Morphometric Relationships and Developmental Patterns of Acacia tortilis and Acacia reficiens in Southern Turkana, Kenya

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Abstract
Size-dependent morphometric relationships were established for two dominant tree species (Acacia tortilis and Acacia reficiens) in an arid tropical ecosystem of northern Kenya. We found relationships for both multi-stemmed species between aboveground biomass and the aggregate of diameters of all stems. Relationships between aggregate stem diameter and crown diameter suggested that large individuals had smaller crown diameter increments per increment in aboveground biomass. Acacia tortilis displayed a pronounced developmental transition from low biomass-open crown to heavy trunk-dense crown morphology at sizes of 63-223 mm stem diameter. Stem diameter of A. tortilis increased by 2 mm for each tree ring among small trees. While rings may not be exactly annual, an average of one ring may be produced per year. Root systems of both species were a mixture of tap and lateral roots. There was a concentration of root biomass in the surface meter of soil and most root biomass was accounted for in the top 2.5 m of soil. A logarithmic relationship between root biomass and stem diameter applied to both small and large trees. Although large trees had tap roots with large diameters, these were not necessarily deep. Root:shoot ratios declined from 1.5 in small trees to 0.2 in mid and large trees.