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Research Questions & Approach

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It is not known how burning of the marsh at BNWR influences belowground production and decomposition, and soil organic matter accumulation, or how these processes interact with marsh elevation, sea-level rise, and loss of this critical habitat. Given these data gaps, we addressed the following questions:

Does the annual prescribed fire regime adversely or positively affect marsh elevation, and does it contribute to marsh loss at BNWR?
If fire reduces soil organic matter accumulation, which lowers marsh elevation relative to sea level, it contributes to marsh loss. Conversely, if fire increases soil organic matter accumulation, which raises marsh elevation relative to sea level, it slows the rate of marsh loss.

What is the fire return interval (i.e., frequency) that would best achieve the refuge’s fire management objectives while maximizing marsh habitat stability through maintenance of marsh elevations?
If prescribed annual burns are found to adversely affect marsh elevation and contribute directly to loss of marsh habitat, an immediate decision will be required from the Refuge Manager on whether to stop burn activities and abandon the fire management objectives or evaluate if less frequent burns (e.g., 3 – 5, or 7 - 10 year return intervals) will reverse the negative effect and yet still meet the goals for fuel loads and plant species cover. Conversely, if annual burns are found to positively affect marsh elevation and slow the rate of marsh loss, the Refuge Manager may decide to continue annual burns and determine if less frequent burns (e.g., 3–5, or 7-10 year return intervals) will enhance the positive effect while still meeting fire management goals.

In this study, we experimentally determine how a rotation of prescribed burns affect soil organic matter accumulation and surface elevation trends in marshes at BNWR. We examine the effects of four treatments (annual, 3-5 year or 7-10 year intervals and a no burn control) on the accretionary processes (sediment deposition and soil organic matter accumulation) sustaining marsh elevation relative to sea-level rise. Our data will be used to identify key processes controlling elevation, and how prescribed burning affects these processes, and, ultimately, marsh elevation change. Experimental data on accretionary processes collected in this study will be integrated into a USGS inundation model that forecasts the effects of sea-level rise on the fate of BNWR marshes. The output of the model will be used to assess the risk that prescribed burning poses to long-term sustainability of tidal marsh habitats at BNWR.

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