Both economic and environmental impacts produced by sheet erosion makes this topic in a worldwide concern1. Several methods, from direct techniques to physical-based and empirical approaches, are used to calculate soil erosion rates on a variety of temporal and spatial scales. Direct techniques use field measurements under natural conditions and are mainly based on the use of Gerlach troughs2, water collectors3, erosion pins4 and profilometers5. Furthermore, models of soil erosion have been increasingly focused on representing in detail the real physical processes responsible for erosion6.
Dendrogeomorphology7 is a subdivision of dendrochronology8 that it is successful in characterizing frequency and magnitude of geomorphic processes9,10,11,12,13,14,15,16,17. Regarding sheet erosion, dendrogeomorphology is usually employed to enhance or replace the methodologies mentioned above, particularly in areas where erosion rates derived from direct techniques are either scarce or unavailable. Dendrogeomorphology is a very flexible method for assessing soil erosion and can be utilized to calibrate physical-based and empirical models, or perhaps as a data source to enhance the reliability of direct estimation techniques18,19. Dendrogeomorphology enables soil erosion to be established over large areas where exposed roots are available. These exposed roots should show clear tree rings limits and respond to annual growth patterns to be considered as optimum to apply dendrogeomorphological techniques20. Further, exposed roots to be sampled should be preferably located in homogenous units based on their reaction to soil erosion21.
The conventional dendrogeomorphical way of estimating sheet erosion is grounded on measuring in situ the eroded soil thickness (Ex) from the time of the very first exposure to the present22,23,24. The ratio between these two variables is utilized to calculate an erosion value in mm∙yr1. Much of the research conducted to date has focused entirely on efficiently identifying the initial year of exposure. As an outcome, modifications in the root due to exposure are analyzed at the macroscopic level25, or at the tissue and cellular levels26,27,28. The principal anatomical change present in the exposed roots of conifers is increasing growth ring thickness, as a consequence of a significant number of cells within the earlywood (EW)26. A cutback has similarly been found within the lumen area of EW tracheids along with an increased cell wall structure thickness of latewood (LW) tracheids24,27,29. These modifications have been described and quantified as beginning when erosion lowers the ground surface over the root to roughly three cm30. Less attention was granted to the adequate determination of the Ex parameter. The age of exposed roots was typically connected with the height of the root's center axis of growth over the ground surface31,32. The estimation of Ex was consequently corrected considering ongoing secondary growth30,33. More recently, these methodological approaches have also integrated the characterization of soil microtopography to obtain reliable erosion rates34,35,36.
We present a laboratory and field protocol to estimate more accurate and reliable sheet erosion rates from dendrogeomorphology. In this particular protocol, we examine the hypothesis that sampling all exposed roots, regardless of orientation relative to runoff path and in conjunction with microtopographical analysis, enables erosion rates to be precisely reconstructed and quantified. Our objective, therefore, is to provide a protocol to estimate erosion rates from maximizing the sample size of exposed roots, using macroscopic and microscopic information found in growth tree-ring series and also high-resolution topographic data.