Experimental plots
We considered comparing pure and mixed stands of oak and pine a suitable approach to identify potential differences in species-specific preferences for occupying (via root placement) certain geologic substrates, rock fractures or soil depths, etc., when growing either in intra- or inter-specific neighborhoods. We established 12 circular experimental plots of 25 m diameter (four plots per stand type) along a 3.5 km long transect running parallel to a narrow watershed, where pine and oak trees were evenly distributed in pure and mixed stands. By simultaneously examining root distribution, plant leaf water potentials and intra-annual soil and rock water availability, we were able to isolate and describe specific geoecohydrological niches.