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Land-use history can play a significant role in shaping forest communities. We considered the effects of agricultural land-use legacies on the distribution of non-native invasive plants a century after abandonment in a watershed in western North Carolina, USA. Forest sites that were previously in cultivation and abandoned ca. 1905 were compared with nearby reference sites that were never cultivated. The most common invasive plants were Celastrus orbiculatus Thunb., Microstegium vimineum Trin., and Lonicera japonica Thunb. Formerly cultivated sites and plots positioned downslope from roads had the most invasives. Soil cation concentration and pH were positively correlated with invasive presence and abundance. Historic agricultural plots where the successional tree Liriodendron tulipifera L. was dominant had the highest soil cation concentrations and soil pH and the greatest abundance of invasive plants. Disentangling the cause-effect relationships between land-use history, the biotic community, and the abiotic template presents a challenge, but understanding the role of land-use legacies may provide important insights regarding the mechanisms underlying the establishment and spread of invasive plants in forest ecosystems. Our results suggest that land-use history at Bent Creek may be facilitating plant invasion indirectly by causing a shift in overstory community composition that in turn creates more suitable understory conditions for shade-tolerant invasive plants. L'utilisation passee des terres peut jouer un role important dans la formation des communautes forestieres. Nous avons examine les effets de l'utilisation passee des terres a des fins agricoles sur la distribution des plantes exotiques invasives, un siecle apres l'abandon de l'agriculture dans un bassin versant le l'ouest de la Caroline du Nord, aux etats-Unis. Les stations forestieres precedemment cultivees et abandonnees autour de 1905 ont ete comparees a des stations temoins situees a proximite et qui n'ont jamais ete cultivees. Les plantes invasives les plus frequentes etaient Celastrus orbiculatus Thunb., Microstegium vimineum Trin. et Lonicera japonica Thunb. Les stations precedemment cultivees et les parcelles situees en aval d'un chemin avaient la plus grande quantite de plantes invasives. La concentration des cations et le pH du sol etaient positivement correles avec la presence de plantes invasives et leur abondance. Les parcelles jadis occupees par l'agriculture, ou dominait l'espece successionnelle Liriodendron tulipifera L., avaient les plus fortes concentrations de cations dans le sol, le pH du sol le plus eleve et la plus grande abondance de plantes invasives. C'est un defi de demeler les relations de cause a effet entre l'utilisation passee des terres, la communaute biotique et la plate-forme abiotique mais la comprehension du role de l'heritage laisse par l'utilisation des terres peut fournir de precieuses indications concernant les mecanismes sous-jacents a l'etablissement et a la propagation des plantes invasives dans les ecosystemes forestiers. Nos resultats indiquent que l'utilisation passee des terres a Bent Creek pourrait indirectement faciliter l'invasion des plantes en provoquant un changement dans la composition de la communaute de l'etage dominant qui a son tour cree des conditions plus favorables en sousbois pour les plantes invasives tolerantes a l'ombre. [Traduit par la Redaction], Introduction Non-native invasive plants represent a significant driver of change in natural ecosystems by displacing native species, disrupting succession, and altering ecosystem structure and function (Vitousek et al. 1996). A [...]

Disturbance regimes are changing rapidly, and the consequences of such changes for ecosystems and linked social-ecological systems will be profound. This paper synthesizes current understanding of disturbance with an emphasis on fundamental contributions to contemporary landscape and ecosystem ecology, then identifies future research priorities. Studies of disturbance led to insights about heterogeneity, scale, and thresholds in space and time and catalyzed new paradigms in ecology. Because they create vegetation patterns, disturbances also establish spatial patterns of many ecosystem processes on the landscape. Drivers of global change will produce new spatial patterns, altered disturbance regimes, novel trajectories of change, and surprises. Future disturbances will continue to provide valuable opportunities for studying pattern-process interactions. Changing disturbance regimes will produce acute changes in ecosystems and ecosystem services over the short (years to decades) and long term (centuries and beyond). Future research should address questions related to (1) disturbances as catalysts of rapid ecological change, (2) interactions among disturbances, (3) relationships between disturbance and society, especially the intersection of land use and disturbance, and (4) feedbacks from disturbance to other global drivers. Ecologists should make a renewed and concerted effort to understand and anticipate the causes and consequences of changing disturbance regimes. Key words: disturbance regime; ecosystem ecology: fire; global change; landscape ecology; MacArthur Address; Pinus contorta; scale; spatial heterogeneity; succession; Yellowstone National Park.

