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, ranging from small patches at the scale of individual plants to long gradients over hundreds of metres. 2 In the New Jersey Pinelands, different 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, with the scale of spatial patterning changing over time and with depth in 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 concentrations 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 any 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 suggest that a more complex, four-dimensional assessment of environmental variation should be incorporated into models of vegetation-environment relationships.