Herbaceous Plant Density Research Articles

Prescribed fire influences occupancy and abundance of grassland-nesting passerines overwintering in pine forests of Central Louisiana

We surveyed longleaf (Pinus palustris) and loblolly pine (P. taeda) stands burned within 0–7 years to examine the influence of prescribed fire on grassland-nesting passerines that overwinter in pine forests of central Louisiana, USA. We modeled occupancy and abundance of Bachman’s sparrows (Peucaea aestivalis), Henslow’s sparrows (Ammodramus henslowii), and sedge wrens (Cistothorus stellaris) in relation to stand type, years since burn, and site-scale vegetation conditions. We also used analysis of variance to compare vegetation conditions across study sites and detection points for these three species. Bachman’s sparrow occupancy was 3.7 times greater in longleaf stands compared to loblolly stands and decreased 30 % with every 10 % increase in canopy cover. We also found a positive relationship between Bachman’s sparrow density and the density of herbaceous plants in both stand types. Henslow’s sparrows used herbaceous vegetation within longleaf pine stands burned 0–2 years ago that was significantly taller than what we observed at the site scale, but the best fit models for Henslow’s sparrow occupancy (maximum vegetation height, bare ground, herbaceous cover) had overlapping confidence intervals. Henslow’s sparrow density was positively associated with bare ground and negatively associated with litter depth. Sedge wren occupancy decreased 50 % with every 10 % increase in canopy cover. Sedge wren density increased with increasing percent herbaceous cover, however, the 95 % confidence intervals for this relationship largely overlapped. Our study reiterated the importance of frequent (<3 years) prescribed fires to maintain habitat used by grassland-nesting passerines that overwinter in southeastern pine forests.

Fire frequency has a contrasting effect on vegetation and topsoil in subcoastal heathland, woodland and forest ecosystems, south‐east Queensland, Australia

AbstractEcosystems managed with contrasting fire regimes provide insight into the responses of vegetation and soil. Heathland, woodland and forest ecosystems along a gradient of resource availability were burnt over four decades in approximately 3‐ or 5‐year intervals or were unburnt for 45–47 years (heathland, woodland), or experienced infrequent wildfires (forest: 14 years since the last fire). We hypothesized that, relative to unburnt or infrequent fires, frequent burning would favour herbaceous species over woody species and resprouting over obligate seeder species, and reduce understorey vegetation height, and topsoil carbon and nitrogen content. Our hypothesis was partially supported in that herbaceous plant density was higher in frequently burnt vegetation; however, woody plant density was also higher in frequently burnt areas relative to unburnt/infrequently burnt areas, across all ecosystems. In heathland, omission of frequent fire resulted in the dominance of fern Gleichenia dicarpa and subsequent competitive exclusion of understorey species and lower species diversity. As hypothesized, frequent burning in woodland and forest increased the density of facultative resprouters and significantly reduced soil organic carbon levels relative to unburnt sites. Our findings confirm that regular burning conserves understorey diversity and maintains an understorey of lower statured herbaceous plants, although demonstrates the potential trade‐off of frequent burning with lower topsoil carbon levels in the woodland and forest. Some ecosystem specific responses to varied fire frequencies were observed, reflecting differences in species composition and fire response traits between ecosystems. Overall, unburnt vegetation resulted in the dominance of some species over others and the different vegetation types were able to withstand relatively high‐frequency fire without the loss of biodiversity, mainly due to high environmental productivity and short juvenile periods.

Shrub encroachment increases soil erosion risk in hillside alpine meadows of the Qinghai-Tibetan Plateau, NW China

