bluuebunny/crossref_metadata_2025_split huggingface dataset:
LANDSCAPE AND REGIONAL IMPACTS OF HURRICANES IN PUERTO RICO
Authors: Boose Emery R. , Serrano Mayra I. , Foster David R. 
Published: June 2007

Puerto Rico is subject to frequent and severe impacts from hurricanes, whose long‐term ecological role must be assessed on a scale of centuries. In this study we applied a method for reconstructing hurricane disturbance regimes developed in an earlier study of hurricanes in New England. Patterns of actual wind damage from historical records were analyzed for 85 hurricanes since European settlement in 1508. A simple meteorological model (HURRECON) was used to reconstruct the impacts of 43 hurricanes since 1851. Long‐term effects of topography on a landscape scale in the Luquillo Experimental Forest (LEF) were simulated with a simple topographic exposure model (EXPOS).Average return intervals across Puerto Rico for F0 damage (loss of leaves and branches) and F1 damage (scattered blowdowns, small gaps) on the Fujita scale were 4 and 6 years, respectively. At higher damage levels, a gradient was created by the direction of the storm tracks and the weakening of hurricanes over the interior mountains. Average return intervals for F2 damage (extensive blowdowns) and F3 damage (forests leveled) ranged from 15 to 33 years and 50 to 150 years, respectively, from east to west. In the LEF, the combination of steep topography and constrained peak wind directions created a complex mosaic of topographic exposure and protection, with average return intervals for F3 damage ranging from 50 years to >150 years. Actual forest damage was strongly dependent on land‐use history and the effects of recent hurricanes. Annual and decadal timing of hurricanes varied widely. There was no clear centennial‐scale trend in the number of major hurricanes over the historical period.
IDENTIFYING BREEDING HABITAT FOR THE IBERIAN LYNX: INFERENCES FROM A FINE‐SCALE SPATIAL ANALYSIS
Authors: Fernández Néstor , Delibes Miguel , Palomares Francisco , Mladenoff David J. 
Published: June 2007

Empirical landscape habitat models are valuable tools for addressing species conservation issues in heterogeneous landscapes. These have been particularly useful for animal populations requiring extensive areas, like large mammalian carnivores. Although models are scale‐dependent, they are often based exclusively on coarse‐grained information on landscape structure and species distribution. However, accurate discrimination and quality assessment of breeding habitats may require more detailed information on both individuals' habitat use and landscape patterns.Here, we modeled breeding habitat for the Iberian lynx (Lynx pardinus), an endangered specialist of Mediterranean native ecosystems, in a human‐dominated landscape. For this, we used radiotelemetry data on breeding individuals and fine‐grained landscape variables obtained over an areal extent encompassing an entire lynx metapopulation. In addition, we restricted the study domain to areas of potential presence within this extent based on previous habitat analyses. This fine‐scale landscape analysis and design aimed to test whether it was possible to obtain detailed inferences on breeding habitat distribution and quality within more coarsely defined habitats that only indicate where the species can be found. Landscape composition factors (i.e., fine‐grain variables of landscape pattern within territories) and context factors (variables on geographical location of territories) were combined in different candidate habitat models. These reflected various hypotheses involving territory presence and size, including vegetation structure characteristics, landscape heterogeneity and complexity, favorable prey habitat, and human disturbance. The best approximating model for territory presence included only one landscape composition variable, namely, density of ecotones between scrubland and pastureland, which favored presence. For this model, classification accuracy was >80% in 94% of cross‐validation tests performed. The best approximating model for territory size explained 65% of the variation in size and included also density of ecotones, plus mean coverage of tall shrubs within territories; both correlated negatively with size. We show how these predictors are also related to prey density and suggest that this low‐hierarchical‐level relationship between the prey and patterns of the landscape can be interpreted as a likely mechanism explaining breeding habitat distribution and quality at a higher level. Our approach shows the potential of fine‐scale landscape analysis to understand patterns of breeder abundance, and to better manage population viability of threatened species in human‐populated areas.
LAND SYSTEMS AS SURROGATES FOR BIODIVERSITY IN CONSERVATION PLANNING
Authors: Oliver Ian , Holmes Andrew , Dangerfield J. Mark , Gillings Michael , Pik Anthony J. , Britton David R. , Holley Marita , Montgomery Margaret E. , Raison Madeline , Logan Vicki , Pressey Robert L. , Beattie Andrew J. 
Published: June 2007

