Effects of native forest restoration on soil hydraulic properties, Auwahi, Maui, Hawaiian Islands

Abstract

Over historic time Hawai‘i's dryland forests have been largely replaced by grasslands for grazing livestock. On‐going efforts have been undertaken to restore dryland forests to bring back native species and reduce erosion. The reestablishment of native ecosystems on land severely degraded by long‐term alternative use requires reversal of the impacts of erosion, organic‐matter loss, and soil structural damage on soil hydraulic properties. This issue is perhaps especially critical in dryland forests where the soil must facilitate native plants' optimal use of limited water. These reforestation efforts depend on restoring soil ecological function, including soil hydraulic properties. We hypothesized that reforestation can measurably change soil hydraulic properties over restoration timescales. At a site on the island of Maui (Hawai‘i, USA), we measured infiltration capacity, hydrophobicity, and abundance of preferential flow channels in a deforested grassland and in an adjacent area where active reforestation has been going on for fourteen years. Compared to the nearby deforested rangeland, mean field‐saturated hydraulic conductivity in the newly restored forest measured by 55 infiltrometer tests was greater by a factor of 2.0. Hydrophobicity on an 8‐point scale increased from average category 6.0 to 6.9. A 4‐point empirical categorization of preferentiality in subsurface wetting patterns increased from an average 1.3 in grasslands to 2.6 in the restored forest. All of these changes act to distribute infiltrated water faster and deeper, as appropriate for native plant needs. This study indicates that vegetation restoration can lead to ecohydrologically important changes in soil hydraulic properties over decadal time scales.

Characteristics of preferential flow paths and their effects on soil properties

“…Perkins et al (2012) found that mean field-saturated hydraulic conductivity in newly restored forest cover with an abundance of preferential flow channels was greater by a factor of 2.0 compared with soils of rangelands. The percent preferentiality in the subsurface increased from an average 1.3 in grasslands to 2.6 in restored forest.…”

“…The effects of preferential flow pathways on SHC have been noted before (Price et al 2010). Perkins et al (2012) found that mean field-saturated hydraulic conductivity in newly restored forest cover with an abundance of preferential flow channels was greater by a factor of 2.0 compared with soils of rangelands.…”

Forests, water and food security in the northwestern highlands of Ethiopia: Knowledge synthesis

“…Wang et al (2012) found that soil moisture is lower under trees than grasslands and crops, while Perkins et al (2012) found subsurface wetting and hydraulic conductivity becomes higher in restored forest lands than grasslands and grazing lands. As the scale of watersheds is increasing, land use impacts on hydrology could be diluted (Blö schl et al, 2007).…”

“…In addition, effects on total flow and high flow are better understood than low flows (Eisenbies et al, 2007;Cui et al, 2012). Part of the difficulty in predicting low flows is the low accuracy of low flow measurement (Ratto et al, 2007), which could contribute to the complexity of the observed responses. High flows are also difficult to measure, but it is important to remember that it is the frequency of high flows which increases, with less certainty about the magnitude of the highest flows.…”

Negative trade-off between changes in vegetation water use and infiltration recovery after reforesting degraded pasture land in the Nepalese Lesser Himalaya

“…The low surface and near-surface K fs reported for grazing conditions is mostly the result of destroyed macroporosity through trampling by cattle and by the much diminished soil faunal activity after forest clearing and burning with the associated loss of topsoil organic matter and surface exposure with erosive precipitation (McIntyre, 1958a, b;Lal, 1988;Deuchars et al, 1999;Colloff et al, 2010;Bonell et al, 2010). Natural forest regrowth on degraded pasture or planting trees followed by uninterrupted plantation development can be expected to gradually improve the soil water intake capacity again through the steady incorporation of organic matter, soil faunal and insect burrowing activity, and root turnover (Gilmour et al, 1987;Bonell, 2005;Ilstedt et al, 2007;Bonell et al, 2010;Colloff et al, 2010;Hassler et al, 2011;Perkins et al, 2012). Conversely, impervious footpaths, yards and roads will remain runoff-producing features in post-forest landscapes (Ziegler et al, 2004;Rijsdijk et al, 2007) as well as in managed (forest) plantation areas (La Marche and Lettenmaier, 2001;Ziegler et al, 2007;Liu et al, 2009).…”