Remains of woody plants from Saouga, a medieval west African village

Charcoal, fruits and seeds of woody plants have been studied from a settlement mound in the Sahel of Burkina Faso. The archaeobotanical results provide information on economy and environmental conditions at the periphery of the medieval kingdom of Songhai at around 1000 A.D. Millet (Penniselum americanum) was the basic crop, cultivated in fields in which also grew useful trees (park savannas). Besides millet, fruits of the park savanna trees and other wild woody plants were an important part of the diet. Stratigraphical changes in the charcoal diagram indicate that millet production was intensified and the park savanna system established in the course of mound formation. The charcoal results show that the vegetation around 1000 A.D. was more diverse than today, containing many Sahelo-Sudanian elements which cannot be found in the area any more. This indicates slightly higher precipitation than today but also less severe human impact.     

Relative importance of tree genetics and microhabitat on macrofungal biodiversity on coarse woody debris

Understanding the contribution of genetic variation within foundation species to community-level pattern and diversity represents the cornerstone of the developing field of community genetics. We assessed the relative importance of intraspecific genetic variation, spatial variation within a forest and microhabitat variation on a macrofungal decay community developing on logs of the Australian forest tree, Eucalyptus globulus. Uniform logs were harvested from trees from eight geographic races of E. globulus growing in a 15-year-old genetic trial. Logs were placed as designed grids within a native E. globulus forest and after 3 years of natural colonisation the presence of 62 macrofungal taxa were recorded from eight microhabitats on each log. The key factor found to drive macrofungal distribution and biodiversity on structurally uniform coarse woody debris was log-microhabitat, explaining 42% of the total variation in richness. Differences between log-microhabitats appeared to be due to variation in aspect, substrate (bark vs wood) and area/time of exposure to colonisation. This findings demonstrates the importance of considering fine-scale (within substrate) variation in the conservation and management of macrofungal biodiversity, an area that has received little previous attention. While a number of recent studies have demonstrated that the genetics of foundation tree species can influence dependent communities, this was not found to be the case for the early log decay community associated with E. globulus. Despite genetic variation in wood and bark properties existing within this species, there was no significant effect of tree genetics on macrofungal community richness or composition. This finding highlights the variation that may exist among guilds of organisms in their response to genetic variation within foundation species, an important consideration in a promising new area of research.     

Slashing Phragmites (Phragmites australis) prior to planting does not promote native vegetation establishment

Phragmites or Common Reed (Phragmites australis) is a tall rhizomatous cosmopolitan grass. While native to Australia, it can be invasive in wetlands, forming dense monocultures and reducing their ecological integrity. We assessed the potential for the cutting of Phragmites reeds prior to planting to promote the establishment of indigenous shrubs that might ultimately outcompete Phragmites. We established ten 5 m × 5 m quadrats in an area dominated by Phragmites, brush‐cut the reeds to ground level in five of them and left five uncut as controls. Within each quadrat, we planted 20 plants (~40 cm tall) of each of five indigenous shrub species, unguarded (4 plants/m²). We surveyed the plants one month after planting and annually for the following four years for survival, height and browsing damage. Browsing damage to plants was common (>50%) and unaffected by cutting. After four years, overall plant survival rates were ~25% and mean plant heights for the five shrub species ranged between 120 and 174 cm. Cutting of Phragmites had no positive effect on plant survival or height. In fact, two Melaleuca species grew taller in the uncut quadrats. Cutting of Phragmites reed beds prior to planting is unlikely to promote the establishment of woody plantings. However, planting within established Phragmites with or without prior brush‐cutting is worthy of further trialling as a potential tool for reinstating native diversity at Phragmites‐dominated sites.     

Season and light affect constitutive defenses of understory shrub species against folivorous insects

Understory shrubs contribute to overall species diversity, providing habitat and forage for animals, influence soil chemistry and forest microclimate. However, very little is known about the chemical defense of various shrub species against folivorous insects. Using six shrub species, we tested how seasonal changes and light conditions affect their constitutive defense to insect damage. We monitored leaf perforation, concentrations of total phenols, condensed tannins, nitrogen (N), and total nonstructural carbohydrates (TNC). Leaf damage caused by insects was low in Sambucus nigra, Cornus sanguinea, and Frangula alnus, intermediate in Corylus avellana and Prunus serotina, and high in Prunus padus. Leaves of all the species, when growing in high light conditions, had high concentrations of defense metabolites. Except for C. avellana, leaves of the other shrub species growing in full sun were less injured than those in shade. This may be due to higher concentrations of defense metabolites and lower concentrations of nitrogen. Similar patterns of the effects of light on metabolites studied and N were observed for leaves with varying location within the crown of individual shrubs (from the top of the south direction to the bottom of the north), as for leaves from shrubs growing in full sun and shrubs in the shade of canopy trees. A probable cause of the greater damage of more sunlit leaves of C. avellana was the fact that they were herbivorized mostly by Altica brevicollis, a specialist insect that prefers plant tissues with a high TNC level and is not very sensitive to a high level of phenolic compounds.     

