bluuebunny/crossref_metadata_2025 huggingface dataset:
Risk, environmental variability and drought-induced impoverishment: the pastoral economy of central Niger
Authors: Starr Martha A.
Published: April 2006

Opening Paragraph

Since the early 1970s the heavy impact of recurrent drought has given rise to the sense that Sahelian pastoralism is in decline. This is usually attributed to increasing aridity, environmental degradation and the destructive effects of colonial policies on traditional mechanisms to spread risk and promote recovery from drought. These factors clearly contribute to the pastoral sector's apparently increasing difficulties in contending with environmental hardship and variability. However, analysts' strong emphasis on forces exogenous to the sector has created a seriously distorted view of a system in uniform decline. In fact, when changes within the pastoral sector are examined, it becomes clear that the movement of people away from full-time transhumant livestock raising since the 1970s reflects not the decline of pastoralism per se but rather the slipping-out by a stratum of producers for whom the risks associated with this activity were simply too great relative to possible returns. Understanding that drought-induced impoverishment has its roots in differential ability to bear risks linked to environmental variability is especially important in formulating sound policies to ensure present and former pastoralists' continued access to income-generating activities, whether in full-time livestock raising or in other areas.
From village autonomy to modern village administration among the Kulere of central Nigeria
Authors: Frank Barbara
Published: April 2006

Opening Paragraph

In studies of change in indigenous political organisations under the impact of colonial administration, the precolonial situation in Africa is often depicted as essentially static. Anthropologists tend to project a relatively ‘uninfluenced’ state of affairs from the early colonial period into the past. Change seems to occur under European influence. This picture is the result less of the conviction of the authors that conditions were static than of a lack of information on precolonial development. This is especially true for ‘acephalous’ societies; centralised societies often possess detailed traditions concerning their institutional history. In the following case, of the political development of a village in the Nigerian Middle Belt, it has been possible to record precolonial changes of organisation in an acephalous society.
The Baye Faal of Senegambia: Muslim Rastas in the promised land?
Authors: Savishinsky Neil J.
Published: April 2006

Spurred on in large part by the emergence of Jamaican and Anglo-Jamaican reggae music on to the global pop music scene in the mid-1970s, the Jamaican Rastafarian movement has within the past two decades managed to expand beyond its island home and attract a diverse and multi-ethnic international following. Apart from the various manifestations of ‘orthodox’ Jamaican Rastafarianism found in Africa today, one finds a number of religious and social formations which share similar features with and have been influenced to some extent by Rastafarian religion, music and culture. This article examines the various links that exist between one such group—the Muslim Baye Faal of Senegambia—and the beliefs and practices of the Jamaican Rastafari.
‘This is actually a good interpretation of modern civilisation’: popular theatre and the social imaginary in Ghana, 1946–66
Authors: Cole Catherine M.
Published: April 2006

West African popular theatre has been the subject of a growing body of scholarship. Yet what has not yet been adquately accounted for in this literature is historical change, both within particular theatre traditions and in their relation to society at large. This article begins to address the gap by focusing on the Ghanaian concert party in the volatile years from the end of World War II through the early years of independence. During this period the Ghanaian concert party underwent profound transformations in form, content, and its modes of production and consumption. Through their geographic mobility and widespread popularity, concert parties participated first-hand in the transformation of public consciousness. Just as the popular press played a central role in the formation of European nationalism, so popular travelling theatre performed a pivotal role among a largely non-literate population during Ghana's transition from colonialism to modern nation state. This article interprets the generic conventions through which the concert party convened and constituted its new public. By deploying an eclectic range of formal techniques to dramatise everyday realities, concert parties became a primary integrative mechanism through which audiences negotiated a tumultuous historical epoch.
Further light on W. R. Bascom and the Ife bronzes
Authors: Ottenberg Simon
Published: April 2006

The publication of Professor Robert L. Tignor's article ‘W. R. Bascom and the Ife bronzes' in Africa a few years ago (1990) aroused my interest, as a former student of this anthropologist, as to whether there was any further correspondence beyond what Tignor employed which would illuminate the controversy, as I felt dissatisfied with some of his interpretations. I was fortunate to have had access to Bascom's personal papers, now on file at the Phoebe Hearst Museum of Anthropology (formerly the Robert Lowie Museum of Anthropology, University of California, Berkeley), through the kind assistance of Bascom's widow, Berta Bascom, and of Frank A. Norick at the museum. The letters in the file present a somewhat different view of the role of Bascom in the matter than Tignor does. His article relies largely on US State Department archives (which do include some Bascom correspondence) and upon some published articles by Bascom, by E. H. Duckworth, then editor of Nigeria Magazine and also Nigerian Inspector of Education, and by others. The whole business of the two Ife heads which Bascom acquired throws light on the history of the gradually evolving Nigerian colonial government policy toward antiquities.
Functional equations and the Galton-Watson process
Authors: Seneta E.
Published: April 2006

