Human-caused Disturbances Research Articles

European Bee-eater (Merops apiaster Linnaeus, 1758) in Hungary: a review

Abstract The European Bee-eater (Merops apiaster Linnaeus, 1758) is known as ‛beekeeper bird’ and an effective ecosystem engineer species. The fact that in 2013 it became ‛The Bird of the Year’ in Hungary offers the possibility to summarise the information about the distribution, population size, breeding and feeding ecology, dispersion, migration, intra- and interspecific relationships as well as the nature conservation status of the bee-eater population breeding in Hungary. Though this review focuses on the Hungarian population trends, but also summarises the major research results from other countries. In the period of 1992-2013, the number of breeding pairs were surveyed in 5897 2.5×2.5 km UTM squares in the frame of the Monitoring of Rare and Colonial Breeding Birds programme. In the surveyed area during the period of 1992-2013, the most accurate estimate suggests a 10600-19600 breeding pair population. The larger nesting colonies were observed in the following regions: Zala Hills, Outer Somogy, Gerecse, Velencei Hills, Mezőföld, Gödöllő Hills, Tápió, Bükkalja, Taktaköz, Körös region. The annual population indices showed marked fluctuation with stable long term population trend in Hungary. The national monitoring and protection project of the European Bee-eater revealed the most important factors endangering the nesting populations, these are weed invasion and the collapse of vertical banks, mining carried out in the nesting period and direct human-caused disturbance (e.g. shooting, tourism).

Deciphering the role of climate- versus human-caused disturbance during the 19th and 20th century: a comparison of isotopic, stoichiometric, pollen, and plant macrofossils from two lakes in the western U.S.

Deciphering the role of climate- versus human-caused disturbance during the 19th and 20th century: a comparison of isotopic, stoichiometric, pollen, and plant macrofossils from two lakes in the western U.S.

A Multi-scale Spatial Analysis of Native and Exotic Plant Species Richness Within a Mixed-Disturbance Oak Savanna Landscape

Impacts of human land use pose an increasing threat to global biodiversity. Resource managers must respond rapidly to this threat by assessing existing natural areas and prioritizing conservation actions across multiple spatial scales. Plant species richness is a useful measure of biodiversity but typically can only be evaluated on small portions of a given landscape. Modeling relationships between spatial heterogeneity and species richness may allow conservation planners to make predictions of species richness patterns within unsampled areas. We utilized a combination of field data, remotely sensed data, and landscape pattern metrics to develop models of native and exotic plant species richness at two spatial extents (60- and 120-m windows) and at four ecological levels for northwestern Ohio’s Oak Openings region. Multiple regression models explained 37–77 % of the variation in plant species richness. These models consistently explained more variation in exotic richness than in native richness. Exotic richness was better explained at the 120-m extent while native richness was better explained at the 60-m extent. Land cover composition of the surrounding landscape was an important component of all models. We found that percentage of human-modified land cover (negatively correlated with native richness and positively correlated with exotic richness) was a particularly useful predictor of plant species richness and that human-caused disturbances exert a strong influence on species richness patterns within a mixed-disturbance oak savanna landscape. Our results emphasize the importance of using a multi-scale approach to examine the complex relationships between spatial heterogeneity and plant species richness.

Response of Grey Herons (Ardea cinerea) to human disturbance in a suburban village in Poland

Human-caused disturbances affect, e.g., the spatial distribution and breeding performance of most organisms, including birds. Here, we assessed the response of Grey Herons (Ardea cinerea) to frequent human disturbance in a large heron colony in Poland during 2009-20 12. The colony covered an area of 2.5 ha and had annually 174-220 occupied nests. We found that egg losses increased and nest occupancy decreased with an increase in the area covered by buildings nearby. The distances to the nearest building or road were not significantly related to egg losses.

