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Type: Journal Article
Author(s): Melissa Savage; Thomas W. Swetnam
Publication Date: 1990

Pattern in ponderosa pine (Pinus ponderosa Laws.) forests in the American southwest is significantly influenced by fire (Cooper 1960). The fire-scar record in tree rings reveals that the occurrence of fire has been greatly reduced throughout the region in the past century (Swetnam, in press). Many authors have argued that this decline was caused by dramatic land-use changes associated with European settlement in the last two decades of the 19th century (Weaver 1951, Cooper 1960, Biswell et al. 1973, Dieterich 1980a, Madany 1981). Herd numbers of domestic grazing animals, particularly sheep, rose steeply in the Southwest at that time (Bailey and bailey 1986). Intense grazing removed the grass that had fueled light, episodic surface fires. After grazing herds dwindled in the 20th century, active fire-suppression policy maintained low fire frequency. A second thesis, that reduced fire frequency at the turn of the century is responsible for major structural changes in ponderosa pine communities, has been postulated by a long lineage of studies. In the early decades of the 20th century, significant increases in establishment and survival of ponderosa pine in the region caused a shift from an open forest to an increasingly young, dense, and even-aged forest. Explanations for this regeneration pulse cite anthropogenic causes, in particular, elimination of frequent fires by livestock grazing, and subsequent fire-suppression activities, Low-intensity fires thin ponderosa stands by killing seedlings and saplings in a patchy manner. In addition, grazing may favor pine recruitment by reducing competition from grass and exposing a mineral seedbed.

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Citation: Savage, Melissa; Swetnam, Thomas W. 1990. Early 19th-century fire decline following sheep pasturing in a navajo ponderosa pine forest. Ecology 71(6):2374-2378.

Cataloging Information

Partner Sites:
  • fire decline
  • fire frequency
  • fire scars
  • livestock grazing
  • Pinus ponderosa
  • ponderosa pine
Record Last Modified:
Record Maintained By: FRAMES Staff (
FRAMES Record Number: 10073
This document is part of the Southwest FireCLIME Annotated Bibliography, which includes published research related to the interactions between climate change, wildfire, and subsequent ecosystem effects in the southwestern U.S. The publications contained in the Bibliography have each been summarized to distill the outcomes as they pertain to fire and climate. Go to this document's record in the Southwest FireCLIME Annotated Bibliography.