Stand-landscape integration in natural disturbance-based management of the southern boreal forest

Forest ecosystem management, based partly on a greater understanding of natural disturbance regimes, has many variations but is generally considered the most promising approach to accommodating biodiversity concerns in managed forested regions. Using the Lake Duparquet Forest in the southeastern Canadian boreal forest as an example, we demonstrate an approach that attempts to integrate forest and stand-level scales in biodiversity maintenance. The concept of cohorts is used to integrate stand age, composition and structure into broad successional or stand development phases. Mean forest age (MFA), because it partly incorporates historic variability of the regional fire cycle, is used as a target fire cycle. At the landscape level, forest composition and cohort objectives are derived from regional natural disturbance history, ecosystem classification, stand dynamics and a negative exponential age distribution based on a 140 year fire cycle. The resulting multi-cohort structure provides a framework for maintaining the landscape in a semi-natural age structure and composition. At the stand level, the approach relies on diversifying interventions, using both even-aged and uneven-aged silviculture to reflect natural stand dynamics, control the passage (“fluxes”) between forest types of different cohorts and maintain forest-level objectives. Partial and selective harvesting is intended to create the structural and compositional characteristics of mid- to late-successional forest types and, as such, offers an alternative to increasing rotation lengths to maintain ecosystem diversity associated with over-mature and old-growth forests. The approach does not however supplant the necessity for complementary strategies for maintaining biodiversity such as the creation of reserves to protect rare, old or simply natural ecosystems. The emphasis on maintaining the cohort structure and forest type diversity contrasts significantly with current even-aged management in the Canadian boreal forest and has implications for stand-level interventions, notably in necessitating a greater diversification of silvicultural practices including more uneven-aged harvesting regimes. The approach also presents a number of operational challenges and potentially higher risks associated with multiply stand entries, partial cutting and longer intervals between final harvests. There is a need for translating the conceptual model into a more quantitative silvicultural framework. Silvicultural trials have been established to evaluate stand-level responses to treatments and operational aspects of the approach.     

The changing Himalayan landscape: pine-oak forest dynamics and the supply of ecosystem services

This review summarizes the current state of knowledge on pine and oak forest dynamics in the mid-montane central Himalayan forest and the ecosystem services associated with these vegetation types. Forest ecosystems play a crucial role in the livelihood of the central Himalayas as well as the adjacent plains, providing a number of tangible and intangible ecosystem services, at each stage of succession. The successional sequence starts from warm temperate grasslands, followed by early successional pine forests, mid-successional pine-oak mixed forests and eventually culminating in a late successional oak community. This successional sequence is considerably influenced by disturbances like fire, grazing, and lopping, which maintain the vegetation types in their current form and can act as potential drivers of change. Fire and grazing in grasslands and pine forests inhibit the successional process by hindering the establishment of pioneer and late successional species, respectively. Potential land-cover changes with forest succession can lead to changes in ecosystem services supply. We found that the number of ecosystem services associated with these vegetation types increase from early to late successional community. Current management approaches fail to include the dynamic nature of vegetation, which is essential for maintenance of ecosystem service supply. In conclusion, the trade-offs between ES of global (biodiversity and carbon) and local importance (fuel wood and fodder) have to be examined carefully in order to have effective conservation and management plans for the region.     

Managing disturbance regimes to maintain biological diversity in forested ecosystems of the Pacific Northwest

Managing for biodiversity in Pacific Northwest forest ecosystems requires a means to predict the interactive effects of natural, introduced, and altered disturbance regimes. Although disturbances are known to be a determinant of patterns of biological diversity, disturbance and diversity principles have not been consistently applied in management of forest ecosystems in the Pacific Northwest. Here we review disturbance and diversity theory and develop a synthetic conceptual model for use in predicting the effects of disturbances of any origin on biodiversity, focusing on the Pacific Northwest. Disturbance principles have traditionally been applied to understanding patterns of species diversity, but they can also be applied to understanding the broader concept of biodiversity. Our conceptual model integrates these principles, illustrating relationships among mechanisms that limit species diversity and those that enhance it. Diversity-limiting factors are: environmental stress due to high levels of disturbance relative to productivity, and competitive exclusion that can arise where disturbance has been suppressed or managed to favor a particular species’ dominance. Conversely, biological diversity will be enhanced by disturbances that are not too frequent to be stressful, and that create functional heterogeneity (spatial and temporal variation in habitat structure and biological legacies that are vital for post-disturbance reproduction and growth). The three disturbance-related mechanisms that determine diversity operate over local to landscape spatial scales and ecological time scales and thus can be readily influenced by management. By comprehensively evaluating existing disturbance regimes and how they are influencing these factors, managers can help maintain or restore the ecological foundation for biodiversity. We describe management approaches to improve this foundation focusing on forests managed for multiple goals in the Pacific Northwest, where there is considerable potential for and interest in maintaining and enhancing biodiversity.     

