Simulated recruitment of riparian trees and shrubs under natural and regulated flow regimes on the Wisconsin River, USA

Abstract

Models that link ecological responses to hydrologic changes are important for assessing the effects of flow regulation on aquatic and riparian ecosystems. Based on the Recruitment Box Model, a graphical model used to prescribe environmental flows for cottonwood (Populus spp.) recruitment, we designed a simulation model to represent the influence of river flow dynamics on seedling recruitment of riparian pioneer woody plants. The model simulates the influence of temporal patterns of river stage on dispersal, germination, initial recruitment and over-winter survival of first-year seedlings of riparian pioneer shrubs and trees. We used the model to simulate seedling recruitment patterns for five species (Acer saccharinum, Betula nigra, Populus deltoides, Salix nigra and Salix exigua) on the Wisconsin River (Wisconsin, USA) under three flow scenarios: historic (1935-2002), simulated natural (1915-1975) and simulated regulated flows . Simulation results agreed well with field-observed relative differences among years (1997)(1998)(1999)(2000) in seedling densities for the five focal species. Simulated successful recruitment years were highly synchronous among species, but species differed in their sensitivity to flows at different times during the growing season, consistent with among-species differences in seed dispersal timing. Comparison of simulated natural and regulated flows for showed that flow regulation decreased monthly flow variability, increased late summer to winter baseflow and reduced the magnitude of spring peaks. Simulated recruitment and over-winter survival of tree seedlings of all species was enhanced under the regulated flow scenario, likely due to increased summer baseflow and reductions in peak flood magnitude. Our analyses show the utility of extending the Recruitment Box Model to include multiple species of riparian shrubs and trees, and the effects of post-colonization flows on their recruitment success. However, some key functional relationships between flow patterns and woody seedling demography (e.g. shear stress thresholds for seedling mortality) have not been adequately quantified and merit further study.

Status and Trend of Cottonwood Forests Along the Missouri River

“…Predictive, spatially explicit modeling of current and future natural cottonwood regeneration will require linking models of cottonwood recruitment (e.g., Rood et al 2005, Dixon and Turner 2006, Shafroth et al 2010) with geomorphic models that realistically represent river dynamics under various flow and sediment management scenarios, climatic trends, and local reach conditions (e.g., Larsen…”

An observation‐based stochastic model for sediment and vegetation dynamics in the floodplain of an Alpine braided river

“…Detailed semideterministic models aim at a spatially explicit description of the above interactions [e.g., Glenz, 2005], but usually require heavy parameterization [Dixon and Turner, 2006]. In this case calibration can be seriously compromised by the often limited amount of available data.…”

Sand and sandbar willow: a feedback loop amplifies environmental sensitivity at the riparian interface

“…Prior studies investigating impacts of river regulation on riparian willows, including sandbar and Gooding's willow (Salix goodingii) (Stromberg 1993;Dixon 2003;Dixon and Turner 2006), revealed correlative patterns suggesting deterministic association between alluvial sands and riparian willows. To more directly test this association, we recognized an ideal study system with Hells Canyon in the western United States, where a sequence of dams and reservoirs exist, along with regulated and free-Xowing river reaches.…”