The theory says that every patch or community of native bush not only has a different species composition from neighbouring areas but also that each and any species occuring within that patch differs, or can differ, genetically from others of its species found in the areas. These genetic differences can express themselves in many different ways, the most obvious being visible variations in plant form or leaf shape (= phenotypic variations), the less obvious being genetic variations that affect plant growth or reproduction or susceptibility to disease, or those which have no apparent affect at all.

If our aim is to preserve as much of our natural environment as we can and where ever possible restore modified areas as close as possible to their natural state, then ECO-SOURCING is a principle worth enacting. Clearly, in highly built up and modified areas such as Manukau City which is well removed from natural stands of indigenous vegetation the application of eco-sourcing need not go past the sourcing of plant material that will survive. However in less modified areas that are close to natural bush stands, such as Titirangi, the Taupo Native Plant Nursery strongly advocates the planting of natives sourced from that area. For our most unmodified areas - our national parks and reserves - that plant material should be sourced from within those parks or reserves.