基于干扰的汪清林区森林生态系统健康评价

以汪清林区60个林班为研究对象,提出基于干扰的森林生态系统健康评价模型H=∑B₂W₂-∑B₁W₁,构建了基于干扰理论的汪清林区森林生态系统健康评价体系。其中,有害干扰指标层选取4个指标:森林病害、森林虫害、森林火险以及人为干扰,生态系统内部的增益指标层选取4个指标:树种多样性、群落层次结构、林分更新状况以及近自然度。利用层次分析法和变异系数结合的主客观赋权法计算得到各指标的权重,提出基于干扰的健康评价模型和等级划分标准。最终评价结果显示:汪清林区60个样地中,处于优质状态的样地有6块,占总样地数的10%,健康指数均大于0.2;处于健康状态的林分13块,占总样地数的21.67%,健康指数在0.1-0.2之间;处于亚健康状态的林分23块,占总样地数的38.33%,健康指数在0-0.1之间;处于不健康的林分18块,占总样地数的30%,健康指数小于0。结果表明,在天然林中,无论是针叶纯林还是针阔混交林、阔叶混交林,大多处于亚健康和健康的状况,这与他们近自然度高,物种多样性丰富、具有良好的自我调节能力有关。而在落叶松人工林分中,由于林分物种多样性低,群落结构简单,近自然度最小,林分的增益能力弱,因此不健康的占有绝大多数。该评价结果可为该林场展开相关的健康经营措施提供参考。;Currently, the study of forest ecosystem health, a new and controversial research field within forestry and forest ecology, provides a scientific basis for forest protection. The study of forest ecosystem health also provides a significant practical service by suggesting ways to increase the level of sustainability in forest management although the definition of forest health remains controversial. The concept of health is well understood as applied to humans but the human concept of health may not be appropriate for ecosystems. The difficulties of defining the optimal conditions for ecosystem health have led to a lack of universally accepted indicators used to measure ecosystem health. Several forest ecosystem health assessment systems have already been developed. For example, ecosystem health can be assessed using measures of resilience, vigor and organization and most of today's assessment systems are based on these concepts. In this research, the forest ecosystem health of 60 sample plots in Wangqing Forest was investigated. A new assessment model of forest ecosystem health based on the disturbance, H=∑B₂W₂-∑B₁W₁, is proposed and used in this study, where <em>H</em> represents a measure of ecosystem health and <em>B</em>₁, <em>B</em>₂, <em>W₁</em> and <em>W</em>₂ represent harmful sources of disturbance, forest ecosystem stability, the weights of <em>B</em>₁ and <em>B</em>₂, respectively. Based on qualitative analysis of existing data, eight indices which were divided into two categories were selected as assessment indices of forest ecosystem health in Wangqing Forest. Several harmful sources of disturbance were considered including forest diseases, forest pest species, wildfires and human-caused disturbances. Measurements of forest ecosystem stability include measurements of biological diversity, forest community structure and measurements documenting how closely a forest study plot resembles expected natural forest conditions. These types of data have frequently been used to measure ecosystem complexity and health. Additionally, two types of analysis, the Analytic Hierarchy Process and coefficient of variation analysis, were used in combination with weighted evaluation indictors to objectively evaluate the forest health of the study plots. We propose a new forest ecosystem healthy assessment model and classification system. The 60 sample plots of Wangqing Forest were divided into four health risk categories: very healthy, healthy, fairly healthy and unhealthy. By calculating a composite value for forest health, the status of forest ecosystem health of individual Wangqing Forest plots was determined. As the results showed, 6, 13, 23 and 18 (or 10%, 21.67%, 38.33%, and 30% of all plots) plots were categorized as very healthy, healthy, fairly healthy, and unhealthy, respectively; the health indices for these four groups of plots were measured as 0.5 ≥ 0.2, 0.2 ≥ 0.1, 0 ≥ 0.1,-0.5< 0, respectively. Most of the forest plots with conditions resembling natural forest conditions, high levels of biodiversity and a strong ability to adjust to environmental change, such as pure natural forest, natural mixed needleleaf/broadleaf forest and mixed broadleaf forest, were categorized as healthy or fairly-healthy, while nearly all plantation forests plots which did not have conditions resembling natural forest conditions, but had low levels of biodiversity and a weak ability to adjust to environmental change were classified as unhealthy. This forest health assessment/indicator system establishes a scientific basis for conducting forest health analysis, provides a context for planning ecosystem restoration, and contributes to the understanding of the physical, biological, and human dimensions of these ecosystems. This research may enrich current theories and methods used in assessing the health of ecological systems.

