Allelopathy or Just Tough Competition?
I have consistently found the presence of black walnut roots to be stunting to most common fruit trees and especially peaches. It is well known that juglones is toxic to many plants, but I had an interesting experience today when transplanting trees at two different sites that has me wondering if that is the only way in which black walnuts are stunting.
At the first site there is a large black walnut near a small orchard I installed three years ago. I was adding a mulberry near it today. Although the orchard is a fair distance from this tree the roots of it are incredibly thick where I planted the fruit trees before and where I planted the mulberry today- much thicker than the kinds of root systems that are sent out by other, similar sized forest trees- species like ash, maple, oak and tulip. The fruit trees have not established as quickly as usual- they are growing, and I am pretty confident they will eventually thrive, but it is taking a while.
At the second site there are no black walnuts, but there are two very large, cold- hardy pecan trees whose roots tightly weave through the soil in the same manner as the black walnuts at the first site. It is a fairly large home orchard and most of it is out of range of these roots but in the area where they do dominate it has been a kind of Bermuda triangle for peach trees over the last several years.
At first, after planting, the trees would be fine, but by the third year they would quickly go into decline and out of productivity, barely surviving. In the process of planting I would create wide holes where competing roots were cut back a significant distance.
Today I transplanted one peach tree from that site to see if I could get it to flourish where those black roots aren't present. This tree had barely grown since I put it there 3 or 4 growing seasons ago- or so I thought. At least the top hadn't grown much. When I began the process of bare root transplanting it I was extremely surprised at how massive the roots had become without coinciding vigorous top growth.
It took me four times as long to transplant as I expected and I have never seen such a great looking root system attached to such a pathetic tree. The annual shoots were not more than 3" long and there weren't enough of them.
I have read that juglone can destroy hair roots but these are pecans and not black walnuts and pecans are not reported to generate levels of juglone adequate to stunt other trees, to my knowledge.
At any rate, I find it quite amazing that a tree can be thoroughly stunted on top while growing a very substantial root system. Clearly that root system was not functioning well and I wonder if the stunting was the result of toxins or just an extraordinarily competitive species grabbing most available water and nutrients from the soil at the expense of less competitive trees. If it is the latter and pecans and black walnuts have similar root systems maybe there is more at play than allelopathy with the way black walnuts stunt other plants.
calistoga_al ca 15 usda 9
lucky_p
Related Discussions
Tsugas canadensis and allelopathy
Q
Can Walnut trees (via juglone) kill Bald Cypress?
Q
Allelopathy in Crepe Myrtle
Q
oaks and allelopathy
Q
glib
alan haighOriginal Author
Michael
alan haighOriginal Author
gator_rider2
alan haighOriginal Author
Michael
daemon2525
glib