林隙微生境及更新研究进展

系统评述了国内外关于林隙干扰及更新的最新研究进展.林隙是一种经常发生的小规模干扰,是森林群落时空格局变化的驱动力.不同的林隙干扰状况导致了林隙内光照的差异,进一步造成林隙内温度、湿度、土壤理化性质的变化,形成了微生境的时空异质性.林隙干扰通过改变微生境而对幼苗的出土、存活、定居和生长产生重要影响.林隙内种子库的物种丰富度变化很大,是幼苗分布格局的重要影响因子.更新幼苗的存活率和生长量受林隙大小及幼苗在林隙中位置的影响.指出了这一领域今后的研究方向.     

林隙影响天然林更新研究进展

林隙干扰是森林循环中经常发生的小规模干扰,林隙的存在为天然林幼苗更新提供了有利的微环境。文中综述了林隙大小、林隙年龄和林隙边缘木在天然林更新过程中所起的作用,以及林隙更新理论在林业生产中实际应用情况,指出林隙更新理论在森林经营上的应用是未来林隙研究中的重要方面。     

林隙对森林生态系统的影响研究进展

树隙是由一棵或多棵树木死亡引起的树冠开口,是世界上许多森林系统的主要干扰形式。林隙在森林生态系统中发挥着重要作用,有助于保护生物多样性和土壤多样性,影响养分循环,维持演替后期森林的复杂结构。该文通过对林隙动态和林隙生态的叙述,重点强调了林隙通过影响森林生态系统中的微环境,进而影响森林生态系统的生长与发育。这能为森林管理者提供科学依据,有利于森林管理者对森林生态系统进行更加科学、精确的管理。     

林隙及其对天然林更新的影响

林隙是森林中由自然或人为小规模干扰形成的,是森林演替和循环中必不可少而又经常发生的现象,为森林的更新提供了有利的微环境。本文通过对林隙尺度、特征和森林微环境变化等叙述,重点分析了我国对天然林林隙的研究现状、分布的区域和森林类型,林隙大小、年龄和边缘木等方面对天然林更新的影响,以及林隙理论在实践中的应用,指出,林隙更新理论是森林经营,尤其是天然林经营中最重要的方面之一。     

茂兰喀斯特森林干扰状况与林隙特征

调查茂兰喀斯特森林林隙干扰特征,并对林隙特征、林隙的形成方式进行探讨。结果表明:1)林隙大小分布表现出以小林隙为主的偏正态分布,但在总林隙面积比例上,大林隙所占的比例较大;2)林隙大多数在20年前形成,估计林隙形成速率为0.55个·hm-2a-1,返回间隔期为270年;3)林隙密度约为20个·hm-2,林隙平均面积(69.7±45.71)m2,扩展林隙平均面积(152.7±79.43)m2,林隙和扩展林隙占所调查林分面积的比例分别为13.9%和30.6%;4)林隙形成方式以折干为主,但因地形差异,槽谷、坡地、漏斗的主要形成方式分别为干中折断、拔根倒和干基折断;5)大多数林隙由1～4株形成木形成,平均每个林隙的形成木为2.5株。大部分林隙形成木为森林建群种,常绿和落叶树种分别占61.5%和38.5%。林隙形成木以小径级为主,表明本地森林林隙干扰十分频繁。     

林隙更新及其空间环境异质性研究进展

林隙是一种经常发生的小规模干扰,它不仅是森林循环和演替的重要场所,也是森林生态系统时空格局变化的重要驱动力。本文主要从时间(林隙年龄)和空间(林隙面积)两种尺度评价了林隙干扰对更新的影响,并结合光照、温湿度、土壤、地形等环境因子对林隙空间环境异质性问题进行了评述,对近年来国内外研究进展进行了概括,并对目前这一领域研究重点进行总结,为以后的相关研究提供参考。     

林隙微环境异质性及物种更新响应研究进展

林隙作为森林循环和演替的重要场所,其内小环境特征随着时间和空间而改变,林隙内资源及其空间分布的不均匀性,为物种的共存和更新提供了环境条件,而物种分布的复杂性又进一步促进了森林小环境的异质性分化。本文从小气候状况、土壤及微地形方面对林隙小环境异质性问题进行了论述,并就林隙内微生境因子的异质性分布格局与物种拓殖策略的关系以及边缘效应对物种多样性形成和维持机制的作用等方面进行了阐述。     

长白山自然保护区阔叶红松林林隙更新状况

该以长白山大面积分布的阔叶红松林林隙为研究对象．系统调查了林隙形成木和林隙填充的特征，并对其主要树种的更新环境进行研究。结果表明，长白山阔叶红松林林隙多数是由1．4株形成木形成的，林隙形成木主要是红松、水曲柳、蒙古栎和紫椴；林隙填充中，紫椴和色木槭的数量最多，红松所占比例较小。不同大小林隙内填充的数量也不同，近似呈一个偏左的正态分布。现有的红松幼树一般都分布在林隙内或林隙边缘，更新环境良好。     

