Influence of Canopy Characteristics of One-seed Juniper on Understory Grasses

Abstract

Studies were conducted in the Sacramento Mountains, New Mexico, to determine the influence of juniper (Juniperus monosperma [Engelm.] Sarg.) canopy on understory vegetation. The basal area of grass species was estimated at 6 locations beneath the canopies of 50 one-seed junipers. Other parameters measured were litter depth, canopy height, canopy cover, canopy closure, tree height, trunk diameter, north-south crown diameter, and east-west crown diameter. Locations adjacent to the trunk had the greatest juniper canopy cover and litter depths, and the lowest height to canopy. Locations at the end of the canopy had the least crown cover and litter depths, and the greatest height to canopy. All but one of the grass species had greater basal areas at the edge locations and the least at the interior locations beneath juniper canopies. Pinyon ricegrass (Piptochaetium fimbriatum [H.B.K.] Hitch.) was the exception; it was never found at the exterior locations. Regression models indicated that shading influenced the basal areas of most grass species. Litter depth was negatively correlated with grass basal cover in only 4 models and positively correlated in 1. Basal area of pinyon ricegrass was positively correlated with trunk diameter, a reflection of tree age, indicating that the grass requires time to become established. Also, basal area of pinyon ricegrass was positively correlated with canopy cover, indicating that this species requires the modified microenvironment afforded by shading.