bluuebunny/crossref_metadata_2025_split huggingface dataset:
A portable LIDAR system for rapid determination of forest canopy structure
Authors: PARKER GEOFFREY G. , HARDING DAVID J. , BERGER MICHELLE L. 
Published: July 2004

SummaryThe functional characteristics of forests are related to the organization of their canopies. However, understanding the relationship between canopy structure and function has been limited by a paucity of methods for determining structure at scales consistent with those of function measurements.We describe here a portable system, assembled from commercially available components, for acquiring measurements of distances to overhead plant surfaces. These measurements can be aggregated to assess canopy structure rapidly at scales of ecological interest. Deployed from the forest floor, the system includes a narrow‐beam rapidly pulsed first‐return laser rangefinder coupled with a data recording system.Tests in an age sequence of broad‐leaved closed‐canopy forests showed that the system provides results significantly more rapidly than previous methods, at spatial scales as small as 1 m in all dimensions. The estimated mean vertical canopy structure is consistent with that found from more laborious, manual approaches, such as the foliage height profile method. The system has some biases due to beam width and range averaging but, from a variety of tests, we found these have relatively little effect on the structure estimates.Various field sampling schemes and methods of aggregating the measurements yield a variety of representations of structure, including mean profiles, tomographic sections, three‐dimensional distributions of canopy surface density and maximum height surfaces. Derivable summary measures include canopy cover and area index, porosity, the size distribution of overhead openings and indices of structural complexity. Moreover, the approach can provide estimates of spatial variability and covariance not previously obtainable.Synthesis and applications.Portable light detection and ranging (LIDAR) systems, such as the one we describe here, provide a new tool for rapid measurement of small‐scale forest structure. These can contribute efficiently and relatively inexpensively to canopy research and forestry programmes, covering a range of ecological and production needs.
Determining impacts of habitat modification on diversity of tropical forest fauna: the importance of spatial scale
Authors: HILL JANE K. , HAMER KEITH C. 
Published: July 2004

Summary

There is an urgent need to understand the impacts of anthropogenic habitat disturbance on biodiversity in tropical forests, but no consensus has yet emerged. We reviewed the literature for the most frequently studied taxon (birds, 37 studies) and found that increased and decreased diversity in response to disturbance (selective logging and shifting agriculture) were reported with approximately equal frequency.
The spatial scale at which studies were carried out significantly affected the reported response to disturbance: studies where disturbed and undisturbed habitats were sampled at large spatial scales were more likely to report increased diversity following disturbance, whereas studies that sampled habitats at small spatial scales were more likely to report decreased diversity. These results were not a consequence of sampling method: we divided the studies into those using capture methods and those using observation methods and the same result was obtained when the analysis was restricted to only those studies using observation methods.
Previously, we have shown that reported impacts of disturbance on Lepidoptera are also affected by the spatial scale of study. We reviewed the Lepidoptera literature published since then and showed that all 12 new studies conformed to the predicted pattern.
While sampling scale significantly affected the reported responses of both birds and Lepidoptera, there were opposite effects of scale in the two taxa: large‐scale bird studies and small‐scale Lepidoptera studies were more likely to report increased diversity following disturbance. Bird studies were generally carried out at larger spatial scales than those of Lepidoptera and these opposite impacts of scale were probably due to a non‐linear effect of habitat disturbance on habitat heterogeneity at different spatial scales.
Synthesis and applications. The rapid loss and degradation of tropical forests means that an understanding of the general patterns of responses of species to habitat disturbance is urgently needed. However, there has been little discussion of the most appropriate methods to ensure comparability of results between studies. Data presented here indicate that the spatial scale of sampling chosen in studies has a marked effect on the results obtained, and future studies need to account for this by examining explicitly the effects of disturbance at different spatial scales. The effect of spatial scale differs between taxa, and this may explain why the search for indicator taxa of disturbance effects has so far proved elusive.
The effects of disturbance on behaviour, habitat use and energy of spring staging snow geese
Authors: BÉCHET ARNAUD , GIROUX JEAN‐FRANCOIS , GAUTHIER GILLES 
Published: July 2004

