Pulses of seed release in riparian Salicaceae coincide with high atmospheric temperature

Riparian shrubs and trees in the Salicaceae family release their seeds when floods that create nursery sites for germination are more frequent, but little is known about the factors controlling temporal variations in seed release within the seed release period. The seed release of three riparian tree species dominating European floodplain forests (Populus alba L., Populus nigra L., and Salix alba L.) was monitored in spring 2007 and 2008 using seed traps placed along the Middle Ebro River, NE Spain. Correlations relating biweekly seed rain intensity (seeds trapped per square meter) to meteorological (atmospheric temperature, cumulative precipitation, relative humidity, solar radiation, mean wind speed) and hydrological (river discharge) variables were investigated. The best combination of environmental variables explaining seed rain intensity was identified using an Akaike information selection criterion‐based backward selection, after accounting for temporal autocorrelation both in seed rain intensity and environmental variables. Seed rain correlated positively with temperature for P. alba, P. nigra, and S. alba, though its effect decreased with relative humidity for P. nigra. Our results can help fine‐tune the design of environmental flows to promote sexual recruitment of Salicaceae trees: Planning water releases during the hottest days of the seed dispersal period, when seed rain peaks, should maximize seed germination density and thus increase the potential for successful seedling establishment.