The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Thursday, January 31, 2008 - 11:00 AM
Influence of Infrequent Heavy Defoliation on Herbaceous Biomass and Basal Cover of Pinyon Juniper Understory
Hector Ramirez1, Alexander Fernald1, Andres Cibils1, and Dawn VanLeeuwen2. (1) Department of Animal and Range Sciences, New Mexico State University, Las Cruces, NM 88003, (2) Agricultural Biometrics Service, New Mexico State University, Las Cruces, NM 88003
Targeted grazing programs that use small ruminants to control invasion of undesired woody plants are increasing across western North America. However, information regarding the potential impact of these hebivory regimes on non-target rangeland vegetation is lacking. We conduced a study in central New Mexico to determine the effects of removing all aboveground herbaceous biomass during winter in plots located beneath (under canopy) or close to (intercanopy) live one-seed juniper trees (Juniperus monosperma) or dead tree snags that had been treated with Tebuthiron 10 years ago. We determined the effects of this defoliation regime on superficial soil moisture and herbaceous aboveground biomass and basal cover of understory species groups. We established 60 plots in three cattle-grazing exclosures; 36 under tree canopies and 24 in intercanopy spaces. Half the plots were totally defoliated in winter during either two consecutive years (under canopy) or a single year (intercanopy). Water content reflectometers were installed in the superficial soil layer (25 cm) in 50 plots. Biomass production and basal cover of total herbaceous vegetation, blue grama (Bouteloua gracilis), all perennial grasses, and all annual forbs were not affected by our defoliation treatment in neither under nor intercanopy plots. Under canopy herbaceous basal cover and above ground biomass were higher under dead tree snags. Blue grama basal cover exhibited a two-fold increase in under canopy plots after the first growing season. Biomass of blue grama and perennial grasses increased slightly (albeit not significantly) in defoliated plots beneath dead and live tree canopies. Superficial soil volumetric water content was not affected by defoliation treatment. However, soil moisture under dead tree snags showed more rapid drying than under lives trees. Infrequent defoliation of herbaceous vegetation during winter did not have detectable detrimental effects on the juniper understory herbaceous vegetation and superficial volumetric water content.