Small-scale edaphic heterogeneity as a floristic-structural complexity driver in Seasonally Dry Tropical Forests tree communities

Our work aimed to test the hypothesis that soil microscale heterogeneity act as a community ecological driver,increasing diversity and promoting structural shifts on the Seasonally Dry Tropical Forest(SDTF)tree community.We evaluated the relationship between microscale edaphic variations and floristic–structural patterns of tree communities in a SDTF fragment located in the southern end of the Brazilian Caatinga domain.Vegetation and soil data were obtained through 27 sample units of 400 m2(20 m 920 m),within each one we measured and identified at species level all arboreal individuals with Circumference at the Breast Height greater or equal to 10 cm,and also collected the soil samples.Through the data we evaluated soil variation influence on the tree community structural and floristic patterns trough generalized linear models.Soil explained the small-scale structural and floristic variations,contributing significantly to biomass,sprouting and to floristic relationships between sample units.It was also observed a possible relation of the result with the Caatinga domain biogeographic history,due the presence of Sedimentary Caatinga species,which are not expected for the study region.Soil plays an important role in driving small-scale complexity and diversity of SDTF,but we also suggest that Caatinga biogeographic events have influence on the high heterogeneity patterns.

Ecoregional variations of aboveground biomass and stand structure in evergreen broadleaved forests

Biotic and abiotic factors control aboveground biomass(AGB)and the structure of forest ecosystems.This study analyses the variation of AGB and stand structure of evergreen broadleaved forests among six ecoregions of Vietnam.A data set of 1731-ha plots from 52 locations in undisturbed old-growth forests was developed.The results indicate that basal area and AGB are closely correlated with annual precipitation,but not with annual temperature,evaporation or hours of sunshine.Basal area and AGB are positively correlated with trees>30 cm DBH.Most areas surveyed(52.6%)in these old-growth forests had AGB of 100–200 Mg ha^-1;5.2%had AGB of 400–500 Mg ha^-1,and 0.6%had AGB of>800 Mg ha^-1.Seventy percent of the areas surveyed had stand densities of 300–600 ind.ha^-1,and 64%had basal areas of 20–40 m^2 ha^-1.Precipitation is an important factor influencing the AGB of old-growth,evergreen broadleaved forests in Vietnam.Disturbances causing the loss of large-diameter trees(e.g.,>100 cm DBH)affects AGB but may not seriously affect stand density.

Relative importance of climatic and edaphic factors as drivers of plantδ^(15)N along a longitudinal transect

Many studies have shown that climatic and edaphic factors influence the variations in nitrogen isotopes(δ^(15)N)in terrestrial ecosystems.However,the relative importance of co-varying climatic and edaphic controls on plantδ^(15)N remains somewhat unclear.To address this issue,regional-scale plant(L.chinensis)and soil samples were collected along a longitudinal transect across the temperate grasslands in northern China.The influences of climatic and edaphic factors on the plantδ^(15)N were disentangled using the variable importance in projection(VIP)approach.We found that the climatic and edaphic variables explained 52.4%and 31.2%,respectively,of the variation in plantδ^(15)N.The mean annual precipitation(MAP),soil N,and mean annual temperature(MAT)were the most important variables,but the soil water content(SWC),aridity index(AI),and soil clay content were also important variables.The soil pH and soil C:N ratios were identified as unimportant variables.Furthermore,a high-performance model for simulating plantδ^(15)N values was constructed based on the important variables(VIP>0.8).Further investigations should focus on the effects of the interaction between the climatic and edaphic variables on the N cycles in the temperate grasslands to provide more reliable predictions of plantδ^(15)N.