by Carl Strang
On Saturday I returned to Maple Grove and Meacham Grove Forest Preserves to complete this year’s measurements of leaf miners in black and sugar maples. Earlier I reported the results for the understory. This time I was looking at fallen leaves to index leaf miner abundance in the forest as a whole. This can be regarded as a measure of these tiny caterpillars in the canopy, in part because the vast majority of leaves grow there and in part because saplings still are holding many of their leaves at this point in the season.
I went to 10 randomly selected points at each preserve and examined 30 leaves per point. The sunny, calm day was good for this as mines can be difficult to see after the fallen leaves have turned brown. I can hold the leaf so the sun shines on each surface, then hold it up so light shines through it.
In the five years that I have taken this measurement I have found few differences between canopy and understory leaf miner abundances. The most common difference is a lower incidence of Phyllonorycter tent mines in the canopy than in the understory, and such was the case this year at Maple Grove. Also at Maple Grove, Caloptilia boxfolds were less common in the canopy than in the understory this year.
All four genera of these tiny moths were in low numbers in the canopies of both preserves. The most abundant were Phyllonorycter at Maple Grove, where I found tent mines on 15 of 300 leaves, or 5%. That was the only species which produced a statistically significant difference between the preserves. In general, populations have been low since I began measuring canopy leaves, so I have yet to see a consistent pattern of differences. The only complete miss this year in understory and canopy combined was an absence of linear mines (probably produced by the non-native moth Stigmella aceris) at Meacham Grove (one turned up in the canopy sample there last year).
I have been interested in the effect of the more intensive management at Meacham Grove on insects and plants I am studying in these preserves. On Saturday I noticed that a burn had been attempted yet again at Meacham.
As you can see, the line of burning fuel dripped along the edge of the trail (which serves as a firebreak) did not take. There still is time for another attempt this fall.