Environmental surrogates (land classes) for the distribution of biodiversity are increasingly being used for conservation planning. However, data that demonstrate coincident patterns in land classes and biodiversity are limited. We ask the overall question, “Are land systems effective surrogates for the spatial configuration of biodiversity for conservation planning?” and we address three specific questions: (1) Do different land systems represent different biological assemblages? (2) Do biological assemblages on the same land system remain similar with increasing geographic separation? and (3) Do biological assemblages on the same land system remain similar with increasing land system isolation? Vascular plants, invertebrates, and microbiota were surveyed from 24 sites in four land systems in arid northwest New South Wales, Australia. Within each land system, sites were located to give a hierarchy of inter‐site distances, and land systems were classified as either “low isolation” (large and continuous) or “high isolation” (small patches interspersed among other land systems).Each type of land system supported components of biodiversity either not found, or found infrequently, on other land systems, suggesting that land systems function as surrogates for biodiversity, and that conservation‐area networks representing land‐system diversity will also represent biological diversity. However, the majority of taxa were found on more than one land‐system type, suggesting that a large proportion of the plant, arthropod, and microbial biodiversity may be characterized by widespread species with low fidelity to particular land systems. Significant relationships between geographic distance among sites and differences among assemblages were revealed for all taxa except the microbiota. Therefore, as sites on the same land system were located farther apart, the assemblages at those sites became more different. This finding strongly suggests that conservation planning based on land‐system diversity should also sample the geographic range occupied by each land system. Land‐system isolation was not revealed to be a significant source of variation in assemblage composition. Our research finds support for environmental surrogates for biodiversity in conservation planning, specifically the use of land systems and similarly derived land classifications. However, the need for explicit modeling of geographic distance in conservation planning is clearly indicated.
VALIDATION OF SIMULATED RUNOFF FROM SIX TERRESTRIAL ECOSYSTEM MODELS: RESULTS FROM VEMAP
Authors: Gordon W. S. , Famiglietti J. S. , Fowler N. L. , Kittel T. G. F. , Hibbard K. A. 
Published: June 2007

Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) Phase 2 model experiments investigated the response of biogeochemical and dynamic global vegetation models (DGVMs) to differences in climate over the conterminous United States. This was accomplished by simulating ecosystem processes using historical climate and atmospheric CO2 records from 1895–1993. We evaluated the behavior of six models (Biome‐BGC, Century, GTEC, LPJ, MC1, and TEM) by comparing simulated runoff in 13 watersheds to gauged streamflow from the Hydro‐Climatic Data Network. Metrics used to assess the “goodness of fit” between simulated and observed values were: (1) Pearson's r to evaluate the overall data set, (2) Kendall's τ to gauge seasonality trends as derived from a time‐series analysis of monthly runoff, and (3) three measures of absolute and relative error.We found small differences in performance among the six models over all watersheds. However, the models yielded highly divergent results depending upon the watershed analyzed. Performance of the ensemble of models in a watershed was positively correlated with observed streamflow: models in the wettest watersheds in this study were associated with the highest model correlations and largest absolute errors, and models in the driest watersheds were associated with the lowest correlations and smallest absolute errors. Mean relative error was small and nearly constant across watersheds. A bias estimator showed that the models tended to underestimate runoff in wet watersheds and overestimate runoff in dry watersheds. Analysis of long‐term trends in runoff using a moving‐average approach demonstrated the ability of the models to reproduce temporal variation in observed data, even though quantitative differences among models were large.Models relying on prescribed vegetation (Biome‐BGC, Century, and TEM) outperformed the two DGVMs (LPJ and MC1); GTEC gave the poorest fit to observations due to the absence of an evaporation function and a snow routine. Across all 13 watersheds, TEM ranked the highest in model performance. The validation results presented here suggest that improvements in the simulation of hydrologic processes in land‐surface models will come, in part, from a more realistic representation of subgrid‐scale soil moisture and from a more detailed understanding and representation of subsurface processes.
INTEGRATING REPRESENTATION AND VULNERABILITY: TWO APPROACHES FOR PRIORITIZING AREAS FOR CONSERVATION
Authors: Lawler Joshua J. , White Denis , Master Lawrence L. 
Published: June 2007

