A function describing all-sized trunk diameter distribution in warm-temperate rain forests

A simple relation (v-lnB) (u-lnx)=c was recognized betweenx as dbh (or individual basal area) andB as the cumulative basal area abovex, for various stands of warm-temperate rain forests of Yakushima Island, southern Japan (v, u andc, parameters). The model parameters explained a difference in the pattern of stand development between secondary succession after clear-felling and gap regeneration within primary forests.     

Growth and turnover of microbial biomass during the decomposition of organic matter(Polygonum cuspidatum) in vitro

Air-dried fresh and dead specimens ofPolygonum cuspidatum were incubated for 250 days in the laboratory, and the growth and turnover of microbial biomass-C in the organic matter were studied. The biomass-C in the fresh leaf and fresh stem attained maximum levels on day 14 and day 7, respectively, and then settled down to stable levels. In the dead leaf and dead stem, increase in biomass-C ceased by day 4 and the biomass-C levels did not change thereafter. The turnover time of the biomass-C was estimated from the amount of biomass-C and the release rate of CO₂-C. The turnover was rapid in the early period of incubation. Then the turnover time became longer and after incubation for 70 days the values approached those in natural soils (longer than 16 days). During the incubation period, nitrogen was not mineralized in any organic matter. In the dead leaf and dead stem, asymbiotic nitrogen fixation activity increased after incubation for about 40 days and disappeared by the end of the incubation period, whereas nitrogen fixation was hardly detected in the fresh leaf and fresh stem.     

Experimental formulations ofBacillus sphaericus for the control of anopheline and culicine larvae

Summary Four experimental formulations ofBacillus sphaericus Neide (2362 isolate) were evaluated for larvicidal activity against culicine and anopheline larvae in several natural and artificial habitats. A granular formulation (5% primary powder) was tested against natural populations of mosquitoes in two simulated habitats in Florida and in maturing and reflooded rice fields in Louisiana. Larvae ofCulex quinquefasciatus Say were reduced by 97 and 99% after application of the granules at the rate of 10 kg/ha to polluted tanks and 2.5 kg/ha to sod-lined potholes, respectively. Anopheline andPsorophora columbiae (Dyar and Knab) larvae were reduced by 68 and 92–100%, respectively, after application of 5 kg granules/ha to rice fields. A flowable concentrate (12.8% primary powder) applied to unpolluted and organically enriched habitats in Florida at 0.25 kg/ha reduced populations ofCulex spp. by 93–100% and 99%, respectively. Sustained-release briquets (5% primary powder) applied at the rate of one half briquet/1.8 m² sod-lined potholes reduced larval populations ofCx. quinquefasciatus by 88–95% for up to 2 weeks in open sunlight. Sustained-release pellets (30% primary powder) applied to small woodland pools in Memphis, TN at the rate of four pellets/pool virtually eliminated larval populations ofCx. restuans Theobald for over 8 days. Variable persistance of larvicidal activity was noted for the other treatments depending on the formulation, target species and habitat.     

Long-term vegetation change in the Juncus squarrosus grassland at Moor House,northern England

Data from the long-term experiment on sheep grazing versus zero sheep grazing (i.e. in an enclosure) on the composition of the Juncus squarrosus grassland at the Moor House NNR are presented. The data have been analysed to assess change in (1) the abundance of individual species, (2) higher plant and bryophyte communities, and (3) vegetation structure. The higher plant data suggested that both the enclosed-and grazed plots were changing in the same direction, but the enclosed plot was moving much faster. The general tendency was towards a blanket bog vegetation dominated by Eriophorum vaginatum and Calluna vulgaris. Juncus squarrosus has declined very quickly in the enclosed plot, but there has also been a slower decline in the grazed one. A significant increase in Calluna vulgaris has occurred only in the enclosed plot. In contrast, the bryophyte data showed completely different successional trajectories in the two treatment plots.The vegetation structure changed markedly after release from grazing, with a decrease in phytomass, but increase in necromass in the lowest height strata. There was no noticeable change in structure over the 18 year period in the grazed plot.Particular problems found in this study were that some species either fluctuated widely in response, or changed in a curvilinear manner.     

Tree species regeneration in a mid-elevation,temperate rain forest in Isla de Chiloé, Chile

The regeneration of canopy and subeanopy species in a mid-elevation, primary rain forest in the Coastal Range of Isla de Chiloé (42°30S), in the cold-temperate region of Chile, was studied by comparing seedling and sapling abundances under the forest canopy, and within 36 tree-fall gaps. The forest was dominated byAmomyrtus luma andLaurelia philippiana (33 and 32% of the main canopy individuals), and two subcanopy species (Myrceugenia ovata, andMyrceugenia planipes) were also important. Uncommon species in the canopy wereDrimys winteri, Amomyrtus meli, andRaphithamnus spinosus. Tree-fall gaps were created generally by the fall of several trees, and the main canopy species were the principal gap-makers. Gap sizes varied between 28 and 972 m², with a mean of 197 m². Seedling and sapling abundances indicate that the dominant species are capable of regenerating below the canopy, but they also germinate and show enhanced growth within small light gaps. For one of the common subcanopy species (M. planipes) and the two infrequent canopy species (D. winteri, andA. meli) regeneration seems to depend entirely on tree-fall gaps. Thus, in this forest, light gaps allow the persistence of infrequent canopy species, but seem less important for the regeneration and maintenance of dominant canopy species.     

