Responses of a riparian forest-floor arthropod community to wildfire in the middle Rio Grande Valley, New Mexico

We documented patterns of species extirpation, shifts in species dominance, and rates of recolonization of litter-layer arthropod species following a catastrophic forest fire. The study site was located along the Rio Grande within the Bosque del Apache National Wildlife Refuge, Socorro County, NM, in a riparian forest dominated by cottonwood [Populus deltoides ssp. wislizenii (S. Watson) Eckenwalder] and salt cedar (Tamarix chinensis Loureiro). The forest-floor arthropod community was sampled with 18 pitfall traps during 1994-1997. The study site burned in June 1996, and the intense fire reduced the litter layer to mineral ash and killed all the above-ground portions of trees; salt cedar and some cottonwood trees began to stump-sprout shortly after the fire, and achieved heights of two in by October 1996. The prefire forest-floor arthropod community consisted of 80 species, dominated by spiders (Lycosidae, Gnapbosidae, Salticidae), beetles (Carabidae, Staphylinidae, Cryptophagidae, Tenebrionidae), isopods (Armadillidae, Porcellionidae) and crickets (Gryllidae). The surviving postfire arthropod community was dominated by generalist ants (Formicidae). The dominant cricket, Gryllus alogus Rehn (Orthoptera: Gryllidae) I exhibited a rapid recovery in abundance following the fire, and the number of certain species that preferred open, bare-ground habitat [e.g., the tiger beetle Cicindela punctulata Olivier (Coleoptera: Carabidae)] increased on the burned site. During the 9 mo following the fire, 79 arthropod species were recorded from the fire site, 29 (37%) of which had not been recorded before the fire. Of the original prefire 80 artbropod species, 30 species (37%) were not recorded after the fire, and overall arthropod abundance was substantially reduced. The extirpated species were generally uncommon before the fire, while the more abundant species displayed more successful recolonization. These results suggest that wildfire in the Rio Grande riparian forest of New Mexico can have a substantial, short-term impact on abundance and species composition of the forest-floor arthropod community, and that both survivor activity and recolonization processes by dominant species can be rapid. Given the capacity for rapid recolonization by these arthropod species, the long-term recovery of the forest-floor arthropod assemblage will likely be driven by the postfire recovery rate of the plant community and eventual structure and composition of the forest floor litter layer.