Reserves protect biodiversity by ameliorating the threats to the persistence of populations. Methods for efficient, systematic reserve selection have generally been designed to maximize the protection of biodiversity while minimizing the costs of reserves. These techniques have not directly addressed the factors threatening species at specific sites. By incorporating measures of site vulnerability into reserve selection procedures, conservation planners can prioritize sites based on both representing biodiversity and the immediacy of factors threatening it.Here we develop two complementary approaches for identifying areas for conservation based on species composition and potential threats facing the species. These approaches build on two established methods of systematic reserve selection. The first approach involves mapping irreplaceability (a statistic derived from reserve selection theory that measures the potential importance of a site for protecting all species) and the degree to which the area is vulnerable to threats from three basic anthropogenic factors (the percentages of a site devoted to agriculture, to urban and suburban development, and to open mines). We classified areas with respect to both irreplaceability and the three indicators of vulnerability, producing a continuous ranking of all sites based on these factors. Our second approach was to incorporate site vulnerability into a reserve selection algorithm. This approach allowed us to locate those sets of sites that protected all species and were most likely to be threatened by human activities. These two analyses can provide regional‐scale guidance for conservation in the Mid‐Atlantic region of the United States, and they demonstrate two potential tools for solving complex conservation‐planning problems.
NON‐TIMBER FOREST PRODUCT EXTRACTION: EFFECTS OF HARVEST AND BROWSING ON AN UNDERSTORY PALM
Authors: Endress Bryan A. , Gorchov David L. , Noble Robert B. 
Published: June 2007

Despite the advocacy for non‐timber forest product (NTFP) extraction as a form of sustainable development, the population ecology of many NTFPs remains unstudied, making it difficult to assess the ecological impacts of extraction. We investigated the demography and population dynamics of the harvested, understory palm, Chamaedorea radicalis in the El Cielo Biosphere Reserve, Mexico. Our objectives were: (1) to describe patterns of C. radicalis abundance and population size structure, (2) to document C. radicalis demography, (3) to test experimentally how this demography was affected by different leaf harvest regimes and livestock browse intensities, and (4) to project their effects on transient and long‐term population dynamics.Data on palm abundance and population size structure were collected from belt‐transects along hillsides. We also exposed 100 adult palms to each of five leaf harvest treatments (N = 500): control, harvest once per year, harvest twice per year, harvest four times per year, and a modified four times per year harvest where only one leaf was removed each harvest. Browse experiments were conducted to assess the effect of burro browse on demography. Experiments were monitored over two years, and results were incorporated with other demographic data to parameterize stage‐based (Lefkovitch) matrices for each year × treatment combination.Topographic position influenced both population size structure and density, with a gradient from valleys (727 palms/ha) to upper slopes (5513 palms/ha). Palm demography was characterized by low mortality, low reproductive activity, and high seed germination rates. Leaf harvest increased adult mortality and reduced fecundity, and it was projected to reduce λ (finite rate of increase). However, λ for harvested populations did not differ significantly from 1. Browsing increased mortality of seedlings, juveniles, and small adults, resulting in populations projected to decline (λ < 1).These findings indicate that browsing by free‐range livestock impacts C. radicalis populations more than leaf harvest and could explain the low density and skewed size structure in valleys. The modest impact of leaf harvest treatments is due in part to the reduction in the availability of marketable leaves. Detection of such feedbacks exemplifies how the incorporation of human management practices enhances the insights that experiments bring to studies of the population ecology of NTFPs.
NET CARBON FLUXES FROM FOREST CLEARANCE AND REGROWTH IN THE AMAZON
Authors: Steininger Marc K. 
Published: June 2007

