Juniper encroachment into aspen in the Northwest Great Basin

Citation
Tg. Wall et al., Juniper encroachment into aspen in the Northwest Great Basin, J RANGE MAN, 54(6), 2001, pp. 691-698
Citations number
37
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Environment/Ecology
Journal title
JOURNAL OF RANGE MANAGEMENT
ISSN journal
0022-409X → ACNP
Volume
54
Issue
6
Year of publication
2001
Pages
691 - 698
Database
ISI
SICI code
0022-409X(200111)54:6<691:JEIAIT>2.0.ZU;2-#
Abstract
In the northwest Great Basin, western juniper (Juniperus occidentalis subsp . occidentalis Hook.) is encroaching into aspen (Populus tremuloides Michx. ) communities. There is a concern that aspen communities in this region are in a state of decline, but their status has not been documented. This stud y determined the timing, extent, and some of the effects of this expansion. Ninety-one aspen stands were sampled for density, canopy cover, age, stand structure, and recruitment of western juniper and aspen. Soils and tree li tter beneath aspen and western juniper were collected to analyze the effect s of western juniper on soils. Additionally, 2 large aspen complexes in sou theast Oregon were intensively aged to determine disturbance (fire) frequen cies. Western juniper encroachment peaked between 1900 and 1939 with 77% of all juniper trees sampled having been established during this period. Thre e-fourths of aspen stands sampled have established populations of western j uniper. Twelve percent of aspen stands sampled were completely replaced by western juniper and another 23% dominated by western juniper. Average densi ty of western juniper in aspen sites was 1,573 trees ha(-1). Seventy percen t of aspen stands sampled had zero recruitment of new aspen. Aspen stands a veraged 98 years old. There was an inverse correlation between aspen canopy cover and western juniper canopy cover. Soils influenced by western junipe r had a higher C:N ratio, pH, salts, lime, and sulfate, and lower amounts o f magnesium, iron, copper, and manganese. Aspen litter had a lower C:N rati o than western juniper litter. Two major aspen complexes sampled had even-a ge, 2-tiered even-age, and multiple-age aspen trees. The absence of presett lement juniper within all sampled aspen stands suggests fire was the primar y stand-replacing disturbance in these northwest Great Basin aspen communit ies. The lack of fire coupled with aspen stand decadence and low recruitmen t levels will allow for the continued encroachment and replacement of aspen communities by western juniper in the northwest Great Basin.