TITLE:
Succession in Quercus gambelii (Gambel’s Oak) Woodlands
AUTHORS:
O. W. Van Auken, J. K. Bush
KEYWORDS:
Gas Exchange, Growth Rates, Light Levels, Oak Replacement, Photosynthetic Rates, Population Dynamics, White Fir, Wood Specific Gravity
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.8 No.2,
January
19,
2017
ABSTRACT: Quercus
gambelii (Gambel’s oak) communities are found in the
mountains of the western United States from Wyoming, Colorado, and Utah south
into northern Mexico. Leaf gas exchange rates were measured for potential
successional species in Q. gambelii communities. Daily average light level below the canopy was 125 μmol/m2/sec.
Light response curves indicated that Pinus
ponderosa and Q. gambelii had
high maximum photosynthetic rates (14.13 and 11.21 μmol/m2/sec) and
were sun species. Abies concolor (white fir) is a shade species with the lowest photosynthetic rate (3.71 μmol/m2/sec).
At low light levels few differences in photosynthetic rates were found between
the species. Pinus ponderosa and Q. gambelii maximum photosynthetic rates were reduced 71% - 73% in
shade and the shade species maximum photosynthetic rates were reduced by 50% - 57%. Comparing annual gas exchange rates for all
species showed that A. concolor had
higher gas exchange rates and could replace Q. gambelii. Growth in height of Q. gambelii was a second order quadratic function reaching a
plateau of about ten meters between 80 and 95 years. Growth estimates of height
of A. concolor in canopy shade were exponential, which would
allow seedlings to reach the Q. gambelii canopy in approximately 35 years. Abies
concolor wood specific gravity is 56% lower than Q. gambelii, which means more carbon is put into growth in height
to reach the canopy at low light levels and low photosynthetic rates. The
additional shading it causes would further reduce Q. gambelii photosynthesis rates and prevent self-replacement in
these Q. gambelii communities,
leading to an A. concolor dominated
community.