As hypothesized, tree communities with D. oliveri were functions
of existing environmental gradients. The main environmental
gradient to which species responded in the study area is one of
relative rich, deep soils in valleys of ephemeral streams to poor,
shallow soils on ridges (Fig. 3). MDF occurred on deeper soils of the
foothills and on less exposed slopes, while dry deciduous
dipterocarp forest (DDFd) occurred on ridge tops and on the driest
or steepest slopes with shallow soil. Stunted trees and higher nitrogen concentrations and CEC in the DDFd may have resulted from recurrent fires. A mesic phase of
the deciduous dipterocarp forest (DDFm) occurred as a transitional
type between MDF and DDFd on more productive sites.