ASSESSMENT OF THE EXPOSURE AND LOADS OF ACIDIFYING AND EUTROPHYING POLLUTANTS AND OZONE, AS WELL AS THEIR HARMFUL INFLUENCE ON THE VITALITY OF THE TREES AND THE SPEULDER FOREST ECOSYSTEM AS A WHOLE J. W. ERISMAN RIVM, Laboratory for Air Research, P.O. Box 1, 3720 BA Bilthoven, The Netherlands G. P. J. DRAAIJERS TNO, Emission Assessment Department, P.O. Box 342, 7300 AH Apeldoorn, The Netherlands E. STEINGR ¨ OVER Agricultural Research Department of the Ministry of Agriculture, Nature Management and Fisheries (DLO), Institute for Forestry and Nature Research (IBN), P.O. Box 23, 6700 AA Wageningen, The Netherlands H. VAN DIJK and A. BOXMAN University of Nijmegen (KUN), Department of Ecology, Research Group of Environmental Biology, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands W. DE VRIES Agricultural Research Department of the Ministry of Agriculture, Nature Management and Fisheries (DLO), Winand Staring Centre (SC), Marijkeweg 11, 6700 AC Wageningen, The Netherlands (Received 28 October, 1996; accepted 8 May, 1997) Abstract. Within the framework of the Dutch Priority Program on Acidification, 10 yr of research was conducted in a Douglas fir stand at Speulder forest. Research was conducted to establish the loads and levels of acidifying and eutrophying pollutants and ozone, to determine forest vitality characteristics and follow growth parameters and nutrient status in time and to determine the effects of reduction of loads and levels by manipulation experiments. Results indicate that during the last 20 yr critical levels for air pollutants have hardly been exceeded except for ozone, which slightly affected assimilation. Elevated nitrogen deposition has caused several adverse effects including (i) inhibited mycorrhizal development, leading to a decreased base cation and phosphorus uptake; (ii) elevated foliage/root (fine and coarse) ratios, making the forest more sensitive to drought and windthrow; (iii) elevated nitrogen and arginine concentrations in the foliage, associated with relative base cation and phosphorus deficiency, and (iv) elevated nitrate leaching polluting the groundwater. High inputs of acidity have caused elevated ratios of Al to base cations, affecting fine root (uptake) and depletion of the readily available Al pool, thus affecting the long-term sustainability. Despite these effects, forest vitality, in terms of defoliation/discoloration, is reasonable and forest growth even increased in response to nitrogen. The exceedances of critical loads for nitrogen and acidity, however, implies a (large) risk for the long-term sustainability of the Speulder forest. Key words: acidification, assessment, eutrophication, Speulder forest, vitality 1. Introduction During the past ten years (1986–1995) research has been conducted at the Speulder forest at the Hoge Veluwe in the centre of the Netherlands. Most research was Present address: ECN, P.O. Box 1, 1755 ZG Petten, the Netherlands. Water, Air, and Soil Pollution 105: 539–571, 1998. c 1998 Kluwer Academic Publishers. Printed in the Netherlands. INTERLINIE: PC3:wate105-3/4:PDF-output:PIPS Nr.:142223 SPACKAP wate2091.tex; 7/07/1998; 13:39; v.7; p.1