bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of the restoration of heathland on successional sites: changes in vegetation and soil chemical properties
Authors: Mitchell R.J. , Marrs R.H. , Le Duc M.G. , Auld M.H.D. 
Published: March 2003

Summary 1. Lowland heaths are high‐profile ecosystems for conservation action in Britain, but many areas have been invaded by Betula spp., Pinus sylvestris, Pteridium aquilinum and Rhododendron ponticum. As succession occurs on heaths, changes occur in both the vegetation and the soil chemical properties of the site. 2. Nine heathland sites in the Poole Basin area of Dorset were studied, where management of successional sites to restore heathland had occurred. The efficacy of heathland restoration in terms of both the vegetation and the soil chemical properties was assessed. 3. The management had allowed many heathland species to establish and the majority of sites to start to become similar to the neighbouring heathland. The reversion of increased soil nutrients was found to be more problematic, with levels of ammonium–nitrogen, phosphorus, pH, calcium and magnesium remaining greater than those of the heathland soils. 4. The vegetation and soil data were analysed using canoco (canonical correspondence analysis) and were then used to test four hypothetical models that related changes in biotic factors (vegetation) and abiotic variables (soil nutrients) following management to the success of the restoration of heathland on successional sites. 5. A second canoco analysis was carried out in which the managed sites were treated as passive samples. This model was used to measure the distances between the heath, successional and managed sites. These distances provided measures of management success and the resilience of the treated late‐successional ecosystem. 6. The successional species present before management affected the success of reversion; management of Pinus sylvestris sites was generally more successful than management of others sites, especially those invaded by Betula. The most significant effect of different management techniques resulted from litter‐stripping, which reduced the nutrients available and improved and accelerated the success of reversion.
Successional response of a tropical forest termite assemblage to experimental habitat perturbation
Authors: Davies Richard G. , Eggleton Paul , Dibog Luc , Lawton John H. , Bignell David E. , Brauman Alain , Hartmann Christian , Nunes Lina , Holt John , Rouland Corinne 
Published: March 2003

Summary 1. Research into the successional responses of tropical forest communities following disturbance has potential applications for habitat restoration. Currently little is known of how these responses relate to the recovery of biodiversity and ecosystem processes. Succession of assemblages of decomposer arthropods is essential for the recovery of the soil community and nutrient cycling processes. 2. This study investigated the successional response of a termite assemblage to the experimental perturbation of forest habitat in southern Cameroon, examining the implications for tropical forest restoration. A randomized block design consisting of four experimental perturbations of differing severity was established in an old secondary forest in the Mbalmayo Forest Reserve. Isolated control sites were left in undisturbed forest. Recovery of the termite assemblage was assessed by measuring termite species richness and abundance at regular intervals over the subsequent 12 months. 3. The speed of recovery of the termite assemblage varied with the type and extent of perturbation. In treatments involving severe soil and canopy disturbance, termite species richness and abundance recovered more rapidly when dead wood was left on the ground following perturbation. The availability of dead wood also resulted in recolonization by a subset of the termite assemblage that was distinct compositionally from that sampled from all other treatments. This subset at sites with additional dead wood included not only certain wood‐feeding species, but also soil feeders. 4. The positive effects upon the termite assemblage of leaving substantial dead wood on the ground has implications for the restoration of tropical forests following human‐induced disturbances such as logging. The accelerated recovery of termite diversity and assemblage composition is a significant component of soil community recovery and the restoration of nutrient cycles. These benefits are expected to influence soil fertility and, ultimately, forest regeneration. The duration and persistence of these effects will depend crucially on the type, scale and intensity of the original disturbance. The impact of termites on soil properties, and vice versa, clearly deserves more attention in studies of tropical forest regeneration and recovery.
Extending Ellenberg's indicator values to a new area: an algorithmic approach
Authors: Hill Mark O. , Roy David B. , Mountford J. Owen , Bunce Robert G. H. 
Published: March 2003

Summary 1. Ellenberg's indicator values scale the flora of a region along gradients reflecting light, temperature, continentality, moisture, soil pH, fertility and salinity. They can be used to monitor environmental change. 2. Ellenberg values can be extended from central Europe, for which they were defined, to nearby parts of Europe. Given a database of quadrat samples, they can be repredicted by a simple algorithm consisting of two‐way weighted averaging, followed by local regression. 3. A database of British samples was assembled from two large surveys. Ellenberg values were repredicted. 4. Except for the indicator of continentality, the correlation of repredicted and original values was in the range 0·72 (light) to 0·91 (moisture). The continentality indicator could not be adequately repredicted by the algorithm, and is unusable in Britain. 5. Discrepancies between original and repredicted values can be attributed to various causes, including wrong original values, differing ecological requirements in Britain and central Europe, biased sampling of the British range of habitats, and the occurrence of small plants in shaded or basic microhabitats within well illuminated or predominantly acid quadrats. 6. The repredicted values were generally reliable, but a small proportion was clearly wrong. Wrong values were due to either inadequate sampling of species’ realized niches in Britain or sampling with quadrats that were too large and included species that were not close associates.
Optimal release strategies for biological control agents: an application of stochastic dynamic programming to population management
Authors: Shea K. , Possingham H. P. 
Published: March 2003

