Riparian ecosystems serve critical ecological functions in western landscapes. The woody plant components in many of these keystone systems are in serious decline. Among the causes are invasion by exotic species, stress-induced mortality, increases in insect and disease attack, drought, beaver, fire, climatic changes, and various anthropogenic activities. The latter include agricultural development, groundwater depletion, dam construction, water diversion, gravel mining, timber harvesting, recreation, urbanization, and grazing. This article examines the factors implicated in the decline and discusses the importance of interactions among these factors in causing decline. It also clarifies issues that need to be addressed in order to restore and maintain sustainable riparian ecosystems in the western United States, including the function of vegetation, silvics of the woody plant species involved, hydrologic condition, riparian zone structure, and landscape features, geomorphology, and management objectives. West. J. Appl. For. 16(4):169-181.
Even-age ponderosa pine stands in the Black Hills can be rated for infestation by the mountain pine beetle on the basis of mean stand diameter, stand density, and spacing. Tree spacing distances, are derived for stands of different hazards and provide guidelines by \ which high-hazard stands can be converted to low-hazard stands.
Ten-year diameter and basal area growth were determined for partially cut stands at 4 locations. Average diameters in the partially cut plots generally increased by 1 inch or more, while average diameter in the uncut controls increased by 0.9 inches or less. Individual tree growth is discussed in relation to potential susceptibility to mountain pine beetle infestation. Basal area increases ranged from 0.9 to 1.9 ft2/acre/ yr in partially cut plots, while basal area increases in the control plots ranged from 0.4 to 1.4 ft2/acre/yr. Endemic mountain pine beetle infestations and snow breakage accounted for most of the mortality on the plots, which decreased the residual basal area and basal area growth. Increases in basal area are used to estimate the length of time required for various stand densities to reach the susceptibility thresholds for mountain pine beetle infestation. Stand marking may influence future susceptibility to beetle infestations.
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