This year’s Harper Prize winner is Rutuja Chitra-Tarak for her paper; The roots of the drought: Hydrology and water uptake strategies mediate forest‐wide demographic response to precipitation. Rutuja received a PhD from the Indian Institute of Science, Bangalore, went onto to do a post-doc at the Smithsonian Environmental Research Center, USA, and is now a post-doctoral researcher at the Los Alamos National Lab in New Mexico, USA. Read part 1 of the interview.
Q. The approach and the results of your study are quite novel and impressive, so tell us, what did you find?
One finding that I found fascinating early on was that the deep rooting zone of the forest showed a more intense and prolonged water scarcity compared to the shallow rooting zone through the multi-year rainfall drought. This delayed recharge phenomenon was also observed in the water-table data, which took four years of normal rainfall to begin recharging.
Also interesting is that of the twelve species we focused on, the four co‐dominant species expected to be in strong competition for the critical resource of water, displayed distinct water-uptake depth indices, supporting the hypothesis that competition drives hydrological niche separation.
And lastly our most interesting result: after the prolonged drought the species that we ranked as relying on deeper water were the ones that died more than the shallow water species, which showed no mortality response to the drought. Counter-intuitive as it may seem for deep-rooted species to show higher vulnerability to drought, it highlights the general expectation from life-history theory that species dependent on high resource levels (in this case deep water that may be normally abundant) would suffer more in the absence of that resource (in this case in the event of a rare drought)–than organisms evolved to tolerate water stress.
Q. How do you think the results of your study improve our knowledge in community ecology and climate change research?
We have shown that, for the long‐lived organisms such as trees, that hydrological niche dynamics play out over decades, and that when we think of droughts as potentially changing communities, it is essential that we know the droughts that are experienced by the community members and not simply a statistical metric of anomalous rainfall (such as the “x-year drought” approach).
The result of co-dominant species that represent half the trees in Mudumalai showing distinct rooting strategies supports the biomass-diversity relationship, and demonstrates a long-term, below-ground explanation for coexistence.
Q. Are you planning on pursuing this work with new (modelling or field) experiments? What are your plans for the future?
Yes, absolutely. In fact, this work has opened up a whole new new research agenda for me that will keep me busy for years to come. First, I am rigorously testing and developing the new framework in various forest types: during my last post-doc at the Smithsonian Environmental Research Center, USA, I led a field campaign to gather the missing pieces of data for this model in its ForestGEO plot, which is a diverse forest in the mid-Atlantic US. We instrumented the stand for hydrology, measured water-uptake depths via isotopic tracers, identified rooting depths with DNA barcodes. I have also been testing this framework at the seasonally dry tropical forest of Barro Colorado Island, Panama. Now as a post-doc with the NGEE-Tropics project at the Los Alamos National Lab in New Mexico, US, I plan to develop this model further so as to better incorporate plant physiology and develop a module that can be incorporated with Earth System Models.
There are plenty of exciting lines of enquiry to pursue. How do rooting strategies coordinate with above-ground hydraulic traits? How general is our result of trees relying on deep water dying more in a rare drought? Can we have a general framework based on climate of a site and what kind of a drought would likely kill a tree? I’m hoping to find a research position that will allow me to build a team of researchers that can pursue these questions.
Read the full paper online: The roots of the drought: Hydrology and water uptake strategies mediate forest‐wide demographic response to precipitation. You can also find the rest of the shortlisted papers in a special virtual issue on the journal website.