Abstract

Land-use changes can alter soil properties and thus affect soil quality. Our understanding of how forest conversion (from tropical rainforest to rubber plantations) affects soil properties and soil quality is limited. An ideal testing ground for analyzing such land-use change and its impacts is Hainan Island, the largest tropical island in China. Based on 21 soil physicochemical and biological properties, a soil quality index (SQI) employed principal component analysis to assess soil quality changes from the conversion of tropical rainforests to rubber plantations. The results showed that (i) soil available potassium, available phosphorus, microbial biomass carbon, cellulose decomposition, acid phosphatase, and urease were vital soil properties for soil quality assessment on Hainan Island. (ii) The SQI of rubber plantations decreased by 26.48 % compared to tropical rainforests, while four investigated soil properties (soil pH, total phosphorus, cellulose decomposition, and actinomyces) increased. (iii) The SQI of both the tropical rainforests and rubber plantations showed significant spatial differences, which, under tropical rainforests, was more sensitive to seasonal changes than those under rubber plantations. (iv) Structural equation modeling suggested that forest conversion directly impacted soil quality and, indirectly impacted soil qualities' spatial variation by their interaction with soil types and geographical positions. Overall, though the conversion of tropical rainforest to rubber plantation did not decrease all soil properties, the tropical rainforest with its high soil quality should be protected.

Highlights

  • Soil pH was acidic in the investigated rubber plantations and tropical rainforests

  • Rainforests and rubber plantations; the concentration of these properties increased from dry to rainy seasons. These results suggested that seasonal patterns substantially affected the chemical and biological properties of the soil, and the soil quality

  • Our study found that most soil properties and functions decreased when converting tropical rainforests to rubber plantations

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Summary

Introduction

The rubber tree (Hevea brasiliensis), an economically valuable forest species, is a large source of natural rubber and is grown in more than 40 tropical countries worldwide (Warren-Thomas, 2015). Due to the increasing development of tire manufacturing and high prices of rubber, the land-mass of rubber plantations has expanded rapidly over the last 20 years in tropical Asia (Ahrends et al, 2015; Warren-Thomas et al, 2015; Lang et al, 2017), which is currently the world’s most prolific region for rubber production (FAO, 2017). The conversion of tropical rainforests to rubber plantations in tropical Asia accompanies the continuously rising demand for rubber worldwide (De Blécourt et al, 2014; Allen et al, 2015; Hassler et al, 2017; Guillaume et al, 2018), which generally has negative impacts on soils and ecosystem services and threatens biodiversity and human livelihoods (Qiu, 2009; Ziegler et al, 2009; Tan et al, 2011; Ahrends et al, 2015; Liu et al, 2019; Singh et al., 2021). Evaluating soil quality generally involves three main steps: definition and selection of soil properties, scoring soil properties, and soil quality index calculation (Andrews et al, 2004; Chen et al, 2013).

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