Summary 1. Establishing biological control agents in the field is a major step in any classical biocontrol programme, yet there are few general guidelines to help the practitioner decide what factors might enhance the establishment of such agents. 2. A stochastic dynamic programming (SDP) approach, linked to a metapopulation model, was used to find optimal release strategies (number and size of releases), given constraints on time and the number of biocontrol agents available. By modelling within a decision‐making framework we derived rules of thumb that will enable biocontrol workers to choose between management options, depending on the current state of the system. 3. When there are few well‐established sites, making a few large releases is the optimal strategy. For other states of the system, the optimal strategy ranges from a few large releases, through a mixed strategy (a variety of release sizes), to many small releases, as the probability of establishment of smaller inocula increases. 4. Given that the probability of establishment is rarely a known entity, we also strongly recommend a mixed strategy in the early stages of a release programme, to accelerate learning and improve the chances of finding the optimal approach.
Habitat structure and egg distributions in the processionary caterpillar Ochrogaster lunifer: lessons for conservation and pest management
Authors: Floater Graham J. , Zalucki Myron P. 
Published: March 2003

Summary 1. The spatial and temporal distribution of eggs laid by herbivorous insects is a crucial component of herbivore population stability, as it influences overall mortality within the population. Thus an ecologist studying populations of an endangered butterfly can do little to increase its numbers through habitat management without knowledge of its egg‐laying patterns across individual host‐plants under different habitat management regimes. At the other end of the spectrum, a knowledge of egg‐laying behaviour can do much to control pest outbreaks by disrupting egg distributions that lead to rapid population growth. 2. The distribution of egg batches of the processionary caterpillar Ochrogaster lunifer on acacia trees was monitored in 21 habitats during 2 years in coastal Australia. The presence of egg batches on acacias was affected by host‐tree ‘quality’ (tree size and foliar chemistry that led to increased caterpillar survival) and host‐tree ‘apparency’ (the amount of vegetation surrounding host‐trees). 3. In open homogeneous habitats, more egg batches were laid on high‐quality trees, increasing potential population growth. In diverse mixed‐species habitats, more egg batches were laid on low‐quality highly apparent trees, reducing population growth and so reducing the potential for unstable population dynamics. The aggregation of batches on small apparent trees in diverse habitats led to outbreaks on these trees year after year, even when population levels were low, while site‐wide outbreaks were rare. 4. These results predict that diverse habitats with mixed plant species should increase insect aggregation and increase population stability. In contrast, in open disturbed habitats or in regular plantations, where egg batches are more evenly distributed across high‐quality hosts, populations should be more unstable, with site‐wide outbreaks and extinctions being more common. 5. Mixed planting should be used on habitat regeneration sites to increase the population stability of immigrating or reintroduced insect species. Mixed planting also increases the diversity of resources, leading to higher herbivore species richness. With regard to the conservation of single species, different practices of habitat management will need to be employed depending on whether a project is concerned with methods of rapidly increasing the abundance of an endangered insect or concerned with the maintenance of a stable, established insect population that is perhaps endemic to an area. Suggestions for habitat management in these different cases are discussed. 6. Finally, intercropping can be highly effective in reducing pest outbreaks, although the economic gains of reduced pest attack may be outweighed by reduced crop yields in mixed‐crop systems.
Effects of dieldrin on population growth rates of sparrowhawks 1963–1986
Authors: Sibly R.M. , Newton I. , Walker C.H. 
Published: March 2003

