Survival ofPseudomonas solanacearum in soil

Summary Studies on the survival ofPseudomonas solanacearum, the causal agent of bacterial wilt of tomato, under laboratory conditions showed that soil amendments had little effect on the population of the pathogen. When the host plant was grown in amended soil there was a positive influence on growth of the pathogen. The population level of the pathogen incorporated into the soil was reduced to one-half within a period of 46 days. The pathogen survived in the rhizosphere of non-host plants belonging to the families Acanthaceae and Leguminosae even in the absence of the natural hosts, but its incidence in the rhizosphere of plants belonging to Graminae and Cyperaceae was comparatively low indicating possibilities of reducing the inoculum potential of the pathogen in tomato fields by allowing such plants to grow during fallow periods. Part of the thesis of the Senior Author presented to the Kerala Agricultural University, Trichur, Kerala State, India.     

Effects of grazing on plant species composition and spatial distribution in rangelands of the Sahel

The effects of grazing by livestock on plant species composition and spatial distribution have been studied at Sadoré, Niger. Herbaceous species were recorded in plots of increasing size from 1/64 to 1024 m² in ten fallow plots subjected to five different grazing treatments over the previous three years. Treatments consisted of three intensities of grazing, and of protection from grazing for either 3 or 14 years. For all treatments, the number of species fitted a normal distribution with the log (ln) of the area inventoried. However, the fit improved slightly when the model included two successive log-normal distributions respectively considered as species distribution within a patch and at the patch mosaic scale. Across treatments, the optimal sampling areas averaged 3.8 ± 1.1 m² for the within-patch and 725 ± 113 m² for the mosaic scale distributions. It is argued that similarity between treatments in the overall log-normal distribution resulted from compensations between the divergent trends that affected species distribution within and across patches depending on the grazing status. Long-term protection resulted in a regular spatial arrangement of highly contrasted, but internally homogeneous patches. Heavy grazing ensued the dominance of a few species in contagious patches but also left niches for scattered individuals of other species. Tests of the relative frequency of each plant species, together with the average area needed to record that species, were used to characterize specific response to grazing. A majority of species encountered in old Sahelian fallows were either fostered by grazing, indifferent or tolerant to grazing. However, more than a third of the species appeared sensitive to heavy grazing, and no relationships were found between species response to grazing and palatability.     

Nitrogen cycling in the seasonally dry forest zone of Belize,Central America

Two forest associations, cohune palm (Cohune Ridge) and mixed tropical hardwood (High Bush), were assessed on the basis of nutrient movement and storage for their suitability for agriculture. Continuous monitoring of soil nitrogen and leaf litterfall over a one-year period provided information on soil building processes in the forest fallow. Destructive cuts revealed the storage of 690 kg N ha^–1 in the standing biomass of the Cohune forest versus 203 kg N ha^–1 in the High Bush. Litter biomass was exceptionally high in the Cohune Ridge (497 kg ha^–1 dry matter) as compared to the High Bush (65 kg ha^–1 dry matter) and other tropical forests. This is probably because of a low rate of decomposition in the Cohune Ridge palm forest. A substantial reserve of nitrogen is present in both forests' fallows, and this can in part be harvested by the small farmer for crop production.

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Ciclo de nitrógeno en la zona de bosque seco estacional de Belize, América Central

Resumen Dos asociaciones boscosas (Palma Cohune y Matorral Alto) se estudiaron en relación a sus reservas y flujos de nutrimentos y sus posibilidades de aprovechamiento agricola. Se siguió la evolución del nitrógeno en el suelo y en la caida de hojarasca durante un año obteniéndose asi información sobre los procesos pedogenéticos en el barbecho del bosque.A través de muestreos destructivos se encontró que en la biomasa del bosque de Palma Cohune habían 690 kg N ha^–1 y en el Matorral Alto solo 203 kg N ha^–1. La biomasa de hojarasca era excepcionalmente alta en Palma Cohune alcanzando un valor de 497 kg materia seca ha^–1; en el bosque de Matorral Alto la hojarasca era de 65 kg materia seca ha^–1. Esto probablemente se deba a la baja velocidad de descomposición en el caso de la palma.Las reservas sustanciales encontradas en ambos barbechos para el nitrógeno podrían ser parcialmente utilizadas para la producción agrícola campesina.

