Variation in Tree Growth along Soil Formation and Microtopographic Gradients in Riparian Forests
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PHYSICAL AND BIOTIC DRIVERS OF CHANGE IN RIPARIAN ECOSYSTEMS
Variation in Tree Growth along Soil Formation and Microtopographic Gradients in Riparian Forests Christian O. Marks 1,2
&
Brian C. Yellen 3 & Stephen A. Wood 4,5 & Erik H. Martin 6 & Keith H. Nislow 7
Received: 24 March 2020 / Accepted: 13 August 2020 # US Government 2020
Abstract Policy makers are interested in managing forests to store carbon. Optimizing this strategy requires understanding how carbon storage varies across environmental gradients. We explored variation in tree growth rate, tree longevity, and surface soil organic matter across 135 Connecticut River riparian forest plots. Tree growth rate did not vary significantly with climate but rather increased with sediment accretion rate, soil pH and decreased with plot elevation, where elevation was measured relative to the stage of the 2-year flood. By contrast, surface soil organic matter was negatively related to pH and tree growth rate. Tree species longevities were greater at higher elevations with coarser soils. The faster growth rates at lower elevations allow for restoring forest structure rapidly, whereas flood intolerant but longer-lived tree species allow more durable carbon sequestration at higher elevations. The close associations of growth rate, sediment accretion, and pH suggest that riverine nutrient inputs are important to maintaining the exceptionally high productivity of floodplains. Environmental assessments of river dams should consider impacts of intercepting sediments and reducing flooding on downstream floodplain fertility and productivity. Restoration of riparian locations with high deposition of sediments and associated nutrients may be an opportunity to maximize both nutrient and carbon sequestration. Keywords Alluvial soils . Bottomland forest . Carbon sequestration . Floodplain forest . Productivity . Sediment accretion rate . Soil fertility . Soil organic matter
Introduction Forest restoration has been proposed as a strategy to help mitigate rising atmospheric carbon dioxide (CO2) concentrations (Canadell and Schulze 2014; Griscom et al. 2017), and several countries have already made ambitious reforestation pledges under the United Nations Environment Program’s
* Christian O. Marks [email protected] Brian C. Yellen [email protected] Stephen A. Wood [email protected] Erik H. Martin [email protected] Keith H. Nislow [email protected] 1
The Nature Conservancy, Northampton, MA, USA
Bonn Challenge and the New York Declaration on Forests (UN Climate Summit 2014). Initial research on this conservation strategy has focused on mapping the land that could be reforested around the globe (Nave et al. 2018; Bastin et al. 2019). The potential for restored forests to capture carbon dioxide from the atmosphere varies by forest type and geographic setting, which implies a need to prioritize sites for
2
Department of Environmental Conservation, University of Massachusetts, Amherst, MA, USA
3
Geosciences Department, University of Massachusetts, Amherst, MA, USA
4
The
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