Splitting Up

I recently spent a day out at Joshua Tree National Park. I was participating in a writing workshop. They included a Ranger in just about every activity, and they told 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. 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 to 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. However 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. Ground sloths, being large, covered large territories so they could feed, so the seeds were dispersed over large areas.

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.

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.) 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.

Send me an email at [email protected]. Or you can comment on my blog at http://mathnerde.blogspot.com/