Pine straw raking increases evaporative flux from forest floor

Litter layer removal by commercial pine straw raking has the potential to increase forest floor evaporation (Es) by strengthening soil surface-atmosphere coupling; however, its effects on Es and soil water availability remain poorly quantified. We investigated the influence of pine straw raking on Es within a closed-canopy loblolly pine (Pinus taeda L.) plantation using non-weighing box lysimeters with both intact and removed litter layers (litter and rake treatments, respectively) over a one-year period, hypothesizing that raking would increase annual Es. We observed that Es was over twofold higher in the rake treatment. Es exhibited positive linear relationships with potential evapotranspiration (PET; R² > 0.70), with a steeper response in the rake treatment, indicating a greater increase in Es with increasing atmospheric demand in the absence of litter. Consistent with higher Es, soil moisture was lower in the rake treatment. Although litter intercepts and stores precipitation, the reduced Es associated with litter accumulation offset the effects of interception on soil water storage. This study provides field-based evidence that pine straw raking impacts hydrologic processes in southern pine plantations by increasing Es and reducing soil moisture. The hydrologic effects of raking may be particularly important during periods of high atmospheric demand or low precipitation and on soils with low water-holding capacity. Consideration of Es and stand-level water budgets can improve assessment of the potential hydrologic consequences of repeated raking, with raking frequency depending on site water availability and soil water-holding capacity rather than managed uniformly across sites.