Recovery of floristic diversity, composition and structure of regrowth forests on fallow lands: implications for conservation and restoration of degraded forest lands in Laos

Eshetu Yirdaw,Adrian Monge Monge,Denis Austin,Ibrahim Toure

doi:10.1007/s11056-019-09711-2

Abstract

In Laos, there are extensive shifting cultivation areas and regrowth forests spontaneously established on fallow lands. The aims of the study were to conduct a comparative study of old-growth and regrowth forests in terms of structure, woody species diversity and composition as well as to investigate the potential role of regrowth forests in the conservation and restoration of degraded forest lands in Laos and the tropics in general. Systematic plot sampling was used to survey the floristic diversity, species composition and structure of old-growth and regrowth forests. Concentric circular plots with an area of 200 m2 and 500 m2 were laid on line transects. A total of 24 plots were sampled from two sites. In comparison to regrowth forests, old-growth forests had higher structural heterogeneity because of higher canopy height variations, vertical stratification, and tree sizes and their variations. Species richness and diversity indices values were similar, but abundance and species composition were significantly different between old-growth and regrowth forests. It appears that species richness recovers first followed by forest structure and species composition. Regrowth forests are important for in situ conservation of tropical biodiversity and they can also serve as a conduit for the restoration of degraded lands and forests. Regrowth forests provide habitats, serve as buffer zones around the fragmented old-growth forests, function as source of propagules, and enhance landscape connectivity. Utilization of regrowth forests for restoration purposes is comparatively inexpensive. Regrowth forests should be given the due considerations in the national forest conservation and restoration policy of Laos.

Highlights

Shifting cultivation, which is a dominant agricultural system covering about 280 million hectares and practiced by 300-500 million people around the world, remains an important driver of change in the tropical forests (Liao et al 2015; Heinimann et al 2017)
The aims of this study were to: (1) conduct a comparative study of old-growth and regrowth forests which are established via autochthonous colonization on fallow lands in terms of structure, woody species diversity and composition; (2) investigate the potential role of regrowth forests spontaneously established on fallow lands in the conservation and restoration of degraded forest lands in Lao People’s Democratic Republic (Laos)
The height and dbh as well as the associated stand attributes of basal area and above ground biomass were considerably smaller in the regrowth forests than in the old-growth forests

Summary

Introduction

Shifting cultivation, which is a dominant agricultural system covering about 280 million hectares and practiced by 300-500 million people around the world, remains an important driver of change in the tropical forests (Liao et al 2015; Heinimann et al 2017). Estimates of the global area of land currently abandoned after swidden is difficult to ascertain, as the reported extent of areas under the agricultural practice vary considerably in the literature. An FAO report (Lanly 1982) estimated the total affected area at 410 million hectares (Mha) by 1980. Current studies based on more reliable multi-temporal Landsat assessments (which delimit forest extent and change) put the global figure at 280 Mha (Heinimann et al 2017), indicating a 30% decline from the 1980 total

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