CR 22:57-72 (2002)  -  doi:10.3354/cr022057

Growing-season temperature and soil moisture along a 10 km transect across a forested landscape

Ming Xu1,*, Jiquan Chen2, Ye Qi1

1Department of Environmental Science, Policy, and Management, University of California at Berkeley, 145 Mulford Hall, Berkeley, California 94720-3314, USA
2Department of Earth, Ecological and Environmental Sciences, University of Toledo, Toledo, Ohio 43606, USA
*Present address: Dept of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ 08901, USA. E-mail:

ABSTRACT: This study characterizes a set of growing-season microclimate variables at the landscape level and examines the relationships between these variables and landscape structure along a transect in the SE Missouri Ozarks. Temperature and soil moisture and their spatial variations at the landscape level were also compared with those at the stand level, a 200 m segment of the transect. We measured air temperature (Ta; at a height of 1 m), soil temperature (Ts; 5 cm in depth), soil-surface temperature (Tsf), and soil moisture (0 to 10 cm in depth) every 10 m along a 10050 m transect using mobile and permanent weather stations during the growing season, June to September, 1996. Topographic features, overstory and understory coverage, and landscape patch types were also recorded at each point. Elevation at each point was measured using a submeter-resolution GPS (global positioning system) in November 1996. We describe the spatial variation of microclimate with standard deviation. We found that the spatial variations of Ta, Ts and Tsf and soil moisture were large along the transect, ranging from 19.6 to 22.7°C for seasonal mean Ta and from 3.5 to 28.6% for gravimetric soil moisture. We found that seasonal means at the landscape level were not significantly different from those at the stand level. However, the spatial variations at the landscape level were significantly different from the variation at the stand level. In addition, the diurnal patterns of the spatial variation at the 2 scales were also different, with high spatial variation observed during the daytime and low variation during the nighttime. The spatial variations of Ts and Tsf had typical Œbell-shaped¹ diurnal patterns, while the diurnal pattern of the spatial variation of Ta was relatively Œflat¹. In general, the peaks of spatial variation at the stand level occurred earlier in the day than those at the landscape level, most noticeably for Ts. No apparent seasonal trend was identified for the spatial variations of the microclimatic variables examined. Based on the data collected, topography (such as aspect, slope position, and elevation), patch type, and overstory canopy coverage explain 22 to 52% of the variation in the microclimatic variables examined.

KEY WORDS: Microclimate · Landscape structure · Transect · Scale · Spatial variation · Topography

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