Shrub encroachment is advancing in alpine meadow ecosystems under climate warming, which can alter meadow community and soil properties. Given the key role of alpine meadows in soil and water conservation, meadow changes that could lead to higher erosion are particularly worrisome. However, little is known about plant and soil characteristics related to erosion resistance change with increasing levels of shrub encroachment. To address this issue, we evaluated multiple plant and soil variables closely related to erosion resistance along a shrub encroachment gradient in the Qinghai-Tibetan Plateau. Plant variables were herbaceous density, richness, root biomass while soil variables included bulk density, moisture, temperature, compressive strength, and shear strength. These were measured at multiple plots at four treatments, including non-encroached hillside alpine meadow (control) and hillside alpine meadow with low (<30% shrub cover), moderate (30%-60% shrub cover), and high (>60% shrub cover) levels of shrub encroachment. Our results showed that shrub encroachment significantly decreased herbaceous plant density and herbaceous species richness of meadow communities and that this effect strengthened along the shrub encroachment gradient. Encroachment also reduced herbaceous root biomass by 40.6%, 59.4%, and 73.3% in low, moderate, and high levels of encroachment at the 0–10 cm soil depth. We also found that shrub encroachment decreased soil bulk density by 10.9%–21.8% and soil moisture by 3.7–13.5% at 0–10 cm soil. Most important, both compressive and shear strength of topsoil gradually decreased with increasing levels of encroachment, and were approximately twice as low on high encroached plots than non-encroached plots. Overall, our results indicate that shrub encroachment leads to sparse community density, fewer herbaceous roots, and topsoil looseness, ultimately decreasing the strength of hillside alpine meadows’ soils. These findings emphasize the role of shrub encroachment in driving the increase of soil erosion risk in hillside alpine meadows under climate changes.

How diverse are sun-grown coffee plantations? Local and landscape heterogeneity drives Andean rove beetle diversity

Compared to shade coffee plantations, sun-grown coffee is not considered very biodiversity-friendly, but little is known about how the management practices for this crop and landscape characteristics affect species diversity. Some predatory staphylinids (rove beetles) are important biological control agents in many agricultural systems, but have not received much attention in tropical agroecosystems or in coffee plantations. After collecting 2074 individuals belonging to 126 species of staphylinid collected from 27 sampling sites in a region dominated by sun-grown coffee in the Colombian Andes, we evaluated how local and landscape heterogeneity affect the diversity, abundance and composition of staphylinids. We found that both local and landscape variables had effects in different directions and of different magnitudes depending on the community attribute evaluated. At the local scale, rove beetle diversity increased with the density of herbaceous plants and coffee plant cover. At the landscape scale, species richness decreased with increasing forest cover, while the number of forest patches had a positive effect. We also found a high degree of species turnover within and between coffee plantations, and this was explained by farmland habitat structural differences between the coffee plantations and also the characteristics of the surrounding landscape. Our results indicate that the Andean sun-grown coffee plantations still host diverse and taxonomically dissimilar staphylinid communities. Therefore, properly managed local vegetation structure and the preservation of forest remnants on the landscape contribute to maintaining high diversity in this coffee production system. Promoting biodiversity conservation and the provision of ecosystem services by agroecosystems—even in intense production systems—requires that environmental heterogeneity on several scales be taken into account.

Cross sectional comparison of chemical treatment on plant biodiversity at Neudamm farm, Namibia

This study determined the impact of Tebuthiuron application on plant biodiversity over a three-year period at Neudamm farm. A total of 40 (1m2) quadrats were randomly nested in three 250 m2 belt transects per each treatment to record the herbaceous plant density, species composition, dry matter and ground cover. Woody plant density, heights and canopy diameters were measured in each 250 m2 belt transects. A General Linear Model (GLM) procedure of SAS (2007) was used for analyses. The herbaceous biomass production was significantly higher (P &lt; 0.05) in chemically treated site of 2015 (975 Kg DM ha-1) and least in the other two sites. The chemically treated site of 2016 had greater (P &lt; 0.05) ground cover percentage than the other treatment sites. The canopy cover and woody plant densities in all woody height categories were higher (P &lt; 0.05) in the control and chemically treated site of 2017, than the other two sites. The study concluded that the Tebuthiuron had impacted on the plant biodiversity of treated rangelands by improving the herbaceous plant species, biomass yields and reduced bush density. The study recommends that aftercare practices and application of arboricides be carried out routinely to allow herbaceous plants recovery.&#x0D; Keywords: Bush encroachment, arboricides, plant density, biomass production, canopy

Effects of Sagebrush Restoration and Conifer Encroachment on Small Mammal Diversity in Sagebrush Ecosystem

