Showing papers in "Ecological Applications in 2002"
TL;DR: A broad and flexible perspective on ecological restoration of Southwestern (U.S.) ponderosa pine forests has been discussed in this article, where the authors suggest principles for ecologically sound restoration that immediately reduce crown fire risk and incrementally return natural variability and resilience to Southwestern forests, and present ecological perspectives on several forest restoration approaches.
Abstract: The purpose of this paper is to promote a broad and flexible perspective on ecological restoration of Southwestern (U.S.) ponderosa pine forests. Ponderosa pine forests in the region have been radically altered by Euro-American land uses, including livestock grazing, fire suppression, and logging. Dense thickets of young trees now abound, old- growth and biodiversity have declined, and human and ecological communities are in- creasingly vulnerable to destructive crown fires. A consensus has emerged that it is urgent to restore more natural conditions to these forests. Efforts to restore Southwestern forests will require extensive projects employing varying combinations of young-tree thinning and reintroduction of low-intensity fires. Treatments must be flexible enough to recognize and accommodate: high levels of natural heterogeneity; dynamic ecosystems; wildlife and other biodiversity considerations; scientific uncertainty; and the challenges of on-the-ground im- plementation. Ecological restoration should reset ecosystem trends toward an envelope of ''natural variability,'' including the reestablishment of natural processes. Reconstructed historic reference conditions are best used as general guides rather than rigid restoration prescriptions. In the long term, the best way to align forest conditions to track ongoing climate changes is to restore fire, which naturally correlates with current climate. Some stands need substantial structural manipulation (thinning) before fire can safely be reintro- duced. In other areas, such as large wilderness and roadless areas, fire alone may suffice as the main tool of ecological restoration, recreating the natural interaction of structure and process. Impatience, overreaction to crown fire risks, extractive economics, or hubris could lead to widespread application of highly intrusive treatments that may further damage forest ecosystems. Investments in research and monitoring of restoration treatments are essential to refine restoration methods. We support the development and implementation of a diverse range of scientifically viable restoration approaches in these forests, suggest principles for ecologically sound restoration that immediately reduce crown fire risk and incrementally return natural variability and resilience to Southwestern forests, and present ecological perspectives on several forest restoration approaches.
936 citations
TL;DR: In this paper, the authors brought together forest sector C budgets for Canada, United States, Europe, Russia, and China that were derived from forest inventory information, allometric relationships, and supplementary data sets and models.
Abstract: There is general agreement that terrestrial systems in the Northern Hemisphere provide a significant sink for atmospheric CO2; however, estimates of the magnitude and distribution of this sink vary greatly. National forest inventories provide strong, measurement-based constraints on the magnitude of net forest carbon uptake. We brought together forest sector C budgets for Canada, the United States, Europe, Russia, and China that were derived from forest inventory information, allometric relationships, and supplementary data sets and models. Together, these suggest that northern forests and woodlands provided a total sink for 0.6–0.7 Pg of C per year (1 Pg = 1015 g) during the early 1990s, consisting of 0.21 Pg C/yr in living biomass, 0.08 Pg C/yr in forest products, 0.15 Pg C/yr in dead wood, and 0.13 Pg C/yr in the forest floor and soil organic matter. Estimates of changes in soil C pools have improved but remain the least certain terms of the budgets. Over 80% of the estimated sink occurred in one-third of the forest area, in temperate regions affected by fire suppression, agricultural abandonment, and plantation forestry. Growth in boreal regions was offset by fire and other disturbances that vary considerably from year to year. Comparison with atmospheric inversions suggests significant land C sinks may occur outside the forest sector.
864 citations
TL;DR: Predictions of four models on the effect of habitat fragmentation on the population extinction threshold are reviewed and reconciled, and results from empirical studies are compared.
Abstract: I reviewed and reconciled predictions of four models on the effect of habitat fragmentation on the population extinction threshold, and I compared these predictions to results from empirical studies. All four models predict that habitat fragmentation can, under some conditions, increase the extinction threshold such that, in more fragmented landscapes, more habitat is required for population persistence. However, empirical studies have shown both positive and negative effects of habitat fragmentation on population abundance and distribution with about equal frequency, suggesting that the models lack some important process(es). The two colonization–extinction (CE) models predict that fragmentation can increase the extinction threshold by up to 60–80%; i.e., the amount of habitat required for persistence can shift from 80% of the landscape, with a shift from completely clumped to completely fragmented habitat. The other two models (birth–immigration–death–emigration, or BIDE models)...
759 citations
TL;DR: A classification of sources of uncertainty under the two main categories: epistemic uncertainty and linguistic uncertainty (uncertainty in language) is provided and how each impacts on applications in ecology and conservation biology is demonstrated.
Abstract: Uncertainty is pervasive in ecology where the difficulties of dealing with sources of uncertainty are exacerbated by variation in the system itself. Attempts at classifying uncertainty in ecology have, for the most part, focused exclusively on epistemic uncertainty. In this paper we classify uncertainty into two main categories: epistemic uncertainty (uncertainty in determinate facts) and linguistic uncertainty (uncertainty in language). We provide a classification of sources of uncertainty under the two main categories and demonstrate how each impacts on applications in ecology and conservation biology. In particular, we demonstrate the importance of recognizing the effect of linguistic uncertainty, in addition to epistemic uncertainty, in ecological applications. The significance to ecology and conservation biology of developing a clear understanding of the various types of uncertainty, how they arise and how they might best be dealt with is highlighted. Finally, we discuss the various general strategies for dealing with each type of uncertainty and offer suggestions for treating compounding uncertainty from a range of sources.
757 citations
TL;DR: It is evident that most manipulative and mensurative fragmentation experiments have not provided clear insights into the ecological mechanisms and effects of habitat fragmentation, and recommendations for improving the design and implementation of fragmentation experiments are concluded.
