sommerfeltia 16 R.H. 0kland & 0. Eilertsen Vegetation-environment relationships of boreal coniferous forests in the Solhomfjell area, Gjerstad, S Norway 1993 r(,;7 sommerf~ is owned and edited by the Botanical Garden and Museum, University of Oslo. SOMMERFELTIA is named in honour of the eminent Norwegian botanist and clergyman S(2!ren Christian Sommerfelt (1794-1838). The generic name Sommerfeltia has been used in (1 ) the lichens by Florke 1827, now Solorina, (2) Fabaceae by Schumacher 1827, now Drepanocarpus, and (3) Asteraceae by Lessing 1832, nom. cons. SOMMERFELTIA is a series of monographs in plant taxonomy, phytogeography, phytosociology, plant ecology, plant morphology, and evolutionary botany. Most papers are by Norwegian authors. Authors not on the staff of the Botanical Garden and Museum in Oslo pay a page charge of NOK 30. SOMMERFELTIA appears at irregular intervals, normally one article per volume. Editor: Rune Halvorsen 0kland. Editor of this volume: Per Sunding. Editorial Board: Scientific staff of the Botanical Garden and Museum. Address: SOMMERFELTIA, Botanical Garden and Museum, University of Oslo, Trond­ heimsveien 23B, N-0562 Oslo 5, Norway. Order: On a standing order (payment on receipt of each volume) SOMMERFELTIA is supplied at 30 % discount. Separate volumes are supplied at the prices indicated on back cover. sommerfeltia 16 R.H. 0kland & 0. Eilertsen Vegetation-environment relationships of boreal coniferous forests in the Solhomfjell area, Gjerstad, S Norway 1993 Publication from the TVLF (Supplies and Effects of Long-Distance Airborne Pollutants) programme of NMF (National Committee for Environmental Research): the project "Effects of Long-Distance Airborne Pollution on Boreal Coniferous Forest Vegetation". Publication No. 27 from TOV (Terrestrial Monitoring Programme of the Directorate for Nature Management). ISBN 82-7420-018-7 ISSN 0800-6865 0kland, R.H. & Eilertsen, 0. 1993. Vegetation-environment relationships of boreal coniferous forests in the Solhomfjell area, Gjerstad, S Norway. - Sommerfeltia 16: 1-254. Oslo. ISBN 82- 7420-018-7. ISSN 0800-6865. The understory vegetation (vascular plants, bryophytes and lichens) in an area dominated by boreal coniferous forests is subjected to detailed ecological analysis. Two hundred meso 2 sample plots (1 m ) are used as basis for vegetation sampling, and provided with measurements of 33 environmental variables. Species abundance is recorded as frequency in 16 subplots. Parallel DCA and 2-dimensional LNMDS ordinations of meso sample plots were largely identical, both provided two coenocline axes interpretable in ecological terms. The first axis is interpreted as the response to a broad-scale topographical complex-gradient, made up of two independent complex-gradients; (1) a topography-soil depth complex-gradient in the pine forest (running from lichen-rich pine forests to submesic Vaccinium myrtillus-dominated spruce forests), and (2) a complex-gradient in soil nutrient status in the spruce forest. The second axis, mainly affecting the species composition of the bottom layer, is interpreted as a fine-scale paludification gradient. The causes of variation along these gradients are discussed: Desiccation tolerance is considered to act directly on the physiology of vascular plant species, setting their limits towards xeric sites. Similarly, cryptogams with optima in the more mesic sites are considered to be excluded from drier sites by physiological tolerance. Limits of cryptogams towards more mesic sites are, however, considered to be set by competitive ability (growth rates) in accordance with the competitive hierarchy theory. N availability is assumed to be the most important factor for differentiation of vascular plants along the nutrient gradient, while bryophytes are expected to respond to a complex of factors, including structural properties of the humus layer. Increasing N accumulation in the humus towards xeric sites may indicate oversaturation due to deposition of airborne N03- or NH/. Fine-scale paludification, mainly of a soligenous type, occurred in sloping terrain with shallow soil. The cryptogams apparently make up a competitive hierarchy also along the paludification gradient. No other coenoclines could be identified by analysis of 0.0625 m2 micro sample plots, most probably because the response of vegetation to micro-scale environmental gradients (probably most important: the variation in microtopography) not essentially different from the meso-scale gradients, and because the importance of random processes increase towards finer scales. Structuring processes are discussed with reference to the observed patterns. The lack of a closed bottom layer in almost all sample plots is considered a strong indication of high importance of fine-scale disturbance and density-independent mortality in the investigated system, while interspecific competition is of lower importance. The methodology in vegetation ecological studies is discussed with particular reference to monitoring. The potential of an integrated concept using permanent plots, parallel investigation of vegetation and environmental parameters, and gradient analysis, is stressed. Several suggestions for future studies, based on this integrated approach, are made. Keywords: Boreal coniferous forests, DCA, Environmental factors, Gradient, LNMDS, Monitoring, Norway, Ordination, Vegetation. Rune H. (Jkland & Odd Eilertsen, Botanical Garden and Museum, Univ. of Oslo, Trondheimsvn. 