Conifer encroachment in sagebrush ecosystems reduces habitat heterogeneity, niche space, and resource availability, all of which negatively affect many wildlife populations. Sagebrush restoration is recommended as a management action to mitigate conifer encroachment and restore wildlife across millions of hectares in the Great Basin. Despite this recommendation, the effects of conifer encroachment and sagebrush restoration are unknown for most wildlife species. Small nonvolant mammal communities include keystone species, consumers and prey; facilitate energy flow and ecological function; and provide important ecological goods and services. We assessed causal relationships between conifer encroachment and sagebrush restoration (conifer removal and seeding native plants) on small mammal communities over 11 yr using a Before-After-Control–Impact design. Sagebrush habitat supported an additional small mammal species, twice the biomass, and nearly three times higher densities than conifer-encroached habitat. Sagebrush restoration increased shrub cover, decreased tree cover, and density but failed to increase native herbaceous plant density. Restoration caused a large increase in the non-native, invasive annual cheatgrass (Bromus tectorum L.). Counter to prediction, small mammal diversity did not increase in response to sagebrush restoration, but restoration maintained small mammal density in the face of ongoing conifer encroachment. Piñon mice (Peromyscus truei), woodland specialists with highest densities in conifer-encroached habitat, were negatively affected by sagebrush restoration. Increasing cheatgrass due to sagebrush restoration may not negatively impact small mammal diversity, provided cheatgrass density and cover do not progress to a monoculture and native vegetation is maintained. The consequences of conifer encroachment, a long-term, slow-acting impact, far outweigh the impacts of sagebrush restoration, a short-term, high-intensity impact, on small mammal diversity. Given the ecological importance of small mammals, maintenance of small mammal density is a desirable outcome for sagebrush restoration.

INFLUÊNCIA DA TOPOGRAFIA E DA ABERTURA DO DOSSEL NA ESTRUTURA DO COMPONENTE HERBÁCEO-ARBUSTIVO EM DOIS FRAGMENTOS FLORESTAIS NA PLANÍCIE DE INUNDAÇÃO DO ALTO RIO PARANÁ

As florestas secundárias têm se expandido significativamente nos últimos anos. Dada a importância que as mesmas têm assumido nos planos de restauração e conservação, um entendimento mais abrangente sobre sua organização e funcionamento, levando em consideração as diferentes formas de vida, torna-se necessário. A fim de comparar a composição e estrutura do componente herbáceo-arbustivo entre dois fragmentos florestais com diferentes idades (RFID- remanescente florestal e FLT- floresta de 57 anos), bem como a influência relativa da topografia e abertura do dossel na organização da comunidade, dados vegetacionais e ambientais foram obtidos em 24 parcelas contíguas em cada área. Utilizaram-se correlogramas I de Moran e testes de Mantel parcial para verificar a correlação entre dados da comunidade e variáveis ambientais. Para testar diferenças entre as áreas amostrais aplicaram-se testes t de Student. As lianas mostraram-se espacialmente estruturadas (agregadas) em ambos os ambientes com um padrão semelhante ao observado para cota média. No RFID, as distâncias de cota média correlacionaram-se positivamente com as distâncias das matrizes, densidade de arbóreas e riqueza total e negativamente com as distâncias da matriz densidade de herbáceas, na FLT correlações significativas foram observadas somente entre as distâncias da matriz, densidade de arbóreas e as distâncias de desnível máximo e entre distâncias dos dados de cota e distâncias da matriz de riqueza total. Somente o componente arbustivo e abertura do dossel não apresentaram diferença significativa entre as duas áreas. A estrutura do estrato herbáceo-arbustivo tem se mostrado associada mais fortemente às características topográficas que à abertura do dossel.

