“New Type” Forest Declines and Restabilization/Revitalization Strategies

Abstract

Annual terrestrial inventories carried out in West Germany since 1984 indicate that for the last 4 yr approximately 50% of the forests were damaged. The damages were and are commonly attributed to the adverse effects of acid rain and other air pollutants. As most decline types are associated with nutritional disturbances, it was found that the application of lime and/or fertilizers could reduce or even remove the damages. Therefore, the West German government has established a nationwide program by which up to 80% of the costs of fertilization in forests revealing “new type” forest damages are subsidized. In practice, a clear distinction is made between compensative and ameliorative fertilization methods. Compensative fertilization means the application of Mg containing lime (generally 3,000 kg·ha^-1) to neutralize further acidic deposition in forest soils. The ameliorative fertilization is focused on the specific application of nutrients, particularly in stands with acute nutritional deficiencies. This is accomplished by means of readily soluble Mg and K fertilizers at application rates of 500 to 1,000 kg·ha^-1. In cases of insufficient P supply or for the activation of microbial decomposer chains in organic top soil horizons, P fertilizers are utilized. For ameliorative fertilization, foliar and soil analyses are recommended as a sound basis for fertilizer selection. In many cases, particularly in the States of Bavaria and Baden-Wuerttemberg, Mg containing lime in combination with fast soluble Mg and/or K (P) fertilizers are applied. Between 1984 and 1987, approximately 400,000 ha of “new type” forest damage areas have been limed and/or fertilized in West Germany. As positive as the application of lime and/or fertilizers appear to be, there exists some potential risks and limitations of these practices with regard to restabilization and revitalization of declining forestt stands.