Studies of Midwestern forest in the USA are showing that alpha-diversity of understory herbaceous plant species is declining in upland forests and increasing in floodplain forests. Differences in colonization and extinction probabilities of species between the two forest types may be driving the differences in this trend. We expected colonization probabilities to be higher in floodplain forests due to increased dispersal ability via rivers and extinction probabilities to be higher for upland forests due to population isolation and competition with invasive species. We used robust-design occupancy models to estimate colonization and extinction probabilities of 55 and 58 understory species from upland and floodplain forests, respectively. Unique to our study is the use of a more recent data set expanding 20 years (1998-2017) to assess colonization and extinction probabilities. T-tests were used to compare colonization and extinction probabilities between and within forest types.
Results/Conclusions
Overall colonization and extinction probabilities did not differ between forest types. Extinction probabilities were higher than colonization probabilities for both forest types. Most species in both forest types had extinction probabilities higher than colonization probabilities. However, a few species were found to have higher colonization probabilities. These results suggest that alpha-diversity is likely to decrease even more into the future for both of these forest types. Species with extinction probabilities much larger than colonization probabilities are the most at risk of extirpation and should be the target of management actions to preserve diversity. In the case of floodplain and upland forests control of invasive species and species re-introductions will be needed to maintain vulnerable species populations.