River Hydrology and Riparian Wetlands: A Predictive Model for Ecological Assembly

Abstract

Riparian wetlands are under heavy pressure from hydrological changes produced by dam construction and water diversion projects. There has been ample documentation of the relationship between the extent of flooding and the composition of shoreline plant communities, yet we have few models that allow us to predict the impact of altered flooding regimes on riparian wetlands. In the humid temperate zone, river regulation commonly affects the distribution of two major vegetation types: wooded wetland and herbaceous wetland. The practice of reducing peak floods and augmenting minimum river flows is often followed by the succession of herbaceous to wooded wetland. We used logistic regression models to describe the distribution of wooded wetland as a function of all possible combinations of seven hydrological variables. The variables were chosen to reflect the depth, duration, and time of flooding and were calculated for four different time intervals (3, 7, 12, and 18 growing seasons). Our best model was a combination of two variables: the last day of the first flood and the time of the second flood. For three of the four time intervals, the vegetation type was correctly identified as herbaceous or wooded for >80% of the sample points. Our results suggest that models based on a few key environmental variables can be valuable tools in the conservation management of the vegetation of temperate and boreal zone wetlands.

A synthetic aperture radar–based model to assess historical changes in lowland floodplain hydroperiod

“…The ecological implications of these changes are significant because forest composition and functioning on many floodplain systems are generally controlled by extreme rather than average conditions, especially during the spring growing season [ Auble et al , 1994; Toner and Keddy , 1997]. For example, competitive sorting for most floodplain species occurs according to the maximum spring flood duration that the species can tolerate [ Townsend , 2001b], whereas a few species (notably bald cypress) require moist but nonflooded conditions for several consecutive growing seasons to become established and thrive [ Conner et al , 1986; Visser and Sasser , 1995].…”

“…In fact, Dynesius and Nilsson [1994] report that dams and other hydrologic modifications have altered flows within the majority of watersheds in the Northern Hemisphere. In particular, the construction of dams on rivers has changed the timing and magnitude of floods by reducing peak flows and augmenting low flows [ Richter et al , 1996; Stanford et al , 1996; Toner and Keddy , 1997; Vörösmarty and Sahagian , 2000]. As a consequence, Graf [1999] has noted that the impacts of dams on river discharge are several times greater than the likely impacts from climate change.…”

Species traits for future biomonitoring across ecoregions: patterns along a human‐impacted river

“…Human impact on ecosystems usually changes natural patterns in habitat variation and disturbance. Thus, the concept potentially could make quantitative predictions of the representation of functional groups of organisms (Croonquist & Brooks 1991; Toner & Keddy 1997), or in other terms, quantify ‘ecosystem health’ through the functional biodiversity of communities. Much work remains to be done before our approach will provide a reliable biomonitoring tool.…”

Riparian Forest Restoration Along Large Rivers: Initial Results from the Sacramento River Project

“…Both difficulties are exacerbated along larger rivers ( Gore & Shields 1995; Toner & Keddy 1997). Larger rivers are likely to have larger natural floods, making them more dynamic; and to have more human use, intensifying the social need to control flooding.…”