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Lack of disturbance as an explanation for the additive basal area phenomenon in a stratified Afrotemperate forest
Author(s) -
LAWES M. J.,
MIDGLEY J. J.,
BOUDREAU S.,
GRIFFITHS M. E.
Publication year - 2006
Publication title -
austral ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.688
H-Index - 87
eISSN - 1442-9993
pISSN - 1442-9985
DOI - 10.1111/j.1442-9993.2006.01607.x
Subject(s) - basal area , stratification (seeds) , canopy , ecology , competition (biology) , disturbance (geology) , limiting , context (archaeology) , tree canopy , forest dynamics , stratum , phenomenon , biology , agronomy , mechanical engineering , seed dormancy , paleontology , germination , dormancy , engineering , physics , quantum mechanics
Explanations for the additive basal area (BA) phenomenon in forests are frequently given in the context of stratification and the avoidance of competition for space or resources (e.g. light, nutrients, moisture). Thus, large individuals avoid competition for light by emerging above the canopy and, in so doing, the BA of emergent individuals is often ‘additive’ to that of the rest of the individuals in a stand. The additive BA phenomenon was evident in a stratified Afrotemperate forest and was not confined to the emergent stratum but occurred also within the canopy stratum where gymnosperm BA appeared to be additive. However, there was no evidence that stand BA was at carrying capacity (i.e. presumably neither space nor nutrient resources were limiting) and there was no statistical evidence of competitive effects. We argue that avoiding competition is an insufficient explanation for how biomass accumulates in stratified forests and suggest that local variation in disturbance regime and tree life‐history provide a more plausible and general explanation for current forest stand structure and dynamics. We suggest that the additive effect is a result of long‐lived individuals persisting in the prolonged absence of disturbance to canopy and emergent strata.