Disturbance-based management and changing species composition in sandplain heathlands

Background/Question/Methods

Current grassland and heathland habitats of New England are relicts of the agricultural practices of early European settlers. While anthropogenic in origin, these habitats play a crucial role in maintaining biodiversity. Disturbance-based management techniques, such as burning and mowing, are used to prevent tree encroachment and maintain the open structure of heathland habitats. Additionally, changing edaphic conditions may be of conservation concern. Heathlands occur on acidic, low nutrient soils, with higher nutrient soils being more conducive to grassland formation.

The objective of this study was to examine changes in plant community composition in two New England sandplain heathlands over the past two decades and relate these changes to management and edaphic conditions. We set out to address the following questions: Is current management effectively promoting biodiversity in this system? How might potentially changing edaphic conditions affect species composition?  In order to accomplish this goal, we resurveyed plots that were established in 1989 and 1999 within three separate sandplain heathland sites in Massachusetts. We collected soil samples within a stratified random subsample of plots. We used a combination of indicator species analysis, NMS ordination, multiple regression, and paired t-test analyses to answer our questions regarding changing species composition over time.

Results/Conclusions

Our three study sites included two that were sandplain heathlands at the time of plot establishment (maintenance sites), and one that was largely shrubland at the time of plot establishment and is being managed to restore heathland habitat (restoration site). Using paired t-tests, we found that changes in species richness differed depending on the site; in one of the two maintenance sites we saw a significant decrease in species richness over the last twenty years, and in the other we saw no significant change. In the restoration site we saw a significant increase in species richness between 1999 and 2009.

Indicator Species Analysis established Carex pensylvanica as an indicator for elevated soil nitrogen and a paired t-test showed an increase in C. pensylvanica within all plots over the past two decades. Using NMS ordination and successional vectors in PC-ORD, we are in the process of disentangling the effects of various factors on changing species composition over the last two decades.

We have seen changes in both species richness and species composition in these valuable habitats. Appropriate management will be necessary to maintain these communities, and our research findings will help guide sandplain heathland monitoring and restoration efforts.