bluuebunny/crossref_metadata_2025_split huggingface dataset:
NATURAL DISTURBANCES AND DIRECTIONAL REPLACEMENT OF SPECIES
Authors: Platt William J. , Connell Joseph H. 
Published: June 2007

The original concept of succession emphasized directional changes in species composition occurring over time on “blank slates” (new substrates or those that followed catastrophic disturbances). In this paper, we explore relationships between different effects of disturbances on residents and the initiation of directional species replacement on sites in a landscape. We present a conceptual model involving recurrent natural disturbances of sites in a landscape containing two species, one of which arrives at sites early and the other arrives late following disturbance. We predict effects of recurrent catastrophic disturbances (no survivors) and non‐catastrophic disturbances (some survivors) on the initiation of directional species replacement, assuming temporal gradients in environmental conditions on sites after disturbance. We predict that directional species replacement will be initiated by catastrophic disturbances, and by non‐catastrophic disturbances when the early species does not survive, but reinvades. Most natural disturbances tend to leave survivors and do not remove early species preferentially. As a result, many post‐disturbance changes are possible on sites; directional species replacement is only one change, and often may not be the most common. One important consequence of the low likelihood that disturbances will initiate directional species replacements should be the precarious existence of early species dependent on disturbances that open sites for colonization. We examined constraints on disturbances, sites, and life histories that might increase colonization by early species. We explored how refuges and life history characteristics might reduce the likelihood of replacement of early species by late species, and we consider how spatial and temporal variation in disturbance effects might influence persistence of early species. In this way, we propose relationships between effects of non‐catastrophic disturbance and the dynamic relationships between species that may be applicable across different ecological systems.Corresponding Editor: S. T. Jackson
TREE AGE ESTIMATION FOR THE TROPICS: A TEST FROM THE SOUTHERN APPALACHIANS
Authors: Baker Patrick J. 
Published: June 2007

The lack of annual growth rings in the majority of tropical tree species greatly limits our understanding of the long‐term dynamics of tropical forests. To address this problem, several methods have been developed to estimate the age of tropical trees from diameter growth data. These past approaches, however, suffer from two major flaws: (1) they assume a deterministic age–size relationship for a tree species, and (2) they have not been verified with independently derived age data. In this paper, I present a new approach that uses diameter growth rates, independent of tree size, that are stratified by crown class to estimate the age of individual trees. Past approaches have assumed that when present‐day canopy trees were juveniles they grew at rates similar to conspecifics currently in the understory. In contrast, the crown class model assumes that present‐day canopy trees have grown at rates similar to conspecifics in the same crown class, irrespective of size, throughout ontogeny.The crown class model was compared to a periodic annual increment (PAI) model typical of past approaches in mixed oak‐hardwood forest in the southern Appalachians, USA. Tree ages were obtained independently from tree cores from three stands of differing age structure. Comparisons between the two models were made for species' population age structures (independent of stands) and stand age structures (independent of species).Age estimation errors for the crown class model were lowest for relatively shade‐intolerant species such as yellow poplar (Liriodendron tulipifera) and chestnut oak (Quercus prinus), but increased with the increasing shade tolerance of the species. The PAI model followed the opposite pattern, providing the most accurate age estimates for shade‐tolerant species. These results were consistent with the underlying ecological assumptions of each model.When predicted age distributions for individual stands were compared to the true age distributions, the PAI approach had higher estimation errors than the crown class model in almost every case. In addition, the PAI model had a strong tendency to overestimate tree ages. A mixed model that used crown class age estimates for shade‐intolerant species and PAI model age estimates for shade‐tolerant species generated the most accurate estimates of stand age distribution. The results of this study suggest new opportunities for the study of long‐term dynamics in tropical forests and underscore the importance and utility of validating models with independent data.
WEASELS, VOLES, AND TREES: INFLUENCE OF MUSTELID SEMIOCHEMICALS ON VOLE POPULATIONS AND FEEDING DAMAGE
Authors: Sullivan Thomas P. , Sullivan Druscilla S. , Reid Donald G. , Leung Maria C. 
Published: June 2007

