Leaf-litter and changing nutrient levels in a seasonally dry tropical hardwood forest,Belize, C.A.

Summary Total above ground plant biomass in a 45 year old seasonally dry tropical hardwood forest was estimated to be approximately 56,000 kg/ha oven dry weight. Nutrients immobilized in the standing vegetation were: N, 203 kg/ha; P, 24 kg/ha; K, 234 kg/ha; Ca, 195 kg/ha; Mg, 47 kg/ha; Na, 9 kg/ha; Mn, 1 kg/ha; Cu, 0.5 kg/ha; Zn, 3 kg/ha; Fe, 4 kg/ha. Total nutrients returned each year through the litter were: N, 156 kg/ha; P, 9 kg/ha; K, 59 kg/ha; Ca, 373 kg/ha; Mg, 32 kg/ha; Na, 5 kg/ha; Mn, 1 kg/ha; Al, 21 kg/ha; Zn, 0.3 kg/ha; Fe, 9 kg/ha. Half of the nutrients immobilized in the standing vegetation were found in the leaves and are returned annually to the soil. Although litter fall is interrupted during the year, the mean nutrient content of the litter was high –5.2%.A decomposition rate of 0.48 percent per day was considered high for a seasonally dry tropical hardwood forest. Fluctuations in soil nutrient levels showed a sharp increase at the start of the rainy season. Later during the dry season nutrient levels decreased to concentrations similar to what they were just prior to the rainy season. Soil organic matter levels were very high –20% in the top 12 cm.     

Nutrient dynamics in milpa agriculture and the role of weeds in initial stages of secondary succession in Belize,C.A.

Nutrient levels, soil moisture and soil organic matter were monitored monthly during a three year period in a site cleared for shifting agriculture (milpa) and in adjacement undisturbed high bush forest soils in Belize. Throughout the study there was no evidence of a decline in available nutrient levels in the cleared site. Sharp changes in P and Mn were considered indicative of wetting and drying periods. Corn yields for the rainy season crop in the first two years were average for the region ca 2500 kg ha⁻¹ dry wt, but declined dramatically in the third year. Total weed biomass for the rainy season crop conversely increased every year and reduced grain yield probably through competition for nutrients (especially N), light and water. Substantial amounts of nutrients were also immobilized in the weed biomass, which served the agroecological purpose of preventing nutrient loss by leaching.     

Woody species and nutrient accumulation during the fallow period of milpa farming in Belize,C.A.

Plant lifeform composition and levels of nutrients accumulated by fallows aged 1, 2 and 3 years under shifting (milpa) cultivation in Belize were measured. Levels of N, P and K allocated to leaves rapidly reached a plateau in 1 year old fallows with little increase in 2 and 3 year old sites. In stem material, K was accumulated rapidly, with little increase after the first year of fallow growth, while N and P accumulation proceeded at steady rates during three years of fallow development. Total biomass in 3 year old fallows averaged 2070 g m^–2 with 10.3 g m^–2 N, 0.73 g m^–2P and 13.2 g m^–2K. Nutrient concentrations in early successional species were higher than in species of later successional status, suggesting different strategies for nutrient utilization.Woody lifeforms dominated the fallow vegetation, accounting for 80% of total biomass in first year fallows and eliminating herbaceous species after 2 and 3 years of fallow growth. The importance of rapid recovery of woody species is discussed as it relates to fallow management and weed control.     

Development and characterization of 11 microsatellite markers in a widespread Neotropical seasonally dry forest tree species,Geoffroea spinosa Jacq. (Leguminosae)

Eleven dinucleotide microsatellites were developed in Geoffroea spinosa (Leguminosae), a widespread tree of the seasonally dry Neotropical forests, and characterized on six populations from Peru, Argentina and Paraguay. Four of them amplified on the Peruvian populations only, probably because of mutations in the microsatellite flanking regions in the other populations. Ten microsatellites were found polymorphic, with within population gene diversities ranging from 0.17 to 0.95, and a number of alleles varying from seven to 19. A significant overall genetic differentiation was also found (θ = 0.212; P < 0.01).     

Host species,and not environment,predicts variation in blood parasite prevalence,distribution, and diversity along a humidity gradient in northern South America

Environmental factors strongly influence the ecology and evolution of vector‐borne infectious diseases. However, our understanding of the influence of climatic variation on host–parasite interactions in tropical systems is rudimentary. We studied five species of birds and their haemosporidian parasites (Plasmodium and Haemoproteus) at 16 sampling sites to understand how environmental heterogeneity influences patterns of parasite prevalence, distribution, and diversity across a marked gradient in water availability in northern South America. We used molecular methods to screen for parasite infections and to identify parasite lineages. To characterize spatial heterogeneity in water availability, we used weather‐station and remotely sensed climate data. We estimated parasite prevalence while accounting for spatial autocorrelation, and used a model selection approach to determine the effect of variables related to water availability and host species on prevalence. The prevalence, distribution, and lineage diversity of haemosporidian parasites varied among localities and host species, but we found no support for the hypothesis that the prevalence and diversity of parasites increase with increasing water availability. Host species and host × climate interactions had stronger effects on infection prevalence, and parasite lineages were strongly associated with particular host species. Because climatic variables had little effect on the overall prevalence and lineage diversity of haemosporidian parasites across study sites, our results suggest that independent host–parasite dynamics may influence patterns in parasitism in environmentally heterogeneous landscapes.     

