Madrean pine-oak forest in Arizona: past dynamics, present problems

Abstract

This paper synthesizes research on presettlement dynamics and modern disruption of Madrean pine-oak forests in Arizona. In response to surface fires characteristic of presettlement times, pines were fire resistant, exhibiting high top-survival, whereas oaks were fire resilient, exhibiting lower top-survival but pronounced resprouting. Thus, low-severity fire favors pines, but resprouting allows oaks to rebound during inter-fire periods. Age structures reveal large increases in stand density, especially for oaks, as a result of modern fire suppression, suggesting more open conditions and higher pine:oak ratio during presettlement times. Stands were, in fact, so open that fire-caused thinning rarely stimulated radial growth. Frequent fires also apparently excluded less fire tolerant species, which have invaded some pine-oak sites. In anomalous stand-replacing crown fires, seedling establishment was very low for pines and oaks, but most oaks resprouted. Pinus leiophylla also resprouted but at low levels, which might nonetheless be an important source of future pines. These results suggest anomalous high severity fires can transform Madrean pine-oak forests into more homogenous oak woodlands. This synthesis argues for urgent restoration using a variety of flexible approaches.

Parent Publication

• Proceedings of the 2002 fire conference: managing fire and fuels in the remaining wildlands and open spaces of the Southwestern United States

Citation

Barton, Andrew M. 2008. Madrean pine-oak forest in Arizona: past dynamics, present problems. In: Narog, Marcia G., tech. coord. 2008. Proceedings of the 2002 Fire Conference: Managing fire and fuels in the remaining wildlands and open spaces of the Southwestern United States. Gen. Tech. Rep. PSW-GTR-189. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: p. 185-192