bluuebunny/crossref_metadata_2025_split huggingface dataset:
An improved method for the rapid assessment of forest understorey light environments
Authors: Brown Nick , Jennings Steve , Wheeler Phil , Nabe‐Nielsen Jacob 
Published: March 2003

Summary 1.  The high spatial and temporal variability of forest understorey light environments requires lengthy and/or extensive sampling in order to characterize it by direct measurement. As this is often impractical, a number of surrogate measures have been developed that estimate light availability from assessments of forest canopy structure. 2.
The subjective crown illumination index developed by Clark & Clark (1992) was compared with Garrison's (1949) moosehorn and two new methods: (i) the crown illumination ellipses method, which compares the size of canopy gaps with a series of standard area ellipses printed on a transparent screen; and (ii) the canopy‐scope that, like the moosehorn, uses an array of 25 dots printed on a transparent screen to assess canopy openness, but is more robust and portable, measuring the largest canopy gap visible from the point of measurement rather than canopy openness overhead. 3.  The new measures were more highly correlated with canopy openness in the range 0–30%, measured from hemispherical photographs, than the crown illumination index, and showed lower levels of between‐observer variability. 4.  The canopy‐scope has the potential to be widely used for the simple and rapid assessment of forest understorey light environments. It has the advantage of giving ratio scale measurements that can be used in parametric statistics. The crown illumination ellipses can be used to score the illumination of crowns that are above head height.
Heterogeneous grazing causes local extinction of edible perennial shrubs: a matrix analysis
Authors: Hunt L.P. 
Published: March 2003

Summary

Population modelling and field measurements of births, growth and deaths were used to investigate the long‐term change in abundance of Atriplex vesicaria (Chenopodiaceae), a long‐lived, palatable, perennial shrub, under sheep grazing. Of particular interest was whether A. vesicaria is at risk of being eliminated throughout grazed paddocks when the recommended practice of continuous grazing at conservative stocking rates is employed.
Time‐invariant matrix population models indicated that the A. vesicaria population was in decline over much of the study paddock, but the rate of decline was greatest nearer to the water point (population growth rate λ ≈ 0·8). Time‐varying stochastic matrix models projected that the A. vesicaria population would become locally extinct at most sites up to approximately 2200 m from water, occurring first closer to water (within 12–29 years). The population was stable (i.e. λ ≥ 1) at sites greater than 2200 m from water over the projection period of 100 years.
Decreases in adult survival and recruitment made the largest contributions to reductions in the population growth rate. However, there were spatial patterns centred on the water point in the degree to which particular demographic processes contributed to these reductions, because of a grazing gradient and the differential sensitivity of demographic processes to grazing. Thus decreases in recruitment contributed to reductions in the population growth rate at greater distances. Such responses, together with the sensitivity of the population growth rate to these processes, determined the spatial pattern in population growth.
The results suggest that piospheres (i.e. the zone of impact) continue to expand over many years under set‐stocking so that the area around the water point that is devoid of A. vesicaria becomes larger. The process of expansion appears to first involve the inhibition of recruitment, followed by eventual mortality of established shrubs.
The large contribution of adult survival to the population growth rate in A. vesicaria suggests that minimizing the mortality of established adults should be a priority for management. This is likely to involve resting from grazing at critical times such as during extended dry periods. This may also permit increased levels of recruitment during subsequent moister periods.
Sustainable timber harvesting in Venezuela: a modelling approach
Authors: Kammesheidt Ludwig , Köhler Peter , Huth Andreas 
Published: March 2003

