基于加权面积比重的乡村人居林总体质量评价方法

选取与乡村人居林关系最为密切的林木覆盖指数、林木结构指数、林网密度指数、林木健康指数和林木稳定指数指标,利用层次分析法确定权重系数,通过间接构建评价指标各要素占评价区域加权面积比重的方法,进行乡村人居林质量评价,结果表明,4个代表型村庄人居林建设质量差异较大,以南书村为最好,上浦村和扁山村其次,茜黄村最差,综合评价得分分别为75.7972分、52.7972分、41.5418分和9.7689分.这种评价方法科学有效、简单快速,实用性强,避免了传统评价方法基础数据获取困难和可操作性不强的缺陷,为乡村人居林质量评价提供依据.     

Deadwood in Relation to Stand Management and Forest Type in Central Apennines (Molise,Italy)

Deadwood is an important component for conserving carbon stock and maintaining species diversity. Scarce information is, at present, available concerning the amount and composition of deadwood in Mediterranean-type ecosystems. In this study, 21 sites were chosen to characterize different forest types among representative managed and unmanaged stands in the Central Apennines (Molise, Italy). Data were collected to assess living tree and deadwood volumes, and the relative abundance of different deadwood components in decay classes. The information gathered was related to human-induced disturbances on a regional scale. There were substantial differences in the deadwood volumes between managed and unmanaged stands, although this was not the case in the living tree volumes. Deadwood volumes were larger in unmanaged than in managed stands. In particular, large amounts of deadwood were found in managed Mediterranean and Anatolian fir forests, probably due to minimal management practices. Dead downed trees were less represented in managed forests as they are normally removed to facilitate logging activities. Logs occurred more frequently in managed stands as logging residues left on site. Most deadwood material belonged to early decay classes. Proportionally larger amounts of deadwood ascribed to class 1 in managed stands correlated with recent cutting activities. The relatively large amounts of deadwood attributed in unmanaged stands to class 3 demonstrate its longer persistence in unmanaged forests. This study represents a first systematic analysis of deadwood occurrence in a typical Mediterranean forest area, and should be useful in defining important objectives for sustainable forest management.     

A Paleoecological Assessment of Phragmites australis in New England Tidal Marshes: Changes in Plant Community Structure During the Last Few Millennia

Although Phragmites has been an upper border tidal marsh species for thousands of years, it is only recently (within the last century or so) that the distribution of this plant within the coastal marsh community has become prominent. Prior to approximately 100 years ago, Phragmites was an upper border/brackish marsh co-dominant in many marsh systems. Occurrence of this species varied between associations of sedges, Typha, forbs and a variety of woody shrubs. Paleoreconstructions rarely show the presence of a Phragmites monoculture or early associations with salt marsh species. However, since the turn of this century (and perhaps as early as the middle of the last century) the distribution of Phragmites has changed substantially. Today, this plant often forms dense monocultures and is commonly found in association with Spartina grasses. The results of this paleoecological investigation show that the changes that have been observed in Phragmites communities during the last 100 years are not part of the long-term cycle of development in these systems and are new to the landscape.     

The Relative Impact of Harvest and Fire upon Landscape-Level Dynamics of Older Forests: Lessons from the Northwest Forest Plan

Interest in preserving older forests at the landscape level has increased in many regions, including the Pacific Northwest of the United States. The Northwest Forest Plan (NWFP) of 1994 initiated a significant reduction in the harvesting of older forests on federal land. We used historical satellite imagery to assess the effect of this reduction in relation to: past harvest rates, management of non-federal forests, and the growing role of fire. Harvest rates in non-federal large-diameter forests (LDF) either decreased or remained stable at relatively high rates following the NWFP, meaning that harvest reductions on federal forests, which cover half of the region, resulted in a significant regional drop in the loss of LDF to harvest. However, increased losses of LDF to fire outweighed reductions in LDF harvest across large areas of the region. Elevated fire levels in the western United States have been correlated to changing climatic conditions, and if recent fire patterns persist, preservation of older forests in dry ecosystems will depend upon practical and coordinated fire management across the landscape. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Author Contributions: The study was conceived and designed by S.P.H., W.B.C., T.A.S, and M. M. The paper was written primarily by S.P.H, with editorial help by T.A.S. and W.B.C. The research itself, including mapping and analysis, was performed by S.P.H., D.P., M.G.W., and M.L. M.M. contributed additional methodologies related to the creation and validations of maps of historical older forests.     

