Branch construction and bud defence status at the canopy surface of a West African rainforest

Abstract

Branch specimens were collected from the very tops of tropical tree crowns in southern Cameroon, West Africa. An analysis of branching patterns revealed a consistency of form across unrelated taxa. All specimens showed evidence of rhythmic growth cither due to the regular occurrence of dormant terminal buds or due to sympodial growth with loss or flowering of terminal buds. Study of bud anatomy revealed an extensive array of protective devices associated with drought tolerance and herbivore defence. Normally a considerable excess of dormant, well protected axillary buds were present which (almost without exception) existed in a viable state. In very many instances the large dormant bud population was due to the presence of accessory buds, i.e. > 1 bud in the axil of each leaf. The microclimate at the outer surface of a tropical rainforest may experience a daily increase in temperature and associated depression in humidity; the canopy surface characteristics are more akin to chaparral shrub vegetation than to familiar rainforest understorey vegetation.

Eucalyptus regnans (Myrtaceae): A fire‐sensitive eucalypt with a resprouter epicormic structure

“…Accessory buds have been found in anatomical studies of other species in the Myrtaceae (Carey, 1931; Shah and Unnikrishnan, 1969; Burrows, 2008; Burrows et al, 2008), but not in some morphological studies (Lee and Rao, 1984). Accessory buds have also been found in a wide range of other families (Bell et al, 1999; Fink 1999). Eucalypt leaf axils appear to be unique as the naked bud is delicate, unprotected and usually abscises shortly after formation, while the accessory buds are long‐lived and buried relatively deeply within the axillary tissues.…”

“…Therefore, we also examined leaf axil structure to provide an indication of the subsequent epicormic potential. Our anatomical analysis was used to determine whether the epicormic structures were of the eucalypt fire‐adapted type (e.g., Burrows, 2000, 2002), the “typical” surface‐level buds of either seeders or basal resprouter species (e.g., Fink, 1983 and 1999) or were completely absent.…”

Contrasting effects of sampling scale on insect herbivores distribution in response to canopy structure

“…In the present protocol, insect samples were taken from the peripheral regions of the tree crowns, in more external branches, coinciding with those places where crown expansion was likely to occur (Hallé et al 1978, Lowman & Wittman 1996, Bell et al 1999, Sterck et al 2001. The lack of a specific response from chewing herbivores to tree host species and crown units, suggest that a set of crowns producing greater amounts of resources should be the main attractive for this guilds, thus likely composed of generalists, as normally found in the canopies (Novotny et al 2002, Ribeiro et al 2005.…”

Gall‐forming and free‐feeding herbivory along vertical gradients in a lowland tropical rainforest: the importance of leaf sclerophylly

“…However, few workers actually measured this trait in the tropics or in the upper canopy of wet forests (Espírito‐Santo and Fernandes 1998, Madeira et al 1998, Ribeiro et al 1999). One noticeable exception is Bell et al (1999) study in southern Cameroon. These authors noticed convergence in leaf defensive traits and crown construction between upper canopy trees of a wet forest and chaparral shrub vegetation.…”