TL DR: Will a vine invasion move an ecosystem toward succession (i.e., from grasses/bacterial to forests/fungal), undo ecosystem succession, or something else?
I look along the highway on the East Coast of the U.S., and I see vines often covering trees -- kudzu, English ivy, Japanese honeysuckle, porcelainberry. You can cut them back, but ultimately fighting invasives is a losing battle. Plants always win. Forest edges get covered in vines.
So what is the impact on a forest in five years? Ten years? Fifty years? Do vines slowly push treelines back by killing trees on a forest edge? Do the taller ones survive?
Ostensibly, vines that cover forest edge have a number of ecological benefits. They cover the earth (whether previously vegetated or not) shading the soil and protecting it from erosion. Vigorous roots hold the soil and moisture and stimulate soil microbiology. A curtain of vines on the forest edge will quickly seal off forest interior from light and wind, which can dry out forest interiors and undo ecosystems, like a scab on a wound. On the whole, more plant mass > less plant mass. Ostensibly invasives are doing the work that less vigorous native and naturalized plants are not. They are filling an ecological niche. They are one of the layers of the permaculture food forest for a reason. These benefits help to make the case that vine invasions are better than the alternative.
(For the purpose of this thread, I'm just talking about a forest-edge scenario. Invasions are often a response to ecosystem disturbances. I'm assuming a vine invasion in the middle of a stable forest ecosystem is much less likely, but feel free to play with any scenario.)
This is a question for which books and teachers don't seem to have a clear philosophy. I understand that the permaculture answer is always "It depends." Should I divine from Tao Orion's book "Beyond the War on Invasive Species" that it would be better to leave it be?
Adding humans to the equation makes it easier to answer. If humans have the resources to manage the space, they can select the plants they want until the ecosystem stabilizes. Maybe they get goats to eat the vines down. Or e.g., harvest kudzu as animal fodder or make biochar. They can encourage the vines they want to fill the ecological niche.
But what about broad-acre situations? State-level highway management? What if you have limited money and people power? Is leaving a kudzu invasion of a forest edge going to do harm?
This may seem like a naval gazing question, but I believe it has important implications. If vine invasions hurt forests, then there's a strong case for managing with people and machines and nasty chemicals. If vines help forests, there's a strong case for leaving them alone and letting e.g., kudzu kill a few trees.