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Baby Lyn Ann Salazar Tanalgo

2011-30330

Soil Nutrients affect spatial patterns of aboveground biomass and emergent tree density inSouthwestern Borneo

I. The effect of soil fertility gradients on aboveground biomass of lowland tropical forest is animportant, but poorly understood component aboveground biomass of ecological variationin the tropics.

A. Structural differences among major forest types on contrasting soils have beendocumented throughout the tropics with lower aboveground biomass and higherstem densities in oligotrophic ecosystems.

1. At a regional scale however, these ecosystems are restricted to the nutrient-poor extreme of soil conditions present in the tropics and are, therefore, lessextensive than upland forests on well-drained mineral soils which also varymarkedly in nutrient content.

2. Soil effects on plant species distribution and diversity in these upland forestshas well been studied but few studies have quantified soil influences on foreststructure.

B. The effect of soil nutrients on aboveground biomass merits greater attention becauseit is not straightforward to predict how biomass should covary with soil fertility.

1. On rich soils, relaxed nutrient limitations on growth could increase the densityand/or maximum size of trees, thereby leading to higher biomass on fertilesites1.1. Lauranceet. al reported positive effects of total soil nitrogen (N), carbon

(C) and exchangeable bases on above ground biomass across anapproximately 1000-km 2 study area in Amazonia.

1.2. In Peru, DeWalt and Chave found higher aboveground biomass in foreston nutrient-rich entisols than in forest on nutrient poor oxisols.

2. However, because forests on rich soils are more dynamic and becausemortality rates could increase faster than growth rates on rich soils, higher soilnutrients could lead to lower biomass with faster rates of turnover on rich sites.

2.1. Schaik and Mirmantoreported lower biomass and faster turnover rates inforest on phosphorous (P)-rich soils across a chronosequence of volcanicterraces in northern Sumatra.2.2. DeWalt and Chave reported similar findings with Schaik and Mirmantoin aregional comparison among four neotropical sites on contrasting soils.

II. Understanding the potential effects of soil nutrients on aboveground biomass would assist inrefining models to quantify the impact of land use change on C emissions, especially fromthe tropics.

III. The study has four aims.A. The first aim is to estimate above ground biomass in a mature lowland rain forest in

southwestern Borneo.B. The second aim is to quantify effects of soil variation on stand structure and

aboveground biomassC. The third aim is to derive a predictive equation of aboveground biomass based on

soil variables.D. The fourth aim is to place these findings in the context of regional soil variation across

Borneo.