Effects of human disturbance on the Hooded Crane (Grus monacha) at stopover sites in northeastern China

There is a lack of information of whether the behavior pattern and physical condition of the Hooded Crane (Grus monacha) have been limited by conditions encountered at stopover sites in Changgou village, which is adjacent to Zhalong Nature Reserve in northeastern China, one of the most important stopover sites of this crane. The objective of our research was to investigate the impact of human-caused disturbances on the Hooded Cranes. We investigated three behavior activities of the Hooded Cranes, i.e., flying time, flushing distance and the duration of vigilance. The results indicate that the auditory stimuli caused by local people provoked the most pronounced disturbances to the Hooded Crane. Human-caused disturbances not only frequently interrupt the feeding process of the cranes, but also lead to an increase of 200% in the duration of their vigilance and a significant increase in flying time from 0.4 to 0.7 h ( p < 0.05). In addition, high-intensity noise can cause larger flushing distances; foraging cranes will flush away by about 600 m when disturbed by the honking of vehicles. Whistles or shouts by local farmers in the field generated the largest sound intensity, about 120 dB, which caused a flushing distance of over 700 m. In order to reduce the negative effect of human-caused disturbances on these cranes, it is imperative to define a buffer zone around sensitive areas during the fall stopover period. To solve the conflict between the interest of farmers and the demand for crops on the part of the cranes requires financial compensation to the farmers for the crops consumed by the Hooded Crane in order to enhance the conservation of this vulnerable bird species.

Aquatic insects indicate terrestrial habitat degradation: changes in taxonomical structure and functional diversity of dragonflies in tropical rainforest of East Kalimantan

As a group of freshwater invertebrates, dragonflies (Odonata) are commonly used as ecological indicators of freshwater ecosystems. Despite earlier studies suggesting that adult odonates may be good indicators for complex changes in a landscape, the utility of odonates as suitable indicators to indicate health of non-aquatic (forest) habitats remains poorly understood. This study analyses the adult dragonfly assemblage pattern against spatial and temporal disturbance characteristics in Indonesia's Sungai Wain Protection Forest. The core of this reserve comprises one of the few remaining fragments of primary rain forest along the East Kalimantan coast, whereas the rest of the reserve is covered by secondary forest, scrub, grassland, and farmland. Adult dragonfly assemblages at individual sampling sites were analysed in relation to (1) their intensity, (2) frequency of human-caused disturbances, and (3) the time since the last such disturbance, while controlling random variables (type of aquatic and terrestrial habitat) were removed. This study tests the effect of these factors on (1) species richness, (2) proportion of Zygoptera, (3) proportion of forest specialists, and (4) proportion of Borneo's endemics. The human-induced disturbances in the rain forest resulted in pronounced changes in the taxonomical composition and functional diversity of the odonate fauna. Results reported here demonstrate that gradual changes in the odonate assemblages correspond to the degree of anthropogenic influences on forest environments. Adult odonates comprise an appropriately sensitive and versatile indicator group for identifying changes in terrestrial forest environments as well as in freshwater habitats.

Exclosure study on the exploitation of macrophytes by summering and moulting waterbirds at Lower Lake Constance

Owing to synchronous moult, most waterbird species are constrained by flightlessness and limited mobility for several weeks. As new feather production is energy demanding, these birds need to choose a safe moulting site with appropriate food supply. Up to 20,000 waterbirds carry out moult at Lake Constance, gathering at sites where they find food close to safe hiding places from predators and human-caused disturbance. In this study, we focused on the food supply at one prominent moulting site, Mettnau Sudbucht, at Lower Lake Constance. We aimed to determine the food items and quantity as well as their utilization by summering and moulting waterbirds. We conducted experiments with exclosure cages which protected macrophytes from bird grazing and compared these sites with unprotected grazed sites. In these experiments, we found that the summering and moulting waterbird community, dominated by Eurasian Coots (Fulica atra Linnaeus), caused a significant decline of the macrophyte biomass at 1.5-m depth (MWL), where they were responsible for a loss of over 40% of the total charophyte biomass. No grazing effect was found at a greater depth (2-m MWL). The available food consisted mostly of Chara spp. with a biomass density of about 350 g m−2. Animal food items were negligible: Macroinvertebrates, mainly Asellus aquaticus Linnaeus, that were associated with the macrophytes, made up only 2% of total biomass, and were very unevenly distributed.