Clustering Timber Harvests and the Effect of Dynamic Forest Management Policy on Forest Fragmentation

To integrate multiple uses (mature forest and commodity production) better on forested lands, timber management strategies that cluster harvests have been proposed. One such approach clusters harvest activity in space and time, and rotates timber production zones across the landscape with a long temporal period (dynamic zoning). Dynamic zoning has been shown to increase timber production and reduce forest fragmentation by segregating uses in time without reducing the spatial extent of timber production. It is reasonable to wonder what the effect of periodic interruptions in the implementation of such as strategy might be, as would be expected in a dynamic political environment. To answer these questions, I used a timber harvest simulation model (HARVEST) to simulate a dynamic zoning harvest strategy that was periodically interrupted by changes in the spatial dispersion of harvests, by changes in timber production levels, or both. The temporal scale (period) of these interruptions had impacts related to the rate at which the forest achieved canopy closure after harvest. Spatial dynamics in harvest policies had a greater effect on the amount of forest interior and edge than did dynamics in harvest intensity. The periodically clustered scenarios always produced greater amounts of forest interior and less forest edge than did their never clustered counterparts. The results suggest that clustering of harvests produces less forest fragmentation than dispersed cutting alternatives, even in the face of a dynamic policy future. Although periodic episodes of dispersed cutting increased fragmentation, average and maximum fragmentation measures were less than if clustered harvest strategies were never implemented. Clustering may also be useful to mitigate the fragmentation effects of socially mandated increases in timber harvest levels. Implementation of spatial clustering during periods of high timber harvest rates reduced the variation in forest interior and edge through time, providing a more stable supply of forest interior habitat across the landscape. Received 19 September 1997; accepted 6 August 1998.     

福建武平米槠林恢复生态学研究

从优势种,分布格局,种丰富度和群落间种相似系数角度,探讨不同人为干扰尺度对福建武平米槠林恢复的影响。结果表明,随着人为干扰尺度（A级择伐更新,B级天然更新,C级人工促进天然更新和D级杉木林）的加大,顶极种米槠重要,不同人为干扰群落与天然来桩群落种相似系数随之降低,降至D级分别为0和40％;而米槠分布格局（聚集强度）和种丰富随之上升,升至B级或C级后显著下降,据此可见,A级属于轻度干扰,现已恢复;B级属于中度干扰,将很快恢复;C级虽然顶级种米槠处于第二优势种,阳性树种裂斗锥处于第一优势种,但种丰富度达到最大值,属中度干扰,但恢复时间要较B级略长;D级属于强度干扰,产难恢复到米桩顶极群落。     

Forest Pattern, Fire, and Climatic Change in the Sierra Nevada

In the Sierra Nevada, distributions of forest tree species are largely controlled by the soil-moisture balance. Changes in temperature or precipitation as a result of increased greenhouse gas concentrations could lead to changes in species distributions. In addition, climatic change could increase the frequency and severity of wildfires. We used a forest gap model developed for Sierra Nevada forests to investigate the potential sensitivity of these forests to climatic change, including a changing fire regime. Fuel moisture influences the fire regime and couples fire to climate. Fires are also affected by fuel loads, which accumulate according to forest structure and composition. These model features were used to investigate the complex interactions between climate, fire, and forest dynamics. Eight hypothetical climate-change scenarios were simulated, including two general circulation model (GCM) predictions of a 2 × CO₂ world. The response of forest structure,species composition, and the fire regime to these changes in the climate were examined at four sites across an elevation gradient. Impacts on woody biomass and species composition as a result of climatic change were site specific and depended on the environmental constraints of a site and the environmental tolerances of the tree species simulated. Climatic change altered the fire regime both directly and indirectly. Fire frequency responded directly to climate's influence on fuel moisture, whereas fire extent was affected by changes that occurred in either woody biomass or species composition. The influence of species composition on fuel-bed bulk density was particularly important. Future fires in the Sierra Nevada could be both more frequent and of greater spatial extent if GCM predictions prove true. Received 5 May 1998; accepted 4 November 1998.     

