Abstract
Forest succession has been reported in forest plantations in tropical forests, but little is known about their successional dynamics because most studies have focused on succession in secondary forests. We assessed changes in species composition and stand structure in secondary and plantation forests in Kakamega rainforest in western Kenya. We used a nested experiment to collect data on tree species types, tree height and stem diameter at breast height from secondary forest stands, mixed indigenous plantations and indigenous and exotic monoculture plantations in three forest blocks. Data were analyzed for variation in species diversity, species similarity to the primary forest, stem density and basal area using analysis of variance in Genstat. The results indicated that species diversity and similarity to the primary forest were not different between secondary and plantation forests. However, successional species occupied all the canopy strata in secondary forests, but they occupied only the shrub and understorey layers of monoculture plantations, and the shrub, understorey and sub-canopy strata of mixed indigenous plantations. Mixed indigenous plantations had become nearly indistinguishable from secondary forests, but monoculture plantations maintained a plantation outlook. Old secondary forest had a significantly lower stem density than plantation forests, but their basal area was not significantly different. Middle-aged and young secondary forests had comparable stem density to plantation forests, but their basal area was significantly lower. The results confirmed that plantation forests are experiencing forest succession in tropical forests, their species composition and stand structure are comparable with secondary forests, but they differ in the emergence pattern of successional species and their distribution in forest canopy strata. Key words: Secondary succession, plantation forests, tropical rainforest, species composition, stand structure. 
Highlights
Many tropical rainforests have been felled and thereafter converted to farmland, human settlement or pasture.Over time, as the farmlands, settlements and pasture are abandoned; these areas either regenerate naturally into secondary forests or are planted as plantation forests (Chazdon et al, 2010; Omeja et al, 2012; Chua et al., 2013)
54% of the tree species were represented in the main forest canopy, 62% were located in the sub-canopy, while 55% and 66 % were located in the understorey and shrub canopy layers, respectively
We looked at this observation from three perspectives, that is the representation of successional species in canopy strata, persistence of planted trees in mature plantation forests, and the effect of stand age on species composition
Summary
As the farmlands, settlements and pasture are abandoned; these areas either regenerate naturally into secondary forests or are planted as plantation forests (Chazdon et al, 2010; Omeja et al, 2012; Chua et al., 2013). License 4.0 International License has been made to describe post-disturbance secondary forest succession in abandoned farmlands and pasture (Guariguata and Ostertag, 2001; Chazdon, 2003; Norden et al, 2009). The first 100 years of secondary forest succession have been described to comprise about three successional phases (Finegan, 1996; Pena-Claros, 2003; Capers et al, 2005; Norden et al, 2009; Bonner et al, 2013). The emergence of shade-tolerant species and other late successional species is thought to occur continuously during the establishment of both early pioneers and long-lived pioneer species (Finegan, 1996; Pena-Claros, 2003; Bonner et al, 2013)
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