We tested the release potential of suppressed giant sequoia (Sequoiadendron giganteum) saplings in a plantation that was overgrown with shrubs at Blodgett Forest Research Station, CA in the mixed conifer forest of the Sierra Nevada. As an ancillary case study, we compared the shrub removal method of release with a clear-and-plant method in an adjacent stand. Measurements of various morphological traits were collected prior to shrub removal, then sapling height growth response was measured periodically after the release treatment. In general, giant sequoia responded quickly to the removal of competing shrubs, growing steadily for 20 years following treatment. Among the morphological traits considered, live crown ratio alone was the most important factor in predicting relative height growth following treatment. Other traits were correlated with release, but had lower importance values as indicated by a model selection procedure. The 16-year-old saplings that were released in this study did not grow as large as 2-year-old seedlings that were planted synchronously with release, but both methods resulted in merchantable-sized trees 20 years after treatment. Planted seedlings outgrew released seedlings by 27% in terms of stature and by 37% in terms of diameter. The released stand is projected with a growth model to take 42 years longer than the planted stand to grow to an average diameter of 38 cm. The misperception of giant sequoia as having a low capacity for release may be related to its ambiguous categorization as a shade intolerant species. (c) 2006 Elsevier B.V. All rights reserved.

Replicated circular openings ranging in size from 0.1 to 1 ha were cleared on a Sierran mixed conifer forest in 1996 at the Blodgett Forest Research Station, California and planted with seedlings of six native species. After 3 years of growth, heights of all trees were measured and analyzed according to species, opening size, and location within the opening. To determine the cause of the edge influence on height, we measured differences along north-south transects in extension growth, pre-dawn water potential, and light availability for three species of trees: giant sequoia (Sequoiadendron giganteum), ponderosa pine (Pinus ponderosa), and Douglas-fir (Ptseudotsuga menziesii var. menziesii). The sequence of mean height from tallest to shortest based on species was: giant sequoia > incense cedar > Douglas-fir > ponderosa pine > white fir > sugar pine. For all species combined, a ten-fold increase in the area of the opening corresponded to a 34% increase in mean height. Trees were tallest on average in the north rows and shortest in the south rows. There was no difference in height between trees in the east and west rows. As expected, resource availability was greatest near the center and least near the edges with north edges receiving significantly more light than southern edges. In general, observed edge effects on sapling height growth were correlated with light and water supply. However there were important differences between species in the nature of the co-limitation. Giant sequoia growth was most sensitive to light and water availability. Together they explained more than 47% of the observed variation in giant sequoia height. In contrast, only light was a significant predictor of ponderosa pine performance. Douglas-fir heights were significantly related to both light and water but there was more unexplained variability in the Douglas-fir model compared to the other species. These highly controlled experimental group openings provide a standard reference for silviculturalists using the group selection method of regeneration. (C) 2002 Elsevier Science B.V. All rights reserved.

Replicated circular openings ranging in size from 0.1 to 1 ha were cleared in 1996 at Blodgett Forest Research Station, California, and planted with seedlings of six native species. After 5 years of postharvest growth, heights were measured and analyzed according to species, opening size, and location within opening. The sequence of mean height from tallest to shortest, according to species, was as follows: giant sequoia (Sequoiadendron giganteum (Lindl.) Buchholz) > incense-cedar (Calocedrus decurrens (Torr.) Florin) > Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) ponderosa pine (Pinus ponderosa Dougl. ex Laws.) > sugar pine (Pinus lambertiana Dougl.) white fir (Abies concolor (Gord. & Glend.) Lindl.). To describe the influence of openings size on seedling height, we use an information-theoretic approach to select from competing models that predicted fifth-year height from group selection opening size. Asymptotic fits (modeled with Michaelis-Menton curves) were selected for giant sequoia, ponderosa pine, sugar pine, and incense-cedar. Quadratic fits were selected for white fir and Douglas-fir. Linear models predicting increasing growth with opening size were consistently ruled out for all species. Although a marked depression in seedling-height growth occurred along the edges within the openings, mean annual radial increment of the 90-year-old border trees surrounding the openings increased by 30%, compared with other canopy trees in the forested matrix between openings.