Plant genetic diversity in tropical lowland rainforest transformation systems in Sumatra (Indonesia)

Abstract

Forest are covering globally 31 % of the terrestrial area. Tropical rainforests cover 5 % of the terrestrial surface and are biodiversity hotspots due to their high number of endemic species and high species richness. The agricultural expansion increases the deforestation rate in Indonesia to the highest worldwide. Main land-use change drivers in Indonesia are logging, mining activities and the production of rubber (Hevea brasiliensis) and palm oil (Elaeis guineensis), which leads to a forest conversion rate of 20 000 km2/ year. Whereas tropical rainforest are an important carbon storage, the global consequences of its conversion, can only be estimated. Local consequences are habitat loss and the fragmentation and degradation of the remnant forest areas. In remaining and degraded forest patches species diversity declines and species composition is altered. Investigations of single species regarding habitat fragmentation effects on genetic diversity of plants showed different responses depending on the specific life history traits of each species. In general, a loss of genetic resources is expected due to genetic drift, reduced gene flow caused by reduced connectivity of remaining forest patches and lower effective population size. This can lead to an altered genetic population structure of the fragmented species, which increases the probability of extinction. The habitat fragmentation effect on the genetic structure was until now only investigated for single species and not for plant communities. In addition, the effect of land-use change on the genetic structure of plants has not been investigated yet. The aim of this study was to estimate the genetic diversity of dominant plant species in four different agricultural intensities in Sumatra, Indonesia. Using the anonymous AFLP marker, the genetic diversity of ten dominant plant species, with ten individuals respectively, was investigated in four different systems: old growth tropical lowland rainforest, jungle rubber, rubber plantation and oil palm plantation. The four systems were investigated in two regions with four replicates, respectively, which leads to a total of 3200 samples collected in all plots. Due to different species compositions, characterized by different life history traits, a decline of genetic diversity from forest to jungle rubber to rubber plantation to oil palm plantation was expected. Two approaches were carried out, one considering all ten species as a community and second analysing single frequently dominant species. For the community based analysis, two analyses were carried out, one fragment pool approach, were all AFLP fragments of the occurring species were combined in one fragment pool and the differentiation was calculated. Moreover, a species approach, where genetic diversity was calculated for each species in all plots, respectively. To test for significant differences among the four systems a mixed effect model was fitted for both approaches. Furthermore, genetic diversity was correlated with the species diversity of plants, mycorrhiza and prokaryotes to test for similar responses to land-use change. For the species based approach frequently collected species were investigated regarding the genetic population structure and differentiation of populations (plots) within and among land-use systems and were grouped according to their life form. Results of the community analyses with fragment pool and species approach, indicate no direct correlation between genetic diversity of dominant plant species and land-use system. Nevertheless, land-use change caused a different species composition with different characteristics influencing genetic diversity and differentiation. The results identified two levels of genetic diversity, high diversity in the tree-dominated systems and low genetic diversity in the plantation systems. The species based analyses showed a high variability of the different species in their responses to land-use change. Forest species results indicate a loss of genetic diversity. The two plantation systems are dominated by invasive, colonizing species, which are adapted to disturbance. Thus, the mean genetic diversity level of the plantation plots were higher than expected. The fragment pool approach present an easy and flexible method to estimate the genetic diversity of different land-use systems. The provided results can be used to identify habitats of high conservational value and support conservational management plans of tropical forests.