Interactions Across Spatial Scales among Forest Dieback,Fire, and Erosion in Northern New Mexico Landscapes

Abstract Ecosystem patterns and disturbance processes at one spatial scale often interact with processes at another scale, and the result of such cross-scale interactions can be nonlinear dynamics with thresholds. Examples of cross-scale pattern-process relationships and interactions among forest dieback, fire, and erosion are illustrated from northern New Mexico (USA) landscapes, where long-term studies have recently documented all of these disturbance processes. For example, environmental stress, operating on individual trees, can cause tree death that is amplified by insect mortality agents to propagate to patch and then landscape or even regional-scale forest dieback. Severe drought and unusual warmth in the southwestern USA since the late 1990s apparently exceeded species-specific physiological thresholds for multiple tree species, resulting in substantial vegetation mortality across millions of hectares of woodlands and forests in recent years. Predictions of forest dieback across spatial scales are constrained by uncertainties associated with: limited knowledge of species-specific physiological thresholds; individual and site-specific variation in these mortality thresholds; and positive feedback loops between rapidly-responding insect herbivore populations and their stressed plant hosts, sometimes resulting in nonlinear “pest” outbreak dynamics. Fire behavior also exhibits nonlinearities across spatial scales, illustrated by changes in historic fire regimes where patch-scale grazing disturbance led to regional-scale collapse of surface fire activity and subsequent recent increases in the scale of extreme fire events in New Mexico. Vegetation dieback interacts with fire activity by modifying fuel amounts and configurations at multiple spatial scales. Runoff and erosion processes are also subject to scale-dependent threshold behaviors, exemplified by ecohydrological work in semiarid New Mexico watersheds showing how declines in ground surface cover lead to non-linear increases in bare patch connectivity and thereby accelerated runoff and erosion at hillslope and watershed scales. Vegetation dieback, grazing, and fire can change land surface properties and cross-scale hydrologic connectivities, directly altering ecohydrological patterns of runoff and erosion. The interactions among disturbance processes across spatial scales can be key drivers in ecosystem dynamics, as illustrated by these studies of recent landscape changes in northern New Mexico. To better anticipate and mitigate accelerating human impacts to the planetary ecosystem at all spatial scales, improvements are needed in our conceptual and quantitative understanding of cross-scale interactions among disturbance processes.     

Landscapes of Settlement in Northern Iceland: Historical Ecology of Human Impact and Climate Fluctuation on the Millennial Scale

Early settlement in the North Atlantic produced complex interactions of culture and nature. The sustained program of interdisciplinary collaboration is intended to focus on ninth- to 13th-century sites and landscapes in the highland interior lake basin of Mývatn in Iceland and to contribute a long-term perspective to larger issues of sustainable resource use, soil erosion, and the historical ecology of global change.     

20th Century Carbon Budget of Forest Soils in the Alps

Dendrochronological studies and forest inventory surveys have reported increased growth and biospheric carbon (C) sequestration for European forests in the recent past. The potential of concomitant changes in forest soil C stocks are not accounted for in the IPCC guidelines for national greenhouse gas inventories. We developed a model-based approach to address this problem and assess the role of soils in forest C balance in the European Alps. The decomposition model FORCLIM-D was driven by long-term (that is, 1900–1985 AD) litter input scenarios constructed from forest inventory data, region-specific dendrochronological basal area indices, and time series of anthropogenic litter removal. The effect of spatial climate variability on organic matter decomposition across the case study region (Switzerland) was explicitly accounted for by constant long-term annual means of actual evapotranspiration and temperature. Uncertainties in forest development, litter removal, fine root litter input, and dynamics of forest soil C were studied by an explorative factorial sensitivity analysis. We found that forest soils contribute substantially to the biospheric C sequestration for Switzerland: Our “best estimate” yielded an increase of 0.35 Mt C/y or 0.33 t C/(ha y) in forest soils for 1985, that is, 27% of the C sequestered by forest trees (BUWAL 1994). Uncertainties regarding C accumulation in forest soils were substantial (0.11–0.58 Mt C/y) but could be reduced by estimating forest soil C stocks in the future. Whereas soils can be important for the C balance in naturally regrowing forests, their C sequestration is negligible (less than 5%) relative to anthropogenic CO₂ emissions in Western Europe at present. Received 25 August 1998; accepted 17 March 1999.     

