4 research outputs found
Assessing the Performance of Sampling Designs for Measuring the Abundance of Understory Plants
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 pointāline 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 (3ā36 replicates for growth-form groups; 8ā14 replicates for common species); however, increasing precision to 25% relative margin of error required sample sizes that may be infeasible (11ā143 replicates for growth-form groups; 28ā54 replicates for common species). All three conventional designs required enormous sample sizes to estimate cover of nonnative species as a group (29ā60 replicates) and of individual less common species (62ā118 replicates), even with a 50% relative margin of error. SACS was the only design that efficiently sampled less common species, requiring only 6ā11% 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
Appendix C. Proof of unbiasedness of the Strip Adaptive Cluster Sampling (SACS) Estimator.
Proof of unbiasedness of the Strip Adaptive Cluster Sampling (SACS) Estimator
Appendix A. A figure showing the location of sampling units within each treatment.
A figure showing the location of sampling units within each treatment