hydrology and ecology meet—and the meeting is good

HYDROLOGICAL PROCESSESINVITED COMMENTARY

Hydrol. Process. 17, 2087–2089 (2003)Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/hyp.5133

Hydrology and ecology meet—and the meeting is good

Barbara Bond*Department of Forest Science,Oregon State University, Corvallis,OR 97331, USA

*Correspondence to:Barbara Bond, Department ofForest Science, Oregon StateUniversity, Corvallis, OR 97331,USA.E-mail: barbara.bond@orst.edu

As a ‘hybrid’ scientist (I call myself an ‘ecophysiologist’) as wellas an ‘eco’ partner in collaborative research with hydrologists, I’vewatched the growth and development of the new hybrid field, ecohy-drology, with great interest. I’ve asked colleagues if they’ve heardof this new paradigm. Hydrologists typically respond enthusiasti-cally by naming people who are helping to define the field, and theyidentify high-profile, international programs and recent conferencesand special issues of journals devoted to ecohydrology. Ecologists,at least in my informal sample, are less likely to be aware of eco-hydrology as an emerging discipline, but many will add somethinglike, ‘but I suppose you could say that’s what I’ve been doing formost of my career’.

Of course, this isn’t surprising, because the ecohydrologyparadigm is emerging from the discipline of hydrology. But ifecohydrology is the science that studies the mutual interactionbetween the hydrological cycle and ecosystems (Porporato andRodriguez-Iturbe, 2002), perhaps it is time for ecologists toparticipate more actively in discussions that seek to defineopportunities for this emerging field. To that end, a group ofecologists, hydrologists and atmospheric scientists at Oregon StateUniversity organized a 10 week seminar series, ‘Perspectives onEcohydrology’, during the fall of 2002.

One goal of this seminar series was to promote cross-disciplinarycommunication. A hydrologist discussed her analyses of long-termstreamflow measurements, inferring change in transpiration by veg-etation in different places or at different times from the stream-flow patterns; another shared studies of flowpaths and residencetimes of water in catchments, leading to discussions of how vegeta-tion influences, and is influenced by, those flowpaths. An ecologistshared studies demonstrating a profound influence of small varia-tions in elevation on species composition of plant communities dueto differences in depth of the water table. She and another ecolo-gist shared their recent data demonstrating significant vertical andlateral ‘hydraulic redistribution’: mass flow of water from moistto dry soil regions through living roots. Other participants talkedabout studies relating soil water content and nutrient cycles, aboutthe potential influence of water tables on growth decline and mor-tality of Alaska yellow cedar, and about the strong influence ofairflow patterns in and above the canopy atmosphere on transpi-ration and transport of water, and hence on soil water availabilityand plant growth. Along the way we taught one another some of ourvocabularies. We learned, for example, that the hydrologists in the

Copyright 2003 John Wiley & Sons, Ltd. 2087 Accepted 22 April 2003

B. J. BOND

group define the ‘riparian area’ of a stream ina fundamentally different way than do the ecolo-gists—as the ‘saturated zone’ versus the regiondefined by a plant community type, respectively.Many of the hydrologists in our group were notfamiliar with the concept of the ‘soil–plant–atmos-phere continuum’ (SPAC; Barbour et al., 1987);many of the ecologists had not heard the term‘discretize’, which was frequently used by hydrol-ogists.

All of the scientists participating in our semi-nar series had been involved for many years, evendecades, in research that could be labelled ‘eco-hydrology’, whether they had heard of the termor not. But it is not ‘news’ that much of what wemight now call ecohydrology is not ‘new’ (Bonnell,2002): it has been around for a long time underdifferent names. A fundamental quest of plant eco-physiology is to understand the role of soil andatmospheric water (in addition to other environ-mental factors) in determining the distribution andfunction of plant species (Billings, 1985). Under-standing how soil water affects distribution andfunction of plants has recently been described asa central component of ecohydrology (Rodriguez-Iturbe, 2000). Peter Eagelson’s (2002) wonderfulnew text, Ecohydrology , provides an up-to-dateexamination of biophysical controls over the fluxesof matter and energy through the SPAC, andintroduces intriguing ideas about optimization ofcanopy structure and function. To many, these top-ics are the very essence of ‘ecosystem science’ (e.g.Waring and Running, 1998).

The participants in our seminar series agreedthat there is no reason why the concept of ‘eco-hydrology’ should not borrow questions and iden-tities liberally from other disciplines. Indeed, thereare great potential advantages if the ‘label’ inspiresmore interdisciplinary communication and collab-oration. A potential pitfall, however, is that sepa-rate communities of scientists could work on sim-ilar problems in parallel rather than in collabo-ration, reporting their findings in journals and atprofessional meetings only to their own commu-nities. Then, we run the risk of ‘reinventing eachothers’ wheels’.

