bluuebunny/crossref_metadata_2025 huggingface dataset:
DOES SCALE AFFECT ECOLOGICAL MODEL PREDICTIONS? A TEST WITH LAKE RESPONSES TO FERTILIZATION
Authors: Irvine Robyn L. , Crone Elizabeth E. , Jackson Leland J. , MacIsaac Erland A.
Published: June 2007

Ecosystem ecologists often face the challenge of predicting long‐term consequences of perturbations such as nutrient enrichment from shorter term experiments. In such experiments, the spatial and temporal scale at which data are analyzed can directly impact extrapolations to larger scales. Here, we assess the level of data resolution required to answer qualitative and quantitative questions about primary production in a set of lake ecosystems. We tested the ability of 40 models containing variable levels of spatial and temporal complexity to (1) fit the relationship between light and primary productivity in a set of 14 British Columbia (Canada) lakes that were part of a large‐scale fertilization experiment, and (2) predict annual primary production. The experimental data had previously been averaged across fertilization treatments for analysis, effectively ignoring spatial and temporal variation. In the limnological literature, data from whole‐lake experiments are often analyzed for each lake to account for among‐lake differences, or analyzed for each lake in each year to account for both lake effect and interannual variation. Using an information‐theoretic approach, we tested these three models (“fertilization status only,” “lake only,” and “lake and year”) against models that included less and more spatial and temporal partitioning of the data. We fit a Monod function to light and primary productivity at 40 spatial and temporal levels of data resolution and ranked the model fits using the second‐order Akaike Information Criterion (AICc). The “fertilization status only” model ranked 37th out of 40 models tested, the “lake only” model ranked 27th, and the “lake and year” model ranked 25th. The top‐ranked model partitioned the data by lake, year, fertilization status, season, and sampling station, and fit the data substantially better than other models. We then calculated primary production with independent light data and the fitted model parameters to compare the top three models from our AICc ranking and the “lake only,” “lake and year,” and “fertilization status only” models. The predicted production differed depending on the model, but all models predicted higher net primary productivity in fertilized lakes. Model selection is therefore important for quantitative predictions, but not necessarily for qualitative assessment of nutrient limitation.
DO NORTH AMERICAN MONARCH BUTTERFLIES TRAVEL TO CUBA? STABLE ISOTOPE AND CHEMICAL TRACER TECHNIQUES
Authors: Dockx Cristina , Brower Lincoln P. , Wassenaar Leonard I. , Hobson Keith A.
Published: June 2007

Since the discovery of monarch butterfly (Danaus plexippus) overwintering colonies in Mexico in the 1970s, it was assumed that monarchs from eastern North America migrated only to Mexico. This paper reveals that monarchs from Canada and the east coast of the United States also regularly travel to Cuba during the migration period. The natal grounds of Cuban monarchs were determined through the combined use of stable hydrogen (δD) and stable carbon (δ13C) isotope measurements and by cardenolide fingerprint analysis using thin‐layer chromatography (TLC). The TLC data revealed that there was an influx of migrants in November to Cuba, and the stable isotope data revealed that migrant Cuban monarchs originated from southeastern Canada and the eastern United States. Our findings suggest that North American migrant monarchs that move to Cuba hybridize with resident populations there and do not return to the continent. The differences in the natal grounds, migratory route, and reproductive stages between monarchs wintering in Mexico and Cuba suggest that there are at least two subpopulations of eastern North American monarchs. The extent to which Cuba may act as a bridge for monarch movement to the Yucatan and other Caribbean islands and the genetic impact of this newly revealed flux in monarch movements remain to be determined.
CONFOUNDING EFFECTS OF THE EXPORT OF PRODUCTION AND THE DISPLACEMENT OF FISHING EFFORT FROM MARINE RESERVES
Authors: Halpern Benjamin S. , Gaines Steven D. , Warner Robert R.
Published: June 2007

Marine reserves affect areas outside reserve boundaries via the displacement of fishing effort and the export of production. Here we focus on how these key factors interact to influence the results seen once reserves are created. For a settlement‐limited fishery, export of increased production from within reserves can offset the effects of displaced fishing effort. We develop simple mathematical models that indicate net fisheries benefits can accrue at closures up to and perhaps beyond 50% of total stock area through the export of production, given documented average increases in biomass within reserves. However, reserve monitoring programs face problems identifying independent control sites because the spatial extent of export is unknown. Efforts to monitor reserve impacts on recruitment are further complicated by the fact that large reserve closures are likely necessary before significant changes in recruitment can be detected above normal interannual fluctuations. Resolving these limitations requires comprehensive monitoring data before reserves are implemented. Fortunately, studies of reserves that used Before–After, Control– Impact (BACI) experimental designs show that control and reserve sites were equivalent prior to protection, and that control sites improved after reserves were in place. Consequently, any bias in our current perception of reserve impacts likely underestimates their effect.
ELEVATED δ15N IN STREAM BIOTA IN AREAS WITH SEPTIC TANK SYSTEMS IN AN URBAN WATERSHED
Authors: Steffy Luanne Y. , Kilham Susan S.
Published: June 2007