大兴安岭北部林区景观格局变化及其影响分析

人为干扰影响着景观格局变化的速率和方向 ,这在景观格局变化过程中的作用越来越大 ,同时景观格局的变化也对人类活动产生了重大影响。通过对大兴安岭北部林区的景观多样性指数、优势度指数等一系列景观指数来研究该地区森林景观格局的变化 ,简要分析了格局变化产生的影响。结果表明 ,大兴安岭森林景观中 ,人为干扰使森林景观短时期内多样性增加、森林的优势度降低 ;景观向破碎化趋势发展 ;景观格局的变化对环境和人类活动产生了重大影响 ,森林向不可持续方向发展 ,因此应该进行合理的人类活动使森林可持续发展。     

玉米地节肢动物群落优势功能集团的组成与演替

近年来 ,对于农作物害虫的研究 ,不再局限于单个害虫的发生规律 ,而偏向于对昆虫群落的研究 ,因为群落是联结种群与生态系统之间的桥梁。对有害生物的综合治理 ,也更加注重对群落结构的影响 ,而不是只考虑某一特定有害生物的本身[9] 。研究和分析节肢动物群落的结构特征 ,对于控制害虫的种群变动及进行综合治理有重要的意义。金翠霞等运用种类丰富度 (ｓ)、均匀性 (ｖ′)和申农系数 (ｓｈａｎｎｎｏｎｉｎｄｅｘＨ′)分析了稻田节肢动物群落和各亚群落多样性的空间层次差异 ,季节动态以及杀虫剂对群落结构的影响[5] 。郝树广等把稻田节肢动…     

Potential Changes in Tree Species Richness and Forest Community Types following Climate Change

Potential changes in tree species richness and forest community types were evaluated for the eastern United States according to five scenarios of future climate change resulting from a doubling of atmospheric carbon dioxide (CO₂). DISTRIB, an empirical model that uses a regression tree analysis approach, was used to generate suitable habitat, or potential future distributions, of 80 common tree species for each scenario. The model assumes that the vegetation and climate are in equilibrium with no barriers to species migration. Combinations of the individual species model outcomes allowed estimates of species richness (from among the 80 species) and forest type (from simple rules) for each of 2100 counties in the eastern United States. Average species richness across all counties may increase slightly with climatic change. This increase tends to be larger as the average temperature of the climate change scenario increases. Dramatic changes in the distribution of potential forest types were modeled. All five scenarios project the extirpation of the spruce–fir forest types from New England. Outputs from only the two least severe scenarios retain aspen–birch, and they are largely reduced. Maple–beech–birch also shows a large reduction in area under all scenarios. By contrast, oak–hickory and oak–pine types were modeled to increase by 34% and 290%, respectively, averaged over the five scenarios. Although many assumptions are made, these modeled outcomes substantially agree with a limited number of predictions from researchers using paleoecological data or other models. Received 12 May 2000; accepted 20 October 2000.     

