The relationship between plant diversity and aboveground biomass in managed and unmanaged temperate forests

In face of climate change and global scale biodiversity loss, assessing the relationship between biodiversity and forest ecosystem functioning is essential, but poorly investigated in temperate forests of Iran. We examined plant diversity aboveground biomass relationships in unmanaged, and forests managed with a single-stem selection system in the Hyrcanian forests ecoregion in Northern Iran. Also, the effect of single-stem selection system on soil nutrient and plant species diversity of tree layer was investigated. Linear models were used to analyze the effect of management and soil characteristics on aboveground biomass and tree layer attributes. Moreover, the relationships between aboveground biomass and plant species diversity metrics and soil characteristics were investigated using simple linear and multiple linear regression analysis by using regression analysis. We found that tree layer species richness and Shannon diversity were significantly higher in managed forests compared to unmanaged forests. While simple regression analysis revealed no effect of tree layer diversity and soil characteristics on aboveground biomass, multiple regression analysis showed that the main positive driver of aboveground biomass was soil nitrogen content (or its equivalent soil organic carbon). These findings indicate that from a biodiversity point of view, the single-stem selection system can be considered a sustainable forest management approach in Hyrcanian forests because it has positive effects on tree layer diversity. This is probably driven by increased habitat heterogeneity and light availability at forest floor through cuttings, while keeping cutting intensity at a level that is too low to significantly affect tree biomass. While the relationship between soil nitrogen and biomass was positive, we found no relationship between species diversity and biomass. Finally, assessment of relationship between biomass and plant species diversity and other underlying factors such as soil nutrients can be considered an important tool to conserve and manage ecosystem services.