Title: Quercus lobata seedlings and conspecific neighbors: Competitors or allies?
Author: Tyler, Claudia; Moritz, Shelly Cole;
Source: Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 425-431
Publication Series: General Technical Report (GTR)
Description: In conducting oak restoration, it is common to plant at least two acorns per location to increase the probability that at least one will germinate and produce a seedling. If both seedlings successfully establish, one is generally removed to reduce possible competition. To test the assumption that the near neighbors are competing, we examined several cohorts of valley oak (Quercus lobata) seedlings established from acorns planted at the University of California Sedgwick Reserve in Santa Barbara County. We assessed correlations between presence/absence of neighbors and individual performance, hypothesizing that seedlings that emerged without a near neighbor (only one of the two acorns produced a seedling) would have better survival and growth than those with both acorns producing seedlings within one planting location. However, over a 7 to 10 year period, we found that survival rates and mean height of Q. lobata with neighbors did not differ significantly from those that emerged and grew without a near neighbor. We also conducted removal experiments in which pairs of established near neighbor seedlings were randomly assigned to one of two treatments: control (both seedlings remain intact) and removal (one seedling in the pair is removed and the target remains). Growth (height, stem diameter at base, absolute and relative growth rates) was not significantly different between control and removals for any year (2011–2014). We also measured access to water via pre-dawn xylem pressure potentials (PDXPPs) in early fall. Contrary to predictions, PDXPPs were not significantly different between the treatments for any year (2011-2014). Both our observational and experimental findings indicate that near neighbors do not have negative impacts on performance for early life stages in Q. lobata. We also suggest that there may be advantages to allowing near neighbors to coexist in restoration plantings, where survival of the target individual is still uncertain.
Keywords: competition, neighbor, predawn xylem pressure potential, seedling growth, seedling survival, water availability
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Tyler, Claudia; Moritz, Shelly Cole 2015. Quercus lobata seedlings and conspecific neighbors: Competitors or allies? In: Standiford, Richard B.; Purcell, Kathryn L., tech. cords. Proceedings of the seventh California oak symposium: managing oak woodlands in a dynamic world. Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 425-431.
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