Multiple disturbance patterns and population structure of a tropical tree species,Afzelia africana(Leguminosae–Caesalpinioideae), in two contrasting bioclimatic zones of the Republic of Benin

Abstract

Understanding how multiple disturbances affect species population structure is crucial for designing a better conservation strategy of threatened species. In this paper, we assessed the disturbance patterns and evaluated their effects on the population structure of Afzelia africana, in two different bioclimatic zones of the Republic of Benin. The main disturbances in the studied area included branch pruning and debarking. Individuals of medium size (20-40 cm) were mostly pruned and debarked. The percentages of pruning and debarking were similar at population level across the two studied bioclimatic zones (t = −0.04, p = 0.96; t = 0.73, p = 0.48). Examining this at individual level, pruning was similar but debarking was higher in the Sudanian zone (12.14 ± 0.93%) than in the Sudano-Guinean zone (7.44 ± 0.88) (W = 40859, p < 0.001). Population structure was bell-shaped in the Sudanian zone regardless of the disturbance level. In contrast, in the Sudano-Guinean zone, mildly disturbed populations showed an inverse J-shaped structure, whereas those highly disturbed were bell-shaped. This underlined the climatic (dryness) and disturbance effects on the establishment and recruitment of small trees into the next life stage in tropical savanna ecosystems. Good regeneration pattern and the largest individuals were found within the protected areas, demonstrating the prominent role of protected areas for the species conservation. Therefore, we suggested that conservation efforts should be extended to populations outside the protected areas. Forestry department should establish firebreaks networks to protect small individuals and facilitate their recruitment, as well as the regulation and enforcement should be improved on the sustainable use of the species.

Heterospecific Tree Density and Environmental Factors Affect Afzelia africana Sm. Population Structure in the Pendjari Biosphere Reserve, West Africa: Implications for Management and Restoration

“…Its wood is durable even for usage in permanent humid conditions, making the timber an excellent asset for exploitation in the international market. The multiple use and the subsequent pressure on its natural populations have put the species on priority research agenda in Benin (Amahowe, Biaou, Natta, & Balagueman, 2017;Assogbadjo, Mensah, & Gle`le`Kakaı¨, 2017;Mensah, Houehanou, Sogbohossou, Assogbadjo, & Gle`le`Kakaı¨, 2014;Mensah, Houe´hanou, et al, 2016), being listed among the top five native trees species that require urgent conservation actions (Akpona, Assogbadjo, Fandohan, & Gle`le`Kakai, 2017).…”

“…Although several local and regional scale research studies have been conducted on A. africana in West Africa, most have fallen short of addressing such ecologically important aspects, especially in protected areas. Currently, there is substantial documentation on the species use patterns, values and management (Balima et al, 2018), human disturbance, land use and climatic influence (Mensah et al, 2014;Nacoulma, Lykke, Traore, Sinsin, & Thiombiano, 2017;Sinsin, Eyog-Matig, Assogbadjo, Gaoue, & Sinadouwirou, 2004), habitat floristic compositions (Bonou, Gle`le`Kakaı¨, Assogbadjo, Fonton, & Sinsin, 2009;Mensah, Houe´hanou, et al, 2016), and structure and height-diameter allometry (Amahowe et al, 2017;Assogbadjo et al, 2017). In the meantime, we still lack information on how the species responds to local environmental variation in protected habitats.…”

Functional traits partially mediate the effects of chronic anthropogenic disturbance on the growth of a tropical tree

“…Afzelia africana is one of the tropical species that exhibited the highest ecological resilience to debarking under stressful arid and semi-arid climate in Benin ( Delvaux et al 2010 ), and this may explain its wide distribution across disturbance and climate gradient in Benin ( Orwa et al 2009 ; Mensah et al 2014 ). The lack of clear and significant effect of debarking on tree growth may suggest that current bark harvesting intensities might be sustainable ( N’Dri 2012 ; Amahowe et al 2017 ). This contrasts with results from previous studies which suggest that the growth rates of many other species in West Africa, i.e.…”

“…In addition to debarking, the species trunk bark is frequently wounded and shows large deep scars. Pruning and debarking intensity are size-dependent ( Amahowe et al 2017 ). The species is sensitive to fire at early age and this is worsened by insect attack ( Stark 1986 ; Delvaux et al 2009 ).…”

“…From an evolutionary perspective, many tree species have evolved to cope with repeated disturbances ( Gutschick and BassiriRad 2003 ) and exhibit various recovery processes that are ultimately shaped by the tree functional strategy. Previous studies have shown that the effects of both debarking and pruning are size-dependent ( Sinsin et al 2004 ; Gaoue and Ticktin 2007 ; Mensah et al 2014 ; Amahowe et al 2017 ), because resource availability and quality are linked to the tree life stage. Failure to account for this size-dependent growth, both in tree performance and in assessing the effect of pruning and debarking, may result into suboptimal management decisions.…”