The Framework Species Approach to Forest Restoration: Using Functional Traits as Predictors of Species Performance.

Abstract: Due to forest degradation and loss, the use of ecological restoration techniques has become of particular interest in recent years. One such method is the Framework Species Approach (FSA), which was developed in Queensland, Australia. The Framework Species Approach involves a single planting (approximately 30 species) of both early and late successional species. Species planted must survive in the harsh conditions of an open site as well as fulfilling the functions of; (a) fast growth of a broad dense canopy to shade out weeds and reduce the chance of forest fire, (b) early production of flowers or fleshy fruits to attract seed dispersers and kick start animal-mediated seed distribution to the degraded site. The Framework Species Approach has recently been used as part of a restoration project in Doi Suthep-Pui National Park in northern Thailand by the Forest Restoration Research Unit (FORRU) of Chiang Mai University. FORRU have undertaken several trials on species performance in the nursery and the field to select appropriate species. However, this has been time-consuming and labour intensive.

It has been suggested that the need for such trials may be reduced by pre-selecting species using their functional traits as predictors of future performance. Here, seed, leaf and wood functional traits were analysed against predictions from ecological models, such as the CSR Triangle and the pioneer concept, to assess the extent to which such models describe the ecological strategies exhibited by woody species in the seasonally-dry tropical forests of northern Thailand.

Seed storage behaviour (orthodox and recalcitrant) was strongly linked to other functional traits and this was the basis of observed differences in performance based on seed size. There was evidence for the existence of a leaf economic spectrum in these forests and for differing positions of deciduous and evergreen species on this spectrum. Wood hydraulic capacity and safety were more strongly linked to leaf traits than wood mechanical strength was; reflecting the importance of seasonal drought in this type of forest.

Selected functional traits were then used to predict the performance of species within the FORRU project. A combination of wood and leaf traits, which encompassed mechanical strength, hydraulic capacity and water storage, best described species growth rates in most years. Survival may be linked to a combination of both drought and pathogen load, which differs by year, due to environmental conditions.

In conclusion, functional traits were found to be valuable indicators of performance in forest restoration projects.