I recently spent a day out at Joshua
Tree National Park. I was participating in a writing workshop. But
they include a Ranger in just about every activity and they always
tell some interesting facts about the Park. This time the Ranger had
some information about Joshua Trees. One of the first items was that
the biologists are splitting the Joshua Tree in to two species.
If you've paid attention, then you may
have noticed that the Joshua Trees around here, like the ones that
dominate Joshua Tree National Park, look different that those you
might see as you drive through the Eastern Mojave, perhaps on your
way to Las Vegas. The eastern species (currently Yucca
brevifolia var. jaegeriana) branches
more readily than the local ones (Yucca
brevifolia var.
brevifolia). Now
species tends to be a fuzzy concept. But it's generally accepted that
if two things cannot have fertile offspring then they are different
species.
Well, the Ranger
informed us that the two types of Joshua Trees have different species
of moth that do their pollination. And the moths are sufficiently
different that they are different species. So the thinking goes that
the two types of Joshua Trees are different species too. Now it will
be some time before this starts turning up in books about the
wildflowers of the Mojave, but botanists are starting to think about
the trees as different kinds.
Which is going to
make conservation of the Joshua Tree even more complicated. And the
Joshua Tree is in need of protection. Climate change is making the
local desert warmer, and Joshua Trees need to have cool temperatures
so that they can bloom. They just need a few nights with below
freezing temperatures, but those are getting to be more rare.
Now one
possibility for the Joshua Tree is the move its range northward. But
the Joshua Tree doesn't have its seeds dispersed over long distances
by birds. Currently the main way that they have their seeds
dispersed is by rodents. The kind that make caches of seeds. Like
pack rats. But these generally don't have large ranges and don't move
seeds very far.
Now in the past,
say about 10,000 years ago when the last Ice Age ended, the Joshua
Tree had its seeds dispersed by one of the ground sloths that were in
the area at the time. In fact, undigested seeds of the Joshua Tree
forms a great deal of the fossilized droppings of those sloths. And
ground sloths, being large covered large territories so they could
feed. So the seeds were dispersed over large areas.
But those sloths
are no longer around. They were too big and ate in the open so were
too tempting of prey for the humans that had moved into the area at
about the same time as the end of the ice age. They went extinct,
victims of climate change and human actions.
So today the
Joshua Trees can only move around very slowly so may not be able to
move northward fast enough to save themselves. (The speed of the
current climate change is unprecedented.) So the fate of the Joshua
Trees, a symbol of our local desert, may be determined by the actions
of humans today. Or more likely our inactions.
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