Though the list of benefits of a diverse, integrated systems are many (broad range of produce year round, disease control, etc) nothing is perfect and there are challenges with a high level of integration on a small scale.
Bent grass (Agrostis spp) , known for its creeping and crawling root mass, Is one of the species that gives lots of difficulty here. It is very hard to get rid of once it establishes anywhere because any broken piece of root left in the soil can regrow. It is a fine grass to have in the orchard, the geese love it, I just watched them hang around a large patch of it in the orchard and eat it right down. Its positive ecological roles are its ability to break up the toughest clays with its sharp pointed, tough roots and to hold together soils prone to erosion. In the garden its a real problem, its vigorous growth and speed to send up new shoots make it harder to control than many of the other common garden weeds. Once an area has had bent grass removed, keeping on top of that area and not letting it get re-established makes management much easier than waiting for it to get dense again. Having lots of areas with edges between perennial and annual, garden beds bordered by trees and along paths, though efficient use of otherwise marginal space create ideal environments for bent grass to creep back into the vegie beds. Larger annual beds make less work from this perspective as they provide less perimeter area for bent grass to enter. Of course the “edge theory”, of increased productivity where two systems meet or overlap, easily observed on the roadside or along a stream, is a key principle of permaculture, but it seems to me that one has to ask questions like: how many edges are worth maintaining? how intensive should a system be? how much integration? all these questions need to be weighed against what the land is capable of, how much labour there is to go in etc as well as factoring in that a certain amount of weeding is part of a productive vegie production system. Where appropriate, establishing other ground covers with more desirable traits under perennial fruit trees is a good way to outcompete and succeed the bent grass. Experiments with different techniques in the garden itself have been tried as well, some more successful than others. Dense planting has the potential to outcompete weeds or at least slow down their growth during the cycle of an annual plant. Things like pumpkins/squashes or brassicas that are widely spaced have the potential to be planted in holes amongst a dense ground cover of something more desirable and beneficial in a sort of hybrid annual/perennial system. We have a patch of dense lucerne that acts like this; it has brassicas planted in holes in the ground filled with compost and the lucerne is cut down regularly and mulched around the brassicas.
I spend a lot of my time off hiking and/or camping in the bush, sometimes with friends, WWOOFers or by myself. This gives me a lot of time to reflect, read landscapes and be inspired by nature. This picture, of a native cherry (exocarpos cupressiformis) in a eucalyptus dominated forest, exemplifies the soil and fertility building charactaristics of the native cherry. The circle of bright green grass around the tree, going right up to the base is easily spotted from the trail I was walking on, on closer inspection the soil under the tree was thick, black and filled with organic matter, unlike any soil nearby.