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Restoration of dryland ecosystems is often limited by low seedling establishment and survival. Defoliation caused by insects and small mammals could be an overlooked cause of seedling mortality. In the sagebrush steppe, we examined the effect of seedling defoliation on the survival of perennial grasses commonly used as restoration materials. Under field conditions, seedlings of three perennial bunchgrass species (non-native Agropyron cristatum, and native grasses Poa secunda and Pseudoroegneria spicata) were defoliated at two intensities (30 % and 70 % leaf length removal) and frequencies (one or two clippings) and compared to a non-defoliated control. Following emergence the first year, clippings occurred at the two-leaf stage; a second clipping occurred 1 month later for repeated defoliation treatments. We monitored seedling survival and tillering for 2 years. We expected higher defoliation intensity and frequency to reduce survival for all species, but only a few treatments reduced Po. secunda survival. Conversely, larger-statured Triticeae (wheatgrasses) benefited from some defoliation treatments. In both years, A. cristatum survival increased with repeated defoliation at both intensities. Defoliation did not affect Ps. spicata survival in the first year, but a single defoliation in the second year resulted in increased survival. In both A. cristatum and Ps. spicata, higher-intensity defoliation reduced the boost to survival resulting from defoliation frequency. Seedlings with more tillers had greater survival probabilities, but tiller number was unaffected by defoliation. Further research may elucidate mechanisms seedlings use to compensate for or benefit from defoliation. In the meantime, managers should aim to select defoliation-tolerant species if they anticipate herbivory will be problematic for restoration sites.

Herbicidal control of spotted knapweed, Centaurea maculosa Lamarck, is rarely cost-effective, and sustainable control may require an integrated approach. Cyphocleonus achates (Fahraeus) is a flightless root-feeding weevil of Eurasian origin that has been introduced into North America for biological control of spotted knapweed. We hypothesized that reducing the density of spotted knapweed using reduced rates of picloram would improve the establishment of C. achates. At two sites in western Montana, three adult weevil densities (none, three, and six weevils m−2) were released in the fall (1995 at site 1 and 1996 at site 2) in 2-m2 plots encircled with enclosures to prevent weevil escape. Six picloram rates (0, 0.03, 0.06, 0.09, 0.12 or 0.15 kg ha−1) were applied the following spring before weevil emergence in a randomized complete-block design with four replications (18 treatments per replication). Spotted knapweed density and spotted knapweed and grass cover were sampled in July each year followin...