Nitrogen and Phosphorus Availability in Treefall Gaps of a Lowland Tropical Rainforest

SUMMARY (1) Nitrogen availability (net nitrogen mineralization) was extremely high in a lowland rainforest on volcanic soil at La Selva, Costa Rica, averaging 50-80 ug g-1 month-' (822 kg ha-' year-'). Available phosphorus concentrations were relatively low (25 ugg-1). (2) Nitrogen mineralization did not increase in the crown-fall zone of treefall gaps, although the possibility of a short-lived increase immediately after treefall could not be ruled out. Phosphorus concentrations increased slightly but not significantly (to 3.3 ,ug g-1). (3) The root-throw zone of treefall gaps had significantly lower nitrogen mineralization and phosphorus concentrations than the crown-fall zone or the zone along the fallen trunk. Low nutrient availability in the root-throw zone could select for colonizing species distinct from those establishing in other zones of treefall gaps.