El NINO

Whether it is linked directly to climate change, it is uncertain, but it has definitely been observed that El Nino events have been increasing in frequency over time (Tewksbury pers comm). It is also uncertain how this may affect mangroves in the future.  On the one hand El Nino has been positively linked to an increase of mangrove abundance in New Zealand due to the flooding of salt beds, expanding suitable mangrove recruitment areas, along with the temporary calming of previously unsuitable water ways for seedling establishment (Lovelock et al, 2010).  Unfortunately this new growth does not provide the erosion and storm protection that coastal mangroves do.

 (An increase in the frequency of El Nino will lead to some increase in Mangroves, particularly inland.)

      There has also been evidence that the warmer weather during El Nino can negatively impact mangroves by causing drought, leading to higher water salinity and a redirection of groundwater flow inland to freshwater wetlands, with a loss of nutrients for the coastal mangroves( Alongi, 2002).

(An increase in the frequency of El Nino can also lead to nutrient loss with a negative affect on mangrove abundance.)

    
     Unfortunately there has been little study done on the relationship between El Nino and mangrove forests, so it is hard to predict which scenarios will dominate.  This is an area that needs further study, however, there is already evidence in several places that mangrove recruitment inland is happening, at a loss to wetlands, and without the benefit of coastal protection as portrayed in Figure 1.  This suggests that the impacts of El Nino on mangroves is not going to be overwhelmingly negative with respect to mangrove abundance, the trees can move.  Although moving may not be possible in all areas, there has been an increase of mangroves in places like Bangladesh and Cuba, despite the increase in El Nino frequency.  This suggests that the nutrient loss due to El Nino is not as significant. (Further study will also need to be done on the effect of converting wetlands to mangrove forests.)