Thu, Aug 05, 2021:On Demand
Background/Question/Methods
The leaf litter layer plays a critical role as a seed bed, habitat, and source of carbon and nutrients in soil formation. In the lower Midwest, parts of the landscape consist of successional forest on sloping sites not amenable to agriculture. While much is known about litter production and decomposition in relation to forest type, this information is not necessarily interpreted from the viewpoint of successional age. Likewise, the impacts of slope position on soil development is apparent in more extreme cases, but it remains hypothetical on more gentle slopes. In this study we examined changes in litter mass, soil organic matter (SOM) and soil pH from early spring (April) to late summer (September) down a slope gradient in representative old growth (> 120 y) and mid-successional (50-60 y) stands. Random sampling points (n = 24 per stand) were arranged along three transects (top of slope, midslope, and base of slope) situated perpendicular to the slope gradient. At each point, all litter was collected from within a 0.25 m2 quadrat frame, oven dried, and weighed. A 15 cm soil core was drawn from the center of the plot and air dried. SOM was determined by mass loss after ignition. pH was measured in a 2:3 soil:deionized water suspension. Data were analyzed by repeated measures ANOVA.
Results/Conclusions In all analyses there was no significant effect of forest age. In spring the density of the litter layer was ca. 0.8-1 kg m-2, and declined by 85-90% by September. Slope position had no effect on the density of the litter layer. Soil organic matter declined ca. 20-30% from spring to late summer. It also did not respond to the slope gradient. pH did not change seasonally, but increased from acidity (ca. 5.7) on upper slopes to near neutrality (ca. 6.8) at the base of the slope. The sharp decline in the density of the litter layer is to be expected in the warm, wet climate of this region during summer. Losses of SOM across the season reflect processing of more recalcitrant materials under warm and wet conditions. The absence of any of the classic responses of SOM to slope was unexpected. Patterns in pH suggest that migration of cations downslope may be substantial, and reflect the higher rates of soil weathering on hilltops. High levels of variability in litter density, SOM, and pH suggest this experiment lacked the power to reveal more subtle patterns.
Results/Conclusions In all analyses there was no significant effect of forest age. In spring the density of the litter layer was ca. 0.8-1 kg m-2, and declined by 85-90% by September. Slope position had no effect on the density of the litter layer. Soil organic matter declined ca. 20-30% from spring to late summer. It also did not respond to the slope gradient. pH did not change seasonally, but increased from acidity (ca. 5.7) on upper slopes to near neutrality (ca. 6.8) at the base of the slope. The sharp decline in the density of the litter layer is to be expected in the warm, wet climate of this region during summer. Losses of SOM across the season reflect processing of more recalcitrant materials under warm and wet conditions. The absence of any of the classic responses of SOM to slope was unexpected. Patterns in pH suggest that migration of cations downslope may be substantial, and reflect the higher rates of soil weathering on hilltops. High levels of variability in litter density, SOM, and pH suggest this experiment lacked the power to reveal more subtle patterns.