This is a great read describing the situation of indian clearings and cultivations at the time of European contact:
Indian New England Before the Mayflower
The author, Howard Russell, also wrote the authoritative history of agriculture in New England, a book I own and have thoroughly enjoyed reading over the years.
LOW
Fires will not spread beyond heat of campfire or brush fire.
MODERATE
Fires will start from open flame, camp or brush fire. Spreads slowly.
HIGH
Fires will start from a lighted match and spread rapidly in dry grass, slower with moisture. Will continue to spread until extinguished.
VERY HIGH
Fires will start readily from match or glowing embers and spreads rapidly as it increases in size. May crown young conifers.
EXTREME
Fires start readily from sparks or cigarette butts. Spread and crown rapidly. Spot fires common. All burn fiercely and may blow up unless controlled promptly.
<1 mph
Calm Still
calm air, smoke will rise vertically, water is mirror-like.
1-4 mph
Light Air
Rising smoke drifts, wind vane is inactive.
4-7 mph
Light Breeze
Leaves rustle, can feel wind on your face, wind vanes begin to move.
8-12 mph
Gentle Breeze
Leaves and small twigs move, light weight flags extend.
13-18 mph
Moderate Breeze
Small branches move, raises dust, leaves and paper.
19-24 mph
Fresh Breeze
Small trees sway.
25-31 mph
Strong Breeze
Large tree branches move, telephone wires begin to "whistle", umbrellas are difficult to keep under control.
32-38 mph
Moderate or Near Gale
Large trees sway, becoming difficult to walk.
39-46 mph
Gale or Fresh Gale
Twigs and small branches are broken from trees, walking is difficult.
47-54 mph
Strong Gale
Slight damage occurs to buildings, shingles are blown off of roofs.
55-63 mph
Whole Gale or Storm
Trees are broken or uprooted, building damage is considerable.
64-72 mph
Violent Storm
Extensive widespread damage.
73+ mph
Hurricane
Extreme destruction, devastation.
