Vegetation Trajectories in Retired Cranberry Bogs in Southeastern Massachusetts

Typical vegetation of pitch pine (Pinus rigida), white pine (Pinus strobus) and red maple (Acer rubrum) and graminoids colonizing the surface of a bog in the Upper Coonamessett Wetlands in Falmouth eight years after bog retirement.

Study Description

This project quantified vegetation in cranberry bogs that were retired from cultivation a different number of years ago. We surveyed understory vegetation and canopy openness and sampled soils in 3 x 3 meter plots and measured tree species and diameters in 4 m radius plots. We used the chronosequence to infer vegetation change over time and to calculate changes to vegetation and soil carbon and nitrogen stocks.

We classified plant species as to life form (tree, shrub, graminoid, forb, vine), origin (native, non-native) and status on the Army Corps of Engineers Wetland Plant List (UPL, FAC UP, FAC, FAC WET, WET). We then examined how different plant groups changed after retirement.

We plan to use this study and an identical methodology to compare the vegetation trajectories in bogs that are retired but not actively restored to bogs that are actively restored by removal of overlying sand and removing water control structures and filling ditches to restore wetland hydrology.

This study is currently submitted for publication.

Abstract

Retirement of cultivated croplands creates potential for ecosystem and wetland restoration, but vegetation and soil legacies of cropping influence the development of post-agriculture vegetation. In low-lying coastal watersheds of southeastern Massachusetts, cranberries (Vaccinium macrocarpon Aiton) are cultivated in commercial "bogs" largely on diked, leveled and sanded bog beds created from historic wetlands. Current low cranberry prices and expanding cranberry production elsewhere now increase the likelihood of cranberry farmland retirement. We quantified the trajectories of plant species richness and cover, and plant characteristics (life form, native or non-native, wetland or non-wetland) in a chronosequence of cranberry bog beds that spanned from cultivated bog beds to those retired from cropping and revegetated for 90 years with no post-cropping management. Species richness increased from active bog beds to 10-20 year-old bog beds and subsequently decreased. Post-retirement species richness was overwhelmingly dominated by native species. Shrub and tree richness and cover increased steadily over time. The richness of wetland, upland and facultative species all increased quickly after retirement and then declined in the oldest retired bog beds. The basal area and canopy cover of red maple (Acer rubrum) and pitch pine (Pinus rigida) increased over time. Vegetation followed a relatively predictable succession trajectory and the plant community after five to nine decades was predominantly forested and dominated by non-wetland plants. Encouragement of long-term persistence of greater diversity and cover of wetland plant species on retired cranberry farms will likely require active hydrological and soil modifications that decrease sand depth and raise water tables.