Nutritional disturbances and histological changes in declining forests

Abstract

“New type” forest damages have been observed in West Germany since the mid-1970's and discussed in North America since the early 1980's. Various types of damage are associated with typical foliar discoloration symptoms related to site characteristic nutritional disturbances. The macronutrients are generally Mg, Ca, and K. Based on foliar and soil analysis results diagnostic fertilization trials were established at a wide variety of sites and stands in West Germany as well as in North America. The appropriate application of fast soluble fertilizers proved that damage symptoms associated with nutritional disturbances can frequently be mitigated within a relatively short period. The observed visual revitalization corresponds well with foliar analysis data obtained continuously for the last 5 yr. Soil analyses also reflect the improved nutrient supply. Investigations of older fertilizer trials indicated that stands fertilized before the appearance of “new type” damage symptoms are considerably more vital when compared to the untreated control plots. Remarkable results were derived from histological research. Microscopic analysis of needles proved the regeneration potential on a histological level for moderately yellowed needles after fertilization. Furthermore, needles of nutrient deficient trees reveal typical differences of tissue damages when compared to SO2 fumigated or O3 impacted needles. Thus, histological investigations can be used as a diagnostic tool to differentiate between direct and indirect forest damages.