ON THE NATURE OF ENVIRONMENTAL GRADIENTS - TEMPORAL AND SPATIAL VARIABILITY OF SOILS AND VEGETATION IN THE NEW-JERSEY PINELANDS

1 Environmental variability can occur over various spatial scales, ran ging from small patches at the scale of individual plants to long grad ients over hundreds of metres. 2 In the New Jersey Pinelands, differen t species in the diverse shrub understorey of pitch pine (Pinus rigida Mill.) forests are patterned at these various scales, 3 Soil moisture , extractable NH4-N and N mineralization rate vary in complex ways, wi th the scale of spatial patterning changing over time and with depth i n the soil profile. Moisture in both mineral and organic horizons, and NH4-N in the organic horizon, have patterns that are more stable over time than the mineralization rate in either horizon, or the NH4-N con centrations in the mineral horizon. 4 Vegetation patterns, as captured in principal components analysis, were poorly explained by any of the soil properties. Only the more temporally stable properties showed an y relationship with vegetation patterns. 5 These results suggest that environmental gradients reflect patterns of environmental variation in four dimensions, Variation in the vertical dimension and over time is as pronounced and important as variation in the horizontal dimensions . 6 Many methods used to analyse vegetation implicitly assume temporal and spatial stability of environmental properties, Our results sugges t that a more complex, four-dimensional assessment of environmental va riation should be incorporated into models of vegetation-environment r elationships.