C.M.A. Hendriks

Intensive monitoring of forest ecosystems in Europe: 1. Objectives, set-up and evaluation strategy

Abstract In order to contribute to a better understanding of the impact of air pollution and other environmental factors on forest ecosystems, a Pan-European Programme for Intensive and Continuous Monitoring of Forest Ecosystems has been implemented in 1994. Results of the Programme must contribute to a European wide overview of impacts of air pollution and the further development of its control strategies, being described in air pollution protocols. Objectives of the Intensive Monitoring Programme related to air pollution are the assessment of: (i) responses of forest ecosystems to changes in air pollution; (ii) differences between present loads and critical loads (long-term sustainable inputs) of atmospheric deposition; and (iii) impacts of future scenarios of atmospheric deposition on the ecosystem condition. Furthermore, the Intensive Monitoring Programme contributes to the assessment of ‘criteria and indicators for sustainable forest management’, such as the maintenance of forests as a net carbon sink to reduce the build up of atmospheric greenhouse gasses and the maintenance of species diversity of ground vegetation. The Intensive Monitoring Programme, which is carried out on approximately 860 selected plots, comprises monitoring of crown condition, forest growth and the chemical status of soil and foliage at all plots and monitoring of deposition, meteorology, soil solution and ground vegetation in a subset of the plots. In order to meet the major objectives of the Intensive Monitoring Programme, studies have been or are presently carried out with respect to the assessment of: (i) correlations between site and stress factors and the “forest ecosystem condition”; (ii) trends in stress factors and/or ecosystem conditions; (iii) critical loads, by evaluating the fate of atmospheric pollutants in the ecosystem with input–output budgets; and (iv) large-scale and long-term impacts of climate and deposition on forests and vice versa. Examples of those studies are given and the potential of the Programme to fulfil the objectives is evaluated.

Effects of acid deposition on Dutch forest ecosystems

Effects of elevated S and N deposition on the solution chemistry of Dutch forest soils are mainly manifested by increased concentrations of Al associated with increased concentrations of SO4 and NO4. Presumed critical Al/base cation ratios are often exceeded below 20 cm soil depth. There is also evidence that elevated N deposion during the last decades affected the forest nutrient status and caused large changes in forest vegetation. About half of the Dutch forests have absolute shortage of P and relative Mg deficiencies compared to foliar N contents. Evidence from field studies of a relationship between soil acidification and nutrient imbalances in the soil and the foliage on one hand and the vitality of forests on the other hand is, however, lacking.

Large scale impacts of acid deposition on forests and forest soils in the Netherlands

Since the early eighties, effects of acid atmospheric deposion have received much attention in the Netherlands. Effects of elevated S and N deposition on soil solution chemistry is mainly manifested by increased concentrations of Al associated with increased concentrations of SO4 and NO3. Presumed critical Al concentrations (0.2 molc m−1) and Al/Ca ratios (1.0 mol mol−1) are generally exceeded below 20 cm soil depth. There is also ample circumstantial evidence that elevated N deposion during the last decades affected the forest nutrient status and caused large changes in forest vegetation. About half of the Dutch forests have foliar N contents exceeding a critical limit (1.8%). Field evidence for a relationship between soil acidification and nutrient imbalances in the soil and the foliage on one hand and the vitality of forests (mainly expressed by defoliation class) on the other hand is, however, lacking. This result implies that an exceedance of critical acid loads, based on critical Al concentrations and Al/Ca ratios observed experiments in relation to effects on root (uptake), do not imply visible effects or even the dieback of forests.

Soil and Soil Solution Composition of 150 Forest Stands in the Netherlands in 1990

Publisher Summary During the period March to May 1990, the chemical composition of the humus layer, the mineral topsoil (0–30 cm), and the mineral subsoil (60–100 cm) has been determined for 150 forest stands. All stands were part of the national forest vitality inventory. They were all located on noncalcareous sandy soils. Tree species included were Scotch Pine, Black Pine, Douglas Fir, Norway Spruce, Japanese Larch, Oak, and Beech. Measurements for the humus layer and mineral topsoil included total contents of C, N, and P and exchangeable contents of H, Al, Fe, Ca, Mg, K, Na, and NH. Soil solution measurements in the mineral soil included the cations mentioned before and NO, SO, C1, HCO, and DOC. An important aim of the research was to assess the effect of deposition levels, tree species, and site characteristics on the level of A1 mobilization (acidification) and N accumulation (eutrophication) in the soil. Important characteristics of the chemical composition of the humus layer and mineral topsoil are presented.