Summary

For many species, human‐induced disturbances can severely influence an individual's pay‐off; however, energy‐cost variations from different disturbance types have rarely been reported.
We evaluated the dynamic behavioural responses of staging greater snow geese Anser caerulescens atlanticus to different types of disturbance in southern Quebec, Canada, between 1997 and 2000. We specifically considered the impact of a unique measure, a spring conservation hunt implemented in agricultural habitats in 1999.
We tracked 237 radio‐tagged females for 2764 h and recorded 697 take‐offs following fortuitous disturbance, scaring and hunting in three regions characterized by different habitats. Geese used cornfields in south‐western Quebec, Scirpus marshes and hayfields in the upper St Lawrence estuary, and Spartina marshes and hayfields in the lower estuary.
Overall, disturbance levels increased in the upper and lower estuary during years with hunting, mostly through an increase in hunting and scaring activities.
The probability of geese returning to a refuge after disturbance in agricultural habitats increased in years with hunting except in the corn‐growing region. The short‐term energy gain of geese resuming feeding after disturbance was less than before disturbance, and this difference was greater in years with hunting. Distances flown after disturbance decreased with flock size and were longer after scaring and hunting than after fortuitous disturbances in the Scirpus region.
Overall, habitat use varied among years and associated estimated energy gain decreased markedly in both years with hunting in the Spartina and corn‐growing region, but did not change in the Scirpus region. Changes in behaviour due to disturbance, and especially those associated with hunting, probably contributed to the reduced body condition of staging greater snow geese during years with hunting.
Synthesis and applications. From a methodological viewpoint, we highlight the importance of tracking the behaviour of individual animals after disturbance to properly evaluate its impact. From a conservation perspective, we provide empirical arguments to limit the hunting of breeding waterfowl during their prenuptial migration in order to facilitate their fattening and forthcoming reproduction. From a management standpoint, we suggest that a side‐effect of disturbance induced by spring hunting to control overabundant populations may be reduced fattening and breeding output among birds that survive. Together, these data emphasize further the importance of measuring the direct and indirect effects of disturbance rather than assuming effects from the incidence of the disturbance alone.
Can we mitigate animal–vehicle accidents using predictive models?
Authors: MALO JUAN E. , SUÁREZ FRANCISCO , DÍEZ ALBERTO 
Published: July 2004

Summary

Vehicle collisions with wild animals are a serious problem that justifies the widespread application of mitigation measures such as road fencing and provision of crossing structures. Models that predict the best location for mitigation measures can improve wildlife survival and road safety.
A database of 2067 records of animal–vehicle collisions was used to create two data sets at different spatial scales. The first comprised records of road sections of 1 km length with high rates of collision in combination with road sections with a low number of collisions. The second comprised records of collision and no collision incidence at points on the road system at a 0·1‐km scale. Logistic regression was used to investigate the relationship between incidence of collision and measured habitat features in each data set. The models were validated with a subset of the original data not used in developing the models.
Road sections with high collision rates were associated with areas having high forest cover, low crop cover, low numbers of buildings and high habitat diversity. The fitted model achieved a significant predictive success during validation (χ2 = 4·82, 1 d.f., P= 0·028), with more than 70% correct classification of cases.
Specific collision points typically had no guard‐rails or lateral embankments, were not near underpasses, crossroads or buildings, and featured hedges or woodland near the road. The fitted model also showed a significant predictive power in validation (64% correct classification, χ2 = 9·51, 1 d.f., P= 0·002) and accurately predicted 85·1% of collision points.
Synthesis and applications. Predictive models of animal–vehicle collision locations should be used at both a landscape level and a local scale during the process of road design and implementation of mitigation measures. Modelling of collision risk could inform decisions on road alignment and on the exact location of crossing structures for mammals, to improve wildlife survival and road safety. This is the first study integrating both landscape and local scales of analysis for the variables associated with animal–vehicle collisions.
Faecal density counts for monitoring changes in red fox numbers in rural Britain
Authors: WEBBON CHARLOTTE C. , BAKER PHILIP J. , HARRIS STEPHEN 
Published: July 2004

