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4

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Why Healthy Pine Seedlings Die after They Leave the Nursery

Forests, 14(3)

10.3390/f14030645

Should forest regeneration studies have more replications?

David B. South ,
David B. South
Curtis L. VanderSchaaf
Curtis L. VanderSchaaf

Published: 01.12.2016.

Volume 0, Issue 3 (2017)

pp. 19-30;

https://doi.org/10.21750/refor.3.03.27

Abstract

When it comes to testing for differences in seedling survival, researchers sometimes make a Type II statistical error (i.e. failure to reject a false null hypothesis) due to the inherent variability associated with survival in tree planting studies. For example, in one trial (with five replications) first-year survival of seedlings planted in October (42%) was not significantly different (alpha = 0.05) from those planted in December (69%). Did planting in a dry October truly have no effect on survival? Authors who make a Type II error might not be aware that as seedling survival decreases (down to an overall average of 50% survival), statistical power declines. As a result, the ability to declare an 8% difference as “significant” is very difficult when survival averages 90% or less.  We estimate that about half of regeneration trials (average survival of pines <90%) cannot declare a 12% difference as statistically significant (alpha = 0.05).  When researchers realize their tree planting trials have low statistical power, they should consider using more replications.  Other ways to increase power include: (1) use a one-tailed test (2) use a potentially more powerful contrast test (instead of an overall treatment F-test) and (3) conduct survival trials under a roof.

References

Amishev, D., & Fox, T. (2006). Impact of weed control and fertilization on growth of four species of pine in the Virginia Piedmont. General Technical Report SRS-92, 121–123.
B. South, D. (2012). Planting Deep Increases Early Survival and Growth of Pinus echinata Seedlings. The Open Forest Science Journal, 5(1), 33–41. https://doi.org/10.2174/1874398601205010033
Blake, J., & South, D. (1991). Effects of plant growth regulators on loblolly pine seedling development and field performance. General Technical Report SE-70, 100–107.
Clabo, D., & Clatterbuck, W. (2015). Sprouting capability of shortleaf pine seedlings following clipping and burning: first-year results. 137–142.
CM, C., WM, A., JR, S., & BD, S. (2015). Survival and growth of restored Piedmont riparian forests as affected by site preparation, planting stock and planting aids. 431–436.

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