Dynamic performance assessment of protected areas

Recognizing the importance of preserving biodiversity and ecosystem services, human society has established extensive protected area networks to conserve these resources in recent decades. Are protected areas working as expected? Empirical coarse-scale assessments of this question across large regions, or even globally, tend to answer “yes”, while fine-scale studies of individual protected areas often and repeatedly answer “no”. We conducted a first fine-scale analysis of Brazil’s extensive Amazonian protected area network (1.8millionkm2) and have quantitatively estimated conservation effectiveness in light of changing human development pressures in the surrounding landscape. The overall network maintained intact forest cover for 98.6% of protected forest lands, largely agreeing with previous coarse-scale studies. However, detailed examination of 474 individual protected areas unveils a broad range of efficacy. Many protected areas (544,800km2) experience default protection simply due to their remoteness. Many others (396,100km2) have provided highly effective protection in the face of substantial human development pressure. Conversely, 12% (38) of protected areas have failed to protect the 27,300km2 that they encompass, and another 7% (23) provide only marginal protection of 37,500km2. Comprehensive landscape assessments of protected area networks, with frequent monitoring at scales matching the patterns of human-caused disturbances, are necessary to ensure the conservation effectiveness and long term survival of protected areas in rapidly changing landscapes. The methods presented here are globally adaptable to all forested protected areas.

A comparison of presettlement and modern forest composition along an elevation gradient in central New Hampshire

Tree species composition is influenced not only by edaphic and climatic factors but also by natural and human-caused disturbances. To understand interactions among these influences, we compared forest species composition data from the time of European settlement with modern data. We derived elevation data for 2529 trees mapped by early land surveys (1770–1850) across a 1000 m elevation gradient in central New Hampshire and compared these with modern data (2004–2009) from the Forest Inventory and Analysis program (123 plots containing 2126 trees) and from permanent plots representing case studies of different land-use histories. Spruce and beech are much less abundant today at all elevations than they were prior to settlement, while maples and birches have increased. Fir, hemlock, pines, and oaks have changed little in distribution, although pines and oaks increased in abundance somewhat. Land-use history (agriculture below 500 m and cutting of various intensities at all elevations) is likely the primary explanation for these shifts, although climate change is also an important factor for some. A clearer understanding of presettlement forest composition improves our ability to separate the relative importance of natural and human-driven influences on the species composition of today’s forests.

Silviculture as a disturbance regime: the effects of clear-cutting, planting and thinning on polypore communities in mixed forests

The structure of modern forest landscapes is profoundly affected by human-caused disturbances, particularly forest management; however, the effects and prospects of individual silvicultural techniques are insufficiently understood. This study distinguishes the effects of clear-cutting, planting and thinning on species richness and community composition of polypore fungi. In 2008–2009, 181 forest compartments (ranging from naturally regenerated deciduous stands to planted Picea abies stands and 0–137 years post clear-cutting) were explored in a hemiboreal landscape subjected to even-aged management. Altogether 104 polypore species were recorded. For species richness, time since clear-cutting was the most influential factor at both stand and landscape scales, followed by thinning. Clear-cuts had distinct polypore communities (including several red-listed species) whose species richness declined in time. Following 20 years post clear-cutting, species richness started to increase along different community–composition pathways determined by regeneration type. The communities developed after planting were moderately species rich at stand scale but homogeneous over larger areas. Thus, at landscape scale, mature unmanaged naturally regenerated stands hosted most species; thinning reduced species richness by approximately 15%, and among thinned stands, planted areas had a further 9–22% fewer species than naturally regenerated areas. In such variably managed landscape, silviculture appeared to create particularly distinct communities in young stands on nutrient-rich soils, which naturally provide polypores with a rich supply of small deciduous snags absent from stands artificially planted with P. abies and intensively thinned.

