|Wu, X - TEXAS A&M UNIVERSITY|
Submitted to: Applied Vegetation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 24, 2001
Publication Date: N/A
Interpretive Summary: The distribution of sunlight at the soil surface in mesic grasslands was studied in areas that have different management histories. Higher levels of sunlight at the soil surface were found in an area that is annually hayed than in two other areas in which vegetation has accumulated. In addition, light levels were more variable in this area than the other two. The negative relationship of light variability with accumulated vegetation and similar spatial heterogeneity of light distribution within all areas throughout the growing season are general patterns that have previously been unreported in grasslands. Both direct (accumulated vegetation) and indirect (species and growth form changes) effects that have occurred as a result of differences in management history contributed to differences in distribution of sunlight at the soil surface. Information generated from this study increases our understanding of functional consequences of structural changes on grasslands, such as invasive plant species and invisibility of grasslands.
Technical Abstract: An experiment was conducted on three mesic grasslands (AH: annually hayed tallgrass prairie; U: unmanaged tallgrass prairie; and C: formerly cultivated (prior to 1939) field to address 1) the spatial patterns and 2) temporal dynamics of light distribution. Frequency distributions of relative light intensity were similar for C and U grasslands at all sample dates, but quite different for the AH grassland. A majority (60-70%) of sample points within C and U grasslands were in the lowest (0-20%) RLI class. In contrast, 28% was the maximum value in this class for AH grassland. Spatial heterogeneity was 3-4 fold greater in the AH grassland than the U and C grasslands in the early growing season. The degree of temporal variation in the normalized lacunarity curves for the three grasslands (U>AH>C) provide a measure of the temporal stability in the spatial configuration of the canopy structure. Consistent spatial heterogeneity of light distribution within the C and AH grasslands across sample dates, and the negative relationship of degree of spatial heterogeneity with standing crop (i.e., high spatial heterogeneity with low standing crop) emerged as general patterns. Lacunarity analysis can be used to characterize and compare the magnitude and timing of seasonal dynamics in spatial heterogeneity of light distribution. Integrating lacunarity analysis and traditional structural measurements may be a way to assess functional consequences of structural changes (e.g., growth form changes) caused by different management in grassland ecosystems.