Summary

Quantifying animal density is a fundamental requirement for the successful management of canid species. Faecal transects along linear features represent a cost‐effective means of quantifying relative density. However, it is unclear whether such counts can be utilized to estimate absolute density.
In Britain, due to proposed legislative changes in permitted culling practices, and as part of a wider monitoring programme, the current and future density of red foxes Vulpes vulpes is of applied interest. In this study, we counted fox faeces in 444 1‐km squares throughout mainland Britain to construct a baseline index of fox density against which future changes could be measured. By incorporating estimates of the defecation rate and the proportion of scats associated with linear features, we estimated absolute density in seven landscapes. These estimates were compared with existing data on fox density.
On average, captive foxes consumed 0·85 kg food day−1. Defecation rate (8 scats fox−1 day−1) was not affected by the type of food consumed.
The proportion of scats associated with linear features was determined by feeding individual free‐living foxes a known amount of food containing an indigestible marker. On average, 5·7% of scats were deposited along linear features.
Mean fox density in landscapes ranged from 0·21 to 2·23 foxes km−2. These estimates agreed closely with the limited data available on fox density in Britain. The total rural fox population was estimated to be 225 000 foxes (95% confidence interval 179 000–271 000). Including foxes in urban areas, the total national population is estimated to be approximately 258 000 individuals.
Synthesis and applications. The results suggest that faecal density counts have the potential to be used to estimate fox density over large spatial scales, although further work on estimating the proportion of scats associated with linear features and the use of faeces in territorial marking by canids is required.
Integrating herbicide and mechanical control treatments with fire and biological control to manage an invasive wetland shrub, Mimosa pigra
Authors: PAYNTER QUENTIN , FLANAGAN GRANT J. 
Published: July 2004

Summary

In Australia, biological control is a promising long‐term management strategy for the woody weed mimosa Mimosa pigra but does not yet provide adequate control. Other management techniques, including herbicides and fire, can be ineffective and their impact on biological control agents is unknown. We investigated the potential of integrating control techniques, including biological control, to provide cost‐effective management.
A large‐scale (128‐ha) split‐plot experiment was performed to measure the impact of single and repeated applications of herbicide and crushing by bulldozer, either alone or in combination, on both mimosa and five introduced biological control agents that were abundant at the site. Herbicides were applied over three seasons (1997–99) and all plots were burned in 2000.
The impact of control options on mimosa cover, biomass, number of stems per ha, stand size structure and seedling regeneration was determined by aerial photography and by sampling permanent and random quadrats. Biological control agent abundance was also quantified.
In isolation, herbicide, bulldozing and fire were not effective, but several combinations of techniques cleared mimosa thickets and promoted establishment of competing vegetation that inhibited mimosa regeneration from seed.
Depending on the species, biological control agent abundance on surviving mimosa plants was either unchanged or increased following herbicide and/or bulldozing treatments. All agents recolonized regenerating mimosa within 1 year of the fire treatment, and Neurostrota gunniella increased dramatically. Carmenta mimosa abundance, however, was reduced by fire.
The abundance of N. gunniella increased in response to all treatments, which we attribute to attack by this species being most common along stand edges. Control treatments separated monocultures of mimosa into smaller patches, thereby increasing the ratio of ‘edge’ to ‘thicket’ plants. The proportion of plants susceptible to N. gunniella attack increased as a result.
Synthesis and applications. We conclude that integrating control techniques can successfully control dense mimosa thickets. Biological control integrates well with other control options and should lead to significant cost reductions for mimosa management. To maximize this benefit, integrated weed management plans should be designed to integrate biological control fully with other methods, rather than separate them spatially or temporarily.
On the loss of saltmarshes in south‐east England and the relationship with Nereis diversicolor
Authors: MORRIS R. K. A. , REACH I. S. , DUFFY M. J. , COLLINS T. S. , LEAFE R. N. 
Published: July 2004

Summary

Two papers, Hughes & Paramor (2004) and Paramor & Hughes (2004), published in Journal of Applied Ecology are discussed. These papers suggest that saltmarsh erosion is linked to bioturbation, and concentrate on the role of the ragworm Nereis diversicolor. The authors also suggest that new saltmarsh will not develop in realignment sites because bioturbation will prevent the establishment of saltmarsh plants. We dispute their analysis and offer evidence that inferences derived from their experimental work are erroneous.
Experience from the current range of managed realignment sites in the UK shows that saltmarsh communities are developing, and include the lower marsh Salicornia communities that they suggest are vulnerable to the effects of bioturbation and grazing by N. diversicolor.
Further evidence of the benefits of managed realignment, even in situations where realignment sites lie below existing seaward mudflat levels, is provided by the saltmarshes that developed on sites that were not re‐enclosed after the 1953 flood in eastern England.
We highlight the importance of maintaining positive sediment budgets in order that saltmarshes may continue to adjust to sea level rise and to ensure that sufficient sediment exists to allow realignment sites to warp up to levels at which pioneer saltmarsh may develop.
We also draw attention to a range of initiatives that seek to maintain sediment levels within estuaries in south‐east England, and highlight the broader conceptual approach that looks upon dredged sediment as an important resource and not a waste material. None of these is designed to change permanently the estuarine tidal prism, as suggested by Hughes & Paramor (2004).
Synthesis and applications. We present evidence to show that coastal realignment is effective in managing and reversing saltmarsh erosion. We dispute the conclusions presented in the recent papers by Hughes & Paramor (2004) and Paramor & Hughes (2004). We suggest that infauna play an essential role in saltmarsh ecology and that N. diversicolor does not play a destructive role in saltmarsh establishment. In the broader context of coastal management, the long‐term benefits of managed realignment in sea defence and in delivering nature conservation benefit are quite clear. Sustainable sediment management will play a key role in sustaining saltmarsh habitats in the future.
Fragmented landscapes, road mortality and patch connectivity: modelling influences on the dispersal of Eurasian lynx
Authors: KRAMER‐SCHADT STEPHANIE , REVILLA ELOY , WIEGAND THORSTEN , BREITENMOSER URS 
Published: July 2004