In the present exposition we are concerned only with the simple Galton-Watson process, initiated by a single ancestor (Harris (1963), Chapter I). Letdenote the probability generating function of the offspring distribution of a single individual. Our fundamental assumption, which holds throughout the sequel, is thatfj≠ 1,j= 0,1,2, …; in particular circumstances it shall be necessary to strengthen this to 0 <f0≡F(0) < 1, which is the relevant assumption when extinction behaviour is to be considered. (Even so, our assumptions will always differ slightly from those of Harris (1963), p. 5.)
A second note on recent research in geometrical probability
Authors: Moran P. A. P.
Published: April 2006

Many problems in geometrical probability have been surveyed in the monograph by Professor M. G. Kendall and myself (Kendall and Moran (1963)). In 1966 I published a note in J. Appl. Frob. 3 describing researches which had either been carried out since that book appeared, or which had escaped our notice. The present paper attempts to describe still further investigations classified roughly as to whether they are concerned with points, lines, planes, estimation of area and length, and coverage.
Species pool: the concept, its determination and significance for community restoration
Authors: Zobel Martin , van der Maarel Eddy , Dupré Cecilia
Published: April 2006

Abstract.The concept of species pool is reviewed. It is suggested to maintain the terms regional pool and local pool but replace actual pool by community pool. The regional and local pool are considered as selections from the regional and local flora based on ecological similarity. It is also suggested to include in the community pool a selection of species present only as diaspores in the diaspore bank (including diaspores from the seed rain), the selection being based on the same ecological criteria.

Four approaches to determine the species pool are discussed: ecological, functional and phytosociological similarity, and an experimental approach. The phytosociological approach appears to be promising. The species pool is elaborated as a fuzzy set in the sense that each species of a community or a local or regional flora is a member of any community, local or regional species pool with different degrees of membership. This membership is defined as a probability of a species to become part of the community pool of a target community which is a function of the ecological (environmen‐tal/functional/phytosociological) similarity of the species with the target community; the shortness of the distance of its nearest populations, the frequency/abundance, the dispersal capacity, the actual presence of dispersal mechanisms, the germinability of newly arrived diaspores, and the longevity of seeds (viability) in the diaspore bank.

The information on species pools is needed for designing experiments where the number of species in a community is to be manipulated, for instance in restoration management.
Current Velocity and Its Effect on Aquatic Macrophytes in Flowing Waters
Authors: Chambers P. A. , Prepas E. E. , Hamilton H. R. , Bothwell M. L.
Published: April 2006

Current velocity significantly affected the biomass and shoot density of aquatic macrophytes in two slow—flowing rivers in western Canada. Studies of aquatic macrophyte communities at three sites on the Bow River, Alberta, Canada, between 1982 and 1985 showed that biomass decreased with increasing current velocity within the weed bed over the range 0.01—1 m/s; at current speeds in excess of 1 m/s, aquatic macrophytes were rare. Transplant experiments in which Potamogeton pectinatus was grown in pails containing three sediments differing in texture at three sites with different current velocities also demonstrated that biomass and shoot density were affected by both the direct effects of current velocity on plant shoots and its indirect effects on sediment nutrient concentrations. These results indicate that current velocity is an important factor regulating aquatic macrophyte biomass in flowing waters and suggest that even a relatively modest increase in current velocity within weed beds reduces the abundance of submerged aquatic plants.
Factors Controlling Nitrogen Cycling and Nitrogen Saturation in Northern Temperate Forest Ecosystems
Authors: Aber John D. , Melillo Jerry M. , Nadelhoffer Knute J. , Pastor John , Boone Richard D.
Published: April 2006

An analysis of the factors controlling rates of nitrogen cycling in northern temperate forest ecosystems is presented based on a quantitative analysis of an extensive data set for forests in Wisconsin and Massachusetts as those data are synthesized in a computer model (VEGIE) of organic matter and nutrient dynamics. The model is of the "lumped—parameter," nutrient—flux—density type, dealing with major components of forest ecosystems rather than stems or species. It deals explicitly with the interactions among light, water, and nutrient availability in determining transient and equilibrium rates of primary production and nutrient cycling. Data are presented for parameterizing the plant component of the system at either the species or community level. A major conclusion is that the ultimate control on equilibrium nitrogen—cycling rates resides not within the nitrogen cycle itself (for example in litter quality or net primary production [NPP] allocation patterns) but rather in ratios of resource—use efficiency by vegetation as compared with the ratios of resource availability. Litter quality and allocation patterns, along with rates of N deposition, do affect the rate at which a system approaches the equilibrium cycling rate. The model is used to explain observed variation in nitrogen—cycling rates among forest types, and to predict the timing and occurrence of "nitrogen saturation" (N availability in excess of biotic demand) as a function of nitrogen deposition rates and harvesting.
Tests of Spatial and Temporal Interaction Among Animals
Authors: Minta Steven C.
Published: April 2006

