Resource heterogeneity in oldfields

Abstract. Spatial heterogeneity of photosynthetically active radiation (PAR), soil moisture and soil N mineralization in a range of oldfield communities was analyzed using semi‐variograms for transect data. Percent transmittance of PAR was examined in eight communities, and soil moisture and N mineralization were examined in the two most common communities. In general, the sites with the highest resource availability had the smallest coefficients of variation. For light, 63% of the transects showed significant non‐zero spatial autocorrelation with sills at 1 ‐ 70 cm distance intervals. Although the grass‐dominated communities had the highest average PAR levels and the lowest coefficients of variation, they also were among those with the greatest percentage of transects that had non‐zero spatial autocorrelation. For light, the average semivariogram range, or distance within which samples were autocorrelated, was 19 cm and different among communities at p = 0.07. For soil moisture, two of three shrub sites and one of three grass sites showed non‐zero spatial autocorrelation with sills at 10 ‐ 300 cm distance intervals. Average semivariance range was 249 cm for the shrub community and 170 cm for the grass community. For N‐mineralization, none of the shrub and one of three grass sites showed non‐zero spatial autocorrelation with a sill, with a semivariance range of 60 cm. Soil moisture and N‐mineralization were higher in the shrub than in the grass communities. Overall, these results indicate that resource variability occurred within patches of uniform vegetation, and the range of resource spatial dependence was different among resources even within a single community type. Our results suggest that different seedlings invading these communities will experience very different patterns of microsite heterogeneity as a result of their specific resource requirements.