Sheet erosion rates determined by using dendrogeomorphological analysis of exposed tree roots: Two examples from Central Spain J.M. Bodoque a, * , A. Dı ´ez-Herrero b , J.F. Martı ´n-Duque a , J.M. Rubiales c , A. Godfrey d , J. Pedraza a , R.M. Carrasco e , M.A. Sanz a a Department of Geodynamics, Complutense University, Jose ´ Antonio Nova ´is s/n, 28040, Madrid, Spain b Geological Hazards Unit, Spanish Geological Survey (IGME), Rı ´os Rosas 23, 28003 Madrid, Spain c Plant Biology E.U., Department of Silviculture and Grazing, Forest Engineering School, Polytechnics University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain d 5110 Burch Creek Drive, Ogden, Utah 84403, United States e Department of Engineering Geology and Mining, University of Castilla-La Mancha, Campus Tecnolo ´gico, 45071 Toledo, Spain Received 27 January 2004; received in revised form 4 July 2005; accepted 19 August 2005 Abstract This paper describes the determination of sheet erosion rates by using dendrogeomorphological methods on exposed tree roots. Two sites on the northern slope of the Guadarrama Mountains, Central Spain, were studied: a popular trail in a Scots pine forest (Senda Schmidt, Valsaı ´n) growing on granites and gneisses, and an open holm-oak forest on granitic slopes (Monterrubio). These sites were selected because they showed high denudation morphologies due to accelerated soil-erosion processes caused by human influence (trampling by continuous trekking and overgrazing), resulting in exposed roots. The method applied is based on the morphological pattern of roots, defined by the growth-ring series of the sampled roots. In order to confirm the validity of the criteria used and to make the estimations of erosion more accurate, several anatomical indicators of exposed and non- exposed Pinus sylvestris roots were characterized. The study entailed a statistical analysis of exposure time and erosion depth. The influence of environmental factors affecting the variation in velocity of the erosion processes was also examined. 0341-8162/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2005.08.002 * Corresponding author. Tel.: +34 91 3944676; fax: +34 91 3944845. E-mail address: jbodoque@geo.ucm.es (J.M. Bodoque). Catena 64 (2005) 81 – 102 www.elsevier.com/locate/catena