Environmental influences on tropical tree seedling growth

1994

English

The tropical high forests of West Africa have been under stress due to a
greater dependence on wood resources. Logging rate has more than doubled within
the last decade. However, the exact effects of logging on vegetation composition
and the degree of canopy opening that should be created in the forest to ensure the
regeneration of timber tree species are not known.
Three major experiments were carried out to determine the ecophysiological
responses of timber tree species in different irradiances and red:far-red ratios. (1)
16 tree species were grown in six neutral shade treatments (2,6,27,42 and 65% full
sim) and their growth assessed by standard measurements used in growth analysis
(biomass, height, stem diameter, leaf area, leaf production and mortality).
(2) Eight species, of which six were also used in the shade house experiment, were
grown in a series of artificially-created gaps in two forest sites differing in annual
rainfall. Gaps created received 1-2,5,10,15,30 and 66% full sun.
(3) Possible differences in the results between shade house and forest experiments
due to differences in light quality (red:far-red ratio) were tested separately.
Differences in red:far-red ratio had little effect of growth but showed some
influence on allocation of biomass. Seedling growth response of species were higher
in shade houses compared to the two field sites and higher in the wet compared to
dry forests. Sixteen tropical timber tree species were ranked on an ecological (shade
tolerance) gradient based on their differential growth response to light. The results
indicate that the ranking of species on an ecological gradient is robust and
potentially more reliable than intuitive classification of species into groups.

Agyeman, V. K.