Summary 1. A recent reappraisal of the evidence of the effects of cyclodiene insecticides on sparrowhawks Accipiter nisus and kestrels Falco tinnunculus in Britain suggested that during 1963–75 at least 29% of sparrowhawks found in an eastern area of high cyclodiene use died directly from dieldrin poisoning, compared with only 6% in a more western area of low cyclodiene use. Here, these data are used in a life‐history analysis of the quantitative effects of dieldrin on some British sparrowhawk populations. Where necessary, life‐history parameters were taken from two British study populations, one stable and one increasing. 2. Four scenarios were analysed. In scenario 1, reflecting high cyclodiene use, the effect of dieldrin poisoning was to increase the instantaneous mortality rate by 0·20 year−1. Life‐history modelling revealed that this would have produced a population decline of 20% year−1 (λ = 0·82 year−1). Adding in possible sublethal effects of dieldrin produced an even more serious decline of 60% year−1 (scenario 2). 3. Data suggested that population growth rate increased linearly as population density decreased. A simple analysis omitting age structure suggested that density‐dependence would not save the scenario 2 population from extinction, but would hold the scenario 1 population at 64% of its former value (scenario 3). The available data suggest the former is correct, i.e. sublethal effects were important during the population decline. 4. During 1976–82, when use of cyclodienes was reduced, the effect of dieldrin poisoning on sparrowhawks in eastern Britain was estimated as an increased instantaneous mortality rate of 0·05 year−1. This is low enough to allow population recovery from low density, at a rate of 13% year−1 (scenario 4). 5. Another way to analyse the effects of dieldrin (or any other additional density‐independent mortality agent) is to ask what reductions in fecundity or survival could be sustained long‐term by an otherwise increasing population. The data suggested that the population could withstand a halving of fecundity (from 2·07 to 1·035) or a reduction of adult survival from 0·74 to 0·55. 6. The analyses presented are based on field data, and are thought to be reasonably realistic of the true impacts of dieldrin and other cyclodienes on British sparrowhawks.
The spatio‐temporal distribution of a rodent reservoir host of cutaneous leishmaniasis
Authors: Fichet‐Calvet E. , Jomâa I. , Zaafouri B. , Ashford R.W. , Ben‐Ismail R. , Delattre P. 
Published: March 2003

Summary 1. The rodent Psammomys obesus is the main reservoir host for Leishmania major, the causative agent of cutaneous leishmaniasis in Tunisia, much of North Africa and mid‐western Asia. An understanding of the population dynamics of this rodent is essential to establish a preventive control strategy based on the early prediction of rodent outbreaks. 2. The study of P. obesus dynamics at a regional scale requires index‐based sampling. Rodent numbers were monitored twice per year at the beginning and end of the breeding season, using transects around the Sidi Bouzid region in central Tunisia. 3. Two different types of dynamics occurred in two drainage basins. Rodents living in the northern basin were at low density and those living in the southern basin were at high density. 4. At the scale of a plot, occupied burrows were generally associated with the presence of three Chenopodiaceae: Arthrocnemum glaucum, Salsola tetrandra and Suæda fruticosa, rarely in monospecific formations. However, in dry periods, occupied burrows drifted to A. glaucum formation linked with high moisture and salinity of the soil (χ2 MacNemar = 6·26). 5. The risk of a P. obesus outbreak can be assessed by a simultaneous knowledge of flooding regimes in the drainage basins, the distribution of halophytic plant formations, and the progressive movements of the rodents as drying out proceeds. The transect indices of rodents are easily repeatable, economical and would be applicable in other developing countries where cutaneous leishmaniasis occurs. 6. This work illustrates that simple ecological methods can assist the assessment of spatial and temporal components of epidemiological risk such as the proximity between rodent colonies and human habitats at the time of outbreaks.
Winter habitat ecology of mountain caribou in relation to forest management
Authors: Terry Eliot L. , McLellan Bruce N. , Watts Glen S. 
Published: March 2003

Summary 1. During winter, mountain caribou Rangifer tarandus caribou live in late successional and old‐growth coniferous forests, where they feed almost exclusively on arboreal lichens. Because some of these forests are also valuable to the forest industry, caribou ecology and forest management remains a central conservation issue in British Columbia. To improve our understanding of caribou habitat use in relation to forest management, we investigated the winter habitat selection patterns of mountain caribou at a range of spatial scales between 1988 and 1993 in the northern Cariboo Mountains, British Columbia. 2. Within winter ranges, caribou selected forest stands dominated by subalpine fir (> 80% Abies lasiocarpa) and with moderate slopes (16–30%) during early winter (November–December). Although stands with moderately high timber volumes (201–300 m3 ha−1) were used the most during early winter, caribou used these stands in proportion to their availability. Caribou primarily used open‐canopy subalpine fir stands (i.e. parkland) later in the winter (January–March), where low stocking and inoperable timber volumes (< 100 m3 ha−1) reduced direct conflicts with forest harvesting. 3. Characteristics of subalpine forests at early winter caribou foraging areas did not differ significantly from random sites for most variables measured. However, a multivariate analysis indicated that sites used by caribou had slightly less total basal area, more moderate slopes and slightly heavier lichen loads than unused sites. 4. Within early winter foraging areas, caribou chose foraging paths with more trees and greater accessible lichen biomass per standing tree compared with random paths. Although windthrown trees and lichen litterfall were encountered infrequently, caribou rarely rejected these sources of lichen when encountered. 5. The relatively low basal area (27 m2 ha−1) and minor component of economically valuable Engelmann spruce Picea engelmannii (< 20%) at early winter caribou foraging areas suggests less conflicts with forestry compared with other caribou populations in southern British Columbia and Idaho. 6. Selection silvicultural systems may provide solutions to caribou–forestry conflicts, particularly in mid‐elevation subalpine fir stands (1325–1525 m) that may have both operable timber volumes and high caribou numbers.
Effects of water regime and competition on the establishment of a native sedge in restored wetlands
Authors: Budelsky Rachel A. , Galatowitsch Susan M. 
Published: March 2003

