Forest decline and soil nutritional problems in pacific areas

Soil nutrient stresses have been determined to contribute to stand-level dieback in two Pacific forest biomes, the HawaiianMetrosideros rain forest and remnants of the eastern AustralianEucalyptus forest. In the Hawaiian dieback, low levels of N limit indigenous forest development early in primary succession on volcanic soils, while later in primary succession, stresses appear to be associated with soil aging, acidification, loss of cations, decreasing levels of P, increases in soluble Al, and, under poor drainage, sharp increases in soluble Fe. These nutrient limitations put a ceiling on stand development and growth and are considered as one of the three causes predisposing stands to dieback. In the rural or New England dieback of eastern Australia, indigenous eucalypts are adapted to ancient soils with very low levels of P, but pasture improvement with clover and fertilization with superphosphate has imposed different stresses on remnant eucalypts in pastures and nearby forest islands. After fertilization, the trees grow faster initially, but their foliage becomes highly nutritious for insects. Other factors also contribute to a build-up of insects as pests, which now threaten the remaining eucalypts. The rural dieback represents an example of how forests with low canopy species diversity, simplified structure, lack of successional species, and which are prone to dieback under natural conditions, can be destroyed by intensification of agricultural development. The paper closes with a summary of generic factors that were found to cause forest dieback under natural conditions and compares these to the anthropogenically superimposed stresses that led to aggravated tree and forest decline in the Australian rural or New England dieback. The suggestion is made that comparative dieback research at the global level will lead to an improved understanding of natural forest dynamics as an aid in interpreting the new stresses imposed on forests by human activity.     

Conservation of beetles in boreal pine forests: the effects of forest age and naturalness on species assemblages

The effort of boreal forest conservation has emphasised the preservation of old-growth forests while the role of young successional stages in maintaining biodiversity has remained largely unstudied. We compared the richness of beetle species and composition of species assemblages between managed and seminatural forests in five stages of forest succession. The sites were in boreal sub-xeric pine-dominated forests in eastern Finland. Seminatural study sites, especially the recently burned sites, were important habitats for threatened and near-threatened species. We propose that young stages of natural succession should be included in the network of protected forest areas. On the other hand, the composition of saproxylic species assemblages in seminatural forests differed from the assemblages in managed forests, indicating also the need to improve the forest management guidelines so that they better address the requirements of species protection. Regeneration methods applied should resemble or mimic the natural disturbances more closely.     

The PAH and organic content of sediment particle size fractions

A comparison of declining forests in Alaska, British columbia, and the Pacific Northwest United States to forest declines in eastern North America indicated that strong similarities existed and justified the use of the western forest region as an ‘acid rain’ control. The current level of wet acidic deposition over the western region was one-quarter that of eastern Canada and the United States. The onset of crown dieback on Chamaecyparis nootkatensis (1900) and Pinus monticola (1936) did not relate to the incidence of regional air pollution but to extreme climatic variation. The injury mechanism differentiating persistent decline on Pinus monticola from sporadic but transient dieback, which was observed on a larger number of conifer and deciduous tree species, was believed to be cavitation. This dysfunction of the xylem was induced by anomalous winter thaw-freeze conditions in 1936 followed by high summer temperatures and evapotranspiration stress in that and subsequent years. Similar extreme climatic conditions were present at the onset of forest declines in eastern North America and central Europe which suggests that the climate-cavitation-forest decline mechanism may be universal.     

Eucalypt plantations as habitat for birds on previously cleared farmland in south-eastern Australia

