New Mexico Geological Society Annual Spring Meeting — Abstracts

Mechanical thinning effects in forested stands have been widely studied, yet at the plot-scale, thinning effects on runoff, soil water flux, and water balance are scarcely reported. The objectives of this study were to identify runoff zones and to calculate soil water fluxes prior to mechanical thinning of mixed conifer stands. The study was carried out on private property near James Canyon approximately 20 km east of Cloudcroft, NM. The study site is underlain by San Andres and Yeso formation mainly composed of Douglas Fir (Pseudotsuga menziesii) and Ponderosa Pine (Pinus ponderosa) with a tree density average of 770 trees ha^-1. Soil type is Typic Argiborolls-Aquic Haploborolls with loam and clay loam soil textures. Two plots (90 x 90 m each) were selected at each of 4 locations characterized by combinations of site (hilltop, slope bottom) and aspect (North-facing, South-facing). Runoff evaluation prior to mechanical treatment was carried out in late June and early July in 2009. A total of 24 rainfall simulations (3 simulations per plot) were done with soil at field capacity. Sixty-min simulated rainfall was applied to each 1m² plot to determine runoff and sediment yield. Infiltration was determined as the difference between simulated rainfall and runoff. A set of three soil moisture and heat dissipation sensors were installed on each plot at 0.07, 0.20, and 0.35 m depth. Soil water flux was calculated by Darcy’s equation. Total potential head was calculated from gravitational and the matric potential measured from heat dissipation sensors using Retention Curve (RETC) software. The gradient-causing flow was calculated from the sum of gravitational potential and matric potential from sensors previously mentioned. Results showed that runoff and sediment yield were negligible likely due to high infiltration rate and limestone bedrock. Runoff as a percentage of total water input was 0.004 % at the hilltop and 0.02 % at the slope bottom. At the hilltop, water flux was 9.34 e^-04- 2.15 e^-04 m h^-1 and at the slope bottom water flux was 6.64 e^-04- 2.21 e^-04 m h^-1. Overall water flux was higher at 7 cm (4.28 e^-04 m h^-1) and 20 cm depth (4.21 e^-04 m h^-1) than at 35 cm depth (5.21 e^-04 m h^-1). Regardless of site and aspect, infiltration responded rapidly to simulated rainfall where possibilities of deep percolation are greater due to fracture limestone. Though preliminary results, this study helped to improve our understanding of the shallow root zone water interactions in forested stands. Data collected from this study will help to determine thinning effects at plot scale on soil water flux, runoff, and water balance.