Linking Grassland Canopy Structure and Function Responses to Field Experimental Drought Both Seasonally and Interannually

ABSTRACT Shifts in species composition in water‐limited ecosystems such as temperate prairies during summer droughts can lead to community‐level changes. In both short‐term experimental and long‐term drought events, C4 species decline in abundance while C3 species increase, causing reductions in above ground net primary productivity (ANPP). Thus, this study focused on linking experimental drought‐induced shifts in species composition with changes in canopy structure and function using remote sensing approaches. We took advantage of a long‐term experimental precipitation study in Central Oklahoma that has established a gradient of seven levels of precipitation in a fully factorial randomized block design: −100%, −80%, −60%, −40%, −20% rainfall exclusion, 0% change in precipitation (i.e., control) and precipitation addition +50%. Our aim was to answer the following questions: (1) How does an experimental precipitation gradient impact canopy spectral reflectance both seasonally and interannually? (2) How does canopy structure and plant species composition vary seasonally and interannually along an experimental precipitation gradient? (3) Can we link variation in canopy reflectance to canopy structure and plant species composition under experimental drought both seasonally and interannually? Our results showed that variation in seasonal and interannual precipitation can be observed in the near‐infrared (NIR) portion of the electromagnetic spectrum. A drier year has lower normalized vegetation index (NDVI) values and higher leaf area index (LAI) values due to reduced canopy greenness and increased plant litter, respectively, due to the limited water availability. High abundance of C3 species such as Lespedeza cuneata that have advantageous traits can mediate canopy responses to drought. Thus, species specific abundance, in this case the high abundance of L. cuneata , can influence canopy reflectance. Future studies should focus on understanding the impacts of resource allocation to canopy architecture as well as the relationship between leaf traits and canopy response and how these affect canopy reflectance.