Anthropogenic inputs of nitrogen from human sewage are a central concern in urban watershed management. However, identifying the locations of these inputs, whether from improperly functioning or ill‐maintained septic tanks or from leaking sewer lines, is difficult. We used nitrogen stable‐isotope analysis of aquatic food webs as indicators of sewage‐derived nitrogen in Valley Creek watershed. Stable nitrogen isotope analysis revealed elevated δ15N in all trophic levels at stations located downstream of the divide between sewered and nonsewered (septic tanks) neighborhoods in the watershed. Stations not located in the septic system area or on the other branch of the creek did not show this elevated level of δ15N. Allochthonus inputs, which do not derive nitrogen from aquatic sources, such as detrital leaf material, showed no difference in δ15N between Valley Creek and Little Valley Creek. Particular fish species that are found throughout both branches, such as blacknose dace and creek chub, had as much as a 10‰ enrichment in δ15N in septic vs. sewered areas. These results indicate that stable‐isotope analysis can be a useful tool for determining the location of inputs of human sewage and may have broad applications in watershed planning and management, especially in urban systems.
THE PERSISTENCE OF QUAKING ASPEN (POPULUS TREMULOIDES) IN THE GRAND MESA AREA, COLORADO
Authors: Kulakowski Dominik , Veblen Thomas T. , Drinkwater Sarah
Published: June 2007

Human activities have caused the decline of numerous species and ecosystems. To promote ecosystem resilience, recent management efforts aim to maintain ecosystem patterns and processes within their historical range of variability. There has been substantial concern that quaking aspen, the most widely distributed tree in North America and the most important deciduous tree in the subalpine forests of the Rocky Mountains, has declined significantly in the western landscape during the 20th century. This reported decline has been attributed to conifer encroachment associated with fire exclusion, as well as other causes. To assess long‐term changes in the extent of quaking aspen in a 175 000‐ha study area in western Colorado, we used a Geographic Information System to compare an 1898 map of vegetation and fires to a modern map of present forest cover types. Based on this comparison, a larger portion of the current landscape is dominated by quaking aspen relative to the late 19th century, a period of extensive burning in this area. During the 20th century, aspen was persistent over most of its extent, even in the absence of fire. Fires of the late 19th century also increased aspen cover in stands that were previously dominated by spruce and fir. The trend toward increased aspen was greater at lower elevations. The total area where spruce and fir have replaced aspen is small in comparison to the area where aspen has increased or has persisted. The successional replacement of aspen by conifers is more pronounced at higher elevations and where the predisturbance vegetation was dominated by conifers. The net effect of severe disturbances during and after the late 19th century has also increased aspen cover relative to the period that preceded these disturbances. Thus, where the successional replacement of aspen by conifers is occurring today, such a trend may be within the range of historical variation. Long intervals between large, severe natural disturbances in ecosystems can result in a broad range of natural ecological conditions, including dominance by particular species.
INDIVIDUAL AND INTERACTIVE EFFECTS OF A PREDATOR AND CONTROPHIC SPECIES ON MOSQUITO POPULATIONS
Authors: Stav Gil , Blaustein Leon , Margalit Yoel
Published: June 2007

Species sharing the same trophic level as mosquito larvae (hereafter, controphic species) may have complex effects on mosquitoes by sharing both predators and food resources. We conducted an outdoor artificial pool experiment to assess the individual and interactive effects of a predator (Anax imperator) and controphic species (primarilyDaphnia magna) on larval populations of two common mosquitoes,Culex pipiensandCuliseta longiareolata.

Controphic species did not significantly affect survival to pupation ofC. pipiensbut did increase time to metamorphosis and reduce size at metamorphosis.Culex pipiensandD. magna, both primarily filter feeders, probably compete for food resources. Controphic species caused a small reduction (21.9%) inC. longiareolatasurvival, an unexpected result given thatC. longiareolatalarvae are thought to be primarily periphyton grazers whileD. magnais a filter feeder. Controphic species did not affectC. longiareolatatime to, or size at, pupation.

Anax imperatorreducedC. longiareolatasurvival to pupation (78%) and size at pupation (11.5%) while increasing development time in males only (11.3%).Anax imperatorcaused a smaller (32.4%), but statistically significant, reduction in the number ofC. pipienssurviving to the pupal stage but did not significantly affect size at or time to pupation. The predator did not reduce controphic species densities, and controphic species did not result in increased predator growth.