黔西北地区不同杜鹃灌丛群落特征和物种多样性

为探明黔西北地区不同杜鹃灌丛群落特征和物种多样性变化，本研究以5个不同的杜鹃群落为研究对象，分析了物种组成、重要值和多样性指数。结果表明，5个群落共有33种植物，属16科23属，灌木层和草本层分别有27种和6种；优势种和共优势种植物分别为小果珍珠花、小果珍珠花+露珠杜鹃、小果珍珠花+露珠杜鹃、露珠杜鹃、露珠杜鹃+黄山杜鹃。5个杜鹃灌丛群落灌木层的α多样性指数差异明显，灌木层的Margalef丰富度指数、Simpson多样性指数均表现为露珠杜鹃+黄山杜鹃灌丛群落(V)最大，小果珍珠花灌丛群落(I)最小；Shannon-Wiener多样性指数和Pielou均匀度指数均表现为小果珍珠花+露珠杜鹃灌丛群落(II)最大，小果珍珠花灌丛群落(I)最小。露珠杜鹃+黄山杜鹃灌丛群落(V)有进一步演替为亚热带常绿阔叶林的趋势。杜鹃属植物覆盖度大的临近群落的Whittaker指数、Jaccard指数和Sorenson指数值均较覆盖度小的临近群落大。     

On vegetation recovery,goats and giant tortoises on Pinta Island,Galápagos,Ecuador

Data on vegetational changes on Pinta Island, Galápagos, collected during the period 1970–1988, show that feral goats have had a destructive impact on the vegetation. Stands of Scalesia baurii ssp. hopkinsii (Asteraceae) and Opuntia galapageia var. galapageia (Cactaceae) were close to a complete collapse, while stands of Bursera graveolens (Burseraceae) apparently were able to persist for a longer time. After the elimination of large numbers of goats, Scalesia, Opuntia and Bursera were recovering rapidly, but the patterns of regeneration differed in accordance with differences in longevity, growth and seedling establishment.It is suggested that the absence of herbivores (the Pinta subspecies of giant tortoise is practically extinct, and feral goats were finally eradicated in 1990) in the long term may lead to decreased diversity in the vegetation of Pinta. As a management experiment aimed at conserving the biological diversity of Pinta, it is proposed to reintroduce giant tortoises to the island, preceded and accompanied by a careful long-term monitoring of vegetational changes.Contribution No. 486 of the Charles Darwin Foundation for the Galápagos Isles.     

Effects of prescribed burning on avian nest survival in the southern Great Plains

Shrubs, such as mesquite (Prosopis spp.) and cholla (Opuntia spp.), now dominate fire-suppressed grasslands in southwestern North America. Responses of birds to prescribed burning of the shortgrass prairie in this region are poorly understood. We examined daily survival rates of mourning dove (Zenaida macroura) and lark sparrow (Chondestes grammacus) nests in an experimental landscape (4,811 ha) of spatially replicated, inter-annual fire frequencies (burning every 2 yr, 4 yr, or 10 yr) near Amarillo, Texas. Herbaceous habitat structure was most developed in infrequently burned plots, but shrub densities were less variable among the burn treatments. We modeled daily nest survival (DSR) against burn frequency, shrub density at nest sites, and nest stage (incubation or nestling). Daily survival of mourning dove nests was not well-related to any measured covariate, but lark sparrow DSR was negatively related to the duration of inter-annual burn frequency. In semiarid grasslands heavily inundated with shrubs, prescribed burning may positively influence the nest success of some bird species. © 2011 The Wildlife Society.     

Biogeographic synthesis of secondary succession rates in eastern North America

Aim Mechanistic models of old‐field plant succession have generally lacked a broader biogeographic context in which climate, soils and species pools could play a significant role in mediating succession rates. We examine broad‐scale patterns in old‐field succession and introduce a hierarchical conceptual model to incorporate potential mechanisms operating at multiple spatial scales. Location We reviewed secondary succession studies across the Eastern Deciduous Forest (EDF) of North America. Methods We collected data from all published studies that reported the time necessary for woody species to reach either 10% or 50% cover in old‐field systems throughout the EDF. We used regression approaches to determine whether rates of succession are controlled by climatic and edaphic factors that vary at broad spatial scales. Results We found that the rate at which woody species colonize and dominate old fields decreases significantly with latitude. Rates of woody succession were highly correlated with both annual temperature (growing degree‐days for years to 10% and 50% cover) and measures of soil fertility (cation exchange capacity and reported pre‐agroindustrial (1930) maize yields for years to 10% cover), all of which show a significant latitudinal trend across the EDF. Main conclusions We suggest that the driver of this pattern is geographic variation in the intensity of competition between herbaceous and woody species, which we relate to the effects of (1) temperature regime, (2) edaphic factors related to soil fertility, and (3) plant traits, which may vary latitudinally in response to climate and edaphic factors. Although insufficient data exist to evaluate the relative importance of these factors, we argue that research in this area is necessary to gain an understanding of how future landscapes will be affected by global climate and land use change.