In parts of Australia, extensive areas of cleared land are now being planted with commercial plantations of native eucalypts. Questions arise about the extent to which such plantations can rectify previous loss of habitat and contribute to biodiversity conservation. This study assessed abundance of bird species (as one aspect of biodiversity) on 105 sites (25 cleared land, 58 plantations and 22 native forest) in two regions of rural Victoria, south-eastern Australia. Generalised linear modelling was used to assess some of the landscape and habitat variables that contributed to the value of plantation sites for particular groups of bird species. These models demonstrated the importance of on-site habitat variables in explaining the abundance of groups of bird species, with landscape context making small additional contributions.Mean abundance of forest and woodland birds was higher in eucalypt plantations than cleared farmland, and marginally lower than in native forest. Patterns differed between bird guilds. For example, insectivores that forage in the canopy and tall shrub layers were at least as common in plantations as in native forest, with birds in the latter group using young eucalypts as if they were tall shrubs. Birds that forage from open ground among trees were more common in plantations than native forest, and may benefit substantially from the new habitat fortuitously provided for them. This group includes several species that have declined in natural woodland habitats. Nectarivores, carnivores and birds that forage among low shrubs were less common in plantations than in native forest. Insectivores that forage from eucalypt bark made little use of plantations. Different approaches to plantation design and management would be needed to cater for groups such as these. Specific measures include planting of rough-barked eucalypts in addition to smooth-barked species, and provision of artificial hollows. Retention of existing remnants of native forest (e.g. old trees and forest patches) is a priority, to supply habitat elements that would otherwise be missing for long periods.     

Acidic deposition: What is fact,what is speculation,what is needed?

In this presentation research findings from the symposium and from the literature are utilized to examine some of the major hypotheses that link acidic deposition with impairment of forest health and productivity in central Europe and eastern North America. Although unequivocal evidence of acid rain damage may be lacking, there is a considerable body of knowledge that implicates air pollutants in recent interference with forest nutrition and health. The nature of the evidence and the inferences that can be drawn from it are still being vigorously debated. The problem of verifying the mechanisms by which air pollutants affect forests still remains. Reports that climatic irregularities have acted as inciting or triggering factors in forest declines are relevant to understanding regional damage. More emphasis on experimental studies that assess interactions of air pollutants and natural stresses with forests is needed.     

The role of climate variability and global warming in the dieback of Northern Hardwoods

The severity of dieback in Northern Hardwood Forests of Canada and the United States this century (1910–1990) was reconstructed from pathology records and compared to indices of extreme weather stresses in the region, and to changes in global temperatures and climatic variability over the same period. Thaw-freeze and root-freeze events in winter and early spring were key factors intriggering (and synchronizing) severe episodes of dieback. Once trees were injured by freezing, forest dieback correlated significantly with heat and drought stress. Freezing (but not drought) stresses in Northern Hardwoods correlated significantly (r = 0.70, p < 0.001) with increasing global mean annual temperatures and low values of the Pacific tropical Southern Oscillation Index. Major diebacks did not occur early in the century at a time of notable freezing stress. Prior to 1940, the Northern Hardwoods consisted of relatively young populations of trees regrowing following extensive cutting and forest burning in the late 19th century (1860–1890). It appears that forest maturation is the key factorpreconditioning trees to climatic injury, and dieback. A simple projection of climate and forest maturation ages suggested the recurrence of major dieback episodes on white/yellow birch, sugar maple and red spruce in the latter half of the 21st century (2045–2085).     

Vulnerability and adaptation of the larch forest in eastern Siberia to climate change

The most widely distributed coniferous forests in the world are the larch forests. In the Russian Federation they occupy 27.6 × 10⁶ ha. In Siberia, the larch species Larix russica generally grows west of the Yenissei River, and Larix gmelinii grows to the east. The morphological and physiological features of L. gmelinii make it possible for this species to grow in the far north of eastern Siberia, where climate conditions are more severe: The range of air temperature fluctuations in this region is more than 100°C, from 38°C down to 64°C below zero. One of the major adaptions to unfavorable soil conditions is provided by a specific feature of root formation in L. gmelinii, in which the apex central root dies off at the permafrost border and a root system develops in upper soil layers. The major larch vulnerability factors are natural and anthropogenic fires and damage caused by insects, which become more frequent with hot and dry weather. The consequences of projected global warming could be both positive and negative for larch forests. Permafrost melting may result in improved soil nutrition in the areas the larch forests occupy, yet the frequency of forest fires and damage by pathogens are likely to increase. Global warming is expected to cause forest die back and increased areas of steppe in the southern regions of eastern Siberia.     