We predicted that controphic species, by serving as competitors, would result in fewerC. pipienssurviving to pupation in the absence of predators. In the presence of the predator, the negative competitive effect of controphic species would be attenuated by the positive effect of serving as alternative prey. Our results followed this pattern although the predator × controphic species interaction was not statistically significant (P= 0.157). Because previous studies showed thatD. magnadid not affect predation rates byA. imperatoronC. longiareolatalarvae, and because controphic species did not have a strong competitive effect, we did not predict and did not find a predator × controphic species interactive effect.
RESPONSES OF UNDERSTORY RAIN FOREST BIRDS TO ROAD EDGES IN CENTRAL AMAZONIA
Authors: Laurance Susan G. W.
Published: June 2007

In the lowland tropical rain forest of central Amazonia, I investigated the responses of understory bird communities to forest edges bordering a narrow (<40 m width), unpaved road. From 3681 mist‐net captures, bird abundance and composition were examined at three distances (10, 70, and 130 m) from forest edge. The degree to which regrowth vegetation along forest borders reduced edge effects was also assessed by contrasting bird communities near roads with varying levels of regrowth.

Forests near road margins had reduced canopy cover and height and higher numbers of fallen trees than did forest interiors. Bird communities near forest edges also differed markedly from those in forest interiors. Total bird captures and captures of insectivores increased with distance from edge, whereas captures of frugivores and nectarivores did not vary significantly. Mature regrowth on edges significantly increased the captures of insectivores. When insectivorous birds were divided into feeding guilds, birds in six of eight guilds showed significant responses to distance from edge; five of these had fewer captures near road margins whereas one guild (edge/gap specialists) had higher captures. For most guilds, significant alterations in abundance and species composition were evident within 10–70 m of road margins.

My results suggest that the majority of Amazonian understory birds respond negatively to artificial edges created by a narrow, unpaved road. Forest regrowth along road margins alleviated negative edge effects for only a limited subset of forest‐dependent species.
TROPICAL DEFORESTATION AND GREENHOUSE‐GAS EMISSIONS
Authors: Fearnside Philip M. , Laurance William F.
Published: June 2007

A recent (2002) analysis concluded that rates of tropical deforestation and atmospheric carbon emissions during the 1990–1997 interval were lower than previously suggested. We challenged this assertion with respect to tropical carbon emissions, but our conclusions were disputed by the authors of the original study. Here we provide further evidence to support our conclusion that the effect of tropical deforestation on greenhouse‐gas emissions and global warming is substantial. At least for Brazilian Amazonia, the net impact of tropical deforestation on global warming may be more than double that estimated in the recent study.
COLONIZATION BY WOODY PLANTS IN FRAGMENTED HABITATS OF A SUBURBAN LANDSCAPE
Authors: Komuro Takeyuki , Koike Fumito
Published: June 2007

Many studies have estimated the parameters of metapopulation dynamics by assuming a steady‐state habitat‐occupation pattern by organisms. However, metapopulations of woody plants in suburban landscapes rarely attain a steady state owing to the long life spans of individuals. We constructed a colonization model for woody plants based on the distance from a seed‐source patch containing mother trees. It is easy to determine colonization parameters with this method, which makes the method useful for conservation planning. Distance from the seed source was the most important factor for predicting the presence of juveniles in a destination patch. The probability of colonization was estimated as a logistic function of the distance from the nearest seed source. Patch‐level simulations using actual colonization parameters and forest distributions (based on field measurements) showed that about half the species studied in Yokohama (Japan) would fail to recolonize the studied region for at least 20 generations. Moreover, patch density was too sparse for 30% of the studied species, which will thus be unable to expand their distributions and reverse local extinctions. Dominant species of the region's climax forest will not reach vacant patches, and normal vegetation succession will be obstructed.
FIRE IN AFRICAN SAVANNA: TESTING THE IMPACT OF INCOMPLETE COMBUSTION ON PYROGENIC EMISSIONS ESTIMATES
Authors: Smith Alistair M. S. , Wooster Martin J. , Drake Nick A. , Dipotso Frederick M. , Perry George L. W.
Published: June 2007

African savannah fires are key sources of trace gases and aerosols, yet their true magnitude remains relatively poorly constrained. Here we present a detailed investigation of the amount of unburned material remaining in the ash produced by such fires, and examine whether this quantity needs to be considered when calculating atmospheric emissions. Emissions estimates for individual fires are usually based upon a calculation of the amount of fuel biomass combusted, usually estimated via a “simple subtraction” of the pre‐ and post‐fire fuel loads. However, certain studies have concluded that this approach leads to gross overestimation of emissions, by perhaps 100%, due to the fact that a proportion of unburned fuel normally remains in the “charred” ash and that the simple subtraction method fails to take this fully into account. Whilst this latter point is true, we show that the mathematical relationship used previously to calculate the implications of this for emissions calculation is flawed. We demonstrate a new first‐principles derivation of the quantity of mass combusted, taking into account any fuel remaining in the ash via measurement of ash mass loss on ignition (LOI). Using data from dry‐season experimental fires in Botswana, we compared estimates of biomass combusted calculated via our LOI‐based method to those obtained via the simple subtraction approach. We found a mean difference of <10%, far less than the factor of 2 difference obtained when using the previous erroneous formula. Similar results are obtained for carbon and nitrogen emissions, and the findings are further supported by reassessment of previous data from early‐to‐mid‐dry season savanna fires in Tanzania. These results indicate that the simple subtraction method overestimates emissions by far less than previously suggested, and that the method is likely to provide sufficient accuracy in most situations where emissions calculations are required. For fires where very substantial amounts of unburned material are expected to remain within the ash, and where an LOI‐based approach to emissions calculation may therefore be particularly warranted, it is important that the correct formula derived herein is used, since errors inherent in the previous formula increase with increasing ash LOI.
GRAZING EFFECTS ON RANGELAND DIVERSITY: A SYNTHESIS OF CONTEMPORARY MODELS
Authors: Cingolani Ana M. , Noy-Meir Imanuel , Díaz Sandra
Published: June 2007

