Patterns of growth and mortality in the endangered Nichol's Turk's Head Cactus (Echinocactus horizonthalonius var. nicholii L. Benson; Cactaceae) in Southeastern Arizona

Abstract

Nichol’s Turk’s Head Cactus (Echinocactus horizonthalonius var. nicholii L. Benson; Cactaceae) occurs in a few isolated populations in the Sonoran desert of southcentral Arizona (Pima and Pinal counties). The populations of this variety are disjunct from the more widespread variety that occurs in the Chihuahuan desert of Texas and Mexico. This species occurs only on limestone-derived soils, and the nicholii variety was federally listed as endangered in 1979. Since 1995 we have monitored study plots of this cactus in the Waterman Mountains (AZ), measuring growth and reproduction of about 175 tagged individuals. Growth rates were slow, averaging 0.3 cm in height and 0.2 cm in width per year. Plants usually began flowering when they reached around 4 cm high and 8 cm wide. Of the 52 deaths recorded since 1995, about half followed a visible decline in condition; the rest were unanticipated. There was a distinct jump in mortality during the past two years, possibly due to drought.

Parent Publication

• Southwestern rare and endangered plants: Proceedings of the Fourth Conference

Citation

McIntosh, M. E.; McDade, L. A.; Boyd, A. E.; Jenkins, P. D. 2007. Patterns of growth and mortality in the endangered Nichol''s Turk''s Head Cactus (Echinocactus horizonthalonius var. nicholii L. Benson; Cactaceae) in Southeastern Arizona. In: Barlow-Irick, P.; Anderson, J.; McDonald, C., tech eds. Southwestern rare and endangered plants: Proceedings of the Fourth Conference; March 22-26, 2004; Las Cruces, New Mexico. Proceedings. RMRS-P-48CD. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 77-82