广西喀斯特次生林地表碳库和养分库特征及季节动态

以自然保护区原生林为对照,调查了广西喀斯特区处于同一次生演替序列中的灌丛、藤刺灌丛、乔灌丛3个群落的地表凋落物存量,同时对凋落物层和土壤表层(0-5 cm)的有机碳,全氮、磷、钾等养分元素的含量、贮量状态及其雨季前后的变化进行了研究.结果表明:地表凋落物存量及有机碳、全氮贮量随演替阶段上升均呈增高趋势;除全磷外,土壤的有机碳和养分元素含量与凋落物层贮量相关性显著(p<0.05);雨季期间,凋落物迅速分解,地表凋落物的分解量要大于当季凋落量,并且次生林的凋落物分解与养分释放量显著高于原生林;雨季后,各群落有机碳和养分的凋落物层贮量以及土壤含量均有所降低.其中凋落物层贮量下降显著的是藤刺灌丛与乔灌丛.土壤养分含量则在灌丛与原生林阶段下降更为明显.在从灌丛向顶级群落演替的进程中,森林的自养能力可能存在一个先增高再降低的过程.     

Principal Forest Dieback Episodes in Northern Hardwoods: Development of Numeric Indices of Areal Extent and Severity

The incidence of forest dieback in the Northern Hardwoods biome of Canada and the United States was determined for period from 1910 to 1990. Information from annual forest service pathology inventories in the two countries and other published literature was coded to estimate yearly the severity and areal extent of dieback on white/yellow birch and sugar maple from 1910 to 1990. Principal dieback episodes occurred as distinct waves coincident with maturation of the forest population in each of six regions. These episodes endured an average of 11 years. It is hypothesized that, once forest populations are mature, they are susceptible to extreme stresses such as freezing and drought which serve to synchronize the onset and subsidence of major dieback episodes.     

Forest health monitoring in Canada: How healthy is the boreal forest?

The Canadian boreal forest covers 299.2 Mha which is two-thirds of Canada's forest and runs in a continuous belt from Newfoundland north and west to the Yukon. The major species are spruce, pines, balsam fir, white birch and trembling aspen often occurring in extensive monocultures. Wildfire is the driving successional force in the boreal forest and has remained so despite fire suppression activities and extensive harvesting. Insects and diseases also cause extensive damage. In order to ensure the sustainability of forests, it is necessary for the forest manager to know the condition of the health of these forests. The CFS established in 1984 the Acid Rain National Early Warning System in order to monitor the health of the forests. National results show that mortality is generally in the normal range of 1–3% and is caused by known stresses; insects, diseases and abiotic damage. No signs of pollution damage have been yet been detected in boreal forests by the system. An early warning system to detect and monitor conditions remains an essential part of our commitment to the sustainability of Canada's forests.     

Bird utilisation of rehabilitated bauxite minesites in Western Australia

Alcoa of Australia Limited rehabilitate bauxite mined areas in the southwest of Western Australia. One of the aims of the revegetation programme is to promote the return of fauna species which inhabited areas prior to mining.This paper discusses the extent to which bird species utilise revegetated bauxite minesites. It was shown that revegetated areas as young as 4–5 years can support similar bird species numbers, densities and diversities as unmined forest. However, the avifaunal populations occupying any rehabilitated area depend largely on the rehabilitation technique used. Factors which may be used to increase further avifaunal utilisation of minesites are discussed.The effects of jarrah dieback and fire on forest birds are compared with results for bauxite mined areas. From this, it is possible to assess the combined impact of dieback, fire and mining on the longer term conservation of jarrah forest bird species.     

甘肃兴隆山自然保护区森林演替对土壤肥力影响的评价

以黄土高原半干旱区森林群落为研究对象,从土壤物理、化学和生物化学因子出发,利用模糊数学和因子分析方法对甘肃兴隆山植物群落演替过程土壤肥力的变化特征进行了综合评价。结果表明:4类林分土壤综合质量由高到低依次是落叶阔叶林、针阔混交林、灌木林、针叶林。证明随着森林群落演替进展,土壤肥力呈降低趋势。解决当前该区针叶林土壤退化的主要措施是利用人为干扰来控制生态演替,以维持地力平衡和提高林地生产力。     

Toward development of silvical strategies for forest restoration of American chestnut (Castanea dentata) using blight-resistant hybrids

