I've been following-up on the issue of tree cover in Seattle. The assertion (noted yesterday on this blog) that tree cover in Seattle has diminished from 40% in 1972 to 18% today intrigues me. To me it is intuitively incorrect i.e. it does not fit with my own personal memory nor some basic facts such as the fact that Seattle is about 50% right-of-way and has been for many many decades. So how Seattle was 40% covered by trees in 1972 is hard to grasp.
So I emailed the reporter who wrote the P-I story (Lisa Stiffler) to find the source. She directed me to an earlier story she had written which made the same assertion and again without sourcing it adequately. In fact the story from last September, 2006 uses 1996 as the latest reference date while the story from yesterday pegs the number to "today."
Yes the numbersd appear to be virtually the same tjough Seattle has (one would think) has undergone tremendous development in the past 10 years.
Here are the images to which the reporter directed me and which supposedly justify the statement that
Since the early 1970s, Seattle has lost more than half of its tree canopy as more businesses and people have moved into the city and smaller homes have given way to apartments and megahouses.

The problem with the satellite photos (if that is what they are — which seems questionable based on the uniformity of the water color) is that
1. The images show far more than Seattle proper. In fact it shows an area from Tacoma to nearly Everett and from Issaquah to west of Bremertton. Yet the story is explicitly about the city of Seattle.
2. No source is provided for the images except "City of Seattle" and I don't believe that the City has its own satellite nor the expertise to analyze such aerial images with authority.
3. Most importantly it is impossible to tell from these images what is happening on the ground especially when the assertion is so precise: "40% to 18%." The images purport to show "evidence" — "pictures don't lie" — but as presented these two images do nothing.
It's important to determine the truth or falsity of the assertion because public policy is being based upon it.
But hey! "What importance are facts," to paraphrase GW Bush, "when the intentions are good?"
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The City of Seattle's own web site repeats the fact and again with no apparent source:
...in 1972 trees covered about 40% of the city, where now tree cover is only about 18%.
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Btw, let me make it clear that I neither believe nor disbelieve inthis fact. Yes it doesn't comport with my own perception of how Seattle has changed over the past 40 years. But I don't deny the possibility; I would just like to see some clear documentation.