Useful model organisms, indicators, or both? Ground beetles (Coleoptera, Carabidae) reflecting environmental conditions

Classic studies have successfully linked single-species abundances, life-history traits, assemblage structures and biomass of carabid beetles to past and present, human-caused environmental impacts and variation in ‘natural’ conditions. This evidence has led many to suggest carabids to function as ‘indicators’ − a term that bears multiple meanings. Here, a conservation-oriented definition for an indicator is used, carabid indicator potential from seven views is evaluated, and ways to proceed in indicator research are discussed. (1) Carabid species richness poorly indicates the richness and abundance of other taxa, which underlines the importance of using multiple taxa in environmental assessments. The ability of assemblage indices and specialist or functional-group abundances to reflect rare species and habitats should be examined in detail. (2) Experimental evidence suggests that carabids may potentially serve as keystone indicators. (3) Carabids are sensitive to human-altered abiotic conditions, such as pesticide use in agro-ecosystems and heavy metal contamination of soils. Carabids might thus reflect ecological sustainability and ‘ecosystem health’. (4) Carabid assemblages host abundant species characteristic of particular habitat types or successional stages, which makes them promising dominance indicators. (5) Carabids reflect variation in ‘natural’ conditions, but vegetation and structural features are more commonly adopted as condition indicators. Carabids nevertheless provide yet another, equally accurate, view on the structure of the environment. (6) Carabids may function as early-warning signalers, as suggested by recent studies linking climate and carabid distributions. (7) Carabids reflect natural and human-caused disturbances and management, but the usefulness of these responses for conservation purposes requires further research. In summary, European carabids appear useful model organisms and possibly indicators because they are diverse, taxonomically and ecologically well-known, efficiently reflect biotic and abiotic conditions, are relevant at multiple spatial scales, and are easy to collect in sufficiently large numbers to allow statistical analyses. The assumption that carabid responses would reflect rare environmental conditions or the responses of rare and threatened species ‒ crucial information for conservationists and managers ‒ has not yet been critically evaluated. Even if it holds, the usefulness will be context dependent: species and their populations vary, conditions vary, questions put forward vary, and assessment goals vary.

Coping with human disturbance: spatial and temporal tactics of the brown bear (Ursus arctos)

In human-dominated landscapes, species with large spatial requirements, such as large carnivores, have to deal with human infrastructure and activities within their home ranges. This is the case for the brown bear ( Ursus arctos L., 1758) in Scandinavia, which is colonizing more human-dominated landscapes, leading inevitably to an overlap between their home ranges and anthropogenic structures. In this study, we investigated fine-scale habitat selection by brown bears to examine how they deal with this potential disturbance. Using Global Positioning System (GPS) data, we studied (i) habitat selection of female brown bears within their home range and (ii) the influence of diurnal variation in human disturbance on fine-scale habitat use. As expected, females selected habitats within their home range that provided abundant food resources and minimized human-caused disturbance. In addition, our temporal analysis of habitat selection revealed an avoidance of disturbed areas and a selection of slopes by bears during periods of highest human activities, i.e., during daylight hours. We clearly demonstrate the importance of considering the fluctuations in human activity when studying habitat selection, especially at fine spatial scales. Failing to do so may considerably reduce the power to detect important fine-scale habitat-selection behaviors.

Simulations show decreasing carbon stocks and potential for carbon emissions in Rocky Mountain forests over the next century

Climate change has altered the environment in which forests grow, and climate change models predict more severe alterations to come. Forests have already responded to these changes, and the future temperature and precipitation scenarios are of foremost concern, especially in the mountainous western United States, where forests occur in the dry environments that interface with grasslands. The objective of this study was to understand the trade-offs between temperature and water controls on these forested sites in the context of available climate projections. Three temperature and precipitation scenarios from IPCC AR4 AOGCMs ranging in precipitation levels were input to the process model Biome-BGC for key forested sites in the northern U.S. Rocky Mountains. Despite the omission of natural and human-caused disturbances in our simulations, our results show consequential effects from these conservative future temperature and precipitation scenarios. According to these projections, if future precipitation and temperatures are similar to or drier than the dry scenario depicted here, high-elevation forests on both the drier and wetter sites, which have in the absence of disturbance accumulated carbon, will reduce their carbon accumulation. Under the marginally drier climate projections, most forests became carbon sources by the end of the simulation horizon (2089). Under all three scenarios, growing season lengthened, the number of days with snow on the ground decreased, peak snow occurred earlier, and water stress increased through the projection horizon (1950-2089) for all sites, which represent the temperature and precipitation spectrum of forests in this region. The quantity, form, and timing of precipitation ultimately drive the carbon accumulation trajectory of forests in this region.

