What are economics to a plant? I told you last time that plant leaves need to be profitable – they should gain more carbon over their life span then they cost to build. If this wasn’t true there would be no plants, because plants are mostly carbon!

But is this economic situation the same in all environments? Do plants have to play a different game when it’s warm instead of cold, or wet instead of dry? High elevation instead of low? We know that leaves change their form across environments. Desert leaves? Thicker and waxier, to keep water in. Shady areas? Big, dark, and flat, to capture as much sunlight as possible. So there’s a wide range of leaf forms (that work differently) around the world.

Surprisingly it turns out not all kinds of leaves exist. Very big, very thick, very short lived leaves? None. Very thin, very long-lived leaves? None. This economic spectrum has been something of a mystery – why are some leaf strategies not allowed?

I’ve been investigated this question at the Rocky Mountain Biological Laboratory. It’s up in the mountains of Colorado, and is a spectacular place to work. Elevations range from 6000 feet (desert) to 13000 feet (alpine, and above treeline), meaning that I get to look at plants trying to make a living in a wide range of environments. There’s lots of plant diversity with so many leaf forms to explore. And it’s a beautiful place to live. Here’s my cabin (built 1930) photographed in late June, with fresh snow on the hills. You can see meadows, aspen stands, and conifer forest, all within this very small range!

One of the things I’m most interested in is how leaf economic strategies change within the same species. It makes sense that a pine tree is doing something different than a violet flower – but can different individual plants of the same species be different too? Can two pine trees be more economically different than a pine tree and a violet? I’m actually trying to work on this question with aspen trees – there’s lots of them, and they grow in all sorts of environments. Individual stands are also clonal, meaning that they share the same genetic makeup, so I can safely focus on environmental (instead of genetic) variation.

Also, aspen trees are a real adventure to climb. Here’s Neill, trying to figure out how to get to the canopy of this one. It turns out they have very slippery and dusty bark!

Next time, I’ll talk about what I’m looking for in each leaf when we finally are able to collect them!