History and Statistical Considerations of Using the One ft2 Quadrat for Monitoring Peak Standing Crop and Residual Dry Matter on California Annual Rangelands

Authors: LARSEN, ROYCE - University Of California Agriculture And Natural Resources (UCANR); Robins, Joseph; Jensen, Kevin; SHAPERO, MATTHEW - University Of California Agriculture And Natural Resources (UCANR); STIBY, KARL - Natural Resources Conservation Service (NRCS, USDA); ALTHOUSE, LYNNEDEE - Althouse And Meade, Inc; GEORGE, MELVIN - University Of California, Davis; HORNEY, MARC - California Polytechnic State University; RAO, DEVII - University Of California Agriculture And Natural Resources (UCANR); Hernandez, Alexander; DAHLGREN, RANDY - University Of California, Davis; BARTOLOME, JAMES - University Of California Berkeley

Submitted to: Rangelands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2023
Publication Date: 8/16/2023
Citation: Larsen, R., Robins, J.G., Jensen, K.B., Shapero, M., Stiby, K., Althouse, L., George, M., Horney, M., Rao, D., Hernandez, A.J., Dahlgren, R., Bartolome, J. 2023. History and Statistical Considerations of Using the One ft2 Quadrat for Monitoring Peak Standing Crop and Residual Dry Matter on California Annual Rangelands. Rangelands. 45(5), 102-108. https://doi.org/10.1016/j.rala.2023.06.002.
DOI: https://doi.org/10.1016/j.rala.2023.06.002

Interpretive Summary: Monitoring herbage peak standing crop (PSC) and residual dry matter (RDM) on California’s annual rangelands by ranchers, researchers, and agency staff are the primary means of documenting production and grazing intensity. One of the most common methods of monitoring these forage metrics is to clip 1-ft2 quadrats that has been used since the 1930's. Using a large data set covering 2014 to 2020 we found that the number of samples required varied from 3 quadrats to achieve a 60% probability of reaching the mean, to over 8 for achieving an 80% probability. The number of samples needed for RDM was higher with 4 to over 11 samples required for achieving 60% and 80% probability, respectively. Variability due to bare ground, vegetation height, and rodent activity contributed to determining the required number of samples.

Technical Abstract: Monitoring herbage peak standing crop (PSC) and residual dry matter (RDM) on California’s annual rangelands by ranchers, researchers, and agency staff are the primary means of documenting production and grazing intensity. One of the most common methods of monitoring these two parameters is to clip 1-ft2 quadrats. The US Forest Service, Bureau of Land Management, universities, and other land managers have been using this size of quadrat since the 1930s. We estimated PSC and RDM at 239 site-year environments from 2014 to 2020 using1-ft2 quadrats. We estimated the best linear unbiased predictors (BLUEs) and 95% confidence intervals for PSC and RDM for each environment. For PSC, the range of samples needed varied from 3 quadrats to achieve a 60% probability of reaching the mean, to over 8 for achieving 80% probability. The number of samples needed for RDM was higher with 4 quadrats needed to achieve 60% probability of reaching the mean, to over 11 for achieving 80% probability. The number of samples needed to meet accuracy goals was heavily influenced by variation in PSC, RDM and bare ground.