Recovery of seedling community attributes during passive restoration of a tropical moist forest in Uganda

Abstract

Aim: There has been a debate about the effectiveness of passive restoration for recovering tropical forests, but few studies quantify the success of passive restoration. The aim of this study was to better understand tropical forest succession under a passive restoration scenario. We compared floristic and functional attributes of seedlings in a passively restored and an old-growth forest, and assessed the effect of restoration age and distance from the old-growth forest on seedling attributes. Location: Kibale National Park, western Uganda. Methods: We measured seedlings in a passively restored and an old-growth forest in 2011, 2014 and 2017. We determined species diversity, structure and composition and searched the literature for functional traits. We used generalized linear mixedeffects models to compare seedling attributes between the restored and old-growth forest and determine the influence of restoration age and distance from the oldgrowth forest. Results: Seedling species abundance, evenness, basal area and height were similar between the restored and old-growth forest. Wood density and abundance of seedlings of different dispersal modes, habitat types, fruit size categories, and regeneration strategies were also similar between the restored and old-growth forest. However, richness, diversity and composition of seedlings were different. We found a positive effect of restoration age on species abundance and abundance of non-zoochorous, medium-fruited, forest-dependent, non-pioneer light demander and shade-tolerant species, and a negative effect on evenness, wood density, abundance of pioneers and compositional dissimilarity. Basal area of seedlings and the abundance of zoochorous and forest-dependent species declined while compositional dissimilarity increased with distance from the old-growth forest. Conclusions: Our results provide empirical evidence on the potential of passive restoration to recover the structure and functionality of tropical forests in a relatively short period of time. We demonstrate that the effect of restoration age and distance from the old-growth forest is not straightforward and depends on the attributes measured.

Remotely sensed vegetation greening along a restoration gradient of a tropical forest, Kibale National Park, Uganda

“…The restoration project area also includes large areas representing passive restoration (Ssekuubwa et al, 2021), that is, protection of natural regrowth from fire (Figure 1). These are areas where the forest was cleared in the past, but natural regeneration was feasible (Ssekuubwa et al, 2021).…”

“…The restoration project area also includes large areas representing passive restoration (Ssekuubwa et al, 2021), that is, protection of natural regrowth from fire (Figure 1). These are areas where the forest was cleared in the past, but natural regeneration was feasible (Ssekuubwa et al, 2021). To the east, the restoration project area is bordered by a belt of primary forest (Figure 1), herein referred to as the reference area, that is, the target state of the restoration.…”

“…The restoration project was established in 1994 in an area where elephant grass ( Cenchrus purpureus (Schumach.) Morrone), a species native to Eastern and Central Africa, and fires, suppressed the natural regeneration of tree seedlings and thereby prevented forest recovery (Ssekuubwa et al, 2021; UWA‐FACE, 2015). In this area, active restoration (i.e., planting with native trees and fire prevention) and passive restoration (i.e., fire prevention), has taken place since 1995.…”

Monitoring recovery of tree diversity during tropical forest restoration: lessons from long-term trajectories of natural regeneration

“…Even censuses based on sample areas of 1 ha or less will miss a significant fraction of rare species that are actually present in the assemblage. Including small size classes in sampling methods may increase the likelihood of detecting increased numbers of species of recent recruits [ 57 ]. Under such a scenario, plot size is an important point to consider.…”

Does restoration success vary with tree size under restoration plantings and regrowth forests?

“…The areas with a high potential for natural recovery (2593 ha) due to the presence of many spontaneously regenerating seedlings were left to undergo natural forest regrowth (Ssekuubwa et al, 2018). The restoration plantings and regrowth sites were protected against fires by controlling poaching, constructing fire lines, and monitoring fire incidences by using watch towers (Ssekuubwa et al, 2018; Ssekuubwa, van Goor, Snoep, Riemer, Wanyama, & Tweheyo, 2021). Fencing and trenching which were carried out to control crop raiding by elephants also guarded against livestock grazing.…”