I report a method for analyzing interaction between two animals around a common object or resource (simple association) or within a shared area (spatial—temporal interaction in home range overlap). The pair's association is reduced to binomial events forming a 2 x 2 classification; each is either present or not in the shared area. For the most common home range overlap description, observed frequencies of presence and absence for each animal are compared to expected frequencies based on two null hypotheses of spatially independent home range use by each animal relative to the other, and one null hypothesis of temporally independent home range use by the two animals. The procedure uses any statistically derived, two—dimensional home range representation that allows spatial overlap to be delineated for each animal pair. The temporal order of simultaneous pairs of locations for the two animals can then be evaluated for a pattern of use regarding the area of overlap (shared area). The window of "simultaneity" is dictated by the animal's primary sensory mode and mobility. An overall chi—squared test with three degrees of freedom is partitioned into spatial "main effects" and temporal "interaction," analogous to analysis of variance. The two main effects are each animal's purely spatial attraction to or avoidance of the shared area. When interaction effects are significant, it is possible to interpret temporal attraction to or avoidance of the shared area. This temporal response is in terms of the pair's simultaneous vs. solitary occupation of the shared area relative to overall home range use. Experimental design and assumptions are discussed because degree of adherence affects the validity of inferences and influences interpretation. Detailed examples of analysis and interpretation from North American badgers (Taxidea taxus) and from mule deer (Odocoileus hemionus) interacting with domestic cattle (Bos taurus) illustrate the range of complexity inherent to even this simple form of interaction analysis.
Prospects for Weed Control Through Crop Interference
Authors: Jordan Nicholas
Published: April 2006

Crop interference with weed growth is a fundamental method of nonchemical weed control. Crop interference, entailing weed suppression, should be distinguished from crop tolerance of weeds, i.e., relatively small yield loss due to the presence of weeds. Tolerance is less desirable than interference in that it may lead to increases in weed seed populations that can cause future yield losses. Ideally, interference should occur as early as possible in growth to prevent resource consumption by weeds. A path analysis of crop—weed interference is presented. The model can be used to estimate the relative magnitude of early vs. later crop interference with weed growth, and to identify crop traits that contribute to the interference with weed growth. Such analysis can identify crop varieties that show strong early interference with weed growth, and traits associated with strong early interference. For illustrative purposes, the model is applied to characterize differences among soybean varieties in interference with common cocklebur. Weed control by crop interference could be enhanced by crop breeding and management. However, several benefits and costs of interference should be evaluated before undertaking such approaches. First, the degree to which crop interference can substitute for other forms of weed control must be determined. Second, yield costs associated with interference should be measured; these may occur in crop varieties that interfere strongly with weeds, particularly when water, temperature, and mineral nutrients are limiting. A more mechanistic understanding of crop interference is needed so that interference can be enhanced through crop breeding and management while minimizing yield costs.
Human Disturbance of an Avian Scavenging Guild
Authors: Skagen Susan K. , Knight Richard L. , Orians Gordon H.
Published: April 2006

In order to investigate the effects of human activities on relationships within foraging guilds, we examined inacanus dynamics of eagles, crows, and gulls scavenging on spawned salmon in the Pacific Northwest. We examined several hypotheses that postulate the asymmetric foraging relationships of the three guild members and that reveal the influence of competition and facilitation in these relationships. Spatial and temporal patterns of resource use by the three primary guild members varied with the presence and absence of human activity at experimental feeding stations. At control (undisturbed) stations, eagles preferred to feed >100 m from vegetative cover, whereas gulls fed <50 m from cover. At experimental (disturbed) stations, eagles rarely fed, and feeding activity by gulls increased at both near and far stations. Crows often fed on alternate food sources in fields adjacent to the river, especially when salmon carcasses were scarce, whereas eagles and gulls rarely did so. We also examined if and how the behavior of single guild members changes in the presence or absence of other guild members. In the absence of eagles, gulls and crows preferred stations far from cover, numbers of both increased at feeding stations, birds were distributed nearer to carcasses, and they fed more. We emphasize that guild theory lends important insights to our understanding of the effects of human disturbance on wildlife communities.
The Role of Riparian Corridors in Maintaining Regional Biodiversity
Authors: Naiman Robert J. , Decamps Henri , Pollock Michael
Published: April 2006

Riparian corridors possess an unusually diverse array of species and environmental processes. This "ecological" diversity is related to variable flood regimes, geomorphic channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. This dynamic environment results in a variety of life history strategies, and a diversity of biogeochemical cycles and rates, as organisms adapt to disturbance regimes over broad spatio—temporal scales. These facts suggest that effective riparian management could ameliorate many ecological issues related to land use and environmental quality. We contend that riparian corridors should play an essential role in water and landscape planning, in the restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.
Comparing Spatial Pattern in Unaltered Old‐Growth and Disturbed Forest Landscapes
Authors: Mladenoff David J. , White Mark A. , Pastor John , Crow Thomas R.
Published: April 2006

