Track-vehicle disturbance on rangeland and design of sap flow gauge for desert shrubs

Rangelands of the arid southwest are used extensively for military training. The impact of track-vehicle traffic on the Ft. Bliss military reservation were evaluated in soil water balance. Military training can reduce vegetation and accelerate erosion. Sustainable management will result from balancing disturbance intensity with recovery times. Military activities can occur during all seasons and the possible impact in the ecology can vary. Season and soil types produce different impact. The objectives of this study were to measure the soil disturbance caused by track-vehicles and the resulting change in site water balance.; Soil disturbance was analyzed with the change in the bulk density, microrelief and erosion rods. Bulk density changed (increased) depending the number of tank passes and season. The surface micro-topography was modified by the tank and remained months after the tank passed. Erosion rods showed soil removal and deposition. Water storage increased about one to 2 cm for 5 pass treatments in one site. There was a slight increase of water storage right after the tank because the destruction of the vegetation reduced plant transpiration.; The Penman method estimated a lower potential evapotranspiration (PET) values than expected under irrigation conditions. Dry soil surface and low vegetative covers produced low net radiation. A relationship between total rain and runoff measures was used in the water balance to estimate runoff. The overall water balances, assuming zero drainage shows that all the rain was used in ET. The actual evapotranspiration (AET) was about 15% of PET. During the growing season the AET is 0.25 cm day{dollar}sp{lcub}-1{rcub}{dollar} in the wettest sites. Dry Sites had a maximum AET of 0.15 to 0.20 cm day{dollar}sp{lcub}-1{rcub}.{dollar}; Direct measurement of plant transpiration has always been a problem under natural conditions. One way to estimate of plant transpiration is the heat balance method. This is an application of heat and accounting the heat input and output used to measure the water flow assuming study-state conditions. The main objective was to design a sap flow gauge that can regulate the quantity of heat required depending on sap flow conditions and avoid the stem damage by overheating when there is low flow.; Controlling heat input to maintain constant temperature difference keeping steady-state condition does not appear to damage the stem. The simple design does not allow adequate correction for conduction losses. The three thermocouple design allows correction for conduction losses. However, calibrations before installation in the field are not possible. Portable heat balance design allows laboratory calibrations before field installation. There was a good agreement between the measurements and the calculated water flux under laboratory conditions. Under greenhouse conditions, the heat balance method calculated the water flow in potted pecan plants quite well when compared with measured water loss.