Lecture: Selective harvesting of trees: Narrator: Listen to part of a lecture in an ecology class. Professor: So, as we've said, selective harvesting of trees is part of maintain an ecosystem. But deciding which trees to harvest, which trees in a specific forest to cut down, is not as easy as you might think. There's a lot of information to consider if you want to maintain the biodiversity of a forest. Simply cutting down old trees to let young trees grow isn't always the best harvesting plan. Old trees serve a number of functions, like providing habitats for animals. Take forest-dwelling bats. There are many different species but they all tend to use older trees for their roosts. Their nests are called roosts. Now, research about forest-dwelling bats is relatively new. So there's a lot of we don't know about that behavior, specifically their roosting behavior. What we do know is that they typically make their nests, their roosts, in older trees that are in the early stages of decay. The trees are usually more exposed; they're in more open areas, either on the edges of the forest or the tree itself is so tall that it rises above the surrounding trees. Why this specific type of tree? Well, older trees are typically larger in diameter so there's more space for more bats. Trees in open areas receive more heat from the Sun and they're easier for young bats to find and access when they first learn to fly. So this leaves some of those trees enough for a few colonies of bats, right? Well, it's not that easy. You see, forest-dwelling bats tend to switch roosts frequently. This is one of the reasons that it's so difficult to study. Sometimes they'll switch to a nearby tree; sometimes they'll find a tree several miles away. Sometimes they'll switch every night, and sometimes they'll wait weeks to switch. Why do they switch trees? Well, we're not really sure. Some researchers speculate that it's to confuse predators. Others claim it's a form of communication and some suggest that it's more about the trees. Certain species of forest-dwelling bats, the very small ones, live in dead trees with loose-peeling bark. They actually roust under the peeling bark. As you know, loose bark eventually falls off completely. So it makes sense that the bats would have to eventually abandon these types of trees, right? Like I've said, there's a need for more research. Knowing why certain species of bats switch their roosts so often, especially since cave-dwelling bats typically stay in the same cave. This research will enable us to make better decisions about which trees to preserve in which forest. And there are several species of forest-dwelling bats living in different types of forests. So, it's important to understand the behavior of each different species. For example, research suggests that big brown bats switch their roosts in order to maintain social relationships with other bats in the colony. Certain species of pipistrelle bats, on the other hand, seem to switch roosts in order to reduce parasite reproduction. Of course, being ecology students you've all realized bats eat a lot of insects and may be a key factor in controlling forest pests. So forest managers have a large incentive to figure out how bats use and contribute to forests.