The importance of limestone bedrock and dissolution karst features on tree root distribution in northern Yucatan, Mexico

With limited soil depth in northern Yucatan (< 30 cm), roots grow deeper through rock fractures and dissolution karst features (i.e., cavities, including soil-filled ones known as soil pockets). We assessed the importance of limestone bedrock and dissolution karst features on tree root growth. Fieldwork was conducted in a limestone quarry where the relative proportions of rock matrix, empty cavities, and soil pockets were calculated by observing recently exposed walls. Physical properties of rocks, topsoil, and soil pockets were analyzed. Root distribution was assessed and roots identified. Soil pockets represented 9% of the rock matrix. The physical properties of rock layers were different with depth. Available water capacity is higher in soil (0.11 m(-3) m(-3)) than in rock layers (< 0.05 m(-3) m(-3)). But potential available water was much higher in subsurface features than top soil. Dissolution karts features allow roots to grow deep into the bedrock, tapping water stored there. Although the limestone upper layer in northern Yucatan is highly restrictive to root growth, subsurface limestone layers and soil pockets are not restrictive and can hold important amounts of water.