PARTITIONING OF EVAPOTRANSPIRATION IN A SEMIARID CHIHUAHUAN DESERT SCRUBLAND 1608

Authors: Cable, William; Scott, Russell - Russ; Emmerich, William

Submitted to: Ecological Society of America Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 4/18/2004
Publication Date: 8/9/2004
Citation: Cable, W.L., Scott, R.L., Emmerich, W.E. 2004. Partitioning of evapotranspiration in a semiarid chihuahuan desert scrubland [abstract]. Ecological Society of America Abstracts.

Interpretive Summary: In general the coupled response of bare soil evaporation and plant transpiration following precipitation pulses is not well understood in desert ecosystems. To better understand how precipitation is partitioned into evaporation and transpiration following natural precipitation pulses we measured whole plant transpiration and evapotranspiration at a semiarid Chihuahuan desert scrubland site in southeastern Arizona. The site is dominated by Larrea tridentata, Acacia constricta, and Parthenium incanum while Flourensia cernua and Rhus microphylla are present in smaller proportions. Whole plant transpiration was measured on individual stems using the heat balance sap flow technique, while evapotranspiration was measured using both the eddy covariance and the Bowen ratio technique. To estimate ecosystem-scale transpiration, sap flow measurements were scaled up using a survey of stem density for the site. During dry periods when evaporation would have been minimal we found good agreement between Bowen ratio estimates of evapotranspiration and sap flow estimates of transpiration further validating our scaling approach. Before the monsoon season began, transpiration was near zero as was evaporation. At the on-set of the monsoon rains evapotranspiration was dominated by evaporation as it took approximately 10 days for the plants to respond to the precipitation input. Following this initial period, periods immediately following rain events were dominated by evaporation while inter-storm periods were dominated by transpiration. The surface of the coarse, well-drained soils dried quickly which rapidly reduced evaporation. Our data suggest that the partitioning of precipitation inputs in these ecosystems is very dynamic and an important component that would be missed by simply measuring whole ecosystem evapotranspiration alone.

Technical Abstract: In general the coupled response of bare soil evaporation and plant transpiration following precipitation pulses is not well understood in desert ecosystems. To better understand how precipitation is partitioned into evaporation and transpiration following natural precipitation pulses we measured whole plant transpiration and evapotranspiration at a semiarid Chihuahuan desert scrubland site in southeastern Arizona. The site is dominated by Larrea tridentata, Acacia constricta, and Parthenium incanum while Flourensia cernua and Rhus microphylla are present in smaller proportions. Whole plant transpiration was measured on individual stems using the heat balance sap flow technique, while evapotranspiration was measured using both the eddy covariance and the Bowen ratio technique. To estimate ecosystem-scale transpiration, sap flow measurements were scaled up using a survey of stem density for the site. During dry periods when evaporation would have been minimal we found good agreement between Bowen ratio estimates of evapotranspiration and sap flow estimates of transpiration further validating our scaling approach. Before the monsoon season began, transpiration was near zero as was evaporation. At the on-set of the monsoon rains evapotranspiration was dominated by evaporation as it took approximately 10 days for the plants to respond to the precipitation input. Following this initial period, periods immediately following rain events were dominated by evaporation while inter-storm periods were dominated by transpiration. The surface of the coarse, well-drained soils dried quickly which rapidly reduced evaporation. Our data suggest that the partitioning of precipitation inputs in these ecosystems is very dynamic and an important component that would be missed by simply measuring whole ecosystem evapotranspiration alone.