Performance of Mixed-Species Plantations Using the Rainforestation Farming System in Leyte Province, the Philippines

The Rainforestation Farming system is a community and smallholder-based form of mixed-species reforestation that has been trialled in the Philippines. Trials commenced in 1995 with the main objective of the system being to find forms of reforestation that provide economic benefits, conserve biodiversity and restore ecosystem functioning. About 100 different indigenous species of pioneer, fruit and Dipterocarp species and some exotic species were used to create 28 small-scale plantations. The main aim of the research presented in this thesis was to examine the performance of these plantations 10 years after their establishment in terms of the growth and biodiversity benefits. This information is then used to develop recommendations for future large-scale planting programs aimed at providing multiple-use benefits. The results showed that the 10 year old mixed species plantations had reached canopy closure with a high species diversity of understorey vegetation, many of which are popular food crops. The abundance of ground cover by litter and understorey vegetation found in these plantations meant lower rock and bare soil which will provide benefits for nutrient and water cycling, and reduce the likelihood of mudslides and erosion. The plantations had also developed a characteristic reverse-J size distribution of old growth forests and a 3-storeyed structure of natural tropical forests. We found 77 tree species at the mixed plantations. A higher productivity was found in stands that were younger and with a lower number of stems per ha that contained species with a lower wood density. The growth rate of individual light demanding trees at age 10 started to slow down in both diameter and height. Native tree species commonly considered by farmers and foresters to be slow growing trees, were found to grow as fast as some exotic species. Mixed-species plantations in Leyte did not achieve as high a growth rate as monocultures of a similar age. Tree density and tree species number of mixed species plantations remarkably declined at sites after 10 years of planting which was likely due to illegal harvesting, thinning, pruning, or death; resulting in a lower-than expected residual basal area. Although the initial species composition was determined by the planting design, after 10 years the plantations differed in their floristic composition. These differences could partially be explained by the differences in environmental conditions between sites. A performance dissimilarity among seven floristic community patterns of plantations related to environmental parameters such as stand age, topographic position, aspect, slope, soil depth and understorey vegetation cover. Soil type was not found to be a significant driver of differences in species composition. The relationship between biodiversity and the productivity of plantations was also examined. Both observed species richness and species evenness were not importantly related with the growth of stands, but functional species components (exotic and fast-growing species) were significantly positively related with on the production of stand in a homogeneous environment of small-scale plantings. However, when site characteristics were included in the mixed-effect model, productivity was not influenced by any measure of species diversity. At densities of 1400 trees/ha growth rates increased significantly; however, at stand densities of more than 3000 trees/ha growth rates decreased significantly. Finally, the Rainforestation Farming system in Leyte could not replace the kaingin system on former fallows and release pressure from primary and still close-to-natural secondary forests. However, the mixed species plantations have reached some ecological and economic goals. These plantations could meet the objectives of developing a multi-species planting including timber, fruit and other non-timber forest products. The mixtures included short-lived species able to generate an early income stream as well as longer-lived trees able to produce higher value timbers. The results from the study suggest that the cost of establishing future plantings could be reduced by initiating plantations with fewer species or using other silvicultural techniques to encourage the acquisition of natural biodiversity from the local area. The initial planting density at Rainforestation Farming sites was very high. At sites where this density was reduced subsequent to planting (e.g. through fire or illegal harvesting), higher productivity was usually achieved. An abundance and diversity of understorey plants and overstorey trees provided benefits of soil stability and increased levels of biodiversity in localized areas and across the landscape. Future research should address questions related to the plantation designs (e.g, matching species and sites) and silvicultural practices (e.g. thinning) as well as environmental impacts of this type of plantings to develop mixed-species plantations suitable for smallholders