Lythrum salicaria was NOT FOUND

During our time outside, I found out that there were no invasive plants in our research Quadrat. We were really surprised that we didn't find any invasive plants such as Purple Loosestrife or Japaneze Knotweed. Some questions that we ran into were, Is it Purple Loosestrife? Are there any ways to stop the spreading of these plants? Also, while we were out there we smelled wet pine, saw a lot of damp trees, and we heard birds chirping.