Ericoid mycorrhizal fungi are common root inhabitants of non-Ericaceae plants in a south-eastern Australian sclerophyll forest

Fungi were isolated from the roots of 17 plant species from the families Apiaceae, Cunoniaceae, Cyperaceae, Droseraceae, Fabaceae-Mimosoideae, Lomandraceae, Myrtaceae, Pittosporaceae, Proteaceae and Stylidiaceae at a sclerophyll forest site in New South Wales, Australia. Internal transcribed spacer (ITS) restriction fragment length polymorphism (RFLP) and sequence comparisons indicated that the isolated fungi had affinities to a range of ascomycetes, basidiomycetes and zygomycetes. Four RFLP types had closest affinities to previously identified Helotiales ericoid mycorrhizal (ERM) or Oidiodendron spp. Isolates representing six RFLP types, which were variously isolated from all 17 plant species, formed ERM coils in hair root epidermal cells of Woollsia pungens (Ericaceae) under gnotobiotic conditions. Three of these isolates formed intercellular hyphae, intracellular hyphae and/or microsclerotia, which are typical of dark septate endophyte infection, in roots of Stylidium productum (Stylidiaceae), indicating an ability to form different types of association with roots of different hosts. Overall the data indicate that a broad range of plant taxa may act as repositories for ERM fungi in sclerophyll forest soil.     

Spatial variation of species diversity across scales in an old-growth temperate forest of China

Species richness and abundance are the two most important diversity variables. Species abundance is additive when aggregated across spatial scale, whereas species richness is non-additive. This study analyzes the effect of spatial scale and site on species abundance and richness in a 25-ha temperate forest plot in the Changbai Mountains, northeastern China. The result shows that species abundance and richness are not only dependent on spatial scales, but also dependent on site. Species abundance responds linearly to changes of spatial scale with no intersection in different sites of the study area. However, although species richness also increases with the increase of spatial scale, there are some intersections for the different sites, suggesting that a species-rich site does not always have a high value if the spatial scale is changed. In all, with respect to additive variables, it is relatively easy to extrapolate them from one spatial scale to another spatial scale, as they and the spatial scale usually form a linear relationship. In contrast, non-additive variables are difficult to extrapolate across spatial scales, because they often respond nonlinearly to spatial scale changes. In order to extrapolate these non-additive variables across spatial scales, it is necessary to estimate the relationships between them and spatial scales. As a result, extrapolation of information among spatial scales may be possible, but very difficult, especially for non-additive variables. Because the 25-ha Changbai plot is very small compared to the extent of the world temperate forests, and the vegetation is a relatively uniform type, more such studies in other ecosystems are needed before theories and generalization about scaling effects can be formulated.     

The soil C pool in different agroecosystems derived from the dry tropical forest of Guanacaste, Costa Rica

Inventories of soil C pools are still lacking from tropical sites. Our objective was to assess total C and N concentrations in the different mineral soil fractions down to 50 cm depth in relation to selected physical and chemical properties of 5 ecosystems at La Flor Sustainable Center in Guanacaste, Costa Rica. The ecosystems studied were a derived savanna with scattered trees, a gallery forest, an abandoned Mango indigofera L. plantation, a Citrus sp. plantation, and a Saccharum officinarum L. (sugarcane) plantation. Significant differences were found for the main fixed factor ecosystem for all variables analyzed (ANOVA). The TSC concentration was significantly higher in the sugarcane plantation compared to the rest of land use systems. The TSC concentration decreased significantly with increase in depth in all ecosystems and ranged from 20.3–38.3 to 4.3–20.9 g kg⁻¹ in the 0–10 and 40–50 cm depth, respectively. In all cases, the clay + silt fraction (<50 μm) contained the highest C concentration. N concentration (0–10 cm depth) at La Flor ranged from 0.32 to 0.19%, and decreased in the order sugarcane > Curatella savanna > Mango and Citrus plantations > gallery forest. A principal component analysis (PCA) performed with all variables studied showed that the ordination of land uses (ecosystems) in the factorial plane defined by the first two axes was significant (Monte Carlo permutation test, P < 0.0001). The highest TSC pool down to 50 cm depth was obtained in the sugarcane plantation (160 Mg C ha⁻¹) while less C was found in the rest of ecosystems, i.e. from 66 (gallery forest) to 80 Mg C ha⁻¹ (Curatella savanna). The TSC concentration obtained in the sugarcane plot is likely the result of the incorporation of surface residues into the soil that would have otherwise been lost through burning, which is the current practice in the region. Further studies on C stabilization in the clay fraction are thus needed to test the hypothesis of soil C enrichment due to residue management. Finally, trade-offs are to be considered for both preservation of the fragile dTf and the productivity of derived land uses that increases soil C at the same time.     

