Ma. White et Jl. Vankat, MIDDLE AND HIGH-ELEVATION CONIFEROUS FOREST COMMUNITIES OF THE NORTH RIM REGION OF GRAND-CANYON NATIONAL-PARK, ARIZONA, USA, Vegetatio, 109(2), 1993, pp. 161-174
We examined the composition and structure of forest communities in a 3
700 ha watershed in relation to environmental gradients and changes in
land management practices. We identified four mixed-conifer forest ty
pes dominated by different combinations of Abies concolor, Picea punge
ns, Pinus ponderosa, Populus tremuloides, and Pseudotsuga menziesii, a
nd a spruce-fir type dominated by Picea engelmannii and Abies lasiocar
pa. The forest types occur in a complex pattern related to elevation a
nd topographic-moisture gradients and variations in past fire regimes.
However, widespread regeneration of A. concolor following possible ch
anges in the fire regime in the late 19th century and continuing with
institution of a fire suppression policy early in the 20th century is
producing a more homogenous mixed-conifer forest with greater horizont
al and vertical continuity of fuel. This shift toward landscape homoge
neity not only may adversely affect biodiversity, but also may be perp
etuated as the probability of large, high-severity fires increases wit
h continued fire suppression.