Understanding nutrient dynamics of young postfire forests may yield important insights about how stands develop following stand-replacing wildfires. We studied 15-year-old lodgepole pine stands that regenerated naturally following the 1988 Yellowstone fires to address two questions: (1) How do foliar nitrogen (N) concentration and total foliar N vary with lodgepole pine density and aboveground net primary production? (2) Is foliar N related to litter production and to rates of gross production, consumption, and net production of soil N[H.sub.4.sup.+] and N[O.sub.3.sup.-]? Foliar N concentration of new lodgepole pine needles averaged 1.38%; only stands at very high density (>80 000 trees*[ha.sup.-1]) approached moderate N limitation. Foliar N concentration in composite (all-age) needles averaged 1.08%, varied among stands (0.87%-1.39%), and declined with increasing tree density. The foliar N pool averaged 48.3 kg N*[ha.sup.-1], varied among stands (3.6-218.4 kg N*[ha.sup.-1]), and increased with aboveground net primary production. Total foliar N was not related to laboratory estimates of net production of N[H.sub.4.sup.+] or N[O.sub.3.sup.-] in soils. Lodgepole pine foliage is a strong N sink, and N does not appear to be limiting at this early successional state. The initial spatial patterns of postfire tree density strongly influence landscape patterns of N storage. La comprehension de la dynamique des nutriments des jeunes forets issues de feux peut fournir des renseignements importants sur le developpement des peuplements a la suite d'un feu entrainant le remplacement des peuplements. Nous avons etudie des peuplements de pin tordu ages de 15 ans qui se sont regeneres naturellement apres les feux de 1988 dans le parc de Yellowstone pour repondre a deux questions : (1) comment la concentration d'azote (N) foliaire et le N foliaire total varient en fonction de la densite de pin tordu et de la production primaire nette aerienne (PPNA)? (2) estce que le N foliaire est relie a la production de litiere et aux taux de production brute, de consommation et de production nette de N[H.sub.4.sup.+] et de N[O.sub.3.sup.-] du sol? La concentration de N foliaire des nouvelles aiguilles de pin tordu etait, en moyenne, de 1,38 %. Seuls les peuplements tres denses (plus de 80 000 tigesha 1) ont approche une limitation moderee en N. La concentration foliaire en N d'echantillons composites d'aiguilles de tous les ages etait, en moyenne, de 1,08 %, variait de 0,87 % a 1,39 % parmi les peuplements et diminuait avec la densite du peuplement. Le reservoir de N foliaire etait, en moyenne, de 48,3 kg N*[ha.sup.-1], variait de 3,6 a 218,4 kg N*[ha.sup.-1] parmi les peuplements et augmentait avec la PPNA. Le N total foliaire n'etait pas relie aux estimations faites en laboratoire de la production nette de N[H.sub.4.sup.+] et de N[O.sub.3.sup.-] des sols. Le feuillage de pin tordu est un puits important de N qui ne semble pas etre limitatif a ce jeune stade de succession. Les patrons spatiaux initiaux de la densite des peuplements issus de feux modifient les patrons d'entreposage de N a l'echelle du paysage. [Traduit par la Redaction], Introduction Wildfire is a natural component of many forest ecosystems, and the frequency of large wildfires is increasing in the northern Rocky Mountains (Westerling et al. 2006) and North American [...]

Northern white cedar (Thuja occidentalis L.) stands throughout the upper Midwestern United States have failed to recruit individuals to the canopy consistently for several decades. To examine local and landscape factors that influence cedar regeneration we recorded the abundance of cedar seedlings and saplings in 24 lowland cedar stands in the Chequamegon-Nicolet National Forest, Wisconsin, during summer 2001. Cedar seedlings (height, INTRODUCTION Northern white cedar (Thuja occidentalis L.) stands throughout much of the Great Lakes region have shown recruitment failure for nearly 60 y (Curtis, 1946; Habeck, 1960; Chimner and Hart, [...]

Biome-scale disturbances by eruptive herbivores provide valuable insights into species interactions, ecosystem function, and impacts of global change. We present a conceptual framework using one system as a model, emphasizing [...]

It remains unclear if patterns of habitat use are driven by animals moving to and increasing residency time in selected areas, or by animals simply returning frequently to selected areas. We studied a population of North American elk (Cervus elaphus) in the Chequamegon National Forest, Wisconsin, to examine how spatial and temporal factors influence residency time in localized areas. We used global positioning system telemetry data from 7 elk and addressed 2 questions. First, does residency time vary as a function of spatial and temporal factors and if so does that relationship vary with measurement scale? Second, can residency time in the summer be predicted by a resource-selection map previously constructed for this population? Cross validation demonstrated that the statistical models had very poor predictive strength of independent data, which indicates that the explanatory variables have very little influence on elk residency time. Resources are patchily distributed on this landscape, and results demonstrate that elk preferentially use areas with high resource-selection function values. Unexpectedly, residency time was unrelated to values of resource-selection functions, which indicates that elk do not slow down in preferred areas. We conclude that patterns of elk habitat use are not driven by residency time but by elk returning frequently to favorable areas on the landscape. Random residency times may be a behavioral mechanism to lower predictability on the landscape and reduce predation risk. Key words: Canis lupus, Cervus elaphus, cross validation, heterogeneity, life-history strategies, predation, resource selection

