Nov 4, 2024
Introduction
Introducing 28 years of land cover change on your favorite trail! This is the latest feature added to Postholer Interactive Maps. It's made possible by Multi-resolution Land Cover Characterization Consortium which produces the National Land Cover Dataset or just NLCD. We've had current year land cover in the online databooks for years. This is different as you can actually see the on-trail change from 1985-2023 at very high resolution, about 30 meters.
To use it, go to your favorite trail map, click on the 'Gear Icon' and select 'Land Cover Change' under 'Charts'. You can also display the most current (2023) land cover base map. Select 'Land Cover 2023' under 'Base Maps' at the very top. Now, every time you pan or zoom the map, the graph will update with historical land cover only along the visible trail. Pan to your favorite section of trail and zoom all the way in if you like to get precise land cover history. Here's an example link to the entire Pacific Crest Trail. Zoom and pan to your heart's content!
Note, only land cover directly on the trail is used, not land cover close to the trail. We think this feature will be very handy for trail managers, trail maintainers and anyone who has an extended interest in the trail.
Changing Land, Changing Trail
Hiking among an evergreen forest devastated by an extremely destructive wildfire can be exceptionally distressing. Camping or sleeping under a burned and scorched stand of snags can be deadly. However, watching the forest rejuvenate itself after the fact has it's own special quality. Imagine walking through an evergreen forest on a warm summer day. Now, imagine hiking that same stretch of trail among Poodle Dog Bush. Same piece of trail, entirely different hike.
Nothing changes the landscape as quickly as a wildfire. What about the opposite, a landscape that remains unchanged for decades? We'll take a look at both.
A Picture is Worth A Thousand Words
The following examples will give you a bird's eye view over a few sections of trail. Primarily, we'll visualize the Pacific Crest Trail as it's near and dear to my heart. While we explore this, a good frame of context might be: the same section of trail you hiked 10 years apart might seem completely dis-simalar.
The 2009 Station Fire, Angeles National Forest
One notable characteristic about this fire is, how hot and intense it was. It burned all vegetation down to the dirt and left nothing behind. Trying to describe it is one thing, visualizing it in a precise manner is another.
(Click image for interactive map)
Let's start with the dark green line on the graph, this represents an Evergreen Forest or pine trees. Between 1985 and 2009 evergreen's represented between 62% and 69% of the ~30 miles of visible trail on the map. In fact, the cover actually increased over time. This is good. Had you been hiking the trail during that time period you would have enjoyed lots of shade and cooler temperatures a pine forest provides. (Fair weather summer hiker speaking).
During that time period Shrub/Scrub represented between 33% and 28% of the visible trail. For this land cover type, it was actually decreasing between 1985 and 2009 as forest gradually increased. Also, we'll make a quick note that a Mixed Forest (Evergreen & Diciduous) was about 3% of the visible trail. Grassland was insignificant or missing altogether.
Let's turn our attention to what occurred after this intense, extremely hot fire passed.
The first thing of note is the glaring demise of the Evergreen Forest, which plummeted from 69% of visible trail cover to absolutely nothing at all. This entire forest was decimated in a matter of weeks. The shrub/scrub faired marginally better, at 5% coverage down from 28% coverage. Grass coverage was insignificant. However, almost immediately after, the grasses made an appearance in a big way. The grass grew from 0% to 92% in coverage in a year! The grasses dominated the landscape for over 4 years.
While the grasses were having their day in the sun, it was to be relatively short lived, as the shrub/scrub began to take hold. 10 years after the fire, shrub/scrub accounted for 95% of trail cover smothering the grasses in the process. Even after 10 years the once dominant evergreen forest was no where to be found. Even now, 14 years later, the young evergeens struggle to account for 2% of the trail.
Summary On Wildfire
Taking a nerd moment here, if you look at the shrub/scrub and grasses on the graph, they are almost a perfect mirror image of each other. You can say they are inversely proportional to each other (there's an algorithm waiting to be found in that, folks). Same situation pre-fire. As the forest increased, the shrub/scrub decreased. This is not unique. As you explore the land cover, you'll see it over and over again.
A summary might be, grasses dominate ashes, shrub/scrub dominates grasses, evergreen dominates both and they all answer to wildfire.
Let's take a moment to use this as a cautionary tale. If you think the idea of fire permits or message of fire prevention is oppressive or draconian, please keep the above scenario in mind. Once gone, forests do not magically return. Be careful out there.
A Healthy Forest, Mt. Theilsen Area
From a graph perspective, healthy forests are boring, we are pleased to announce. In our next example, we'll look at a ~35 mile stretch of trail where the land cover has not been affected by a major wildfire in at least 70 years (we have fire perimeters layer between 1950 and 2023 turned on). Evergreen and shrub/scrub are the dominant fauna and their presence is consistent, ad nauseum. Again, it's a good thing.
(Click image for interactive map)
Recovering Logging, Lassen National Forest
While I'm not certain this has been logged or for how long, the road network clearly suggests logging activity. The Protected Area layer shows much of this land is unprotected, available for logging, mining and OHV use. Further, the land cover graph suggests logging as well. Again, there have been no major fires since 1950 here, either. The evergreen forest shows consistent growth while shrub/scrub show consistent decline. This is unlike the previous, healthy forest example, that show no change.
You'll also note this to be a small peninsula of unburned land. It's almost completely surrounded by the 2021 Dixie Fire, which has the dubious honor of being the largest, non-complex fire in California history at 963,309 acres. Thank you PG&E.
(Click image for interactive map)
Happy Trails!
That sums the latest land cover feature. We hope you find it as educating and useful as we do. See you all out on the trail!
-postholer
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