Abstract: Ecologists have used a variety of comparative mensurative and manipulative experimental approaches to study the biological consequences of habitat fragmentation. In this paper, we evaluate the merits of the two major approaches and offer guidelines for selecting a design. Manipulative experiments rigorously assess fragmentation effects by comparing pre- and post-treatment conditions. Yet they are often constrained by a number of practical limitations, such as the difficulty in implementing large-scale treatments and the impracticality of measuring the long-term (decades to centuries) responses to the imposed treatments. Comparative mensurative studies generally involve substituting space for time, and without pre-treatment control, can be constrained by variability in ecological characteristics among different landscapes. These confounding effects can seriously limit the strength of inferences. Depending on the scale of the study system and how “landscape” is defined, both approaches may be limited by the difficulty of replicating at the landscape scale. Overall, both mensurative and manipulative approaches have merit and can contribute to the body of knowledge on fragmentation. However, from our review of 134 fragmentation studies published recently in three major ecological journals, it is evident that most manipulative and mensurative fragmentation experiments have not provided clear insights into the ecological mechanisms and effects of habitat fragmentation. We discuss the reasons for this and conclude with recommendations for improving the design and implementation of fragmentation experiments.
679 citations
TL;DR: In this article, the integrity of freshwater ecosystems depends upon adequate quantity, quality, timing, and temporal variability of water flow, and these attributes impart relatively unique characteristics of productivity and biodiversity to each ecosystem.
Abstract: Human society has used freshwater from rivers, lakes, groundwater, and wetlands for many different urban, agricultural, and industrial activities, but in doing so has overlooked its value in supporting ecosystems. Freshwater is vital to human life and societal well-being, and thus its utilization for consumption, irrigation, and transport has long taken precedence over other commodities and services provided by freshwater ecosystems. However, there is growing recognition that functionally intact and biologically complex aquatic ecosystems provide many economically valuable services and long-term benefits to society. The short-term benefits include ecosystem goods and services, such as food supply, flood control, purification of human and industrial wastes, and habitat for plant and animal life—and these are costly, if not impossible, to replace. Long-term benefits include the sustained provision of those goods and services, as well as the adaptive capacity of aquatic ecosystems to respond to future environmental alterations, such as climate change. Thus, maintenance of the processes and properties that support freshwater ecosystem integrity should be included in debates over sustainable water resource allocation.
The purpose of this report is to explain how the integrity of freshwater ecosystems depends upon adequate quantity, quality, timing, and temporal variability of water flow. Defining these requirements in a comprehensive but general manner provides a better foundation for their inclusion in current and future debates about allocation of water resources. In this way the needs of freshwater ecosystems can be legitimately recognized and addressed. We also recommend ways in which freshwater ecosystems can be protected, maintained, and restored.
Freshwater ecosystem structure and function are tightly linked to the watershed or catchment of which they are a part. Because riverine networks, lakes, wetlands, and their connecting groundwaters, are literally the “sinks” into which landscapes drain, they are greatly influenced by terrestrial processes, including many human uses or modifications of land and water. Freshwater ecosystems, whether lakes, wetlands, or rivers, have specific requirements in terms of quantity, quality, and seasonality of their water supplies. Sustainability normally requires these systems to fluctuate within a natural range of variation. Flow regime, sediment and organic matter inputs, thermal and light characteristics, chemical and nutrient characteristics, and biotic assemblages are fundamental defining attributes of freshwater ecosystems. These attributes impart relatively unique characteristics of productivity and biodiversity to each ecosystem. The natural range of variation in each of these attributes is critical to maintaining the integrity and dynamic potential of aquatic ecosystems; therefore, management should allow for dynamic change. Piecemeal approaches cannot solve the problems confronting freshwater ecosystems.
Scientific definitions of the requirements to protect and maintain aquatic ecosystems are necessary but insufficient for establishing the appropriate distribution between societal and ecosystem water needs. For scientific knowledge to be implemented science must be connected to a political agenda for sustainable development. We offer these recommendations as a beginning to redress how water is viewed and managed in the United States: (1) Frame national and regional water management policies to explicitly incorporate freshwater ecosystem needs, particularly those related to naturally variable flow regimes and to the linking of water quality with water quantity; (2) Define water resources to include watersheds, so that freshwaters are viewed within a landscape, or systems context; (3) Increase communication and education across disciplines, especially among engineers, hydrologists, economists, and ecologists to facilitate an integrated view of freshwater resources; (4) Increase restoration efforts, using well-grounded ecological principles as guidelines; (5) Maintain and protect the remaining freshwater ecosystems that have high integrity; and (6) Recognize the dependence of human society on naturally functioning ecosystems.
599 citations
TL;DR: I analyzed the stabilization of the schematic view of fragmentation by the early 1980s, using a genealogical narrative as a methodological approach and found that this view was supported by the reduction of empirical research to species–area curve fitt...
Abstract: The concept of habitat fragmentation has become an important theme in conservation research, and it is often used as if fragmentation were a unitary phenomenon. However, the concept is ambiguous, and empirical studies demonstrate a wide variety of direct and indirect effects, sometimes with mutually opposing implications. The effects of fragmentation vary across organisms, habitat types, and geographic regions. Such a contrast between a schematic concept and multifaceted empirical reality is counterproductive. I analyzed the stabilization of the schematic view of fragmentation by the early 1980s, using a genealogical narrative as a methodological approach. The main assumptions behind the schematic view were: (1) fragments are comparable to oceanic islands; (2) habitats surrounding fragments are hostile to a majority of the organisms; and (3) natural pre-fragmentation conditions were uniform. The stabilization loop of this view was supported by the reduction of empirical research to species–area curve fitt...
594 citations
TL;DR: In this article, a complementary approach to stream assessment based on evaluating ecosystem level processes is proposed, where leaf litter breakdown is a prime candidate to consider in this context, because of the pivotal role that allochthonous litter plays in streams, the demonstrated effects of anthropogenic perturbations on litter breakdown, and the relative ease of implementation.
