Twenty-Third Annual Meeting and Symposium of the
Desert Tortoise Council, April 3-5, 1998
Abstracts

Because creosote bush (Larrea tridentata) is the dominant evergreen shrub of many desert communities in the Southwest, what happens to this woody plant species during human disturbance has profound effects on this ecosystem. Military training on these desert landscapes has two easily demonstrated impacts on the local plants, breakage and crushing of shoots by heavy vehicles and coating resinous leaves by dust. Studies conducted at Fort Irwin National Training Center in the central Mojave Desert, where tank warfare is rehearsed, have provided quantitative data for physical damage to creosote bushes from different levels of military training. At high disturbance by vehicles, nearly all individuals showed measurable breakage and greater than 50% of the plants lost the original canopy, whereas less damage and more intact shrubs appeared at sites with less vehicular traffic. Creosote bush has a characteristic pattern of resprouting and can recover from surface traffic damage, amazingly returning to its original canopy design within five years. New shoots of resprouts are markedly different in physiological and morphological traits than canopy old growth. Heavy dust does not kill creosote bush, but leaves dusted by road traffic showed net photosynthesis reduced to 21% of controls and leaf temperature substantially increased. Dust seems to reduce plant carbon gain by impairing tolerance to water stress and decreasing water-use efficiency, but creosote bush can recover from heavy coating with clay particulates by experiencing new growth and shedding old leaves. Studies are underway to determine at what level or periodicity of military training death of creosote bush is observed, because that signals the point when the plant community cannot return to its original condition, given that reestablishment by seedlings is exceedingly rare. Loss of creosote bushes, with important aboveground biomass, also probably corresponds with a loss of fertile islands and associated animal habitats.