We used geographic information systems (GIS) to analyze the structure of a second—growth forest landscape (9600 ha) that contains scattered old—growth patches. We compared this landscape to a nearby, unaltered old—growth landscape on comparable landforms and soils to assess the effects of human activity on forest spatial pattern. Our objective is to determine if characteristic landscape structural patterns distinguish the primary old—growth forest landscape from the disturbed landscape. Characteristic patterns of old—growth landscape structure would be useful in enhancing and restoring old—growth ecosystem functioning in managed landscapes. Our natural old—growth landscape is still dominated by the original forest cover of eastern hemlock (Tsuga canadensis), sugar maple (Acer saccharum), and yellow birch (Betula allegheniensis). The disturbed landscape has only scattered, remnant patches of old—growth ecosystems among a greater number of early successional hardwood and conifer forest types. Human disturbances can either increase or decrease landscape heterogeneity depending on the parameter and spatial scale examined. In this study, we found that a number of important structural features of the intact old—growth landscape do not occur in the disturbed landscape. The disturbed landscape has significantly more small forest patches and fewer large, matrix patches than the intact landscape. Forest patches in the fragmented landscape are significantly simpler in shape (lower fractal dimension, D) than in the intact old—growth landscape. Change in fractal dimension with patch size, a relationship that may be characteristic of differing processes of patch formation at different scales, is present within the intact landscape but has been obscured by human activity in the disturbed landscape. Important ecosystem juxtapositions of the old—growth landscape, such as hemlock with lowland conifers, have been lost in the disturbed landscape. In addition, significant landscape heterogeneity in this glaciated region is produced by landforms alone, without natural or human disturbances. The features that distinguish disturbed and old—growth forest landscape structure that we have described need to be examined elsewhere to determine if such features are characteristic of other landscapes and regions. Such forest landscape structural differences that exist more broadly could form the basis of landscape principles to be applied both to the restoration of old—growth forest landscapes and the modification of general forest management for enhancing biodiversity. These principles may be particularly useful for constructing integrated landscapes managed for both commodity production and biodiversity protection.
Seedling Response of Four Birch Species to Simulated Nitrogen Deposition: Ammonium vs. Nitrate
Authors: Crabtree R. C. , Bazzaz F. A.
Published: April 2006

Chronic nitrogen deposition has the potential to alter seedling shade tolerance and growth in the temperate forests of northeastern United States, by affecting both the form and the quantity of available nitrogen. Simulated deposition treatments were applied to seedlings of four birch species that co—occur at Harvard Forest (Betula lenta, B. alleghaniensis, B. populifolia, and B. papyrifera). Seedlings were individually potted in forest soil, and grown under light treatments representative of forest understory and treefall gap light levels. In a split—plot design, N was applied at 25 and 50 kg°ha—1°yr—1, as either nitrate, ammonium nitrate, or ammonium, within each light environment. While B. populifolia and B. papyrifera, and B. lenta all showed increased biomass allocation to leaves with increased N, only B. lenta showed a significant growth response to the type of N added, and this response was conditional on rate of N application and light environment. At low light, nitrate—fed B. lenta grew best, and also at low rate of supply, nitrate treatments out—performed ammonium treatments. Greater growth under these conditions is probably the result of higher biomass allocation to leaves, and greater specific leaf area, which increased the leaf area ratio, and improved the capacity for carbon gain. Under N deposition regimes that increase soil nitrate availability, the differences in response of B. lenta and B. alleghaniensis to nitrate at low light may potentially lead to changes in the species composition of the seedling communities in the understory. When a treefall occurs, a different species mix of seedlings will be released, with potential consequences for sapling and tree species mix.
Modeling the Dynamics of Snags
Authors: Morrison Michael L. , Raphael Martin G.
Published: April 2006

Many wildlife species required standing dead trees (i.e., snags) as part of their habitat. Therefore, the ability to predict future density, distribution, and condition of snags can assist resource managers in making land—use decisions. Here we present methods for modeling the dynamics of snags using data from a 10—yr study on the rates of decay, falling, and recruitment of snags on burned and unburned plots in the Sierra Nevada, California. Snags (all species) in advanced stages of decay usually fell within 5 yr, and snags created by fire decayed rapidly and fell quicker (within 10 yr) than those on unburned plots. Pine (Pinus spp.) snags decayed more rapidly than fir (Abies spp.). Although there was an overall net increase in snag density on unburned plots, most of this increase was in the smaller (>13—38 cm diameter at breast height [dbh]) size classes; there was a net decrease in the larger (>38 cm dbh) snags preferred by many birds for nesting and feeding. Overall, snags remained standing the longest that were larger in diameter, shorter in height, less decayed, fir rather than pine, and lacking tops. A Leslie matrix model of snag dynamics predicted changes in snag decay and density only when adjusted for the specific environmental factors(s) causing initial tree mortality. Many snags are created by episodic events, such as fire, disease, drought, and insects. Models of snag dynamics must include the species and condition of trees becoming snags, as well as the factor(s) causing the tree to die. Forest managers must consider this episodic creation of snags when developing snag—management guidelines, and when planning tree—salvage programs based on short—term inventories.
Sampling to Detect Rare Species
Authors: Green Roger H. , Young Richard C.
Published: April 2006