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2007.01329.x Byline: Katharine I. Predick (*), Monica G. Turner Keywords: anthropogenic disturbance; exotic species; flood regime; landscape pattern; landscape ecology; land-use history; habitat quality; invasive species; riparian forest; soil nutrients Abstract: Summary Invasive species are present worldwide, yet predicting which invasive species will become problematic in which ecosystems remains an important ecological challenge. Floodplains are at particular risk for invasion, especially when subjected to anthropogenic disturbance. We examined how components of flood regime, habitat quality and habitat configuration influenced the presence and abundance of three invasive shrubs in the floodplain of the Wisconsin River. Shrub taxa included two non-natives (Lonicera spp. and Rhamnus spp.) and one native (Zanthoxylum americanum). Observations of taxa presence and abundance were recorded in nine forested river reaches, spanning three physiographic regions. We also compared the productivity of Z. americanum across a flood control levee in one reach. Physiographic region significantly predicted the presence and abundance of these three taxa, acting as a synthetic indicator of differences in climate, geography and topography. Invasion was greatest in regions where modifications to flood regime and land use were most pronounced. Physiographic region was excluded from subsequent analyses to assess more specific predictors of shrub distributions. Habitat configuration and quality both predicted shrub taxa presence and abundance. Shrub taxa were most frequently observed and most abundant in small forest patches, near roads, and in sandy soil with low nutrient content. Edge habitats have many of these characteristics. Edges appear to be favoured by avian shrub dispersers and provide conditions suitable for invasive establishment. Flooding influenced non-native and native invaders differently. Non-native taxa were observed less frequently and at lower abundances in frequently flooded areas, probably because of a sensitivity to flooding. However, the presence, abundance and productivity of the native invader increased with flooding. Anthropogenic modifications to the flood regime limited hydrologic connectivity and may have reduced the competitive advantage of flood-tolerant traits, which allowed the invasion of upland species. Synthesis. In the floodplain of the Wisconsin River, anthropogenic modifications that created edge habitat and altered flood regime facilitated shrub invasions, whereas unfragmented forest and intact flood regime limited invasion. Large patches of floodplain forest, less regulated flooding regimes, and lower road densities may help reduce the spread of invasive shrubs in temperate floodplains. Article History: Received 7 January 2007; accepted 12 October 2007 Handling Editor: Rob Brooker Article note: (*) Correspondence author. School of Natural Resources, University of Arizona, Biological Sciences East, 1311 E. 4th Street, Tucson, AZ 85721-0043, USA. E-mail: kipredick@arizona.edu

Explaining and predicting animal movement in heterogeneous landscapes remains challenging. This is in part because movement paths often include a series of short, localized displacements separated by longer-distance forays. This multiphasic movement behavior reflects the complex response of an animal to present environmental conditions and to its internal behavioral state. This state is an autocorrelated process influenced by preceding behaviors and habitats visited. Movement patterns depending on the behavioral state of an animal represent the broad-scale response of that animal to the environment. Quantifying how animals respond both to local conditions and to their internal state reveals how animals respond to spatial heterogeneity at different spatial scales. We used a state-space statistical approach to model the internal behavioral state and the proximate movement response of elk (Cervus elaphus) to available forage biomass, landscape composition, topography, and wolf (Canis lupus) density during summer in Yellowstone National Park, USA. We analyzed movement paths of 16 female elk fitted with global positioning system (GPS) radio collars that recorded locations at 5-h intervals. Habitat variables were quantified within 175 m radii (one-half of the median 5-h displacement) centered on the beginning location of each interval. Stepwise model selection identified models that best explained the movement distances of each animal. The behavioral state changed very slowly for most animals (median autocorrelation r = 0.93), and all animals responded strongly to time of day (with more movement in the crepuscular hours). However, the spatial variables included in the best-fitting models varied substantially among individual elk. These results suggest that strong patterns of habitat selection observed in other studies may result from frequent visits to preferred areas rather than a reduction of movement in those areas. Key words: animal movement; Cervus elaphus; elk; heterogeneous landscapes; Kalman filter; landscape ecology; multiphasic movement path analyses; state-space; ungulate; wapiti; Yellowstone National Park, USA.

