Natural forest succession on human‐disturbed lands is often slow because the resources necessary for succession are depleted. In such landscapes, forest succession may be dependent on arrival of seeds from off‐site, many of which are dispersed by fruit‐eating animals. We studied bat and bird seed dispersal in a deforested agricultural area adjacent to Kibale National Park, Uganda. Seed rain was monitored for 6 mo in short (<0.5 m) and tall (2–5 m) grassland, and below short (1–3.5 m), medium (3.5–10.0 m), and tall (≥10.0 m) isolated trees within grassland. Seed rain (numbers of seeds and seed species) under trees of all heights was greater than in short or tall grasslands. Bats dispersed seeds mostly below tall trees, while birds dispersed seeds mostly below both tall and midsized trees. More seeds and seed species were dispersed under tall trees than below short trees. Within 150 m of the forest there was no relationship between the seed rain under trees and the distance to the forest edge. Nearly half of the >11200 seeds collected were from hemi‐epiphytic Ficus that are unable to grow from the ground. One‐third of collected seeds were from shrubs, and most of the remainder were from trees. Nearly all tree and shrub seeds collected (>99%) were species typically found in disturbed grassland, not in forest. These results suggest that in this African region, forest succession may proceed very slowly on degraded lands.

Forest succession on degraded tropical lands often is slowed by impoverished seed banks and low rates of seed dispersal. Within degraded landscapes, remnant forests are potential seed sources that could enhance nearby forest succession. The spatial extent that forest can influence succession, however, remains largely unstudied. In abandoned agricultural lands in Kibale National Park, Uganda, recurrent fires have helped perpetuate the dominance of tall (2–3 m) grasses. We examined the effects of distance from forest and grassland vegetation structure on succession in a grassland having several years of fire exclusion. At 10 and 25 m from forest edge, we quantified vegetation patterns, seed predation, and survival of planted tree seedlings. Natural vegetation was similar at both distances, as was seed (eight species) and seedling (six species) survival; however, distance may be important at spatial or temporal scales not examined in this study. Our results offer insight into forest succession on degraded tropical grasslands following fire exclusion. Naturally recruited trees and tree seedlings were scarce, and seed survival was low (20% after 7 mo). While seedling survival was high (95% after 6 to 8 mo), seedling shoot growth was very slow (x̄= 0.5 cm/100 d), suggesting that survivorship eventually may decline. Recurrent fires often impede forest succession in degraded tropical grasslands; however, even with fire exclusion, our study suggests that forest succession can be very slow, even in close proximity to forest.

One of the greatest challenges for ecologists this century will be restoring forests on degraded tropical lands. This restoration will require understanding complex processes that shape successional pathways, including interactions between trees and other plants. Shrub species often quickly invade disturbed tropical lands, yet little is known about whether they facilitate or inhibit subsequent tree recruitment and growth. We examined how shrubs and other vegetation (e.g., vines, grasses, herbs) affect tree recruitment, survival, and growth during the first 6 years of forest succession in Kibale National Park, Uganda. The study was undertaken in two recently logged exotic softwood plantations. We studied the successional trajectories in two recently logged areas that varied in their initial densities of trees and shrubs. Analyses suggested tree seedling presence and density were not strongly related to shrub density or height during succession. Tree sapling presence and density were positively significantly related to shrub density and height. We found little response in the tree community to experimental shrub removal, and although removal of all nontree vegetation temporarily enhanced tree growth, the effect disappeared after 2 years. Some early‐successional trees benefited from reduced competition, whereas some mid‐successional trees benefited from the presence of other vegetation. Some specific tree species responded strongly to vegetation removal. We interpret our findings in light of designing manipulations promoting forest restoration for biodiversity conservation and conclude with four tentative guidelines: (1) manage at the species level, not the community level; (2) increase facilitation for seedlings, reduce competition for saplings; (3) be cautious of assumptions about plant interactions; and (4) be adaptable and creative with new strategies when manipulations fail.

This paper reviews the mechanisms that limit animal-mediated seed dispersal during forest succession on degraded tropical lands. These limitations are illustrated with examples from Kibale National Park in Uganda, and the findings are related to the work done throughout the moist tropics. Several proposed strategies to overcome seed dispersal and recruitment limitations on degraded lands are proposed. The principles discussed are relevant to forest succession in other tropical and temperate regions.

Reports of tool usage by birds tend to be anecdotal as only a few individuals may be involved and the behaviour observed can often be interpreted in other ways. Here we describe the widespread collection of mammalian dung by burrowing owls (Athene cunicularia) and show that they use this dung as a bait to attract dung beetles, a major item of prey. Our controlled investigation provides an unambiguous estimate of the importance of tool use in a wild animal.