I’m currently enamored with the concept of “nurse plants”, and the cyclical succession described by Dutch ecologist Frans Vera in his rich and rather controversial book “Grazing Ecology and Forest History”. researchgate.net/public…

To put it simply, Vera posits that the prehistoric landscape of the temperate world was one shaped by large herbivores (duh!), with as much open grassland and savanna as closed-canopy forest. Tree and forest regeneration, in this context of intense herbivory, follows different rules. Rather than regenerating under an existing canopy or in small gaps, forest patches in Vera’s model move around the landscape, failing to regenerate in their cores while advancing into scrub and grassland at their outer edges.

In this model, herbivore-tolerant scrubby species, armed with thorns, unpalatable aromas, or toxic chemistry, are the keystones. Whereas tree saplings in the forest understory are stunted or browsed to death by herbivores, those which start their life amidst scrub in the high-light conditions of forest edges or undergrazed grassland which allow for scrub to take hold are protected (a phenomenon known as “associational resistance”) and “nursed” until they are above the browse line. Eventually, maturing trees shade out the scrub, and the whole process advances. Over the centuries, forest and grassland continuously swap places in a game of musical chairs.

This model is especially salient for light-demanding tree species which, even in the absence of herbivores, struggle to reproduce in closed-canopy forests. This includes the almighty oak, begetting the apocryphal saying “the thorn is the mother of the oak.”

I was so struck by this idea for two reasons: 1) my livelihood requires protecting trees from deer, and the most effective and economical means I have for doing so, plastic tree tubes, are basically landfill burden and microplastic pollution waiting to happen. I’m actively looking for a better way and 2) it turns the whole conversation around white-tailed deer overpopulation and the looming widespread failure of oak regeneration in eastern North America on its head. What if the issue is not deer overpopulation, but the human constraints placed on the necessary succession and migration of whole grassland and forest ecosystems? What if forests need to fail at regeneration, and revert to grassland? What if grasslands need to succumb to woody encroachment, and revert to forest? What if the current habit in conservation of maintaining habit types in distinct patches is suffocating the dynamism of our landscape?

I’ve even come across a paper claiming that white tailed deer are not, in fact, overpopulated relative to pre-columbian baselines: harvardforest1.fas.harv… If anything, we have even less herbivore presence on our landscape today, given all of the other species we’ve lost.

So yeah, here are some pictures of nurse plants / associational facilitation from the other day. First two pictures show a mulberry nursed by juniper (mulberry is perhaps the most delicious tree species for all herbivores). Third pic is tracing a yellowbud hickory emerging from tangles of multi-flora rose at the forest edge — very little hickory is regenerating under the canopies of mature trees further into the forest, where shade is high and scrub cannot survive. The last pic is an adolescent oak emerging from a honeysuckle thicket. Yes, invasive species often perform this vital task quite well if you let them….