23B, N-0562 Oslo, Norway. 4 SOMMERFELTIA 16 (1993) CONTENTS INTRODUCTION . 8 THE INVESTIGATION AREA . 12 GEOLOGY AND GEOMORPHOLOGY 12 CLIMATE 14 CONSERVATIONAL STATUS, FOREST HISTORY AND HUMAN INFLUENCE 15 PHYTOGEOGRAPHY 16 PREVIOUS INVESTIGATIONS IN THE AREA 16 MATERIALS AND METHODS ................................. 17 THE SAMPLING DESIGN 17 RECORDING OF VEGETATION 18 RECORDING OF ENVIRONMENTAL VARIABLES 19 Background information and tree measurements 19 Macro scale variables 21 M eso scale variables 22 M eso scale humus layer variables 24 DATA MANIPULATION: TRANSFORMATION OF ENVIRONMENTAL VARIABLES 24 CLASSIFICATION OF VEGETATION 25 Terminology and basic assumptions 25 Classification of the vegetation of the investigation area by the direct · gradient approach 25 Basic assumptions 25 Separation of site-types 26 Site-types codes 26 Description of site-types: material and presentation 26 ORDINATION OF VEGETATION 27 Ordination methods 27 Comparison of ordination results 27 RELATIONSHIPS BETWEEN ENVIRONMENTAL VARIABLES 28 Correlation analysis 28 PCA ordination 28 RELATIONSHIPS BETWEEN VEGETATION AND ENVIRONMENTAL VARIABLES. INTERPRETATION OF ORDINATION RESULTS 28 Correlation analysis 28 Visual aids to inte,pretation of ordination diagrams 28 Variation in species abundance along DCA axes 29 NOMENCLATURE AND TAXONOMIC NOTES 29 SOMMERFELTIA 16 (1993) 5 RESULTS .................................................... 31 CLASSIFICATION 31 The classification system 31 Differentiation of site-types 34 The topoghraphic moisture gradient 34 The gradient in nutrient status 35 The gradient in fine-scale moisture 35 RELATIONSHIPS BETWEEN ENVIRONMENTAL VARIABLES 35 Correlation analysis 35 PCA ordination 38 RELATIONSHIPS BETWEEN BIOTIC VARIABLES 44 ORDINATION OF THE MESO SAMPLE PLOTS: THE FULL SPECIES COMPOSITION 44 Characteristics of the ordinations 44 DCA 44 LNMDS, two-dimensional solution 48 LNMDS, three-dimensional solution 48 Correlations between ordination axes and environmental variables 48 DCA 48 LNMDS, two-dimensional solution 53 LNMDS, three-dimensional solution 53 Comparison of ordinations 53 Interpretation of the DCA ordination by means of the classification into site-types 54 Interpretation of the DCA ordination by means of the environmental variables 54 Vector fitting 56 Variation of environmental variables 56 Correlations between the ordination axes and environmental variables within Subsets A and B 80 Interpretation of the DCA ordination by means of the biotic variables 81 Variation in species abundances along the axes of the DCA ordination 89 ORDINATION OF THE MESO SAMPLE PLOTS: SUBSETS A AND B 120 ORDINATION OF THE MESO SAMPLE PLOTS: SEPARATE LAYERS 120 The field layer 120 The bottom layer 126 ORDINATION OF THE MESO SUBPLOTS 132 Characteristics of the ordination and correlation with axes of the sample plot ordination 132 Within meso sample plot variation in meso subplot scores 133 ORDINATION OF THE MICRO SAMPLE PLOTS 133 PASSIVE ORDINATION OF THE MICRO SAMPLE PLOTS 135 DISCUSSION ................................................. 138 ORDINATION METHODS: DCA OR LNMDS? 138 ENVIRONMENTAL INTERPRETATION OF GRADIENTS IN VEGETATION 139 6 SOMMERFELTIA 16 (1993) Division of the main, broad-scale topographic gradient 139 Pine forests: the topography-soil depth complex-gradient and its relation to soil moisture deficiency 139 Variation in nutrient content and associated variables along the gradient 139 Interpretation of soil moisture measurements and the soil moisture deficiency hypothesis 140 The response of vascular plants to soil moisture deficiency 143 Vascular plants along the topography-soil depth complex- gradient: relevance of pattern to process 143 The response of bryophytes and lichens to soil moisture deficiency 144 Bryophytes and lichens along the topography-soil depth complex- gradient: relevance of pattern to process 145 Spruce forests: the complex-gradient in nutrient status 146 Variation in environmental variables along the gradient 146 Factors controlling the nutrient status of the humus layer 147 The response