bluuebunny/crossref_metadata_2025_split huggingface dataset:
DISTURBANCE AND STAND DYNAMICS IN PONDEROSA PINE FORESTS IN ROCKY MOUNTAIN NATIONAL PARK, USA
Authors: Ehle Donna S. , Baker William L. 
Published: June 2007

Fire is thought to be the dominant disturbance agent in pure ponderosa pine (Pinus ponderosaLaws.) forests, but fire severity and disturbances other than fire, and the effects of these events over time, have rarely been analyzed. We first created systematic criteria to (1) identify the causes of tree regeneration and mortality events and (2) classify the severity of these events. These criteria were then applied to understand the effect of events on ponderosa pine forests in Rocky Mountain National Park (RMNP), Colorado.For each of nine intensive study plots sampled in the pure ponderosa pine zone of RMNP, we mapped and dated live and dead trees and the spatial extent of fire and non‐fire events using dendrochronology. Events were identified using evidence of disturbance agents, such as blue‐stain fungus in the case of mountain pine beetles, fire scars, and climatic reconstructions. Disturbance severity was classified based on amounts and spatial distribution of regeneration, mortality, and survivors. We studied the temporal and spatial relationships between events and tree age structures to determine historical and contemporary stand dynamics.We identified 103 events among the nine study plots; 97% of these events were fire. High‐severity events were 7% of events, 2% of events were mixed‐severity, and the other 70% were low‐severity. The severity of 20% of events could not be determined. All but one of the high‐severity events were fire. In seven plots, at least one crown fire occurred within the last 300 years. In RMNP, pre‐EuroAmerican settlement crown fires led to dense, even‐aged stands. Subsequent surface fires killed some trees and facilitated the regeneration of others, leading to less dense, uneven‐aged stands after ∼200–300 years. Climate may be the cause or co‐cause of one or two regeneration pulses within the last 300 years, but most regeneration and mortality is associated with fire. The historical occurrence of crown fires, as well as surface fires, in pure ponderosa pine forests in RMNP indicates that the fire regime is more variable than previously thought. Suppression of crown fires, though not completely possible, would move the fire regime outside its historical range of natural variability.Corresponding Editor: D. R. Strong
QUANTIFYING SCALE IN ECOLOGY: LESSONS FROM AWAVE‐SWEPT SHORE
Authors: Denny Mark W. , Helmuth Brian , Leonard George H. , Harley Christopher D. G. , Hunt Luke J. H. , Nelson Elizabeth K. 
Published: June 2007

Understanding the role of scale is critical to ecologists' ability to make appropriate measurements, to “scale up” from local, short‐term experiments to larger areas and longer times, to formulate models of community structure, and to address important conservation problems. Although these issues have received increased attention in recent years, empirical measurements of the scales of ecologically important variables are still rare. Here, we measure the spatial and temporal scales of variability of 15 ecologically relevant physical and biological processes in the wave‐swept intertidal zone at Mussel Point, near Hopkins Marine Station in California. We analyze temporal variability in wave height, ocean temperature, upwelling intensity, solar irradiance, and body temperature for periods ranging from ten minutes to fifty years. In addition, we measure spatial variation in shoreline topography, wave force, wave‐induced disturbance, body temperature, species diversity, recruitment, primary productivity, and the abundances of grazers, predators, and the competitive dominant occupier of space. Each of these spatial variables is measured along three horizontal transects in the upper intertidal zone: a short transect (44 m long with sampling locations spaced at ∼0.5‐m intervals), a medium transect (175 m long with sampling locations spaced at ∼1.7‐m intervals), and a long transect (334 m long with sampling locations spaced at ∼3.4‐m intervals). Six different methods are used to quantify the scale of each variable.Distinct scales are evident in all but one of our temporal variables, demonstrating that our methods for quantifying scale can work effectively with relatively simple, periodic phenomena. However, our spatial results reveal basic problems that arise when attempting to measure the scale of variability for more complex phenomena. For a given variable and length of transect, different methods of calculating scale seldom agree, and in some cases estimates differ by more than an order of magnitude. For a given variable and method of calculating spatial scale, measurements are sensitive to the length of a transect; the longer the transect, the larger the estimate of scale. We propose that the “1/f noise” nature of the data can explain both the variability among methods for calculating scale and the length dependence of spatial scales of variation, and that the 1/f noise character of the data may be driven by the fractal geometry of shoreline topography. We conclude that it may not be possible to define a meaningful spatial scale of variation in this system. As an alternative to the boiled‐down concept of “scale,” we suggest that it is more appropriate to examine explicitly the pattern in which variability changes with the extent of measurement (e.g., the spectrum). Knowledge of this pattern can provide useful ecological scaling “rules” even when a well‐defined scale (or hierarchy of scales) cannot be discerned.
OAK FOREST CARBON AND WATER SIMULATIONS: MODEL INTERCOMPARISONS AND EVALUATIONS AGAINST INDEPENDENT DATA
Authors: Hanson P. J. , Amthor J. S. , Wullschleger S. D. , Wilson K. B. , Grant R. F. , Hartley A. , Hui D. , Hunt, Jr E. R. , Johnson D. W. , Kimball J. S. , King A. W. , Luo Y. , McNulty S. G. , Sun G. , Thornton P. E. , Wang S. , Williams M. , Baldocchi D. D. , Cushman R. M. 
Published: June 2007

