Great pattern, difficult only because of my colourwork. Perfect for Environmental Science. Mods: Detailed below for each intarsia section. If you want to follow and need more help, PM me. 10 center chart repeats, only significant mods for one intarsia sequence. If I did this differently, I would have bought one more skein of brown and one less of green. Basically, my mods were:

Leaves:
for every stitch between the FIRST and LAST yarnovers of the Leaf Chart, work in green. Do the yarn overs and first and last stitch themselves in green, so the leaves look like they are coming out of the tree bark.

Brown/tree bark:
Main body and first and last stitch of Leaf Chart, plus the first and last yarnover of Leaf Chart, in brown. Loop the different colours in the back like any normal intarsia. If this is your first intarsia and you are somehow thinking this is a great first go, work a little swatch of the acorn on the Leaf Chart first. I may do a video tutorial soon, but no promises.

Acorns in Leaf Chart:
Work the kfb in the acorn colour, along with the yarn over that is right below the kbtl, all in acorn colour (yellow here).
Work the acorn top colour (pale green here) from the kfb row up to the k2tog 3x row, then cut yarn and work the k3tog in the leaf colour. Work the kfb 6x on the chart as purl front and back 6x instead.

Finishing:
Put on something entertaining to weave in ends by after blocking.