Mangroves: getting swamped by climate change?

What is it about?

Mangroves are forested coastal wetlands. These important habitats have a fascinating relationship with the sea and thus also with climate change. In this review, the authors examine the interplay between mangroves and soil surface elevation changes necessary for keeping pace with rising seas. UNDERLYING PROCESSES Increases in the elevation of the top layer of soil in the mangrove forest can be influenced by multiple biophysical processes, including: • Increase in groundwater • Land movement • Sedimentation • Plant litter and debris deposition • Root accumulation Losses in elevation of the soil surface can be caused by: • Organic matter decomposition • Soil compaction • Erosion • Hurricanes and tsunamis • Tree mortality compromising root turnover • Land movement CLINGING ON FOR DEAR LIFE One particularly important factor to soil accumulation and erosion prevention is the mangrove roots. The authors note several experiments in which increases in mangrove root volume can affect the soil surface elevation. Mangroves are also affected by features, like nutrient availability, water salinity, flooding and sediment characteristics. For example, flooding can increase nutrient availability for the mangroves to a point, but after a certain depth and duration, the amount of roots is often reduced. In this instance, there is clearly interplay between the nature of the mangroves and the environment. FEEDBACK FORMS Fascinatingly, many of the biophysical processes described in the review are dependent on climate change, i.e. increases in carbon dioxide and sea level, and variation in rainfall. In particular, feedback effects from a rise in sea level have been observed in field studies. Changes in mangrove soil surface elevation tend to occur slowly over long periods. However, when sea levels are high for extended amounts of time, mangroves can die off. Overall, the authors hope for improved conservation efforts so that sea level rise does not outpace the mangrove soil surface elevation change rate.

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