Often a sampling program has the objective of detecting the presence of one or more species. One night wish to obtain a species list for the habitat, or to detect the presence of a rare and possibly endangered species. How can the sampling effort necessary for the detection of a rare species can be determined? The Poisson and the negative binomial are two possible spatial distributions that could be assumed. The Poisson assumption leads to the simple relationship n = —(1/m)log @b, where n is the number of quadrats needed to detect the presence of a species having density m, with a chance @b (the Type 2 error probability) that the species will not be collected in any of the n quadrats. Even if the animals are not randomly distributed the Poisson distribution will be adequate if the mean density is very low (i.e., the species is rare, which we arbitrarily define as a true mean density of <0.1 individuals per sample unit), and the spatial distribution is not highly aggregated. Otherwise a more complicated relationship based on the negative binomial distribution would have to be used. Published sampling distributions of 37 unionid mollusc species over river miles (distance measured along the path of the river; 1 mile = 1.609347 km) in two southern Appalachian rivers were evaluated to determine the appropriateness of the simple Poisson—based formula for estimation of necessary sample size to detect species presence. For each of 273 species x river mile combinations we estimated the mean, the variance, and the negative binomial parameter k, and then estimated "necessary n" from both the Poisson— and the negative—binomial—based formulae. We defined "Poisson adequacy" to be the proportion that the Poisson estimate is of the negative binomial estimate of necessary sample size, and stated the requirement that it be >0.95. Only 8 of the 273 cases represented rare species that failed this requirement. Thus we conclude that a Poisson—based estimate of necessary sample size will generally be adequate and appropriate.
Nitrogen Assessments in a Constructed and a Natural Salt Marsh of San Diego Bay
Authors: Langis Rene , Zalejko Malgorzata , Zedler Joy B.
Published: April 2006

Soil nitrogen pools were lower in a 4—yr—old constructed salt marsh than in an adjacent natural marsh of San Diego Bay. Aboveground biomass and foliar nitrogen content of Spartina foliosa were both lower for the constructed marsh. Soil organic carbon, which was highly positively correlated with total nitrogen, was also lower in the constructed marsh. Rates of nitrogen fixation were higher for the natural marsh in surface soils (1 cm depth) but not in the rhizosphere (10 cm depth). Experimental additions of organic matter increased rates of nitrogen fixation substantially for both the constructed and natural marsh soils, with glucose stimulating greater increases than Spartina foliosa detritus (roots and rhizomes). In comparison with natural marshes studied elsewhere, the San Diego Bay sites have low nitrogen pools and little soil organic carbon. Nitrogen mineralization rates (in situ incubations) were high in both marshes studied. The low nitrogen pools reflect low tidal import and infrequent streamflow influxes and, possibly, high nitrogen demands of vegetation stressed by hypersaline soils.
Soil Microbial Community Response to Silvicultural Intervention in Coniferous Plantation Ecosystems
Authors: Ohtonen Rauni , Munson Alison , Brand David
Published: April 2006

Five years after planting and initial treatment, we examined the response of a microbial community to three intensive silvicultural practices: soil surface modification (scarification), fertilization, and control of competing vegetation by herbicide. We correlated microbial response with changes in environmental conditions following treatment, including soil temperature and moisture, total and available nutrients in soil, and light intensity in the tree canopy. The microbial biomass C (2.1—5.3 mg/g in the F/H horizon and 0.14—0.62 mg/g in the surface mineral soil) as determined by the fumigation—extraction method was reduced by vegetation control and fertilization. The ratio of microbial to total organic carbon (Cmic/Corg) was also reduced by vegetation control, and tended to increase in the new organic horizon developed during the 5 yr after soil surface scarification. Microbial biomass N (0.15—0.40 mg/g in the F/H horizon and 0.014 to 0.057 mg/g in the mineral soil) was not affected by the treatments. The microbial community structure (relative volumes of bacteria and fungi) was evaluated on glass slides placed in the litter bags of pine and aspen litter. The treatment effects on the relative volumes of microorganisms on slides were similar to effects noted for microbial biomass C in the soil. Five years of vegetation succession resulted in conservative N cycling and N limitation of the plant community in control plots. In response to silvicultural treatments this state may either remain relatively unchanged after fertilization, the N limitation may be increased (scarification), or apparent C limitation induced (vegetation control). Reducing the nutrient pool by scarification caused an apparent nutrient limitation, and the microbial community tended to widen the C/N ratio. Increasing the nutrient pool by fertilization or vegetation control tended to narrow the C/N ratio of microbial biomass.
Vegetation Responses to Edge Environments in Old‐Growth Douglas‐Fir Forests
Authors: Chen Jiquan , Franklin Jerry F. , Spies Thomas A.
Published: April 2006

