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How many trees are too many?

When walking through a mature forest, have you ever looked up? That's a silly question, of course you have. What I meant to say is, have you ever noticed how the crowns of some trees seem to avoid touching the crowns of other trees? Crown shyness - yes, it has a name - most often occurs in homogenous forests, which is a fancy way of saying 'all the same' - like a monoculture, but with trees. It can also occur in mixed species forests as well, when the different trees are sharing the same canopy space. There are plenty of theories on why crown shyness occurs, but I am most interested in the benefits that this tendency provides.

The first benefit is a degree of protection from pathogens and insect infestations - an air gap of sufficient size is a deterrent to most of these. The second, more important benefit of crown shyness is the light that is permitted, even with a full canopy. Allowing even a small amount of light through to the understory and herbaceous layers increases the diversity and resilience of a forest ecosystem. If one was stretching for an analogy, A forest is a bit like one of those middling schools, where athletes are held in high regard. Imagine that the main athletic event of this seminarial congregation is to "Grow Tall, and Fill the Canopy Layer".

One might picture the most valuable player, the star of the team basking in the admiration of their peers .. the top athlete in this competition will gain the first benefits of photosynthesis - captured carbon, arranged in convenient storage molecules called 'sugars' .. but there is more energy being captured than our champions need. They send out excess sugars in root exudates, feeding microbes and fungi - some of these fungi form connections with the roots of the other trees in the forest, passing along the 'prize' sugars, in a way that is somewhat similar to an entire school being able to proudly claim a trophy.

There are always those quiet kids, though .. the ones lurking in the back of the room. They haunt the fringes, never caring about the trophy in the cabinet. They don't attend the pep rallies, and tend to 'do their own thing'. The fungal network does not connect them, and if they are to be able to do their own thing, they will need sufficient light .. and that is where crown shyness becomes a benefit. Why should we care about the outliers and misfits? We are most comfortable with the familiar, after all, and tend to mistrust the weird.

In the real world, those misfits grow up to become some of the world's greatest problem solvers, owing to their ability to think and act differently from the average member of society. In our forest analogy, I am thinking of sunlit edges where helianthus grow .. they are annuals that might form an association with an arbuscular mycorrhizal network, but gain no benefit from an ectomycorrhizal network - the kind that supports the pecan trees that make the canopy layer in this forest. (for more on mycorrhizal networks, read "The Internet of Trees" post):

If one has spent any time driving in the country, particularly in the fall, one will have seen the fall webworm, or more specifically its domicile: a mass of webs marring the landscape, each tangle filled with hungry, leaf devouring caterpillar-like worms. Web worms do not just attack in the fall, they often have two full life cycles each year, and they love gobbling up the leaves of a variety of trees, not just pecans .. but they do have a particular love for pecan leaves.

Now this pest's predilection presents a particular problem for the prospective producer of pecans: Aside from burning out infestations with a torch, the only other common remedy for web worms involves spraying pesticide .. lots and lots of pesticide. Eventually, the trees get too tall to manage webworm nests with a torch, and one must resign one's self to experiencing a certain amount of crop loss to the worms .. or, shudder - reach for the poison.

At the time that I write this, I am also in the process of assembling a body of film clips, of different wild birds participating in what is called by bird enthusiasts 'multispecies flocking', and hopefully, I might make the relevance clear, shortly. There are a few wild birds that might assault a webworm nest in order to have at the juicy morsels inside .. the Carolina Wren is one that I have witnessed attempting this endeavor, battering the nest ferociously in search of a meal. Other obligate insectivores may also hunt and pick the insects off, particularly when they are in transit, from ground to tree.

These birds, so helpful to our beloved pecan trees have no reason to visit our trees, specifically .. they could hunt worms in the wild with abandon, if they choose .. and plenty do. In order to get them to come here, we sweetened the pot: Surface water in birdbaths and pools, thickets, hedgerows and brush piles for shelter, housing opportunities, and supplemental food in the form of helianthus .. which brings us back to the matter. By allowing sufficient light in our spacing of pecan trees, we permit sunflowers to grow, which in turn provide that extra incentive for a multispecies flock. The wrens do not need anything in the bird feeder, but appreciate the security that a flock provides .. likewise, downy woodpeckers don't need to eat sunflowers, yet they will visit to consume a treat, and stay to inspect the tree trunk for unwanted pests if they feel safe.

