Structure and function of C3and C4Chihuahuan Desert plant communities. Energy balance components

During the past 150 years, the C3shrubs creosotebush [Larrea tridentata(DC.) Cov.], mesquite [Prosopis glandulosaTorr. var.glandulosa], and tarbush (Flourensia cernuaDC.) have invaded extensive areas of former C4grasslands in deserts of the south-western United States. We measured energy balance components of these grass and shrub communities in the Chihuahuan Desert. Midday net radiation in theP. glandulosacommunity was about 20% less than that in the others, where it was about equal. Midday soil heat flux was large in all communities and was greater in communities with small leaf areas. Midday and daily latent heat fluxes (or evapo-transpiration rates, ET) were about equal in all communities except theF. cernuacommunity, where they were about 50% greater due to greater leaf area and water supply. The fraction of ET made up of soil evaporation varied from 0•3 to 0•6 and was greater inL. tridentataandP. glandulosacommunities. Differences of surface energy balance components of plant communities in this desert environment were generally small and were more related to surface characteristics (e.g. leaf area) and water supply than to photosynthetic pathway or vegetation type.