Found this interesting 1927 Fire Weather Study (archive) recently, which included a couple interesting observations:
The fire records are for the following counties: Worcester County, the western half of Middlesex County, and the eastern half of Franklin, Hampshire, and Hampden Counties. The total area of the region is approximately 1,750,000 acres, the greater part of which is included in the so-called white pine region.
This is before the 1938 Hurricane, and it would be interesting to research further if it was still considered “white pine region” after that storm.
Of all the major forest types in the Northeast, the white pine type is inherently the most hazardous. Its leaf litter is highly inflammable because of the resin content. The size and form of pine needles produce a duff with practically no matting but with a great deal of porosity, so that the run-off after rainfall is extremely rapid. … White pine in New England is confined generally to the poorer soil types — those composed chiefly of sand. … Daily rainfalls of one-tenth of an inch or less do not keep the duff above the danger zone. Even with greater amounts of precipitation, the duff moisture content does not remain above 10 per cent for long unless the rains occur at short intervals.
That’s an interesting point about how quickly pine needles dry, and makes sense compared to broad hardwood leaves which would slow the drainage of water.
There is a table that shows the distribution of forest fires between April 11 and July 10, 1927 by relative humidity. The size of fires are surprising my modern standards:
11-15% 45 fires, 7,643 acres = 170 acres average
16-20% 140 fires, 4,059 acres = 29 acres average
21-25% 90 fires, 2,123 acres = 24 acres average
26-30% 94 fires, 1,395 acres = 15 acres average
(Fires drop off dramatically above 30%)
100+ acre fires are now quite rare, perhaps three in a bad fire season now.
