The effects of thinning trees and scattering slash on runoff and sediment yield within dense piñon-juniper woodlands in New Mexico, United States

Abstract

This study evaluated the hydrologic effects of thinning piñon-juniper (P-J) (Pinus edulis var. Engl. and Juniperus spp.) woodlands in conjunction with oil and gas (O&G) development in dense woodlands. Utilizing rainfall simulation we compared the effects on the thinned areas to pipelines, undisturbed sites, and existing nearby roads with specific interest in (1) runoff and runoff per unit of precipitation (runoff/ppt), (2) infiltration, and (3) suspended sediment and sediment yield. Trees were removed with a combination of chainsaw cutting and mastication in 2004. Randomly selected within each of the eight research blocks and five treatments, rainfall simulation plots were randomly placed within intercanopy and canopy areas. Thinned intercanopy plots with basal areas of 1.2 m² ha⁻¹ (5 ft² ac⁻¹) had significantly less runoff and lower runoff/ppt levels when compared to the basal area 2.3 m² ha⁻¹ (10 ft² ac⁻¹) and control intercanopy plots. Roads exhibited significantly greater runoff than every other treatment in the analysis. Suspended sediment was hypothesized to trend similar to runoff; however, the results of this analysis revealed that only roads differed statistically from other treatments. Sediment yield was similar to the results for suspended sediment with the exception of the intercanopy plots. Both thinning treatments (363.1 and 234. 7 kg ha⁻¹ [324.2 and 209.6 lb ac⁻¹]) were significantly less than the control mean (719.7 kg ha⁻¹ [642.7 lb ac⁻¹]). When comparing whole treatments (combining basal area 5 [BA5] and basal area 10 [BA10] plots), there is convincing evidence that mean runoff/ppt was different among all treatments, except between the control and pipeline. Analysis of suspended sediment indicated that all treatments were significantly different from the roads, but not between all other treatments. There was, however, convincing evidence (p = 0.0033) that sediment yield of the treatment was less than the control. These whole treatment comparisons demonstrate the success of the treatments in reducing runoff/ppt and sediment yield within P-J woodlands and the potential for management to improve the hydrological function along O&G disturbances within the San Juan Basin.