Ground-dwelling arthropod community responses to recent and repeated wildfires in conifer forests of northern New Mexico, USA

The increasing frequency and severity of wildfires in semi-arid conifer forests as a result of global change pressures has raised concern over potential impacts on biodiversity. Ground-dwelling arthropod communities represent a substantial portion of diversity in conifer forests, and could be particularly impacted by wildfires. In addition to direct mortality, wildfires can affect ground-dwelling arthropods by altering understory characteristics and associated deterministic community assembly processes (e.g., environmental sorting). Alternatively, disturbances have been reported to increase the importance of stochastic community assembly processes (e.g., probabilistic dispersal and colonization rates). Utilizing pitfall traps to capture ground-dwelling arthropods within forest stands that were burned by one or two wildfires since 1996 in the Jemez Mountains of northern New Mexico, United States (USA), we examined the potential influences of deterministic versus stochastic processes on the assembly of these diverse understory communities. Based on family-level and genera-level arthropod identifications, we found that the multivariate community structures differed among the four fire groups surveyed, and were significantly influenced by the quantities of duff, litter, and coarse woody debris, in addition to tree basal area and graminoid cover. Taxon diversity was positively related to duff quantities, while taxon turnover was positively linked to exposed-rock cover and the number of logs on the ground. Despite the significant effects of these understory properties on the arthropod community structure, a combination of null modeling and metacommunity analysis revealed that both deterministic and stochastic processes shape the ground-dwelling arthropod communities in this system. However, the relative influence of these processes as a function of time since the wildfires or the number of recent wildfires was not generalizable across the fire groups. Given that different assembly processes shaped arthropod communities among locations that had experienced similar disturbances over time, increased efforts to understand the processes governing arthropod community assembly following disturbance is required in this wildfire-prone landscape.