ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...

CLIMATE OF EAST TEXAS/INTRODUCTION 75
the past 300+ years (Stahle & Hehr 1984; Stahle et al. 1985; Stahle & Cleaveland 1988,
1993, 1995; D. Stahle, pers. comm.). Examples include tree-ring data from numerous trees
in the 250 to nearly 350 year range sampled at such East Texas sites as Brazos River in
Milam Co., Capote Knob in Guadalupe Co., Coleto Creek in Goliad Co., Ecleto Creek in
Guadalupe Co., Pecan Bayou in Red River Co., and Yegua Creek in Burleson Co. (Stahle et al.
1985; National Oceanic and Atmospheric Administration 2002; D. Stahle, pers. comm.). The
oldest living post oak known in East Texas, dating from 1658, is from the Yegua Creek site.
David Stahle (pers. comm.) also noted that many of the oldest trees are hollow and thus
impossible to accurately date. He believes that some of these veteran Texas post oaks may
reach 500 to 600 years old. Interestingly, the tree-ring data show a connection between the
Texas climate and the El Niño/Southern Oscillation (ENSO), which impacts climate globally
(Stahle & Cleaveland 1993, 1995).
Changes in phytogeography (plant distributions) can also reflect climate change. An
example is shown by the long-term McWilliams study (1995) of the distribution of
Tillandsia recurvata (ball-moss, Bromeliaceae). This species has expanded its geographical
range in Texas over the last 80 years, with much of the expansion occurring since the
1940s (note that White et al. [1998a] questioned this interpretation). McWilliams suggested
that even slight changes in temperature or moisture conditions can have significant
implications for the survival of plants at the margins of their ranges. The loss from Texas
of species currently limited to the mesic conditions of deep East Texas and the northward
shift of southerly species could both be expected based on climate models which predict
increased temperature (and thus evapotranspiration) and decreased regional precipitation
and soil moisture (Houghton et al. 1990; Packard & Cook 1995; Schmandt 1995). Since
many species (e.g., a number of forest trees) reach their southwestern range limits in East
Texas, and since changes associated with shifts in global climate will most likely occur first
at such range limits, East Texas will be an excellent area in which to study climate changeinduced
responses in plant communities (Harcombe et al. 1998). Climate change will
almost certainly affect biological diversity in Texas. In the words of Packard and Cook
(1995), “it is certain that the assemblages of native plants and animals that we know today
would change in distribution and/or composition as a result of global warming.” This is a
troubling thought when it is considered that “an increase in temperature is indicated for
the entire midwestern U.S., with reduced precipitation and drier soil conditions for the
Texas area” (Ward & Valdes 1995).
While the magnitude and long-term effects of human-induced climate change are still
much debated and difficult to predict, to quote Stahle and Cleaveland (1995),
It is sobering to recall that the ‘consensus’ estimate for global temperature change by the middle
of the 21 st century due to a doubling of atmospheric CO2 is +1.5˚ C (IPCC 1990). This would
represent some 30% of the glacial to postglacial temperature rise that took place in Texas over at
least 5000 years…if such warming were sustained indefinitely then the ecosystem changes that
could result in Texas are not pleasant to contemplate. B