Backcross breeding has provided a viable means to restore American chestnut (Castanea dentata (Marsh.) Borkh.) to eastern North American forests, where the foundation species was essentially extirpated by an introduced pathogen. With the prospect of American chestnut reintroduction imminent, it is critical to formulate restoration strategies based on the ecology and silvics of the species, operational confines, social or policy limitations, and ecological implications. American chestnut was apparently adapted to a relatively wide range of site conditions, has evolved a capacity to survive for prolonged periods beneath forest canopies yet respond rapidly to disturbance, and demonstrates extraordinary growth and competitive ability. These characteristics are discussed in reference to operative planting techniques and potential for migration of regeneration from hybrid chestnut plantings into forests of the original American chestnut range. The use of hybrid trees for American chestnut reintroduction may generate social and policy ambiguities that require conciliation. Additionally, potential long-term ecological implications associated with reintroduction of American chestnut to the original species range, or introduction to areas outside its original range, must be realized and integrated into reintroduction strategies. Limitations in genetic fitness, potential for disease mutation, and threats from other exotic insects and pathogens may serve as continual challenges to American chestnut restoration. This paper helps establish preliminary guidelines for restoration plantings and creates awareness of imposing ecological issues and barriers that must be overcome to successfully restore American chestnut to its natural range, while simultaneously maintaining ecological integrity and ensuring conservation benefits to eastern North American forests.     

A new fertilization strategy in declining forests

In central Europe and to some degree in North America, the so called “new type” forest damages occur over large areas. Various studies indicate the declines are more or less frequently associated with nutritional disturbances that have developed within rather short time periods. The most common disorder is a Mg deficiency that produces specific discoloration symptoms such as tip-yellowing in Norway spruce. But also K deficiencies and other disturbances exist in coniferous as well as in deciduous forests. Good correlations between the site specific substrate chemistry and the actual nutritional status of the trees and stands were found. To explain the sudden and widespread development of the forest declines adverse anthropogenic influences such as increased N and H⁺ deposition, land use and forestry mismanagement as well as natural stresses are discussed. The hypothesized causal mechanisms are multiple, but include generally soil degradation processes associated with losses of alkaline nutrient ions from the rooted solum. Recent and previous fertilization (and liming) experiments have shown that a fast and sustained revitalization and restabilization of declining forest ecosystems marked by nutrient deficiencies can be achieved. This was demonstrated by chemical and histological foliar analyses and the visible improvement of the trees. Soil analyses also revealed a positive change of the chemical soil status when site and stand specific fertilizer applications were utilized in the appropriate amounts. However, under certain site and stand conditions risks and limitations exist that have to be evaluated when fertilization practices are discussed.To overcome or minimize these influences the treatments. must be adapted to the site, and stand specific fertilization needs as indicated by soil and foliar analysis, humus form, hydrologic parameter and atmospheric deposition rates.     

Factors predisposing forests to canopy collapse in the southern Ruahine Range, New Zealand

The introduced brushtail possum Trichosurus vulpecula Kerr is recognised as the primary agent of defoliation and stand-level dieback in New Zealand broadleaved forests (except Nothofagus). The distribution and magnitude of canopy collapse of forest in 33 500 ha of the southern Ruahine Range, New Zealand was mapped from 1995 polychrome aerial photographs. Relationships between canopy collapse and forest type, altitude, aspect and slope were analysed using generalised additive models. Canopy composition was the strongest factor predicting the extent of collapse and modification: broadleaved-conifer forest is most affected, with 68–87% of the area of six such forest types replaced by scrub-low forest and tree-fernland; and surprisingly, three Nothofagus-dominated types have up to 28% of their former area now in shrubland or tussock grassland. The susceptibility to collapse of Nothofagus forest was positively correlated with distance to non-Nothofagus forest types. Subalpine scrub, which is dominated by species not favoured by possums, has increased in area by 32%, replacing former upper montane forest. Physiographic factors were much less important in multiple regressions. However, in general terms, forests on steeper slopes, in the upper montane-subalpine zone, and on warm westerly and northerly aspects were more susceptible to collapse and modification than elsewhere. It is postulated that possums were the primary agent responsible for collapse of non-Nothofagus broadleaved forest, and that red deer Cervus elaphus and goats Capra hircus were responsible for inhibiting canopy replacement by eliminating regeneration in forest understoreys. Secondary effects, such as outbreaks of defoliating insects and mechanical damage from wind also contributed to canopy collapse and were possibly triggered by possums opening up the canopy. Collapse of Nothofagus canopies possibly results from a breakdown in the recruitment phase of stand turnover, by the smothering effects of deer-induced shrubs and tussock grasses on seedlings and saplings.     

