The Role of Isolated Trees in Facilitating Tree Seedling Recruitment at a Degraded Sub‐Tropical Rainforest Site

Abstract

Successional development at abandoned farmlands in southern Queensland, formerly occupied by sub‐tropical rain forest is centred around scattered, isolated trees. Soil seed banks contain few woody plants and most tree species appear to be recruited from seed dispersed into the site by birds or bats. Scattered, low‐growing trees <3 m in height act as the initial focus for the activities of seed‐dispersing birds, but this process is accelerated by the development of taller trees> 6 m in height that act as bird perches. The identity of these trees and whether or not they offer a fruit reward appears to matter less than their structure and suitability as a bird perch. The process of seedling recruitment may be accelerated when two or more trees form a cluster. The proportion of seedlings that survive and grow beyond 150 cm in height appears to be very small. Most of those that do can be classed as secondary rather than primary forest species, even though many primary forest species initially colonize the site. These observations were used to develop guidelines to accelerate the recovery of rainforest at degraded sites. The guidelines promote the early establishment of species that are usually poorly dispersed (e.g., large‐fruited species), planted in scattered clumps. The guidelines should be suitable for situations where relatively large areas are in need of rehabilitation.

Seed dispersal of woody plants in tropical forests: concepts, examples and future directions

“…Some bird and bat species move over and into open areas, where they deposit seeds mostly, but not exclusively, beneath isolated trees or other emergent structures (Duncan & Chapman 2002;Slocum & Horvitz 2000). Because abiotic conditions for seedling regeneration are better under isolated trees (Toh et al 1999), relatively high seed deposition in these areas can also be considered directed dispersal.…”

“…Studies have shown that seed rain is much greater beneath emergent structures such as isolated trees and snags (Duncan & Chapman 2002;Slocum & Horvitz 2000), because birds and bats are more likely to visit there (da Silva et al 1996). Seedling densities and diversities also tend to be higher in these areas (Toh et al 1999). This suggests that planting trees or adding artificial perches or other structures could enhance tree seed input and thus forest regeneration in degraded tropical areas, just as they do in some temperate systems (McClanahan & Wolfe 1993).…”

“…However, an experiment in which artificial perches were added to abandoned pasture found no difference in recruitment beneath them relative to nearby open areas (Holl et al 2000). It appears that microclimate differences beneath isolated trees are at least as important for tree regeneration as seed input (Toh et al 1999). As a result, establishment of some sort of preliminary woody cover, via plantations or other means, may be necessary to enhance both seed rain and seedling establishment of tropical forest species on degraded lands, and thereby jumpstart succession (Holl et al 2000;Wunderle 1997).…”

Role of nurse rocks on woody plant establishment in a South African grassland

“…We attribute this result at least partly to the perch effect, which leads to increased seed deposition by frugivorous birds because (1) most seedlings recorded at the edges of rocky outcrops and beneath E. crispa had characteristics associated with dispersal by birds (Table 1), and (2) it is known that tall structures receive more seed rain from bird-dispersed plant species than do short ones (Holl 1998, Toh et al 1999). For instance, Toh et al (1999) found that bird-dispersed seeds were more abundant under artificial perches that were 6 m tall than under 3 m tall perches.…”

Artificial roosts as seed dispersal nuclei in a cerrado area in Triângulo Mineiro, Brazil

“…The use of living trees, which are characterized as natural roosts, is also an efficient strategy in recruitment of seeds and seedling establishment (VIEIRA et al, 1994;TOH et al, 1999;CARRIÈRE et al, 2002) and can contribute to the restoration of degraded areas.…”