The role of predators, particularly small mustelids, in regulating vole (Microtus spp.) populations has been the subject of much scientific inquiry over the past several decades. From a management perspective, voles cause economic damage by feeding on seedlings planted on cutover forest land in temperate and boreal zones. Because of the close relationship between small weasels (Mustela erminea and M. nivalis) and voles, could the indirect effect of weasel scent disrupt vole populations and reduce their damage to forest plantations? This study was designed to test the hypotheses that synthetic weasel odor would: (1) reduce abundance, reproduction, survival, and movement of montane (Microtus montanus) and meadow (M. pennsylvanicus) vole populations; (2) enhance the activity of small weasels; and (3) reduce feeding damage by voles to tree seedlings. Study areas were located near Summerland and Gavin Lake in south‐central British Columbia, Canada. Vole populations were intensively live‐trapped on replicate sites from April 1994 to May 1995 during a peak year in abundance. Synthetic weasel odor was continually present on treatment sites from early summer 1994 to spring 1995. Weasel activity was measured by the number of individuals captured in live‐traps and by the number of snow tracks on control and treatment sites. Overwinter mortality to planted lodgepole pine (Pinus contorta) seedlings from vole feeding was measured on all sites in May 1995.Mean vole abundance (n = 4) was similar between control (32–121 voles/ha) and treatment (37–118 voles/ha) sites. Montane voles declined by 17–36% on treatment sites during early summer when trappability of this species declined dramatically at Summerland. This pattern was not observed for meadow voles at Gavin Lake. Recruitment of new voles was generally similar between control and treatment sites. Weasel odor had no effect on reproduction, in terms of number of successful pregnancies and index of early juvenile survival, or on total survival, movements, or body mass of voles. Activity of small weasels appeared to be higher on treatment than control sites at Gavin Lake. Weasel odor did not reduce mortality of tree seedlings caused by vole feeding.This study is the first investigation of the population responses of free‐living voles to synthetic odor of the short‐tailed weasel, a principal predator of Microtus spp. Our results demonstrate that by the time voles have reached high densities, it is too late to reduce numbers or curtail feeding damage, regardless of weasel odor‐induced antipredatory behavior or enhanced activity of predators. Application of weasel odor during the low phase of the vole population cycle would be a critical test of the hypothesis that small mustelids could lengthen the period of low vole numbers and potentially protect forest plantations from vole damage.
THE IMPACT OF INSECTICIDES AND HERBICIDES ON THE BIODIVERSITY AND PRODUCTIVITY OF AQUATIC COMMUNITIES
Authors: Relyea Rick A. 
Published: June 2007

Pesticides constitute a major anthropogenic addition to natural communities. In aquatic communities, a great majority of pesticide impacts are determined from single‐species experiments conducted under laboratory conditions. Although this is an essential protocol to rapidly identify the direct impacts of pesticides on organisms, it prevents an assessment of direct and indirect pesticide effects on organisms embedded in their natural ecological contexts. In this study, I examined the impact of four globally common pesticides (two insecticides, carbaryl [Sevin] and malathion; two herbicides, glyphosate [Roundup] and 2,4‐D) on the biodiversity of aquatic communities containing algae and 25 species of animals.Species richness was reduced by 15% with Sevin, 30% with malathion, and 22% with Roundup, whereas 2,4‐D had no effect. Both insecticides reduced zooplankton diversity by eliminating cladocerans but not copepods (the latter increased in abundance). The insecticides also reduced the diversity and biomass of predatory insects and had an apparent indirect positive effect on several species of tadpoles, but had no effect on snails. The two herbicides had no effects on zooplankton, insect predators, or snails. Moreover, the herbicide 2,4‐D had no effect on tadpoles. However, Roundup completely eliminated two species of tadpoles and nearly exterminated a third species, resulting in a 70% decline in the species richness of tadpoles. This study represents one of the most extensive experimental investigations of pesticide effects on aquatic communities and offers a comprehensive perspective on the impacts of pesticides when nontarget organisms are examined under ecologically relevant conditions.
EFFECTS OF AN HERBICIDE AND AN INSECTICIDE ON POND COMMUNITY STRUCTURE AND PROCESSES
Authors: Rohr Jason R. , Crumrine Patrick W. 
Published: June 2007

