Initial mortality and root and shoot growth of Valley Oak Seedlings outplanted as seeds and as container stock under different irrigation regimes

Abstract

Direct seeding of valley oak (Quercus lobata Nee [Fagaceae]), commonly used in restoration in the Central Valley of California, may be preferable to using container stock, at least in nonirrigated sites and where acorn predation can be controlled. In a stratified random experiment we tested initial growth and survival of oaks either: 1) outplanted as acorns; 2) outplanted as 3-mo-old container seedlings; 3) outplanted as 3-mo-old container seedlings that had been transplanted into larger containers 6 wk before outplanting; and 4) outplanted as 1-y-old container seedlings (commercial stock). We subjected each of these to 3 different irrigation regimes: 1) none; 2) drip; or 3) overhead. Half of the irrigated oaks were watered for 1 y, and half for 2 y. In nonirrigated plots, oaks grown from acorns that survived initial seed predation survived significantly better than oaks planted from containers. Across stock type (acorns, plants of different ages, and different sizes of containers), initial differences in plant height remained after 18 mo of growth, but growth rates were similar. Oaks grown in containers usually had more branched and more distorted root systems but all stock types successfully produced deep roots. Irrigated plants grew faster than nonirrigated plants. Plants weaned from irrigation during their second year grew as well thereafter as those that were never irrigated.