Diversity and community composition of herbaceous plants in different habitat types in south‐east Cameroon

AbstractThe composition of herbaceous vegetation was evaluated with the aim of characterizing forests at various ages of stand development. Herb stems were sampled in 250 4‐m² square plots distributed within six habitat types. A total of 36 herb species belonging to 15 families were recorded. Species richness did not significantly differ between habitat types. Most herb species occurred in all habitat types and were therefore generalists. However, a few indicator herb species were detected, and the results roughly suggested that herb species of the families Poaceae and Araceae were indicative of late successional forests; Zingiberaceae are indicative of early successional forests; and Commelinaceae, Costaceae, Cyperaceae and Marantaceae are indicators of flooded habitats. Species diversity and stem density of herbaceous plants did not change with forest succession as a decrease in abundance and frequency of occurrence of pioneer species in late successional forests was counterbalanced by the presence of generalist and late successional species. However, increasing proportions of dwarf stems in late successional forests translated to changes in the vertical structure of herbaceous plant communities. Herbivory pressure by gorillas did not have a notable effect on herbaceous plant community development. This study contributes to the definition of herbaceous ecological indicators of forest succession in different settings.

Dune-scale distribution pattern of herbaceous plants and their relationship with environmental factors in a saline–alkali desert in Central Asia

Sand dunes are the main landforms in modern deserts worldwide. As an important type of desert vegetation, herbaceous plants have long been acknowledged for their important ecological functions. We focus on the dune-scale distribution pattern of herbaceous plants and their relationship with the environment. During the early summer of 2010, the herbaceous plant density, coverage, aboveground biomass and eighteen environmental factors were surveyed from 214 plots (5m×5m) across two linear sand dunes (220m×110m) located in the Gurbantunggut Desert, China, a typical saline–alkali desert in Central Asia. Data were analyzed using univariate, ordination, and geostatistical techniques. Three vegetation variables represent a significant clumped distribution (P<0.01) across the entire study site. Obvious differences were observed among different slope positions/transects, with the lowest values observed at the summit. Geostatistics indicated that all of the variables showed a moderate spatial dependence and obvious zonal distribution along the sand dunes. The ranges (lag distance) of density (32.2m) and coverage (33.5m) were close to the average width (31.4m) of the transects. The biomass range (74.1m) was almost equal to the average width (75m) of the sand dunes. Pearson's correlation analysis and nonmetric multidimensional scaling analysis consistently demonstrated that the distributions of herbs on sand dunes were dominantly influenced by sand dune topography (slope position, convexity, and relative height), soil nutrients (total nitrogen and phosphorus) and deep-rooted shrubbery (Ephedra distachya). Compared to large, mobile and steep sand dunes, low, fixed and gentle sand dunes contribute to herbaceous plant abundance and distribution as well as the stability maintenance of the whole desert ecosystem.

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Sand dunes are the main landforms in modern deserts worldwide. As an important type of desert vegetation, herbaceous plants have long been acknowledged for their important ecological functions. We focus on the dune-scale distribution pattern of herbaceous plants and their relationship with the environment. During the early summer of 2010, the herbaceous plant density, coverage, aboveground biomass and eighteen environmental factors were surveyed from 214 plots (5 m × 5 m) across two linear sand dunes (220 m × 110 m) located in the Gurbantunggut Desert, China, a typical saline–alkali desert in Central Asia. Data were analyzed using univariate, ordination, and geostatistical techniques. Three vegetation variables represent a significant clumped distribution (P < 0.01) across the entire study site. Obvious differences were observed among different slope positions/transects, with the lowest values observed at the summit. Geostatistics indicated that all of the variables showed a moderate spatial dependence and obvious zonal distribution along the sand dunes. The ranges (lag distance) of density (32.2 m) and coverage (33.5 m) were close to the average width (31.4 m) of the transects. The biomass range (74.1 m) was almost equal to the average width (75 m) of the sand dunes. Pearson's correlation analysis and nonmetric multidimensional scaling analysis consistently demonstrated that the distributions of herbs on sand dunes were dominantly influenced by sand dune topography (slope position, convexity, and relative height), soil nutrients (total nitrogen and phosphorus) and deep-rooted shrubbery (Ephedra distachya). Compared to large, mobile and steep sand dunes, low, fixed and gentle sand dunes contribute to herbaceous plant abundance and distribution as well as the stability maintenance of the whole desert ecosystem.

