Heartrot fungi's role in creating picid nesting sites in living aspen

To determine the number of cavity-containing aspens in old-growth (> 80 yea rs), we counted the number of stems containing cavities in 132 0.02-ha plot s in Wyoming. There were 8.7 cavities/ha of aspen type. At least 84 % of th e cavity stems were alive when the initial cavity was constructed; 60% were alive when examined. Fruiting bodies and Phellinus tremulae (a heartrot fu ngus) were present on 71 % of all cavity-bearing stems but on only 9.6 % of allstems > 75 cm d.b.h. Cavities were present in 7.7% and 0.2% of living s tems with and without fruiting bodies, respectively. Average d.b.h. of cavi ty stems was 27.4 cm. During a 4-year interval, 74 of 226 snags > 75 cm d.b .h. fell, giving an average instantaneous rate of snag loss of r = -0.099. Ninety-six new snags > 75 cm d.b.h. were created during the 4-year study pe riod. Our results indicate that some primary cavity-nesting birds in northw est Wyoming preferentially selected living aspens with heartrot as nest sit es and that the average longevity of aspen snags > 15 cm d.b.h. is about 10 .7 years.