Vegetation Inventory, Classification and Monitoring for Walnut Canyon National Monument

Jenkins, Philip; Reichenbacker, Frank; Johnson, Kristen; Gondor, Anne

This report presents the results of studies of the vegetation and flora of Walnut Canyon National Monument, Coconino Co., Arizona. Tasks for the project included: (1) classify plant communities of the Monument according to the Brown, Lowe, and Pase system to the subassociation level; (2) map the plant communities of the Monument; (3) list the native and alien floras; (4) establish a minimum of ten permanent vegetation monitoring plots and obtain a spring and summer reading for each; (5) report on the geology, soils, and human history of the Monument; and (6) locate and rephotograph at least five historic photographs that illustrate possible changes in the vegetation and other natural features. A total of five plant subassociations were described and mapped: two Rocky Mtn. Montane Conifer Forest communities, two Great Basin Conifer Woodland communities, and one Rocky Mtn. Riparian Deciduous Forest community. Ponderosa pine forests dominate the rims on the west side of the Monument, while the drier eastern parts are dominated by pinon-juniper woodland. The canyon slopes are dominated on the cooler sites by Douglas fir and Gambel oak, and on the drier sites by banana yucca and pinon-juniper. The canyon bottom is characterized by patches of deciduous trees and open areas. Ten permanent vegetation monitoring plots were established that ranged in size from 10 m x 20 m to 25 m x 25 m. The spring and summer readings indicated relatively minor differences in species composition between the two seasons. The native flora consists of 285 vascular plant species in 62 families, of which the Sunflower Family is the most represented, and the alien flora consists of 21 species in 12 families, with the Grass Family the largest. The historic photographs show that the density of some trees, especially Douglas fir, has increased dramatically in the past four to six decades. This is attributed to a drastic alteration in the pre-settlement fire regime. Management recommendations include: (1) studies of the role of fires in the natural ecology of Walnut Canyon; (2) study of the feasibility of removal of some of the alien plant species; (3) the monitoring plots should not be revisited more than once every five to ten years; (4) sample only woody and herbaceous perennial plants in the monitoring plots and and only take one reading in May; (5) pressed scientific plant collections should be housed at an easily accessed regional herbarium.