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Influence of Boulders on Netleaf Hackberry (Celtis reticulata) Growth and Distribution in the Wasatch Foothills

Argyle, Alex, Stevens, Michael T.
Western North American naturalist 2013 v.73 no.4 pp. 525-529
Celtis, hills, landscapes, melting, microhabitats, mountains, snow, thermal radiation, vegetation, Utah
In a landscape, abiotic features, such as boulders, influence microhabitats and consequently affect patterns of vegetation. We hypothesized that boulders in the foothills of the Wasatch Mountains east of Provo, Utah, affected the growth patterns of netleaf hackberry (Celtis reticulata) by providing shade on their north faces. To test this hypothesis, we set up 3 transects 6 m wide and up to 50 m long. Along these transects, we measured all hackberries taller than 30 cm (n = 249). We recorded whether the hackberries grew within 0.5 m of a boulder that was at least 0.5 m along one dimension. We found that hackberries at our study site were more likely to be associated with boulders (n = 225; 90.4%) than to be growing alone (n = 24; 10.7%) (x² = 162.25, df = 1, P < 0.001). For each hackberry associated with a boulder, we took a direction bearing from the center of the boulder to the place where the hackberry was rooted. We found that hackberries associated with boulders were more likely to grow near the south (n = 92; 40.9%) side than near the north (n = 35; 15.6%), west (n = 55; 24.4%), or east sides (n = 43; 19.1%) (x2 = 33.90, df = 3, P < 0.001). These results suggest that boulders influence patterns of hackberry growth and may actually provide thermal radiation that melts snow in the Wasatch foothills, rather than shade protection as we had originally hypothesized.