Two independent models concerning the effects of grazing on vegetation have gained wide acceptance in the last decade: Westoby et al.'s state‐and‐transition (S– T) model, and Milchunas et al.'s generalized model of the effects of grazing on plant community structure and diversity (MSL model). These two prevailing models, as they stand, are conceptually divergent. The MSL model implicitly assumes that, at a given site, for each grazing intensity there is a single equilibrium situation with a single diversity value. The S–T model suggests that rangeland dynamics include irreversible transitions and alternative equilibria. Here we propose a modification of the original MSL model, to encompass a wider range of real situations and to place it within the context of the S–T model. The four extreme cases proposed in the original MSL model are revisited, taking into account that (1) the “moisture” gradient can be generalized as a “productivity” gradient; (2) the selective pressure of herbivores on systems with long history of grazing has fluctuated over time, allowing the development of different pools of species adapted to low or high grazing intensities; and (3) systems with long evolutionary history of grazing have developed resilience mechanisms that allow reversible shifts in floristic composition with changes in grazing intensities. The grazing intensity vs. diversity curves thus postulated for systems with a long evolutionary history of grazing are similar to those proposed by the original MSL model because resilience mechanisms allow for reversible changes associated with grazing intensity. In contrast, the curves postulated for systems with short evolutionary history of grazing include different alternative branches, indicating irreversible transitions, because resilience mechanisms to grazing were not fully developed. By incorporating these modifications, the divergence between the original MSL and S–T models can be resolved. A set of published examples from real systems is presented and compared with the predictions of the modified model. The modified MSL model is applicable to a wider range of real situations than the MSL model in its original formulation.
USING AIRBORNE MULTISPECTRAL IMAGERY TO EVALUATE GEOMORPHIC WORK ACROSS FLOODPLAINS OF GRAVEL‐BED RIVERS
Authors: Lorang M. S. , Whited D. C. , Hauer F. R. , Kimball J. S. , Stanford J. A.
Published: June 2007

Fluvial processes of cut and fill alluviation and channel abandonment or avulsion are essential for maintaining the ecological health of floodplain ecosystems characteristic of gravel‐bed rivers. These dynamic processes shape the floodplain landscape, resulting in a shifting mosaic of habitats, both above and below ground. We present a new and innovative methodology to quantitatively assess the geomorphic work potential necessary to maintain a shifting habitat mosaic for gravel‐bed river floodplains. This approach can be used to delineate critical habitats for preservation through land acquisition and conservation easements, often critical elements of river restoration plans worldwide. Spatially explicit modeling of water depth, flow velocity, shear stress, and stream power derived from surface hydraulic measurements was combined with airborne multispectral remote sensing for detailed modeling of floodplain water surfaces over tens to hundreds of square kilometers. The model results were then combined within a GIS framework to determine potential nodes of channel avulsion that delineate spatially explicit zones across the floodplain where the potential for geomorphic work is the greatest. Results of this study demonstrate the utility of integrating existing multispectral remote sensing data coupled with time‐lagged ground‐based measures of flow hydraulics to model fluvial processes at relatively fine spatial resolutions but over broad regional extents.
EXAMINING THE RECENT CLIMATE THROUGH THE LENS OF ECOLOGY: INFERENCES FROM TEMPORAL PATTERN ANALYSIS
Authors: Hessburg Paul F. , Kuhlmann Ellen E. , Swetnam Thomas W.
Published: June 2007

Ecological theory asserts that the climate of a region exerts top‐down controls on regional ecosystem patterns and processes, across space and time. To provide empirical evidence of climatic controls, it would be helpful to define climatic regions that minimized variance in key climate attributes, within climatic regions—define the periods and features of climatic regimes, and then look for concordance between regional climate and ecosystem patterns or processes. In the past, these steps have not been emphasized. Before we evaluated the recent climate of the northwestern United States, we established a Northwest climatic region by clustering time series of the Palmer Drought Severity Index (PDSI) for the period of 1675–1978, for the western United States. The background climatic regime and anomalies of the recent northwestern U.S. climate were then identified through temporal pattern analysis involving application of correspondence analysis to the same PDSI time series.

Our analysis distinguished 10 distinct periods and four unique types of regimes (climatic signals). Five of the 10 periods (79% of the ∼300‐year record) were marked by mild and equitable moisture conditions (Pacific regime), the “background” climate of the Northwest. The remaining periods were anomalies. Two periods displayed a high‐variance, mixed signal marked by switching between severe to extreme annual to interannual dry and wet episodes (High/Mixed regime; 9% of the record). Two more periods displayed a moderate‐variance, mixed signal marked by switching between moderate to severe annual to interannual dry and wet episodes (Moderate/Mixed regime; 5%). Only one period was unidirectional and relatively low variance, marked by persistent yet mild to moderate drought (Low/Dry regime, 7%).

