My post about walking distance got me thinking about changes in our area over time.  I wanted to go back and look at some old USGS maps, and was surprised to learn that you can now download all of the maps from your region as pdf files for free!  (The last time I played with topo maps, about six years ago, you either had to buy a paper copy from the USGS or snag screenshots from various websites that were trying to sell paper maps.)

For our area, the maps available were from 1935 (first map) and 1957 (second map), and I also took a screenshot of google maps' current satellite photo (third map) for a more up-to-date view.  Then I layered them all together in the Gimp.  I cropped a bit of the 1935 map off and made the top map slightly transparent in the first image in this post so you can see what I'm talking about when I refer to layering.

The property I'm taking a look at here is the same potential Walden Effect annex I mapped the soil for.  I was interested to see that, except for the ridge (south end of map), the propery was entirely devoid of trees between 1935 and 1957.

Solid black squares on a topo map represent houses, dotted lines are small roads or trails, and outlined squares are generally barns or other large, non-residential structures.  With that information in mind, you can see that someone was living on the property during both 1935 and 1957, probably grazing animals or possibly growing corn and tobacco on most of the acreage.

Between 1957 and the present, the majority of folks stopped farming in our region and started getting jobs in town.  Although it's sad that people were no longer living off the land, the earth rejoiced by sprouting up trees everywhere.  Only a few acres on the northwest side of the property remained clear of trees by the time of the 2011 aerial photo.

I merged all three of these maps together to create the version above, which gives a rough estimate of canopy cover over time.  The lightest color is areas that are currently forested, the bright green represents 1957 trees, and the dark green is 1935 trees.  (I didn't bother with the area on the other side of the river, and you'll notice some irregularities between 1935 and 1957 forest borders that are probably a sampling error due to the low resolution on the earlier map.)

Why does it matter which areas had trees in the past?  It's handy to know that the woodland is at least 77 years old on the ridgetop, because that kind of forest will be chock full of plants and animals found in few other places and is best left alone.  On the other hand, twenty-plus years of farming on the rest of the property may mean the topsoil has been eroded away, and definitely means I'll feel less guilty about clearing spots for sustainable agricultural purposes.  And, of course, it's just plain fun to guess what the land was like decades in the past.

Have you discovered even better sources of historical maps or aerial photos online?  Since it's the weekend, I can probably sink my teeth into some more....