Development issues in extending plant-based IBIs to forested wetlands in the Midwestern United States

Abstract

Most plant-based indices of biotic integrity (IBIs) developed for wetlands have focused on emergent wetlands. A Vegetation Index of Biotic Integrity (VIBI-Forest) was developed for forested wetlands in the four large ecoregions of the Ohio. Assessing the effect of human disturbance on the ecological condition of wetland forests is complicated by several factors. First, forest canopies can remain largely intact even after significant degradation of the herb and shrub stratum. Second, increases in total diversity may not be good. In forested wetlands, a major artifact of disturbance is the addition of non-wetland or wetland native or adventive plant species adapted to full sun conditions to their floras. Initial versions of the VIBI-Forest metrics were very sensitive to disturbance-induced increases in diversity. Correcting this problem required modifying or replacing metrics so that only forest dependent species were included in metric calculations. The final VIBI-Forest included metrics which evaluated each forest stratum including the ground layer (% bryophyte), herb layer (shade or seed-less vascular plant species), shrub layer (subcanopy importance value (IV), relative density of young trees), canopy (canopy IV), and composite metrics for all vertical strata (Floristic Quality Assessment Index score, % hydrophytes, % sensitive, % tolerant). Assessing wetland forest condition is further complicated by the fact that some successional communities after canopy death or destruction (shrub swamp, marsh, wet meadow) may have intrinsic value as wetland community types. The solution is not to attempt to derive a one-size-fits-all assessment method but to derive separate protocols for other successional phases that are of value or interest.

Appendix A

Scoring ranges for assigning metric scores for vegetation-forest

Metric	Type	Description	Score 0	Score 3	Score 7	Score 10
Shade	Richness	Number of native shade or shade facultative species. Shade tolerance codes are in Mack (2004b).	0–7	8–13	14–20	≥21
SVP	Richness	Number of seedless vascular plant (fern, fern ally) species	0	1	2	≥3
FQAI	Richness index	The Floristic Quality Assessment Index score calculated using Eq. 7 and the coefficients in Andreas et al. (2004)	0–14.0	14.1–19.0	19.1–24.0	≥24.1
%Bryophyte	Dominance ratio	Relative cover of bryophytes (mosses and aquatic liverwort genera Riccia and Ricciocarpos)	0–0.01	0.01–0.03	0.031–0.06	≥0.06
%Hydrophyte	Dominance ratio	Sum of relative cover values of shade or partial shade tolerant FACW and OBL plants in the herb and shrub stratums	0–0.1	0.1–0.15	0.151–0.28	≥0.281
%Sensitive	Dominance ratio	Sum of relative cover of plants in herb and shrub stratums with a Coefficient of Conservatism of 6–10 (Andreas et al. 2004)	0–0.035	0.035–0.12	0.12–0.3	0.31–1.0
%Tolerant	Dominance ratio	Sum of relative cover of plants in herb and shrub stratums with a Coefficient of Conservatism of 0–2 (Andreas et al. 2004)	0.45–1.0	0.30–0.45	0.15–0.30	0–0.15
Small tree (pole timber) density	Density ratio	Sum of relative density of tree species in 10–15 cm, 15–20 cm and 20–25 cm size classes	0.32–1.0	0.22–0.32	0.11–0.22	0–0.11
Subcanopy IV	Importance value	The sum of the mean importance value for native shade tolerant subcanopy species plus the mean importance value of facultative shade subcanopy species	0–0.02	0.02–0.072	0.072–0.13	≥0.131
Canopy IV	Importance value	The mean importance value of canopy species (species which at maturity will inhabit the upper canopy of the forest even if at the time of sampling they are growing in the subcanopy)	0.21–1.0	0.17–0.21	0.14–0.17	0–0.14