Our method distinguished decadal‐ to interdecadal‐scale regimes, defined regime periods, and detected both mixed and unidirectional anomalies from the background climate. The ability to distinguish the variance, direction, and period of sequential climatic regimes provides a plausible basis for examining the role of past climate within terrestrial ecosystems of the Northwest. For example, we found concordance between the period of the Low/Dry anomaly and a period of tree establishment in the Olympic Mountains of Washington, close alignment between tree growth with the Moderate/Mixed and High/Mixed signals in Oregon, and a mixed fire response to mixed climatic signals in northeastern Oregon. Linking historical climatic regimes to particular ecosystem patterns and processes also aids in the prediction of future ecosystem changes by providing evidence of the kinds of interactions that may be anticipated.
IDENTIFYING ECOLOGICAL CHANGE AND ITS CAUSES: A CASE STUDY ON CORAL REEFS
Authors: Fabricius Katharina E. , De'ath Glenn
Published: June 2007

The successful management of ecosystems depends on early detection of change and identification of factors causing such change. Determination of change and causality in ecosystems is difficult, both philosophically and practically, and these difficulties increase with the scale and complexity of ecosystems. Management also depends on the communication of scientific results to the broader public, and this can fail if the evidence of change and causality is not synthesized in a transparent manner. We developed a framework to address these problems when assessing the effects of agricultural runoff on coral reefs of the Australian Great Barrier Reef (GBR). The framework is based on improved methods of statistical estimation (rejecting the use of statistical tests to detect change), and the use of epidemiological causal criteria that are both scientifically rigorous and understood by nonspecialists. Many inshore reefs of the GBR are exposed to terrestrial runoff from agriculture. However, detecting change and attributing it to the increasing loads of nutrients, sediments, and pesticides is complicated by the large spatial scale, presence of additional disturbances, and lack of historical data. Three groups of ecological attributes, namely, benthos cover, octocoral richness, and community structure, were used to discriminate between potential causes of change. Ecological surveys were conducted along water quality gradients in two regions: one that receives river flood plumes from agricultural areas and one exposed to runoff from catchments with little or no agriculture. The surveys showed increasing macroalgal cover and decreasing octocoral biodiversity along the gradients within each of the regions, and low hard coral and octocoral cover in the region exposed to terrestrial runoff. Effects were strong and ecologically relevant, occurred independently in different populations, agreed with known biological facts of organism responses to pollution, and were consistent with pollution effects found in other parts of the world. The framework enabled us to maximize the information derived from observational data and other sources, weigh the evidence of changes across potential causes, make decisions in a coherent and transparent manner, and communicate information and conclusions to the broader public. The framework is applicable to a wide range of ecological assessments.
THE USE OF ECOLOGICAL SCIENCE BY RURAL PRODUCERS: A CASE STUDY IN MEXICO
Authors: Castillo A. , Torres A. , Velázquez A. , Bocco G.
Published: June 2007

The role of ecological science in promoting sound environmental decisions has concerned ecologists worldwide and it has been stressed that the application of ecological knowledge requires new interactive and participatory forms of research, as well as sound partnerships between ecologists and land managers. However, concrete examples of ecological science as part of rural decision making have rarely been examined, especially in intertropical countries. We analyzed interactions between ecological scientists from the National Autonomous University of Mexico (UNAM) and a rural indigenous community involved in forest management in Central‐Western Mexico. Using qualitative research methods (such as observing participants, conducting interviews; generally focusing on the meanings that social actors give to phenomena), we compared the perspectives of the academic and community sectors in relation to benefits, products, problems, and obstacles faced when conducting integrative forest management. The research showed the relevance of rural communities demanding scientific information for ecosystem management and of academic institutions accepting to respond to these demands. Participatory approaches and continuous communication between sectors were essential for establishing trust and commitment for everyone involved. The obstacles found were related to an academic institution's inability to support such an experience and to accept capacity building of rural managers as part of its scientific mission. We concluded that applied ecological science in developing countries, such as Mexico, should regard rural communities as key ecosystem managers and should respond to their needs and demands in order to convert pure scientific findings into wise environmental decisions.
WHAT IS THE BEST PREDICTOR OF ANNUAL LYME DISEASE INCIDENCE: WEATHER, MICE, OR ACORNS?
Authors: Schauber Eric M. , Ostfeld Richard S. , Evans, Jr Andrew S.
Published: June 2007

