Abating pocket gophers (Thomomys spp.) to regenerate forests in clearcuts

Abstract

Pocket gophers have long suppressed forest regeneration in clearcuts in western North America, despite the application of intensive and costly, large-scale abatement practices, which also kill non-target wildlife and may increase soil erosion. At four national forests in northern California, gophers (Thomomys bottae and T. monticola) on 50 clearcuts were baited with a 0.5% strychnine concentration on wheat or oat groats, which were presented as loose grains or in 1 × 2 cm paraffin pellets for added durability. The various baits and baiting regimes usually reduced gopher abundance by 50-100% within one month. However, gopher populations recovered too quickly to protect seedlings planted for forest regeneration, especially on plots baited with a mechanical burrow-builder. In some plots where abatement was most successful initially, gopher densities increased to levels exceeding those in control plots by 7-13 months later. As gopher populations recovered following abatement, active burrows first appeared at the plot peripheries and advanced toward the plot centres, suggesting that abated territorial residents were replaced by immigrants dispersing from the surrounding landscape.

Whereas conventional abatement practices can reduce gopher abundance in clearcuts, the small spatial and temporal scales of application encourage reinvasion of vacated ecological space. These population responses defeat the goal of forest management by increasing gopher density in clearcuts; at the same time the conifer seedlings are vulnerable to gopher predation. Predation of conifer seedlings might be reduced by not abating gophers or by using alternative harvest regimes. These alternative strategies would avoid creating the conditions under which gophers contribute to slowing forest regeneration following timber harvests, and they would avoid the widespread and possibly long-term environmental damage caused by applying acute poisons and by using the burrow-builder.