Root disease and canopy gaps in developed areas of Yosemite Valley, California

Root disease in conifers is among the most important vegetation management considerations in the Yosemite Valley of Yosemite National Park, California . Large trees with root decay have fallen in the valley causing human fatal ities and property damage. Many of the problems associated with root diseas e can be traced back to the history of vegetation management in Yosemite Va lley. Wildfire suppression and meadow draining have led to increased densit ies of conifers at the expense of meadows and oak woodlands, Root diseases, primarily caused by Heherobasidion annosum and Armillaria mellea, associat ed with bark beetles have led to conifer mortality and the formation of gap s in the forest canopy. We mapped 279 canopy gaps (mean area 1788 m(2), ran ge 29 m(2) to 5.4 ha) that occupied about 30% of 169 ha of mixed-conifer fo rest in the developed eastern end of Yosemite Valley. In 1971, canopy gaps associated with root disease occupied only 8.7% of gap area detected in 199 9. Gaps associated with H. annosum occupied 41 ha (82% of all gap area). Se ven of these gaps were larger than 1 ha and resulted from coalescence of mu ltiple smaller gaps. Armillaria mellea was identified as the causal agent i n gaps with a total area of 4.1 ha (mean area 511 m(2), range 29-5343 m(2)) . Hazardous trees in canopy gaps have been felled by the park service since the 1970s, but the option of tree removal in developed areas must be conti nually evaluated in relation to the often competing requirements for public safety, aesthetics, and ecosystem function. (C) 2001 Elsevier Science B.V. All rights reserved.