Succession in &amp;lt;i&amp;gt;Quercus gambelii&amp;lt;/i&amp;gt; (Gambel’s Oak) Woodlands

O W Van Auken,J K Bush

doi:10.4236/ajps.2017.82008

Succession in &lt;i&gt;Quercus gambelii&lt;/i&gt; (Gambel’s Oak) Woodlands

O W Van Auken, J K Bush

Open Access

https://doi.org/10.4236/ajps.2017.82008

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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.

Highlights

Many Quercus populations in North American forests and woodlands appear to be changing and changes are widespread [1], species independent [2] and associated with a lack of replacement of mature trees [3] [4] [5]
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
Maximum photosynthetic rate (Amax) for leaves of P. ponderosa was highest at a mean photosynthetic flux density (PFD) of 2000 μmol/m2/sec, which was significantly greater than the Amax for other species (Table 2)

Summary

Introduction

Many Quercus (oak) populations in North American forests and woodlands appear to be changing and changes are widespread [1], species independent [2] and associated with a lack of replacement of mature trees [3] [4] [5]. Deviations in many Quercus populations appear to be related to community succession [6]-[11], to changes in light levels as succession proceeds, changes in fire frequency, and high levels of herbivory [12]-[20]. In protected areas of western North America, large herbivores reduced populations of cottonwood (Populus deltoids), various willows (Silax sp.) and possibly quaking aspen (Populus tremuloides) [21]. (Gambel’s oak) populations or communities in western North America We have not found any reports of top-down predator reintroduction effects on Q. gambelii Nutt. (Gambel’s oak) populations or communities in western North America

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