Forest edges created by dispersed—patch clear—cutting have become a conspicuous landscape feature in western North America, but the effects of edge on forest structure and function are still poorly understood. In this paper we describe responses of stocking density, growth, mortality, and regeneration for three conifer species from the clear—cut edge into the interior of old—growth forest patches adjacent to 10—15 yr old clearcuts in southern Washington and central Oregon. The significance of edge effects for each variable was tested through a single—factor (distance) analysis of variance (F test). Relationships between these variables and depth—of—edge influence (i.e., edge width) on old—growth forest were characterized by nonlinear regression models. Near the edge (forest—clearcut boundary line), the old—growth forest has (1) reduced stocking density, as measured by canopy cover, number of stems per hectare, and basal area; (2) increased growth rates of dominant Douglas—fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla), as calculated by an index of relative growth rate; (3) elevated rates of tree mortality, as measured by standing dead and down trees (snags and logs); and (4) greater numbers of Douglas—fir and western hemlock seedlings (@<100 cm tall) and saplings (101—200 cm) but fewer of Pacific silver fir (Abies amabilis). The depth—of—edge influence, when calculated as the point along the clearcut—forest gradient at which a given variable has returned to a condition representing 2/3 of the interior forest environment, ranged from 16 to 137 m for variables related to distance from the edge. The amount of a square forest patch affected by edge decreased as patch size increased and varied greatly with the depth—of—edge influence. With increasing concerns about organisms and processes that require interior forest habitat, determining the area of residual forest influenced by adjacent clearcut is critical to current and future resource management. Responses of additional biological variables must be explored and information on edge phenomena should be extended to the scale of landscapes.
Ecotone Hierarchies
Authors: Gosz James R.
Published: April 2006

Ecological phenomena are evident over a broad spectrum of space and time scales. Ecotones, being defined as zones of transition between adjacent ecological systems, also must occur over an equally broad spectrum of space and time scales. Scale—dependent constraints influence ecological phenomena and resulting zones of transition; however, in traditional ecotone studies little treatment has been given to these influences. This paper addresses aspects of the ecotone concept that relate to the strength of interactions between adjacent systems for a hierarchy of ecotones in a biome transition area in central New Mexico on the Sevilleta National Wildlife Refuge. Zones of transition occur at plant, population, patch, landscape, and biome levels in the hierarchy suggested here. Constraints differ across this hierarchy, primarily because of the different scales at which these constraints exert their influences. The basic strategy to understand these cross—scale influences must be to perform studies at different scales, and a hierarchical approach identifies those scales. This also is important for identifying the appropriate technologies that focus at the scales where transition zones between ecological systems/phenomena are expressed. A broad array of technologies are available for integrating the pattern–process relationships that occur across the many scales in ecological systems.
Fish Assemblage Recovery Along a Riverine Disturbance Gradient
Authors: Kinsolving Alan D. , Bain Mark B.
Published: April 2006

Artificial fluctuations in streamflow have been documented to alter the composition and structure of stream communities. This study tests the hypothesis that a spatial recovery gradient in fish assemblage structure exists downstream of a hydroelectric dam, and that recovery can be identified by the presence and abundance of species largely restricted to flowing—water habitats (fluvial specialists). A longitudinal gradient of change in a shoreline fish assemblage was quantified in a 66—km reach of a mid—sized, species—rich river (Tallapoosa River, Alabama) with daily flow fluctuations from hydropower generation. The shoreline fish assemblage in a nearby and similar river (Cahaba River, Alabama) was quantified as a regional reference for the occurrence of fish assemblage gradients. Fish were collected with prepositioned area electrofishers in 240 randomly located sampling sites, and physical habitat was quantified. Using distributional and habitat use information, fish species were categorized as fluvial specialists or macrohabitat generalists (species that occur in a wide variety of aquatic systems). Sampled habitats were similar between rivers and along each study reach. The longitudinal pattern of species occurrence and fish abundance was consistent in the free—flowing river. A longitudinal gradient of increasing abundance and richness of only fluvial specialist species existed downstream of the hydroelectric dam. No similar spatial gradient existed for macrohabitat generalists in either river. Although a fish community recovery gradient was identified, a recovery endpoint was not evident because assemblage change was gradual and possibly incomplete. The preservation and management of riverine fish faunas will partly depend on incorporating spatial recovery into decisions about permitting and siting of anthropogenic changes like hydroelectric dams.
Testing Forest‐BGC Ecosystem Process Simulations Across a Climatic Gradient in Oregon
Authors: Running Steven W.
Published: April 2006

