Question: What is the influence of remnant trees on secondary forest structure and composition in tropical pastures many years after abandonment?

Location: Neotropical lowland wet forest, La Selva Biological Station, Costa Rica.

Methods: Tree and sapling density, basal area, and species richness were quantified at three distances from remnant trees, 0 – 10 m (inner), 20 - 30 m (intermediate), and ca. 50 m (distal) zones. A total of 15 remnant trees were sampled in pastures ~23 years after abandonment.

Results: Tree density decreased along a gradient from inner (1117 ± 377 individuals/ha) to distal (592 ± 282 individuals/ha) zones, and the number of large-seeded individuals (seeds > 1 cm diameter) was significantly greater in the inner zone. Basal area of tree individuals was greater in the inner (25.6 ± 12 m²/ha) and intermediate (28.3 ± 15.6 m²/ha) zones than the distal zone (14.7 ± 7.2 m²/ha), but there were no differences between inner and intermediate zones. Similar patterns are reported for species richness. Additionally, saplings (1 - 5 cm DBH) had higher density directly beneath and adjacent to remnants, suggesting that remnant trees can affect recruitment even many years after pasture abandonment and the formation of a surrounding secondary forest.

Conclusions: Results indicate that remnant trees facilitate forest recovery over a broad temporal range, and appear to ‘nucleate’ forest regeneration by expanding their sphere of influence outward over time.