| A disease known as "red pine pocket mortality" (RPPM) has been reported relatively recently affecting older plantation-grown red pines in the Lake States. A common symptom of RPPM is a large, often circular, area of dead trees (pocket), surrounded by trees showing reduced diameter and height growth, thinning crowns and browning foliage. The causes of this disease are as yet unknown. This study investigated the potential causes of the disease particularly those that are "abiotic" in origin. The condition of red pines at mortality sites was tracked over a five-year period (1991-1995) and the element contents of soil, needle, and root samples from disease versus non-disease locations were determined.; Plots were established at pocket decline sites within the Huron-Manistee National Forest, Newago County, Michigan for comparison with check plots of healthy plantation red pines within and outside of the Huron-Manistee National Forest. Analysis of variance was used to identify significant differences at the 0.05 level between element contents from areas within disease plots, including the center of the pocket, the edge of the decline, and the outer region where trees appear healthy; and between healthy check-plot stands.; Results of disease progress studies indicated that drought may be a contributing factor to the decline; measures of disease intensity tended to increase during drought years and decrease during non-drought years. Increasing gradients in live fine-root (roots {dollar}<{dollar} 3 mm in diameter) were found from the center to the edge, to the outside region of disease plots, and finally to the healthy plantation check plots. These increasing gradients suggested that fine roots are dying first before symptoms are seen in tree crowns.; Statistical analyses of nutrient contents indicated that manganese (Mn) followed by magnesium (Mg) in soil, needle, and root samples were the nutrient factors most strongly associated with areas of decline and were significantly lower in disease plots versus non-disease plots. Further, increasing gradients in Mn and Mg and corresponding decreasing gradients of metals, particularly aluminum (Al), from diseased to healthy areas, suggested that the pattern of disease spread is associated with nutrient stress. |
