|DUNIWAY, MICHAEL - Us Geological Survey (USGS)|
|TWEEDIE, CRAIG - University Of Texas - El Paso|
Submitted to: Ecological Society of America (ESA)
Publication Type: Abstract Only
Publication Acceptance Date: 4/20/2014
Publication Date: N/A
Technical Abstract: Projected changes in rainfall for the western United States are uncertain with respect to seasonality and direction. In many spatially extensive arid and semi-arid environments in the western U.S., plant community responses to rainfall are dramatic and marked by high interannual variability. Plant phenological patterns (e.g., initiation of growth and production of flowers and fruit) are discrete plant responses to changing climate and effective indicators for ecosystem services such as net carbon exchange and pollination. To elucidate the role of environmental drivers in the timing of phenological events, standardized repeated phenology observations are required with coincident climatological and soil moisture measurements. We related daily phenocam estimates of canopy greenness with weekly field phenology observations using Spearman rank correlation to evaluate the effectiveness of greenness metrics as a proxy for field estimates of percent green. We also examined the role of precipitation on canopy development. Phenocam greenness estimates and weekly field observations of phenology using ocular estimates of percent canopy greenness were made for five deciduous C3 shrubs honey mesquite (Prosopis glandulosa) and five C4 perennial black grama grasses (Bouteloua eriopoda) at an arid upland grassland site in southern New Mexico through two growing seasons (Feb 2012 - Dec 2013). Results/Conclusions: Green chromatic coordinate index (gcc) values were strongly correlated with field observations of canopy greenness for mesquite (all p < 0.001, range = 0.759 to 0.853) and black grama (all p < 0.001, range = 0.588 to 0.619) supporting interpretations of phenocam estimates of canopy development. Mesquite transitioned from minimum to maximum greenness over 15 days between 20 Apr and 5 May in both years. This pattern coincides with long-term phenology patterns in which mesquite leaf out has occurred between mid-April and mid-May in 75% of 90 observations. Black grama green up quickly follows summer rain events over six days in 2012 (8-13 Sep) and 2013 (11-16 Aug). The synchronous decline in greenness for mesquite and black grama suggests that minimum air temperature or changes in day length may trigger senescence. Daily depictions of greenness demonstrate that canopy development in this water-limited system occurs rapidly and that phenocams can provide data needed to characterize greenness; however field sampling once to twice weekly is required to monitor flower and fruit or seed production. Next steps are to examine the role of soil moisture and examine relationships between environmental variables and phenophase transitions using a proportional hazards model.