Green blog post on forb pannes

The Boston Globe takes an interest in salt marsh forb pannes!
Some water-loving plants may be out of a home as temperatures rise

Spartina likes it hot

Some like it hot. Spartina patens, the dominant grass in New England salt marsh, does, but many salt marsh forb species, pictured above, do not. In field experiments warming areas of salt marsh on the border of Spartina grass and forb panne zones, I found that the species in the forb panne, a unique and diverse group of stress tolerant forbs, were outcompeted by Spartina under warmer conditions. Plant diversity rapidly declined in experimentally warmed plots as Spartina took over.

From these results, my co-author, Mark Bertness, and I predict declines in salt marsh plant diversity and reductions in forb panne area in the near future due to global warming. In fact, in the warm years when we did our experiment (2004-2006), forb panne area was lost even in control plots, and forb pannes were lost before our very eyes. Read all about it in this month's Ecology Letters.

marsh restoration in the Gulf of Mexico

Here is a photo of the type of wave protection being put on salt marsh restorations in the Gulf of Mexico, like the ones referred to in Rusty Feagin's comment. Thanks for the photo, Rusty!

plants vs. soil - a meaningless fight

Salt marshes and mangroves are reported to protect coasts from erosion and reduce storm surges. Salt marsh area has been correlated with reduced property damage from hurricanes along the Gulf Coast (Costanza et al. 2008, Ambio), and mangrove forest purportedly protected villages and reduced the death toll of a 1999 Indian cyclone (Das and Vincent 2009, PNAS).

However, a new study about to be published in Proceedings of the National Academy of Sciences (PNAS) reports that the soil, not the vegetation, in marshes is the important the feature preventing coastal erosion. The study, led by Rusty Feagin of Texas A&M, put large cores of marsh with and without vegetation in a wave tank and observed erosion patterns. Vegetation did not affect the rate of erosion, but sandy soils eroded more quickly than organic soils. The report questions the efficacy of salt marsh restorations that aim to prevent coastal erosion.

I look forward to reading the full publication. While I am sure it is a worthy scientific contribution, I think drawing conclusions about restoration efforts from these findings is misguided. The key about marshes is that they are biogenic - the organisms (in this case, plants) build the habitat. Were the plants not present, there would not be bare soil, but rather open water. Therefore, the idea of erosion protection from marsh soils without plants is nonsensical. Additionally, the key to maintaining the habitat is not erosion resistance, but sediment balance: how quickly sediment is added compared to the rate it is eroded. The plants likely act on the sediment addition end, even if they don't always contribute to the prevention of erosion (although they likely also do this in peaty soils, like in New England marshes). Finally, the coastal protection value of marshes comes from erosion prevention AND wave attenuation. In models, it is mostly the wave attenuation process that affords coastal protection from storms.

You can read a brief about the article published online at Nature.