Virtually all species live within complex food webs, and many of these organisms are exposed to contaminants. However, we know little about how community processes, such as competition and predation, influence susceptibility to contaminants or how different types of contaminants shape communities. The objective of our study was to determine how realistic concentrations of the herbicide atrazine and the insecticide endosulfan influence the structure of a pond community when the presence of common community members was manipulated. We employed a factorial design in mesocosms to evaluate the effects of pesticide treatments (25 μg/L of atrazine, 10 μg/L of endosulfan, solvent control; two pulses separated by two weeks) and the presence or absence of wood frog tadpoles (Rana sylvatica), adult snails (Planorbella trivolvis), and caged dragonfly larvae (Anax junius) on a freshwater community.Tadpoles, snails, and chironomid larvae, Polypedilum sp. (Dipterans), all competed for periphyton. As a result, tadpoles reduced the survival, mass, and reproduction of snails; snails reduced the growth, development, inactivity, and dragonfly avoidance of tadpoles; snails and tadpoles reduced the abundance of chironomid larvae; and chironomid larvae reduced snail mass. The adverse effect of snails on tadpole growth and behavior was greater in the presence of the caged tadpole predator, A. junius. Neither pesticide affected dragonfly survival, but endosulfan directly reduced zooplankton (Daphnia), and atrazine indirectly reduced chironomid abundance. Atrazine also directly decreased periphyton, and endosulfan decimated chironomid larvae, resulting in indirect increases and decreases in competition for both snails and tadpoles, respectively. Consequently, relative to endosulfan, atrazine tended to decrease snail mass and reproduction and reduce tadpole mass, development, inactivity, refuge use, and dragonfly avoidance. However, the indirect effects of pesticides depended upon the presence of heterospecifics. The indirect benefit of endosulfan on snail mass was greater in the presence of caged dragonfly larvae, and endosulfan's indirect benefit on tadpole mass was greater in the absence of snails. The effect of pesticides on tadpole activity depended on both caged dragonflies and snails. Thus, environmentally realistic concentrations of pesticides directly and indirectly shaped species responses and community composition, but the initial composition of the community influenced these pesticide effects. These results emphasize the importance of quantifying the effects of contaminants within complex natural communities.
OPTICAL INSTRUMENTS FOR MEASURING LEAF AREA INDEX IN LOW VEGETATION: APPLICATION IN ARCTIC ECOSYSTEMS
Authors: van Wijk Mark T. , Williams Mathew 
Published: June 2007

Leaf area index (LAI) is a powerful diagnostic of plant productivity. Despite the fact that many methods have been developed to quantify LAI, both directly and indirectly, leaf area index remains difficult to quantify accurately, owing to large spatial and temporal variability. The gap‐fraction technique is widely used to estimate the LAI indirectly. However, for low‐stature vegetation, the gap‐fraction sensor either cannot get totally underneath the plant canopy, thereby missing part of the leaf area present, or is too close to the individual leaves of the canopy, which leads to a large distortion of the LAI estimate. We set out to develop a methodology for easy and accurate nondestructive assessment of the variability of LAI in low‐stature vegetation. We developed and tested the methodology in an arctic landscape close to Abisko, Sweden.The LAI of arctic vegetation could be estimated accurately and rapidly by combining field measurements of canopy reflectance (NDVI) and light penetration through the canopy (gap‐fraction analysis using a LI‐COR LAI‐2000). By combining the two methodologies, the limitations of each could be circumvented, and a significantly increased accuracy of the LAI estimates was obtained. The combination of an NDVI sensor for sparser vegetation and a LAI‐2000 for denser vegetation could explain 81% of the variance of LAI measured by destructive harvest. We used the method to quantify the spatial variability and the associated uncertainty of leaf area index in a small catchment area.
LOGGING STRATEGY INFLUENCES COLONIZATION OF COMMON CHLOROLICHENS ON BRANCHES OF PICEA ABIES
Authors: Hilmo Olga , Holien Håkon , Hytteborn Håkan 
Published: June 2007