Summary

Reliable data on the growth and yield of logged‐over forest, to determine sustainable cutting cycles, are widely missing for the tropics.
We used the process‐based model formind2.0 to analyse the growth and yield of logged‐over forest in Venezuela under different logging scenarios over a period of 240 years, and compared results with unlogged stands. The performance of the model was evaluated with a detailed stability and sensitivity analysis.
In the absence of further logging, the logged‐over stand approached the stand structure of mature forest in terms of bole volume and basal area after about 50–100 years.
Thirty‐year cutting cycles with conventional logging methods and net extraction volumes of 45 and 60 m3 ha−1 cycle−1 did not provide sustainable yields under either of two minimum felling diameters (35 and 50 cm) that were applied. Only the 60‐year cutting cycle provided sustainable yields under conventional and reduced‐impact logging, with the different minimum felling diameters and a range of net volumes extracted (30–60 m3 ha−1 cycle−1).
With the longest cutting cycle (60 years), bole volume recovered to levels similar to the mature unlogged stand, but the species composition was very different.
Scenarios with reduced‐impact logging provided a significantly higher timber volume than under conventional logging. The conservation of forest resources will only be possible with long cutting cycles (at least 60 years) in combination with reduced‐impact logging.
Enhancement of acetylcholine‐induced desensitization of guinea‐pig ileal longitudinal muscle in Ca2+‐free conditions
Authors: Horio S. , Nagare T. , Moritoki H. 
Published: March 2003

1 To determine the role of cellular Ca2+ in desensitization, acetylcholine(ACh)‐induced desensitization was studied under Ca2+‐free condition in guinea‐pig ileal longitudinal muscle. 2 Pretreatment of the tissue with 10−−4 m ACh (desensitizing treatment) in normal Tyrode solution caused desensitization of the responses both to ACh and histamine. The desensitizing treatment performed in Ca2+‐free solution enhanced desensitization of the responses to ACh and histamine significantly. 3 The desensitizing treatment with ACh caused suppression of the responses to high K+ (tonic component) and Bay K 8644. The desensitizing treatment performed in Ca2+‐free solution potentiated the suppression of the responses to high K+ and Bay K 8644 significantly. 4 ACh‐induced desensitization was enhanced significantly in the presence of a protein kinase C inhibitor, 1‐(5‐isoquinolinesulfonyl)‐2‐methylpiperazine(H‐7, 10−−4m) to a similar extent as desensitization obtained under Ca2+‐free condition, but not in the presence of a non‐specific and less potent kinase inhibitor, N‐(2‐guanidinoethyl)‐5‐isoquinolinesulfonamide hydrochloride(HA1004, 10−−4 m). 5 These results suggested that voltage‐gated Ca2+ channels were involved in ACh‐induced desensitization and that intracellular Ca2+, which was increased during the stimulation with ACh, inhibited desensitization through the activation of protein kinase C. This kinase could have activated or protected Ca2+ channels during the desensitization process to reduce desensitization.
Spontaneous baroreflex sensitivity as a dynamic measure of cardiac anticholinergic drug effect
Authors: Penttilä J. , Vesalainen R. , Helminen A. , Kuusela T. , Hinkka S. , Rahi K. , Kaila T. , Scheinin H. 
Published: March 2003

1 In this study, the analysis of spontaneous baroreflex sensitivity (BRS) was applied to the dynamic assessment of cardiac anticholinergic drug effect in healthy male volunteers. 2 The anticholinergic effects of single intravenous (i.v.) injections of atropine (10 μg kg–1), glycopyrrolate (5 μg kg–1) and scopolamine (5 μg kg–1), as well as a 2‐h infusion of glycopyrrolate (5 μg kg–1 h–1) were investigated. Baroreflex sensitivity, a validated measure of cardiac parasympathetic reflex regulation, was repeatedly measured from 5‐min recordings of electrocardiogram (ECG) and continuous blood pressure by using the sequence technique, a method based on detection of spontaneous fluctuations in blood pressure and heart rate. 3 Single injections of atropine, glycopyrrolate and scopolamine decreased the mean BRS by 71 ± 32, 68 ± 23 and 27 ± 45%, respectively, whereas the slow glycopyrrolate infusion gradually decreased BRS (up to 83 ± 11% reduction) and increased both systolic (SAP) and diastolic arterial pressures (DAP) (on an average, by 9 mmHg). 4 During the withdrawal of the parasympathetic blockade (indicated by increasing BRS), the proportion of baroreflex sequences in the recordings increased transiently from 10 up to 20–25%, probably reflecting the restoration of the baroreflex integrity and the baroreflex‐induced attempt to counteract the blood pressure increase. 5 The sequence method to study BRS seems to be feasible in the assessment of cardiac anticholinergic drug effects, and it also provides good time resolution for the dynamic measurements.
Ecological comparisons between Eastern Asia and North America: historical and geographical perspectives
Authors: Guo Qinfeng 
Published: March 2003

