Forests in Flux
Advancing vegetation mapping
It seems like the most newsworthy aspect of forests is how they change. From somber accounts of deforestation in the world’s remaining intact forests to striking images of charred timber after a wildfire blaze. On the brighter side, there’s the news of cities worldwide planting trees to increase their urban greenscapes. Indeed, forests have and will always be in a state of flux. When EarthDefine began work on its US Tree Map — the nation’s first and most accurate high-resolution tree canopy geospatial dataset — we knew such data would be put to use to understand those changes (if you’re unfamiliar with the US Tree Map, you can read out our introductory post to learn more). Let’s check out three mini-case studies to see how high-resolution tree canopy can be used to illustrate and analyze changes across America’s forests.
A Decade of Intensive Forest Use
In Washington State, the Cascade Mountains bisect the region and help define the entire region’s ecology. The range puts up a mighty rain shadow; one side of the Cascades is starved of water, while the other side is host to a literal rainforest. The amply watered westside can grow some impressively large trees. Having grown up in Washington, this is something that, frankly, I easily took for granted. Almost as easy to take for granted regarding Washington’s forests is the timber industry. It’s simply part of the landscape.
The last part is true — physically, economically, culturally… Logging has been an integral part of the region’s economy for the last two centuries, and even today the WA Department of Commerce names the forest products industry as one of the state’s key economic sectors. The forest products industry generates approximately $28-billion in business income and employs over 100-thousand workers a year.
The logging associated with such a prevalent industry shapes the region’s forests from year to year. Access to high-resolution spatial data allows us to map and analyze physical changes to forests. A simple side-by-side comparison like the one below illustrates the change over a decade on privately owned lands just outside Mt. Rainier National Park. A “mosaic” most appropriately describes what we see: a mixture of forested plots and riparian corridors, clearcut stands, and regenerating forest.
Beyond the compelling graphics of a changing environment are the numbers. For example, in a slice of the Cascade Mountains roughly the size of New York City (~290-square miles): 29-square miles of forest have been lost, whereas 42-square miles of forest grew back. That’s like losing a Manhattan and gaining a Bronx.
Granted, this is just an exercise. But there is real-world value to having high-resolution land cover data at your fingertips. Monitoring changes in tree canopy is a crucial element for managing our forests as resources and ecosystems.
A City in a Forest
Atlanta, Georgia is affectionately nicknamed “the city in a forest.” Indeed, tree canopy occupies nearly 50% of Atlanta’s area — making it one of the most forested cities in the United States (Georgia’s cities actually claim the top three spots for the greatest percentage of tree canopy by area: Athens, Columbus, and Augusta). Unsurprising perhaps, Atlanta’s urban forest has declined quite a bit in recent years. Rapid development and the expansion of its suburban neighborhoods resulted in a 45% decrease in its tree canopy between 1974 and 1996.
That said, a quick analysis offers modest, yet encouraging signs that Atlanta’s urban tree canopy is on the upswing. Between 2009 and 2019, The city’s overall tree canopy cover increased by nearly 2,500 acres (or a gain of just over 1%) despite the city’s population increasing over a percent as well. Much of the tree growth that we see in that time frame comes the maturation of young trees around newer developments, and in what appears to be a re-greening of Atlanta’s urban center.
Assessing the change by neighborhood shows high-proportions of growth in neighborhoods adjacent to downtown, as well as those in the southwest part of the city. The relatively green and affluent neighborhoods of the northern part of the city experienced declines in canopy cover, mainly as the result of new construction. The fact that the urban heart of Atlanta is experiencing a “green-up” over the last decade might point, in part, to the endeavors of an engaged community. Take for example the non-profit Trees Atlanta, which has coordinated the plantings of over 140,000 trees across the Atlanta Metro — targeting urban centers and transportation corridors where trees are needed most.
Mapping the distribution and changes in tree canopy will be a crucial tool for cities like Atlanta as they continue to plant trees and invest in their urban forests. This will be especially so if a new tree protection ordinance finds itself before the Atlanta city council this year. A new public ordinance would drive the preservation of trees, and dictate when and where new ones would be planted to offset loss from development. Such initiatives make it clear that the populous of Atlanta cherishes it’s city’s urban forest and wishes to see it thrive in years to come.
The 416 Fire
The summer of 2018 was a hot, dry one in Colorado — leading to an unusually intense fire season for the state. The official report of the 416 Fire, which eventually burned over 50-thousand acres of the San Juan National Forest, states that the fire ignited when hot cinder was cast from a coal-powered train into dry brush near the tracks. Evacuations followed in the communities near Durango while fire crews battled the blaze for the next two months.
Wildfire has always been an integral part of the American West, and for better or for worse, blazes like the 416 Fire have become the norm each season (fortunately, no lives nor structures were lost in the 416). An aerial snapshot of the Western States after each season would reveal a landscape in transition as forests and grasslands are lost or in various stages of regeneration. The image juxtaposition below reveals the startling devastation of the 416 Fire; the images and tree canopy were mapped one year before and one year after the fire.
Observing the change in the tree canopy, one year prior to and one year following the fire, we’re able to visualize the fire’s severity across the landscape. The deep ravine that Hermosa Creek traverses through was particularly hard hit, where nearly every tree succumbed to the flames. Perhaps we can better understand and predict how wildfires move across the landscape by analyzing the spatial patterns associated with the loss of tree canopy.
Data in Flux
The above case studies all assess changes in tree canopy across different time frames, whether it be a decade or a couple of years. Our Nation’s forests are changing even as I write this. Wildfires continue to rage across the west, making that change even more salient. From a data perspective, it would seem near impossible to keep up on the ceaseless fluctuations of canopy cover. This problem is compounded by the desperate need to be able to do just that. We are fortunate to have access to a public source of high-resolution aerial imagery: one that is updated regularly and has a data archive over a decade old (I am referring to The National Agriculture Imagery Program, of course). Here at EarthDefine, we apply advances in artificial intelligence to sources like NAIP to develop a robust algorithm capable of classifying trees across the nation, and in any time series available. suddenly have a wellspring of accurate tree canopy data — ready to meet the challenges of a changing world.
