Spatial and environmental constraints on natural forest regeneration in the degraded landscape of Hong Kong

Abstract

Tropical forests are the main reservoirs for global biodiversity and climate control. As secondary forests are now more widespread than primary forests, understanding their functioning and role in the biosphere is increasingly important. This includes understanding how they achieve stability, how they accumulate species and build biodiversity and how they cycle nutrients and carbon. This study investigates how we can restore tropical secondary forests to resemble high biomass, highly biodiverse and stable ecosystems seen today only in primary, undisturbed forests. The study used historic aerial photographs and recent highresolution satellite images from 1945 to 2014 to map forest patches with five age categories, from 14-years to over 70-years, in Hong Kong´s degraded tropical landscape. A forest inventory comprising 28 quadrats provided a rare opportunity to relate patterns of species composition at different stages during the succession with topographic and soil characteristics.The topographic variables accounted for 15 % of the variance in species abundance, and age of forest stands explained 29 %. Species richness rapidly increased after the first 15 years, but was lower in old-growth, than in medium age forest. This is attributed to the inability of latesuccessional species to disperse into the 'new, young' forests as the natural dispersal agents (birds, mammals) have been lost. Light-loving pioneers which are unable to tolerate the shade of older forests, cannot regenerate in their own shade, therefore species diversity declines after a few decades. For ecosystem restoration in tropical secondary forests, introduction of latesuccessional species is necessary to assist natural succession, given the absence of native fauna, seed dispersal agents, and the surrounding altered environment. We also show that remote sensing can play a pivotal role in understanding the recovery and functioning of secondary forest regeneration as its role in the biosphere is increasingly important.

Study towards Integrating Secondary Forests into Future Land Use Development in Singapore for Biodiversity Objectives

“…This strategy is linked with Lee et al's research in the urban forests of Hong Kong, which indicates the idea that planting native species in urban forests can enrich the biodiversity of these sites [36]. Relevant theory is also mentioned in Abbas et al's research on the secondary forests of Hong Kong, in which the necessity of introducing late-succession species for ecosystem restoration in tropical secondary forests is emphasized [25]. Optimizing the structure of secondary forests will also enhance biodiversity, so constructing multi-layer canopies in lower-density vegetation areas could improve the complexity of the community and the biomass abundance [37].…”

“…Biodiversity is affected by deforestation and reforestation worldwide [24]. Compared with primary forests, secondary forests are more widespread worldwide, playing an essential role in the biosphere [25]. For the biophysical value, secondary forests are playing a significant role in broader biodiversity in Singapore.…”

Sex‐specific outbreeding advantages and sexual dimorphism in the seedlings of dioecious trees

“…Diospyros morrisiana (Ebenaceae) is a dioecious deciduous tree that inhabits slopes, ravines, and streams in East Asian monsoon subtropical forests. It is mostly found at elevations of 100–1000 m. It is a dominant species in early‐ and mid‐successional subtropical forests in southern China and can grow to ≤20 m in height and ≤30 cm diameter at breast height (DBH; Abbas et al, 2021). Its reproductive season starts in May–June and fruits mature in November.…”

Effects of Rodent-mediated Dispersal Limitation on Ridge Regeneration

“…Considering niche differentiation and dispersal limitation simultaneously may better explain successional mechanisms in tropical forests (Dalling et al , 2002), and dispersal limitation may be more important than ecological niche differentiation in determining species composition in habitats where dispersers are scarce and forest cover is low (Dent and Estrada-Villegas, 2021). For example, dispersal limitation due to the disappearance of seed dispersers such as birds and mammals in tropical forests has been a major factor in the inability of later successional species to spread into young forests (Abbas et al , 2021). Therefore, birds and mammals are believed to play an important role in seed dispersal (Willson, 1993;Glyphis et al , 1981).…”