I wonder what affect 30+ years of "free tree" programs that various states and environmental clubs run for arbor day and such has had. Growing up in the midwest/great plains, ever year in elementary school we were given trees to take home and plant for arbor day. Little sticks, maybe a foot long with a small handful of roots, wrapped in damp paper towels to survive the trip home.
Someone says "oh, white oaks grow alright across the entire state, and their acorns are a good food source for the local wildlife" and they send out a few thousand of them for arbor day via elementary schools.
Some of them even survive. 30+ years later, those trees have dropped millions of acorns, most of which feed squirrels and deer or rot away, but some turn into trees.
Rinse and repeat every year. Seems like you could, over the course of nearly 40 years, unintentionally shift the population of a tree species.
The interesting question for me is this: is there a reason to believe human seed distribution is biased towards the west?
If it is human-influenced, what are the determinative factors? Do humans favour certain seeds/trees in this selection? Are the seeds geographically distributed evenly, or is distribution biased towards the west? Is the westward growth bias caused by seed distribution, or locale viability? If humans weren't distributing the seed, are there other vectors that would provide an equivalent function?
I'm not saying it explains everthing they found (they may even have corrected their stats for it), but the area they studied seems closer to the east coast then to the west coast. Moving long distances east is hard there for trees. First, they would hit larger populations centers; then, the ocean.
Agreed, I think humans planting "exotic" trees have a lot more to do with tree migration than just global warming alone.
Also, last year before we turned my childhood home into a rental I cleared out a large Coniferous tree I planted when I was a young sapling. It was much, much larger than 12 inches tall.
The "no one knows why" seems to be a stretch. It mentions in the article that western areas are less moist and moisture levels have been increasing. Seems like they're pretty confident that's the reason.
Yeah, the <title> of the page is the non clickbait version: "Climate Change Is Forcing Trees to Move Northwest". Completely at odds with the headerline...
What really should interest/worry you about this is the ecological changes that will follow.
Different animals and birds have special relationships with certain types of trees. When forests change, animals change. This can have a compounding effect, as animal changes can change forests in turn. A few small changes here and there can be the catalyst for much larger changes over time.
Doesn't say how much of this is due to new trees on the leading edge compared to less trees on the other end. In the analogy of a line of people, adding people to one end will move center that way as long as you don't add more to the other. The trees could grow each way or shrink each way and still show a movement, as long as one side is doing so at a different rate.
Trees have been around for a very long time, hundreds of millions of years. Much longer than we have been. Possibly something they "know" at a genetic level is a sort of risk assessment where species are calculating better long term odds for the species based on local trend. They could be migrating toward areas where less adaptation is needed to survive; or maybe even a substantial but available path to adaptation via recessive genes.
This migration isn't the first. They've been doing this all along.
Pretty much, yeah. "Fei and his colleagues argue that at least 20 percent of the change in population area is driven by changes in precipitation, which are heavily influenced by human-caused climate change". Could be more than 20%, but that's what they have solid evidence for so far.
Someone says "oh, white oaks grow alright across the entire state, and their acorns are a good food source for the local wildlife" and they send out a few thousand of them for arbor day via elementary schools.
Some of them even survive. 30+ years later, those trees have dropped millions of acorns, most of which feed squirrels and deer or rot away, but some turn into trees.
Rinse and repeat every year. Seems like you could, over the course of nearly 40 years, unintentionally shift the population of a tree species.