林窗理论在山地型城市森林建设中的应用前景

从森林循环演替、森林特殊的生境、边缘效应、森林植被物种多样性及森林景观格局多样性等方面论述了林窗干扰作用,并讨论了林窗理论在山地型城市森林建设中森林动态管理、森林景观格局优化和林相改造等方面的应用前景。     

长白山云冷杉针阔混交林林隙结构与更新研究

通过对金沟岭林场云冷杉针阔混交林36.5 hm2中的75个林隙的调查,研究了人工经营条件下天然云冷杉针阔混交林生态系统中的林隙大小结构,以及不同大小结构下的林隙更新情况。结果表明:该类森林内的林隙形成方式以择伐为主,40~60 m2的林隙数量最多,该类林隙多由2~3棵形成木构成,林隙密度是20.5%;在20~40 m2的林隙中更新情况最好,多由1~2株林木被伐形成。因此建议采伐作业时不要连续采伐2株以上,以保持好的天然更新环境,维护森林生态系统的连续性和稳定性。     

THE DYNAMIC SIMULATION MODEL OF MANAGEMENT FOREST RESOURCES SYSTEM

INTRODUCTIONThemanagementofforestresourceisalargescalesystemwiththecharactCristicsofdpondcs,non-linearityandmulticircuits.ltrelatestoagreatnumberoffactors,includingnotonyplantationsandnatUralresourcesec-tors,butalsosomeotherfactorsaboutmap-ageInentandutilization.Thesefactorsaremu-tUaldePCndenceandinterachononeanotherwithsomesortsofdpodricfeedbackprocc-uurs.fossystCm,whichisconstantlychange-ableastiInepasses,hasaheavilyrelationtootherSystCms.ItisimPossibletoclearIyunder-standsuchaconti…     

Deer density effects on vegetation in aspen forest understories over site productivity and stand age gradients

Studies examining the interacting effects of ungulate herbivore pressure and site productivity on vegetation are mostly on grassland-grazing systems and have shown conflicting patterns. Here we examine the effects of deer density (>30 years differences in density between two landowners), site productivity (site index, SI) and stand age on subcanopy vegetation characteristics in 60 closed canopy, clear-cut origin Populus tremuloides dominated stands, Michigan, USA. Stand age effects were included because age varied among stands and can affect subcanopy vegetation patterns. Compared with fewer deer, stands with more deer had greater total forest floor vegetation mass, and its major components bracken fern (Pteridium aquilinum), sedge (mostly Carex pensylvanica) and trees/shrubs <0.25 m tall, but lower forb mass and lower forest floor vegetation species richness and diversity. Deer density and SI had strong interacting effects on total forest floor mass, forb mass, and species richness. Forb mass increased with SI, but only in stands with fewer deer, whilst total vegetation mass was greater in stands with more deer at lower SI and declined with SI more sharply than for stands with fewer deer. Species richness increased with SI but more so at lower than higher deer density. Deer density and age had interacting effects on mass of trees/shrubs <0.25 m tall and sedge. Compared with fewer deer, stands with more deer had greater sedge and tree/shrub mass, and sedge mass decreased and tree/shrub mass increased more sharply with age. In lower deer stands there was a dense subcanopy tree and shrub strata within and beyond the reach of deer 0.9-10 m tall whereas in higher deer stands this vegetation layer was nearly absent. We conclude that higher deer browse pressure in early successional Populus stands (1) strongly limits the recruitment of woody stems to larger (>0.9 m tall) size classes, which could affect long-term successional trajectories, and (2) diminishes forb density and species richness, especially at higher site productivity, but increases total forest floor vegetation mass (mostly bracken fern and sedge), especially at lower site productivity. Given associations of bracken fern and sedge with poorer and/or more open sites and assuming high palatability of forbs, this pattern may result from the combination of selective herbivory and higher light availability caused by limited recruitment of trees and shrubs to taller strata.     

Post-logging recovery time is longer than expected in an East African tropical forest

Uncertainty in recovery times of tropical forests can lead to mismanagement, such as in setting inappropriate harvesting rates or failing to achieving conservation targets. We use long-term plot data (17 y) to estimate recovery times of separate forest compartments, which experienced different levels of timber extraction within Kibale National Park, Uganda. We estimate that structural recovery (basal area) of heavily logged and moderately logged compartments will take respectively 112 and 95 y, when compared to adjacent mature forest. Our data suggests that recovery in terms of species composition will take significantly longer. Our estimates of structural recovery are derived from rates of change of diameter at breast height and basal area measurements which have been used traditionally as indicators of forest growth and productivity. Our results suggest that the severity of the logging has an impact on the rate of recovery, with current recovery rates estimated at 0.32 m² ha⁻¹ y⁻¹ in a moderately logged compartment and 0.25 m² ha⁻¹ y⁻¹ in heavily logged areas, highlighting the possible benefits of reduced impact harvesting in increasing long-term yields. We investigate how some representatives of the wildlife community were affected by differential recovery times and find that recovery times of frugivorous primate's forest habitats were 2.5 times slower when compared with folivorous primates.     