     

Floristic inventory of secondary vegetation in agricultural systems of East-Amazonia

Small farmers in the Bragantina (East-Amazonia, Brazil) traditionally apply a rotation of 2 years cultivation and 4–10 years forest fallow. More recently introduced pepper plantations fell fallow after fungus hazards. We studied the floristic composition of this young secondary vegetation by means of 92 vegetation relevés in 58 plots of forest fallow and 34 plots of pepper fallow with sizes ranging from 40 to 300 m². The age of the fallow vegetation ranged from 4 months to 10 years. We found 673 species belonging to 97 families. The list of plant species presented in the Appendix totals 827 species, including species collected in additional field surveys. The species are registered with scientific and local names as well as growth forms. The families with the largest numbers of species were Myrtaceae (34 species), Leguminosae (87), Sapindaceae (17), which contain mainly trees and shrubs, and Bignoniaceae (29), Connaraceae (12), Smilacaceae (22) with mainly vines, the forb dominated families Asteraceae (25), Euphorbiaceae (21), Rubiaceae (20), and Cyperaceae (16) and Poaceae (35). A comparison with local and regional inventories shows similarities to fallow vegetations and secondary forests, and floristic distance to primary forests.     

The “males earlier than females” phenomenon in the fawning season of fallow deer (Dama dama)

Twenty years ago, Gaede (in Hemmer, Nutztier Damhirsch Rheinischer Landwirtschafts-Verlag, Bonn, pp 95–112, 1986) pointed to a trend that male fawns of farmed fallow deer were born predominantly within the first half of the fawning season, whereas female fawns were born primarily during the second half. The data basis collected during 25 years of pedigree breeding in the fallow deer domestication project directed by the author shows this “males earlier than females” phenomenon to be real and statistically highly significant. It seems to depend on the age of the siring bucks and may mirror the “fat-season-syndrome” during the rut.This paper is dedicated to Dr. agr. Ernst-Adolf Gaede, former director of the Lehr- und Versuchsanstalt für Viehhaltung Neumühle (Münchweiler an der Alsenz), for his 80th birthday on July 15, 2006.     

Managing open habitats by wild ungulate browsing and grazing: A case‐study in North‐Eastern Germany

Question: Can wild ungulates efficiently maintain and restore open habitats? Location: Brandenburg, NE Germany. Methods: The effect of wild ungulate grazing and browsing was studied in three successional stages: (1) Corynephorus canescens‐dominated grassland; (2) ruderal tall forb vegetation dominated by Tanacetum vulgare; and (3) Pinus sylvestris‐pioneer forest. The study was conducted over 3 yr. In each successional stage, six paired 4 m²‐monitoring plots of permanently grazed versus ungrazed plots were arranged in three random blocks. Removal of grazing was introduced de novo for the study. In each plot, percentage cover of each plant and lichen species and total cover of woody plants was recorded. Results: Wild ungulates considerably affected successional pathways and species composition in open habitats but this influence became evident in alteration of abundances of only a few species. Grazing effects differed considerably between successional stages: species richness was higher in grazed versus ungrazed ruderal and pioneer forest plots, but not in the Corynephorus sites. Herbivory affected woody plant cover only in the Pioneer forest sites. Although the study period was too short to observe drastic changes in species richness and woody plant cover, notable changes in species composition were still detected in all successional stages. Conclusion: Wild ungulate browsing is a useful tool to inhibit encroachment of woody vegetation and to conserve a species‐rich, open landscape.     