SummaryThe close floristic affinities between eastern Asia and North America have long been recognized and intensively studied, however, the ecological and biogeographical consequences of such a floristic relationship between these two remotely separated regions has been largely neglected until recently. Quantitative investigations of such relationships could greatly improve our understanding of many global and historical aspects of species diversity, vegetation dynamics, and biogeography, especially with the rapid developments of cladistic methods of phylogenetic reconstruction. All comparisons and predictions will depend on understanding past and present physical and biological processes (i.e. geological history of the continents and the evolutionary history of organisms), as well as human impacts in both regions. Both species level (life history characteristics, distribution, ecological functions) and community level (species composition, structure, endemism) variables should be investigated. Comparisons should be conducted spatially across vegetation zones and temporally through geological episodes. Emphases on the phylogeny and geological history of component taxa by analysing and synthesizing multidisciplinary data would be helpful, especially with regard to the current trends in global climate change. Diversity measured on different scales (i.e. α‐, β, and g‐diversity) could provide invaluable information about local‐regional relationships and their ecological implications in continental or even global biodiversity patterns.
The epiphyte vegetation of Annona glabra on Barro Colorado Island, Panama
Authors: Zotz Gerhard , Bermejo Patricia , Dietz Hansjörg 
Published: March 2003

Summary Aim Information on the community composition, structure, and dynamics of epiphyte vegetation is scarce. A survey of the epiphytes occurring on all individuals of one particular host tree species in a well‐studied neotropical research site allowed us a comparison of the epiphyte flora of this tree with the local epiphyte flora, the analysis of spatial distribution patterns and the use of these patterns as indications for changes in time. In the future, our results can be used as a baseline data‐set for the direct observation of the long‐term dynamics in epiphyte communities. Location The study was conducted on Barro Colorado Island (BCI), Panama. Methods We recorded all individuals of the vascular epiphytes growing on Annona glabra L., a flood‐tolerant, multiple‐stemmed tree, which is restricted to the shoreline of BCI. Data on tree biometrics, epiphyte species, and epiphyte abundances were collected for more than 1200 trees. Results In total, we encountered almost 15,000 epiphytic individuals in sixty‐eight species, corresponding to more than one third of the entire epiphyte flora of Barro Colorado Island. The component species differed strongly in abundance: the four most important species accounted for >75% of all individuals. In most cases, the same four species were also the first to colonize a tree (=phorophyte). Colonization patterns indicated no replacement of early colonizers by late arrivals. Species richness and epiphyte abundances showed a positive correlation with the size and the density of the host trees. All species showed a highly clumped distribution and the physiognomy of epiphyte communities of individual trees was dominated either by one or several of the four most common species or by a set of frequently co‐occurring tank bromeliads. Other species were dominant only in exceptional cases. Most species were always rare. A distance effect on community composition was mostly confined to a local scale with an increased similarity in the species assemblage of stems of a tree v. neighbouring trees. Main conclusions The epiphytes on a single small phorophyte species may encompass a surprisingly large proportion of the local epiphyte flora. The observations that most tree crowns are inhabited by a single or only very few species, and that all epiphyte species show highly clumped distributions suggest a predominance of very local dispersal within a tree crown, which is only infrequently interrupted by successful long‐distance dispersal between crowns.
Neotropical seasonally dry forests and Quaternary vegetation changes
Authors: Toby Pennington R. , Prado Darién E. , Pendry Colin A. 
Published: March 2003

