One winter day while researching my hiking guide, Base Camp Denver: 101 Hikes in Colorado’s Front Range, I headed to Pine Valley Ranch Park, near the town of Pine in Jefferson County. I was looking for a lower-elevation forest hike to feature in the book for winter walkers, and figured this would be just the ticket. The trail began at an elevation of only 6,700 feet and topped out below 8,000. As I drove, I anticipated a snow-free amble through butterscotch scented ponderosas.
Back then I was still a neophyte to this particular area; not fully aware of what had gone down, forest fire-wise, in the previous decades.
I began walking in lush second-growth forest, skirting the edge of Pine Lake, which up into the 1920s supplied ice to Denver. Before ice, lumber was king in Pine (hence the name), especially after the narrow-gauge railroad came through in 1878. It took a little over a decade to cut down most of the accessible forest, and then the industry largely died and the trees grew back.
As I headed uphill on Park View Trail, I noticed some singed ponderosas. Clearly a fire had recently lapped the edges of this park. Then I climbed a ridge into the next valley, turned onto Strawberry Jack Trail, and became struck by the sight before me: hillsides covered with bare blackened trunks, some standing but thousands toppled like pick-up sticks. Slopes once denuded by logging had been stripped yet again—this time by fire.
As I hiked across a charred landscape that felt otherworldly in its desolate beauty, I found it easy to imagine the fire had happened, if not yesterday, then perhaps a year or two before. I could not spot a single new tree growing anywhere. Not a seedling.
The truth is, however, that this June will mark the nineteenth anniversary of the fire that torched these hillsides. This was the Hi Park Fire, of 2000. That’s right: It’s nineteen years later, and there are still no seedlings.
Shouldn’t there be seedlings here by now? According to historical patterns, there should be. But in a paper published in the journal Ecosphere in 2016, researchers Monica Rother and Thomas Veblen confirmed numerically what any hiker can readily see when visiting these areas. The title of the paper puts it succinctly: “Limited conifer regeneration following wildfires in dry ponderosa pine forests of the Colorado Front Range.”
Rother and Veblen conducted a methodical study of six lower-elevation ponderosa pine forest fires that occurred between 1996 and 2003, including Hi Park. They examined a total of 302 widely-dispersed plots, each measuring 100 square meters. Eight to fifteen years later, according to historical patterns, there should have been at least an initial pulse of new conifer seedlings in most of these plots. But what the researchers found was the same as what I was seeing in front of me. Depending on the fire, only between 2% and 38% of the plots were deemed as being “on their way to recovery.” In fact, 59% of the plots had no seedlings at all, and ALL of the plots situated below an adjusted elevation of 7,700 feet (adjusted per latitude) had no seedlings.
Incidentally, on the same week in the year 2000 that the Hi Park fire was burning, so was Bobcat Gulch near Loveland (another of the six sites studied). I wrote about Bobcat in a blog post last year, and commented on its stark treeless-ness, which is even more severe than Hi Park. And yes, Bobcat Gulch is below that critical elevation where the researchers found “no seedlings.”
What is hindering ponderosa pine regeneration? What is preventing these forests from bouncing back like they did over the previous century-plus, after fires and logging?
Of the many factors affecting seedling reestablishment, Rother and Veblen identified the two most important: (1) elevation and (2) directional aspect (i.e. degree of north or south-facing). In other words, it is about temperature. Ponderosa seedlings are doing better at higher elevations not in the direct blast of the sun. In a companion study, published in 2015, the authors showed that increasing the average temperature by just 2.7 degrees F, while maintaining normal precipitation levels, severely limits ponderosa seedling survival and growth.
Here’s some additional data: in the past 50 years, the average temperature in Colorado has risen by about 2.5 degrees F. And it’s expected to keep going up: another 2.5 to 6.5 degrees by the year 2050.
It has only been a couple of decades since these fires, and the window for seedling reestablishment has certainly not closed. The pines could still come back. But we need to get used to the idea that they might not. After disturbances such as these, it’s the species best suited to the current climate that grows, not the species that was favored a hundred years ago. It is quite possible these burned areas will convert to grasslands and shrublands in the coming decades, at least in the lower band of what was once the “ponderosa zone.”
Hiking the scorched landscape that day took a little getting used to, but it was haunting and beautiful, and it came with some surprise perks. As I ascended a gully, rouged rocks appeared all around which I wouldn’t have seen had there been trees. I reached a barren crest, and an unimpeded 360-degree view came out which included the snow-caked massif of Mount Evans. All was eerily silent, like a tomb, save for a few distant bird squawks. The experience felt unusual and entirely groovy.
From the crest I could also see the edge of the burn! The distant line of healthy trees appeared far away, but steady marching brought their scents, shade, and sounds soon enough.
My continued walk in the real live forest was all the more delightful, thanks to its contrast with the burn.