Three dimensional tree and gap architecture affected by forest managemen t- A comparison of different forest types in the Pacific North West, USA based on terrestrial laser scanning

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Until the Northwest Forest Plan came into effect in 1993 the US area covered by old-growth forests has been decreasing in an alarming rate. Douglas-fir (Pseudotzuga menziesii (Mirbel) Franco) as one of the economically most important tree species of the Pacific North West was planted after clear-cutting and monospecific even-aged stands replaced the ancient forests. Today, silviculture in the US is undergoing a change in the management paradigm. Alternative silvicultural regimes have been proposed in order to create stand structures resembling old-growth features which are believed to provide ecosystem services and functions, such as habitat diversity, aesthetics for recreation purposes and may enhance ecosystem resilience and stability. However, along with increasing complexity in horizontal and vertical structures of forests the growing conditions of trees become more heterogeneous. The first part of the proposed study will evaluate whether or not the applied management practices actually resulted in more complex spatial structures which resembles the spatial complexity of old-growth forests. This question will be answered by a comparison of tree/crown structures in old-growth and young managed stands. Terrestrial laser scanning will be used for a three-dimensional assessment of structural parameters that characterize the comprehensive spatial aspects of complexity in forests. Old-growth forests, traditional production oriented stands and plantations which had explicitly been managed towards more structural diversity will be contrasted in order to identify differences in their spatial structure, e.g. vertical layering of the canopy and crown profiles of individual trees. The second part of the study aims at comparing tree/crown structures in edge versus stand interior trees. It will be investigated if altered forest structure and growing conditions result in significant changes in tree habitus, crown profiles, and related wood quality attributes such as branchiness. As gaps play an important role in the management for spatial complexity, the size and shape of gaps are of special interest. Gaps will be measured in all three dimensions using terrestrial laser scanning and will be related to the tree and crown shape and external attributes of wood quality of adjacent trees.The main goal of the proposed study is to test the suitability of artificial gaps aiming at resembling the spatial structure of old-growth forests in plantations. Furthermore, it will be qualitatively described how management for complexity affects the shape and external attributes of wood quality of the remaining trees. Finally, the study will derive suggestions on how to design silvicultural measures which may balance the two possibly diverging management goals: structural diversity and high quality timber production.