Growth and development of the root system of Norway spruce (Picea abies) in forest stands -: a review

The present article portrays root growth and root system development with special reference to Picea abies. Root phenology and ontogeny are depicted, and the biological responses of the roots to adverse growing conditions appraised. Norway spruce is regarded as a species which is able to grow under a wide range of soil physical and chemical conditions, provided sufficient soil aeration is guaranteed. The root system of spruce is however sensitive to any dislocation of its primary taproot. Nursery handling and planting damage often affect the root system development of the young tree. Soil acidity and Al-toxicity represent other significant restraints to root growth of spruce. Rooting patterns and mycorrhizal communities are influenced by atmospheric deposition of nitrogen and acidity. Root system spread is closely related to the tree's competitive status in the forest stand and responds to forest management practices. The preference of Norway spruce roots for humus-rich soil horizons and patches is repeatedly reported. Though, a general characterisation of P abies as a primary 'surface-rooter' has been disproved. Different structures and functions of long and short roots can be identified. Periodic shedding of small and fibrous root structures is a natural phenomenon and is influenced by ambient (i.e. climatic) conditions. Nonetheless, adverse growing conditions result in an increased frequency of adventitious root formation. Permanent root system damage will occur when such root replacement strategies fail. The resulting occurrence of root derangement points and the loss of ramification orders, advances from the fine- to the coarse-root structures. The result is an irregular arrangement of the structural root system, with increasing frequency of damaged roots and disturbance of the root system symmetry. Damaged coarse roots are characterised by discolouration following decay. A damage class scheme for Norway, spruce that depicts general stages of root system vitality and decay is provided. The work illustrates that root parameters are good indicators of the sustainability of forest sites. (C) 2002 Elsevier Science B.V. All rights reserved.