Bud burst is a behavior only partly mediated by genes. Plants are responding to cold temperatures in the winter (twigs need to be exposed to X number of weeks of sub-freezing temperatures – typically 6-8 for species in the northeast – before they can be forced to burst open). By experimenting with forcing twigs we can start to tease out what specific external cues a tree is responding to in its environment.
Each step of our process above has variables that we can manipulate to test the relative importance in determining leaf out timing. Here are some modifications you can make to upgrade your leaf out observations into a full-blown experiment:
- Species: Try a bunch of different species to see which ones leaf out first. You can then start to piece together patterns: which groups leaf out earlier – conifers/broad-leaf trees, understory/overstory species, thick twigs/thin twigs, ring-porous/diffuse-porous species, determinate/indeterminate growth, etc.
- Sunlight: Does exposing a twig to sunlight affect when/if it leafs out?
- Temperature: Put some twigs outside your door or in the refrigerator and some next to your thermostat, just don’t let the water freeze.
- Water: Sap flow draws sugar and minerals up the trunk to the buds. Try putting sugar water in one, tums in another, or anything else you want.
- Oxygen: Plants need oxygen to fuel the early growth of their leaves (check the image below), so try putting your twigs/cup setup in a bag to limit the oxygen supply
And you can probably think of another 5 variables to tweak. Once you start to find differences in leaf out times then you can start to answer the really interesting question: why?
Good luck, and let me know how it goes!