Potential effects of the increase in carbon dioxide and climate change on the dynamics of vegetation

The continued CO₂ loading of the atmosphere appears to be responsible for inducing three new force factors controlling dynamic changes in the world's vegetation. They come from (1) enhanced fertilization with the single most important plant nutrient, (2) the widely expected global temperature increase, and (3) aggravated weather disturbances. Increased CO₂ absorption may enhance plant growth but it may also increase soil-nutrient limitations. It surely will enhance the metabolism of forest trees similarly as global warming will enhance plant metabolism, but both factors may also shorten the lifespan of perennial plants. Increased weather disturbances can be expected to produce new physiological stresses on the standing vegetation, particularly on habitats with poor soils. Since wide-spread forest decline has been reported from both the Atlantic and Pacific region, it seems possible that the roughly synchronie mass mortality of trees during the past two decades is related to the global increase in CO₂. The paper gives an overview of forest decline and dieback as known from past and present research and suggests how the changing atmospheric environment may interact in this widely observed contemporary phenomenon of vegetation dynamics.     

Threshold effect of eucalypt density on an aggressive avian competitor

General guidelines available to revegetation planners focus on the spatial context and dimensions of the revegetated site. However, site-specific habitat factors can have overarching importance for habitat value, especially where interactions with competitors or predators may play an important role. Current revegetation projects in Australia which aim to restore slow-growing buloke (Allocasuarina luehmannii) woodland, a threatened habitat important for bird conservation, usually include faster-growing eucalypts in plantings. This research aimed to identify whether eucalypt presence in buloke woodland facilitates invasion by the noisy miner (Manorina melanocephala), an aggressive competitor that is absent from pure buloke woodland. Birds were surveyed in buloke woodland remnants that contained eucalypts as a sub-dominant species at densities of 0-16 per ha. The probability of noisy miner presence in buloke woodland increased markedly where eucalypts were present at a density of approximately five per hectare. The presence of noisy miners resulted in a substantial difference in bird assemblage structure and composition. Small-bodied insectivorous birds which are experiencing population declines in southern Australia were recorded on average six times more often in transects without noisy miners (low-eucalypt density transects). Avian behaviour and habitat use was also altered, with birds flying more frequently in transects where noisy miners were present. A minor difference in habitat composition results in substantial degradation of the conservation value of non-eucalypt woodland in eastern Australia due to invasion by aggressive avian competitors. Revegetation and restoration practices should take into account the potential for such subtle floristic differences to result in substantial variation in conservation outcomes.     

The interaction of climate and land use in future terrestrial carbon storage and release

The processes controlling total carbon (C) storage and release from the terrestrial biosphere are still poorly quantified. We conclude from analysis of paleodata and climate biome model output that terrestrial C exchanges since the last glacial maximum (LGM) were dominated by slow processes of C sequestration in soils, possibly modified by C starvation and reduced water use efficiency of trees during the LGM. Human intrusion into the C cycle was immeasurably small. These processes produced an averaged C sink in the terrestrial biosphere on the order of 0.05 Pg yr^?1 during the past 10,000 years. In contrast, future C cycling will be dominated by human activities, not only from increasing C release with burning of fossil fuels, and but also from indirect effects which increase C storage in the terrestrial biosphere (CO₂ fertilization; management of C by technology and afforestation; synchronous early forest succession from widespread cropland abandonment) and decrease C storage in the biosphere (synchronous forest dieback from climatic stress; warming-induced oxidation of soil C; slowed forest succession; unfinished tree life cycles; delayed immigration of trees; increasing agricultural land use). Comparison of the positive and negative C flux processes involved suggests that if the C sequestration processes are important, they likely will be so during the next few decades, gradually being counteracted by the C release processes. Based only on tabulating known or predicted C flux effects of these processes, we could not determine if the earth will act as a significant C source from dominance by natural C cycle processes, or as a C sink made possible only by excellent earth stewardship in the next 50 to 100 yrs. Our subsequent analysis concentrated on recent estimates of C release from forest replacement by increased agriculture. Those results suggest that future agriculture may produce an additional 0.6 to 1.2 Pg yr^?1 loss during the 50 to 100 years to CO₂ doubling if the current ratio of farmed to potentially-farmed land is maintained; or a greater loss, up to a maximum of 1.4 to 2.8 Pg yr^?1 if all potential agricultural land is farmed.     