Abstract: Assessment of the condition of ecosystems is a critical prerequisite for alleviating effects of the multiple anthropogenic stresses imposed on them. For stream ecosystems, a multitude of approaches has been proposed for this purpose. However, they all rest on the assessment of structural attributes, even though it is generally recognized that adequate characterization of ecosystems requires information on both structure (pattern) and function (process). Therefore, we propose a complementary approach to stream assessment based on evaluating ecosystem level processes. Leaf litter breakdown is a prime candidate to consider in this context. This is because of the pivotal role that allochthonous litter plays in streams, the demonstrated effects of anthropogenic perturbations on litter breakdown, and the relative ease of implementation. Leaf breakdown is governed by a variety of internal and external factors that complicate the partitioning of effects due to anthropogenic stress and natural variability (background noise), thus potentially limiting the sensitivity and robustness of litter breakdown assays. However, internal regulation factors can be controlled by standardizing assessment procedures, while variability due to external factors can be accounted for by stream classification and/or a comparative approach (e.g., downstream-upstream comparisons). Composite parameters such as ratios of break- down rates in fine-mesh and coarse-mesh bags may further increase the power of litter breakdown assays. Analyses may also be extended to include both leaf-associated decomposer assemblages (i.e., structural measures) and processes (i.e., additional functional measures). Significant efforts are required for developing standard assessment schemes as refined as extant procedures based on structural stream attributes (e.g., structure of macroinvertebrate assemblages). These efforts are nevertheless worthwhile in view of the new dimension that is added to current assessment procedures when functional elements are incorporated.
551 citations
TL;DR: Data indicate that spatial configuration is important to mitigate extinction risks when habitat availability in a landscape is low, whereas no effect will be observed when overall area of habitat is high.
Abstract: Habitat destruction and fragmentation of remaining habitat are major threats to global biodiversity. In this paper, we drew upon data from grassland butterflies, legume- feeding herbivores and their parasitoids, and the interactions between rape pollen beetles and their parasitoids in the agricultural landscapes of Germany to explore the following issues: (1) the relative importance of small habitat fragments for the conservation of bio- diversity (in contrast to the prevailing arguments in favor of large fragments); (2) the disruption of interspecific interactions in fragmented habitats; and (3) the relative impor- tance of the spatial arrangement of habitat fragments in landscapes of different complexity. The percentage of polyphagous butterfly species and their abundance were higher in small than in large calcareous grassland fragments, showing the relative importance of the landscape surrounding habitat fragments for less specialized species. A landscape per- spective is also needed to explain why several small fragments supported more butterfly species (even when only endangered species were considered) than the same area composed of only one or two fragments. Analyses of insects on legumes showed trophic-level dif- ferences, in that species numbers of parasitoids, but not of herbivores, benefited from habitat subdivision in landscapes. As percentage of parasitism (i.e., the strength of ecological interactions) increased with fragment area, both the ''several small'' and ''single large'' strategies appeared to have merit. An intermediate-fragmentation strategy of habitat con- servation in human-dominated landscapes may combine the advantages. Small habitat frag- ments should be scattered enough to cover a range of geographical area wide enough to maximize beta diversity and the spreading of risk, but with large habitat fragments close enough to enable dispersal among fragments, to reduce the extinction probability of area- sensitive species, and to stabilize predator-prey interactions. Parasitism of rape pollen beetles exhibited a distinct edge effect: it was higher near the crop field edge, i.e., near the parasitoids' overwintering sites (such as grassy strips). How- ever, this was only true in landscapes dominated by annual crops; in landscapes with a high percentage of permanent noncrop area ( .20%), such edge effects disappeared, pre- sumably because of the high overall density of these parasitoids. These data indicate that spatial configuration is important to mitigate extinction risks when habitat availability in a landscape is low, whereas no effect will be observed when overall area of habitat is high.
502 citations
TL;DR: This article studied the Bill Williams River in western Arizona, USA, to understand dam-induced changes in channel width and in the areal extent, structure, species composition, and dynamics of woody riparian vegetation.
Abstract: River damming and flow regulation can alter disturbance and stress regimes that structure riparian ecosystems. We studied the Bill Williams River in western Arizona, USA, to understand dam-induced changes in channel width and in the areal extent, structure, species composition, and dynamics of woody riparian vegetation. We conducted parallel studies along a reference system, the Santa Maria River, an unregulated major tributary of the Bill Williams River. Flood magnitude on the Bill Williams River has been dramatically reduced since the closure of Alamo Dam in 1968: the 10-yr recurrence interval flood in the pre-dam era was 1397 m3/s vs. 148 m3/s post-dam. Post-dam average annual flows were higher due to increased precipitation in a few years, but increases in post-dam May–September flows are largely attributable to dam operation. An analysis of a time series of aerial photographs showed that channels along the Bill Williams River narrowed an average of 111 m (71%) between 1953 and 1987, with most narrowi...
395 citations
TL;DR: In this article, the authors reviewed the empirical evidence for true fragmentation effects in boreal bird communities in Fennoscandia and Canada, and concluded that most responses may be attributed to pure habitat loss in landscapes where forest harvesting is the dominant land use practice.
Abstract: Although habitat loss and fragmentation are widely regarded as major factors contributing to the decline of many populations, the relative importance of each phenomenon is seldom evaluated. Some researchers have questioned the generality of responses to habitat fragmentation, given variation in life history characteristics, the natural dynamics of sys- tems, and land use patterns. Furthermore, a fundamental mismatch may exist between ecological theory, with its emphasis on the spatial configuration of habitats, and empirical observations of population response. Nevertheless, the paucity of quantitative land man- agement guidelines often leads to inappropriate generalizations of conservation paradigms to regional issues. We reviewed the empirical evidence for true fragmentation effects in boreal bird communities in Fennoscandia and Canada, and concluded that most responses may be attributed to pure habitat loss in landscapes where forest harvesting is the dominant land use practice. In these dynamic landscapes, total forest cover may not change, and predicting patterns of species decline requires identification of the habitats and species of concern. We constructed simple empirical models of benchmark communities in boreal forests of Finland and Canada based on species composition, species abundance distribution, and habitat requirements, in order to identify features of bird species sensitive to the loss of older forests. These models require a solid understanding of the underlying structure of the community of interest, and predict species loss based on a random-sample hypothesis. Our results were consistent with observed patterns of bird population decline and species loss in these regions. This approach provides null models for comparison with habitat remnants in order to test for fragmentation effects, and a basis for more detailed exploration of population dynamics and persistence in these systems. The results of our review and analyses indicated that system- and species-specific considerations are important when assessing the potential outcome of habitat loss and fragmentation on regional biota. Indis- criminate application of conservation paradigms may lead to misguided research efforts and poor management guidelines.
