The role of seed dispersal in the natural regeneration of rain forest after strip-cutting in the Peruvian Amazon

Abstract

Seed dispersal and forest regeneration were studied on a 30 × 150 m strip cleared by ‘strip-cutting,’ a system of forest management designed for sustained yield (Hartshorn 1989), in high terrace rain forest in the Department of Loreto, Peru. After one year the strip was dominated by seedlings of a few batand bird- dispersed pioneer tree species (Cecropia spp., Melastomataceae, and Alchornea triplinervia); stump sprouts from cut trees and saplings that survived the clearing were less numerous. The density of saplings (< 2 m in height) surviving the clearing was 903 per hectare; 94% of these survived the subsequent 18 months. About 30% of 417 stumps (< 7.5 cm diameter at breast height) resprouted within 3 months, with an additional 10% sprouting in the subsequent 10 months. Sprouting frequency was greater for small stumps than large and varied greatly among plant families. Seed deposition over this year was much lower in the interior of the strip, both in species richness and numbers of seeds, than within the forest; strip edges were intermediate in richness and number. The decline in seed input from forest to edge to strip, both in species and in numbers of seeds, was most pronounced for bird-dispersed taxa (primarily Melastomataceae); bat- and wind- dispersed taxa were more evenly distributed. The similarity in bat species composition between the strip and nearby primary forest was higher than the similarity in bird species composition between these habitats, reflecting a failure of many forest bird species to venture into the strip. The predominance of Cecropia spp. and other pioneers of minimal commercial value in the regeneration question the sustainability of strip-cutting. Subsequent succession and future tree species composition on the cleared strip will depend not only on the survivorship and growth of sprouts, survivors, and seedlings, but also on responses of different seed-dispersing animal taxa to changes in the species composition and structure of the vegetation in the strip.