UVM Theses and Dissertations
Format:
Print
Author:
Stovall, Jeremy
Dept./Program:
Natural Resources
Year:
2007
Degree:
MS
Abstract:
Late-successional riparian forests regulate autotrophic production in low order streams through shading provided by adjacent and over-hanging canopies. However, few studies have directly linked forest structure with periphyton biomass in adjoining stream reaches. Our hypotheses were: 1) heterogeneous horizontal structure in old-growth forests creates a more spatially variable below-canopy light environment compared to mature forests; and 2) variability in light availability over streams correlates with the spatial distribution of periphyton biomass. We surveyed 15 low-order stream reaches in old-growth and mature northern hardwood-hemlock forests of the Adirondack Mountains of New York. Riparian forest structure was inventoried, and the below-canopy light environment over the center of neighboring stream channels was quantified using hemispherical canopy photography. We measured the chlorophyll a density of periphyton sampled from artificial substrates in late summer at the same locations where light was measured. Multivariate analyses (AIC[subscript c] and CART) were performed to describe the below-canopy light environment as a function of forest structure and topography, and periphyton biomass as a function of the light environment.
CART results indicated that belowcanopy light decreased as forest structural characteristics progressed with stand development, but spatial variability in available light increased. Multivariate models of horizontal forest structure (e.g. gapiness) and topography showed strong relationships with the below-canopy light environment of late-successional forests, specifically regarding mean light intensity and spatial variability. Chlorophyll a density was highly correlated with the spatial distribution of light availability. Structurally complex old-growth riparian forests create a mosaic of heterotrophic (shaded) and autotrophic (lighted) micro-habitats along low-order stream reaches. These results indicate that headwater streams within late-successional temperate forests include a heterogeneous mix of high and low light locations. This contrasts with the prevailing assumption that such streams typically rely upon heterotrophic inputs from a closed canopy forest for organic production.
CART results indicated that belowcanopy light decreased as forest structural characteristics progressed with stand development, but spatial variability in available light increased. Multivariate models of horizontal forest structure (e.g. gapiness) and topography showed strong relationships with the below-canopy light environment of late-successional forests, specifically regarding mean light intensity and spatial variability. Chlorophyll a density was highly correlated with the spatial distribution of light availability. Structurally complex old-growth riparian forests create a mosaic of heterotrophic (shaded) and autotrophic (lighted) micro-habitats along low-order stream reaches. These results indicate that headwater streams within late-successional temperate forests include a heterogeneous mix of high and low light locations. This contrasts with the prevailing assumption that such streams typically rely upon heterotrophic inputs from a closed canopy forest for organic production.