The response of herbaceous-layer vegetation to anthropogenic disturbance in intermittent stream bottomland forests of southern Indiana, USA

Between 1993 and 1995 we sampled herbaceous layer vegetation on 84 plots in Platanus/Asarum Wet-Mesic Bottomland forests to determine how these forest s have responded to human disturbance. Four different disturbance types wer e sampled (abandoned agricultural are as, clearcuts, group-selection openin gs, and single-tree selection openings), and uncut 80-100 year-old referenc e stands were sampled for comparison. Detrended Correspondence Analysis (DC A), distance analyses (chord distance and normalized Euclidean distance) an d similarity analysis (Bray-Curtis similarity coefficient) suggest that agr icultural use has shifted herbaceous-layer vegetation composition away from that typical of the reference forests, but that clearcutting. group-select ion harvest, and single-tree selection harvest have not greatly shifted her baceous composition. This shift in vegetation on abandoned agricultural lan d resulted from a loss of indicator species, such as Cardamine concatenata (Michx.) Sw., Stellaria pubera Michx., and Laportea canadensis (L.) Weddell and an influx of disturbance, exotic, and nonforest species (e.g., Lycopod ium complanatum L., Lonicera japonica Thunb. and Senecio aureus L.). Howeve r, only two species found in reference stands, Erigenia bulbosa (Michx.) Nu tt. and Sphenopholis obtusata (Michx.) Scribn., were missing from clearcuts , group-selection openings, and single-tree selection openings. The species richness values of abandoned agriculture, clearcut, and group-selection pl ots were generally greater than those of single-tree selection and referenc e plots. Abandoned agricultural areas had much greater total species richne ss because of the influx of dry-site, exotic, disturbance, and non-forest s pecies.