6.1 Conservation of understorey and ground-nesting forest bird
Forest disturbance and the consequent forest margin areas can ameliorate the determinant factors which are responsible for predation pressure such as edge effects, predator composition and abundance, vegetation structure, persistence of top predators and human activities. These factors may play important role on predation pressure in forest margin habitats which furthermore, might be a serious threat for forest bird populations. Since many bird species are poorly adapted for increased predation pressure in these habitats (Gates and Gysel 1978; Sieving 1992; Laurance 1993), forest margin areas accompanied with high predation risk tend to be “ecological traps” for those birds. If nest predation acts in performance with the other crucial factors like food and climate, a relatively small increase in nest predation could cause extinctions of bird populations (Wilcove, 1985).
Since nest predation is an important process affecting the local demography of nesting birds and potentially of avian populations, understanding the factors affecting predation rates could contribute to conservation approaches for forest bird populations (Chalfoun et al., 2002).
It is clear that the most detrimental effects of forest destruction emerged along edges and forest margin areas suffered the high predation rates in this region. Increased amount of edges may contribute to the exposure of bird nests to a variety of nest predators. Results of this study are in agreement with those of other studies indicating the occurrence of edge effects on predation rates of shrub nests. With increased connection to agricultural fields, transients and dirt road, the influx of introduced nest predators from surrounding areas such as house rats, feral cats and dogs, would be more pronounced. It was found that forest margin may host a variety of nest predator communities including marsupials and squirrels which were absent in natural forest.
The vegetation structure is also changing over time and understorey layers in forest margin habitats is gradually decreasing due to the intensive activities of humans. Sparse vegetation cover in these areas may reduce nest concealment and support the strategies of different predators to find bird nests. Reducing over-harvesting on forest resources and allowing the
vegetation to recover along forest margin areas may result in sufficient cover and lower detectability of shrub nests from nest predators.
The absence of top predators in forest margin areas may indirectly lead to the decline of bird populations, because they play an important role in regulating the number of small mammals which are responsible for high predation pressure. Conflict between wildlife and humans should be avoided, in order to maintain the persistence of top predators. Birds tend to successfully reproduce their offspring in conditions where the population of small mammals as mesopredators is regulated by the presence of top predators (Crooks and Soulé, 1999).
Even though artificial nests used in this study were neither defended by adult birds nor as well concealed as most natural nests, it is considered that the predator fauna detect and respond to artificial nests in a manner similar to natural nests (Gibbs, 1991). It means that all understorey birds nesting with open-cup form on the shrub or fork of the trees along edges and forest margin habitats, such as Black-naped Monarch and Yellow-bellied white-eyes, will be affected by the high predation rates.
Most understorey bird species are still found in both forest margin habitats and natural forest (Waltert et al., in prep.). However, their long-term persistence will largely depend on remaining forest habitats. Understorey birds are most sensitive to disturbances in forest structure, therefore they ought to be reliable indicators for forest regeneration (Wong, 1985). Many species of understorey and ground nesting birds occupying Palolo valley and Napu valley are endemic. Regarding the current management plans of Lore Lindu National Park, the endemism has been determined as one of the main criteria for conservation approaches. Knowledge about the effect of deforestation on nest predation may hopefully influence decisions about reserve design.
6.2 Land-use and park management
Considering the effects of forest disturbance and habitat alteration on predation pressure, the current and on-going land-use occurring and emerging in these parts of protected area should be managed appropriately. Several efforts may be crucial when designing land management policies in order to reduce the size of forest edges. The extension of land-use
such as coffee plantation and forest garden may reduce the intact forest and threaten the viability of natural habitats for forest birds. Because the interspersion of habitat with land-use may provide additional sustenance for nest predators (Chalfoun et al., 2002), it is therefore of crucial importance to make restrictions for land owners and farmers continuing clear-cutting and opening natural forest in the park areas.
In Lore Lindu National Park, the existence of vertebrate fauna have been surveyed and monitored to support the design of park zoning (TNC, 2002). It was found that understorey and ground-nesting birds also inhabit forest margin areas and several forest bird so-called edge species, still use this area for breeding and foraging. When the assessment for park management is undertaken based on this knowledge only, forest margin habitats could be categorised as suitable areas for the forest birds. However, forest margin areas including edges could not provide suitable and viable habitats for understorey forest birds, because of elevated nest predation and subsequent ecological traps. It is clear that the creation of habitat edge by partial clearing of forest for human land-use may have negative consequences for birds breeding in remaining forest patches (e.g. Kroodsma, 1984; Piper et al., 2002). Therefore, the knowledge of interaction among vertebrate fauna (in this case, nest predation) and the effects of habitat disturbance on this ecological process should be considered as important aspects for National Park management.
Since the intensive human activities are correlated positively to the elevated predation rates along forest margin areas, particular attention should be given to managing the interaction between local people and protected areas. Clear and detailed information about National Park boundaries and zoning should be delivered to local people living in the surrounding these areas. Furthermore, law enforcement from National Park authorities might play important role in reducing the extension of land-use practices within the park areas.
Natural forest can provide "source habitat" for forest bird populations. It is therefore important that contiguous areas of natural forest should be left intact. These areas as core zone is ideally the most important zone for maintaining biological diversity. In terms of park zoning, it is better that reserves of natural forest should be surrounded by areas of managed forest than by farmland (Collins et al, 1991). Agroforestry systems might be one among other available alternatives that can be used as a buffer zone in managing the park area which may integrate the existence of local people living in areas surrounding
protected areas. If the existing forest margin habitats can be managed properly, they may be used as a buffer zone to preserve the core zone of protected areas from intense activities of humans. Since forest margin areas and buffer zones of the National Park constitute significant elements in management plans, the results of this study could be considered as a contribution to land-use management both within and surrounding the protected areas. In turn, this can facilitate better sustainable management practices at Lore Lindu National Park for the benefit of both wildlife and humans.