Abstract:
Black Butte presents a unique natural laboratory for ecological
study. It is a volcanic cone of uniform configuration located in the
rain shadow on the east flank of the Oregon Cascades. Soils are of
very recent origin with no obvious development of horizons.
Physical and chemical analysis revealed little dissimilarity within
the study area. However, fire has played an important ecological
role. Dendrochronological analysis of cross sections of mature
Pinus ponderosa revealed repeated widespread burning at an average
interval of 12.3 years for the years 1830 to 1903. The Forest
Service has practiced fire exclusion since that time.
The vegetation of the lower :slopes is dominated by mature
Pinus ponderosa. Libocedrus decurrens, Pseudotsuga menziesii,
Abies grandis, Pinus albicaujis, and Abies lasiocarpa become
successively more abundant at progressively higher elevations.
Tree, shrub and herb data were gathered via the point centered
quarter method at 1000 foot elevation intervals along eight transects
radiating from the summit. In subsequent analysis, designed along
the lines of a continuum analysis, it was possible to demonstrate via
relative importance values that some species gradually give way to
other species along environmental gradients. However, considerations
of the age class patterns of mixed stands revealed that they are
not stable and therefore with freedom from disturbance by fire or
other catastrophe will come to be less heterogeneous in overstory
composition.
In most instances, this will be at the expense of Pinus
ponderosa which, due to its superior resistance to fire, has been
able to occupy and thrive in habitats considerably more mesic than
its true habitat type. After 60 years of fire exclusion, species of
greater shade tolerance and with generally higher moisture requirements
are now responding with relatively greater reproduction than
Pinus ponderosa on these mesic sites.
These patterns of reproduction allow one to project to six
climax associations which will come to occupy six different habitat
types. Due to the uniformity of soil and topography within climatic
climax zones, these may be interpreted theoretically as encompassing
single habitat types with variation in seres being due to rate of
succession following fire.
These distributional patterns are very similar to those described by other workers for the east slope of the Cascades. However,
due to the relatively xeric conditions of Black Butte, equivalent
types occur at approximately 500 feet higher elevation.
