Mini-Review: Stemflow as a Resource Limitation to Near-Stem Soils

Abstract

Stemflow, a precipitation and solute supply to soils near tree stems, can play a wide array of roles in ecosystem functioning. However, stemflow’s ecohydrological functions have been primarily studied in forests with voluminous stemflow because resource subsidy is currently considered stemflow’s only impact on near-stem soils. This common assumption ignores controls that stemflow generation may exert via resource limitation (when stemflow < open rainfall and near-stem throughfall is negligible). We reviewed selected literature across numerous forests to evaluate the predominance of stemflow as a potential resource limitation to near-stem soils and characterized the concentrated, but meager, solute flux from low stemflow generators. Global observations of stemflow were highly skewed (skewness = 4.6) and leptokurtic (kurtosis = 28.8), where 69% of observations were ≤2% of rainfall. Stemflow ≤ 2% of rainfall is 10–100 times more chemically enriched than open rainfall, yet low volumes result in negligible solute fluxes (under 1 g m-2 y-1). Reduced stemflow may be the global and regional norm, creating persistently dry near-stem soils that receive infrequent, salty, and paltry precipitation flux if throughfall is also low. Ignoring stemflow because it results in scarcity likely limits our understanding of ecosystem functioning as resource limitations alter the fate of soil nutrients, energy flows, and spatial patterning of biogeochemical processes.

Importance of rainfall partitioning in a northern mixed forest canopy for soil water isotopic signatures in ecohydrological studies

“…They were also an order of magnitude lower than values from Levia and Germer () and for red pine and deciduous species in eastern North American studies cited in Buttle and Farnsworth (). Nevertheless, Van Stan and Gordon () noted that 45% of SF observations in temperate forests gave SF : P g ratios <0.01. Ratios seen here were also similar to values from Buttle and Farnsworth (), Buttle et al (), and Bialkowski and Buttle () for pine and mixed hardwood stands in southern Ontario, all of whom derived SF depth by dividing SF volume by projected crown area as was done here.…”

“…Our inability to observe greater SWC s close to the tree bole relative to distal sites may reflect the macroporous nature of the soil (Buttle & McDonald, ) combined with the time lag between rainfall events and SWC measurements (up to six days), which would have allowed SF inputs to drain through the upper soil. SF contributions to near‐bole soils may also have been countered by reduced TF inputs to the soil surface near the bole (Van Stan & Gordon, ). Bialkowski and Buttle () reported increased TF with proximity to the bole of a sugar maple in southern Ontario but did not observe a significant change in TF with distance from the bole for 36‐ and 57‐year‐old red pines.…”

“…Increased branch biomass and bark surfaces near the bole (Levia & Herwitz, ) might reduce canopy gaps that otherwise would allow TF to reach the near‐bole soil. In addition, SF fluxes measured at the height of the installed tubing may overestimate water reaching the near‐bole soil surface, because SF may be taken up by vascular and nonvascular epiphytic vegetation, which tends to be densest by the base of tree boles (Van Stan & Gordon, ) although it is not known if epiphytes were present on the boles of the instrumented trees. This highlights the continued need to explore controls on SF and TF production and their implications for water delivery to the soil surface with increasing distance from the tree bole.…”

Rainfall partitioning varies across a forest age chronosequence in the southernAppalachianMountains

“…These results agree well with expectations of stemflow generation from previous research that showed wide variations in stemflow and bark water storage among a similar suite of species (Levia & Herwitz, 2005;Van Stan & Gordon, 2018). Although we did not quantify it specifically, we also observed that younger trees generally had smoother bark than older trees, especially in A. rubrum, B. lenta, and Carya spp.…”

“…Our model is one of only a few methods that can estimate how variations in litter biomass and climate affect litter interception in forests (Guiditta, Coenders-Gerrits, Wenninger, Greco, & Rutigliano, 2018;Van Stan & Gordon, 2018). Our model is one of only a few methods that can estimate how variations in litter biomass and climate affect litter interception in forests (Guiditta, Coenders-Gerrits, Wenninger, Greco, & Rutigliano, 2018;Van Stan & Gordon, 2018).…”