Variation in the Structure of Scrub Oaks and its Effect on Thermal Microclimates in the Albany Pine Bush

Thermal microclimates are vital within ecosystems because they contribute to forming appropriate niche space for many species. Variation in microclimates may impact animal thermoregulation and be especially important in the face of climate change. The goal of this study is to determine how the size and structure of Quercus ilicifolia (Scrub Oak) individuals influences temperature gradients in their vicinity. We hypothesized that differences in leaf density and leaf area index (LAI) would cause variation in the thermal regimes within and around shrubs (temperature gradients), and that shrubs with higher LAI would form steeper temperature gradients. Five Q. ilicifolia shrubs that differed in size (1-3 m tall) were selected within the Albany Pine Bush Preserve (Albany, NY). At each shrub, five temperature logging devices (iButtons) were placed 8 cm above the ground surface in a transect from the shrub center to the surrounding vegetation. At each point, hemispherical canopy photos were obtained to estimate canopy cover, and leaf area was measured by collecting leaves from each shrub; leaf area index (LAI) was calculated by dividing leaf area by ground area. Additionally, terrestrial laser scanning was performed by scanning shrubs to obtain a 3D reconstruction and to calculate shrub ground area and volume. Characteristics of shrub structure (height, canopy cover, LAI, canopy volume) were compared to each other and to measurements of thermal regime (average, maximum and minimum daily temperatures). Leaf area and shrub volume were positively correlated (r2 =0.96) and LAI ranged between 1.0-1.9 (m2/m2), but was not associated with canopy cover. Daily maximum temperatures formed a gradient from shrub edges to the openings, whose magnitude was independent of shrub size or leaf area. Likewise, temperature environments within shrubs were fairly constant, but there was a linear gradient from the shrub edge to the surrounding vegetation. On average, shrubs caused a 5.2°C temperature depression in the daily maximum temperatures. These results suggest that temperature gradients form independently of shrub size and structure, but are nonetheless present underneath and directly adjacent to shrubs. Overall, we have shown that TLS is a useful way to support field measurements of shrub structure.

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Union College (Schenectady, N.Y.). Department of Biology