I'd be glad it try to explain 'dominion' and 'communion,' though I'm not sure I'd do the best job. My impressions of the two concepts have come, for the most part, from what I've read, but I don't really know if there even is an exact definition.
The idea of Dominion originated in the book of Genesis, when God told Adam & Eve that all the creatures and things on the earth were theirs to name and that they were to be caretakers, ensuring that animals and plants would be "fruitful and multiply." The label "dominion," comes from the fact that man, when acting in accordance to this viewpoint, can actively manipulate, use, and use-up animals, land, and other natural resources. I'm pretty sure it comes from the Latin root that spawned words like "domain, dominate, etc..." Essentially, the concept of Dominion recognizes man as the primary moral agent in regards to controlling and cohabiting with nature.
"Communion" is a little more abstract, though it denotes the same activity as a church communion, sharing and becoming a part of something else. Authors have used it interchangeably with words like "wholism" and "animism" and even "pantheism," a religious belief that God is in everything and that everything must therefore be revered. Essentially, the idea of communion places all life at the same level because each being has the same inherent value and man has no right to take charge.
The two ideas aren't necessarily incompatible, unless either view is taken to the extreme. Regardless, communion and dominion are also ways to experience nature, like "sense of place" and "sense of time" that Bump has/will explained. Just a more encompassing view of the entire experience.
Hope I haven't been more harm than help. Feel free to email me or whatever, I know my explanation wasn't very clear.