Venerable Trees

This white pine is the largest and possibly the oldest tree on my property. It has a DBH (diameter at breast height or 1.3 meters) of 92 cm, and I estimate its age at about 180 years old.

The white pine probably began growing sometime around 1845. This was at the beginning of the white pine logging era in Minnesota. By 1900, it would have been large enough to cut for timber, but it was missed. The 1918 fires that swept through the area also missed it by just two short miles.

All through the 20th century, it continued to grow undisturbed. Over time, a forest of paper birch, aspen, balsam fir, and spruce grew under the pine. Beneath the trees, clubmosses, poverty oats, rough rice grass, purple melic grass, twinflower, and hairy goldenrod covered the ground. The forest had come back.

The big white pine as seen from ground level.

When other white pines on this 40-acre section were cut down for lumber in 1960, this huge white pine was not cut down. So were four other large white pines and five large red pines. I don’t know how or why this happened, but I am glad they were overlooked. What would this forest be without them?

One of the big white pine’s neighbors. This white pine tree had a DBH of 82 cm in 2015. I estimate its age at 170 years.

Logging of Minnesota’s white pine forests began in the 1830s, but it wasn’t until the 1870s, with the advent of railroads and new settlements, that it really took off. By 1900, Minnesota had produced almost 1.2 billion board feet of white pine timber. This was not to last, and by 1929, nearly all of Minnesota’s white pine forests were depleted, bringing white pine logging to an end. While not remnant trees from old-growth forests, these white and red pine trees are survivors from that time.

One of the old red pines, DBH 56 cm, age estimate 121 years.
Another of the old red pines, DBH 70 cm, age estimate 148 years.
White pines I planted in the early 2000s. These trees were grown from seeds produced by another old and enormous white pine on my land. They are part of my project to re-wild a former hayfield and pasture.

I found some more leaf mines

A leaf mine in a big-leaf aster leaf that was probably made by the larva of an Ophiomyia sp., a genus of leaf-mining flies.

Recently, I’ve become more interested in leaf mining insects after finding what might be the serpentine leaf mine of a Stigmella moth in a blackberry leaf. This wasn’t the first moth leaf mine I have found. In 2017, I identified another leaf mining moth, Phyllocnistis populiella, recognizing it from its leaf mine in a balsam poplar leaf.

Later, in 2019, I found the adult of another poplar leaf mining species, Phyllonorycter nipigon. Beyond that, my findings of leaf miners have been sporadic and by chance when photographing micro-moths at my moth lights.

Changing weather, changing focus

With the colder fall weather, it is more difficult to find insects and other arthropods. So, now I am turning my attention to the signs of them.

Out on my walks in the woods late last month, I came across five more serpentine leaf mines. The first was in a big-leaf aster (Eurybia macrophylla), which is shown in the photo at the top of the page. The other four were in wild red columbine (Aquilegia canadensis), coltsfoot (Petasites palmatus), goldenrod (Solidago gigantea), and bunchberry (Cornus canadensis). I couldn’t find larvae in any of them, but I think I have a good idea of what made them.

This leaf mine in a columbine leaf was probably made by a larva of Phytomyza aquilegivora.

Possible identifications

The leaf mine in the aster leaf was probably made by the larva of a species of fly in the genus Ophiomyia, leaf mining flies in the family Agromyzidae.

Phytomyza agromyzina in bunchberry
Phytomyza albiceps group in coltsfoot
Phytomyza solidaginophaga in goldenrod

While I’m not absolutely certain, the leaf mines in the other four plants were probably made by the larvae of leaf mining flies in the genus Phytomyza, also in the family Agromyzidae.

I’ve probably seen the adult Phytomyza flies, but didn’t give them a second thought, assuming they were just some more pesky flies buzzing around my head looking for blood or sweat. Next year, I’ll be paying more attention.

Leaf mining flies are species-rich

There are at least 600 named species of Phytomyza, making it the largest genus of leaf mining flies in the world. Ophiomyia has over 200 species. Species of Phytomyza and Ophiomyia are host-specific, which accounts for much of the diversity in their genera.

Cerodontha is another species-rich leaf mining fly genus in the Agromyzidae, with 285 species worldwide. Cerodontha is a monocot specialist mining the leaves of sedges (Cyperaceae), soft rushes (Juncaceae), irises (Iridaceae), and grasses (Poaceae). Some Cerodontha species have been found in Minnesota and neighboring Wisconsin.

A quick search of species of Phytomyza and Ophiomyia that might occur in northern Minnesota shows at least twenty species and five species, respectively. The number of Cerodontha species in Minnesota is unknown. I think next summer is going to be an interesting one.

Further Reading

Every leaf of this bunchberry has a leaf mine.