Where Have All the Grasslands Gone?

Fire and Vegetation Change in Northern New Mexico (page 3 of 5)

Author: Craig D. Allen. Adapted from: Allen, C.D. 1998. Where have all the grasslands gone? Quivera Coalition Newsletter, Spring/Summer.

Tales That Trees Tell

One particularly useful approach to uncover local ecological histories has been to use dendrochronological (tree-ring) methods to reconstruct patterns of fire occurrence and forest change over the last several hundred years, primarily in the Jemez Mountains but also in the Sangre de Cristos. Old trees can tell many stories if one knows how to decipher the information contained in their wood. This tree-ring work is being accomplished through a cooperative effort involving the U.S. Geological Survey’s Jemez Mountains Field Station (located at Bandelier National Monument), Professor Tom Swetnam’s group at the Laboratory of Tree-Ring Research (University of Arizona), and the Santa Fe and Carson National Forests. Since 1988 we have determined over 4,000 prehistoric fire dates from fire scars on more than 550 sampled trees, snags, logs, and stumps at 30 sites in the Jemez Mountains. In the Sangre de Cristos we have about 170 prehistoric fire dates from over 50 sampled trees at four sites. Elevations of sampled sites ranged between about 6,500 and 11,000 ft; vegetation varied correspondingly from piñon-juniper woodlands up through ponderosa pine to mixed conifer and spruce forests. Each scar is dated to its precise year of formation, and in most cases even the season in which the fire occurred was determined. Fire dates extend back to 1422 AD in the Jemez Mts. and to 1230 AD in the Sangre de Cristos.

The fire scar histories show that fire was frequent and widespread at most sites prior to the 1890s. For example, fire scar samples from El Valle (near Las Trampas) record 35 different fire years between 1607 and 1890 AD, while Monument Canyon in the Jemez Mts. records 47 fires from 1591 to 1892 AD. It must be emphasized that these were largely surface fires burning with low-intensity in primarily grassy fuels. These low-intensity fires thinned the forest by killing some of the younger trees, while most mature trees survived unscathed, protected by their thick bark. Trees that were damaged but not killed by a fire often developed an open wound which was subject to repeated scarring by subsequent fires—some Jemez trees recorded over 30 fires without being killed. The frequent fires stimulated the growth of herbaceous plants in the open forests, prevented the buildup of thick layers of needles and excessive amounts of dead wood, and promoted the rapid cycling of nutrients for plant growth.

Follow these links to:
Fires in the Forests: Then and Now
Restoring the Balance