PS 5-47 - CANCELLED - Hydrologic and geomorphic process domains provide a synthesis of disparate riparian forest types

Background/Question/Methods

The action of flowing water in riparian (river corridor) ecosystems can drive both biotic disturbance and geomorphic development. Some riparian forests are clearly structured by flood damage or inundation. Others more so by the patterns of channels and landforms within the landscape. The concept of “process domains” – spatial variability in hydro-geomorphic processes that can drive temporal patterns of ecological disturbance and development – offers one unifying framework for the impressive diversity both within and among riparian forests. We have extensively studied the geomorphology, hydrology, and riparian forests of multiple 4^th – 6^th-order stream corridors of the Lake Erie Gorges of western New York State, where the Allegheny Plateau borders the Great Lakes Plains. These systems are highly varied within a geographically local range. We propose that riparian process domains are defined here, as they may be elsewhere, by the intersection of hydro-geomorphic properties of sediment composition and channel confinement. Stream channels present a continuum from tightly to minimally confined, but sediment size class offers three distinct erosional conditions: erosion-resistant cohesive silts and clays, erosion-resistant large cobbles and boulders, and highly erodible sands and fine gravels. Thus, this framework offers six process domains.

Results/Conclusions

Confined channels are not maintained in highly-erodible sediments, and the bar-braided systems where they are unconfined are typically too transient to develop forest vegetation. Additionally, confined coarse-sediment corridors, often simple and dominated by colluvial processes (gravity/landslide), tend not to develop riparian stands distinct from surrounding forests. In contrast, both confined and unconfined silt/clay channels, and unconfined cobble/boulder channels promote long-term riparian forest development if located within a forested biome. Upland stream corridors of the Lake Erie Gorges are coarse-sediment dominated but unconfined within their broader valleys, and support primary successional chronosequences linked to deposition and stabilization of complex landform mosaics. There is minimal flood disturbance after stand initiation. In contrast, Lake Plain reaches promote flood-mediated stands along confined meandering silt/clay channels, with stand age and development reflecting secondary succession after discrete disturbances. Where silt/clay channels are unconfined, physical flood destruction is instead minimal. However, large expanses of terrain are more gently inundated for extended periods, restricting forest composition to species tolerant of this. We suggest that, viewed within this sediment x channel confinement process domains framework, riparian forests can be broadly categorized into three fundamental types: primary-successional, flood-mediated secondary-successional, and inundation-habituated.