Assessing the influence of harvesting intensities on structural diversity of forests in south-west Germany

Felix Storch,Gerald Kändler,Jürgen Bauhus

doi:10.1186/s40663-019-0199-6

Abstract

BackgroundTo increase ecosystem resilience and biodiversity, the maintenance and improvement of structural and compositional diversity of forests has become an important goal in forest management for many forest owners and jurisdictions. At the same time, future harvesting intensity (HI) may increase to meet the demand for woody biomass by an increasing bioeconomy sector. Yet, the influence of HI on forest structural diversity is largely unknown. Here, we address this issue by analyzing the relationship between HI and structural diversity based on large-scale national forest inventory (NFI) data, where the latter is quantified using a previously developed Forest Structure Index and HI is expressed as wood volume removal during the period 2002–2012 for the same inventory plots.ResultsOur results show a surprisingly small impact of harvesting intensity on changes in structural diversity for most of the analysed types of forests. Only intense harvesting (> 80%–90% of initial growing stock) led to a significant reduction in structural diversity. At low to moderate HI most aspects of structural diversity were positively influenced. Only the quadratic mean DBH and the volume of large trees (≥ 40 cm DBH) were substantially negatively influenced at HI > 60% and 70% of initial growing stock, respectively.ConclusionsIn several forest types, HI could be increased without a reduction in overall structural diversity. Hence, structural diversity in these selectively managed forests appears to be a very resistant forest property in relation to HI. Other indicators at stand and landscape scale may be needed to adjust levels of HI that are suited to maintain forest biodiversity.

Highlights

To increase ecosystem resilience and biodiversity, the maintenance and improvement of structural and compositional diversity of forests has become an important goal in forest management for many forest owners and jurisdictions
Structural diversity index (FSI) Based on data of NFI2002 and NFI2012 for the state of Baden-Württemberg, an index to assess the level of structural diversity of forests was developed (Storch et al 2018) following the approach described by McElhinny et al (2006b) and modifications suggested by Sabatini et al (2015)
Mean harvesting intensity for the inventory period 2002–2012 varied surprisingly little for the different forest types analysed and was between 30% and 40% of the standing timber volume of NFI2002

Summary

Introduction

To increase ecosystem resilience and biodiversity, the maintenance and improvement of structural and compositional diversity of forests has become an important goal in forest management for many forest owners and jurisdictions. Lindenmayer et al 2000; Parrotta et al 2002; Kuuluvainen 2009) and there is a general concern that forest biodiversity and ecosystem functioning are negatively impacted by increasing harvesting intensity (Raison et al 2001; Bauhus et al 2017a; Urli et al 2017). While the status of unharvested forest reserves can be reasonably well described and defined, harvested forests can cover a wide range of harvesting intensities, ranging from clearfelling to single tree selection. These simple comparisons between unharvested and harvested forests provide little information on the influence of harvesting intensity on forest structure and biodiversity (Fig. 1)

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Conclusion