Summary 1.
Restoration of depressional wetlands in mid‐continental North America typically involves reflooding formerly drained basins. There have been several thousand restorations in this manner over the past 10 years. Deliberate revegetation is rarely attempted as it is assumed that native vegetation will eventually establish naturally. Carex (sedges), which occur commonly on the periphery of native wetlands and in adjacent saturated meadows, do not readily re‐establish in reflooded basins. It is unlikely that Carex will reappear without deliberate reintroduction. Criteria for introduction and establishment of native sedges do not currently exist because environmental constraints are not well understood. 2.
In this study we investigated the environmental constraints that might limit the establishment of the native wetland sedge, Carex lacustris, in reflooded wetland basins. Immature sedges were planted in three experimental wetlands with different water‐level fluctuation regimes (i.e. falling, rising, static) along an elevational gradient, to determine the effects on survival and stand development of changing water level, water depth, competition from naturally recruited vegetation, and planting density. 3.  The response of immature sedges to water‐level fluctuation in the first growing season did not indicate the outcome of mature stand development by the end of three growing seasons. Whereas initial survival and growth were lowest in the falling water basin, stem density, height and biomass were greatest under this type of water‐level fluctuation by the third growing season. 4.  Interspecific competition was most intense at the upper elevations, particularly in the rising water basin. Although sedge growth was limited by increasing water depth in the absence of competition, growth was uniformly low across all elevations in the presence of competition. Competition reduced sedge growth to differing degrees in the rising vs. falling and static water basins. 5.
Results suggest that C. lacustris can produce dense stands under a primarily annual weed community within two to three growing seasons, but that Phalaris arundinacea (reed canary grass) can preclude successful establishment of C. lacustris. 6.  Control of water‐level conditions and competition is most crucial during the first growing season to ensure appropriate conditions for successful stand establishment. The potential for growth as well as mortality is greatest during this first year. 7.
Competition can be a significant constraint on the successful establishment of C. lacustris and should be considered explicitly when developing a restoration plan.
The interactive effects of management on the productivity and plant community structure of an upland meadow: an 8‐year field trial
Authors: Smith R.S. , Shiel R.S. , Millward D. , Corkhill P. 
Published: March 2003

Summary 1.
Agricultural policy in the Pennine Dales Environmentally Sensitive Area in northern England aims to enhance plant species diversity in agriculturally improved meadows and return them to a ‘traditional’ species composition. The interacting effects of management on vegetation and productivity were tested in a split‐split‐split plot experiment. Three grazing treatments (autumn grazing with cattle and sheep, spring grazing with sheep, both regimes) were applied between 1990 and 98. Two fertilizer treatments (25 kg ha−1 N plus 12·5 kg ha−1 P2O5 and K2O, no fertilizer); three hay cut date treatments (14 June, 21 July, 1 September) and two seed addition treatments (no seed, seed of many species) were used within the grazing treatments. 2.  By 1998, all the main treatments had produced small but significant changes to plant species diversity. A particularly large increase in diversity occurred with the combination of autumn and spring grazing, 21 July hay cut date and seed addition treatments. This change was achieved by an episodic rather than a regular increase in species over time. 3.

Rhinanthus minor spread to most plots after its introduction as a constituent of the seed treatment. By 1996 it was particularly abundant in all treatment combinations that included autumn grazing, no mineral fertilizer and a July haycut. Populations of > 40 plants m−2 were associated with the lowest yields of hay. 4.

‘Unimproved‐traditional’ plant communities, mainly Festuca ovina–Agrostis capillaris–Galium saxatile grassland, occupied more than 66% of the trial area. Anthoxanthum odoratum–Geranium sylvaticum grasslands were most abundant in 1996, being primarily associated with the combination of autumn and spring grazing, 21 July and 1 September hay cut dates and seed addition treatments, over both fertilizer treatments. 5.  Yields of herbage biomass initially declined over time in all treatment combinations. Lowest yields in most years were associated with the autumn and spring grazing, 14 June cutting date and no fertilizer treatments. 6.  Management to increase the number of plant species in agriculturally improved mesotrophic grassland requires the joint implementation of appropriate cut date and grazing regimes, probably to provide regeneration niches, and the application of seed to provide species to fill these niches. The small amount of mineral fertilizer used in this experiment had a measurable effect, but was of lesser importance.