How many trees is too many? Let me have my way, and I would see this planet swathed in riotous forests, thick from canopy to ground, and bursting with life .. and that means not planting the upper canopy too thick - not exactly a function of specimen numbers, as every species has different dimensions. I like nine pecans per acre, or better yet, eight pecans, with a 60 foot surface pond in the middle .. pecans have a mature spread of about 60 feet.

By opening up the canopy and then maintaining that openness, we permit the misfits and outliers - sometimes with entirely parallel, and occasionally cooperative networks to thrive .. and they, in turn lend their strength to the ecosystem as a whole. I sat down today with an intent to write a list of all of the trees that we currently have, on 1/3 acre, and possibly some that I might add in the future, space permitting:

Pecans, 2 approximately 8 years of age or so, and another, squirrel-planted specimen, beneath a common maple that we intend to do away with, eventually (the maple .. not the Pecan) There are a couple of pecans that we air layered as well, though I do not expect any of those to ever grow beyond shrub-height .. I only mention them as a curiosity. Next there is a Bur Oak, which I consider an understory tree in this forest - 60 foot tall at maturity, perhaps, and a rival to the height that our pear trees might reach, if we did not prune them every other year or so. Those pears are an Anjou, and a Bartlett, the Bartlett being several years the senior, and the survivor of a pair that I planted before I became obsessed with planting more varieties, when a cross pollinator was called for.

The lost pear tree has since been replaced with an Asian Persimmon, right about the same time that I planted an All-in-one Almond, presumably hardy up to zone 5, but I'm really just curious .. if it blooms, they will be pretty. Close at hand, there are a pair of cherry trees, one Meteor tart cherry, and a sweet Stella - neither of those trees gets very large, so they don't threaten the stand of redbud trees nearby. That cluster, along with a young blue Rose of Sharon tree frame the site of a future pond. I am slowly excavating the site, taking time to transform the clay subsoil before relocating it elsewhere, if possible.

Across from that slowly developing wonder, we have one of the aforementioned pecan trees, flanked by a pair of hazelnuts, a goumi, and another Rose of Sharon, this one a more white with red blushes, very pretty flowers. A grape arbor is nestled underneath the shelter of that pecan, decked with scuppernong grapes, and sheltering a pair of very very hardy fig trees. As we pass the front of the house, take note of the juvenile redbud trees flanking the porch: they are being trained to grow as shrubs, although they would be perfectly happy to be understory trees, as well.

South of the driveway, between the second pecan tree and the older pear are another two hazelnut trees. These four Hazels in the front yard are what is left from six that I planted originally .. gophers love to chew hazelnut roots, it turns out. I neglected to label them at the time of planting, so all I can say of them is that they are among three different improved cultivars developed by Oregon State University .. Jefferson, Eta, and Yamhill, respectively. I have two more Jefferson, and one more each of the Eta and Yamhill cultivars in the back yard hedge, plus an additional improved cultivar called 'Doris', which I did remember to label. That's nine hazelnut trees in all.

The back yard features our ongoing experiment with ducks and vegetable gardening .. we use them to control grasshoppers in our corn, and to weed the garlic and onion patches. There are trees mixed in this area as well: an Ozark plum, a 'Coco' Jujube (said to taste a bit like coconut) and a somewhat reluctant 'Li', with larger fruit, when it chooses to grace us with leaves and flowers, that is. It may not be warm enough for this one, or maybe its just a slow starter .. time will tell. Turning the corner towards the duck pond (to be excavated this dry season!) there is another planting bed, this time with a June Yellow plum - a dessert plum, like a green gage, but golden yellow, and tasting of pineapple and mango .. it is still a suitable cross pollinator for the stodgy old Ozark plum across the yard!

Farther out from the duck yard are three black mulberry trees, and one native red mulberry, that makes some of the tastiest fruit imaginable. I'm trying to clone that one, so stay on the lookout for rooted cuttings! Finally we have our hedgerow, with the hazelnut trees that I mentioned before, a peach tree, a Chinese mahogany tree, another goumi, another redbud, an albizzia (mimosa) tree, and three Alleghany Chinquapin trees. I believe that is somewhere between 42 and 43 productive trees .. we do have space for a few more, I think .. but I am having to be very picky about what I add, these days!

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