Vegetation patterns,regeneration rates and divergence in an old-field succession of the high tropical Andes

Vegetation restoration during old-field succession was studied in an alpine Andean ecosystem (paramo). 123 plots with different fallow times (1 to 12 years) and 8 plots under natural vegetation were sampled. The results indicate that secondary succession in the paramo, like in other extreme environments, can be interpreted as an autosuccession: there are mainly changes in species relative abundance and little floristic relay (i.e. species turnover). Only a few herbaceous species, mostly introduced (e.g. Rumex acetosella), act as strict pioneers and strongly dominate the early stages. Then, they undergo a progressive decline, while native forbs (e.g. Lupinus meridanus) and grasses (e.g. Vulpia myuros) have their peak abundance in intermediate stages. The characteristic paramo life forms, sclerophilous shrubs (e.g. Baccharis prunifolia, Hypericum laricifolium) and giant rosettes (e.g. Espeletia schultzii), appear very early and gradually increase in abundance during succession, becoming dominant in the late stages and showing a dual behaviour, both as ruderal and stress tolerant species. The 1st axis of a Detrended Correspondence Analysis arranges the sites according to their fallow time. The 2nd and 3rd axes, associated with diverging pathways of regeneration, are correlated with topographic factors and physio-chemical soil characteristics. Hence, structural divergence between plots increases along succession as community composition starts to reflect the conditions of each site. We found evidence of a constant rate of succession during the first 12 years, contradicting the generally accepted hypothesis in the succession literature of a continous slow down up to the climax. Regeneration of vegetation physiognomy is relatively fast, questioning the prevailing idea of slow restoration in alpine ecosystems. However, 12 years of fallow are insufficient to attain the species richness of the natural paramo. Under the current trend of fallow length reduction observed in traditional potato cultivation in the Andes, our results raise doubts about the conservationist value of this management strategy.     

Development of feeding selectivity and consistency in food choice over 5 years in fallow deer

In order to better understand the development and maintenance of feeding selectivity, several feeding experiments were performed with fallow deer (Dama dama L.). In experiments performed when the fawns were between ten and 27 days old, it was found that all fawns showed preferences for sucrose but aversions towards tannic acid and ascorbic acid. However, differences in selectivity towards tannic acid were present already before the fawns became functional ruminants and these individual differences lasted 5 years. Moreover, individuals that ingested overall less tannic acid, searched more thoroughly between food sources. When the foraging behaviour was compared with age (11–41 days old and 65–97 days old), it was found that the time a fawn spent eating, increased with age, and the time spent on exploration, smelling and tasting plants decreased with age. Furthermore, the fawns increased their intake of grass and herbs, while the intake of soil and dead plant material decreased with age.     

Intolerance amongst deer species at feeding: roe deer are uneasy banqueters

The function of inter-specific interactions in large herbivore assemblies is under debate. We have studied inter-specific interactions between roe and fallow deer on pastures, to assess whether competition between these Cervidae occurs through behavioural interference. Roe were displaced by fallow deer (i.e. the former moved away from the latter at a distance of >50 m) in 83% of cases (N = 127). Ninety-four percentage (N = 83) of displacement events occurred while roe deer were feeding; in 50% of these cases (N = 78), roe stopped grazing and left the feeding ground. Even when fallow deer did not show any sign of direct aggression to roe, these moved away from fallow in 72% of cases (N = 127). Vigilance rate was significantly greater in roe than in fallow deer, irrespectively of the presence of the other species. When roe and fallow deer grazed within 50 m from each other, vigilance rate increased significantly in roe, but not in fallow deer. Roe deer, in a group, were significantly more tolerant of the presence of fallow deer (even in group), than when solitary. Fallow deer seemed to be able to exclude roe deer from feeding sites through behavioural intolerance.     

An Anthropogenic Escape Route from the “Gulliver Syndrome” in the West African Savanna

A major challenge for ecologists has long been to develop a model to explain the coexistence of grasses and trees in the savanna. The recent shift in emphasis to non-equilibrium-based theories has resulted in a rethinking of this problem. As resource allocation models have been replaced by demographic ones, the focus has shifted to plant life histories. The tree/grass ratio is now conceptualized as a function of disturbance history. Empirical studies demonstrate that repeat fires trap tree sprouts in perpetual juvenile states. Ecologists suggest natural pathways for juveniles to escape, reach maturity, and maintain tree/grass ratios. This study documents how long-fallow agriculture serves as an anthropogenic pathway. The study compares tree cover on long-fallow and unfarmed savanna plots in southern Mali where burning is annual. Tree height, girth, and species were recorded for 29 quadrats. The results demonstrate a significant difference in the size, number, and species of trees; those on fallow plots were taller, more numerous, and more diverse.