The first place I looked for a tree company when I needed one was on the net. Im a web designer, where else would I look. I did the same thing when I needed a roofer. I think tree companies and contractors fall into the same catagory.
People look in the phone book because that is the only place to look.
The internet is the perfect place for companies like this because they have enough room to give you real information about their company so that you can make some kind of intelligent decision about who to hire. Putting up tree care information will also make the site useful. I have talked to contractors that were very dissapointed in the response to their web sites. The reason was someone one took their money, built them a site and did nothing to promote it or built them a one page site that was just like a phone book ad. People want real information, not names and addresses.