Vegetation assessment of native tree species in Broussonetia papyrifera‐dominated degraded forest landscape in southern Ghana

Abstract

Abbreviations F = Farmland; FU = Forest understorey; LGB = Large canopy gaps dominated by Broussonetia papyrifera; LGC = Large canopy gaps dominated by Chromolaena odorata; LR = Logging road; MAP = Mansonia altissima plantation; MDT = Modified Taungya System; NDP = Nauclea diderrichii plantation; NPLD = Non-pioneer light-demander; P = Pioneer; SB = Shade-bearer; ST = Skid trail; TIP = Terminalia ivorensis plantation. Abstract Question: Does the invasive tree species Broussonetia papyrifera facilitate the natural regeneration of native tree species in a degraded tropical forest landscape? Location: Afram Headwaters Forest Reserve, southern Ghana.Methods: We established sampling areas and assessed seedlings and saplings <5 cm DBH in nine habitats. The habitats were logging road, skid trail, large canopy gaps dominated by B. papyrifera, large canopy gaps dominated by invasive Chromolaena odorata, Nauclea diderrichii plantation, Mansonia altissima plantation, Terminalia ivorensis plantation, abandoned farmland and unlogged forest.Results: We found that the abundance of pioneers declined with increasing abundance of B. papyrifera. This trend was more pronounced in the farmland and in the N. diderrichii plantation. By contrast, increased abundance of B. papyrifera did not lead to a decrease in the abundance of the shade-tolerant species. B. papyrifera seedlings and saplings were absent in the forest understorey. We also found a lower abundance and richness of some vulnerable tree species and valuable timber species in the N. diderrichii plantation and in gaps dominated by B. papyrifera. However, we recorded both shade-tolerant and shade-intolerant species in the gaps dominated by B. papyrifera. Conclusions:We found both shade-tolerant and shade-intolerant species in the B. papyrifera-dominated gaps. This can provide a basis for future studies to explore the potential of such tree species in restoration programmes targeted at B. papyrifera-invaded sites. Our results also suggest that the integrity of the undisturbed forest patches in the landscape must be protected to help prevent B. papyrifera from spreading further. We suggest further studies should be conducted at replicated sites with a similar habitat that represent varying levels of invasion by B. papyrifera to draw conclusions regarding the species' potential to facilitate regeneration of native tree species.

Natural Regeneration of Indigenous Tree Species in Broussonetia papyrifera Invaded Sites in Pra -Anum Forest Reserve

“…ough a few studies have attempted to assess the effects of the species on native vegetation, there are still contentions as different scientists have reported different effects of the species on native vegetation. For instance, while Agyeman [10] reported a positive effect of the species on indigenous species regeneration, Apetorgbor and Bosu [1] reported that the species impacts negatively on the abundance of indigenous species. Consequently, there is a need for more extensive studies on the species to establish its effect on native vegetation.…”

The effect of Broussonetia papyrifera invasion on the regeneration of selected native timber species in a tropical moist forest in Uganda

“…The fact that the juvenile abundance of certain native species is not affected by invasion is not clearly understood but could partly be linked to species functional traits such as the seedlings of the unaffected species being shade tolerant and are therefore not affected by canopy closure by B. papyrifera (V. K. Agyeman et al, 2010;Kiama & Kiyiapi, 2001). It has also been suggested that B. papyrifera may have facilitative effects by fostering the establishment of seedlings and saplings of some native species (V. Agyeman et al, 2016;Yalley et al, 2020) but this remains a subject for further research.…”

“…Consequently, there are still contentions as different scientists have reported inconsistent effects of the species on native vegetation. For instance, while Agyeman et al (2016) reported a positive effect of B. papyrifera on indigenous species regeneration in Ghana, Apetorgbor and Bosu (2011) reported that the species reduces the abundance of native species. Besides, locally, there is still scanty information about the effects of B. papyrifera on the recruitment of indigenous species.…”

Spatial distribution and interspecific association patterns between Mansonia altissima A. Chev., Ceiba pentandra (L.) Gaertn and Triplochiton scleroxylon K. Schum. in a moist semi-deciduous forest

“…They can act as facilitators in species with different shade tolerances and growth forms (Ledo 2015). Agyeman et al (2016) found that the richness and abundance of timber species seedlings and saplings are mainly due to the presence of facilitating pioneer tree species.…”

“…Ripley's K-function allows the analysis of spatial distribution patterns at several spatial scales and the detection mixed processes (association and repulsion at some scales) (Fonton et al 2012;Fajardo et al 2006). Since reforestation with native species may strongly contribute to the regeneration or restoration of degraded forests (Omelko et al 2018;Agyeman et al 2016), such analyses are important in forest management since they could improve our understanding of the role of pioneer species in maintaining plant diversity. They should enable a reasoned choice about distances between conspecific or heterospecific trees for ecological restoration of habitats and sustainable management of threatened species.…”