Field measurements from the Oregon Transect Ecological Research project (OTTER) were used to validate selected process simulations in the FOREST—BGC ecosystem model. Certain hydrologic, carbon, and nitrogen cycle process simulations were tested in this validation, either comparatively across sites, or seasonally at single sites. The range of simulated ecosystem—process rates across the OTTER sites was large; annual evapotranspiration (ET) ranged from 15 to 82 cm, net photosynthesis (as carbon) from 2.2 to 22.8 Mg/ha, and decomposition (as carbon) from 1.0 to 7.2 Mg°ha—1°yr—1. High correlations between predicted and measured data were found for: aboveground net primary production, R2 = 0.82; 100—yr stem biomass, R2 = 0.79; and average leaf nitrogen concentration, R2 = 0.88. However, correlations for pre—dawn leaf water potential and equilibrium leaf area index (LAI) were much lower, because successful simulation of these variables requires accurate data for soil water—holding capacity. Defining the water—holding capacity of the rooting zone and the maximum surface conductance for photosynthesis and transpiration rates proved to be critical system variables that defied routine field measurement. Although many other processes are simulated in FOREST—BGC, no other processes had repeated field data sets for validations. Problems in parameterizing the model from disparate data sets are also evaluated, with suggestions for using ecosystem modeling in future integrated research programs.
Biological Inventory Using Target Taxa: A Case Study of the Butterflies of Madagascar
Authors: Kremen Claire
Published: April 2006

Biotic inventories provide critical data for conservation planning, but frequently, conservation decisions are made without surveys, due to lack of time, funds, or appropriate methodology. A method, target taxon analysis, is therefore proposed for streamlining regional biotic inventories, while simultaneously increasing their taxonomic coverage and spatial resolution. In this method, regional inventories focus on a number of narrowly defined target taxa, chosen to represent collectively an array of higher taxa. Such target taxa should be information rich; in other words, the pattern of species distributions in these taxa should correlate either with patterns of environmental heterogeneity or with distributional patterns of species in unrelated taxonomic groups. It is suggested that clades that experienced an evolutionary radiation within the region are likely to be information rich for conservation planning at or within this regional scale. Such clades will be identifiable as low—ranking, species—rich taxa with high endemism. The information richness of these potential target clades can then be evaluated by direct gradient methods of analysis that relate community compositional change to environmental factors, or by correlating distributional patterns of species among separate target clades. To assess this approach to biological inventory, a species—rich genus and subgenus of endemic butterflies from the island of Madagascar were chosen as target taxa and were evaluated for information richness in comparison to the entire butterfly fauna of Madagascar. Using canonical correspondence analysis and other analytical techniques, the subgenus of Malagasy Henotesia species (Satyrinae) proved to be as good or better than the entire butterfly fauna at delineating a variety of environmental gradients at both local and landscape scales. The endemic genus Strabena (Satyrinae) was only able to delineate such patterns under a restricted set of conditions. However, this genus, while species rich in Madagascar, was not exceptionally diverse nor were its species members abundant within the study area. It is concluded that target taxon analysis is a potentially useful tool for providing high—quality data while expanding coverage of taxonomic diversity for conservation planning.
Enrichment Planting in Selectively Logged Rain Forest: A Combined Ecological and Economic Analysis
Authors: Schulze Peter C. , Leighton Mark , Peart David R.
Published: April 2006

We demonstrate how research on innovative agroforestry systems, incorporating new species and management approaches, can benefit from preliminary financial appraisals that include both economic and ecological variables in quantitative cost—benefit models. Model results provide vital information for planning further research, and thus increase the likelihood of finding practical solutions to urgent resource management problems within reasonable funding and time constraints. As a case study, we evaluate the potential of enrichment plantings of three native fruit—producing genera in selectively logged rain forests of Kalimantan, Indonesia. The models use preliminary estimates of 8 ecological parameters (e.g., survival, growth rate, fruit production) and 11 economic parameters (e.g., planting and harvesting costs, market prices) to predict net present value (NPV) over a variety of project durations and discount rates. Sensitivity analyses examine the effect of changes in input parameters. The genera were chosen (1) for ecological complementarity in the use of light resources and (2) to produce fruit at times when commonly harvested species are unavailable in markets. Dialium spp. are canopy trees that produce timber and a relatively nonperishable fruit; Willughbeia spp. are fast—growing lianas that produce fruit; Garcinia spp. are understory fruit trees. Sensitivity analyses indicate that all three genera have potential for substantial positive NPV, and that NPV projections depend heavily upon fruit price, fruit production, age of first reproduction, juvenile survivorship, and harvesting and marketing costs. In addition, these analyses demonstrate that preliminary, combined ecological—economic analysis can guide the selection of species and research strategies for experimental trials.
Effects of Climate Change and Land Use on Duck Abundance in Canadian Prairie‐Parklands
Authors: Bethke Raymond W. , Nudds Thomas D.
Published: April 2006

