Abiotic and biotic factors used to assess decline risk in red pine (Pinus resinosa Ait.) plantations

Abstract

This study was conducted to assess causes of unprecedented rates of mortality in maturing, commercial-sized red pine (Pinus resinosa Ait.) plantations in southern Ontario, Canada. Concentrated and diffuse mortality as well as windthrow of living trees were observed in many plantations, while others seemed disease-free. Nine sites exhibiting recent mortality (diseased) plus three not exhibiting disease (healthy) were selected. In sample plots at each site, abiotic site factors, host characteristics, and insect pests and fungal pathogens were assessed. Tree mortality was attributed to Armillaria root disease, annosus root rot, black pineleaf scale, drought, and iron deficiency. The single abiotic factor that distinguished healthy sites from diseased sites was C soil horizon pH, which averaged 8.35 on diseased sites compared to 6.55 on healthy sites. Rooting was also deeper on healthy sites than on diseased sites. We suggest that an alkaline C horizon may result in shallower rooting and greater susceptibility to drought stress, rendering trees less resistant to root disease pathogens and insect pests. The pH of the C horizon and the depth of the A and B horizons may be useful as indicators of the likelihood of red pine mortality and to guide the choice of management objectives for plantations.