Functional and Morphological Diversity of Trees in Different Land Use Types along a Rainforest Margin in Sulawesi, Indonesia

Abstract

This work was conducted in Central Sulawesi, Indonesia, as a part of the German-Indonesian research project SFB 552, studying morphological, chemical and physiological leaf traits in sun leaves of mature trees in the four prevailing tree-based land use types: natural and secondary forest (NF, SF), forest garden (FG) and agroforestry system (AF). The interrelations between traits were analysed, as well as the degree of functional and morphological diversity among land use types and at intra- and interspecific level. Amax and gs were measured with portable porometer systems in an in-depth study comprising 60 trees of 19 selected species. The NF species showed the lowest mean Amax, 7.5 ± 3.7 mmol m-2 s-1, compared to 17.5 ± 3.3 mmol m-2 s-1 among SF species. The AF had a mean Amax of 13.2 ± 5.9 mmol m-2 s-1. The NF species also had the lowest mean gsmax among the three land use systems (NF: 368 ± 232, SF: 609 ± 205, AF: 521 ± 267 mmol m-2 s-1), whereas no significant difference in mean water use efficiency could be detected. The random sampling for assessment of chemical and morphological leaf traits included 354 mature tree individuals of 107 species occurring in four land use types and revealed i.e. that SF had the largest, roundest leaves, while AF showed the smallest leaves with highest specific leaf area (SLA). NF had relatively small, elongated leaves, with low SLA. NF and FG had the lowest P-concentration, AF intermediate and SF the highest. Foliar N-concentration was lowest in NF and FG, intermediate in SF and highest in AF. Generally, N had much less influence on leaf physiology in the studied species than often proposed, instead P was the more important factor in the studied sample. In the 19-species sample, covering three land use types, a combination of P and SLA gave the best prediction of leaf physiology. However, it was found that for a more precise prediction of leaf physiology partly different parameters should be used for gsmax and Amax and for different land use types. The main result of the analysis of the coefficient of variance for the studied leaf traits was that interspecific diversity was highest within NF for a majority of the included parameters. P showed higher variance than N within all land use types, except SF. Species with generalist life histories often had a higher variance in the studied leaf traits than other species. Additionally, different sampling designs for comparative leaf morphological and chemical studies were evaluated and various ways of identifying functional groups of the studied species were tested and discussed. A cluster analysis for division of the 107 studied species into ten given functional groups suggested that the functional diversity of tree species is considerable within both natural and secondary forest. Yet, if taking the coefficient of variance and life histories into account, it could be concluded that conversion of natural forest into agroforestry land or secondary forests leads not only to a reduction of taxonomic diversity, but also to a great loss of functional diversity and ecosystem reliability.