Human impact diminishes seedling species richness in Kakamega Forest, Kenya

Anthropogenic forest fragmentation and other kinds of human disturbance, such as selective logging, can reduce the diversity of plant and animal species. To evaluate the impact of fragmentation and small-scale disturbance on forest regeneration, we assessed species richness and total abundance of adult trees in comparison with seedlings in the heavily fragmented and disturbed Kakamega Forest, western Kenya. In nine differently disturbed 1-ha study blocks distributed across the main forest and fragments, we mapped all trees >10 cm in diameter at breast height. Additionally, we established ninety 1-m² seedling plots within these 1-ha study blocks which were monitored over 2.5 years. We recorded altogether 74 species of adult trees (30–43 per block) and 64 seedling species (24–41 per block). Neither fragmentation nor small-scale disturbance had an impact on adult tree species richness or total tree abundance. Yet, fragmentation and especially small-scale disturbance significantly reduced seedling species richness, particularly of late-successional species. While human impact did not affect diversity of adults, the impoverished species richness of seedlings suggests a reduced potential for regeneration and a loss of tree diversity in the long-term.     

Population Growth and Land Use Intensification in a Subsistence-based Indigenous Community in the Amazon

Shifting cultivation practiced by indigenous peoples living at low population densities in tropical forests has often been described as sustainable and compatible with conservation. However, shifting cultivation at increasing population densities has historically been, and still is, a main cause of deforestation worldwide. As many indigenous peoples in tropical forests currently experience rapid demographic growth, this raises the question to what extent their agricultural activities actually contribute to deforestation. This paper examines land use change in an indigenous community in the Ecuadorian Amazon which is only loosely connected to the market economy, and where agriculture is almost exclusively subsistence oriented. During the last seven decades, people have increasingly begun to clear fallows instead of old-growth forest to farm. Although the population was growing at an estimated 1.6% per year, the expansion of the area of land used for agriculture was only 0.4% per year, corresponding to an annual deforestation rate of only 0.015%. Whereas these changes may seem negligible in terms of deforestation, they do cause hardships to the local people, because of increasing walking distance to old-growth forest, and problems with weeds, pests, and decreasing soil productivity when farming after reclearing fallows.     

A New Initiative to Use Carbon Trading for Tropical Forest Conservation

I describe a new initiative, led by a coalition of developing nations, to devise a viable mechanism for using carbon trading to protect old-growth tropical forests. I highlight some of the practical and political hurdles involved in forest-carbon trading, and explain why this initiative is rapidly gaining broad-based political support.     

Variation in Sexual Expression in Jacaratia mexicana (Caricaceae) in Southern Mexico: Frequency and Relative Seed Performance of Fruit-Producing Males

Dioecy, the segregation of male and female structures among individuals, is widespread in tropical plants, encompassing 10–30 percent of species in some sites. In many cases, interindividual sex separation is not complete, as individual plants, although nominally dioecious, may produce both types of reproductive structures. A common form of this sexual variation is the production of female structures in otherwise male individuals, commonly referred to as fruiting males. Here we report the existence of fruiting males in the dioecious tropical tree Jacaratia mexicana (Caricaceae). We show that fruiting males can constitute up to 45 percent of all males in some populations of a tropical forest in Southern Mexico. In order to determine the functional significance of fruiting males for the breeding system of J. mexicana , we compared the relative performance of male- and female-borne seeds. Our results show that seeds from fruiting males are three times less likely to germinate and survive than seeds from female trees. Based on relative seed fitness data, and sex ratios in natural populations, we estimate that 6–15 percent of the genes contributed by fruiting males to the next generation are transmitted via ovules, meaning that morphological variation in gender is at least partially accompanied by functional gender variation. Finally, our seed fitness estimates for fruiting males suggest that fruiting males will not replace female plants in natural populations.
Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp .     

Rain Forest Structure at Forest-Pasture Edges in Northeastern Costa Rica

Land-use change in the Sarapiquí region of Costa Rica has resulted in a fragmented forest landscape with abrupt edges between forest and pasture. Forest responses to edge effects vary widely and can significantly affect ecosystem integrity. Our objective was to examine forest structure at 20+ yr old forest-pasture edges in Sarapiquí. Three transects with 0.095-ha plots at seven distances from forest edges were established in each of six forest patches. Stem density, basal area, and aboveground biomass in trees and palms ≥ 10-cm diameter at breast height were measured in all plots. In addition, hemispherical photographs were taken to determine leaf area index, understory light availability, and percent canopy openness. Linear mixed-effects models showed significantly higher tree stem density at forest edges, relative to interiors, a pattern reflected by increased stem density, basal area, and aboveground biomass in small diameter trees (≤ 20 cm) growing near edges. No differences in total tree basal area, aboveground biomass, or hemispherical photograph-derived parameters were detected across the forest edge to interior gradient. The recruitment of small diameter trees following edge creation has contributed to the development of dense vegetation at the forest edge and has aided in the maintenance of similar tree basal area and aboveground biomass between edge and interior environments. These data reflect on the robustness of forest edges in Sarapiquí, a characteristic that will likely minimize future detrimental edge effects and promote a number of high-value environmental services in these forests.