Hidden in Plain Sight: the Secret Tree Diversity of Cultural National Parks in the East
Last summer, my daughter received All Aboard! National Parks, a whimsical board book that devotes full-page spreads of colorful, kid-friendly illustrations to nine National Parks along a fictional railroad route. The National Parks skew western — Olympic, Yosemite, Yellowstone, Grand Canyon — with Acadia and Great Smoky Mountains representing the entire eastern half of the U.S.
But, the book is a skewed representation of the National Park System in another way too: it only showcases the large, iconic, and “wild” national parks. Where are the National Battlefields, the National Recreation Areas, the National Scenic Rivers, and the National Historic Sites? A recent paper from Forest Ecology and Management has me thinking that the cultural parks of the east that fall under the National Park Service umbrella deserve their own board book!
In the eastern United States, our National Parks dot the landscape as constellations of historic battlefields, homes of important historical figures, and wild islands of nature scattered across an eastern seaboard of cities, development, and fragmentation. But, it turns out that these small, cultural protected areas are harboring incredible tree species diversity. Dr. Kathryn Miller and colleagues from the National Park Service and University of Maine published “Eastern National Parks protect greater tree species diversity than unprotected matrix forests” after comparing tree species diversity measured in National Park Service Inventory & Monitoring plots to the species diversity recorded in nearby US Forest Service Forest Inventory and Analysis plots.
Miller considered five metrics of diversity in each plot — number of individuals, tree species richness (how many species were in each plot?), Shannon evenness (are the species in the plot relatively as abundant as each other or are some super common and others very rare?), McNaughton Dominance (what is the relative abundance of the two most abundant species?), and Percent Rare N/S (what percent of species in a plot have fewer individuals than the average species abundance in that plot?). The title of Miller’s paper is a spoiler alert — the parks were more diverse than the matrix (non-park) forests — with park forests comprising higher species richness and a more even, less dominated distribution of abundance across species. She found this pattern of higher species diversity across the majority of the parks in the study, but it was most consistent in the lower latitude parks. Over a decade of publicly available data from the National Park Service’s Inventory & Monitoring plots and the Forest Service Forest Inventory and Analysis plots allowed Miller and her team to explore tree species diversity across 39 eastern National Parks, each containing between 4 (Sagamore Hill National Historic Site) and 171 (Acadia National Park) forest plots.
Before Dr. Miller began her PhD at UMaine, she led field crews that collected some of the data in the National Park Service Inventory and Monitoring Program. Miller told me, “My field experience sampling and hiking around eastern forests has definitely helped me frame the types of research questions to ask, and interpret whether the results are meaningful. When I started this study, I suspected that at least some of our parks, particularly the larger ones (e.g. Delaware Water Gap National Recreation Area, New River Gorge National River), would have greater tree diversity. I was surprised, however, to find out that many of our cultural parks, which tend to be smaller and haven’t been protected as long, also have greater stand-level tree diversity than matrix forests.”
Miller’s results are both expected and unexpected. First, there’s a general understanding among ecologists that eastern US forests today are smaller, younger, and more homogenous than they were before centuries of European settlement, land clearing, and timber harvesting. And, we know on a basic level that forests in US National Parks are largely protected from development and harvesting. So, it shouldn’t be shocking to find that forests managed by an agency that is dedicated to promoting ecological integrity and natural disturbance regimes are full of lots of species — not just the early successional ones. But, on the other hand, we often don’t imagine Minute Man Historical National Park — a battlefield replete with actors in Revolutionary War costumes — as bastion of biodiversity. Or, in the case of All Aboard! National Parks, we don’t imagine these cultural parks as national parks at all.
So how did Miller land on this question — what made her interested in comparing the tree species diversity in parks and unprotected forests in the east? She muses that “this research question in particular was a follow-up to [our 2016 Ecosphere paper] “National parks in the eastern United States harbor important older forest structure compared with matrix forests” which compared metrics of forest structure in eastern national parks with surrounding matrix forests.” In that study, she found that “parks, regardless of park designation (e.g. National Park, National Recreation Area, or National Historical Park), had consistently older forest structure than matrix forests.” Were these older forests also more diverse? The same forest plot databases could answer that question as well!
I asked Miller if her research changed her view of the ecological value of cultural national parks. “For me, the results of this study were very encouraging, and confirmed that our efforts to monitor and keep even the smallest parks’ forests healthy are worthwhile. I am hopeful that the results of these studies are empowering to the resource managers in our cultural parks, and lead to stronger emphasis and additional resources for maintaining healthy forests in these parks. Ultimately our research also makes a strong case for the importance of protected areas in preserving forest biodiversity, even small urban parks.”
This research seems relevant to managers outside of National Parks as well — and Miller hopes that private landowners, state parks, and NGOs take note. She recognizes that resilience to global change is a big contemporary concern for many land managers. “In forests, tree diversity and structural complexity are important components of resilience, and our results demonstrate the positive influence that protection, particularly protection from logging, can have on forest resilience. In addition, park managers often receive pressure from well-meaning members of the public, and even other park staff to “clean up” forests after natural disturbances. In fact, this was typical management practice in the early days of national parks before we knew better.” She tied together her species diversity and forest structure research and reflected that, “coarse woody debris, dead and dying trees, and blow-downs all contribute to the overall diversity of a forest, and our research has shown that protected forests have more of these features than unprotected forests. Hopefully our research can help inform and support managers’ decisions not to clean up after disturbances unless there is a concern about human safety (e.g. hazard trees).”
Miller and I both work in Acadia — the kind of classic wild National Park that appears in our imaginations and children’s books as an iconic protected landscape. But as Miller points out, “Interestingly, Acadia National Park did not come out as being more diverse than surrounding matrix forests, particularly because the park has more extensive late successional forests that are largely dominated by red spruce.” She explains, “this isn’t necessarily a bad thing, but it does suggest that the forests in Acadia may be more vulnerable to stressors than matrix forests, particularly stressors that could impact red spruce. While this isn’t the greatest news, this is important information for park managers to know.” Like many folks in the greater Boston area, I drive hours to Acadia and feel like I am stepping into a wilder, more biodiverse ecosystem when I lace up my hiking boots at the trailhead to Cadillac Mountain. But, there are pockets of protected tree species diversity hidden in plain sight across the eastern US. Miller’s research makes me rethink my summer road tripping plans — perhaps I should seek out some of those old, diverse forests in National Recreation Areas and Historical Parks, maybe some are actually accessible by railroad… I’m going all in on my research for the All Aboard! Cultural National Parks of the East board book pitch!
Miller, K.M., McGill, B.J., Mitchell, B.R., Comiskey, J., Dieffenbach, F.W., Matthews, E.R., Perles, S.J., Schmit, J.P. and Weed, A.S., 2018. Eastern national parks protect greater tree species diversity than unprotected matrix forests. Forest Ecology and Management, 414, pp.74-84.
Miller, K.M., Dieffenbach, F.W., Campbell, J.P., Cass, W.B., Comiskey, J.A., Matthews, E.R., McGill, B.J., Mitchell, B.R., Perles, S.J., Sanders, S. and Schmit, J.P., 2016. National parks in the eastern United States harbor important older forest structure compared with matrix forests. Ecosphere, 7(7).