Emulating natural disturbance regimes as a basis for forest management: A North American view

It is widely accepted that for many North American forest ecosystems, changes in species composition and structure are associated with departures from natural disturbance regimes (e.g., fire exclusion). It also widely accepted that restoration of species composition and structure, similar to those which existed under natural disturbance regimes, will in turn restore and maintain: (1) ecosystem resilience to a broad range of environmental challenges; (2) important elements of ecosystem function; and (3) disturbance-adapted species assemblages and thus conservation of biodiversity. Much of the research relevant to emulating natural disturbance regimes (ENDR) in North America has focused on natural fire regimes, particularly those characterized by frequent/low-severity fires. Increasingly, attention is being focused on natural disturbance regimes other than fire and on interactions between different disturbance types. However, the greatest challenges to implementation of ENDR are socioeconomic rather than ecological. There is, for example, limited social acceptance of management based on high-severity natural disturbance regimes. And while there is much broader acceptance of ENDR based on frequent/low-severity disturbance regimes, there is nevertheless strong disagreement concerning how ENDR is to be implemented.     

Response of arthropod biodiversity to foundation species declines: The case of the eastern hemlock

Widespread declines of foundation species, such as many corals, kelps, and overstory trees, are of grave concern because, by definition, these species create and maintain habitat that supports other species. Nevertheless, past responses to their declines, many of which were caused by invasive species, have been late and ineffective, underscoring the need to predict changes in biodiversity and ecosystem function associated with species invasions and foundation species losses. One predictive, but under-used, approach is to compare the species and functions associated with the afflicted foundation species to its projected replacement communities. The taxa associated with the foundation species and subsequent successional stages would be expected to decline and increase, respectively. We used this approach to generate hypotheses for how arthropod diversity might change in response to extensive losses of eastern hemlock trees caused by the invasive, hemlock woolly adelgid (insect: Hemiptera, Adelgidae). Our all-strata survey of the arthropods in an eastern hemlock forest and its expected replacement climax community in the mid-Atlantic region of the United States, mixed hardwood forest, suggests that eastern hemlock losses might initiate increases in arthropod abundance, alpha diversity, and 23 arthropod taxa, might produce no change in evenness or composition of arthropod functional groups, but might trigger decreases in beta diversity and seven hemlock indicator taxa. These predictions are consistent with observed trends in arthropod responses to hemlock losses in other studies, and thus might be useful for targeting early monitoring, management, and conservation efforts. This research is exploratory, however, and tests of these predictions across larger spatial scales will be necessary to determine the generality of the findings.     

Persistent Acacia savannas replace Mediterranean sclerophyllous forests in South America

Mediterranean ecosystems are global hotspots of biodiversity threaten by human disturbances. Growing evidence indicates that regeneration of Mediterranean forests can be halted under certain circumstances and that successional stages can become notoriously persistent. The Mediterranean sclerophyllous forest in central Chile is been largely transformed into savannas dominated by the invasive legume tree Acacia caven as result of interacting management and ecological factors. We used multi-temporal satellite imagery to study the transition dynamics of these major vegetation types over the last four decades (1975-2008). Vegetation changes were related to indicators of resource availability (topography, water availability, solar radiance), potential propagule availability (distance to forest remnant patches) and disturbance regimes (grazing, fire occurrence and distance to roads and cities). During this study period, forests were mostly converted into Acacia savannas (46.1%). Acacia savanna was the most persistent natural vegetation type. The probability of sclerophyllous forest degradation into Acacia savanna increased on drier northern-exposed slopes, close to roads and further away from forest remnants. In contrast, forest regeneration from Acacia savanna was higher on moister southern-exposed slopes and closer to forest remnants. Acacia savannas are increasingly being converted into cultivated land on the moister locations or switching into a bare soil state in locations close to cities and further away from forest remnants. These results highlight the vulnerability of diverse sclerophyllous forests and its increasing conversion into persistent Acacia savannas in the Mediterranean region of central Chile and identify the ecological conditions for successful conservation and restoration of the native sclerophyllous forest vegetation that can be used for sensible land use planning.     

