Coastal forest monitoring report, Cape Cod National Seashore: Comparison of 2003 and 2013 data

Smith, Stephen

Forests and woodlands occupy the largest area within Cape Cod National Seashore (CACO) and are largely a reflection of the harsh coastal environment and past land-use history. Forest ecosystems in CACO are, and will continue to be, influenced by a number of different natural and anthropogenic factors. These include groundwater withdrawal, fragmentation, introduction of exotic species, disease and plant pests, and various aspects of climate change. Documenting changes in forest structure and function is an important priority for the Seashore in terms of understanding the resource and ultimately managing it. In 2003 and 2013, forest vegetation was surveyed in permanent plots situated in the different forest types across CACO. Comparisons of the 2003 and 2013 tree data show that secondary succession within the forest overstory, as would be manifested in changes in tree species composition, has not occurred to any significant extent. Instead, existing trees are still growing and filling in open space rather than being outcompeted by other species. This is reflected in the total number of live trees which decreased for most species, suggesting that intraspecific competition and the continued growth of fewer, but hardier trees is occurring. Of all tree species within the CACO forest monitoring sites, P. rigida and Q. velutina are growing the most rapidly. There has been a 12% average increase in canopy cover between 2003 and 2012. This has resulted in a shift to more shade-tolerant species such as Carex pensylvanica (Pennsylvania sedge; sedge), Trientalis borealis (starflower; forb), and Mianthemum canadense (Canada Mayflower; forb). Q. velutina and Q. alba both increased in frequency in the understory by 11% and 5%, respectively. Tree seedling densities actually decreased quite dramatically between 2003 and 2012. Understory species richness generally exhibited an increasing trend at the sites – another indicator of early successional processes. However, while a number of new species appeared between 2003 and 2012, overall plant community composition did not change significantly. In contrast, the proportion of the various growth forms did, with shrub species exhibiting large decreases compared to forb vegetation (the latter increasing at most sites). This makes sense given that there are many more herbaceous species that are shade-tolerant than there are shrub species. In general, the forests in CACO are young and many of the processes typical of older growth forests are not yet evident (e.g., significant community-level change; replacement of tree species). The next survey scheduled for 2022 will shed more light on the rate at which this processes is occurring.

Coastal forest monitoring report, Cape Cod National Seashore: Comparison of 2003 and 2013 data

Series

Collections