TL;DR: In this article, changes in aboveground vegetation, roots, and soil characteristics were examined from a 12-yr chronosequence of formerly cultivated fields restored to native C4 grasses through the Conservation Reserve Program (CRP).
Abstract: Changes in aboveground vegetation, roots, and soil characteristics were examined from a 12-yr chronosequence of formerly cultivated fields restored to native C4 grasses through the Conservation Reserve Program (CRP). Following 6–8 yr in the CRP, the native grasses dominated vegetation composition, and the presence of forbs was negligible. Productivity of the restored grasslands did not exhibit any directional changes with the number of years in the CRP, and productivity was generally higher than native prairie in this region. Over time, the restored grasslands accumulated root biomass of decreasing quality as indicated by increasing root biomass and C:N ratio of roots along the 12-yr chronosequence. Root biomass, root C:N ratio, C storage in roots, and N storage in roots of restored grasslands approached that of native tallgrass prairie within the 12 yr of restoration. Establishment of the perennial vegetation also affected soil physical, chemical, and biological characteristics. Soil bulk density in the ...
TL;DR: The data support a model in which both plasticity and adaptive evolution can contribute to the invasive potential of introduced species, by examining the degree of genetic differentiation within and among populations from the latitudinal extremes of its introduced range.
Abstract: Two major mechanisms have been proposed to explain the ability of intro- duced populations to colonize over large habitat gradients, despite significant population bottlenecks during introduction: (1) Broad environmental tolerance—successful invaders possess life history traits that confer superior colonizing ability and/or phenotypic plasticity, allowing acclimation to a wide range of habitats. (2) Local adaptation—successful invaders rapidly adapt to local selective pressures. However, even with bottlenecks, many introduced species exhibit surprisingly high levels of genetic variation and thus the potential for evolutionary increases in invasive traits and plasticity. Here we assess the invasive potential of Tamarix ramosissima, by examining the degree of genetic differentiation within and among populations from the latitudinal extremes of its introduced range. Using growth chamber experiments we examined ecologically important variation in seedlings, both in trait means and their reaction norms across temperature environments. Although we found no genetic variation for gas exchange traits, within or among populations, we did find significant genetic variation for growth traits, both in the trait means and in the degree of plasticity in these traits. Northern ecotypes invested more in roots relative to southern ecotypes but only under low temperatures. Both ecotypes increased shoot investment in warm temperatures. Increased root investment in cold temperatures by northern ecotypes may increase their first winter survival. Genetic differences in seedling root investment may contribute to the ability of this species to successfully tolerate and invade a broader latitudinal range. Our data support a model in which both plasticity and adaptive evolution can contribute to the invasive potential of introduced species.
TL;DR: In this paper, a closed-canopy Liquidambar styraciflua (sweetgum) forest stand was assessed for three years in a free-air CO2-enrichment (FACE) experiment.
Abstract: A central question concerning the response of terrestrial ecosystems to a changing atmosphere is whether increased uptake of carbon in response to increasing at- mospheric carbon dioxide concentration results in greater plant biomass and carbon storage or, alternatively, faster cycling of C through the ecosystem. Net primary productivity (NPP) of a closed-canopy Liquidambar styraciflua (sweetgum) forest stand was assessed for three years in a free-air CO2-enrichment (FACE) experiment. NPP increased 21% in stands ex- posed to elevated CO2, and there was no loss of response over time. Wood increment increased significantly during the first year of exposure, but subsequently most of the extra C was allocated to production of leaves and fine roots. These pools turn over more rapidly than wood, thereby reducing the potential of the forest stand to sequester additional C in response to atmospheric CO2 enrichment. Hence, while this experiment provides the first evidence that CO2 enrichment can increase productivity in a closed-canopy deciduous forest, the implications of this result must be tempered because the increase in productivity resulted in faster cycling of C through the system rather than increased C storage in wood. The fate of the additional C entering the soil system and the environmental interactions that influence allocation need further investigation.
TL;DR: In this article, the authors put an upper bound (or limit) on carbon storage in the Pacific Northwest (PNW) of the United States using field data from old-growth forests, which are near steady state conditions.
Abstract: Placing an upper bound to carbon (C) storage in forest ecosystems helps to constrain predictions on the amount of C that forest management strategies could sequester and the degree to which natural and anthropogenic disturbances change C storage. The potential, upper bound to C storage is difficult to approximate in the field because it requires studying old-growth forests, of which few remain. In this paper, we put an upper bound (or limit) on C storage in the Pacific Northwest (PNW) of the United States using field data from old-growth forests, which are near steady-state conditions. Specifically, the goals of this study were: (1) to approximate the upper bounds of C storage in the PNW by estimating total ecosystem carbon (TEC) stores of 43 old-growth forest stands in five distinct biogeoclimatic provinces and (2) to compare these TEC storage estimates with those from other biomes, globally. Finally, we suggest that the upper bounds of C storage in forests of the PNW are higher than current estimates of C stores, presumably due to a combination of natural and anthropogenic disturbances, which indicates a potentially substantial and economically significant role of C sequestration in the region. Results showed that coastal Oregon stands stored, on average, 1127 Mg C/ha, which was the highest for the study area, while stands in eastern Oregon stored the least, 195 Mg C/ha. In general, coastal Oregon stands stored 307 Mg C/ha more than coastal Washington stands. Similarly, the Oregon Cascades stands stored 75 Mg C/ha more, on average, than the Washington Cascades stands. A simple, area-weighted average TEC storage to 1 m soil depth (TEC 100 ) for the PNW was 671 Mg C/ha. When soil was included only to 50 cm (TEC50), the area-weighted average was 640 Mg C/ha. Subtracting estimates of current forest C storage from the potential, upper bound of C storage in this study, a maximum of 338 Mg C/ha (TEC100) could be stored in PNW forests in addition to current stores.
