Sampling techniques for evaluating afforestation success in the Lower Mississippi Valley

Greater than 250,000 ha of abandoned agricultural fields have been planted to bottomland forests in the Lower Mississippi Valley. Few survival studies of planted trees or natural woody invaders have been conducted, and no standard protocols have been established. Evaluations of seedling survival have ranged from casual observations to establishment of permanent study plots along transects. Using field data of species occurrence, we ran simulations to determine the effects of various evaluation techniques and study plot sizes. The most effective method of evaluating survival to within 90% of known values was to measure the average distance between adjacent seedlings, within a row, at randomly located points across the field. The number of study plots required to make this same determination depended on both the survival rate and the size of the plots. Seventy five small plots (40.5 m² each) or eight large plots (200 m² each) were required to confirm 100% survival of planted oaks. Determination of woody invader numbers depended on the seedling density for each species and the size of the study plots. Woody invaders with low numbers required more plots. For example, 24 small plots or 8 large plots were required for elms (250/ha), and approximately 44 small plots versus 7 large plots were required for box elder (51/ha). Sampling effort and efficiency is better served with fewer large plots than with many small plots.