INTERACTIONS BETWEEN THE HERBACEOUS AND SHRUBBY-ARBOREAL COMPONENTS IN A SEMIARID REGION IN THE NORTHEAST OF BRAZIL: COMPETITION OR FACILITATION?

ABSTRACT: Under conditions of high stress, interactions between species can be positive. Islands of perennial vegetation can improve the conditions of the understory and facilitate the establishment of herbaceous plants. The hypothesis of this study is that islands of perennial vegetation in an area of caatinga harbor, a greater richness, diversity and density of herbaceous plants, and that individuals reach a greater height and diameter than in open spaces. The study was conducted in Petrolândia, Pernambuco, Brazil. Twenty-seven plots were installed in the center of the islands, 38 at the edge of the islands (in a total of 38 islands) and 35 in the open spaces. A total of 51 species were recorded in the center and 55 on the edge of the islands and 48 in the open spaces. The mean richness of the open spaces was lower than on the islands. The diversity was greater in the center of the island and became less on the edge of the island and in the open spaces. The mean density was lower in the open spaces than on the islands. The mean density at the edge of the islands was greater than in the center of the islands. There was no difference in mean diameter of herbaceous plants. The mean height of the individuals was higher in the center of the islands. The herbaceous community growing on the islands exhibited higher richness, diversity, density and height than in open spaces. Thus, islands of perennial vegetation facilitate the establishment of herbaceous species.

荒漠草原区柠条固沙人工林地表草本植被季节变化特征

研究荒漠草原人工林固沙区地表草本植被季节变化特征及其和柠条林龄的关系，对于分析柠条人工林地表草本植物的季节适应性和制订合理的人工林管理措施均具有重要的科学意义。选择6、15、24年生和36年生柠条人工林为研究对象，通过调查每个样地5月、8月和10月地表草本植物密度、物种数、盖度和高度，分析了荒漠草原区柠条人工固沙林生长过程中地表草本植被季节变化特征及其影响因素。结果表明，地表草本植物物种数在柠条林龄6和15a时受季节改变的影响较小，在24a之后受到季节变化的显著影响（<em>P</em><0.05）。地表草本植物密度在柠条林龄6a时受季节改变的影响较小，但在15a之后季节变化显著影响地表草本植物个体数分布（<em>P</em><0.05），而且在10月具有最多的地表草本植物个体数。地表草本植被盖度和高度均受到季节变化的显著影响（<em>P</em><0.05），而受林龄的影响较小；不同年龄林地地表草本植被盖度和高度均表现为10月和8月较高，5月较低。研究表明，荒漠草原柠条人工林固沙区，柠条林发育生长和灌木形态的改变不仅影响土壤营养条件，而且还可以调控由于季节改变而引起的土壤温湿度变化，柠条林龄和季节更替二者交互作用，共同影响地表草本植被的季节变化特征。;It is a very valuable study on seasonal changes of ground vegetation characteristics under artificially plantations and its relation to stand age in desert steppe. These results will be beneficial to understand the adaptation of ground vegetation under artificial plantations to seasonal changes, and to give rational management on these artificial plantations. An investigation on ground vegetation characteristics including herbaceous plant species richness, density, cover and height, was carried out in May, August and October, in four artificial plantations (<em>C. intermedia</em>) at age of 6, 15, 24 and 36 yeas respectively. The seasonal changes of ground vegetation under artificial plantations during stand development were discussed, together with the related affecting factors. As the results were shown, there were marked different seasonal adaptations of ground vegetation to varying artificial plantations with age. There was a significant impact of seasonal changes on herbaceous plant species richness, not at age of 6 or 15 years but at age of 24 and 36 years (<em>P</em><0.05). When (at age of 24 and 36 years), herbaceous plant species were significantly lower in May than in October (<em>P</em><0.01). There was also a significant impact of seasonal changes on herbaceous plant density not at age of 6 years but at age of 15, 24 and 36 years (<em>P</em><0.05), when there was a significantly higher herbaceous plant density in October than in May (<em>P</em><0.05). Whiles ground vegetation cover and height were not affected by stand age, but by seasonal changes (<em>P</em><0.05). There was a significantly higher ground cover and height in October and August than in May (<em>P</em><0.05), irrespective of stand age. Pearson correlation analysis implied that the main forces were shrub height and basal diameter on herbaceous plant species richness, and shrub morphological characteristics and soil moisture on herbaceous plant density. While soil moisture and temperature with seasonal changes was the main limiting factors on ground vegetation cover and height, respectively. It was suggested that the changing shrub characteristics during stand development not only facilitated soil nutrient conditions, but regulated soil moisture and temperature due to seasonal changes in these artificial plantations. The interaction between stand age and seasonal changes (soil moisture and temperature) co-affected the seasonal dynamics of ground vegetation under artificial plantation in desert steppe.

