Results/Conclusions A total of 11,029 plants distributed in 155 species (52 trees, 103 shrubs) were recorded.  Fragment metrics ranged from 12 to 3,206 ha (area); 5–328 Km (perimeter); and 70–385 m ha^-1 (perimeter/area ratio).  In general, the same relationship with fragment metrics and diversity indices were detected for both trees and shrubs.  This relationship was positive logarithmic for fragment area and perimeter, and negative logarithmic for perimeter area ratio.  Shannon and Simpson indices were less sensitive to fragment metric changes than Jack2 and Fisher alpha, in particular for shrubs.  Overall, small changes in diversity were observed for larger fragments, but in fragments under 40 ha or 30 km perimeter, small fragment reductions resulted in high tree diversity declinations.  Shrubs required higher reductions in fragment size than trees before drastic changes in diversity could be detected.  These results can be used as guides for oak forest management and conservation in the Upper Mixtec region.