Asymmetric Root Distributions Reveal Trade-offs between Storm and Sea Level Rise Vulnerability in Retreating Coastal Forests

Abstract:

Sea level rise, enhanced flooding, and saltwater intrusion are driving the conversion of forests to marshes in many low lying coastal landscapes. Forest mortality typically occurs in a step-wise fashion following storm events, but the interactive role of gradual sea level rise and extreme events is unclear, and spatially heterogeneous. Here, we analyze patterns of forest retreat in the face of both acute (high winds or flooding events) and chronic (increased soil salinity) stress on several islands in the York River, a tributary of the Chesapeake Bay (USA). In a novel effort to understand the effects of saltwater intrusion on coastal forests, we surveyed the root plates of over 100 windthrown trees. These trees disproportionately allocated their biomass away from the area of inundation. The largest and longest roots were consistently uphill, furthest from the encroaching marsh. The windthrown trees consistently fall in the uphill direction regardless of aspect and prevailing wind direction, suggesting that asymmetric rooting reduces their ability to withstand high winds . Together, these observations suggest that chronic soil salinization leads to asymmetric roots that reduce the ability of coastal forests to survive high winds during acute storm events.