TL;DR: In this article, a highly predictive relationship between whole-canopy nitrogen concentration and aboveground forest productivity in diverse forested stands of varying age and species composition across the 360 000-ha White Mountain National Forest, New Hampshire, USA is presented.
Abstract: The concentration of nitrogen in foliage has been related to rates of net photosynthesis across a wide range of plant species and functional groups and thus rep- resents a simple and biologically meaningful link between terrestrial cycles of carbon and nitrogen. Although foliar N is used by ecosystem models to predict rates of leaf-level photosynthesis, it has rarely been examined as a direct scalar to stand-level carbon gain. Establishment of such relationships would greatly simplify the nature of forest C and N linkages, enhancing our ability to derive estimates of forest productivity at landscape to regional scales. Here, we report on a highly predictive relationship between whole-canopy nitrogen concentration and aboveground forest productivity in diverse forested stands of varying age and species composition across the 360 000-ha White Mountain National Forest, New Hampshire, USA. We also demonstrate that hyperspectral remote sensing can be used to estimate foliar N concentration, and hence forest production across a large number of contiguous images. Together these data suggest that canopy-level N concentration is an important correlate of productivity in these forested systems, and that imaging spectrometry of canopy N can provide direct estimates of forest productivity across large landscapes.
TL;DR: In this paper, the effectiveness of a plant community-based bioassessment tool, the floristic quality assessment index (FQAI), was tested in 20 depressional wetlands in Ohio, USA.
Abstract: Biological indicators of ecosystem integrity are increasingly being sought for use in ecosystem assessment and goal-setting for restoration projects. We tested the effectiveness of a plant community-based bioassessment tool, the floristic quality assessment index (FQAI) in 20 depressional wetlands in Ohio, USA. A priori, the 20 depressional wetlands were classified by type and ranked to form a disturbance gradient according to the local landscape condition. Ranks were based on surrounding land cover characteristics, vegetated buffer characteristics, and the extent of human-induced hydrologic alteration at the wetland site. The index was negatively correlated with the disturbance rank of a wetland and with the distance to neighboring wetlands (P = 0.01). Index values were lower for wetlands surrounded by agricultural or urban land use, wetlands with less vegetation on the wetland perimeter, and wetlands with more hydrologic modification, and at sites with greater distances to other wetlands. The wetlands w...
TL;DR: In this article, the relationship between flow regime, channel morphology, dispersal phenology, and seed deposition patterns was evaluated using experimentation in a flume using color-coded Betula fontinalis seeds released over each 10min trial.
Abstract: Rivers are important corridors for movement, migration, and dispersal of aquatic organisms as well as for dispersal of the seeds and vegetative propagules of riparian plants In this investigation, the relationships between flow regime, channel morphology, dispersal phenology, and seed deposition patterns were evaluated using experimentation in a flume A channel with geomorphic features common to a wide range of stream morphologies was constructed in a 18 × 20 m experimental flume through which three hydrologic regimes (one natural and two typical of dam releases) were routed in replicated trials Relationships between dispersal phenology and hydrologic regime were examined using color-coded Betula fontinalis seeds released over each 10-min trial Spatial patterns of seed deposition along stream margins were then compared to determine the individual and combined effects of flow regime, fluvial feature, and timing of seed release Reynolds number, Froude number, Weber number, flow velocity, and a dimensi
TL;DR: In this paper, the effects of past land use, topography, soil type, and other environmental variables on tree species composition in a subtropical wet forest in the Luquillo Mountains, Puerto Rico were compared.
Abstract: The effects of historical land use on tropical forest must be examined to understand present forest characteristics and to plan conservation strategies. We compared the effects of past land use, topography, soil type, and other environmental variables on tree species composition in a subtropical wet forest in the Luquillo Mountains, Puerto Rico. The study involved stems > 10 cm diameter measured at 130 cm above the ground, within the 16-ha Luquillo Forest Dynamics Plot (LFDP), and represents the forest at the time Hurricane Hugo struck in 1989. Topography in the plot is rugged, and soils are variable. Historical documents and local residents described past land uses such as clear-felling and selective logging followed by farming, fruit and coffee production, and timber stand im- provement in the forest area that now includes the LFDP. These uses ceased 40-60 yr before the study, but their impacts could be differentiated by percent canopy cover seen in aerial photographs from 1936. Using these photographs, we defined four historic cover classes within the LFDP. These ranged from cover class 1, the least tree-covered area in 1936, to cover class 4, with the least intensive historic land use (selective logging and timber stand improvement). In 1989, cover class 1 had the lowest stem density and pro- portion of large stems, whereas cover class 4 had the highest basal area, species richness, and number of rare and endemic species. Ordination of tree species composition (89 species, 13 167 stems) produced arrays that primarily corresponded to the four cover classes (i.e., historic land uses). The ordination arrays corresponded secondarily to soil characteristics and topography. Natural disturbances (hurricanes, landslides, and local treefalls) affected tree composition, but these effects did not correlate with the major patterns of species distributions on the plot. Thus, it appears that forest development and natural disturbance have not masked the effects of historical land use in this tropical forest, and that past land use was the major influence on the patterns of tree composition in the plot in 1989. The least disturbed stand harbors more rare and endemic species, and such stands should be protected.
TL;DR: In this paper, the authors define the concept of net ecosystem production (NEP) as the net carbon accumulation by ecosystems and explicitly incorporate all the carbon fluxes from an ecosystem, including autotrophic respiration, heterotrophic respiratory, losses associated with disturbance, dissolved and particulate carbon losses, volatile organic compound emissions and lateral transfers among ecosystems.