We compared long-term change in two lake districts, one in a forested rural setting and the other in an urbanizing agricultural region, using lakes as sentinel ecosystems. Human population growth […]

Understanding ecosystem processes as they relate to wildfire and vegetation dynamics is of growing importance as fire frequency and extent increase throughout the western United States. However, the effects of severe, stand-replacing wildfires are poorly understood. We studied inorganic nitrogen pools and mineralization rates after stand-replacing wildfires in the Greater Yellowstone Ecosystem, Wyoming. After fires that burned in summer 2000, soil ammonium concentration peaked in 2001 (33 mg N[H.sub.4]-N*-[kg.sup.-1.sub.soil]; soil nitrate increased subsequently (2.7 mg N[O.sub.3]-N* [kg.sup.-1.sub.soil] in 2003) but was still low. However, annual net ammonification rates were largely negative from 2001 to 2004, indicating ammonium depletion. Thus, although net nitrification rates were positive, annual net nitrogen mineralization (net ammonification plus net nitrification) remained low. Aboveground net primary production (ANPP) increased from 0.25 to 1.6 Mg*[ha.sup.-1].[yr.sup.-1] from 2001 to 2004,but variation in ANPP among stands was not related to net nitrogen mineralization rates. Across a broader temporal gradient (stand age zero to >250 yr), negative rates of net annual ammonification were especially pronounced in the first postfire year. Laboratory incubations using [sup.15]N isotope pool dilution revealed that gross production of ammonium was reduced and ammonium consumption greatly exceeded gross production during the initial postfire years. Our results suggest a microbial nitrogen sink for several years after severe, stand-replacing fire, confirming earlier hypotheses about postdisturbance succession and nutrient cycling in cold, fire-dominated coniferous forests. Postfire forests in Yellowstone seem to be highly conservative for nitrogen, and microbial immobilization of ammonium plays a key role during early succession. nitrification | nitrogen mineralization | Rocky Mountains | Pinus contorta | lodgepole pine

Abstract: Spatial variation in vegetation and coarse wood is a major source of forest heterogeneity, yet little is known about how this affects ecosystem processes. In 15-year-old postfire lodgepole pine [...]

Many conifer forests experience stand-replacing wildfires, and these fires and subsequent recovery can change the amount of carbon released to the atmosphere because conifer forests contain large carbon stores. Stand-replacing [...]

Past land use can impart soil legacies that have important implications for ecosystem function. Although these legacies have been linked with microbially mediated processes, little is known about the long-term influence of land use on soil microbial communities themselves. We examined whether historical land use affected soil microbial community composition (lipid profiles) and whether community composition was related to potential net nitrogen (N) mineralization rates in southern Appalachian (USA) forest stands abandoned from agriculture or logging and reforested >50 yr ago. Microbial community composition was determined by a hybrid procedure of phospholipid fatty acid (PLFA) and fatty acid methyl ester (FAME) analysis. We found that community composition varied significantly with past land use. Communities in formerly farmed stands had a higher relative abundance of lnarkers for gram-negative bacteria and a lower abundance of markers for fungi compared with previously Jogged and reference (i.e., no disturbance history) stands. Potential net N mineralization rates were negatively correlated with fungal and gram-negative bacterial markers in both farmed and reference stands, and fungal abundance and soil bulk density effectively predicted mineralization rates in all stands. Our results indicate that the alteration of microbial communities by historical land use may influence the ecosystem processes they mediate. This is in contrast to typical expectations about microbial community resilience to change. Here, the decrease in fungal abundance observed from disturbance appeared to result in decreased nitrogen mineralization over the long term. Key words: bacteria, FAME; fungi; land-use history and ecosystem function: PLFA; soil microbial communities; southern Appalachians (USA).

Landscape ecology offers a spatially explicit perspective on the relationships between ecological patterns and processes that can be applied across a range of scales. Concepts derived from landscape ecology now permeate ecological research across most levels of ecological organization and many scales. Landscape ecology developed rapidly after ideas that originated in Europe were introduced to scientists in North America. Key research questions put forth in the early 1980s that catalyzed landscape-level research focused on the formative processes that produce spatial pattern; effects of spatial heterogeneity on the spread of disturbance and fluxes of organisms, material, and energy; and potential applications of landscape ecology in natural resource management. This article describes the development of landscape ecology in North America, discusses current questions and new insights that have emerged, and comments on future directions that are likely to produce new ecological insights. Ecology faces a broad array of challenging questions that require a plurality of approaches and creative insights. Landscape ecology should continue to push the limits of understanding of the reciprocal interactions between spatial patterns and ecological processes and seek opportunities to test the generality of its concepts across systems and scales. Key words: landscape context; landscape ecology; scale; spatial heterogeneity; spatial pattern.