Density of herbaceous plants and distribution of western gorillas in different habitat types in south‐east Cameroon

AbstractThe study of forest herb availability improves knowledge of ecology and conservation of gorillas that depend on such herbs. Density patterns of herbs and location of western gorilla nest sites were studied in different habitat types at a site in south‐east Cameroon to assess their relationship. Herb stems of the families Marantaceae and Zingiberaceae were identified and counted in 10,713 1‐m2 plots distributed within six habitat types. Stem density correlated with light availability and ranged from 2.38 stems m−² in near primary forest to 4.66 stems m−² in light gaps. Gorillas showed marked preferences for habitats with high herb densities such as light gaps, swamps and young secondary forest. However, no clear relationship exists between terrestrial herbaceous vegetation and gorilla densities across Central Africa. It is suggested that differences in ecological factors and land use history within and between sites may explain differences in herb density and diversity which partly account for variations in the historical and present population distribution and density of western gorillas. Formerly logged and swamp forests, which are characterized by an abundance of herbs, may prove to be of great value in the conservation of western gorillas given appropriate forest management practices, adequate protection from poaching and limited human encroachment.

Influence of Post‐Clearing Treatment on the Recovery of Herbaceous Plant Communities in Amazonian Secondary Forests

Secondary forests are an increasingly common feature in tropical landscapes worldwide and understanding their regeneration is necessary to design effective restoration strategies. It has previously been shown that the woody species community in secondary forests can follow different successional pathways according to the nature of past human activities in the area, yet little is known about patterns of herbaceous species diversity in secondary forests with different histories of land use. We compared the diversity and abundance of herbaceous plant communities in two types of Central Amazonian secondary forests—those regenerating on pastures created by felling and burning trees and those where trees were felled only. We also tested if plant density and species richness in secondary forests are related to proximity to primary forest. In comparison with primary forest sites, forests regenerating on non‐burned habitats had lower herbaceous plant density and species richness than those on burned ones. However, species composition and abundance in non‐burned stands were more similar to those of primary forest, whereas several secondary forest specialist species were found in burned stands. In both non‐burned and burned forests, distance from the forest edge was not related to herbaceous density and species richness. Overall, our results suggest that the natural regeneration of herbaceous species in secondary tropical forests is dependent on a site's post‐clearing treatment. We recommend evaluating the land history of a site prior to developing and implementing a restoration strategy, as this will influence the biological template on which restoration efforts are overlaid.