Abstract: The conceptual framework used by ecologists and biogeochemists must allow for accurate and clearly defined comparisons of carbon fluxes made with disparate techniques across a spectrum of temporal and spatial scales. Consistent with usage over the past four decades, we define “net ecosystem production” (NEP) as the net carbon accumulation by ecosystems. Past use of this term has been ambiguous, because it has been used conceptually as a measure of carbon accumulation by ecosystems, but it has often been calculated considering only the balance between gross primary production (GPP) and ecosystem respiration. This calculation ignores other carbon fluxes from ecosystems (e.g., leaching of dissolved carbon and losses associated with disturbance). To avoid conceptual ambiguities, we argue that NEP be defined, as in the past, as the net carbon accumulation by ecosystems and that it explicitly incorporate all the carbon fluxes from an ecosystem, including autotrophic respiration, heterotrophic respiration, losses associated with disturbance, dissolved and particulate carbon losses, volatile organic compound emissions, and lateral transfers among ecosystems. Net biome productivity (NBP), which has been proposed to account for carbon loss during episodic disturbance, is equivalent to NEP at regional or global scales. The multi-scale conceptual framework we describe provides continuity between flux measurements made at the scale of soil profiles and chambers, forest inventories, eddy covariance towers, aircraft, and inversions of remote atmospheric flask samples, allowing a direct comparison of NEP estimates made at all temporal and spatial scales.
TL;DR: To evaluate why forests do not regenerate naturally and to identify potential species for use in reforestation of degraded areas, 15 000 seeds of 20 native tree species were planted in abandoned Panamanian farmland dominated by the exotic grass, Saccharum spontaneum.
Abstract: Deforestation in the tropics often leads to unproductive agriculture and results in abandoned, degraded grasslands that tree species recolonize poorly. To evaluate why forests do not regenerate naturally and to identify potential species for use in reforestation of degraded areas, we planted 15 000 seeds of 20 native tree species, varying in seed size and shade tolerance, in abandoned Panamanian farmland dominated by the exotic grass, Saccharum spontaneum . To determine the effects of above- and belowground constraints on tree seedling germination, survival, and growth, we used four mowing and shading treatments of the Saccharum. Shading the Saccharum effectively eliminated it, whereas mowing led to increased light aboveground, but did not reduce Saccharum growth rate. Germination, survival, and growth of tree seedlings approximately doubled in shade treat- ments compared to the unshaded control, but were lowest when the Saccharum was mowed three times. Fire significantly decreased germination and survival. Some species did not follow these general trends, however; we identified four species groups that varied in their response to Saccharum competition. Very small-seeded, light- demanding species performed poorly, and we do not recommend their use in reforestation because they tolerate neither above- nor belowground constraints imposed by the Sac- charum. Light-demanding species with large seeds were limited by aboveground constraints, namely, shading. Small-seeded, shade-tolerant species were limited by belowground con- straints imposed by the Saccharum. Large-seeded, moderately to highly shade-tolerant species performed well in the Saccharum; we recommend a reforestation strategy that includes planting this last group.
TL;DR: The results indicate that the appropriate scale of habitat measurement for predicting cutthroat trout translocation success in fragmented watersheds is at the patch rather than landscape scale, which is similar to results for other salmonids and vertebrate taxa in general.
Abstract: Translocation is an important management strategy in conservation programs for endangered or threatened species, including native cutthroat trout (Oncorhynchus clarki) in the western United States. Most subspecies of cutthroat trout have declined to <5% of their historical range, and both historical and translocated populations now persist in small isolated fragments of habitat. Success rates for translocations of fishes are generally <50%, and habitat quality or quantity are frequently cited as the cause of failure. Therefore, we conducted field surveys of stream-scale habitat and measured basin-scale habitat using a Geographic Information System for 27 streams where two subspecies of cutthroat trout were translocated in Colorado and New Mexico, to identify specific habitat attributes that contribute to the success of translocations. We used polytomous logistic regression to develop models that predict three categories of cutthroat trout translocation success (high, low, absent) from habitat attributes at two spatial scales. Models based on stream-scale habitat attributes indicated that cold summer water temperature, narrow stream width, and lack of deep pools limited translocations of cutthroat trout. Cold summer temperatures are known to delay spawning and prolong egg incubation, which reduces the growth of fry and likely limits their overwinter survival. Furthermore, small streams with few deep pools may lack the space necessary to permit overwinter survival of a sufficient number of individuals to sustain a population. Models based on basin-scale habitat were not as effective as stream-scale habitat models for dis- tinguishing among translocation sites with high, low, or absent population status but in- dicated that a minimum watershed area of 14.7 km2 was useful as a coarse filter for separating sites with high numbers of cutthroat trout from those with low or absent status. Watersheds larger than this are expected to encompass low-elevation habitat that provides warmer summer temperatures and to have relatively wide stream channels of sufficient length to provide an adequate number of deep pools. These results indicate that the appropriate scale of habitat measurement for predicting cutthroat trout translocation success in fragmented watersheds is at the patch rather than landscape scale, which is similar to results for other salmonids and vertebrate taxa in general.
TL;DR: The results of this study suggest that, at the neighborhood level, diversity can limit invasibility and may reduce the impact of an invader.
Abstract: In a microcosm experiment, I tested how species composition, species rich- ness, and community age affect the susceptibility of grassland communities to invasion by a noxious weed (Centaurea solstitialis L.). I also examined how these factors influenced Centaurea's impact on the rest of the plant community. When grown in monoculture, eight species found in California's grasslands differed widely in their ability to suppress Centaurea growth. The most effective competitor in monoculture was Hemizonia congesta ssp. Iuzulifolia, which, like Centaurea, is a summer- active annual forb. On average, Centaurea growth decreased as the species richness of communities increased. However, no polyculture suppressed Centaurea growth more than the monoculture of Hemizonia. Centaurea generally made up a smaller proportion of com- munity biomass in newly created ("new") microcosms than in older ("established") mi- crocosms, largely because Centaurea's competitors were more productive in the new treat- ment. Measures of complementarity suggest that Centaurea partitioned resources with an- nual grasses in the new microcosms. This resource partitioning may help to explain Cen- taurea's great success in western North American grasslands. Centaurea strongly suppressed growth of some species but hardly affected others. An- nual grasses were the least affected species in the new monocultures, and perennial grasses were among the least affected species in the established monocultures. In the new micro- cosms, Centaurea's suppression of competing species marginally abated with increasing species richness. This trend was a consequence of the declining success of Centaurea in species-rich communities, rather than a change in the vulnerability of these communities to suppression by a given amount of the invader. The impact of the invader was not related to species richness in the-established microcosms. The results of this study suggest that, at the neighborhood level, diversity can limit invasibility and may reduce the impact of an invader.
