Abstract:
Key message The paper demonstrates the prospects and
applications of dendrochronology for understanding
climate change effects on riparian forests in the savanna
landscape.
Abstract Riparian trees in savannas have a potential for
dendro-climatic studies, but have been neglected hitherto.
We examined ring-width series of Afzelia africana (evergreen) and Anogeissus leiocarpus (deciduous) to study the
influence of climatic factors on the growth of riparian trees
in the humid (HS) and dry (DS) savanna zones of the Volta
basin in Ghana. A total of 31 stem discs belonging to A.
africana and A. leiocarpus were selected from HS and DS
to establish species-specific local chronologies of tree
growth. Each individual of A. africana and A. leiocarpus
from the two savanna sites showed distinct growth rings.
Cross-dating of individual tree-ring patterns was successful
using standard dendrochronological techniques. The mean
annual growth rates of A. africana in the HS (1.38 ± 0.09) and DS (1.34 ± 0.08) were not statistically different.
Furthermore, mean annual growth rate of A. leiocarpus in
the DS (3.75 ± 0.27) was higher than in the HS
(2.83 ± 0.16) suggesting that species in drier environment
can have higher growth rates when sufficient soil moisture
is available. The growth rates of both species at the same
sites were different, which might indicate different water
use strategies. High correlations of individual tree-ring
series of A. africana and A. leiocarpus trees at HS and DS
suggest a strong climatic forcing controlled by the seasonal
movement of the inter-tropical convergence zone. The
annual growth of A. africana and A. leiocarpus at both the
HS and DS was significantly correlated with local temperature and precipitation. The negative correlations of the
growth of the two tree species to global sea surface temperatures were however, indications that the growth of
riparian forests can be impacted during El Nin˜o-Southern
Oscillation years. The result of our study shows that
riparian trees in the humid and dry savanna zones of West
Africa can be successfully used for dendrochronological
studies.