CONTROLS ON VEGETATION STRUCTURE IN SOUTHWESTERN PONDEROSA PINE FORESTS, 1941 AND 2004

Long-term studies can broaden our ecological understanding and are particularly important when examining contingent effects that involve changes to dominance by long-lived species. Such a change occurred during the last century in Southwestern (USA) ponderosa pine (Pinus ponderosa) forests. We used five livestock grazing exclosures established in 1912 to quantify vegetation structure in 1941 and 2004. Our objectives were to (1) assess the effects of historical livestock grazing on overstory structure and age distribution, (2) assess the effects of recent livestock grazing and overstory on understory vegetation, and (3) quantify and explain changes in understory vegetation between 1941 and 2004. In 1941, canopy cover of tree regeneration was significantly higher inside exclosures. In 2004, total tree canopy cover was twice as high, density was three times higher, trees were smaller, and total basal area was 40% higher inside exclosures. Understory species density, herbaceous plant density, and herbaceous cover were negatively correlated with overstory vegetation in both years. Most understory variables did not differ between grazing treatments in 1941 but were lower inside exclosures in 2004. Differences between grazing treatments disappeared once overstory effects were accounted for, indicating that they were due to the differential overstory response to historical livestock grazing practices. Between 1941 and 2004, species density declined by 34%, herbaceous plant density by 37%, shrub cover by 69%, total herbaceous cover by 59%, graminoid cover by 39%, and forb cover by 82%. However, these variables did not differ between grazing treatments or years once overstory effects were accounted for, indicating that the declines were driven by the increased dominance of the overstory during this period. Our results demonstrate that historical livestock grazing practices are an aspect of land-use history that can affect ecosystem development. Grazing history must be considered when extrapolating results from one site to another. In addition, the understory vegetation was more strongly controlled by the ponderosa pine overstory than by recent livestock grazing or by temporal dynamics, indicating that overstory effects must be accounted for when examining understory responses in this ecosystem.

Ecosystem Restoration of Jhum Fallows in Northeast India: Microbial C and N Along Altitudinal and Successional Gradients

Abstract To characterize the altitudinal and successional trends in microbial biomass and to understand their role in soil nutrient dynamics during the aggradation phase (vegetation recovery) of abandoned shifting cultivation systems, we determined the soil properties and microbial C and N in jhum (slash‐and‐burn) cultivation systems at different altitudes and 1‐, 7‐, and 16‐year‐old fallow agricultural lands at lower and higher altitudes in the northeastern Indian hills. Density of ground vegetation was lower in the undisturbed forest than in the jhum fallows. In general, 1‐year jhum fallow had greater herbaceous vegetation both at lower and higher altitudes. Although woody plants were observed in 7‐ and 16‐year‐old jhum fallows, their density was highest in the forest. Soil moisture, organic C, and total N also increased gradually with increasing altitude and progressive secondary succession. Soil pH showed a negative correlation with altitude (as also confounded by soil type) and fallow age. Both microbial C and N had a close correlation with altitude and fallow age. Contribution of microbial C to soil organic C was 2.0–2.6% and microbial N to total N 1.4–2.2% in jhum fields, 2.4–4.3% and 1.2–2.1%, respectively, in jhum fallows, and 2.5–2.9% and 1.6–1.9% in the forests. Microbial C and N showed a negative correlation with herbaceous plant density. Microbial biomass in the jhum fallows and forest stands had a positive relationship with woody vegetation. Along an altitudinal and/or successional gradient, microbial C and N were positively correlated with water‐holding capacity, soil moisture, organic C, and total N and negatively correlated with soil pH. Microbial C and N were positively correlated with each other. Therefore, the study suggests that the altitudinal and successional dynamics of microbial C and N are linked to, among other properties, soil organic matter and total nitrogen contents in the soil during community development after land abandonment from shifting cultivation.

Microenvironmental and vegetational heterogeneity induced by phytogenic nebkhas in an arid coastal ecosystem

The nebkhas of woody plants represent distinct habitats in arid and semiarid ecosystems. Nebkhas are mounds composed of wind-borne sediment within or around shrub canopies. We studied the effects of widely spaced nebkhas of Retama raetam shrub on their microenvironment and associated herbaceous vegetation in the Mediterranean coast of Sinai Peninsula. Our measurements included nebkha size (height and width) and shrub size (canopy height and diameter). We identified four distinct microsites at each nebkha: crest, mid-slope, edge, and internebkha space. We measured soil temperature and moisture, photosynthetically active radiation (PAR), and soil properties. The plant species grown at each microsite were identified and their densities were measured. Average soil temperature and PAR were highest at internebkha space and lowest at nebkha crest. The maximum diurnal temperature and PAR of internebkhas exceeded that of nebkhas. Soil moisture and nutrient concentrations showed a gradient of spatial heterogeneity and were highest at the nebkha edge. Regression analysis indicated that total herbaceous plant density was significantly related to nebkha size, and to shrub canopy diameter and area. Detrended correspondence analysis indicated that patterns of species composition were correlated with the spatial variability in soil moisture and nutrient content along the gradient of increasing distance from the nebkha crest. It is assumed that shrub canopy and its nebkha interact in governing ecosystem functioning in this environment.