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

The 1988 Yellowstone fires resulted in a complex mosaic within which post-fire lodgepole pine seedling densities varied by over five orders of magnitude. Investigators have speculated that such postfire mosaics of vegetation structure may persist until the next large disturbance, but the fate of the initial structural variability of postfire communities is currently poorly understood. We studied lodgepole pine (Pinus contorta var. latifolia Englem. ex Wats.) stands in Yellowstone National Park (Wyoming, USA) unburned by the 1988 fires to determine how variation in stand structure changes with increasing stand age. The coefficient of variation in stand density decreased from 231% in 12-yr-old stands to 91% in stands aged 50-100 yr, and to 37% for stands ages 200-250 yr. Substantial variability in age distributions both within and among age classes suggested that both gradual infilling of initially sparse stands and self-thinning of initially dense stands are important processes affecting variation in stand density. Variation in stand density was explained primarily by stand age (P < 0.0001) and by geographic location (P < 0.01). Field estimates and reconstructions of stand density trajectories suggest the importance of biotic processes and the contingent effects that produce initial patterns of stand density. Variation in stand density is substantially reduced 125 yr following fire and remains relatively unchanged beyond approximately 200 yr. These results suggest that large, infrequent fires impose a pattern of stand structural variability that may persist for centuries, but stand density likely converges within the fire-free interval in this landscape. Key words: convergence; fire; forest; landscape; lodgepole pine; self-thinning; stand density, stand dynamics, stand structure; subalpine forests; succession; Yellowstone National Park, Wyoming (USA).

Quaking aspen (Populus tremuloides Michx.) is a long-lived clonal species in which many genetically identical stems (ramets) arise from a common root system. Establishment by seed is extremely rare in the Rocky Mountain region, where most clones that exist today are thought to have established hundreds or thousands of years ago. However, recruitment of new genetic individuals through sexual reproduction has occurred periodically throughout the Holocene, and widespread establishment of seedling aspen occurred in Yellowstone National Park, USA, following the extensive 1988 fires. We combined extensive survey methods with manipulative experiments to investigate the patterns and mechanisms of new aspen genet establishment, growth, and survival during their first decade of development. Excavation and aging of 173 aspen stems in 1996 demonstrated that 65% had established within the first three years after the 1988 fires, and that none predated 1988. Random amplified polymorphic DNA (RAPD) genetic analyses revealed that 92% of the plants were genetically distinct individuals, and 8% were ramets. Annual surveys of 22 permanently marked aspen seedling plots revealed that 24% of 417 seedlings tallied in 1996 had died by 2000. However, mortality varied greatly among the 22 plots, from 40%, with greater mortality at lower elevations and where soil organic matter was low. To evaluate the mechanisms underlying seedling persistence or mortality, we constructed exclosures in three sites to protect aspen seedlings from ungulate browsing, and applied four experimental treatments from 1996 to 1998: (1) clipping of current year's growth to simulate browsing, (2) removal of potential competitors including lodgepole pine (Pinus contorta var. latifolia) saplings and herbaceous plants, (3) clipping and competitor removal, and (4) control, i.e., no treatment except protection from browsing. Clipping prevented stem elongation, but removing competitors had no significant effect on height growth of aspen seedlings. Even with protection from browsing, most aspen stems grew slowly (mean increment 2 m tall in 2003 and appeared vigorous. The aspen cohort that germinated after the 1988 fires appears to be in the earliest stage of a long-term population process, a process that likely will entail a shift from many genetically distinct individuals but few ramets, to relatively few genets having numerous ramets. We predict that many or most of the post-1988 aspen seedlings will die within the next few decades, with little lasting effect on broad-scale vegetation patterns or postfire successional trajectories. However, some new genets appear likely to survive and to establish new aspen clones, with potentially important consequences for demographic and genetic structure of the Yellowstone aspen population. Key words: browsing; Cervus elaphus; clonal plants; elk; experimental studies; herbivory; Populus tremuloides; quaking aspen; random amplified polymorphic DNA (RAPD) genetic analyses; Yellowstone.

Ecologists are often asked to contribute to solutions for broadscale problems. The extent of mast ecological research is relatively limited, however, necessitating extrapolation to broader scales or to new locations. [...]

