The Hydrologic Resilience of Temperate Forests

I have recently returned from 10 months in Tokyo, where I have been studying how hydrologic function (evaporation, transpiration, soil moisture, runoff generation, etc.) recovers from forest disturbance. Fulbright Japan funded me to spend these months with my colleagues at the University of Tokyo to synthesize our basic understanding of the mechanisms underlying hydrologic recovery of forests. Surprisingly, the hydrologic resilience of forests is not well studied. So, we compared U.S. and Japanese examples of forest disturbance due to forest harvesting, storm damage, insect outbreaks, and diseases, and tried to quantify the recovery time. Does a planted forest recover faster than one let to grow back naturally? Does stream flow recover faster in wetter or drier climates? How do hydrologic processes compensate for one another in order to produce hydrologic stability? These are examples of the questions we posed as we dug deeper and deeper into the ideas and data surrounding forest hydrologic recovery.

University of Tokyo Chiba Experimental Forest

Japan is covered by about two thirds forest, and 80 percent of that is plantation of Japanese cedar and cypress which are culturally important trees that make up those plantations. These plantations often exist on incredibly steep slopes (30 percent slope is common), so when stands on these plantations are harvested, a major concern is landslides. Soil water and groundwater increases after forest harvest, which increases the pressure on devegetated slopes to fail, often times catastrophically. Coming from the White Mountains of New Hampshire, this was a wakeup to how relatively tame our landscapes are.

Ashley Hyde, a graduate research assistant from PSU joined us in Tokyo to work on her thesis and gave a presentation on the NH volunteer science river monitoring network LoVoTECS

During my time in Japan, I was hosted in a 'sabo' laboratory at the University of Tokyo. Sabo is a term for erosion control, a major issue in the steep forests surrounding the minimal flat, inhabitable land in Japan. Forest hydrology in the U.S. is pretty diverse; some of us link hydrology with ecology, geochemistry, or geomorphology. It is similar in Japan, but it seemed like all forest hydrologists are aware of the relevance of their findings to landslides. This perspective was new to me given that soils at my local research site, the Hubbard Brook Experimental Forest, seem to have been largely in tact since the last glaciation. Again, this fact was a reminder of the relatively stable landscape we inhabit in New Hampshire.

Beyond my rewarding research experience, I also had a great cultural experience in Japan. Baseball, shrines, izakaya, jam-packed subways, bullet trains, and many other cultural highlights filled my free time in Japan. Getting to know the culture and building new research idea with Japanese colleagues made this an extremely enriching ten months.

Posted by Mark Green, Assistant Professor of Hydrology, Center for the Environment, Plymouth State University and Research Hydrologist, Northern Research Station, U.S. Forest Service