TL;DR: In this article, the authors quantify the amount and location of potentially suitable lynx habitat in Germany, estimate the connectivity between patches of suitable habitat, and evaluate lynx conservation programs.
Abstract: Conservation biologists often must make management decisions based on little empirical information. In Germany, biologists are concerned that the recovery and reintroduction of Eurasian lynx (Lynx lynx) may fail because the remaining suitable habitat may be insufficient to sustain a viable population. However, no comprehensive study ad- dressing this concern has been made that not only considers distribution of suitable habitat, but also connectivity to other populations. The aims of this study were (1) to quantify the amount and location of potentially suitable lynx habitat in Germany, (2) to estimate the connectivity between patches of suitable habitat, and (3) to evaluate lynx conservation programs. Habitat preferences of lynx were described in a rule-based model based on the availability of forest cover (defined by patch size) and the spatial structure of the habitat. Rules were implemented in a geographic information system to predict locations of suitable habitat. Optimal connections among patches were modeled using a cost-path analysis based on habitat-specific probabilities of lynx crossing patches. Results indicated wide variation in the size of patches of suitable habitat, with 10 areas each sufficiently large to sustain .20 resident lynxes. Overall, a total of 380 lynxes could be sustained by the 10 areas. Uncertainty analyses of model parameters and assumptions revealed little variation in pre- dicted habitat, primarily because results were constrained by the actual distribution of forest habitat. Our analyses suggest that lynx reintroduction programs should emphasize large, connected areas and consider broad-scale habitat connectivity in the landscape. Our ap- proach also demonstrates how biologically plausible rules can be applied in conservation to identify areas in which success is most likely, even when few empirical data are available.
TL;DR: The hypothesis that the introduction of an alien aquatic macrophyte (Trapa natans) may have had dramatic impacts on the frequency and extent of low DO events in the Hudson River is explored.
Abstract: In aquatic systems low dissolved oxygen (DO) has been identified as a serious water quality problem. Here we use empirical data and modeling to explore the hypothesis that the introduction of an alien aquatic macrophyte (Trapa natans) may have had dramatic impacts on the frequency and extent of low DO events in the Hudson River. Continuous measurements with moored instruments demonstrated that in large macrophyte beds dom- inated by a native species (Vallisneria americana) DO never declined below 5 mg/L during the summer growing season. In contrast, during this same time period, extremely low DO was common in large beds dominated by Trapa natans, with DO values below 2.5 mg/L occurring up to 40% of the time. This difference in DO can be modeled based on species differences in the balance of respiration and in-water photosynthesis. The low DO values in Trapa beds suggest that these beds may be poor habitats for sensitive fish and inver- tebrates and that redox sensitive chemical reactions may be altered within Trapa beds.
TL;DR: The potential of predators to control pest populations in fragmented landscapes may ultimately reflect the extent to which thresholds in landscape structure interfere with the aggregative response of predators.
Abstract: Habitat fragmentation may adversely affect the ability of natural enemies to control pest outbreaks in agricultural landscapes by interfering with their search behavior and ability to aggregate in response to prey. We determined how landscape structure affected the ability of two ladybird beetles (Coleoptera: Coccinellidae) to track aphid populations in experimental landscapes that differed in the abundance and degree of fragmentation of red clover (Trifoliutn pratense). One coccinellid was a native species (Coleomegilla ma- culntn Pallas) and the other (Hartnonia a~ridis Timberlake) was introduced specifically for the biological control of crop pests such as pea aphids (Acyrrlzosiphon pisurn Harris; Homoptera: Aphididae). Landscape structure exhibited a threshold in lacunarity (a measure of interpatch dis- tances) below 20% habitat. at which point clover patches became significantly more isolated. This threshold in landscape structure was mirrored by a similar threshold in the distribution of pea aphid populations. The distribution of the biocontrol agent, H. nxyridis, tracked this threshold in aphid distribution, but the native coccinellid. C. maculata, was unable to do so in fragmented clover landscapes. Although C. maculata was a more active forager within clover cells, overall it was less mobile and moved significantly less among clover cells and between landscapes than H. axyridis, which may have contributed to its inability to track aphid populations in fragmented landscapes. The two coccinellids did not differ in their search success within fragmented landscapes. however. and it was only in clumped land- scapes that H. axyridis maximized search success and foraged within clover cells that had 2.5-3 times more aphids than those in which C. rnnculntn occurred. Thus, the potential of predators to control pest populations in fragmented landscapes may ultimately reflect the extent to which thresholds in landscape structure interfere with the aggregative response of predators. In this system, the aggregative response of cocci- nellids was more closely tied to thresholds in the distribution of clover than aphids. With its greater mobility, H. nxyridis was more effective than the indigenous C. maculata at tracking aphids when they occurred at low patch occupancy (below the threshold in land- scape structure), which is a requisite for successful biocontrol. If native insect predators are generally more sensitive to habitat fragmentation, greater reliance may be placed on the introduction of exotic species for biocontrol, which is not without economic cost and potential ecological impacts to native insect communities. Our study demonstrates that. in addition to economic thresholds. there are also ecological thresholds that must be sur- mounted if biocontrol measures are to be successful. In addition to enhancing vegetational diversity within agroecosystems, conservation biological control should also strive to mit- igate fragmentation effects on natural enemies, especially if thresholds in landscape structure disrupt predator-prey interactions and compromise the efficacy of biocontrol programs.
TL;DR: This work studied the application of free-living nematode communities as model indicators of physical and chemical disturbance of agricultural soil and assigned relative direct and indirect tillage sensitivity and chemical/nutrient sensitivity ratings to soil genera found in two test data sets.
