Old-Field Plant Succession on the Pajarito Plateau

Foxx, Terealene; Tierney, Gail; Mullen, Mary; Salisbury, Mary

Eight fallow historic fields of the ponderosa pine and pinon-juniper cover types were surveyed to determine species composition and distribution. The purpose of the study was to understand plant succession on old fields as related to mechanically manipulated sites such as material disposal areas (MDAs). Additionally, we wanted a listing of species on disturbed lands of the Pajarito Plateau to aide in the reclamation planning of MDAs using native species. We also wanted to determine if any species could be used as an indicator of disturbance. The eight historic fields were all within Los Alamos County, New Mexico, and had been abandoned in 1943. Two sites were within the boundaries of Los Alamos National Laboratory and were studied both in 1982 and 1993. The other sites were in the northern part of Los Alamos County, on Forest Service lands, and were studied only in 1982. The study provides a description of each of the field sites, historic information about the homesteads from patent applications, a photographic record of some of the sites, and a listing of species found within each field. Statistical analyses were used to compare the information obtained from each field, data collected in two fields in 1982 and 1993, and data from MDAs in a similar time period with the old field data. We also determined which plant species were the most dominant on each site and compared that data with information for adjacent forested areas. The study showed that there were 78 different plant species found on disturbed sites. Of these 78 species, 23 were found to be dominant on one or more of the MDAs or old fields. However, only 5 species were common on all sites. The species in the genus Artemisia (A. carruthii and A. dracunculus) were found to be dominant on both MDAs and old fields. Both species were a good indicator of disturbance. When we compared the 1982 data with the 1993 data collected on two fields, we found forb species were replaced by grass as succession proceeded. A cluster analysis comparing old fields with MDAs showed that the old fields and MDAs were dissimilar. However, the cluster analysis did show that MDAs were similar to MDAs and old fields similar to old fields. The MDAs appeared to have more species common to earlier successional stages than did the old fields. Historically, the MDA disturbance is more recent than the old-field disturbance by 10 to 20 years. Species such as sweet clover and cheat grass were found on MDAs but only occasionally in old fields. Mid- to late-successional species were commonly found on old fields. Although, the disturbance history of each site is imperfectly known, the study does provide an indication of successional processes within disturbed sites of the Pajarito Plateau. Additionally, it provides a listing of species that will invade disturbed sites, species that may be used in site reclamation.