Estimates of net carbon exchange resulting from forest clearance and regrowth were made for three areas in the Brazilian and Bolivian Amazon. The study areas, ranging in size from 600 to 10 000 km2, include communities that practice a range of land uses from small‐scale, rotational agriculture to long‐term pasture. Carbon emissions from deforestation were estimated based on rates of deforestation derived from Landsat satellite data and published estimates of mature forest biomass. Estimates of carbon uptake by secondary forest regrowth were based on area estimates from the satellite data and biomass estimates from field surveys. Estimates of carbon emissions from the clearance of secondary forest were included. The total carbon emissions were partitioned into that immediately released by biomass burning during clearance and that from subsequent decomposition and burning of felled biomass. A range of net carbon fluxes from secondary forest regrowth and clearance was estimated by extrapolating land‐use patterns in each study area to the entire area of deforested landscape in Amazonian Brazil and Bolivia, and by varying average biomass accumulation rate of regrowing forest and fallow period.Over 60 km2 of forest were cleared from 1988 to 1995 in each of the Brazilian study areas, and over 940 km2 were cleared from 1986 to 1996 in the Bolivian study area. This resulted in 30–200 Mg C/yr emitted from biomass burning during deforestation. If the carbon that is committed to subsequent burning and decomposition of felled biomass is included, total committed emissions of 75–650 Mg C/yr resulted from deforestation in each study area. The carbon uptake by secondary forests was 33–435 Mg C/yr. However, emissions from the reclearance of secondary forests were nearly as large: 17–365 Mg C/yr. Extrapolation of these results to the Brazilian and Bolivian Amazon suggests that, at the national level, carbon uptake by secondary forests offset less than one‐fifth of the carbon emissions from deforestation. Despite differences in land‐use pattern, average fallow period, and rate of biomass accumulation used in the extrapolation, net carbon uptake by secondary forests was consistently small when compared to the total emissions from deforestation.
A NEW TECHNIQUE FOR MAXIMUM‐LIKELIHOOD CANONICAL GAUSSIAN ORDINATION
Authors: Yee Thomas W. 
Published: June 2007

Canonical correspondence analysis (CCA) is probably the most popular ordination method in community ecology. However, it is only a heuristic approximation to maximum‐likelihood estimated canonical Gaussian ordination (CGO), which is the “ideal” method. When proposed in the mid‐1980s, CCA held two advantages over CGO: it was computationally cheaper, and its algorithm was not complex. However, an exponential increase in computing speed over the last two decades has meant that computation cost is no longer such a compelling advantage. The computational complexity of CGO has always been its major difficulty, even though it is statistically more sound and simpler to understand than CCA. For these reasons, no general computational framework or software has appeared until now.This article proposes a new class of statistical regression models called quadratic reduced‐rank vector generalized linear models (QRR‐VGLMs) for maximum‐likelihood estimated CGO. This is achieved by extending a recently developed class of statistical models called RR‐VGLMs. The extension is named QRR‐VGLMs because of the addition of a quadratic form to each linear predictor, with the consequence that bell‐shaped responses can be modeled as functions of latent environmental variables or gradients. QRR‐VGLMs have several major positive features; for example, their framework is unifying and broad, so that canonical Gaussian ordination can potentially be performed on a wide range of data types. The two most important special cases of CGO in ecology, multispecies presence/ absence and Poisson abundance data, are considered in this article. The methodology is illustrated with a real data set using a software implementation written by the author in the S statistical language. The code, called the VGAM package in R, is object‐oriented and free, and it allows QRR‐VGLMs to be fitted to moderate‐sized data sets conforming reasonably closely to the Gaussian model.
EFFECTS OF PAST LAND USE ON SPATIAL HETEROGENEITY OF SOIL NUTRIENTS IN SOUTHERN APPALACHIAN FORESTS
Authors: Fraterrigo Jennifer M. , Turner Monica G. , Pearson Scott M. , Dixon Philip 
Published: June 2007