Abstract: During the past 50 yr, ecological and agricultural scientists have pursued an integrated definition and metric of soil quality. In the past 20 yr, considerable attention has been paid to nematodes, demonstrating that these ubiquitous members of the soil community reflect change in ecological structure and function of soils in ways more predictable and efficient than for other soil flora or fauna. With the help of multivariate analysis, we studied the application of free-living nematode communities as model indicators of physical and chemical disturbance of agricultural soil. We used canonical correspondence analysis (CCA) and partial CCA to segregate effects of tillage and chemical/nutrient treatments. With the results of CCA, we assigned relative direct and indirect tillage sensitivity and chemical/nutrient sensitivity ratings to soil genera found in two test data sets, each containing three matrices: (1) sites by species or genera, (2) sites by soil properties, and (3) sites by management practices. Of ...
TL;DR: In this paper, the effects of forest management on understory plant communities in northern hardwood forests and assess the processes governing differences in species composition, diversity, and spatial patterns were evaluated.
Abstract: Forest management can significantly affect both the diversity and spatial patterning of understory vegetation. However, few studies have considered both diversity and spatial patterning at a stand scale. Our objective was to evaluate the effects of forest management on understory plant communities in northern hardwood forests and assess the processes governing differences in species composition, diversity, and spatial patterns. We sampled understory vegetation (all species ,2 m tall) and percentage of light transmission levels in three forest types in 12 mesic northern hardwood stands in northern Wisconsin and the Upper Peninsula of Michigan, USA: old-growth, undisturbed forests; even-aged forests resulting from clearcut logging (;65-85 yr old); and uneven-aged forests with recent selective logging. Estimated understory species richness per stand, mean species richness per quadrat, and mean percent cover per quadrat were lower in old-growth forest than in even-aged, second- growth forests and lower in even-aged than in uneven-aged, second-growth forests. Dif- ferences in species composition among the three forest types were related to available light and to coarse woody debris; however, differences between the cover of most plant groups were not significant. The mean patch size of species diversity and cover is highly variable and could not be related to forest stand type. However, understory communities in old- growth forests have significantly smaller community patch sizes and larger compositional heterogeneity. Community patch size is correlated with both coarse woody debris and light heterogeneity. Each forest stand type produces a characteristic combination of understory composition, diversity, and spatial patterning of communities. Although harvesting has negligible effects on understory alpha diversity in these mesic hardwood forests, spatial structure is slower to recover and has not recovered in the even- and uneven-aged northern hardwood forests studied. If management objectives include preserving or restoring the ecological character of the forest, harvesting may need to be altered or delayed predicated on the character of the understory.
TL;DR: In this paper, the response of woodland caribou to land-cover type, predation risk, energetic costs of movement, and patch configuration at multiple spatial scales was assessed.
Abstract: We assessed the response of woodland caribou (Rangifer tarandus caribou) to land-cover type, predation risk, energetic costs of movement, and patch configuration at multiple spatial scales. We applied a nonlinear model to frequent locations collected with Global Positioning System (GPS) collars to identify discontinuities in the scales of movement by caribou found in forested and alpine (above tree line) habitats. We differ- entiated intra- from interpatch movements and identified collections of patches (multiple- patch scale) where caribou concentrated intrapatch movements. On average, intra- and interpatch movements were 450.7 and 1268.8 m, respectively, and multiple-patch move- ments occurred over an area of 182 ha. Intrapatch movements were highly correlated, indicative of a strong relationship between behavior and place. Caribou in the forest selected patches of Pine terrace, whereas caribou in the alpine selected patches of Alpine-little vegetative cover. Predation risk was not a factor influencing movements of caribou at the intrapatch scale. Selection of cover types was more variable during interpatch movements. At that scale, caribou selected patches of Pine terrace, Lakes/rivers, Alpine-little vegetative cover, and Alpine-grass. The routes selected by caribou had lower energetic costs relative to surrounding terrain, and during some winters, caribou were subjected to higher levels of predation risk during those movements. At the multiple-patch scale, selection was more specific and encompassed patches of Alpine-little vegetative cover, Alpine-grass, and Pine terrace. Predation risk was relatively unimportant at the multi-patch scale, but animals that moved from forested to alpine habitats reduced their relative risk of predation. Patch con- figuration was a poor predictor of those areas where caribou concentrated intrapatch move- ments. There was some evidence of caribou selecting patches of Pine terrace within a matrix of Wetlands and Pine-black spruce/black spruce patches. Caribou in the alpine avoided patches of Alpine-little vegetative cover adjacent to forest types. Our results indicate that forest managers should maintain widely distributed patches of Pine terrace and implement silvicultural regimes that do not stimulate predator populations across areas used for in- terpatch movements.
TL;DR: In a recent publication of Science, data from a large number of forest inventory plots were used to estimate biomass trends in old-growth tropical forests as discussed by the authors, and although no evidence was found of net biomass change in mature Paleotropical forests, old growth of the humid Neotropics was inferred to have been a substantial biomass carbon sink in recent decades.
Abstract: In a recent (1998) publication of Science, data from a large number of forest inventory plots were used to estimate biomass trends in old-growth tropical forests. Al- though no evidence was found of net biomass change in mature Paleotropical forests, old growth of the humid Neotropics was inferred to have been a substantial biomass carbon sink in recent decades. Methodological artifacts affected this analysis, however. Many humid Neotropical plots were measured strictly at breast height, where tropical trees frequently have buttresses and other protruberances. Because biomass allometric equations are based on above-buttress tree diameters, and because bole irregularities show disproportionately rapid radial increments, estimates of biomass and biomass increase must be based on above- buttress measurements. In addition, some plots were on recent floodplains, where forests undergo biomass accretion during primary succession. The data set includes 25 sites from the humid lowland Neotropics that were measured above buttresses with standard techniques and that were not on recent floodplains. Mean estimated biomass change for these sites was 0.3 Mg-ha-' yr-', with a 95% confidence interval including 0.0 (-0.3 to +0.9 Mg.ha-'.yr-1). While the Science study was a laudable attempt to address an important aspect of the global carbon budget, the underlying data do not indicate a significant biomass carbon sink in old-growth forests of the humid Neotropics.