Patterns of Land-use Abandonment Control Tree-recruitment and Forest Dynamics in Mediterranean Mountains

Abstract Mediterranean ecosystems have been impacted for millennia by human practices, particularly agricultural and pastoral activities. Since the middle of the nineteenth century, land-use abandonment has lead to scrubland and forest expansion, especially in mountain areas of the northern Mediterranean basin. This study aimed at analyzing how grazing history affects subsequent forest dynamics at a site located in the limestone foothills of the Southern Alps (France). The approach combines archival documents and dendroecology to investigate the origin, establishment and development of forest following land-use abandonment. Scots pine (Pinus sylvestris) started to colonize quickly in the 1870s, with the recruitment rate increasing during the first decade of the 1900s, associated with a decline of the local human population and regional livestock. Since the 1960s, European beech (Fagus sylvatica) and silver fir (Abies alba) have regenerated in the understorey of Scots pines. Regeneration is controlled by a threshold of grazing pressure. Noticeably, the rate of reforestation differs according to the former land-use, with pastures being colonized more quickly than ploughed areas. Different previous land-uses leading to different times of grazing cessation, combined with variable herbaceous competition explain the contrasting micro-scale regeneration patterns. Agricultural land-use and abandonment are both significant driving forces of vegetation dynamics. Knowledge of these factors is thus necessary to understand present patterns and to predict future forest pathways in the Mediterranean mountains.     

长白山红松针阔混交林倒木站杆树种组成和贮量的调查

倒木是天然森林生态系统的重要组成部分,在生态系统结构和功能方面起着重要作用。它们的存在不但具有减少水土流失、影响土壤发育,提供动植物生境的功能,而且起到贮存营养、碳素和水分,供给养分和能量的作用。倒木贮量的调查是评价倒木生态功能的基础。以往国内森林凋落物研究中,片面     

Impacts of Elevated Carbon Dioxide and Temperature on a Boreal Forest Ecosystem (CLIMEX Project)

To evaluate the effects of climate change on boreal forest ecosystems, both atmospheric CO₂ (to 560 ppmv) and air temperature (by 3°–5°C above ambient) were increased at a forested headwater catchment in southern Norway. The entire catchment (860 m²) is enclosed within a transparent greenhouse, and the upper 20% of the catchment area is partitioned such that it receives no climate treatment and serves as an untreated control. Both the control and treatment areas inside the greenhouse receive deacidified rain. Within 3 years, soil nitrogen (N) mineralization has increased and the growing season has been prolonged relative to the control area. This has helped to sustain an increase in plant growth relative to the control and has also promoted increased N export in stream water. Photosynthetic capacity and carbon–nitrogen ratio of new leaves of most plant species did not change. While the ecosystem now loses N, the long-term fate of soil N is a key uncertainty in predicting the future response of boreal ecosystems to climate change. Received 18 November 1997; accepted 13 April 1998.     

Assessing the Rate, Mechanisms, and Consequences of the Conversion of Tallgrass Prairie to Juniperus virginiana Forest

We assessed the determinants and consequences of the expansion of Juniperus virginiana L. (red cedar) populations into central US grasslands using historical aerial photos and field measurements of forest extent, tree growth, fire-induced mortality, and responses in herbaceous species diversity and productivity. Photos from northeast Kansas dating back to 1956 indicate that native tallgrass prairie can be converted to closed-canopy red cedar forest in as little as 40 years (a 2.3% increase in forest cover per year). Mean tree density in 21 forested sites ranged from 130 to 3500 trees/ha, with most sites at more than 800 trees/ha. In younger stands, maximum growth rates of individual red cedar trees exceeded 20 cm/y in height. Land management practices were critical to the establishment and growth of red cedar forest. Grazing reduced the fuel loads by more than 30% in tallgrass prairie. Based on measurements of mortality for more than 1800 red cedar trees, fire-induced mortality in grazed areas averaged 31.6% versus more than 90% at ungrazed sites. When tallgrass prairie was converted to red cedar forest, herbaceous species diversity and productivity were drastically reduced, and most grassland species were virtually eliminated. Consequently, community structure shifted from dominance by herbaceous C₄ species to evergreen woody C₃ species; this shift is likely to be accompanied by alterations in carbon storage and other ecosystem processes in a relatively short time period. Here we present a conceptual model that integrates the ecological and socioeconomic factors that underlie the conversion of grassland to red cedar forest. Received 29 August 2001; accepted 5 February 2002.