Sunday, August 18, 2019

Spread of Microstegium vimineum (Japanese Stiltgrass) in the Delaware Water Gap

Microstegium vimineum seems on first glance to be ubiquitous in the Delaware Water Gap National Recreation Area. It lined many of the local roads that wound their way along Worthington State Forest on the New Jersey side, and it was one of the most abundant species even on trails such as the popular Mt. Tammany Red Dot Trail.

Japanese Stiltgrass lining the path on Red Dot Trail
In addition to creating dense mats along the sides of the trail, Microstegium vimineum even sprouted from the bases of large stones along the trail path itself!

Growing along the bases of stones on the path
In a previous post, I mentioned that this species is quite invasive, and possible evidence of its aggressive nature was in full view in the area.

Understory of fern
A multitude of fern species normally thrives in the Gap, their elegant leaves forming a dark green carpet under the shade of the tree canopies.

Microstegium vimineum colony (left) next to a stand of ferns (right)
However, infestations of Japanese Stiltgrasss can now be found next to stands of these ferns, from a few blades existing as small clumps to the side of the ferns, to entire monocultures of the invasive grass.

Fern plant being engulfed by Microstegium vimineum
I also frequently saw individual fern plants almost totally surrounded by Japanese Stiltgrass, the larger leaves of the fern rising from the sea of grasses like the frantic arms of a drowning man.

Fern plants surrounded by climbing Japanese Stiltgrass
The ability of this C4 species to grow in relatively shaded areas was also in evidence, with lush carpets of Japanese Stiltgrass sometimes blanketing the ground under the tree canopy.

Carpet of Japanese Stiltgrass under tree canopy

I was even amused to discover new colonies of the invasive grass clustering around the shaded bases of large trees, an area not usually conducive to the growth of grasses.

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