Laboratory and Field Protocol for Estimating Sheet Erosion Rates from Dendrogeomorphology

This method can help answer key questions in the field for the dendrogeomorphology about the importance of ground microtopographic characterization for obtaining reliable sheet erosion rates. The main advantage of this technique is that it yields acceptable estimates of soil erosion over comparable large areas at a reasonable locus. The implication of these techniques extend towards improving the replicability and utility of dendrogeomorphology by broadening the typology of bio-indicators that can be used for quantifying erosion rates.

Generally, individuals new to this technique would be able to replicate it easily due to the versatility of the methodology. Visual demonstration of this method is critical as it is based on the completion of several steps related to different methodological approaches. Begin by locating exposed roots that are farther than 1.5 meter from the trunk.

And using a handsaw to cut at least 30 exposed roots with a diameter greater than five centimeters into 15 centimeter long sections. Select two slices approximately 1.5 centimeters thick and use a gauging trowel, a handsaw, and a measuring tape to sample at least 1/3 of the total exposed roots at different soil depths, up to a maximum of 20 centimeters to establish the minimum soil thickness below which the roots begin to have an anatomical response due to exposure. For microtopographic characterization of the exposed roots of an easily accessible location, use a terrestrial laser scanning device that can measure up to 50, 000 points per second with a one millimeter precision at a scanning distance of less than 120 meters, to consider at least two different conventional terrestrial laser scanning locations without shadow zones.

Use a minimum of four high definition surveying targets positioned to cover the entire area to merge the two locations. Scanning an average area of 300 centimeters squared from the selected locations at a spatial resolution of one millimeter. For microtopographic characterization of the exposed roots in difficult and steep terrain, place a microtopographic profile gauge perpendicular to the exposed root and subsequently level the gauge horizontally for all of the measurements in such a way that different data sets can be compared.

Ground surface microtopographic characterization is critical for obtaining accurate erosion rates and can be accomplished inexpensively using a microtopographic gauge regardless of the study site topography. Then, draw the profile obtained on graph paper to allow estimation of the amount of eroded soil along the profile with sub-millimeter precision. To determine the root exposure timing by macroscopic analysis, use the increase in late wood percentage and larger growth ring widths as indicators of stress induced by exposure.

And mark at least four to five radii along the diameter of the slices that exhibit the highest variability in growth ring widths. Then, use an image analysis system to measure the tree ring width and compare the variability in the growth ring widths between the different radii for visual cross-dating to both improve the dating precision for the first year of exposure to soil erosion and to correctly date the subsequent rings. To determine the root exposure timing by microscopic analysis, for both exposed and non-exposed root samples, use a sliding microtome to obtain approximately one-centimeter wide, 20-micron thick radial cross-sections.

Stain the cross-sections with safranin and dehydrate the samples with ascending ethanol water immersions in up to 96%ethanol, until the water runs clear. Soak the samples in an appropriate clearing agent, and mount them on coded slides with a cover slip of hardening epoxy. After allowing the samples to dry at room temperature, image the sections under 125x magnification to compare the anatomical footprint of both the exposed and non-exposed root samples.

Then use an appropriate image analyser to obtain microscopic measurements of the growth ring widths, number of cells per ring, percentage of late wood, and lumen area in early wood. In this macroscopic analysis, changes in the tree ring growth pattern were observed due to the death of the cambium on the top part of the root. Including a shift from the concentric to eccentric growth and the presence of some partially destroyed outer tree rings.

In this microscopic analysis, the first time of exposure can be observed when there is dramatic change in ring width. An increase in the number of vessels is also noticeable, and traumatic resin dots appear in some scarred roots. Late wood is readily visualized due to its multiple rows of thick-walled tracheids.

With a significant decline in the tracheid lumen of the early wood observed upon exposure. Characterization of the ground surface microtopography plays a critical role in obtaining accurate sheet erosion rates. This morphological exposed root pattern ends at a specific distance from which the ground surface is only shaped by sheet erosion, indicating the location where the erosion should be measured.

Here, 114 exposed root samples were analyzed. Enabling a multidecadal characterization of sheet erosion. The analysis of 10 buried roots revealed that they began to anatomically respond to exposure when they were approximately three centimeters below the ground surface.

Which is an essential indicator for improving the accuracy of erosion rates. While attempting this procedure, it's important to remember that the proper microtopographical characterization of the roots and their immediate vicinity has been demonstrated to be a key factor in the reliable estimation of sheet erosion rates. The protocol is replicable in any geographical area, provided that the available tree species demonstrate a good aptitude for the use in tree root research, as applied for soil erosion assessments.

Following this procedure, the addition of other methods that use instrumental catchments, or experimental plots may improve the spatial representativeness of the erosion analysis. This technique can be used to design best management practices, that could ultimately prevent, or at least reduce, soil erosion. Facilitating the application of more sustainable management practices.