Several lines here, not necessarily all relevant:
1 – Import, export, trans country and trans continental trade – everywhere we travel we cross transfer not just ourselves but also micro-organisms, seeds, spores and larvae. A worry some time ago it has now become routine and blasé has set in. “We have medicines”.
2 – Consider your natural ash key. It spins down from its parent tree, maybe in the autumn, as it ripens, or some time over the next twelve or more months. The first to hit the ground can germinate pretty much at once or maybe after the first winter. Those that stay on the tree ripen and on hitting the ground can be two or three years in germination and all seedlings can remain 100 to 500mm plants for decades, living in the shade of the woodlands, not needing to increase in bulk. Given tree loss in the canopy – wind blow, for example – suddenly the tiny saplings can accelerate and a few will win the competition to fill the gap. My goodness these plants have done their apprenticeship, they understand their environment and are ready for their role.
3 – The nursery ash sapling is usually not local provenance seed, is forced to grow quickly in controlled conditions, often in a polytunnel, transplanted, lined out and undercut to keep it manageable, and then transported, often bare-rooted, in containers, over long distances, even overseas, to its eventual planting destination. Here it is unceremonially thrust into the ground, pegged to mark it, even provided with protective sheath and anti-grazing devices. And then left to grow. Or not!
4 – The planting site can be recently felled forest – even conifer plantation – or retired farmland. Either way, it has often got no mature edaphic ecology – locally developed and responsive soil populations – derived from the support of and symbiosis with mature ash woodland.
5 – Resoundingly, too, we should also consider the macro-environmental changes – residual and ongoing acid rain type industrial pollution, global climate change and agricultural impacts such as soil erosion and eutrophic effects arising from gross use of fertilisers.
OK, OK well the ash is a widely tolerant species and our common ash – Fraxinus excelsior – has this name whether it originates in Poland, Serbia or West Wales. As I showed in my report “Phenotypic variation in Fraxinus excelsior from different European provenances” (1999) , seedstocks of different provenances perform very differently when grown on a common site. Yes, there is clear sub-speciation. One can reasonably assume, then, that the sub-speciation attains to the edaphic ecology as well, as outlined above, and the indicated influences upon it.
I have always said that the best way I can see to establish a woodland is to fence an area off and wait whilst natural seeding and successional ecologies develop. In many situations a mixture of impatience and emergency (Oh yes, climate change is real and happening all around us now.) drive the above planting mechanisms to be adopted. Obviously more active site seeding and detailed on-site establishment-management should be developed henceforward in new woodland establishment – techniques such as are used in French oak forest regimes, often under such systems for many centuries.