We examined patterns of nutrient heterogeneity in the mineral soil (0–15 cm depth) of 13 southern Appalachian forest stands in western North Carolina >60 yr after abandonment from pasture or timber harvest to investigate the long‐term effects of land use on the spatial distribution and supply of soil resources. We measured soil carbon (C), nitrogen (N), acid‐extractable phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations and pools, and potential net N mineralization and nitrification rates to evaluate differences in mean values, variance at multiple scales, and fine‐scale spatial structure.While comparisons of averaged values rarely indicated that historical land use had an enduring effect on mineral soil or N cycling, differences in variance and spatial structure suggested that former activities continue to influence nutrient distributions by altering their spatial heterogeneity. Patterns differed by element, but generally variance of soil C, N, and Ca decreased and variance of soil P, K, and Mg increased with intensive past land use. Changes in variance were most conspicuous and consistent locally (<28 m), but C, Ca, P, and Mg also exhibited appreciable differences in variance at coarser scales (>150 m). High variability in soil compaction resulted in some changes in scale‐dependent patterns of nutrient pool variance compared with nutrient concentration variance. It also affected the variance of N cycling rates, such that mass‐based rates varied less and area‐based rates varied more in intensively used areas than in reference stands. Geostatistical analysis suggested that past land use homogenized the spatial structure of soil C, K, and P in former pastures. In contrast, logged stands had highly variable spatial patterning for Ca.These results suggest that land use has persistent, multi‐decadal effects on the spatial heterogeneity of soil resources, which may not be detectable when values are averaged across sites. By interacting with patterns of variability in the plant and heterotrophic biota, differences in nutrient distribution and supply could alter the composition and diversity of forest ecosystems. Scale‐dependent changes in nutrient heterogeneity could also complicate efforts to determine biogeochemical budgets and cycling rates.
INFLUENCE OF LANDSCAPE STRUCTURE AND CLIMATE VARIABILITY ON A LATE HOLOCENE PLANT MIGRATION
Authors: Lyford Mark E. , Jackson Stephen T. , Betancourt Julio L. , Gray Stephen T. 
Published: June 2007

We analyzed and radiocarbon‐dated 205 fossil woodrat middens from 14 sites in central and northern Wyoming and adjacent Utah and Montana to document spatiotemporal patterns of Holocene invasion by Utah juniper (Juniperus osteosperma). Holocene migration into central and northern Wyoming and southern Montana from the south proceeded by a series of long‐distance dispersal events, which were paced by climate variability and structured by the geographic distribution and connectivity of suitable habitats on the landscape. The migration of Utah juniper into the region involved multiple long‐distance dispersal events, ranging from 30 to 135 km. One of the earliest established populations, on East Pryor Mountain in south central Montana, is currently the northernmost population of the species. Establishment by long‐distance dispersal of that population and another in the Bighorn Basin occurred during a period of relatively dry climate between 7500 and 5400 years ago. Further expansion of these initial colonizing populations and backfilling to occupy suitable sites to the south was delayed during a wet period from 5400 to 2800 years ago. Development of dry conditions 2800 years ago led to a rapid expansion in which Utah juniper colonized sites throughout its current range. Landscape structure and climate variability play important roles in governing the pattern and pace of natural invasions and deserve close attention in studying and modeling plant invasions, whether exotic or natural.Corresponding Editor: D. R. Strong