Seedling Submergence Tolerances Accurately Predict Riparian Tree Species Distributions: Insights to Help Design Environm
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PHYSICAL AND BIOTIC DRIVERS OF CHANGE IN RIPARIAN ECOSYSTEMS
Seedling Submergence Tolerances Accurately Predict Riparian Tree Species Distributions: Insights to Help Design Environmental Flows Christian O. Marks 1,2
&
Hanna Atia 3
Received: 28 February 2020 / Accepted: 1 September 2020 # Society of Wetland Scientists 2020
Abstract Quantification of flooding thresholds that govern species distributions on microtopographic gradients in floodplains can help design environmental flows, but the multiple correlated dimensions of flooding such as frequency, depth, duration, and timing are a challenge. We postulated that species distributions are limited by the most stressful combination of flooding dimensions when the plants are in their most susceptible developmental stage. To test this idea, we measured survival of young seedlings in pots subjected to flood treatments that completely submerged the seedlings in stagnant water with and without suspended sediments for durations of up to 6 weeks during the growing season. This measure of flood tolerance predicted floodplain distributional limits of 16 tree species with high accuracy (adj. r2 = 0.91). The strength of the result suggests that seedling ability to survive complete submergence in stagnant water for prolonged periods is an important mechanism limiting species distributions in riparian forests. We propose that environmental flows that completely submerge the seedling layer in floodplain forest with stagnant water for at least 3 weeks are likely to be more effective at eliminating invading upland species than flows that only flood the soil up to the root collars of seedlings. Keywords Bottomland forest . Floodplain forest restoration . Flood tolerance . Median lethal time . Riparian vegetation zonation
Introduction Alteration of flood regimes by dams has degraded floodplain forest ecosystems on many large rivers around the world (Dister et al. 1990; Friedman et al. 1998; Merritt and Cooper 2000; Garófano-Gómez et al. 2013; Greet et al. 2013; Smith et al. 2013; Sun et al. 2014; Gope et al. 2015). Environmental flow prescriptions for regulated rivers seek to diminish those impacts by restoring critical components of the flood regime (Richter and Richter 2000; Rood et al. 2005; Poff et al. 2010; Arthington et al. 2018). For example, the Sustainable Rivers Project is a partnership between the United States Army Corps
* Christian O. Marks [email protected] 1
The Nature Conservancy, Northampton, MA 01060, USA
2
Department of Environmental Conservation, University of Massachusetts, Amherst, MA 01003, USA
3
Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
of Engineers and The Nature Conservancy to develop environmental flows through adaptive reservoir management on major rivers across the United States (Warner et al. 2014). The Army Corps operates 14 flood control dams on tributaries of the Connecticut River. There are also 36 large hydropower and water storage dams in the watershed. These dams have reduced flooding, especia
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