Awesome job, it seems like it's been a while since someone posted a new level and this is a great one. I LOVE the chart that shows a real-time display of how you're doing against the other teams. Could you add the score to the end message? It would be a nice way of seeing how well you did on each play through. And is it possible to display the time remaining during the round?
I managed to beat the level on my third attempt, and here's my strat:
The key to victory is twofold: rapid development of the seedling economy, and focus on conquering one branch of the map as early as possible. Plant dyson trees only and upgrade your best trees as soon as flowers are available. Once you have secured an entire branch, you should be comfortably in the lead, with at least 500-600 total seedlings counting all asteroids. Keep flooding new seedlings into the center and move large armies (300+) on attacks, while also leaving an equally large force in the center to absorb invasions.