Measuring medium-term sheet erosion in gullies from trees: A case study using dendrogeomorphological analysis of exposed pine roots in central Iberia

Dendrogeomorphology in badlands: Methods, case studies and prospects

“…In this sense, the application of dendrochronology to geomorphol ogy has allowed the dating and study of processes from a different perspective, Dendrogeomorphology (Alestalo, 1971) offers a great versatility as a method to characterize erosive processes in badlands, either to be used to study ungauged watersheds, to calibrate empiri cal methods, or as a tool to complement other methods of direct esti mation, So, dendrogeomorphology enables to obtain erosion rates over large areas, provided that there are exposed roots of tree species with good dendrogeomorphological aptitude (Grissino-Mayer, 1993) and they are located in homogenous units in terms of their response to erosion (Bodoque et aL, 2011), Other methods of direct estimation (e,g" erosion plots) allow to obtain more accurate data regarding soil erosion at event scale, However, it is not feasible from an economic standpoint and human resources availability to install such devices in all basins that make up a badland site, Although erosion rates obtained from dendrogeomorphology define average values in units of mm yr-t, however, this method can provide information regard ing the characteristics of the erosive process, Specifically, the seasonal period in which exposure occurs can be determined, As a conse quence, it may be established if erosion soil existing in a given site is a result of the occurrence of few precipitation events, instead of being a representative mean value of the whole year. In the early studies, conducted by La Marche (1963Marche ( , 1968 and Eardley and Viavant (1967), the methodology for estimating soil denudation using exposed roots was developed, These were followed by the work by Carrara and Carroll (1979), Hupp and Carey (1990) and Danzer (1996) and the methodology was extended to studying: sheet erosion in different environments (MaHk, 2008;McAuliffe et al, 2006;Perez-Rodriguez et aL, 2007); human impact on mountain hiking trails Pelfini, 1999); erosion on lake shores (Fantucci, 2006); or along river banks (Begin et al, 1991;Hitz et aL, 2008;Malik and Matyja, 2008;Stoffel et aL, 2012); debris flow tracks (Gartner, 2003, Gartner et al, 2001; and even to deter mine fluctuations in caribou herds in Canada (Boudreau et al, 2003), Furthermore, the analysis of adventitious roots has been also used for dating sedimentation events resulting from different geo morphic processes, such as debris flow (Friedman et aL, 2005;Kent et al, 2...…”

“…Slopes are generally higher in the drainage area and much lower in the deposition zone. The most approporiate proce dure is to define and map Hydrologic Response Units (HRU) within the studied area, including homogeneous geological substratum, soil, surface deposits, canopy cover and vegetative residue surface cover, and establishing a range of slope gradients (Bodoque et al, 2011). The interrelationships between bedrock, topography, soil and vegetation re flect a common hydrological and erosive response within each HRU (Luda et al, in press).…”

“…The interrelationships between bedrock, topography, soil and vegetation re flect a common hydrological and erosive response within each HRU (Luda et al, in press). This can be done with aerial photos and field sur veys with topographic devices (GPS, Total Station), taking soil samples to ensure a homogeneous hydrological response in terms of textural characteristics, organic matter content, permeability and cohesiveness (Bodoque et al, 2011). To interpret the erosion rate data obtained, a time-based analysis from historic aerial photos or from historic data is also useful (Vicente et al, 2009).…”

“…All empir ical equations used for erosion rate estimation are related to the dif ference in amount of eroded soil divided by the time defined by the root exposure (Bodoque et al, , 2011Corona et al, 2011;Gartner, 2007;Lopez-Saez et al, 2011;Vandekerckhove et al, 2001).…”

“…Malik (2008) studied gully erosion by mean of floating exposed roots in dif ferent points of small gullies in shouthern Poland, he obtained a gully retreat of 0.63 m yr-t• Three studies have recently appeared which represent advances in both practical application to unrecorded areas and in methodology. Bodoque et al (2011) applied tree-ring analysis to exposed roots to determine the sheet erosion rate in a set of slope gullies on the northern piedmont of the Guadarrama Mountains (Spanish Central System). The most significant contribution was to take into account the hydrological response units (HRUs) approach during the sampling stage, so that the erosion rates estimated can be extended to similar gullied areas.…”