PARENT SESSION
Poster Session # 14: Forest Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Using radial growth and foliar ¹³C as measures of drought sensitivity in trees at ecotone forest communities in northern Arizona.

Adams, Henry^*,1, Kolb, Thomas¹, ¹ School of Forestry, Northern Arizona University, Flagstaff, AZ

ABSTRACT- Climate change has the potential to seriously impact forest ecosystems in northern Arizona. An increase in temperature and changes in the amount and distribution of precipitation may alter forest growth and tree species composition. Past tree responses to climatic variability may provide insight about future forest responses. We used two approaches to compare drought sensitivity among tree species in ecotone forests of northern Arizona: 1) the ratio of radial growth during dry years to growth during wet years (D/W) for selected years between 1950 and 2000, 2) leaf ¹³C for 2001 (average precipitation) and 2002 (severe drought). At the pinyon-juniper woodland - ponderosa pine forest ecotone, we compared drought sensitivity between Pinus ponderosa and P. edulis on three soil types based on different parent materials representing a gradient in water availability: sedimentary, flow basalt, and basalt cinders. At the ponderosa pine - mixed conifer forest ecotone we compared sensitivity among P. ponderosa, P. flexilis, and Pseudotsuga menziesii. We expected that trees growing in soils with greater water availability and higher in their elevational range would be less sensitive, and sensitivity would vary among co-occurring species and would be similar based on D/W and ¹³C. At low elevations P. ponderosa was more sensitive to drought based on D/W than P. edulis and was more sensitive on cinder soils. In contrast, response of ¹³C to drought suggested no difference between these species at the leaf level. P. ponderosa at the ponderosa pine - mixed conifer ecotone was less sensitive than P. flexilis and Pseudotsuga menziesii based on both D/W and ¹³C, and P. ponderosa at high elevations was less sensitive than at low elevations for both measures of sensitivity.

Key words: carbon isotope ratio, dendroecology, drought sensitivity, ecotone