The role of forest stand structure as biodiversity indicator

Biodiversity conservation is a key objective for sustainable forest management, but the multi-dimensional and multi-scale character of biodiversity renders full assessment difficult at large scale. Therefore, indicators are often used to monitor biodiversity. Important cost-benefit synergies can be achieved if indicators are derived from existing data. In this study, a model for classifying forest stand structures was developed and tested as an indicator of overall plant species diversity at stand level. The model combines four stand structure parameters: canopy coverage, age of canopy trees, tree species composition and canopy stratification. Using data from the National Inventory of Landscapes in Sweden and General Linear Mixed Model, plant species diversity (Shannon diversity index, SHDI) and composition (Sorensen-Dice index, SDI) were tested between 26 different stand structure types and nine soil classes. The results showed that mature stands with a stratified canopy had the highest plant species diversity across the soil classes, particularly if they comprised mixed coniferous and broadleaved species with a semi-open canopy. In contrast, young (<30 years) single-layered stands had consistently low species diversity. Of the four stand structure parameters in the model, age of canopy trees was most influential for SHDI value, followed by canopy stratification, tree species composition and canopy coverage. According to the SDI values, different stand structure types represented different species composition regardless of soil class and species diversity (SHDI value). However, most SDI values were higher than 0.5, indicating that fewer than 50% of the species changed between stand structure types. The stand parameters included in the model can probably be extracted from national forest inventories in many countries and understood without specialist taxonomic knowledge, making the model applicable in practice to support forest management decision-making on enhancing forest biodiversity at stand level. (C) 2014 Elsevier B.V. All rights reserved.