AbstractSeasonally dry tropical forests have been largely ignored in discussions of vegetation changes during the Quaternary.We distinguish dry forests, which are essentially tree‐dominated ecosystems, from open savannas that have a xeromorphic fire‐tolerant, grass layer and grow on dystrophic, acid soils. Seasonally dry tropical forests grow on fertile soils, usually have a closed canopy, have woody floras dominated by the Leguminosae and Bignoniaceae and a sparse ground flora with few grasses. They occur in disjunct areas throughout the Neotropics. The Chaco forests of central South America experience regular annual frosts, and are considered a subtropical extension of temperate vegetation formations.At least 104 plant species from a wide range of families are each found in two or more of the isolated areas of seasonally dry tropical forest scattered across the Neotropics, and these repeated patterns of distribution suggest a more widespread expanse of this vegetation, presumably in drier and cooler periods of the Pleistocene.We propose a new vegetation model for some areas of the Ice‐Age Amazon: a type of seasonally dry tropical forest, with rain forest and montane taxa largely confined to gallery forest. This model is consistent with the distributions of contemporary seasonally dry tropical forest species in Amazonia and existing palynological data.The hypothesis of vicariance of a wider historical area of seasonally dry tropical forests could be tested using a cladistic biogeographic approach focusing on plant genera that have species showing high levels of endemicity in the different areas of these forests.
Biogeographical implications of mitochondrial DNA variation in the Bockadam snake (Cerberus rynchops, Serpentes: Homalopsinae) in Southeast Asia
Authors: Karns Daryl R. , O’Bannon Ashley , Voris Harold K. , Weigt Lee A. 
Published: March 2003

AbstractAim The biogeography of Southeast Asia has been greatly affected by Pleistocene sea‐level changes and the consequent alteration of coastline and land mass configurations. We investigated the effect of these Pleistocene events on genetic divergence in Cerberus rynchops, the Bockdam, an Asian water snake (Homalopsinae) associated with tidal mudflats and coastal mangrove forests in Southeast Asia.Location Localities for the Cerberus included the Andaman sea coast of Thailand, Sumatra, and Borneo (Sunda Shelf localities), the Philippines and Sulawesi, and from northern Australia (Sahul Shelf).Methods We analysed mtDNA sequences (12 s, 16 s, and cyt b) from seven C. rynchops populations (twenty‐six specimens), from two specimens of Cerberus microlepis (a freshwater species known only from Lake Buhi in the Philippines), and from one Enhydris enhyris (Schneider), another homalopsine used as an outgroup.Results We found a strong correlation between genetic divergence and geographical distance (r = 0.922, P < 0.001) and the biogeographic history of the region. Cerberus rynchops populations from the Sunda Shelf localities, the Philippines, Sulawesi and C. microlepis from the Philippines were genetically similar (mean divergence = 2.1%, range = 0.7–2.8%) compared to the C. rynchops population from northern Australia (mean divergence from all other Cerberus populations = 6.6%, range = 6.0–7.3%). This divergence was comparable to that observed between the E. enhydris outgroup and all Cerberus populations (mean distance = 7.3%, range = 6.8–8.6%).Main conclusions These findings suggest a relatively high degree of movement and gene flow among Sunda Shelf localities, the Philippines, and Sulawesi (biogeographic region west of Weber’s Line) and isolation of the northern Australian (Sunda Shelf) Cerberus. Taxa will be differentially affected by these Pleistocene sea level changes dependent on their physiology and ecology. We discuss how the dispersal of the coastal, saltwater tolerant C. rynchops would have been affected by changing configurations of Pleistocene coastlines and the implications of these results for the systematics of Cerberus.
Effects of fire protection on savanna structure in Central Brazil
Authors: Moreira Adriana G. 
Published: March 2003