Vegetation succession among and within structural layers following wildfire in managed forests

Question: How does vegetation develop during the initial period following severe wildfire in managed forests? Location: Southwestern Oregon, USA. Methods: In severely burned plantations, dynamics of (1) shrub, herbaceous, and cryptogam richness; (2) cover; (3) topographic, overstory, and site influences were characterized on two contrasting aspects 2 to 4 years following fire. Analysis of variance was used to examine change in structural layer richness and cover over time. Non-metric multidimensional scaling, multi-response permutation procedure, and indicator species analysis were used to evaluate changes in community composition over time. Results: Vegetation established rapidly following wildfire in burned plantations, following an initial floristics model of succession among structural layers. Succession within structural layers followed a combination of initial and relay floristic models. Succession occurred simultaneously within and among structural layers following wildfire, but at different rates and with different drivers. Stochastic (fire severity and site history) and deterministic (species life history traits, topography, and pre-disturbance plant community) factors determined starting points of succession. Multiple successional trajectories were evident in early succession. Conclusions: Mixed conifer forests are resilient to interacting effects of natural and human-caused disturbances. Predicting the development of vegetation communities following disturbances requires an understanding of the various successional components, such as succession among and within structural layers, and the fire regime. Succession among and within structural layers can follow different successional models and trajectories, occurs at different rates, and is affected by multiple interacting factors.

SEGSAMP: A Pixel Window Sampling Method Based on Image Segmentation

Pixel windows are often used to average the image spectral response values that represent the area over which field measurements are collected to estimate biophysical parameters such as forest stand structure, aboveground biomass, and leaf area index. Averaging spectral values within a pixel window ensures the resulting spectral response is representative of the biophysical parameter, and reduces sampling error from spatial mis-registrations between the image and plot locations. These spectral values are related to field plot measurements through empirical models that may result in poor estimates if (a) the plot is located too close to a spectrally different land feature; and (b) natural and human-caused disturbance occurs between the field data collection and image acquisition. This paper introduces SEGSAMP (SEGmentation SAMPle), an image sampling method to extract pixel values within a segmented sampling window that would be more spectrally representative of biophysical parameters measured from field plots. Written in Arc Macro Language, the method uses a point and polygon shapefile from which to sample only those pixels that are within a defined pixel window size and the image segment the plot is contained in. The output forms a segmented pixel window grid, which can be used to extract pixel values from imagery. A case-study application demonstrates that segmented pixel windows resulted in models whose coefficient of determination values were higher for prediction of stand height and crown closure (height Radj 2 = 0.65 ; crown closure Radj 2 = 0.57) than from square windows (height Radj 2 = 0.57 ; crown closure Radj 2 = 0.48).

Who’s invading what? Systems thinking about invasive species

While invasive plant species have dramatic and varied effects, this paper examines the focus of this symposium on their “threat to native biodiversity and ecosystems”. This claim implies that there is (i) an enduring something, (ii) it is native, and (iii) it is under threat from invasive species. I examine these implications in turn, first considering the role of the observer in invasion biology, particularly in preferring a nature characterized by stability rather than flux. Second, I examine the concept of “native” given that humans are thoroughly embedded within natural ecological systems. Third, I demonstrate how our exclusion of humans conditions us to consider invasive species a primary threat rather than one among many interacting causal agents of global change; in particular, recent evidence indicates that these agents, which include human-caused disturbances and global warming (not to mention human population growth and global trade), may overwhelm the effects of invasive species per se. For these and other reasons, some ecologists have argued that ecological change is inevitable and that our concerns about invasive species are unjustified. I discuss these issues and suggest ways for ecologists to conduct engaged research through appropriate advocacy and engagement with stakeholders dealing with local invasive species. Key words: Advocacy, culture, philosophy of nature, sociology of science

