Succession of an Iowa sand prairie into an adjoining old-field

Native plant succession studies were conducted in 2000 and 2001 at the Cedar Hills Sand Prairie northwest of Cedar Falls, IA. The study site consisted of a remnant sand prairie with an adjoining old-field that had been undergoing secondary succession since the mid-1970s. Vegetation was sampled over a 100 m transect of the remnant prairie and a 200 m transect of the old-field. The transect was sub-divided into 50 m subsites to examine progression of native species into the old-field. To analyze changes in vegetation, the similarity of the sub-sites were compared for percent canopy cover and number of species for the following categories: overall total, natives, native forbs, native grasses, sedges and rushes, non-natives, non-native forbs and non-native grasses. Additional studies examined the seed rain and seed bank. The old-field vegetation of the sub-site adjacent to the remnant was most similar to the remnant and similarity decreased as distance increased. Between 50 and 150 m north of the remnant, native canopy cover diminished although the number of native species remained similar to the prairie. Apparently, this is a transition zone where native species are becoming established, but remain less prominent. Beyond this point, the vegetation in the most distant sub-site resembled a typical old-field. The number of species dropped 2 1//2 to 3 1/2 times less than the other areas of the study. Non-native species accounted for 98.5% of the canopy cover and the number of species was 2 1/2 to 3 times less than the other sites. Additionally, only one native grass was present while four to six native grass species were present in other sub-sites. Fifty species and 2086 seeds from the seed rain were compared to vegetation surrounding each seed trap to determine species movement. A low percentage of the species and seeds in the seed traps could have originated from the nearby vegetation. Apparently seeds are moving further than expected. Half the seed bank species were not present in the sampled vegetation, including several native species. Native grasses, common in the vegetation and seed rain, were scarce in the seed bank. Sedges and rushes, scarce in the vegetation and seed rain, were prominent in the seed bank. Succession is an important field of study to determine what species are moving, where they are moving to and if they are becoming part of the vegetation. Over one quarter of the studies species were not present in the vegetation, signifying potential future changes in the existing vegetation. Secondary succession of prairie vegetation from the sand prairie remnant into the adjoining old field is proceeding slowly. Twenty-five years after the initiation of succession, the vegetation of the proximal portion of the old-field is similar to that of the adjoining remnant prairie. However, the most distant sample site of the old-field still resembles a typical abandoned agricultural field although intermediate sites are in transition to native prairie