Causal effects of latitude, disturbance and dispersal limitation on richness in a recovering temperate, subtropical and tropical forest
Do regional differences in latitude, and local factors of disturbance and distance from mature forest, influence dispersal syndromes, rate of accumulation of species and total richness in a recovering temperate, subtropical and tropical forest?
Temperate old-growth red pine forest, Canada; subtropical Araucaria Atlantic forest, southern Brazil; tropical Gallery forest, central Brazil.
We used path analysis to determine causal relationships of regional (latitude) and local (disturbance intensity, distance of recovering site from forest) factors on percentage zoochory, exponent z from species–area relationships and total richness.
Path results showed linear decreases in percentage zoochory, z and richness with increasing latitude. Disturbance and distance from mature forest each reduced richness by similar amounts; however responses of percentage zoochory and z were inconsistent between the two local factors. A second path model, using only the subtropical and tropical forest, greatly increased model significance, yielded insignificant regional effects and strengthened effects of local factors on the three richness responses. Important results from this path model were linear decreases of z (0.1) and percentage zoochory (10%) and a log-decrease of richness (five-fold) 100 m from the mature subtropical and tropical forest.
Regional differences in latitude and local effects of dispersal limitation can influence forest richness as strongly as disturbance alone. Isolated, recovering subtropical and tropical forest fragments of southern and central Brazil may therefore be recovering at much slower rates than estimates made from those adjacent to mature forest stands.