盘锦市生态状况分析与保护对策研究

根据收集的现有资料,结合盘锦地区的环境状况及区域开发利用情况,对盘锦市的植被群落、土地利用、湿地生态、生物多样性等生态状况进行分析,探讨在维护现有生态系统平衡的原则下,如何在区域开发利用中保护各种资源,使植物、湿地等资源的生态功能保持最大化,并结合环境管理需求和实践,提出有效的保护对策。     

Rapid assessment of biological richness in a part of Eastern Himalaya: an integrated three-tier approach

Biodiversity conservation necessitates not only preservation of single or multiple species but also the habitat as a whole along with its environment. Biological richness (BR) is a cumulative property of an ecological habitat and its surrounding environment, which has emerging implications in terms of management and planning. Six biodiversity attributes (i.e., spatial, phytosociological, social, physical, economical and ecological) were linked together based on their relative importance to qualitatively stratify biological richness of forest vegetation in Subansiri district of Eastern Himalaya using customized software, Bio_CAP. Higher biological richness was assigned to the habitats with (i) high species diversity, (ii) high degree of ecosystem uniqueness (EU), (iii) high economical value, (iv) complex terrain and (v) low disturbance level. This simple idea of integrated ‘three-tier modeling approach’ of (i) utilization of geospatial tools, (ii) limited field survey and (iii) landscape analysis; formed the basis of rapid assessment of biological richness.Satellite image interpretation using hybrid classification approach provided spatial distribution of vegetation types (corresponding to ecological habitats), with 89% accuracy. Landscape analysis was done using various quantitative indices that measured the heterogeneity and evaluated the patch characteristics. A methodology was developed for deriving relative adjacency weights from field data for calculation of juxtaposition of vegetation types. Biotic disturbance buffers (i.e., proximity zones around roads and human settlements) along with landscape parameters were combined to calculate disturbance index (DI), which in turn became an intermediate surrogate for BR assessment. Species diversity patterns along fragmentation and biotic disturbance gradients were adjudged to derive relative weights for DI computation. Species diversity (Shannon's index), ecosystem uniqueness (endemism status) and biodiversity value (BV) (total importance value (TIV)) were enumerated quantitatively that provided relative weights for BR computation. Terrain complexity (TC) was generated by calculating variance of the elevation image. Fifty-nine of total 764 species were found endemic to Eastern Himalaya with over all species endemism of 13 per ha. Shannon's index increased with decrease in fragmentation levels and increase of distance from sources of disturbance. BR index of the district was presented in five qualitative levels. Subtropical forests claim highest degree of biological richness as well as high disturbance index. This methodology has implications for rapid biodiversity assessment. Forest managers can use the DI and BR maps for gap analysis and prioritization of conservation activities viz., introduction of locale-specific species, thus protecting the forest habitats in situ.     

Influence of tree species on understory vegetation diversity and mechanisms involved—A critical review for temperate and boreal forests

Tree species composition is a primary attribute of forest ecosystems, and is often manipulated by silvicultural practices. Forest management to diversify tree species is now being promoted to favor biodiversity. To assess the soundness of this policy we reviewed and analyzed the literature on the relationship between tree species composition and floristic diversity, including the mechanisms involved therein. Coniferous forests generally provide less diversified vascular understories than broadleaved forests. At the tree species scale, there are not enough reports to draw firm conclusions on the effect of any particular species. Mixing of deciduous and coniferous tree species generally affects understory diversity, but in almost all cases maximum diversity is observed in one of the pure stands, not in mixed stands. Understory vegetation is influenced by overstory composition and structure through modifications of resource availability (light, water and soil nutrients) and other effects, such as physical characteristics of the litter layer. Overstory light transmittance and diverse properties of forest litter are factors that have been most fully studied to date, but other factors such as throughfall water quantity and chemistry may also play a role. While the relative importance of mechanisms that account for the effect of overstory on understory biodiversity has often been discussed, these mechanisms have rarely been the subject of formal experiments. Overall, varying management practices and site attributes make it difficult to generalize results. They combine with the effects of tree species in influencing understory vegetation diversity, but they have been rarely considered. Future research is needed to gain a better understanding of the relationship between overstory and understory diversity and establish general laws.     

