Ecosystem Convergence in Spearfish Canyon

It is a rare, special place where we can easily see the boundaries between so many known ecological systems. On the east coast, the forest mosaic changes subtly and gradually as we move through the landscape, central hardwoods such as oak blending seamlessly into northern hardwood trees such as beech and sugar maple. It can be hard to tell where the forest mosaics of dominant species are adjusting and why. Not so in the mountain west region of the United States, where drastically different ecosystems clash on full display in a beautiful fashion.

One particularly fantastic example of this phenomenon is Spearfish Canyon, which sits on the northern edge of the Black Hills in South Dakota, the oldest mountain range in the United States. The Black Hills is famous for Mount Rushmore, but is often overlooked for its unique proximity to the Rockies, northern latitude, and lower elevations of the Great Plains. Go to Mount Rushmore alone, and you will likely only see one of four special ecosystems in this area, the Ponderosa Pine forest, and you may only see it from a distance!

Spearfish Canyon features Ponderosa Pine forest, particularly in the upper elevations. However, it is also host to various other species that we don’t often find in other Ponderosa Pine dominated areas. The white spruce is an incredibly striking figure in the landscape, a perfect Christmas Tree shape in comparison to the often jagged, fire resistant Ponderosa Pine. It only thrives in cooler, wetter zones of the Black Hills, and does not spread past the Wyoming border at all. Ecologists are not entirely sure why this is the case, but upon my anecdotal observation, the region past the Wyoming border seems particularly drier and more fire prone than the eastern portion of the Black Hills. This may have been due to particular seasonal conditions at the time that I went, but assuming it’s a trend it may explain why white spruce doesn’t like it over there!

Another surprising find was paper birch, also known as white birch. In certain areas of New England forests, these trees are very common, though they can often be seen sporadically throughout New England. In the nearby Colorado Rockies, white birch don’t exist at all. They also seem to prefer more moist areas and congregated around the streambed in the canyon. Interestingly, white birch populations seem to have more complex genetic mixing and variation than previously believed. The leaves on these white birches were strikingly different from some of the examples I recall encountering in New England. They tend to have narrower, more pointed leaves, whereas the white birch appearing in southern New England had a more rounded leaf shape. You can read more about white birch species variation here.

The last species we see a lot of, which provides a striking contrast to the prior mosaic, is the prevalence of oak trees and shrubs in the region. Bur Oak is presumed to be the most common species in this area, but some examples I saw seemed more reminiscent of Gambel Oak, which is more common in Colorado and further south. Only recently have people begun reporting findings of Gambel Oak in the Black Hills, and since they readily hybridize with Bur Oak, identification becomes even more difficult. It’s unclear whether they are spreading here naturally or if they are a sort of “escaped” cultivated species, since Gambels and hybrids are readily sold in plant shops.

Add all of these distinct species up against a backdrop of limestone canyon walls and a variety of waterfalls, and you end up with one of the most spectacular scenes in the country. A variety of hikes, ranging from easy to difficult, are available for exploring this incredible ecosystem. We took the Roughlock Falls Trail, which was mostly flat with very slight inclines and is about 2 miles out and back from the start of the trail. There was plenty of parking at the start of the trail, and even more as you follow Route 222 up towards the waterfall, along with picnic areas that were quite busy in early September. The terminus of this main trail ends at the waterfall and is easy to find. Summers tend to be hot, sunny, and muggy, so bring a hat, sunscreen, and plenty of water!