Terry M., Trout K., Williams B., Herrera T., Fowler N., Limitations to natural production of Lophophora williamsii (Cactaceae) II. Effects of repeated harvesting at two-year intervals in a South Texas population, Journal of the Botanical Research Institute of Texas, 2012, 6(2):567-577
Four-year observations of the same population compare the control, a single crown removal and repeated damage every two years. They analyse survival, decline in fresh mass, crown number and changes in estimated volume. They discuss the hypothesis of gradual reserve depletion through repeated loss of the plant's photosynthetic part, and regional trade data from the study period.