Assessing the performance of sampling designs for measuring the abundance of understory plants

Lana L. Abrahamson, Cara R. Nelson, David L.R. Affleck

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Accurate estimation of responses of understory plants to disturbance is essential for understanding the efficacy of management activities. However, the ability to assess changes in the abundance of plants may be hampered by inappropriate sampling methodologies. Conventional methods for sampling understory plants may be precise for common species but may fail to adequately characterize abundance of less common species. We tested conventional (modified Whittaker plots and Daubenmire and point-line intercept transects) and novel (strip adaptive cluster sampling [SACS]) approaches to sampling understory plants to determine their efficacy for quantifying abundance on control and thinned-and-burned treatment units in Pinus ponderosa forests in western Montana, USA. For species grouped by growth-form and for common species, all three conventional designs were capable of estimating cover with a 50% relative margin of error with reasonable sample sizes (3-36 replicates for growth-form groups; 8-14 replicates for common species); however, increasing precision to 25% relative margin of error required sample sizes that may be infeasible (11-143 replicates for growthform groups; 28-54 replicates for common species). All three conventional designs required enormous sample sizes to estimate cover of nonnative species as a group (29-60 replicates) and of individual less common species (62-118 replicates), even with a 50% relative margin of error. SACS was the only design that efficiently sampled less common species, requiring only 6-11% as many replicates relative to conventional designs. Conventional designs may not be effective for estimating abundance of the majority of forest understory plants, which are typically patchily distributed with low abundance, or of newly establishing nonnative plants. Novel methods such as SACS should be considered in investigations when cover of these species is of concern.

    Original languageEnglish
    Pages (from-to)452-464
    Number of pages13
    JournalEcological Applications
    Volume21
    Issue number2
    DOIs
    StatePublished - Mar 2011

    Keywords

    • Adaptive cluster sampling
    • Daubenmire transect
    • Forest restoration
    • Modified Whittaker plot
    • Nonnative plants
    • Point-line intercept
    • Sample size
    • Sampling efficiency
    • Understory vegetation

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