Predicting fluctuations in annual risk of Lyme disease would be useful in focusing public health efforts. However, several competing hypotheses have been proposed that point to weather variables, acorn production, or mouse abundance as important predictors of Lyme disease risk. We compared the ability of acorn production, mouse density, and four relevant weather variables to predict annual Lyme disease incidence (detrended) between 1992 and 2002 for Dutchess County, New York, and seven states in the northeastern United States. Acorn production and mouse abundance measured in Dutchess County were the strongest predictors (r ≥ 0.78) of Dutchess County Lyme disease incidence, but the increase in mouse abundance from 1991 to 1992 was contrary to a decrease in Lyme disease in the following years. The Palmer Hydrologic Drought Index (PHDI) was a significant positive predictor of Lyme disease incidence two years later for three states (0.58 ≤ r ≤ 0.88), but summer precipitation was generally negatively correlated with Lyme disease incidence the next year (−0.79 ≤ r ≤ 0.02). Mean temperatures for the prior winter or summer showed weak or inconsistent correlations with Lyme disease incidence. In four states, no variable was a statistically significant predictor of Lyme disease incidence. Synchrony in Lyme disease incidence between pairs of states was not significantly concordant with synchrony in any weather variable that we examined (0.02 ≤ r ≤ 0.21). We found that acorns and mice were strong predictors of Dutchess County Lyme disease incidence, but their predictive power appeared to be weaker spatially. Moreover, evidence was weak for causal relationships between Lyme disease incidence and the weather variables that we tested. Reliable prediction of Lyme disease incidence may require the identification of new predictors or combinations of biotic and abiotic predictors and may be limited to local scales.
WINDSTORM DISTURBANCE EFFECTS ON FOREST STRUCTURE AND BLACK BEAR DENS IN SOUTHEAST ALASKA
Authors: DeGayner Eugene J. , Kramer Marc G. , Doerr Joseph G. , Robertsen Margaret J.
Published: June 2007

We examined the relationships among forest susceptibility to windstorm damage, forest structure, and black bear winter den site selection in the coastal temperate rain forests of southeastern Alaska, USA. Forest susceptibility to maritime windstorms was determined by applying a wind‐disturbance model (WINDSTORM) to two study areas where bear dens had been identified by radio telemetry. We evaluated model predictions for forest structure against field data for one study area. As predicted, forests in wind‐protected landscapes contained features indicative of later stages of forest development where larger and older trees are more abundant. By contrast, forests located in storm‐susceptible locations contained higher tree densities, less variation in tree diameters, smaller trees, and less evidence of large, old trees with heart rot. Analysis of habitat use relative to its availability on the landscape indicates that bears selected wind‐protected landscapes over storm‐prone landscapes in both study areas for winter dens. The majority (58%) of den sites were located in forests most protected from catastrophic storm effects. By contrast, only 6% were located in forests most exposed to storm damage. Results suggest that forests most protected from catastrophic windstorm disturbance contain more suitable overwinter habitat for black bears as evidenced by den site selection.
EFFECTS OF CONIFERS AND ELK BROWSING ON QUAKING ASPEN FORESTS IN THE CENTRAL ROCKY MOUNTAINS, USA
Authors: Kaye Margot W. , Binkley Dan , Stohlgren Thomas J.
Published: June 2007

Elk browsing and conifer species mixing with aspen (Populus tremuloidesMichx.) present current challenges to aspen forest management in the western United States. We evaluated the effects of conifers and elk browsing on quaking aspen stands in and near Rocky Mountain National Park using tree rings to reconstruct patterns of aspen establishment, growth, and mortality over the past 120 years. High conifer encroachment and elk browse were both associated with decreased aspen recruitment, with mean recruitment dropping over 30% from pure aspen to mixed stands and over 50% from low‐browse to high‐browse stands. Maximum aspen recruitment was lower in mixed stands than in pure stands with the same tree basal area. High levels of elk browsing were also associated with a 30% decrease in stand‐level growth of aspen. Neither high conifer abundance nor elk browse affected the growth of individual trees or aspen mortality. Aspen establishment was negatively influenced by conifers and elk browsing; however, aspen growth and mortality appeared to be resilient to these two external influences. Overall, these results suggest that long‐term preservation of aspen forests could be achieved by enhancing aspen recruitment.
ROBUST DECISION‐MAKING UNDER SEVERE UNCERTAINTY FOR CONSERVATION MANAGEMENT
Authors: Regan Helen M. , Ben-Haim Yakov , Langford Bill , Wilson William G. , Lundberg Per , Andelman Sandy J. , Burgman Mark A.
Published: June 2007

In conservation biology it is necessary to make management decisions for endangered and threatened species under severe uncertainty. Failure to acknowledge and treat uncertainty can lead to poor decisions. To illustrate the importance of considering uncertainty, we reanalyze a decision problem for the Sumatran rhino, Dicerorhinus sumatrensis, using information‐gap theory to propagate uncertainties and to rank management options. Rather than requiring information about the extent of parameter uncertainty at the outset, information‐gap theory addresses the question of how much uncertainty can be tolerated before our decision would change. It assesses the robustness of decisions in the face of severe uncertainty. We show that different management decisions may result when uncertainty in utilities and probabilities are considered in decision‐making problems. We highlight the importance of a full assessment of uncertainty in conservation management decisions to avoid, as much as possible, undesirable outcomes.
WEAK VS. STRONG INVADERS OF NATURAL PLANT COMMUNITIES: ASSESSING INVASIBILITY AND IMPACT
Authors: Ortega Yvette K. , Pearson Dean E.
Published: June 2007

