You’re invited to a mixer! The theme is Southwestern, with some tropical influences. The guest list is rather extensive. This event will draw participants from the Rocky Mountains to the north and the Sierra Madre cordillera to the south. Some Chihuahuans may show up, and certainly plenty of Sonorans, and maybe even some from the California and Nevada Mojave. Oh, and one more thing: for the most part, this is a dry mixer.

This mixer is essentially Arizona. For such an arid environment – right in the global belt of deserts at 30 degrees north – it is incredibly diverse biologically. The Sonoran Desert, which is the region encompassing Tucson, is bordered by the Chihuahuan Desert to the east and the Mojave to the north and west. As far as I can tell, in the days of Settling the West these were all lumped in together as the Great American Desert, but now we recognize the differences in the regions. You can see it in the pictures I have taken (below).

Mojave Desert
Sonoran Desert
Chihuahuan Desert

Then there are the mountains. The Sierra Madres to the south, a frightening place full of drug running and violence, have species migrating in from the tropical occidente. The Rocky Mountains to the north, through Utah (my hometown) up to Canada, allow more artic-y species to intrude further south on their ribbon-like finger of alpine climate. Arizona connects those ranges with a series of “Sky Islands,” small mountain ranges with pine forests clinging to their crowns, bordered by an inhospitable sea of desert. It may be the only place where you can essentially drive from Mexico (complete with parrots but lacking wolves) to Canada (complete with Douglas fir and black bears, but no longer any grizzlies) in an hour or two.

Between the relatively low biomass on the desert floor (making math and models tractable), the isolation between the islands in the sky (giving replication), and the gradient of climates and juxtaposition of all these opportunities, this mixer is a great place to study biodiversity.

The top of Mount Lemmon is dominated by Douglas fir and quaking aspen.
Compare this to the Sonoran Desert shot above. This oak-grassland chaparral is only a couple miles up Mount Lemmon's Sky Highway.

A few miles further, you get into oak-pine forest. Students are removing a straw-sized core from the tree to count its rings and tell its age. The tree will plug the hole within hours using sap.

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