10 November 1999
William H. Moir & John A. Ludwig
A CLASSIFICATION OF SPRUCE-FIR
AND MIXED CONIFER HABITAT TYPES
OF ARIZONA AND NEW MEXICO
U.S. Department of Agriculture, Forest Service, Research Paper RM-207, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO, July 1979, 47 pages, black-and-white photgraphs, maps
Nineteen major forest habitat types (HT's) are described on the basis of extensive reconnaissance data thoughout the major mountain ranges of Arizona and New Mexico. Eight of these HT's are within spruce-fir forests where either Picea engelmannii or Abies lasiocarpa are the climax dominants; the remainder are within mixed conifer forests where Abies concolor, Picea pungens and Pseudotsuga menziesii are climax dominants or codominants. Sixteen other HT's are briefly described based on limited data, usually from one geographic location.
William H. Moir, Consultant
Rodeo, New Mexico
John A. Ludwig, Associate Professor
New Mexico State University
Spruce-fir forests occupy less than 0.55% of Arizona and about 2% of New Mexico. Despite this limited distribution, these high elevation forests are important and valuable resources, providing major snow catchement and watershed areas and serving as focal points for winter and summer recreation. The subtending mixed conifer forests, covering about 3% and 4% of Arizona and New Mexico, respectively, are intensively utilized for timber, range and wildlife production, watershed management, and recreation. These forest types respond in complex ways to many man-caused and natural impacts and treatments such as timber harvesting, fire, recreation usage, and foraging by livestock and game.
Scientists and land managers have recognized the need to classify these forests intc, units of like biological potential (Alexander 1974, Jones 1974, Layser 1974). This study gives a classification of the spruce-fir and mixed conifer forests based upon the concept of habitat types (Daubenmire and Daubenmire 1968). Each habitat type embraces a relatively narrow range of environmental variation and can be identified in oldgrowth forest stands (late seral to climax) by the dominant plants in each vegetation layer (canopy layer, tree regeneration, shrub, and herbaceous layers). The effeus of management practices or natural impacts within a forest habitat type can be understood and predicted in terras of seral communities, growth rates and potentials for various tree species, and rates of succession. The biological potential and forest responses are more uniform within a habitat type than across different habitat types. By stratifying a forest region into habitat types, managers are given an ecological basis for predicting effects of forest treatments and attaining maximum productive potential (Layser 1974, Pfister 1974).
Existing knowledge of habitat types in spruce-fir and mixed conifer forests in Arizona and New Mexico is rudimentary. Regional vegetation maps are very generalized, usually including within a single mapping unit very different forest habitat types (New Mexico Agricultural Experiment Station 1957, Choate 1966, Kuchler 1964, Nichol 1937, Spencer 1966). Daubenmire (1943) reviewed generalized relationships of the elevational sequences of forests in the Rocky Mountains (including Arizona and New Mexico).
Spruce-fir forests generally have been recognized by dominance or regeneration potential of either or both Picea engelmannii and Abies lasiocarpa. The lower boundary of these forests has been confused when Abies concolor, Pseudotsuga menziesii, Picea pungens, or species of Pinus command significant portions of either the overstory or understory. These trees constitute mixed conifer forests when occurring purely or in mixture but to the exclusion (or only accidental presence) of Picea engelmannii or Abies lasiocarpa. The lower forest boundary of the mixed conifer region is also poorly defined, with conflicting definitions in the literature. Much of this confusion arises from insufficient knowledge of the successional rates of forest communities and from preoccupation with canopy dominance or cover type rather than habitat type.
Descriptions of high elevation forest communities have been published for the North Kaibab Plateau (Merkle 1954), the Sierra Ancha Range (Pase and Johnson 1968), and the Pinaleno and Santa Catalina Mountains (Whittaker and Niering 1965). In New Mexico, Hanks and Dick-Peddie (1974) studied forest succession after fire in the mixed conifer forests of the Sacramento Mountains, and at higher elevations Dye and Moir (1977) described a spruce-fir forest type. However, little is known about the homogeneity of these forests or their relationship and similarity to other high elevation forests in Arizona and New Mexico. The objective of this paper, therefore, is to present stratification by habitat type of spruce-fir and mixed conifer forests in both states.
RESULTS AND DISCUSSION
DESCRIPTION OF SPRUCE-FIR HABITAT TYPES
Picea engelmannii Series
Abies lasiocarpa Series
DESCRIPTION OF MIXED CONIFER HABITAT TYPES
Picea pungens Series
Abies concolor Series
Pseudotsuga menziesii Series
SPRUCE-FIR FOREST: OTHER HABITAT TYPES
MIXED CONIFER FOREST: OTHER HABITAT TYPES
SUMMARY AND CONCLUSIONS
KEY TO THE HABITAT TYPES BY REGION
Table A-1. Dynamic status of trees
Tables A-2 to A-5. Species importance values by habitat type