Effects of roads,topography, and land use on forest cover dynamics in the Brazilian Atlantic Forest

Roads and topography can determine patterns of land use and distribution of forest cover, particularly in tropical regions. We evaluated how road density, land use, and topography affected forest fragmentation, deforestation and forest regrowth in a Brazilian Atlantic Forest region near the city of São Paulo. We mapped roads and land use/land cover for three years (1962, 1981 and 2000) from historical aerial photographs, and summarized the distribution of roads, land use/land cover and topography within a grid of 94 non-overlapping 100 ha squares. We used generalized least squares regression models for data analysis. Our models showed that forest fragmentation and deforestation depended on topography, land use and road density, whereas forest regrowth depended primarily on land use. However, the relationships between these variables and forest dynamics changed in the two studied periods; land use and slope were the strongest predictors from 1962 to 1981, and past (1962) road density and land use were the strongest predictors for the following period (1981–2000). Roads had the strongest relationship with deforestation and forest fragmentation when the expansions of agriculture and buildings were limited to already deforested areas, and when there was a rapid expansion of development, under influence of São Paulo city. Furthermore, the past (1962) road network was more important than the recent road network (1981) when explaining forest dynamics between 1981 and 2000, suggesting a long-term effect of roads. Roads are permanent scars on the landscape and facilitate deforestation and forest fragmentation due to increased accessibility and land valorization, which control land-use and land-cover dynamics. Topography directly affected deforestation, agriculture and road expansion, mainly between 1962 and 1981. Forest are thus in peril where there are more roads, and long-term conservation strategies should consider ways to mitigate roads as permanent landscape features and drivers facilitators of deforestation and forest fragmentation.     

The effects of fire on the regeneration of a Quercus douglasii stand in Quail Ridge Reserve, Berryessa Valley (California)

Wildfire is an important element in the dynamics of the blue oak (Quercus douglasii) stand. We evaluated the effect of fire in the regeneration of a stand in Quail Ridge. This protected area is located on a peninsula formed by the flooding of Berryessa Valley (California) which has helped it maintain many elements of the native flora. Major vegetation types are blue oak woodland and forest (Q. douglasii, Fagaceae), chamise chaparral (Adenostoma fasciculatum, Rosaceae), and grasslands. In the blue oak stand, 14 plots were randomly located: seven in the burned area and seven outside of the burned areas (control). The effect of fire on sexual regeneration, asexual regeneration, mortality and species composition was analyzed. The fire caused changes in canopy cover, soil cover and litter cover. Asexual regeneration was significantly favored by the fire, but the effect on sexual regeneration was not significant. Fire caused a significant reduction in the basal area of Q. wislizeni and Arctostaphylos manzanita and a reduction in the density of Heteromeles arbutifolia. We concluded that fire does not have a significant effect on the sexual regeneration of Q. douglasii or Q. wislizeni. Fire does stimulate asexual regeneration in both species of oaks, but grazing reduces the regenerative effect of fire. Fire increases regeneration of Arctostaphylos manzanita and Heteromeles arbutifolia by stimulating asexual and sexual regeneration. The occupancies of these chaparral species are further enhanced by their lower palatability compared to both species of oaks.     

Using Landsat images to detect oak decline in the Mark Twain National Forest, Ozark Highlands

Following the severe drought in 1999–2000 there was a widespread outbreak of oak decline in the Ozark Highlands. Over 400,000 ha of dead and dying oak trees were observed by the USDA Forest Service in this region. Although oak forests that are dead can be easily interpreted from air photos or classified from satellite images, it is difficult to detect dying trees that are still green but will die back or recover in the following years. In this study, we applied a normalized difference water index (NDWI) to map the continuous forest dynamics related to oak decline. The Landsat TM image in 1992 and the ETM+ image in 2000 were processed to calculate the differential NDWI which revealed moisture variation primarily caused by the drought and the associated red oak borers. A simple thresholding method was used to map oak dying back, recovery and non-change areas in the study area. The died-back areas were extracted from the modified land use/land cover maps created by the Missouri Resource Assessment Partnership (MoRAP). The forest dynamics map was compared with the online FIA database in which tree species at randomly selected sites were recorded in 1989 and 2003. The overall accuracy of forest dynamics mapping with remote sensing imagery was 75.95%. The user's accuracy of dying/recovery area mapping was also high although the producer's accuracy is questionable because of the limitation in ground data collection. The continuous dying/recovery map in this study could provide valuable information on the prediction of oak decline and evaluation of damage when another period of environmental stresses occurs.     