AbstractAimFire protection gradually changes the density of woody plants in numerous savannas around the world. In this study changes of structure in two tropical savanna areas with contrasting history of fire protection in the central Brazilian Cerrado is documented.LocationVegetation was sampled with line intercept transects in two adjacent sites in Brasilia, Federal District. These transects were located within a nature reserve protected from fire since 1972 and within an adjacent reserve area that burns every 2 years.MethodsFive savanna physiognomies, from a low forest (‘cerradão’) to an open savanna (‘campo sujo’), were sampled in both sites.ResultsFire protection increased the abundance of woody plants and favoured fire‐sensitive species. With some exceptions, shrubs tended to be less affected by fire than trees. Species distribution was affected by a complex interaction of fire and physiognomy. Fire had the strongest effect on ‘campo sujo’ savanna, and a less significant effect on the intermediate physiognomies.Main conclusionsProtection permits the establishment of fire sensitive species. A long enough protection against fire could lead to the appearance of more wooded physiognomies in the Cerrado.
A phytogeographical characterization of the vine flora of the Sonoran and Chihuahuan deserts
Authors: Krings Alexander 
Published: March 2003

AbstractAim  This study presents a phytogeographical characterization of the vine flora of two lower North American desert regions as a biogeographical framework for further ecological inquiry into desert vines.Location  The phytogeography of the vine flora of the Sonoran and Chihuahuan Deserts was c haracterized based on 263 known species.Methods  Checklists of the vines of each desert were developed. Represented genera were then grouped into 10 phytogeographical elements based on worldwide distribution patterns. To compare the floristic composition of the desert floras, an index of species similarity was calculated.Results  About a third more species of vines occur in the Sonoran Desert than in the Chihuahuan Desert. Based on the analysis, cosmopolitan genera are the only group more numerous in absolute terms in the Chihuahuan Desert than in the Sonoran Desert. Tropical elements are represented in about the same proportion in each desert as the number of species, however, nearly twice as many pantropical and neotropical genera are represented in the Sonoran Desert as in the Chihuahuan Desert. Proportionately, more genera of temperate elements occur in the Chihuahuan Desert than in the Sonoran desert, although the absolute number of genera is slightly higher in the latter.Main conclusions  As these deserts are relatively recent ecological formations and as vines evolved in forest ecosystems, the composition of the desert vine floras is the result of the interaction between historical vegetation types, their constituent taxa and climatic and geological history. The main differences in the vining floras of the present‐day Sonoran and Chihuahuan Deserts appear to be the result of greater historical influence in the Sonoran Desert of (1) tropical vegetation types and (2) the emergence of the Gulf of California. The Chihuahuan Desert vine flora seems to be the result of (1) a more pronounced historical temperate vegetation, (2) the lack of an important isolating event, such as the creation of the Baja California peninsula, and (3) a cooler climate with shorter growing seasons.
The climatic response of Phyllocladus aspleniifolius (Labill.) Hook. f in Tasmania
Authors: Allen K. J. , Cook E. R. , Francey R. J. , Michael K. 
Published: March 2003

AimTo examine the response of ring widths of Phyllocladus aspleniifolius to maximum and minimum temperatures and to a zonal index (ZI).LocationTasmania, Australia.MethodsBetween two and four increment cores were obtained from approximately 20 trees at each of 16 sites of P. aspleniifolius across Tasmania. Four regions were defined and temperature data for climate stations from each of these regions were transformed into dimensionless time series appropriate for each region. The ZI was constructed from Melbourne and Hobart mean sea level pressure (MSLP). Correlations were calculated between climate data and ring widths over most of the 20th century. Data were then segregated into two subperiods to assess whether or not temporal changes in ring width response have occurred over the 20th century.ResultsThe dominant feature of the correlation functions was a negative correlation with temperatures of the previous growing season. Correlation between the ZI and ring width is most significant, and positive, in November and March of the previous growing season. Differences in the shape of the correlation functions, and their strength is apparent over the course of the century. In general, correlations have become weaker and less consistent among the 16 sites for the latter part of the century. Temperatures have generally increased during the 1900s over which time period correlations have been calculated.Main conclusionsThe temporally changing climatic response in ring widths is consistent with a hypothesis of competition for resources between different parts of a plant. A nonlinear response to climate over a short‐time period violates one of the basic assumptions of dendroclimatology, therefore suggesting further investigation of both the physiology of trees used for dendroclimatological purposes and the statistical methods used for climatic reconstruction.