Gulf Coast Riceland Seed Biomass Estimates for Waterfowl Habitat Conservation

Biomass estimates of potential waterfowl foods are fundamental to estimating foraging carrying capacity of waterfowl habitat by conservation planners and managers of the North American Waterfowl Management Plan‐Gulf Coast Joint Venture (GCJV). Rice and moist‐soil seeds in Gulf Coast rice fields provide principal sources of energy for waterfowl during migration and winter. We investigated spatio‐temporal biomass dynamics of these seeds and modeled their variation in production and idled rice fields in southwestern Louisiana, southeastern Texas, and the Texas Mid‐Coast, USA, in August and November 2010–2013. We hypothesized that previous estimates of November rice and moist‐soil seed biomass from the Mississippi Alluvial Valley were not applicable to the GCJV region because climate and agricultural production practices (e.g., ratooning, crayfish [Procambrus spp.] aquaculture) are primary inter‐regional contrasts. Waste‐rice biomass was greatest in November in fields with an unharvested second crop of rice from tillers of original plants (i.e., ratoon crop; 837.7 kg[dry]/ha; CV = 16.7%) and least in fields without a ratoon crop (119.3 kg/ha; CV = 18.5%). Moist‐soil seed biomass was greatest in idled rice fields in October (477.3 kg/ha; CV = 24.8%), where substrate and rice stubble were disked at the time of sampling, and in idled fields with standing native vegetation in November (304.8 kg/ha; CV = 17.1%). Field‐level variation in waste rice in production fields in November was best explained by an interaction between field management (e.g., harvested ratoon) and rice variety. We were unable identify a reliable predictor of field‐level variation in moist‐soil seed biomass in idled fields for July–August or November (i.e., null model was best or competitive). Substituting existing seasonal moist‐soil and rice seed biomass estimates in GCJV planning models with those from our study would result in a seasonally flooded habitat objective 76% (101,974 ha) greater than the current GCJV estimate for 3 rice‐growing planning areas. We encourage conservation planners in the GCJV region to use biomass estimates from our study because they are reasonably precise for planning and implementation (i.e., CV ~ 20%) and represent most contemporary patterns of farming practices and food abundance in this region. Further, programs and incentives that promote production of ratoon rice crops and allow growth of naturally occurring vegetation in idled rice fields, followed by shallow flooding during November–February, would significantly enhance food resources for waterfowl and other waterbirds in this important landscape for North American avifauna. © 2020 The Wildlife Society.