Effects of Casuarina pauper litter and grove soil on emergence and growth of understorey species in arid lands of South Australia

Localized effects of large persistent plants in arid lands can substantially affect the distribution of smaller plants through several mechanisms. Usually these micro-environments sustain more species and higher productivity. In arid lands of southern Australia the density of herbaceous plants inside Casuarina pauper groves is lower than in adjacent open areas. We used a series of glasshouse experiments to assess the effects of litter and different soils on the emergence and growth of two herbaceous species common in the system: Carrichtera annua, an introduced annual forb, and Danthonia caespitosa, a native grass. We also wanted to separate the physical and chemical effects of litter. Soil collected inside groves had higher contents of organic carbon and total nitrogen than soil outside groves. Soil type had no significant effect on the emergence of either species, but litter significantly reduced their emergence. The addition of artificial litter (i.e. pieces of plastic with similar physical properties) had the same effect on emergence as natural litter. Watering with litter leachates reduced the emergence of D. caespitosa, but had no effect on C. annua, suggesting a specific allelopathic effect. The results indicate both physical land chemical effects of litter. Litter had no effect on the growth of seedlings of either species, while D. caespitosa, but not C. annua, seedlings grew better in soil collected inside groves. Our results demonstrate that litter of Casuarina, and to a lesser extent soil properties, may be an important factor determining the difference in annual plant community structure inside and outside groves.

Population Density of Chimpanzees and Gorillas in the Petit Loango Reserve, Gabon: Employing a New Method to Distinguish Between Nests of the Two Species

We studied the vegetation and population density of chimpanzees (Pan troglodytes troglodytes) and gorillas (Gorilla gorilla gorilla) in the Petit Loango Reserve, Gabon. The study site consists mainly of primary and secondary forest, and it also includes patches of savanna, inundated forest, and coastal scrub. The density of herbaceous plants of Marantaceae and Zingiberaceae, which serve as important foods for great apes at other study sites, is extremely low. It was very difficult to distinguish between the nests of chimpanzees and gorillas because most gorilla nests were made in trees. We developed a new method to identify the builder of nests via a combination of field observation of nests and fecal samples, and examination of hair samples under a scanning electron microscope. Nests of chimpanzees were mainly in primary forest, and the estimated density (0.78 individual per km2) is higher than the average density in Gabon and comparable to the nest density in the Lope Reserve, Gabon. Nests of gorillas were mainly in secondary forest, and their estimated density (0.21) is similar to the average next density in Gabon but lower than the gorilla nest density in the Lope Reserve. The low density of herbaceous foods seemed to influence the density of gorillas but not the density of chimpanzees.

Vegetation Changes following Brush Control in Creosotebush Communities

Changes in herbaceous plant density and canopy cover of creosotebush (Larrea tridentata Sesse & Moc. ex DC) and associated shrubs following brush control treatments were measured in Sonoran and Chihuahuan Desert communities. Treatments were applied in 2 successive years st the Santa Rita Experimental range, Arizona, and 3 locations in Chihuahua, Mexico. Across all locations and years 1.5 kg/ha tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N'-dimethylurea) > 1.0 kg/ha tebuthiuron= disking = disking with furrowing >2-way railing >0.5 kg/ha tebuthiuron > land imprinting in reducing canopy cover of creosotebush and associated shrubs. At the Santa Rita Experimental Range annual precipitation was above long-term mean in 1982, 1983, 1984, and 1985; and grass density increased on all treated and untreated plots. Annual precipitation was below long-term mean during 1986 and 1987 and grass density decreased on both treated and untreated plots but did not decrease to pre-treatment densities. Forb densities were less than 3 plants/m2 throughout the study, except in 1987 when Russian thistle (Salsola iberica Sennen & Pau) increased on all plots. At the Chihuahuan locations, grass densities usually increased during the first year of the study, but very low precipitation throughout the study caused subsequent reductions in grass and forb densities. In dry years brush control treatments did not increase herbaceous plant density.