Summary

Although many reintroduction schemes for the Eurasian lynx Lynx lynx in Germany have been discussed, the implications of connectivity between suitable patches have not been assessed.
We introduce an individual‐based, spatially explicit dispersal model to assess the probability of a dispersing animal reaching another suitable patch in the complex heterogeneous German landscape, with its dense transport system. The dispersal model was calibrated using telemetric data from the Swiss Jura and based on a map of potential lynx dispersal habitat.
Most suitable patches could be interconnected by movements of dispersing lynx within 10 years of reintroduction. However, when realistic levels of mortality risks on roads were applied, most patches become isolated except along the German–Czech border. Consequently, patch connectivity is limited not so much by the distribution of dispersal habitat but by the high mortality of dispersing lynx. Accordingly, rather than solely investing in habitat restoration, management efforts should try to reduce road mortality.
Synthesis and applications. Our approach illustrates how spatially explicit dispersal models can guide conservation efforts and reintroduction programmes even where data are scarce. Clear limits imposed by substantial road mortality will affect dispersing lynx as well as other large carnivores, unless offset by careful road‐crossing management or by the careful selection of release points in reintroduction programmes.
Functional traits of graminoids in semi‐arid steppes: a test of grazing histories
Authors: ADLER PETER B. , MILCHUNAS DANIEL G. , LAUENROTH WILLIAM K. , SALA OSVALDO E. , BURKE INGRID C. 
Published: July 2004

Summary

Understanding variability in ecosystem response to grazing is essential for improving management. Recent efforts have focused on the role of plant functional traits but do not identify factors influencing trait development. As traits are legacies of historical selective pressures, they may indicate the importance of a plant community's evolutionary history of grazing.
We compared grazing‐resistance traits of graminoids collected in the Patagonian steppe of Argentina, presumed to have a long evolutionary history of grazing, and the sagebrush steppe of the north‐western USA, known to have a short grazing history. The purpose of this comparison was to test the influence of grazing history and aridity on resistance traits, and to generate predictions about the vulnerability of these ecosystems to grazing impacts. We measured both morphology and leaf chemical composition on common species from an arid and a semi‐arid site in each region, then performed a principal components analysis on the species‐by‐traits matrix.
The first axis of the ordination was correlated with measures of forage quality such as leaf tensile strength, fibre and nitrogen content, while the second axis was correlated with plant stature. The dominant species from the drier Patagonia site scored significantly lower on the first axis (lower forage quality) than dominants from the sagebrush steppe. Plants from the wetter Patagonia site were intermediate in forage quality. Sagebrush steppe species scored significantly higher on the second axis (taller) but this difference was not significant when we considered only dominant species.
The intercontinental differences in plant traits are consistent with evidence indicating a longer evolutionary history of grazing in Patagonia. Differences in traits between the dry and wet sites in Patagonia are consistent with the hypothesis that aridity promotes grazing resistance, although trait contrasts between the drier and wetter sagebrush sites were not significant.
Differences in soil texture, which may influence nitrogen availability, offer an alternative explanation for differences in forage quality between Patagonia and sagebrush steppe, and between the drier and wetter sites within Patagonia.
Synthesis and applications. Our comparison of plant traits suggests that interactions between evolutionary history of grazing and abiotic covariates, especially soil texture, have selected for low forage quality in Patagonia relative to sagebrush steppe. This contrast in grazing‐resistance traits leads to the prediction that livestock grazing will have less impact on upland plant communities in Patagonian steppe compared with the sagebrush steppe of the USA, particularly if low nitrogen content limits offtake. Plant functional traits represent an easily quantified link between evolutionary grazing history and ecosystem responses to contemporary management.