In response to the profound threat of exotic species to natural systems, much attention has been focused on the biotic resistance hypothesis, which predicts that diverse communities should better resist invasions. While studies of natural communities generally refute this hypothesis, reporting positive relationships between native species diversity and invasibility, some local‐scale studies have instead obtained negative relationships. Most treatments of the topic have failed to recognize that all exotic invaders do not behave alike: while “weak” invaders become minor components of communities, “strong” invaders become community dominants at the expense of native species. At the same time, the specific impacts of strong invaders on communities are poorly documented yet critical to understanding implications of diversity loss. With these shortfalls in mind, we examined local‐scale relationships between native and exotic plant taxa in bunchgrass communities of western Montana, USA. We found that measures of native species diversity and invasibility were positively correlated in communities with low levels of invasion where both weak and strong invaders occurred at low densities, but negatively correlated in communities with high levels of invasion where the strong invader Centaurea maculosa dominated. Furthermore, at both low and high levels of invasion, weak invaders tended to vary positively with native species richness while strong invaders varied negatively. Weak invaders determined positive overall relationships between native and exotic species in low invasion communities and appeared to coexist with native taxa. Strong invaders prevailed in high invasion communities, driving negative overall relationships therein. That negative relationships primarily reflected strong invader impacts was supported by the fact that negative correlations of C. maculosa with native species diversity and abundance held when we statistically controlled for levels of native species representing preinvasion conditions. In addition, negative associations of C. maculosa with native taxa varied in strength by functional group and species, with large effects on numerically dominant species, suggesting a dramatic shift in community composition and structure. The distinction between weak and strong invaders is important for reconciling conflicting results from previous studies of natural communities, and moving attention beyond the current debate surrounding the biotic resistance hypothesis.
PLANT TRAITS AND ECOSYSTEM GRAZING EFFECTS: COMPARISON OF U.S. SAGEBRUSH STEPPE AND PATAGONIAN STEPPE
Authors: Adler Peter B. , Milchunas Daniel G. , Sala Osvaldo E. , Burke Ingrid C. , Lauenroth William K.
Published: June 2007

Plant functional traits provide one tool for predicting the effects of grazing on different ecosystems. To test this approach, we compared plant traits and grazing response across analogous climatic gradients in sagebrush steppe, USA (SGBR), known to have a short evolutionary history of grazing, and Patagonian steppe, Argentina (PAT), where generalist herbivores exerted stronger selective pressures. We measured grazing response by sampling vegetation and soils across distance‐from‐water gradients at arid, semiarid, and subhumid study areas in both regions. Based on a previous analysis of graminoid traits, we predicted that: (1) high forage quality in all three SGBR communities would lead to high utilization and large grazing effects, whereas low quality in arid PAT would constrain utilization and grazing impacts, with semiarid and subhumid PAT intermediate in quality and grazing response; and (2) grazing in arid PAT would cause shifts in relative abundance within the graminoid functional group, due to the large range of forage quality among graminoids, but in SGBR, where all graminoids are relatively palatable, shifts in abundance would occur between grasses and shrubs.

Utilization in locations close to water was higher in SGBR than in PAT study areas. This utilization difference led to differences in grazing effects consistent with our first prediction. Abundance of graminoids increased with distance from water in all three SGBR communities and in subhumid PAT, but not in arid PAT. Shrub and total production decreased with distance in SGBR but not PAT study areas. Grazing variables explained less variation in species composition in arid PAT (43%) than in any other study area (59–74%). Grazing did not significantly influence species richness. Evidence for our second prediction was mixed. Grazing did alter the relative abundance of SGBR graminoids and shrubs, but abundance shifts among the graminoids in SGBR communities were larger than in PAT communities, counter to our prediction.

This case study demonstrates how plant traits can explain relative effects of grazing on ecosystem structure and functioning, although predicting species‐specific responses remains a challenge. Regardless of their evolutionary origin, poor‐quality graminoids make the arid Patagonian steppe more resistant to overgrazing than communities dominated by more nutritious species.
DISTURBANCE HISTORY AND HISTORICAL STAND DYNAMICS OF A SEASONAL TROPICAL FOREST IN WESTERN THAILAND
Authors: Baker Patrick J. , Bunyavejchewin Sarayudh , Oliver Chadwick D. , Ashton Peter S.
Published: June 2007

Disturbances influence forest dynamics across a range of spatial and temporal scales. In tropical forests most studies have focused on disturbances occurring at small spatial and temporal scales (i.e., gap dynamics). This is primarily due to the difficulty of reconstructing long‐term disturbance histories of forests in which most tree species lack annual growth rings. Consequently, the role of past disturbances in tropical forests is poorly understood. We used a combination of direct and indirect methods to reconstruct the historical disturbance regime and stand development patterns in mature and regenerating seasonal dry evergreen forest (SDEF) in the Huai Kha Khaeng Wildlife Sanctuary in western Thailand. Direct estimates of long‐term establishment and growth patterns were obtained from 12 tree species that form annual growth rings as a consequence of the region's strong intra‐annual rainfall seasonality. Indirect estimates of establishment patterns were obtained from analyses of stand structure and individual tree architecture and application of age‐estimation models to 10 dominant canopy‐tree species using demographic data from a large‐scale, permanent forest‐dynamics plot.

