Tree Diversity and Soil Characteristics in a Tea–Forest Interface in Southwest Sri Lanka

Nalaka Geekiyanage,Adikari Appuhamilage Dulanjala Sandamali,Savitri Gunatilleke,Nimal Gunatilleke,Don Menige Sudesh Duminda,Sriyani Gamage,Shamodi Nanayakkara,Srimal Rathnayaka

doi:10.3390/f12111506

Nalaka Geekiyanage, Adikari Appuhamilage Dulanjala Sandamali + Show 6 more

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https://doi.org/10.3390/f12111506

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Abstract

Fragmented and degraded ecosystems should be restored to ensure the biological connectivity among fragmented forest landscapes. The tropical rainforests of Southwestern Sri Lanka are highly degraded and fragmented due to plantation agriculture and human settlements. However, the high spatial variation in environmental factors and ecosystem functions challenge the success rate of restoration interventions. The aim of this study was to assess the vegetation composition and stand structure in relation to the spatial variation in key soil physicochemical parameters in the Endane Biodiversity Corridor that links peripheral forest reserve to the Sinharaja Rainforest Complex (SRC). The site that extends over 24 ha was classified into five land-use categories (productive tea lands, marginal tea lands, scrub—abandoned three years ago, and two woodlands—abandoned 15 years ago) in which the vegetation composition, stand structure, and physicochemical parameters of soil were assessed and mapped. Results revealed that the Shannon diversity index in the scrub and the woodlands were higher than in the tea lands. The diversity among the secondary forest patches was similar. However, with a mean record of 14 species, the species richness was high in sites close to the SRC. In comparison to the SRC (358 Mg ha−1), there was a substantial potential to sequester more carbon in the restoration sites (12–108 Mg ha−1). While explaining 31% of abundance and species distribution, the ordination results revealed a close relationship of the soil parameters to vegetation composition and species abundance. The calculated coefficient variation values for soil parameters (TN, EC, Av.P, Ex.K, OC, and BD) were beyond 12%, indicating high or moderate soil spatial variability among the land use categories. Coefficient of variation for soil pH was estimated to be 9%, revealing low soil spatial variability among the land use categories. The maps of these soil parameters corresponded with the type of land use and fertilizer application to tea fields. The highest and the lowest total N contents were observed in the scrub and woodlands, respectively, which appears to be mediated by the relative composition of N-fixing trees between the two groups. Our results facilitate effective matching of sites to species for restoration of the Endane Biodiversity Corridor that may be replicated in similar restoration contexts in tropical Asia.

Highlights

Natural forests are under tremendous pressure and are being deforested at an annual rate of 10 million ha per year, while those remaining are severely being degraded [1]
Moraceae was the dominant family in the area, which was represented by five species (Appendix A, Table A1)
We conclude that this secondary forest is progressing towards a climax forest community where it lies between mid-successional and climax forests

Summary

Introduction

Natural forests are under tremendous pressure and are being deforested at an annual rate of 10 million ha per year, while those remaining are severely being degraded [1]. To avert the negative impacts from deforestation and forest degradation, the world is not on track to meet three major already-set targets: Sustainable Development Goal 15.3—by to restore degraded lands and soils to achieve a land degradation-neutral world; Aichi Biodiversity Target 5—by 2020, the rate of loss of all natural habitats including forests is at least halved while significantly reducing forest degradation and fragmentation; and the United Nations Strategic Plan for Forests Goal 1—to reverse the loss of forest cover worldwide through sustainable forest management including protection, restoration, afforestation, and reforestation. Whereas forests are restored to achieve national restoration targets and to reinstate lost ecosystem services, less attention is paid to connect patches of forests with contiguous protected areas as an integral element of restoration projects [3]. In tropical biodiversity hotspots such as Sri Lanka, where plant endemism is remarkably high, alleviation of the negative consequences of forest fragmentation and soliciting the ways to reconnect such habitats are of paramount importance

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