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NatureScience

Why Are There Fewer Large Trees in Yosemite?

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We’ve all heard the legend of Johnny Appleseed, the legendary apple tree planter of the United States. He walked across the country with his walking stick, and a bucket of seeds, just walking and planting as he went. Everywhere he went, apple trees sprouted up. And he was a hero. It is such a hero that Yosemite is looking for now.

The number of large trees is falling in Yosemite National Park, but no Johnny can be found. And the decrease is bad news for many species, including spotted owls, mosses, orchids and fishers (a carnivore related to weasels). These species, as well as others, are losing their habitat with the loss of the trees.

And it doesn’t look like the trend is going to change any time soon. The number of large-diameter trees dropped 24 percent between the 1930s and the 1990s. With fewer trees comes fewer seeds, which means that fewer trees will grow. Such a decrease in large trees is not only detrimental to individual species, but to the entire forest as a whole. Large-diameter trees generally resist fire more than small-diameter trees, so fewer large trees could also slow forest regeneration after fires.

Another threat to the area is that areas that have not experienced fires for centuries have gone through a change. Instead of fire-tolerant ponderosas, the forest is heavy with white firs and incense cedars, which are both fire-intolerant. In burn areas, ponderosa pines remain the dominant species.

But scientists don’t know for sure what has caused the decrease in large trees. “Although this study did not investigate the causes of decline, climate change is a likely contributor to these events and should be taken into consideration,” said USGS scientist emeritus Jan van Wagtendonk. “Warmer conditions increase the length of the summer dry season and decrease the snowpack that provides much of the water for the growing season. A longer summer dry season can also reduce tree growth and vigor, and can reduce trees’ ability to resist insects and pathogens.”

With an increased vulnerability to fire and a decline in reproduction, the fate of Yosemite remains uncertain. Perhaps the forest will take care of itself (as forests used to do before man’s management); or perhaps it is a matter of greater responsibility on our part. And perhaps, one day, humankind will take responsibility for humankind and let nature take care of nature.

But until that day, I’ll keep looking for Johnny Appleseed.

More: Why plant trees?

Source: Science Daily

Photo Credit: Jared Kelly via flickr under Creative Commons License




2 comments
  1. Yosemite-Mono Lake Paiutes

    Are you related to the famous Yosemite geologist Francious Matthes??

    He was such a famous well-known person for us.

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