The combination of direct and indirect methodologies revealed a complex disturbance history in the seasonal evergreen forest over the past 250 years. In the mid‐1800s, 200–300 ha of forest were destroyed by a catastrophic disturbance, which led to the synchronous establishment of many of the trees that presently dominate the forest canopy. Since then widespread disturbances of variable intensity have occurred at least three times (1910s, 1940s, and 1960s). These disturbances created discrete temporal pulses of establishment in small to large gaps in the forest matrix across several square kilometers. Background mortality and gap formation were evident in every decade since 1790, but these varied in intensity and frequency.

The SDEF retains a distinct structural and floristic legacy from the catastrophic disturbance of the mid‐1800s. The single‐age cohort that established after the disturbance has developed a complex three‐dimensional structure as a consequence of differences in interspecific growth patterns of the canopy‐tree species and subsequent disturbances of moderate and low intensity. While no single methodological approach provided a complete picture of the disturbance history and stand development patterns of the seasonal evergreen forest, taken together they offered new insights into the long‐term dynamics of a primary tropical forest. In particular, the study highlighted the role of disturbance at multiple spatial and temporal scales and varying intensities in determining the structure and composition of a complex, species‐rich tropical forest and raises important questions about the role of rare, catastrophic events on tropical forest dynamics.
PHYSICAL FACTORS VS. BIOTIC RESISTANCE IN CONTROLLING THE INVASION OF AN ESTUARINE MARSH GRASS
Authors: Dethier Megan N. , Hacker Sally D.
Published: June 2007

We examined the relative roles of biotic resistance and abiotic factors in controlling the establishment and early survival of an invasive marine grass, Spartina anglica, in the Pacific Northwest. S. anglica can invade diverse estuarine habitats, including established salt marshes, mudflats, and cobble beaches; these vary in native species assemblages and in abiotic conditions, especially sediment salinity, water content, and composition. In four habitat types in northern Puget Sound, we conducted a seed addition experiment to quantify germination and early growth. In vegetated habitats we also manipulated plant neighbors. Seed germination and early growth varied with habitat and zone, but physical factors played a more important role than species interactions. Seedlings in low‐salinity marshes and mudflats grew almost 10 times larger than those in coarse‐grained or high‐salinity habitats. Patterns of seedling persistence among habitats matched those of natural seedling abundances and mirrored the degree of invasion in different habitat types in the region. The lack of biotic resistance may be due to the stressful nature of saline systems or the lack of species that can compete with or consume the invader. In such systems, managers should focus on how physical vulnerabilities of the habitat can provide invasion “windows of opportunity.”
SUBSTRATE FORM DETERMINES THE FATE OF BRYOPHYTES IN RIPARIAN BUFFER STRIPS
Authors: Hylander Kristoffer , Dynesius Mats , Jonsson Bengt Gunnar , Nilsson Christer
Published: June 2007

Studies on the effectiveness of forest buffer strips left along streams after logging have long overlooked the biota of the buffers themselves, despite their high species richness. We investigated mosses and liverworts (bryophytes), abundant and species‐rich groups in boreal forests, before and 2.5 years after logging along 15 small streams. In each site, two 1000‐m2(20 × 50 m) plots along the stream were inventoried; one plot in an area subjected to clear‐cutting, and another in a buffer strip (10 m wide on each side of the stream). Ten plots along small streams in forest reserves in the same region were used as references. We found that less than half as many bryophyte species per plot disappeared after logging in the buffer strips compared to the clearcuts. The changes in bryophyte cover and in species composition were smaller in the buffer strips, and the species that were negatively affected in the clearcuts were less affected in the buffer strips. However, there was a significant change in species composition in the buffer strips compared to the references. Substrate form and taxonomic group were important factors in understanding this turnover. Many species growing on substrates with a convex form (e.g., logs, tree bases, and mesic ground) decreased or disappeared, while species on concave substrates were rather unaffected. This held for both mosses and liverworts, although liverworts were generally more sensitive than mosses. The difference in response of assemblages on convex vs. concave substrates makes changes in microclimate due to logging a likely explanation. The species in most need of protection (i.e., the red‐listed species) were among the ones with strongest declines in the 20 m wide buffer strips. In order to function optimally for bryophyte conservation, forests along small streams need to be protected from high windthrow frequency and strong edge effects. Increasing the width of buffer strips at sites with known or potential values (e.g., large amounts of woody debris or boulders) should be considered a better strategy than using narrow buffer strips with a fixed width.