Plant communities on sand dunes of the Navajo Nation

Leanna Begay, Purdue University

Abstract

Ongoing drought in the southwestern US has produced more sand dunes that potentially impact natural vegetation as they move across the landscape. I studied the plant communities of five dunes over two years near Tuba City, AZ to address the following hypotheses: (1) dunes intensify the physiological stress on desert plants, so that the density and diversity of plants on dunes and behind dunes should be reduced compared to the plant communities ahead of dunes; (2) deposition on the leeward side of a dune produces different physiological pressures than erosion by wind scouring on the windward face of a dune, so that species composition should differ on lee and windward faces, reflecting species’ different ecological adaptations; and (3) traditional ecological knowledge will recognize the effects of dunes, particularly on plants of practical significance, and the potential for some native plants to stabilize dunes. The pool of plant species in this desert environment is rich: 71 species were identified on three dunes and incorporated into a field guide. On a stabilized dune, the plants were more diverse and more dense, compared to more active dunes where crests of open moving sand produced stronger zonation in species composition. Two active dunes showed parallel patterns of zonation in species composition from the leading leeward edge to the windward edge, in which species diversity was lowest near the crest, and least similar to the plant community ahead of the dune. On the windward slope of the dune, diversity and composition recovered somewhat, but the area behind the dune showed lasting reduction of diversity. Interviews with Navajo elders showed that changes in the vegetation associated with dunes and drought are recognized, and many of the adaptations of individual species that confer hardiness are also recognized and sometimes incorporated into the Navajo names for plants. Some of these adaptations, like root systems that can adapt to depositing or eroding sand, are parallel those found in other dune systems. In a region where changing climate is likely to increase dune activity, understanding plants’ adaptations to harsh dune microhabitats will improve our ability to project future plant communities and adjust resource management.

Degree

M.S.

Advisors

Rabenold, Purdue University.

Subject Area

Plant biology|Ecology|Natural Resource Management

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