Exploring forest structural controls on soil and litter evaporation via experimental simulations

Evaporation from soil and litter (E sl ) is a key but poorly understood component of forest evapotranspiration (ET), with its magnitude influenced by atmospheric conditions, forest structure, and forest management. We simulated the relative influence of canopy shade and leaf litter accumulation on E sl using full factorial manipulations (shade = 0, 40, 71, 91%; litter = 0, 200, 400, 800 g m⁻²) over lysimeters in a well-drained sandy soil. To isolate forest structural effects, E sl was measured under primarily energy-limited conditions, and to control for changing atmospheric conditions, E sl was relativized (E Rel ) using bare soil E sl (E Ref ), which was positively related to potential ET (ET 0 ), vapor pressure deficit, and solar radiation (r 2 = 0.93, 0.96, and 0.83). Averaged across litter levels, canopy shade reduced E Rel by 17 to 32% relative to no shade, and averaged across shade levels, litter accumulation reduced E Rel by 21 to 52% relative to no litter. Empirical relationships between E sl and ET o generated coefficients (K e ) that declined as shade and litter increased, supporting a muted but persistent coupling of E sl with atmospheric drivers. Both canopy shade and litter accumulation independently influenced E sl ; however, evidence suggests litter exerts stronger mechanistic control than shading. Specifically, the highest level of litter reduced E Rel more than the highest level of shade, and the decrease in K e was generally larger as litter increased than as shade increased. These findings reveal that litter accumulation plays a dominant mechanistic role in moderating E sl and suggest that maintaining accumulated litter may be an effective management strategy for minimizing soil water loss.