Historical fire and vegetation dynamics in dry forests of the interior Pacific Northwest,USA, and relationships to Northern Spotted Owl (Strix occidentalis caurina) habitat conservation

Regional conservation planning frequently relies on general assumptions about historical disturbance regimes to inform decisions about landscape restoration, reserve allocations, and landscape management. Spatially explicit simulations of landscape dynamics provide quantitative estimates of landscape structure and allow for the testing of alternative scenarios. We used a landscape fire succession model to estimate the historical range of variability of vegetation and fire in a dry forest landscape (size ca. 7900 km²) where the present-day risk of high severity fire threatens the persistence of older closed canopy forest which may serve as Northern Spotted Owl (Strix occidentalis caurina) habitat. Our results indicated that historically, older forest may have comprised the largest percentage of the landscape (∼35%), followed by early successional forest (∼25%), with about 9% of the landscape in a closed canopy older forest condition. The amount and condition of older forest varied by potential vegetation type and land use allocation type. Vegetation successional stages had fine-grained spatial heterogeneity in patch characteristics, with older forest tending to have the largest patch sizes among the successional stages. Increasing fire severities posed a greater risk to Northern Spotted Owl habitat than increasing fire sizes or frequencies under historical fire regimes. Improved understanding of historical landscape-specific fire and vegetation conditions and their variability can assist forest managers to promote landscape resilience and increases of older forest, in dry forests with restricted amounts of habitat for sensitive species.     

Bird species diversity in riparian buffers,row crop fields,and grazed pastures within agriculturally dominated watersheds

In response to concern about the loss of ecosystem services once provided by natural riparian systems, state and federal agencies have established incentive programs for landowners to convert sensitive lands from agricultural to conservation uses. Enhancement of wildlife habitat, while identified as a function of such systems, has often been of secondary importance to soil conservation and water quality objectives. Though greatly important, little consideration has been given to how specific species will respond to the design and management of riparian buffers or other conservation lands. This study compared avian communities within a chronosequence of riparian buffers established on previously cropped or pastured land with those of the nearby matrix land cover types (row crop fields and an intensively grazed pasture). The riparian buffers consisted of native grasses, forbs, and woody vegetation established at three different times (2, 9, and 14+ years prior to survey). At each site, 10 min point counts for breeding birds were conducted using 50 m fixed radius plots, which were visited eight times between May 15 and July 10, 2008. A total of 54 bird species were observed over all of the study sites. The re-established riparian buffers in this study had higher bird abundance, richness, and diversity than the crop and pasture sites. These results suggest that re-establishing native riparian vegetation in areas of intensive agriculture will provide habitat for a broad suite of bird species, but that specific species will reflect successional stage, horizontal and vertical vegetative structure, and compositional diversity of the buffer vegetation. These results emphasize the importance of matching buffer design and management to species requirements if the objectives are to attract specific target species or species groups.     

Plant-soil biodiversity relationships and nutrient retention in agricultural riparian zones of the Sacramento Valley,California

Forested riparian buffers in California historically supported high levels of biodiversity, but human activities have degraded these ecosystems over much of their former range. This study examined plant communities, belowground biodiversity and indicators of multiple ecosystem functions of riparian areas across an agricultural landscape in the Sacramento Valley of California, USA. Plant, nematode and soil microbial communities and soil physical and chemical properties were studied along 50-m transects at 20 sites that represented the different land use, soil and vegetation types in the landscape. Riparian zones supported greater plant diversity and nearly twice as much total carbon (C) per hectare compared to adjacent land managed for agricultural uses, but had generally lower soil microbial and nematode diversity and abundance. When woody plant communities were present in the riparian zone, plant diversity and species richness were higher, and soil nitrate and plant-available phosphorus levels were lower. Belowground diversity and community structure, however, appeared to depend more on plant productivity (as inferred by vegetation cover) than plant diversity or species richness. Greater plant species richness, nematode food web structure, total microbial biomass, woody C storage and lower soil nitrate and phosphorus loading were correlated with higher visual riparian health assessment scores, offering the possibility of managing these riparian habitats to provide multiple ecosystem functions.     

