Last week, we posted an interview with American Forests Science Advisory Board member Dr. Jerry Franklin about the importance of big, old trees. He told us how old trees fill an ecological niche that young trees just can’t provide: “Big, old trees have suffered the slings and arrows of climate, insects and diseases, and so they typically have a lot of features like cavities, which are really important from the standpoint of wildlife,” says Dr. Franklin.

This week, a new study illustrates his point. The largest owl in the world — the Blakiston’s fish owl of eastern Russia — relies on riparian old growth both for breeding and for feeding, says the study, which is a joint project of the Wildlife Conservation Society and the University of Minnesota. The owl has a six-foot wingspan, so only big, old trees have cavities large enough to accommodate its nests. The birds’ dietary habits also benefit from big, old trees. A favorite food of the owl is salmon. When big, old riparian trees die and fall into streams and rivers they create diversity in the water’s flow; as the stream makes its way around, over and under these obstacles, areas of different current speed and depth are created, which are necessary for salmon in different stages of life.

The researchers, whose study will be published in October in the journal Oryx, say the health of the population of Blakiston’s fish owl, currently listed as endangered by the International Union for Conservation of Nature (IUCN), is a strong indicator of the health of the forest. The 7,804 square miles of forest that were studied are also home to a number of species of salmon and trout, other owl species and the Siberian tiger, among other wildlife.

Of course, big, old trees on their own are do not make for a healthy forest. “You really need all stages of successional development of forests in our federal forest landscapes. … We need to be thinking about the early stages of succession, as well as the old stages,” says Dr. Franklin, which relates to another new study published this week.

A study in Nature Climate Change has found that Europe’s forests are reaching a carbon sink saturation point sooner than expected — as soon as 2030 — due in part to a lack of age diversity. According to the study, replanting projects were common in Europe following World War II, and now, those aging trees’ rate of carbon absorption is slowing, while younger trees poised to absorb more carbon are being harvested. The research team recommends including some old-growth forests in harvesting programs in these areas.

Examples are all over the globe: From providing wildlife habitat to sequestering carbon, age diversity is a key to healthy forests.