The influence of disturbance events on pileated woodpeckers in Northeastern Oregon

The pileated woodpecker ( Dryocopus pileatus) is a species of conservation concern and an indicator of mature and old forest habitat conditions in the Pacific Northwest. The effects of natural and human-caused disturbance on density of nesting pairs, reproductive success, and traditional home ranges were compared over 30 years in two areas and over 15 years in five additional areas. In one study area, density of nesting pairs of pileated woodpeckers decreased from five to one after extensive regeneration cuts eliminated most of the stands of mature and old-growth grand fir ( Abies grandis) and reduced the density of nest and roost trees and foraging substrate since 1990. Density of nesting pairs, reproductive success, and home range location remained fairly consistent over 30 years in a second study area with extensive tree mortality resulting from insect outbreaks but without regeneration harvests. The amount of unharvested stands and closed canopy stands in home ranges were positively correlated with reproductive success, and the amount of area in harvested stands was negatively correlated with reproductive success in 2003–05. High tree mortality and subsequent loss of canopy closure in stands of grand fir and Douglas-fir from insect outbreaks did not appear to be detrimental to pileated woodpeckers provided that dead trees and logs were abundant and that stands were not harvested.

Aspen in the Sierra Nevada: Regional Conservation of a Continental Species

Quaking aspen (Populus tremuloides Michx.), a common species in North America, is a minor species in the Sierra Nevada of California. However, the limited coverage of aspen in this area appears to carry a disproportionate biodiversity load: numerous species are dependent on the unique components of aspen forests for habitat. Land managers in the region believe the species is declining due to fire suppression policies of the past century. Recent research from other regions shows mixed results when assessing the extent of decline. This review focuses on the crossroads between human and natural history to describe a broader picture of aspen ecology in the Sierra Nevada. The method used here combines a review of the ecological literature with historical synthesis. A central conclusion is that the current “decline” in aspen must be placed in the context of an unusual regeneration pulse brought on by intensive Euro-American resource extraction activities of the late 19th century. We address unique features of the Sierra aspen population, the interface of climate change and human-caused disturbance, and conservation strategies for restoration of an aspen community more closely aligned with contemporary climate-disturbance cycles. Conservation recommendations include reintroduction of mixed-severity natural fires and complimentary wildlife, such as top predators, where practical, plus allowance for local flexibility where deviations are appropriate based on ecology and social concerns.

Research article Canopy dynamics and human caused disturbance on a semi-arid landscape in the Rocky Mountains, USA

Invasion of grasslands by woody plants has been identified as a key indicator of changes in ecosystem structure and function in arid and semi-arid rangelands throughout the world. We investigated changes in the balance between woody and herbaceous components of a semi-arid landscape in western Colorado (USA) using historical aerial photography. Aerial photographs from 1937, 1965–67, and 1994 were sampled at matched locations within overlapping photographs. We modeled change in spatial pattern and heterogeneity across the entire landscape and found a small, net decrease in woody canopy cover; however means disguised normal distributions of change that demonstrated offsetting increases and decreases. We described a region of widespread canopy decline within pinon-juniper forests between 2300 and 2600 m (7500–8500 feet) and a region of predominant increase at lower elevations, between 1800 and 2250 m (5900–7400 feet). It remains unclear whether this shift was driven by climate or by human-caused or natural disturbance. Mean conifer cover decreased within coniferous forests, which counteracted a trend of increased conifer cover in mixed forests, savanna-like woodlands, and the shrub steppe. Disturbance had a significant interaction with cover change in several communities, including forests, savanna and shrublands. Anthropogenic disturbances counteracted successional trends toward canopy closure more than wildfires, but this did not entirely explain observed canopy decline. The natural dynamics in this region also caused diverse changes rather than a simple progression towards increased forest cover. Importantly, temporal change in vegetation varied spatially across the landscape illustrating the importance of landscape level, spatially explicit analyses in characterizing temporal dynamics.