从景观异质性分析近自然森林经营

从景观生态学的核心理论——景观异质性理论着手分析了近自然森林经营模式:其本质是对森林景观异质性的维持和促进,是森林经营学发展的一种历史必然,具有充分利用异质时空,提高森林系统生产力、生物多样性、景观多样性,增强系统抗干扰性和稳定性等诸多优点,从而有利于森林的可持续发展。     

林下植被组成和功能研究进展

林下植被作为森林生态系统的一个重要组成部分, 在维护森林多样性、推动森林生态系统流程和功能中扮演着重要的角色。目前, 关于林下植被的研究已有上百年历史, 其中在森林群落分类、更新演替、养分循环及稳定生产力等方面做了大量研究。文中从林下植被的定义及其组成、演替和功能等方面综述了近年来林下植被的研究进展, 并探讨了如何综合研究演替以及干扰对林下植被组成的影响、林下植被对气候变化的可能响应以及如何将林下植被作用及功能的研究理论应用于近自然人工林建设和管理实践中。     

When and where to actively restore ecosystems?

Given the extent of land use and land cover change by humans on a global scale, conservation efforts have increasingly focused on restoring degraded ecosystems to provide ecosystem services and biodiversity. Many examples in the tropics and elsewhere, however, show that some ecosystems recover rapidly without human intervention which begs the question of in which cases and to what extent humans should actively work to facilitate ecosystem recovery. We recommend that all land managers consider a suite of ecological and human factors before selecting a restoration approach. Land managers should first consider what the likely outcome of a passive restoration (natural regeneration) approach would be based on the natural ecosystem resilience, past land-use history, and the surrounding landscape matrix. They should also identify the specific goals of the project and assess the resources available. Conducting these analyses prior to selecting restoration approaches should result in a more efficient use of restoration resources both within and among projects and should maximize the success of restoration efforts.     

Biodiversity Values and Measures Applied to Forest Management

Abstract

With the new emphasis in land management agencies (particularly the USDA Forest Service) on ecosystem management, new attention is being paid to measurements of biological diversity (biodiversity). Forest managers faced with incorporating the maintenance of biodiversity into their analyses, plans, and decisions need reliable, quantitative biodiversity measures. Deciding which measures to use requires land managers to understand why biodiversity is valued, which components of diversity are of most value, and how to measure these components feasibly. In this paper, the values associated with biodiversity and the principal indices available to forest managers are reviewed. Attention is drawn to the differing emphases of biodiversity indices-species richness, heterogeneity, and evenness-and to how diese differences address different values. Potential applications for these indices in forest management plans-including ways to use habitat models to approximate biodiversity-are also discussed.     

茂兰喀斯特植被不同演替阶段的生物量和净初级生产力估算

2007年8月-2007年10月,在贵州茂兰喀斯特森林国家自然保护区内,选取其中有代表性的2个基质类型（石生群落和土壤群落）上的5个演替阶段（草本群落、灌草群落、灌木群落、次顶级常绿落叶阔叶林和顶级常绿落叶阔叶林）共10个样地,分别利用相对生长方程法、平均标准木机械布点法和树木年轮宽度值来估算群落地上生物量、地下生物量和净初级生产力。结果表明：1）喀斯特森林群落正向演替极显著增加了群落地上生物量;从石生草本群落的4．76t／hm2到土壤顶级群落的144．66t／hm2。而同一演替阶段石生群落和土壤群落地上生物量差异不显著。2）喀斯特森林群落正向演替极显著增加了地下生物量,即从石生草本群落的2．63t／hm2增加到石生顶级乔木群落的58．15t／hm2。3）总生物量随正向演替的进行而显著增加,从石生草本群落的7．39t／hm2增加到土壤顶级群落的202．15t／hm2。4）石生系列群落净初级生产力随着正向演替的进行而呈递增趋势,从草本群落的2．73t·hm^-1·a^-1递增到顶级常绿落叶阔叶林的13．58t·hm^-2·a^-1;土壤系列群落无此特征。     

Rocky Mountain ecosystems: diversity, complexity and interactions

The interior west of North America provides many opportunities to study ecosystem responses to climate change, biological diversity and management of disturbance regimes. These ecosystem responses are not unique to the Rocky Mountains, but they epitomize similar scientific problems throughout North America. Better management of these ecosystems depends on a thorough understanding of the underlying biology and ecological interactions of the species that occupy the diverse habitats of this region. This review highlights progress in research to understand aspects of this complex ecosystem.