Identifying roots of northern hardwood species: patterns with diameter and depth

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Forest canopies are often stratified by species; little is known about the depth distribution of tree roots in mixed stands because they are not readily identified by species. We used diagnostic characteristics of wood anatomy and gross morphology to distinguish roots by species and applied these methods to test for differences in the rooting depth of sugar maple ( Acer saccharum Marsh.), American beech ( Fagus grandifolia Ehrh.), and yellow birch ( Betula alleghaniensis Britt.) in two northern hardwood forests. We also distinguished hobblebush ( Viburnum lantanoides Michx.) and white ash ( Fraxinus americana L.) roots. Analysis of plastid DNA fragment lengths confirmed that 90% of the roots were correctly identified. The vertical distribution of fine roots of these species differed by 2–4 cm in the median root depth (P = 0.03). There was a significant difference in the distribution of roots by size class, with fine roots (0–2 mm) being more concentrated near the soil surface than coarser roots (2–5 mm; P = 0.004). The two sites differed by <2 cm in median rooting depths (P = 0.02). The visual identification of roots for the main tree species in the northern hardwood forest allows species-specific questions to be posed for belowground processes.