Patterns and Changes in Orchid Frequencies in Southern New England

We examined town-level frequencies of orchid species in the southern New England states of Connecticut, Massachusetts, and Rhode Island and their changes over time. Our analyses were based on detailed floristic studies of two Massachusetts counties, specimens in New England herbaria, and data from state Natural Heritage Programs and iNaturalist. Recent herbarium collections and data from iNaturalist proved inadequate to represent town-level occurrences in the absence of other data sources. The town-level frequencies of nearly all native orchid species have declined, and these declines were significantly greater than those of a matched group of non-orchid species of comparable historical frequency. We examined associations between orchid decline and several variables related to historical frequency, habitat affiliation, floral morphology, pollination, and geographical range. The only significant pattern was a tendency for greater declines in northern species among the state-listed species in southern New England. There was some evidence of greater declines among large-leaved orchids than small-leaved orchids and among insect-pollinated species compared to primarily autogamous species. We conclude that orchid declines are real and widespread in southern New England but that causes are unlikely to reflect a single variable. Rather, we believe that causation involves multiple factors whose effects vary among species and perhaps in different regions.