The time interval between stand-replacing fires can influence patterns of initial postfire succession if the abundance of postfire propagules varies with prefire stand age. We examined the effect of fire interval on initial postfire lodgepole pine (Pinus contorta var. latifolia Engelm.) density in Yellowstone National Park (YNP) following the 1988 fires. We asked whether postfire propagule abundance, measured as prefire percent serotiny, varied with fire interval and could explain patterns in postfire succession. The response of lodgepole pine density to variation in fire interval was explained by spatial and temporal variation in prefire serotiny. At low elevations, postfire lodgepole pine recruitment correlated strongly with prefire percent serotiny, which varied nonlinearly with prefire stand age. As a result, postfire lodgepole pine densities varied nonlinearly with tire interval. In contrast, at high elevations serotiny was low, varied little with stand age and did not influence postfire lodgepole pine densities, although, fire interval was still a significant predictor of postfire densities. At high elevations, fire interval varied nonlinearly with postfire lodgepole densities, presumably due to the temporal variation in propagule abundance from open cones in adjacent unburned stands. Temporal variation in stand-level serotiny at low elevations was best explained by age of individual trees. Logistic regression indicated that trees expected to be serotinous had a low probability of exhibiting serotiny at a young age, with increasing probability as trees matured up to 140 yr. This increase in serotiny with tree age likely accounts for the initial increase in stand-level percent serotiny with stand age at low elevations. The spatial variation in serotiny was correlated with variation in historical fire regimes. Fire interval models derived from lower elevations in YNP indicate that fire occurred historically at 135-185-yr intervals, whereas at higher elevations fires occurred at 280-310-yr intervals. The spatial patterns of serotiny appear to have been influenced by variability in historical fire regimes across the Yellowstone landscape, which has conditioned contemporary successional responses to disturbance. Key words: climate change; disturbance; fire ecology; fire interval; landscape ecology; multiple successional pathways; Pinus contorta var. latifolia; postfire succession; serotiny; Yellowstone National Park.

Long-term ecological research is particularly valuable for understanding disturbance dynamics over long time periods and placing those dynamics in a regional context. We highlighted three case studies from Long Term [...]

We investigated the influence of physical characteristics at the local (quadrat) and landscape (sandbar, channel, and river cross-section) scale on the distribution of pioneer tree seedlings (Acer saccharinum, Betula nigra, Populus deltoides, and Salix spp.) on 30 sandbars along a 16-km reach of the Wisconsin River in 1998. At the landscape scale, new seedlings were most frequent in side channels that wore inactive (stagnant) at low river flow, older seedlings were most frequent in narrower side channels, and saplings were most frequent on higher sandbars and in narrower channels. At the local scale, seedling occurrence in individual 1 x 2 m quadrats (n = 692) was significantly related to the horizontal and topographic position and the vegetative cover on the quadrat. Landscape relationships for species that dispersed prior to a small midsummer flood (Acer and Betula) were stronger than models for later dispersers (Populus and Salix), and models for old seedlings and saplings were stronger than those for new seedlings. Both local and landscape variables were significant for explaining local seedling occurrence, and significant landscape x local scale interactions suggested that the influences of some local variables on seedling occurrence were conditional on landscape context. All in all, our results suggest that both local and landscape variables influence the distribution of riparian vegetation, that the influence of local variables may be constrained by landscape context, and that the influence of landscape variables may increase with seedling age. Key words: Acer saccharinum; Betula nigra; fluvial geomorphology; hierarchy; landscape ecology; multiple spatial scales; plant demography; Populus deltoides; riparian vegetation; Salix exigua; Salix nigra; succession.

An overview is presented on trends in freshwater resource management and development. Subjects include biogeochemical cycles, altered hydrological regimes, riparian management, altered land use and interaction between water resource planning and climatic changes.

The Yellowstone fires of 1988 affected [is greater than]250 000 ha, creating a mosaic of burn severities across the landscape and providing an ideal opportunity to study effects of fire size and pattern on postfire succession. We asked whether vegetation responses differed between small and large burned patches within the fire-created mosaic in Yellowstone National Park (YNP) and evaluated the influence of spatial patterning on the postfire vegetation. Living vegetation in a small (1 ha), moderate (70-200 ha), and large (500-3600 ha) burned patch at each of three geographic locations was sampled annually from 1990 to 1993. Burn severity and patch size had significant effects on most biotic responses. Severely burned areas had higher cover and density of lodgepole pine seedlings, greater abundance of opportunistic species, and lower richness of vascular plant species than less severely burned areas. Larger burned patches had higher cover of tree seedlings and shrubs, greater densities of lodgepole pine seedlings and opportunistic species, and lower species richness than smaller patches. Herbaceous species present before the fires responded individually to burn severity and patch size; some were more abundant in large patches or severely burned areas, while others were more abundant in small patches or lightly burned areas. To date, dispersal into the burned areas from the surrounding unburned forest has not been an important mechanism for reestablishment of forest species. Most plant cover in burned areas consisted of resprouting survivors during the first 3 yr after the fires. A pulse of seedling establishment in 1991 suggested that local dispersal from these survivors was a dominant mechanism for reestablishment of forest herbs. Succession across much of YNP appeared to be moving toward plant communities similar to those that burned in 1988, primarily because extensive biotic residuals persisted even within very large burned areas. However, forest reestablishment remained questionable in areas of old ([is greater than]400 yr) forests with low prefire serotiny. Despite significant effects of burn severity and patch size, the most important explanatory variable for most biotic responses was geographic location, particularly as related to broad-scale patterns of serotiny in Pinus contorta. We conclude that the effects of fire size and pattern were important and some may be persistent, but that these landscape-scale effects occurred within an overriding context of broader scale gradients. Key words: disturbance; fire ecology; landscape ecology; patch size; Pinus contorta; secondary succession; spatial heterogeneity; spatial pattern; Wyoming; Yellowstone National Park., INTRODUCTION A key challenge in ecological research involves determining the influence of spatial patterns on ecological processes (Levin 1992, Kareiva 1994). Spatial pattern has demonstrable effects on habitat use and [...]

