During the last two years, southern California has experienced unprecedented drought accompanied by high temperatures. Our lab examined the seasonal water utilization traits of eight fern species in the Santa Monica Mountains. So far, we have found incredible variation in the way that these ferns utilize water to survive.
We have found some ferns that are highly dehydration tolerant, remaining green throughout the long summer drought. This species is Dryopteris arguta, pictured below.
At the end of the 2013 extended summer drought (one of the worst in California’s history!), D. arguta was barely hanging on. However, it was still green and photosynthetically active (pictured below). To our surprise, the water status of D. arguta repeatedly dropped below -8 MPa (units of tension). This is an incredibly dehydrated state for a fern, more extreme than anything we have seen in the literature.
Other evergreen ferns avoid dehydration altogether by growing only in locations with running water – an increasingly limited option in the Santa Monica Mountains! (Woodwardia fimbriata, pictured below)
Similarly, Adiantum capillus-veneris is restricted to a water fall.
Some ferns “escape”
the drought through dormancy, as seen in Adiantum jordanii, pictured on the right in the image below (Dryopteris arguta on the left).
Perhaps the most exciting survival “strategy” is that of the resurrection fern. These ferns become completely desiccated (dried out) during the summer drought. When it rains, the “dead” leaves uncurl and come back to life!
Here are two resurrection ferns after only 0.2″ rain. You can already see the shorter leaves uncurling and turning green.
We plan to continue to track seasonal water status in all these ferns during the anticipated El Nino. We have seen their different water utilization traits during the driest year on record. It will be exciting to see how they respond during one of the wettest years in California!
We recently published this research in the American Journal of Botany!
Holmlund H.I., V.M. Lekson, B.M. Gillespie, N.A. Nakamatsu, A. M. Burns, K.S. Sauer, J. Pittermann and S.D. Davis. 2016. Seasonal Changes in Tissue Water Relations for Eight Species of Ferns during Historic Drought in California. American Journal of Botany 103(9): 1607-1617.