Recent declines in the number of breeding ducks in the Canadian prairie‐parklands have been hypothesized to be due to loss of habitat to agriculture. However, prairie‐parkland also has experienced wetland loss to drought as well as to agriculture. If habitat restoration is to be implemented and monitored successfully, it is important to separate the effects of anthropogenic changes to the landscape on duck populations from those caused by changes in climate. We used data from annual air–ground surveys and from precipitation records to develop relationships between indices of abundance of each of 10 species of ducks and indices of wetland conditions during 1955‐1974. We used these relationships to predict annual abundance of each species during 1975‐1989. We compared predicted and observed abundances over the period 1975‐1989 to distinguish declines in duck abundance greater than those accounted for by drought alone and to determine the magnitude and location of real "deficits" in duck abundance. Average annual deficits within Canadian prairie‐parkland over the period 1975‐1989 were estimated at 1.2 x 106 birds for both Mallard (Anas platyrhynchos) and Northern Pintail (A. acuta), 480 000 for Blue‐winged Teal (A. discors), 190 000 for American Wigeon (A. americana), 175 000 for Northern Shoveler (A. clypeata), 50 000 for Gadwall (A. strepera), 10 000 for Green‐winged Teal (A. crecca), 40 000 for Canvasback (Aythya valisineria), 25 000 for Lesser Scaup (A. affinis), and 5000 for Redhead (A. americana). Overall, the effect of agricultural expansion in the east on prime waterfowl habitat since 1951 appears to have been negligible. There, as much as 90% had been already lost prior to 1951. In the west, however, where prime waterfowl habitat was still relatively abundant in 1951, agricultural development has encroached substantially. The relationship between the lost area of the best breeding habitats and the size of population deficits for Mallards and Northern Pintails in the entire Canadian prairie‐parkland region was significant for both species (P < 0.0027 and P < 0.0001, respectively). Consequently, habitat restoration programs located where the highest quality waterfowl habitat and the lowest quality agricultural lands overlap most should have the greatest potential to affect recovery of breeding duck populations in the Canadian prairie‐parklands.
Recovery From Small‐Scale Anthropogenic Disturbances by Northern California Salt Marsh Plant Assemblages
Authors: Allison Stuart K.
Published: April 2006

A series of experimental disturbances by sediment deposition were conducted in the salt marsh at Bolinas Lagoon to examine the ability of marsh plants to recover from small‐scale anthropogenic disturbances. Results from these experiments demonstrated that species differ in their ability to recover, with Distichlis spicata and Salicornia virginica recovering most quickly from disturbances that occurred at any time of the year. Other species, such as Frankenia grandifolia and Jaumea carnosa, only recovered from disturbances that occurred early in the growing season. Recovery was by vegetative ingrowth of plants surrounding a disturbed patch or by growth of buried plants up through the sediment. Seedling establishment was rare and did not significantly influence recovery. Anthropogenic disturbances such as excessive sedimentation may cause lasting changes by eliminating or reducing the cover of species sensitive to sediment deposition, and by changing the substrate so that recruitment from seeds is limited.
Distribution and Diet of Bison and Pocket Gophers in a Sandhills Prairie
Authors: Steuter A. A. , Steinauer E. M. , Hill G. L. , Bowers P. A. , Tieszen L. L.
Published: April 2006

Native herbivores are generally preferred over introduced species for managing prairie preserves. However, contemporary prairies are fragments of the original ecosystem, and their size and management may not match the foraging and/or social behavior of native herbivores. We conducted field studies from May 1988 through April 1991 within a 3000‐ha sandhills prairie to describe bison (Bos bison) and pocket gopher (Geomys bursarius) use of native Great Plains grassland at a size relevant to current land ownership and management units. The distribution and diet of bison and pocket gophers were compared to vegetation patterns at several scales. The study area is characterized by a matrix of warm‐season grasses occurring on four range sites (topo‐edaphic units). Patches characterized by forbs, shrubs, and trees occur within the matrix communities associated with the four range sites. Bison distribution appears to be influenced by a complex interaction between seasonal forage availability, herd size, and habitat openness. Bison diets during the growing season are strongly linked to the warm‐season grasses of the prairie matrix. Pocket gopher activity is ubiquitous throughout the study area, but is particularly high in forb patches and appears to be responsive to bison impacts. Pocket gopher diets are strongly linked to forbs, both in the forb patches and in the prairie matrix. Field data indicate that bison and pocket gophers use herbage resources that have distinctly different distributions within the sandhills prairie. It appears that bison remain well adapted to prairie remnants of the size we studied, and through interactions with other herbivores and vegetation patterns, will support a diverse landscape.