Forest regeneration under Tectona grandis and Terminalia amazonia plantation stands managed for biodiversity conservation in western Panama

Abstract

Plantations of Tectona grandis in Central America are widely perceived to suppress forest regeneration in their understories, yet few studies have tested this assumption. We surveyed the understory woody vegetation growing in 7-year-old stands of T. grandis and the native tree species Terminalia amazonia in a plantation in western Panama that was managed with both commercial timber and biodiversity conservation objectives. We predicted that if T. grandis suppressed forest regeneration then the understories of T. grandis stands would have a lower density of woody stems, smaller stems, and fewer species than stands of T. amazonia. None of our predictions were supported. Densities of woody stems were 0.56 ± 0.21 m−2 (mean ± SE) and 0.64 ± 0.10 m−2 in T. grandis and T. amazonia understories, respectively. Stem height structure was similar under both species, where stems <1 m height dominated. Understory species richness did not differ between the two species; in total, 27 and 30 woody species were sampled in T. grandis and T. amazonia stands, respectively. However, understory species composition differed between the two crop species. Overall, our results are inconsistent with the idea that T. grandis plantations suppress forest regeneration and suggest that the lack of woody vegetation in other T. grandis plantation understories may be attributable to management actions, such as understory thinning, rather than species effects of T. grandis. Further research is needed to compare T. grandis and native species for their effects on forest regeneration.