Data and code from: Tree species identity effect on herb-layer species community distribution

The impact of canopy tree species identity on the distribution of herbaceous layer species is known to be influenced by various factors, such as light availability, soil structure and composition, and seedling competition. However, these relationships have been rarely demonstrated empirically across a wide range of species and large spatial areas.

We examined the response of 85 herb-layer species distribution to the cover of 108 tree species across 7255 sites in mainland France. By accounting for site characteristics and canopy diversity, we ensured that the associations between herbaceous and tree species were not a reflection of these factors. We then predicted the distribution of herbaceous species by considering these environmental factors and comparing them with the addition of individual tree species cover.

Our models revealed that tree species identity (using cover data) relationships are important for all herbaceous layer species. While all species benefited with information from tree species, we found that non-forest and open vegetation species were more sensitive to tree species identity. Moreover, generalist non-forest species were the most negatively impacted by them. Models also highlighted that tree species identity cannot be fully replaced by unidimensional functional tree groups based on trophic, dynamic, hydric, or Raunkiaer classification.

Our study emphasizes that incorporating tree species identity composition can enhance the prediction of herbaceous layer distribution at new sites. Consequently, we provide an empirical demonstration of successful improved prediction leveraging on species associations, which synthesizes various factors that are challenging to measure in situ.

Synthesis

Our study is an empirical evidence of the importance of tree species identity in shaping the distribution of the herbaceous layer, surpassing the effects of tree diversity alone. By considering the significance of tree species identity, we can improve forest management or the prediction of the spatial distribution of this herbaceous layer. Overall, this represents a significant advancement in understanding the herbaceous layer relationship with the tree layer.