Skip to Main Content
Detecting change in advance tree regeneration using forest inventory data: the implications of type II errorAuthor(s): James A. Westfall; William H. McWilliams
Source: Environmental Monitoring and Assessment
Publication Series: Scientific Journal (JRNL)
Station: Northern Research Station
Download Publication (330.0 KB)
DescriptionAchieving adequate and desirable forest regeneration is necessary for maintaining native tree species and forest composition. Advance tree seedling and sapling regeneration is the basis of the next stand and serves as an indicator of future composition. The Pennsylvania Regeneration Study was implemented statewide to monitor regeneration on a subset of Forest Inventory and Analysis plots measured by the U.S. Forest Service. As management techniques are implemented to improve advance regeneration, assessments of the change in the forest resource are needed. When the primary focus is on detecting change, hypothesis tests should have small type II (β) error rates. However, most analyses are based on minimizing type I (α) error rates and type II error rates can be quite large. When type II error rates are high, actual improvements in regeneration can remain undetected and the methods that brought these improvements may be deemed ineffective. The difficulty in detecting significant change in advance regeneration when small type I error rates are given priority is illustrated. For statewide assessments, power (1-β) to detect changes in proportion of area having adequate advance regeneration is relatively weak (≤0.5) when the change is smaller than 0.05. For evaluations conducted at smaller spatial scales, such as wildlife management units, the reduced sample size results in only marginal power even when relatively large changes (≥0.20) in area proportion occur. For fixed sample sizes, analysts can consider accepting larger type I error rates to increase the probability of detecting change (smaller type II error rates) when it occurs, such that management methods that positively affect regeneration can be identified.
- Check the Northern Research Station web site to request a printed copy of this publication.
- Our on-line publications are scanned and captured using Adobe Acrobat.
- During the capture process some typographical errors may occur.
- Please contact Sharon Hobrla, firstname.lastname@example.org if you notice any errors which make this publication unusable.
- We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
- This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
CitationWestfall, James A.; McWilliams, William H. 2012. Detecting change in advance tree regeneration using forest inventory data: the implications of type II error. Environmental Monitoring and Assessment. 184(9): 5601-5611. https://doi.org/10.1007/s10661-011-2365-3.
KeywordsType II error, Tree seedling, Species composition, Forest inventory
- Sample-size needs for forestry herbicide trials
- Are Current Seedling Demographics Poised to Regenerate Northern US Forests?
- The power of FIA Phase 3 Crown-Indicator variables to detect change
XML: View XML