Increased knowledge about how lichen colonization responds to logging is a prerequisite for developing guidelines in forest management aimed to maintain biodiversity. Within an experimentally logged boreal spruce forest we studied effects of different logging strategies and distance to the forest edges on colonization of epiphytic chlorolichens. Within a fine‐grained (23 clearcuts, 0.2 ha each) and a coarse‐grained area (3 clearcuts, 2.25 ha each) we sampled 90 branches. In addition 20 branches were sampled in an untouched control area. The 15 youngest annual shoots along the main axes on each branch were analyzed.Establishment of the dispersed diaspores, most of themHypogymnia, was mainly limited to shoot ages 4–6 where the needles also were present. Independent of logging strategy the occurrence of small lobules increased with increasing distance from the edges, indicating unfavorable conditions for establishment at the edges or a lower supply of diaspores. A distinct decrease in the number of thalli ofCavernularia hulteniiwas observed in the two logged areas compared to the control branches. The colonization ofHypogymniaspp. andPlatismatiaspp. was successful in the fine‐grained area, while a coarse‐grained pattern of logging caused a significant decrease in the number of thalli, from shoot age 5 forHypogymniaand shoot age 9 forPlatismatia. An early drop of needles in the coarse‐grained area, especially at the forest edges, supports the assumption that the occurrence of needles is important for a successful colonization. A higher rate of growth of these species in the coarse‐grained area, compared to the other two areas, illustrates that logging does not necessarily cause unfavorable conditions for growth of already established thalli.In conclusion, establishment of the diaspores is less successful in logged areas. Thus, a fragmented logging pattern influences the colonization negatively, even for common chlorolichens. Moreover, the response to logging strategy is species‐specific. Development of management guidelines should be based on wide scientific knowledge about the species life‐history characteristics.
STRUCTURAL AND FUNCTIONAL RESPONSES OF A SUBTROPICAL FOREST TO 10 YEARS OF HURRICANES AND DROUGHTS
Authors: Beard Karen H. , Vogt Kristiina A. , Vogt Daniel J. , Scatena Frederick N. , Covich Alan P. , Sigurdardottir Ragnhildur , Siccama Thomas G. , Crowl Todd A. 
Published: June 2007

Little is known about ecosystem‐level responses to multiple, climatic disturbance events. In the subtropical forests of Puerto Rico, the major natural disturbances are hurricanes and droughts. We tested the ecosystem‐level effects of these disturbances in sites with different land use histories. From 1989 to 1992, data were collected to determine the effects of Hurricane Hugo and two droughts on litterfall inputs, fine‐root biomass, and decomposition rates in three topographic locations (stream, riparian, upslope) within two watersheds. From 1994 to 1998, we added a third watershed and an experiment in which coarse‐wood levels were manipulated to simulate hurricane inputs. Data were collected on tree and palm growth rates, litterfall inputs, fine‐root biomass, and decomposition rates. From 1994 to 1998, four hurricanes and three droughts were recorded.Measured parameters had unique responses and recovery rates to hurricanes and droughts. Litterfall inputs returned to long‐term mean rates within one month following droughts and small‐to‐moderate hurricanes but required five years to recover after an intense hurricane. In contrast, fine‐root biomass recovered seven months after an intense hurricane but failed to recover after five years following a severe drought. Despite the dramatic effects of these weather events on some ecosystem parameters, we found that aboveground measures of tree and palm growth were more affected by preexisting site conditions (e.g., nitrogen availability due to past land use activities) than hurricanes or droughts. The addition of coarse woody debris increased tree and palm growth, fine‐root biomass, and litter production; however, in the case of tree and palm growth, this effect was least measurable in the sites with the highest productivity. We found that decomposition rates were more controlled by litter quality than weather conditions. In conclusion, we found that certain ecosystem structures (e.g., canopy structure and fine‐root biomass) generally recovered more slowly from disturbance events than certain ecosystem processes (e.g., plant growth rates, decomposition rates). We also found that past land use activities and disturbance legacies were important in determining the responses and recovery rates of the ecosystem to disturbance.
CARBON, NITROGEN, AND PHOSPHORUS ACCUMULATION IN FLOODPLAINS OF ATLANTIC COASTAL PLAIN RIVERS, USA
Authors: Noe Gregory B. , Hupp Cliff R. 
Published: June 2007

