Variation in Nutrient Distribution and Potential Nutrient Losses by Selective Logging in a Humid Tropical Forest of Rondônia, Brazil1

Abstract

Despite having one of the world's highest deforestation rates, the tropical forest of RondBnia state in the southwest Amazon is virtually unknown in terms of nutrient dynamics. To fill this knowledge gap, the distribution of nutrients in a humid tropical forest located in the Ecological Reserve of Samuel, RondBnia state, was addressed. A total of 474 trees with diameter at breast height (DBH) > 10 cm were mapped at the Ecological Reserve of Samuel, a 20,000-ha area bordering the Samuel Hydroelectric Reservoir, which is located 50 km south of Porto Velho, RondBnia state, Amazon region, Brazil. These individuals belonged to ca 220 species distributed in 41 families. From this total, leaves of 354 trees were collected for chemical compositional analysis; boles of 96 trees and fine branches of 75 trees also were collected. Soil samples were gathered for fertility analysis at two soil depth intervals: 0-50 and 50-100 cm. In general, soils were acidic and very poor in terms of elemental contents. For plants, the highest concentrations of K, and Mg were found in leaves and fine branches, and the highest concentration of Ca was in the litter. The lowest nutrient concentration was observed in boles. The nutrient concentrations of leaves collected at Samuel were similar to that found in other terra jirme forests of the Amazon region and other tropical forests growing on poor soils. Comparisons of nutrient concentrations among families, genera, and species revealed that only N concentrations were distinct among botanical taxa; the variability found in concentrations of other nutrients were larger and did not reveal any significant differences. Like aboveground biomass, the total nutrient stocks of trees was concentrated in a few large individuals. This fact reveals important implications about the impacts caused by selective logging. Although few trees are cut per hectare in this activity, the effects on the ecosystem structure, due tn the loss of nutrients, may be underestimated.

Using indirect methods to constrain symbiotic nitrogen fixation rates: a case study from an Amazonian rain forest

“…Detailed descriptions of the sites can be found elsewhere (Kauffman et al 1995;Neill et al 1997;Germer et al 2007), but all are in primary tropical forests, are similar topographically and climatologically, and soils at all the study sites are classified as Ultisols (Table 1). We also obtained data on legume abundance from a study conducted at the nearby Samuel Ecological Reserve in northern Rondônia (Martinelli et al 2000). For the purposes of this analysis, data from these adjacent sites were Modeled estimates of BNF Several models have attempted to examine patterns and regulation of N fixation on land (Vitousek and Field 1999;Vitousek et al 2002).…”

“…We estimated symbiotic N-fixer abundance in the Rondônia primary forest from empirically measured abundances of Fabaceae species in the forest at the Samuel Ecological Reserve (Samuel) (Martinelli et al 2000) and from information on known nodulation (2000) Organic P 13.8 lg/g Garcia-Montiel et al (2000) Sorbed P 6.1 lg/g Garcia-Montiel et al patterns of species within the Fabaceae. Namely, legumes represent 13% of total tree species abundance in the Samuel forest (Martinelli et al 2000).…”

“…Namely, legumes represent 13% of total tree species abundance in the Samuel forest (Martinelli et al 2000). Seventyfive percent of the legumes surveyed at the site occupy genera within the Caesalpiniaceae subfamily, and *20% of the Caesalpiniaceae surveyed to date have the capacity to nodulate (Sprent 2005).…”

“…More accurate direct estimates of BNF will only be achieved when we overcome methodological limitations of measuring N fixation, just as more robust watershed-level estimates of N losses require improved methods for measuring gaseous N fluxes from soils and along hydrologic flowpaths. However, in the absence of a direct method for measuring symbiotic N fixation, we suggest that employing a strategy that combines modeling and empirical techniques-including analyses of natural abundance 15 N pools (see Houlton et al 2006), potential symbiotic N-fixer abundances (e.g., Martinelli et al 2000), freeliving N fixation rates (e.g., Reed et al 2007), trace gas fluxes (e.g., Garcia-Montiel et al 2003), and N losses via hydrologic pathways (e.g., Chaves et al 2007)-in a series of small watersheds and in a range of biome types-offers an opportunity to further --N g -1 dry soil and water to field capacity plus 10 kPa acetylene (? water ?…”

Seasonal dry deposition and canopy leaching of base cations in a subtropical evergreen mixed forest, China

“…The significant canopy leaching of Ca 2+ was observed also in the present study. Throughfall has been reported to have a major importance for potassium transfer in tropical moist forest, while litterfall represented the major flux for calcium (Martinelli et al 2000).…”