Without seeing what you are describing, my best guess is white clover, but that is a guess only, i'd need to see it or a picture to be able to positively ID it. Invasives are a problem, and are required to be managed for in forest operations, but despite best efforts, they are highly efficient in colonizing available growing space. Part of the issue is invasive plants are a regional district, not provincial responsibility, which causes a disconnect.
The issue with managing for browse species in plantations is they are competing with the trees we are trying to grow for a crop species (mostly conifers, some broadleaves in certain areas). Due to government policy requiring these crop trees to be out growing and not impeded by these brush (browse) species, licensees are required to manage brush to ensure the future crop of trees is able to grow and develop at its potential, instead of stagnating while fighting the brush species. While there are policy changes developing to allow more broadleaves than previously allowed, it is slowly developing and still requires the crop of trees is growing at a sufficient rate to outcompete the brushy species. Broadcast herbicide is the least expensive method, and highly effective way to control brush species, but it isn't selective about which brush it kills. Backpack herbicide or manual brushing is selective, targeting only the brush that is impeding crop trees, but is much more labour intensive and costs more (sometimes not a lot more, other times much more). Without aerial herbicide, it may mean we are not able to treat all the ground that needs brushing, which will reduce growth and impact future timber supply. It also means more employment for those willing to do the very hard work, but also more browse retained. The real answer isn't necessarily to jump to banning aerial herbicide, but to using the most appropriate tool for the job. In the past, in order to meet government requirements, within a limited timing window for effective brushing in each season has pushed licensees to the quickest, most effective and cheapest option.
The real way to effect change is through research that can demonstrate the impacts of the brush (or lack of), combined with government policy changes to reflect these results, and then using the most appropriate vegetation management tool for the situation out on the landbase. This work is ongoing, but research takes years to be able to provide us these answers.