Most stands of trembling aspen (Populus tremuloides) in northern Yellowstone National Park appear to have become established between 1870 and 1890, with little regeneration since 1900. There has been controversy throughout this century regarding the relative roles of browsing by elk (Cervus elaphus) and fire suppression in preventing aspen regeneration. Fires in 1988 burned 22% of the northern ungulate winter range in the park, and created an unusual opportunity to investigate interactions between fire, ungulate browsing, and aspen regeneration. We tested two hypotheses. (1) The fires would stimulate such prolific sprouting of new aspen stems in burned stands that many stems would escape ungulate browsing and regenerate a canopy of large aspen stems. (2) Browsing pressure would be so intense that it would inhibit aspen canopy regeneration in the burned stands, despite prolific sprouting, but increased forage production in the burned areas would attract elk so that they would not seek out remote aspen stands, and hence, aspen regeneration would occur in unburned aspen stands remote from the burned areas. We sampled aspen sprout density, height, growth form, and browsing intensity in six burned aspen stands, six unburned stands close ([is less than] 1 km) to the burned area, and six unburned stands remote ([is greater than] 4 km) from the burned area. Density of sprouts was generally greater in the burned stands than in the unburned stands in spring 1990 (2 yr after the fires), but was approaching the density of unburned stands by fall 1991. There were no significant differences in browsing intensity (percent of aspen sprouts browsed by ungulates) in 1990 or 1991 among burned, unburned close, or unburned remote stands, nor were there differences in relation to growth form (juvenile vs. adult sprouts). Unbrowsed sprouts generally were lower than the depth of the snowpack, suggesting that elk browsed nearly all sprouts that were accessible. The age distribution of 15 aspen stands across the northern winter range indicated that regeneration of large canopy stems had been episodic even prior to the establishment of the park in 1872. The period 1870-1890, when the present-day aspen stands were generated, was historically unique: numbers of elk and other browsers were low, climate was relatively wet, extensive fires had recently occurred, and large mammalian predators of elk (e.g., wolf, Canis lupus) were present. This combination of events has not recurred since 1900. The recent paucity of aspen regeneration in northern Yellowstone National Park cannot be explained by any single factor (e.g., excessive elk numbers or fire suppression) but involves a complex interaction among factors., Key words: aspen (Populus tremuloides); elk (Cervus elaphus); fire; herbivory; Yellowstone National Park. Introduction Much concern has been expressed in recent decades that trembling aspen (Populus tremuloides Michx.) is declining [...]

In response to environmental problems, such as global climate change, land-use change, habitat fragmentation, and loss of biodiversity, ecologists are expanding the scope and scale of their inquiry. The landscape [...]

Yellowstone's Destabilized Ecosystem: Elk Effects, Science, and Policy Conflict. Frederic H. Wagner. Oxford University Press, New York, 2006. 392 pp., illus. $64.50 (ISBN 9780195148213 cloth). Yellowstone National Park (YNP) and [...]

How Increasing [CO.sub.2] and Climate Change Affect Forests The strong relationship among climate, atmosphere, soils, biota, and human activities provides a solid basis for anticipating changes in terrestial biomes in [...]

1 Residential development is often concentrated near aquatic ecosystems and understanding riparianulittoral zone interactions is therefore critical for assessing its ecological effects. 2 Introduction of wood from riparian forests into the littoral zone, where it becomes habitat for aquatic organisms, is an important, but poorly understood, process. We related the density of littoral coarse wood both among and within 45 lakes in Vilas County, Wisconsin, USA, to forest structure, abiotic drivers and land use. 3 Among all lakes and among a subset of low-development lakes, the best predictor of the density of littoral coarse wood was the density of riparian coarse wood. At the within-lake (site) level, two alternative models explain variability in coarse wood abundance: as a function of exposure to wind and amount of riparian coarse wood or as a function of exposure to wind and land-use intensity. 4 Both among and within lakes, areas more modified by humans had a lower density of littoral coarse wood. Conversely, areas with little (current) human impact were tremendously variable; some sites and lakes had abundant wood and others had virtually none. 5 Contrary to previous studies, there was no relationship between living trees and coarse wood density, suggesting that riparian and littoral coarse wood densities may be strongly influenced by past disturbance, both human and natural. 6 This study highlights the importance of cross boundary subsidies in understanding the impact of development on ecosystems. The concentration of residential development at the boundary between terrestrial and aquatic ecosystems appears to reduce the flow of coarse wood from forests to lakes. Loss of this resource may have negative consequences for lake biota and the aquatic food web.

