How is Climate Change Effecting the Park?

An eastern meadowlark perches on a plant in the meadows

Photo Bill Moses

Meadows and Biodiversity

Valley Forge National Historical Park manages over 3500 acres of land, about one third of which is meadow habitat. The park works hard to manage this land to provide and maintain the greatest biodiversity in each area, creating a resilient habitat that is home to a plethora of wildlife. The biggest threat to these ecosystems comes in the form of invasive vegetation. Invasive plants such as lesser celandine, asiatic bittersweet, and bush honeysuckle outcompete native plants, and overtake large areas or land leaving little room for other species, especially native ones, to grow.
Native plants are often specialized to grow best in a specific set of conditions, which in a given geographic range historically do not change very quickly, if at all. On the other hand, invisive species are often able to grow in a wide variety of conditions, making them more able to quickly adapt to a changing climate- that is one reason why these species are so readily able to 'invade' new areas! In order to fight against invasive plants taking over the habitats in the park and limiting biodiverity, our natural resource management team uses a variety of methods to remove these invasive species and allow more variety of native species to grow in their place. The methods include protecting the existing native species, planing new native plants, and removing invasive vegetation using both mechanical and chemical methods.

Our meadows are home to many species such at the meadowlark, grasshopper sparrow, and bobolink, all of which are meadow indicator species. Only a healthy, biodiverse meadow can host these unique bird species, and in the past few year all of these birds have been spotted in our meadows, showing us that out management practices are working!

 

Eterior wall of Washington's Headquarters, featuring cracking mortar.

NPS Photo, C. Wusteney

Historic Buildings

The landscape of Valley Forge still holds many historic structures and buildings, some from the encampment era, and others dating back to the 18th and 19th centuries. These structures have withstood the test of time, indicating that they were well built. Many of these building are evidently built with the climate of southeastern Pennsylvania in mind. Historically, buildings (especially homes) were built to be comfortable to live in in the most extreme weather that could be expected in the area. For example, the southern United States is known for very hot summers, while the winters were relatively mild- therefore, homes were built to stay as cool as possible. Conversely, homes in more northern states could be expected to experience harsh winters with warm, but more tolerable summers.

Now, with a more rapidly changing climate, these historic structures are begin faced with more extreme heat and cold, as well as more severe storms than their builders may have anticipated. While some of these structures have stood for centuries, climate change is now a real threat that must be considered when making decisions to take care of historic buildings. Sometimes modern materials, though easier to find, are more damaging than helpful. For this reason, going back to the basics and taking notes from the hisoric building materials that helped these structures stand for so long can be the best course of action.

For example, Washington's Headquarters is one of Valley Forge's most visited sites, built circa 1773, is showing some clear signs of difference in modern vs historic materials. Traditionally, it would be expected that stone buildings like this one would have a limestone based pointing mortar that would allow the stones to naturallly expand and contract, and moisture to move naturally in and out of the walls of the house. However, at some point in this building's life that traditional material was replaced with a more modern cemement mortar, which would in theory be more durable and require less maintenance. However, that mortar is now cracking because the nature of cement is much more rigid and impermeable than limestone. There are now plans in place to replace this with the more traditional mortar which will be better able to handle fluctuations in moisture which will likely be exacerbated by climate change.

We can also learn about pat climate conditions from old buildings like these. Tree ring dendrology is a process that can take cores of wood from the timbers used to build historic structures, and from the pattern of the tree rings, can track what the climate was like from the time the tree was planted to when it was harvested. The rings of trees as many know cantell us the age of a tree, but is can also give us an idea of the temperature and rainfall of each season of the tree's life. This is one process that has helped to support the fact that the climate has changed significantly from the historic patterns. Learn more about this process and how researchers have developed a robust database here!