Tree species richness influence productivity and anatomical characteristics in mixed fir-pine-beech forests

Abstract

Tree species richness (SR) and stand structural diversity (SSD) have general positive influences on stand productivity, while several studies highlight the remaining uncertainty in our knowledge of the relationships among productivity, species richness and structural diversity. Moreover, our knowledge about how SR influences anatomical cell characteristics is still limited. This study examined if stand productivity was influenced by SR and SSD by comparing the productivity of three forest types; (i) pure Trojan fir (Abies nordmanniana subsp. equi-trojani) forest, (ii) mixed Trojan fir-Scots pine (Pinus sylvestris L.) forest, and mixed Trojan fir-Scots pine-Oriental beech (Fagus orientalis L.) forest. Moreover, the study also monitored if SR and SSD affected the anatomical characteristics of fir trees in these forest types. Linear mixed-effect models were utilized to observe the relationships among species richness, stand characteristics and productivity. Stand density index, SR, and an interaction (SR × SSD) had significant effects on stand productivity. This was likely due to the complementary resource use among tree species in the mixed forests where more stratified canopies due to varying levels of shade tolerance and tree growth rates were present. Significant relationships between species richness and anatomical cell characteristics of fir were also explored. The findings of this study will enhance our understanding of species diversity controls in stands comprised of fir, pine and beech.