Forest Health in North America: Some perspectives on Actual and Potential Roles of Climate and Air Pollution

The perceived health of forest ecosystems over large temporal and spatial scales can be strongly influenced by the frames of reference chosen to evaluate both forest condition and the functional integrity of sustaining forest processes. North American forests are diverse in range, species composition, past disturbance history, and current management practices. Therefore the implications of changes in environmental stress from atmospheric pollution and/or global climate change on health of these forests will vary widely across the landscape. Forest health surveys that focus on the average forest condition may do a credible job of representing the near-term trends in economic value while failing to detect fundamental changes in the processes by which these values are sustained over the longer term. Indications of increased levels of environmental stress on forest growth and nutrient cycles are currently apparent in several forest types in North America. Measurements of forest ecophysiological responses to air pollutants in integrated case studies with four forest types (southern pine, western pine, high elevation red spruce, and northeastern hardwoods) indicate that ambient levels of ozone and/or acidic deposition can alter basic processes of water, carbon, and nutrient allocation by forest trees. These changes then provide a mechanistic basis for pollutant stress to enhance a wider range of natural stresses that also affect and are affected by these resources. Future climatic changes may ameliorate (+ CO2) or axacerbate (+ temperature, + UV-B) these effects. Current projections of forest responses to global climate change do not consider important physiological changes induced by air pollutants that may amplify climatic stresses. These include reduced rooting mass, depth, and function, increased respiration, and reduced water use efficiency. Monitoring and understanding the relative roles of natural and anthropogenic stress in influencing future forest health will require programs that are structured to evaluate responses at appropriate frequencies across gradients in both forest resources and the stresses that influence them. Such programs must also be accompanied by supplemental process -oriented and pattern -oriented investigations that more thoroughly test cause and effect relationships among stresses and responses of both forests and the biogeochemical cycles that sustain them.     

Values of village fengshui forest patches in biodiversity conservation in the Pearl River Delta, China

Chinese village fengshui forests (VFF) are small remnant forest patches that coexist with natural villages. The indigenous residents protect the forest patches under traditional Chinese geomancy beliefs (namely fengshui). However, the VFF community features and conservation values and relationships with the indigenous people remain poorly understood. In this study, we evaluated tree species diversity conservation of regional VFF patches by sampling a 1200 m² transect within each patch. We also tested our hypothesis that patch size did not significantly impact interior forest community features of well-protected VFF patches. Thirty-two well-protected VFF patches in the Pearl River Delta, China were investigated. The average coefficient of similarity between transects (CS) was employed to evaluate community heterogeneity. Five forest community parameters (tree species richness per 1200 m², tree stem density, tree basal area density, Shannon–Wiener diversity index (SWI), and Simpson diversity index (SI)) were measured and compared with regional well-developed evergreen broadleaved, coniferous and coniferous-broadleaved mixed forests. The relationships between the five parameters versus patch size and elevation were analyzed. A total of 266 tree species comprised of 57 families were recorded in 32 transects, of which 258 (97%) species were indigenous and eight (3%) were exotic. Ten tree species were endangered, rare or nationally protected by the Chinese government, and 57 species were endemic to China. The average CS was 0.38; and the average five forest community parameter values were as follows: 46.8 for tree species richness; 3403 plants/ha for stem density, 49.1 m²/ha for basal area, 4.04 for SWI and 0.90 for SI. These values were consistent with well-developed evergreen broadleaved forests and greater than coniferous and coniferous-broadleaved forests. No significant correlation was detected between the five community parameters and patch area or elevation. We conclude that VFF patches preserve abundant tree species and heterogeneous habitats, which are important for maintaining regional biodiversity. The interior community features of VFF patches were not significantly affected by patch size. We recommend protection of both large and small VFF patches, which can be substantially enhanced by the preservation of associated traditional relic village cultures.