Models represent our primary method for integration of small‐scale, process‐level phenomena into a comprehensive description of forest‐stand or ecosystem function. They also represent a key method for testing hypotheses about the response of forest ecosystems to multiple changing environmental conditions. This paper describes the evaluation of 13 stand‐level models varying in their spatial, mechanistic, and temporal complexity for their ability to capture intra‐ and interannual components of the water and carbon cycle for an upland, oak‐dominated forest of eastern Tennessee. Comparisons between model simulations and observations were conducted for hourly, daily, and annual time steps. Data for the comparisons were obtained from a wide range of methods including: eddy covariance, sapflow, chamber‐based soil respiration, biometric estimates of stand‐level net primary production and growth, and soil water content by time or frequency domain reflectometry. Response surfaces of carbon and water flux as a function of environmental drivers, and a variety of goodness‐of‐fit statistics (bias, absolute bias, and model efficiency) were used to judge model performance.A single model did not consistently perform the best at all time steps or for all variables considered. Intermodel comparisons showed good agreement for water cycle fluxes, but considerable disagreement among models for predicted carbon fluxes. The mean of all model outputs, however, was nearly always the best fit to the observations. Not surprisingly, models missing key forest components or processes, such as roots or modeled soil water content, were unable to provide accurate predictions of ecosystem responses to short‐term drought phenomenon. Nevertheless, an inability to correctly capture short‐term physiological processes under drought was not necessarily an indicator of poor annual water and carbon budget simulations. This is possible because droughts in the subject ecosystem were of short duration and therefore had a small cumulative impact. Models using hourly time steps and detailed mechanistic processes, and having a realistic spatial representation of the forest ecosystem provided the best predictions of observed data. Predictive ability of all models deteriorated under drought conditions, suggesting that further work is needed to evaluate and improve ecosystem model performance under unusual conditions, such as drought, that are a common focus of environmental change discussions.
PREDICTING THE TIME OF TREE DEATH USING DENDROCHRONOLOGICAL DATA
Authors: Bigler Christof , Bugmann Harald 
Published: June 2007

Complex interactions of various environmental factors result in high variability of tree mortality in space and time. Tree mortality functions that are implemented in forest succession models have been suggested to play a key role in assessing forest response to climate change. However, these functions are based on theoretical considerations and are likely to be poor predictors of the timing of tree death, since they do not adequately reflect our understanding of tree mortality processes. In addition, these theoretical mortality functions and most empirical mortality functions have not been tested sufficiently with respect to the accuracy of predicting the time of tree death.We introduce a new approach to modeling tree mortality based on different growth patterns of entire tree‐ring series. Dendrochronological data fromPicea abies(Norway spruce) in the Swiss Alps were used to calibrate mortality models using logistic regression. The autocorrelation of the data was taken into account by a jackknife variance estimator.Model performance was assessed by two criteria for classification accuracy and three criteria for prediction error. The six models with the highest overall performance correctly classified 71–78% of all dead trees and 73–75% of all living trees, and they predicted 44– 56% of all dead trees to die within 0–15 years prior to the actual year of death. For these six models, a maximum of 1.7% of all dead trees and 5% of all living trees were predicted to die >60 years prior to the last measured year. Models including the relative growth rate and a short‐term growth trend as explanatory variables were most reliable with respect to inference and prediction.The generality of the mortality models was successfully tested by applying them to two independentP. abiesdata sets from climatologically and geologically different areas. We conclude that the methods presented improve our understanding of how tree growth and mortality are related, which results in more accurate mortality models that can ultimately be used to increase the reliability of predictions from models of forest dynamics.
TWO CENTURIES OF MULTIPLE HUMAN IMPACTS AND SUCCESSIVE CHANGES IN A NORTH ATLANTIC FOOD WEB
Authors: Lotze Heike K. , Milewski Inka 
Published: June 2007

