Trend to increasing structural diversity in German forests: results from National Forest Inventories 2002 and 2012

Abstract

Key message: Six structural diversity indices were calculated from the German 2002 and 2012 National Forest Inventory (NFI) data. We found a slight trend of increasing structural diversity in German forests both for broadleaved and coniferous stand types. The results correspond well with current findings in forest ecology and silviculture and might serve as an initial step for further refinement of NFI analyses. Context: Structural diversity, i.e., the variability in forest stand structures, is an integral part of current forest ecology discussions. We addressed the question of whether the scope of the German National Forest Inventory (NFI) can be widened by evaluating structural diversity indices. Diversity indices are neither an explicit subject of the current NFI protocol nor have they been derived from NFI data yet. Aims: Six spatially inexplicit indices were applied to NFI data and methodologically discussed. An initial contribution for further methodological refinement of the NFI should be provided. Using these indices, changes in structural diversity between 2002 and 2012 were subsequently quantified and discussed. Methods: Mean values and changes of the diversity indices were calculated for indicative forest stand types using tree data from angle count sampling. Estimation techniques for single stage cluster sampling were applied. Results: With few exceptions, the results showed slight increases for each index and stand type. The results correspond well with current findings in forest ecology and silviculture and supplement published results of the NFI. Conclusion: The indices proved to be appropriate within the framework of the NFI. This study should be considered as a cornerstone that supplements published results of the German NFI. It might be helpful within future discussions about structural diversity in German forests.