Forest disturbance and arthropods: small-scale canopy and understory disturbances alter movement of mobile arthropods

Dispersal of ground-dwelling arthropods is understudied in forest ecosystems, which hinders understanding of effects of disturbances on population dynamics. The objective of the study was to quantify movement of ground-dwelling arthropods in response to a factorial combination of canopy gap formation via girdling and understory vegetation removal, which was shown in a companion study to alter arthropod abundance and species richness. Arthropod movement was quantified using a self-mark-capture technique where arthropods were marked as they crossed three concentric bands of different colored fluorescent powders located 3, 8, and 15 m from the center of 30 x 30 m experimental quadrats. The number of colors found on an individual was considered representative of dispersal such that the more colors detected, the more an individual moved. The likelihood that arthropods were marked with fluorescent powder and the number of colors detected differed among taxonomic groups. Most taxa were marked with one color and a high proportion of those individuals were collected adjacent to the band in which they were marked, suggesting limited dispersal. Canopy gaps and understory vegetation removal influenced movement of three taxa of highly mobile arthropods: Parajulidae and Paradoxosomatidae (detritivores), and Opiliones (scavengers). Opiliones were less likely to be marked with fluorescent powder in canopy gaps than under closed canopy in July, but more likely to be marked in August. Paradoxosomatidae were less likely to be marked in canopy gaps than under closed canopy in August, but their movement was unaffected in July. Parajulidae were more likely to be marked with fluorescent powders when understory vegetation was removed in July and August. Limited dispersal of most other ground-dwelling arthropods suggests that these more sessile taxa may experience decreased survival and reproduction if they are unable to cope with environmental change in response to natural and anthropogenic disturbances. Understanding how disturbances mediate arthropod movement can inform biodiversity conservation strategies and sustainable forest management.