Spatial and temporal effects on recruitment of an Afromontane forest tree in a threatened fragmented ecosystem

• Published in: Biological conservation Vol. 142; no. 3; pp. 518 - 528
• Main Authors: Lehouck, Valérie, Spanhove, Toon, Gonsamo, Alemu, Cordeiro, Norbert, Lens, Luc
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.03.2009; Kidlington, Oxford: Elsevier Science Ltd; Elsevier
• Subjects: Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Conservation, protection and management of environment and wildlife; Eastern Arc; field experimentation; forest ecosystems; forest regeneration; forest trees; Fundamental and applied biological sciences. Psychology; General aspects; Germination; habitat fragmentation; Kenya; microhabitats; Monomiaceae; Parks, reserves, wildlife conservation. Endangered species: population survey and restocking; Plantation; Regeneration; seed dispersal; seed germination; seedling growth; Seedling survival; spatial variation; temporal variation; tree mortality; wild birds; Xymalos monospora; Kenya; Xymalos monospora; Seedling survival; Regeneration; Plantation; Germination; Eastern Arc; Plant juvenile growth stage; Forest tree; Threatened ecosystem; Survival; Fragmentation; Recruitment; Habitat; Environmental protection
• ISSN: 0006-3207; 1873-2917
• DOI: 10.1016/j.biocon.2008.11.007

Tropical forest fragmentation affects animal and plant populations in different ways. For plants, early stages (seed to seedling) are more sensitive to habitat alteration than adults, and can shape their future spatial patterns. Therefore, studying how seed germination and seedling growth and survival vary at different spatiotemporal scales enhances our understanding about plant recruitment in fragmented ecosystems. In this study we examine if, and to what extent, recruitment at early life-stages of Xymalos monospora (Monomiaceae), a bird-dispersed Afrotropical tree, differs between and within forest fragments that vary in size, surrounding matrix and microhabitats. Three years of field experiments (2004–2006) in south-east Kenya, revealed that patterns of seed germination and seedling survival and growth were largely inconsistent, both in space and time. Recruitment was not consistently higher in larger or less disturbed fragments. At smaller spatial scales within forest fragments, recruitment was subject to high between-year variation too, with decreased germination in gaps only in the dry year of 2004. However, performance of seeds and seedlings was consistently better away from than under conspecific fruiting trees. Our results imply that fragmented tree populations of X. monospora may become age-structured, or ultimately go extinct, if recruitment fails in subsequent years. This may especially affect populations in small, disturbed forest fragments, where seed dispersal and buffering against stochastic processes are generally reduced. Exotic plantations bordering indigenous forest fragments may provide suitable conditions for native tree recruitment; hence, forest expansion through enrichment planting should be considered in future conservation plans.