Impacts of black stain root disease in recently formed mortality centers in the pi?on-juniper woodlands of southwestern Colorado

Thirty discrete black stain root disease (BSRD) mortality centers, caused by Leptographium wageneri (Kendr.) Wingf. var. wageneri, were examined in 1999 to determine the effects of BSRD on the composition and structure of pi?on–juniper woodlands at the tree, shrub, and herbaceous plant levels and on tree-seedling regeneration. In these recently formed mortality centers, the majority (68%) of all pi?on (Pinus edulis Engelm.) was dead, 76% of pi?on were affected by BSRD, and 70% had evidence of pi?on ips bark beetle (Ips confusus Leconte) attack. BSRD mortality centers had a mean area of 0.28 ha (range 0.07 to 0.63 ha). There were no statistically significant (p > 0.05) differences in shrub composition, cover, or diversity between mortality centers and the unaffected surrounding woodlands. Herbaceous plant cover was significantly greater (p < 0.001) within mortality centers and frequency responses were species specific. There were no significant (p= 0.629) differences in the density of pi?on regeneration inside mortality centers compared with outside mortality centers. The pathogen was regularly isolated from pi?on roots dead for 5–8 years and once from a root dead for 16 years. The rate of radial expansion of mortality centers averaged 1.1 m/year (0.07 SE). The rate of mortality center expansion was not significantly (p > 0.05) related to available water-holding capacity, percent organic matter, pH of soils, pi?on density, or any other site data recorded.