1 Former human practices can persistently influence forest ecosystems, particularly by altering the distribution and abundance of vegetation. Previous research has focused on the role of colonization success in governing plant community patterns in abandoned forests, but few studies have explored how changes in the performance of adult plants may contribute to changes in plant populations. 2 We examined patterns of biomass allocation and growth of 12 herbaceous plant species in southern Appalachian forest stands that have developed after agricultural abandonment or logging at least 55 years ago, to determine whether plant performance varied with land-use history. Soil nutrient availability and canopy closure were also investigated. 3 Adult plant biomass allocation varied appreciably among stands with different histories. Herbs in farmed stands generally allocated the most to leaves and the least to stems, while reference stands showed the opposite pattern. Plants in previously farmed sites had the highest rate of growth, although we observed considerable interspecific variation in plant performance. Stem allocation and relative growth rate were positively correlated in reference stands, but not in farmed or logged stands. Similarly, the growth of plants was clearly associated with soil nutrient concentration in reference stands but not in farmed or logged stands. 4 Differences in understorey density and soil nutrient availability may account for the observed patterns. Total herbaceous cover was appreciably lower in farmed and logged stands (58% and 51%) than in reference stands (78%), and soil phosphorus was higher in farmed stands than in logged and reference stands. Thus, competition for light and nutrients may be lower in farmed and logged stands than in reference stands, despite there being no difference in canopy closure with land-use history. 5 Overall, these results suggest that land-use history may influence environmental variables in ways that can enhance the performance of some herbaceous species. However, not all species may respond similarly to these changes.

A study on the reciprocal interactions between spatial pattern and ecological processes is presented. Landscape ecology should continue to refine knowledge of when spatial heterogeneity is fundamentally important, rigorously test the generality of its concepts, and develop a more mechanic understanding of the relationships between pattern and process.

Resource selection functioning was used to study summer habitat use in a reintroduced and expanding elk population in the Chequamegon National Forest, Wisconsin, and USA. Factors were examined that influenced where elk established homes ranges and that influenced habitat use within established home ranges.

Widespread establishment of seedling aspen (Populus tremuloides) occurred in Yellowstone National Park (YNP) following the extensive 1988 fires. Aspen stands occupy ~2% of YNP and aspen stems are intensively browsed by native ungulates. Chemical composition, especially secondary compounds, may influence levels of herbivory and, hence, survival of aspen, but concentrations of such compounds in aspen in the northern Rocky Mountains are not known. Quantitative profiles of foliar nitrogen and secondary compounds (condensed tannins and the phenolic glycosides, salicortin and tremulacin) in aspen were assessed to address the following questions: (1) Do concentrations of secondary compounds differ between seedling and mature aspen stands? (2) Do concentrations of secondary compounds in seedling aspen differ between unbrowsed and artificially browsed seedlings? (3) Among mature aspen stands, do concentrations of secondary plant compounds differ among, (a) burned and browsed, (b) unburned and browsed and (c) unburned and unbrowsed stands? Concentrations of phenolic glycosides were significantly higher in seedlings than in mature stands, although condensed tannin concentrations and leaf nitrogen were higher in mature stands. Concentrations of leaf nitrogen and all secondary compounds were greater in unbrowsed seedlings than in seedlings subjected to simulated browsing. Concentrations of secondary compounds did not differ between mature aspen stands that were unburned regardless of whether they were browsed; however, burned stands (all of which were browsed) had significantly greater concentrations of secondary compounds and leaf nitrogen than the unburned stands. Results from this research suggest that foliar phenolic glycosides and tannins are not active defenses induced in response to browsing by large mammals. Rather, variation in levels between juvenile and mature ramets represents ontogenetic shifts in expression of defense, whereas variation between clipped and unclipped seedlings results from shifts in carbon/nutrient availability.

This unique collection of diverse readings from the primary literature in ecology is an ideal companion to the groundbreaking text Ecology (OUP, 1998, Dodson et al.) and can also be [...]

Abstract. Land use and land cover can have a significant impact on water chemistry, but the spatial scales at which landscape attributes exert a detectable influence on aquatic systems are [...]

Abstract. Methods for predicting the ecological impacts of land use change on biodiversity and ecosystem function are needed to guide land planning and resource management decisions. This study explores the [...]

Primary Succession and Ecosystem Rehabilitation. Lawrence R. Walker and Roger del Moral. Cambridge University Press, Cambridge, United Kingdom, 2003. 456 pp., illus. $130.00 (ISBN 0521800765 cloth). Natural and anthropogenic disturbances [...]