of mature forest, with four moss species being common in mature stands but absent from both younger stages. Compared to what has been reported for lower elevation coniferous forests, e.g. in the U.S. Pacific Northwest, redevelopment of the understory appears to be slow after harvesting in these high elevation mountain forests. Rotation intervals that consider the natural temporal pattern of species turnover and the occurrence interval of major natural disturbances (here: fire) should provide effective approaches to sustainable forest management of these forests.