Net nutrient accumulation rates were measured in riverine floodplains of the Atlantic Coastal Plain in Virginia, Maryland, and Delaware, USA. The floodplains were located in watersheds with different land use and included two sites on the Chickahominy River (urban), one site on the Mattaponi River (forested), and five sites on the Pocomoke River (agricultural). The Pocomoke River floodplains lie along reaches with natural hydrogeomorphology and on reaches with restricted flooding due to channelization and levees. A network of feldspar clay marker horizons was placed on the sediment surface of each floodplain site 3–6 years prior to sampling. Sediment cores were collected from the material deposited over the feldspar clay pads. This overlying sediment was separated from the clay layer and then dried, weighed, and analyzed for its total carbon (C), nitrogen (N), and phosphorus (P) content.Mean C accumulation rates ranged from 61 to 212 g·m−2·yr−1, N accumulation rates ranged from 3.5 to 13.4 g·m−2·yr−1, and P accumulation rates ranged from 0.2 to 4.1 g·m−2·yr−1 among the eight floodplains. Patterns of intersite variation in mineral sediment and P accumulation rates were similar to each other, as was variation in organic sediment and C and N accumulation rates. The greatest sediment and C, N, and P accumulation rates were observed on Chickahominy River floodplains downstream from the growing metropolitan area of Richmond, Virginia. Nutrient accumulation rates were lowest on Pocomoke River floodplains that have been hydraulically disconnected from the main channel by channelization and levees. Sediment P concentrations and P accumulation rates were much greater on the hydraulically connected floodplain immediately downstream of the limit of channelization and dense chicken agriculture of the upper Pocomoke River watershed. These findings indicate that (1) watershed land use has a large effect on sediment and nutrient retention in floodplains, and (2) limiting the hydraulic connectivity between river channels and floodplains minimizes material retention by floodplains in fluvial hydroscapes.
The Dynamics of Gender and Class in Access to Health Care: Evidence from Rural Karnataka, India
Authors: Iyer Aditi , Sen Gita , George Asha 
Published: June 2007

This is the second part of the special section, edited by Professors Margaret Whitehead and Göran Dahlgren, on the equity impacts of different health care systems, which includes studies conducted within the framework of the Affordability Ladder Program. In the early 1990s, India embarked upon a course of health sector reform, the impact of which on an already unequal society is now becoming more apparent. This study sought to deepen understanding of equity effects by exploring gender and class dynamics vis-à-vis basic access to health care for self-reported long-term ailments. The authors drew on the results of a cross-sectional household survey in a poor agrarian region of south India to test whether gender bias in treatment-seeking is class-neutral and whether class bias is gender-neutral. They found evidence of “pure gender bias” in non-treatment operating against both non-poor and poor women, and evidence of “rationing bias” in discontinued treatment operating against poor women overall, but with some differences between the poor and poorest households. In poor households, men insulated themselves and passed the entire burden of rationing onto women; but among the poorest, men, like women, were forced to curtail treatment. There were economic class differences in continued, discontinued, and no treatment, but class was a gendered phenomenon operating through women, not men.
New approach to the problem of globally convergent frequency estimator
Authors: Bobtsov Alexey A. 
Published: June 2007

AbstractThis note proposes a solution to the problem of real‐time globally convergent estimation of the frequency of a bias sinusoid signal. The method is an alternative to known approaches. The new frequency estimator is a fourth‐order system for the case of bias sinusoidal signals and has significant advantages over prior methods. Copyright © 2007 John Wiley & Sons, Ltd.