I first learned the value of fishing partially submerged trees about 20 years ago while casting for crappie on the Rideau system, just outside of Ottawa.

It was early spring, the ice had been gone for about two weeks and the crappie had moved in shallow to spawn. I was walking along the shore casting when I came upon a large tree that had lost the battle to snow and ice and had fallen into the water. I made a half-hearted cast along one side of the tree and suddenly my small float dipped out of sight. I quickly set the hook and landed a good-sized crappie. I cast back along the tree, and my float disappeared again. Another plate-sized crappie. The action continued virtually non-stop for two more hours.

I have no idea how many fish I caught that morning, but it sure made a significant entry in the fishing diary in my brain. Over the next 20 years, the memory of that outing helped turn many a so-so fishing day into a great fishing day.

I fish trees throughout the open-water year, and don't just fish them for crappie. You can catch just about every species in trees at one time or another -- walleye, smallmouth, largemouth, brookies, rainbows, salmon, pike, muskie and panfish.

Trees make productive structure for several reasons. For starters, they offer plenty of cover and shade, which make fish feel secure and protected, and which help them ambush their prey. Also, because they sit along the shoreline, trees usually serve up a multi-course meal -- how about minnows, followed by insects, frogs and crayfish. And, lastly, when there's a strong current, trees give fish a place to rest, so they don't have to constantly fight an upstream battle.

Of course, some trees attract more fish than others. For example, as you'd expect, the bigger the underwater portion of the tree, the more cover and shade it provides and the more fish you'll find underneath. Especially on a brilliantly sunny day.

Water depth is also important. Six inches of water under a tree may hold fish occasionally, but for the most part you want more water. In my experience, two feet of water is about right.

Lead-in weed cover also contributes to a tree's fish appeal. When the weed growth runs tight up to and even under a tree, it makes the tree all the better. And when this weed cover links up with deep water nearby, you may have hit the jackpot. Deep water means bigger fish, and the close proximity of the tree usually means that these fish will constantly replenish the honeyhole. So you can catch three or four good fish in a day by returning every few hours.

The last thing I look for is human activity around the tree. If there is a marina or public beach nearby, or a swinging rope hanging from a branch, the tree probably won't hold many -- or any -- fish. And there's no point in barking up the wrong tree.