Chop Down Those Trees!
According to [biologist Dr. Jens] Roland, the altitude of the tree line in the Canadian Rockies is rising--likely due to global warming--and, outside of national parks, forest fires are usually suppressed. [That's human intervention!] These factors are combining to create larger forests and smaller alpine meadows. This is bad news for butterflies in the Rockies, such as the Parnasissus, which Roland studies, because they require two things that they can easily find in meadows: sunlight and stone crop.Rowland doesn't mention as a cause environmentalists' largely successful efforts to stop logging in forests throughout Canada and the U.S. When combined with fire supression, there's little natural or unnatural thinning of trees going on nowdays. Of course, environmentalists often oppose fire supression, but it does occur nonetheless, in order to protect homes. Fire supression areas abut areas where thinning and cutting are prohibited, and the result is choked out butterflies. (h/t Greenie Watch)
Butterflies need sunlight to elevate their body temperatures in order to fly, and forests are generally too shady for them to travel through with quickness and ease. Parnasissus also need stone crop, a plant that grows in meadows and is the only suitable host for alpine butterfly larvae. Therefore, alpine butterflies do not generally travel beyond the meadows they are born in, and the shrinking meadows could lead to inbreeding and the decreased diversity in the gene pool, Roland said.
Historic photographs of the Sierra Nevada mountains, taken before any forestery operations were undertaken, uniformly show less dense forests when compared to contemporary photographs of the same setting, as explained by George E. Gruell is author of Fire in Sierra Nevada Forests: A Photographic Interpretation of Ecological Change Since 1849:
I have published scores of historic photos side-by-side with modern retakes from the same locations that show how much less dense Sierra Nevada forests were about a hundred years ago.
Our current forest conditions differ greatly with the historic norm - as detailed in my book.... California's forests have experienced massive increases in tree cover resulting from human activities, particularly the suppression of natural fires. Similar changes are evident in vegetation throughout the West.
As a wildlife biologist, I know evidence strongly suggests that increasingly dense forests are detrimental to wildlife, including numerous songbirds, rabbits, squirrels, and deer. Historically, wildlife populations adapted to ecosystems that were subjected to frequent low-intensity fires. Today, thicker forests burn in high-intensity crown fires. (source)