European colonization of North America severely altered terrestrial and aquatic ecosystems alike. Here, we integrate archaeological, historical, and recent data to derive the ecological history of the Quoddy Region, Bay of Fundy, Canada, an upwelling region rich in marine diversity and productivity. We document successive changes on all trophic levels from primary producers to top predators over the last centuries. Our objectives were to (1) construct a baseline of “what was natural in the coastal ocean,” and (2) analyze the sequence and potential interaction of multiple human impacts.Archaeological records highlight the abundance and diversity of marine species used by indigenous people over the last 2000–3000 years. Europeans colonized the area in the late 1700s and rapidly transformed the environment by multiple “top‐down” (exploitation), “bottom‐up” (nutrient loading), and “side‐in” (habitat destruction, pollution) impacts. Most large vertebrates were severely overexploited by 1900, leading to the extinction of three mammal and six bird species. Diadromous fish dramatically declined after river damming in the early 1800s, and recovery was prevented by subsequent river pollution. Overfishing of groundfish stocks started in the late 1800s, gradually leading to a final collapse in the 1970s. In the 20th century, decline of traditional fisheries induced a shift to low trophic level harvesting and aquaculture, which increased exponentially over the past 20 years. Eutrophication caused shifts in seaweed and phytoplankton communities: Some long‐lived rockweeds were replaced by annual bloom‐forming algae, and diatoms were replaced by dinoflagellates.Today, the once unique Quoddy Region shows the most common signs of degradation found in highly impacted coastal areas worldwide. Multiple human influences have altered abundance and composition of every trophic level in the food web and reduced upper trophic levels by at least one order of magnitude. We highlight cumulative and indirect effects that impair the ability to predict and manage highly impacted coastal ecosystems. On the other hand, simple protection and restoration measures in the 20th century led to the recovery of some species. It is these successes that provide guidance for a more sustainable interaction of humans with their marine environment.
LITTER PRODUCTION AND LITTER NUTRIENT CONCENTRATIONS IN A FRAGMENTED AMAZONIAN LANDSCAPE
Authors: Vasconcelos Heraldo L. , Luizão Flávio J. 
Published: June 2007

We analyzed the effects of distance to forest edge and soil texture on fine‐litter production and on nutrient concentrations in the leaf fall in an experimentally fragmented landscape in Brazilian Amazonia. Production of fine litter (leaves, twigs <2 cm in diameter, flowers, and fruits) was measured over a 3‐yr period. Litter traps were installed in plots located near (<100 m) and far (>250 m) from forest edges, and in clayey or sandy soils. In total, 28 plots were established, with 10 litter traps per plot. Results reveal a significant effect of distance to forest edge on litter production, but no significant effect of soil type or interaction between soil type and edge distance. On average, annual litter production on edge plots exceeded that on the interior plots by 0.68 Mg/ha (9.50 ± 0.23 vs. 8.82 ± 0.14 Mg·ha−1·yr−1, mean ± 1 se, based on a 3‐yr period). With regard to nutrient concentrations in the leaf fall, we detected a significant effect of soil type on three of eight nutrients analyzed. Concentrations of N, Mg, and Mn were greater in leaves on clayey than on sandy soils. Distance to forest edge only significantly affected the concentration of Ca, which was greater near than far from edges, perhaps due to strong Ca mobilization by the roots of pioneer trees.Several factors may account for the observed increase in litterfall near forest edges, including the greater prevalence of winds, increased plant desiccation stress, and higher rates of tree recruitment, especially of pioneer trees, near edges. Elevated rates of litterfall are likely to have cascading effects on the ecology of fragmented forests, affecting the invertebrate fauna, increasing seed and seedling mortality, and causing forest fragments to be more vulnerable to destructive surface fires.
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.
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.