Effects of the lack of forest management on spatiotemporal dynamics of a subalpine Pinus cembra forest

Knowledge about the stand structure and dynamics of subalpine forests is crucial to preserve their multifunctionality. In the present study, we reconstructed the spatiotemporal dynamics of a subalpine Pinus cembra forest in the eastern Italian Alps in response to natural disturbances and forest management. We adopted a concurrent point pattern, dendroecological and growth dominance (GD) analysis. We mapped and measured all trees of Pinus cembra and Larix decidua in a 1?ha plot. We analyzed intra- and interspecific spatial patterns and spatial autocorrelation of tree size and age. We explored establishment dynamics and shifts in competition by analyzing growth suppression/release patterns and GD trends. Results showed a clumped, uneven-aged, multilayered structure where pine was dominant. The synergic action of ecological and human-induced factors is discussed to explain the prevalence of pine over time. Spatial pattern and autocorrelation analyses suggest a different colonization strategy of the two species, in which pine established after small-scale perturbations and experienced a stronger inter- and intra-specific competition. The interruption of tree establishment and shift in GD toward large trees resulting from the lack of forest management are the most important findings of this research. This highlights the importance of an active management to avoid the homogenization of the forest structure that is generally associated with a reduction in biodiversity and protective ability of forests.     

Mangrove community recovery potential after catastrophic disturbances in Bangladesh

The objective of this study was to compare the variation in the soil seed banks and the aboveground vegetation in relation to three habitats, i.e., swamp forests, grassland and sand dunes within the Sundarbans mangrove forests of Bangladesh. We collected vegetation data (species and their percentage cover) by using quadrat sampling: 10 m × 10 m for swamp forests and 5 m × 5 m for grassland and sand dunes. We estimated the density of viable seeds of species in the seed bank by counting germinants from soil cores in a germination chamber. Species richness and composition of both aboveground vegetation and the soil seed banks differed significantly among habitats. We identified a total of 23 species from the soil seed bank. Of these, two were true mangrove species and the remaining were non-mangrove species, including halophytic grasses, herbs and mangrove associate species. Our results confirm that mangrove species do not possess a persistent soil seed bank. The presence of high-density non-mangrove and associated mangrove species in the soil seed bank implies that after frequent catastrophic disturbances which limit incoming propagules from adjacent forest stand, large canopy gaps can easily become invaded by non-mangrove and mangrove associate species. This would result in the formation of a cover of non-mangrove species and cryptic ecological degradation in mangrove habitats. We suggest that forest managers should actively consider gap plantations with mangrove species in the large canopy gaps created after catastrophic disturbances to counteract the invasion of non-mangrove species and cryptic ecological degradation.     

Decay dynamic of coarse and fine woody debris of a beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) forest in Central Germany

Decay rates of woody debris were estimated and used to model the decay of various diameters of branches and stems in a beech stand in Central Germany. In addition, use of wood density, volume and mass loss to quantitatively describe the degree of decay was tested. The mass loss during decay could be described by a simple exponential function. Under the presented climatic conditions, beech coarse woody debris (CWD) with a diameter >10 cm decays completely in about 35 years. In the first 8 years of decay the mass loss is determined by the decrease in wood density, and subsequently by the loss in volume. Estimation of wood density allows the first three of the four classes of decay to be distinguished, while trees in the last two decay classes could be distinguished using wood volume. Beech fine woody debris with a diameter between 1 and 10 cm decays within about 18 years. The litter fraction of <1 cm is part of the humus layer after 4 years. If there are goals for the amounts, types and dimensions of woody debris to be provided for conservation of biological biodiversity and other ecological functions in managed beech forests, this study offer indications for how long existing woody debris can meet its functions and how frequent new input of CWD is required.     

Modelling diameter class distribution with a second-order matrix model

Matrix models of forest dynamics rely on four hypotheses: independence hypothesis, Markov’s hypothesis, Usher’s hypothesis, and temporal homogeneity hypothesis. We investigate the consequences of relaxing Markov’s hypothesis, allowing the state of the tree at time t to depend on its states at time t−1 and t−2. The methodology for building and testing the relevance of second-order matrix model is thus proposed. The derivation of second-order transition probabilities turns to be sensitive to the width of the diameter classes. A strategy for choosing diameter classes is proposed. A second-order matrix model is then built for a tropical rain-forest in French Guiana. A different behaviour is detected between small (dbh ≤30 cm) and large trees, the smaller trees being more sensitive to their past history: small trees that have well grown have a tendency to grow well again, and small trees that have not grown tend to have a higher probability to die. The widths of the diameter classes that are selected are much less than the widths usually retained, that favour first-order selection.