I spent over a decade as a forest scientist working to improve the genetic quality of various hardwood tree species. To put it another way, to maniupate NATURE. It became increasingly obvious to me that we must never ignore NURTURE. We must work with both nature and nurture when creating and managing sustainable forests.
The nature vs nurture dimension has been most apparent in my work growing and testing walnut trees. I created a series of trials across England using some of the best available common walnut Juglans regia planting stock: RA464 Lozeronne sourced from France. This was planted with and without a mixture tree and shrub companion or nurse species: alder (Alnus cordata), silver birch (Betula pendula), wild cherry (Prunus avium), western red cedar (Thuja plicata), hazel (Corylus avellana), autumn olive (Elaeagnus umbellata) and elder (Sambucus nigra).
The planting design, shown below, was a little complicated but essentially placed the walnuts at 5×5 m spacing (400 trees per hectare). The results after five years were dramatic. Walnut growth varied hugely between those with some companion trees/shrubs, and those without. The figure on the right shows that walnuts (shown in green) were twice the width and height when planted with Elaeagnus and Alder, than when planted without.
So a simple lesson is learnt: however good the nature genetics, nurture silviculture is fundamentally important.
You can read more about this work here and in the various papers I’ve published:
JR Clark, GE Hemery, and PS Savill, “Early growth and form of common walnut (Juglans regia L.) in mixture with tree and shrub nurse species in southern England,” Forestry 81, no. 5 (2008): 631-644.