just like the perma in permaculture..nothing is forever..however..I do try to do things that will be sustained during my lifetime and maybe be there for the lives to come after mine..
My most sustainable contributions would be my trees..as I plant most of them from small seedlings or seeds..of some sort..they will be growing during my entire lifetime, unless of
course they meet an untimely end..and in several years they are not only growing and being sustained, but are having children..which we are removing and sending on their merry ways to neighbors and friends.
Then of course there are the understory
trees which are slightly less sustainable, as their lifetimes are shorter than the
canopy layer, such as fruit and nut trees, but they do help to sustain LIFE more than the canopy trees do so they are somewhat sustainable and semipermanent.
Following them are the shrub layers..which if properly revived, can go on for pretty much our lifetime and those of our children. They can be quite sustaineable and can sustain a lot of life by using a highly diverse number of species...so i tend to collect shrubs as well as trees, for sustainability of my gardens.
Feeding the soil by allowing most of the droppages of leaves also sustains their fertility, and adding other nutrients back to the soil when possible..follows in sustaining the trees and shrubs.
I have an overabundance of sustainable perennials..they need to be well managed, but they always produce babies for me that can be added to other peoples properties, whether seeds or
roots, and many of them provide human or animal food. Every year there are MORE perennials rather than fewer, so they are very sustainable. Occasionally there are some annuals brought onto the property that are somewhat sustainable, if they are heirloom and allowed to produce seed that is saved, but i tend to avoid annuals other than some seasonal food crops for the simple fact that they are NOT sustainable..I always lean toward things that will grow back year after year without relanting. I consider sustainability, even if it is only semipermanent, a key to everything I attempt to do on our property.