Our seminar participants also agreed that theecohydrology paradigm offers many fundamen-tally new ideas and opportunities. One of the

most important of these is the goal of the scien-tific inquiry. Ecohydrology is widely touted as atool in sustainable development and managementof water resources (e.g. Zalewski, 2000). Histori-cally, hydrologists have focused more than ecol-ogists on applied problems. Ecologists stand tobenefit hugely from the credibility, infrastructureand pragmatism of hydrologists in jointly solvingreal-world problems.

Finally, seminar participants concurred thatcollaboration between hydrologists and ecologistsopens up important new scientific questions. Wewere not able to explore these exhaustively in the10 week term, but our discussions included the fol-lowing:

ž Biodiversity . Can we predict the hydrologicalenvironments that produce the most diverseecosystems?

ž Intra-inter-event interactions . The hydrologists inour seminar group tend to focus on phenomenathat occur during ‘events’, such as storms ordebris flows, whereas the ecologists and atmo-spheric scientists tend to focus on inter-eventconditions and longer term averages. Combiningthese perspectives offers possibilities for muchricher understanding.

ž Dimensionality of fluxes . Another important dif-ference that emerged between hydrologists andecologists in our group is their perspectives onthe ‘dimensions’ of fluxes. Ecologists and atmo-spheric scientists tend to develop vertical (1-D) conceptual models of exchanges of matterand energy between the geosphere, biosphereand atmosphere. Most spatially explicit ecosys-tem models are comprised of multiple, con-tiguous pixels, each of which exchanges matterand energy independently through the SPAC.Hydrologists tend to develop 3-D conceptualmodels, but often these are restricted to the geo-sphere. Again, by combining these perspectives,a much richer understanding is possible.

ž Basin-scale focus . Perhaps the greatest opportu-nities lie in establishing a common scale of focusfor hydrologists and ecologists by expanding theview of ‘watersheds’ to ‘airsheds’, ‘carbonsheds’,etc. As gravity defines the geographic bound-aries of water flow, it also defines heterogeneousregions through which matter and energy flow

Copyright 2003 John Wiley & Sons, Ltd. 2088 Hydrol. Process. 17, 2087–2089 (2003)

INVITED COMMENTARY

and circulate. Transpiration by upslope vegeta-tion affects water availability to downslope veg-etation at some point in the future, and theseinteractions impact productivity of the water-shed as a whole and complicate vegetation influ-ences on streamflow patterns. Night-time emis-sions of energy from plant canopies cause air tocool and sink, perhaps flowing out of the ‘air-shed’, carrying water vapour and respired CO2with it along the same pathways as streams, orperhaps warming at the surface and setting upbasin-scale circulation patterns. These interac-tions, and their temporal dynamics, have impor-tant implications both to basic science and sus-tainable resource management.

Above all, members of our seminar group con-cluded that the blending of ecology and hydrologyhas great synergistic potential; ecohydrology canand should be more than a simple sum of the twodisciplines. To accomplish this, we need to continueand expand our interdisciplinary communication.

REFERENCES

Barbour MG, Burk JH, Pitts WD. 1987. Terrestrial Plant Ecol-ogy, 2nd Edition. Benjamin/Cummings Publishing Company:Menlo Park, CA.

Billings D. 1985. The historical development of physiologicalplant ecology. In Physiological Ecology of North American PlantCommunities , Chabot BF, Mooney HA (eds). Chapman and Hall:New York; 1–15.

Bonnell M. 2002. Ecohydrology—a completely new idea?Hydrological Sciences 47: 809–810.

Eagelson PS. 2002. Ecohydrology . Cambridge Scientific.

Porporato A, Rodriguez-Iturbe I. 2002. Ecohydrology—a chal-lenging multidisciplinary research perspective. Hydrological Sci-ences 47: 811–821.

Rodriguez-Iturbe I. 2000. Ecohydrology: a hydrologic perspec-tive of climate–soil–vegetation dynamics. Water Resources Research23: 349–357.

Waring RH, Running SW. 1998. Forest Ecosystems: Analysis atMultiple Scales . Academic Press.

Zalewski M. 2000. Ecohydrology—the scientific background touse ecosystem properties as management tools toward sustain-ability of water resources. Ecological Engineering 16: 1–8.

Copyright 2003 John Wiley & Sons, Ltd. 2089 Hydrol. Process. 17, 2087–2089 (2003)