ENLARGEMENT OF TREE-MORTALITY CENTERS SURROUNDING PINE STUMPS INFECTED BY HETEROBASIDION-ANNOSUM IN NORTHEASTERN CALIFORNIA

Enlargement of 53 tree-mortality centers surrounding pine stumps infec ted for about 35 years by Heterobasidion annosum (Pr.) Bref. was studi ed in northeastern California. At the end of the study period (1992), mean area for all centers was 209 m(2) (range 16-701 m(2)), and the me an rate of radial enlargement was 0.22 m/year (0.7 ft/year). Rates dec reased over time and center enlargement essentially ceased at most cen ters 20-30 years after stump infection. However, 7 centers (13%) conti nued to enlarge into surrounding stands at a mean rate of radial enlar gement of 0.39 m/year (1.3 ft/year), and averaged 557 m(2) (0.14 acre) by 1992. Continued enlargement of centers and extension of mortality beyond center stump root zones were associated with adjacent dead tree s larger than 20 cm DBH. Many individual centers had different rates o f enlargement at different points along their boundaries, ranging from 0 to 0.78 m/year (2.5 ft/year).