Role of lammas growth in recovery of Douglas-fir seedlings from deer browsing, as influenced by weed control, fertilization, and seed source

Abstract

This study examined the effects of weed control, nitrogen fertilization, and seed source on lammas growth (second flushing) in Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings. It also assessed the occurrence of deer browsing as related to these silvicultural treatments and examined the role of lammas growth in seedling recovery and escapement from deer browsing. Weed control significantly increased the occurrence of lammas growth, presumably because of greater soil moisture and nutrient availability. Nitrogen fertilization decreased lammas growth significantly, at least in part by favoring weed growth. Lammas growth was not influenced by seed source. The increased lammas growth associated with weed control mediated the effects of deer browse. Although multiple-year browsing occurred more commonly on weeded than unweeded seedlings, after two growing seasons weeded seedlings that were repeatedly browsed were twice as large as nonbrowsed, nonweeded seedlings. On one site, stock of wild origin was more heavily browsed than that from a seed orchard.