Recent increases in the frequency and severity of large-scale disturbances due to climate change pose serious threats to biodiversity, ecosystem functions and the security of our societies. In particular, one of the most problematic large-scale disturbances under recent climate change is landslides. Forest restoration is becoming an increasingly important tool for mitigating climate change and conserving biodiversity and ecosystem function under recent disturbance regimes. According to the Biodiversity and Ecosystem Functioning (BEF) theory, diversity enhances ecosystem functions such as primary productivity. This relationship may be useful for more efficient reforestation after landslides. However, it is not well understood how BEF can be applied to landslide reforestation. This is because there are several limitations to previous research. First, until recently, most BEF studies have focused on grasslands rather than ecosystems as complex as forests. Second, previous BEF studies have used a field experimental approach using a common garden, whereas post-landslide studies use a field monitoring approach without replications at a stochastic and locally occurring landslide site. Thirdly, BEF research, particularly on the effects of species and genetic diversity on primary productivity, has been of recent interest, but there are no known cases of assessing the interactive effects of both species and genetic diversity, where genetic aspects of multiple species are assessed. Finally, knowledge of temporal changes in diversity effects is also very limited.
In order to integrate BEF knowledge and forest restoration application towards the development of efficient tools, we conducted experimental studies to overcome the above-mentioned problems. Experimental plots mimicking a landslide were constructed in the field under forest restoration conditions with species diversity manipulation of common forest tree species in Hokkaido, Japan. This experiment also uses the pool GBS method to quantify, rather than manipulate, the genetic diversity of all component species at the plot population level, in order to examine both species and genetic diversity effects.
Initially, increases in both species and genetic diversity resulted in reduced mammal damage and increased productivity. Furthermore, genetic diversity between species influenced the effects of species diversity on damage and productivity. However, the effect of species diversity changed from positive to negative a few years later. However, the effect of genetic diversity on species diversity effects was continuously positive. These results indicate the importance of considering genetic diversity effects across multi-species assemblages in future BEF studies. In addition, I would like to discuss other new findings from our experimental studies.