Nutrient cycling in a tropical seasonal rain forest of Xishuangbanna, Southwest China. Part 1: tree species: nutrient distribution and uptake

Tropical rain forests are characterized by large numbers of the species with diverse growth habits. The objective of the present study was to determine the distribution of nutrient content in the major trees of the tropical rain forests in Xishuangbanna. This will improve the understanding of the nutrient losses from such sites that result from harvesting and flow of nutrients within the ecosystem and lead to the development of effective and rational forest management strategies. Based on the results in this study, the distribution of nutrients among biomass components of trees varied: The ordering of major elements concentrations was K>N>Mg>Ca>P in branch, stem and root tissues but was N>K>Mg>Ca>P in leaves. The maximum amount of all nutrients per ha occurred in the stems followed by branches, roots and leaves. Of the total uptake of 6167.7 kg ha⁻¹ of all nutrients, the contribution of various nutrients was found to be N (2010.6 t ha⁻¹), P (196.3 t ha⁻¹), K (2123.8 kg ha⁻¹), Ca (832 kg ha⁻¹) and Mg (1005 kg ha⁻¹). However, comparing the nutrient uptake of other tropical and sub tropical forests, the results indicated that rates for the Xishuangbanna forests were 20–35% lower than previously reported values.     

Protecting a single endangered species and meeting multiple conservation goals: an approach with Guaiacum sanctum in Yucatan Peninsula,Mexico

Aim New protected areas should consider safeguarding high conservation value sites based on multiple criteria and not just the presence of a single endangered or charismatic species. However, the extent to which complementary criteria coincide is usually unknown. We use the case of Guaiacum sanctum (Zygopyllaceae), an endangered timber tree species, to explore whether the protection of forests where this species is most abundant would meet other complementary conservation goals, such as capturing regional plant biodiversity, protecting other threatened/endemic species or safeguarding ecosystem services. Location Yucatan Peninsula, southern Mexico. Methods We conducted an analysis of the structure, composition and diversity of tree communities (including stems ≥5 cm dbh) at eight G. sanctum forest sites. We identified endemic and threatened tree species and quantified above‐ground tree biomass and carbon storage in these G. sanctum forests. Results Guaiacum sanctum forests contain 35–59 tree species on plots as small as 1000 m². The species composition of tree communities changed rapidly (high β‐diversity) across soil boundaries and rainfall regimes. Twenty‐one endemic and eight threatened tree species were recorded in our inventories. Individuals of G. sanctum represented up to 55% of the above‐ground carbon for trees ≥5 cm dbh. The high basal area of G. sanctum forests plus the high wood density, abundance, large size and longevity (more than 500 years) of G. sanctum and other tree species enhance the potential importance of these forests for carbon storage. Main conclusions A conservation strategy focused on protecting important populations of G. sanctum in the Yucatan Peninsula would have significant co‐benefits for conservation of regional tree species biodiversity and provision of critical ecosystem services. Our study illustrates a multiple criteria approach useful for the selection of areas with high conservation value on the basis of endemic, threatened species, species richness and ecosystem services.     

鼎湖山针阔叶混交林优势种树干液流特征及其与环境因子的关系

运用Granier 热扩散式探针法,于2010年干湿季对鼎湖山自然保护区针阔混交林4种优势树种马尾松、锥栗、木荷和广东润楠的树干液流密度进行连续监测,并同步观测气温、相对湿度和光合有效辐射等环境因子的变化,研究其树干液流特征及其对环境因子的响应.结果表明： 在干湿季,4种优势树种的树干液流速率日变化均呈“昼高夜低”的典型单峰曲线,阔叶树锥栗、木荷和广东润楠的平均液流速率和峰值以及日液流量均显著大于针叶树马尾松;马尾松、锥栗、木荷和广东润楠的最大树干液流密度分别为29.48、38.54、51.67、58.32 g H₂O·m-2·s-1.优势树种树干液流速率的变化与环境因子的昼夜变化存在时滞;液流速率变化与光合有效辐射、水汽压亏缺和气温等环境因子的变化呈显著正相关,其中湿季以光合有效辐射为主导因子,干季以气温为主导因子.     

Agricultural activities and land use in a Neolithic village around 3900 B.C.: Hornstaad Hörnle I A, Lake Constance, Germany

The archaeobotanical investigations in the Neolithic pile settlement of Hornstaad Hörnle I A, Lake Constance, Germany (3919–3905 cal B.C.) has answered many questions concerning agricultural activities and land use in Neolithic times. Very large carbonized stores of unthreshed cereals there showed that every household had 210–280 kg of naked wheat, einkorn, barley and emmer. As most of the wild plant remains in the cereal stores were from annual field weeds it is concluded that the arable land was cultivated continuously, probably for the whole duration of the settlement's occupation. No hints of short or long period fallows were found. Intensive soil treatment such as hoeing and digging is indicated by the rarity of perennial weeds. Because of the high quality of the cultivated soils, manuring was not necessary. The cereals were harvested high on the culm, and the harvest was first stored unthreshed, probably to dry it completely. Every house (family) had its own cereal stores with various cereals. Naked wheat and probably naked barley were threshed outside the settlement, while dehusking of einkorn and probably of emmer took place inside the village. Evidence of cereal cleaning, winnowing, sieving and sorting by hand were found. More than 700 carbonized remains of food products showed that porridge made from ground and shredded wheat was one of the main foods in the settlement.