Forest-level analysis of stability under exploitation: depensation responses and catastrophe theory

Stability analysis of whole forests is proposed as a qualitative tool for the study of forest responses to partial or patchy harvests or mortality. Instead of modeling every tree or stand, aggregate tree biomass is modeled. In order to aggregate stands, spatial effects must be incorporated. It is shown that depensation growth responses (reduced growth at low biomass) are common because forests often modify harch environments to be more suitable for their growth. Depensation can result from thinning, partial mortality, patchy cutting, or clearcutting, depending on forest type and abiotic factors. Examples of these types of behaviors are given. Stability analysis of different growth regimes under exploitation are related to catastrophe theory and to optimal harvesting policies. Such qualitative analysis is shown to be applicable to data-poor regions such as the tropics where there is great concern over responses of forests to exploitation.     

The effect of fluctuations in tidal inundation frequency on a salt-marsh vegetation

Over a period of 15 years recordings were made of the species cover in permanent plots on the salt marsh of one of the West Frisian Islands, Schiermonnikoog (The Netherlands). Correlations between annual changes in the cover of the major species, and fluctuations in the monthly frequency of inundation by seawater were studied. First, a spectral analysis was carried out on the inundation frequency data to look for predictable patterns. Subsequently, fluctuations were defined as deviations from these predictable patterns. In a repeated multiple regression model, the effects of the season in which the fluctuations occurred, and the elevational position of the plots on the salt marsh were studied as factors influencing the correlation patterns. The behaviour of various species is discussed in relation to their seed bank characteristics and their salt tolerance.     

Response to grazing after nine years of cattle exlusion in a Flooding Pampa grassland,Argentina

This paper reports on changes induced by the introduction of cattle in a grassland that had remained ungrazed for 9 yr, in comparison with two adjacent grasslands: one that remained enclosed and one that has been continuously subject to grazing. Basal cover was measured on 25 interception lines, each 1 m long, three times during one year. The variables studied were: total cover, cover of grasses and dicots, cover of creeping grasses, floristic composition, and dissimilarity among sites. At the first sampling, 2 yr after cattle re-introduction, the newly grazed site was more similar to the ungrazed than to the grazed site. The newly grazed site had very low cover of dicots; the species of dicots present were different from those found in the continuously grazed area. Creeping grasses had higher cover in the newly grazed site than in the other sites, and continued to increase. At the last sampling, one year later, the newly grazed site had become more similar to the contiuously grazed site. Only after 5 yr of cattle grazing the exotic dicots that were dominant in the continuously grazed site, were recorded in the re-opened site. The absence of propagules of these species or the absence of safe sites may account for this delayed invasion.     

Adaptive foraging by predators as a cause of predator-prey cycles

Summary When foraging has costs, it is generally adaptive for foragers to adjust their foraging effort in response to changes in the population density of their food. If effort decreases in response to increased food density, this can result in a type-2 functional response; intake rate increases in a negatively accelerated manner as prey density increases. Unlike other mechanisms for type-2 responses, adaptive foraging usually involves a timelag, because foraging behaviours do not often change instantaneously with changes in food density or risks. This paper investigates predator-prey models in which there are explicit dynamics for the rate of adaptive change. Models appropriate to both behavioural and evolutionary change are considered. Both types of change can produce cycles under similar circumstances, but under some evolutionary models there is not sufficient genetic variability for evolutionary change to produce cycles. If there is sufficient variability, the remaining conditions required for cycles are surprisingly insensitive to the nature of the adaptive process. A predator population that approaches the optimum foraging strategy very slowly usually produces cycles under similar conditions as does a very rapidly adapting population.     

Influence of soil type on the transfer of plasmid RP4p from Pseudomonas fluorescens to introduced recipient and to indigenous bacteria

Abstract Transfer of plasmid RP4p from introduced Pseudomonas fluorescens to a co-introduced recipient strain or to members of the indigenous bacterial population was studied in four different soils of varying texture planted with wheat. Donor and recipient strains showed good survival in the four soils throughout the experiment. The numbers of transconjugants found in donor and recipient experiments in two soils, Ede loamy sand and Löss silt loam were significantly higher in the rhizosphere than in corresponding bulk soil. In the remaining two soils, Montrond and Flevo silt loam, transconjugant numbers were not significantly higher in the rhizosphere than in the bulk soil.
The combined utilization of a specific bacteriophage eliminate the donor strain and the pat sequence as a specific marker to detect RP4p was found to be very efficient in detecting indigenous transconjugants under various environmental conditions. The numbers of indigenous transconjugants were consistently higher in rhizosphere than bull soil. A significant rhizosphere effect on transconjugant numbers of transconjugants were recovered from Flevo and Montrond silt loam; these soils possess characteristics such as clay or organic matter contents which may be favorable to conjugation.