Pine forests seem like fragrant, soft places where anyone could relax and be comfortable. Looks and smells are deceiving. All pine forests are dedicated only to other pines. When pine needles fall to the ground, they prevent other plants and trees from growing underneath. Pine needles release various acids and organic compounds that leach into the ground as the needles begin to decompose. These chemicals don’t hurt the pine tree, its roots or its fungal symbionts. They do deter nearly all non-pines from settling anywhere close.
You might say pines establish a pine privilege. A hickory nut which rolls into a pine forest doesn’t have much of a chance. The pine fragrance we like so much is the reason. This fragrance is caused by a class of chemicals called terpenes found in the needles. These particular pine terpenes retard germination and new growth. Retardation of germination can be a good thing for a gardener. It helps to keep weed seeds from germinating. For the hickory trying to survive in an alien environment, the terpenes are death. Plant as many hickory nuts or oak acorns as you wish in a bed of fresh pine needles. None of them will germinate.
Pine like pines. They are like all species in nature, they have methods for perpetuating their own kind and discouraging anyone who is not a pine.
Unless you are an azalea, a rhododendron or a blueberry. These acid loving plants thrive under pines. Except when the pine forest gets tall enough and thick enough to shade them out. Then it’s all pines all the time. Diversity is as minimal as in a Southern country club at tee time. Or a Colored Methodist Episcopal church on Sunday morning. Or an inner city ghetto any time.
In plants this effect is called allelopathy. Luckily for most other species, pine allelopathy is short lived. The acids and terpenes dissolve readily in water and dissipate into the air. By the time pine needles are brown and dry, most of the terpenes have evaporated. Once that wonderful pine fragrance has gone out of the needles, so have the terpenes, the source of that fragrance.
So you can use pine straw as a mulch without fear. It may hinder germination a little, but that will be good for the gardener who doesn’t like to pull weeds.
Every species in nature tries to perpetuate itself. The pines have perfected one method. Sunflowers, black walnuts, wormwoods, sagebrushes, and trees of heaven have their own chemical methods. The creosote bush is so good at controlling other plant species in the desert that it is called “gobernadora” (Spanish for “governess”) due to its ability to secure more water by inhibiting the growth of nearby plants.
In the 1970’s, an animal rights activist coined the term speciesism. This term expands the idea of racism to whole species. Man is accused of speciesism because he wants to preserve his own species. We are learning that all species try to help their own kind. No species survives for long if it doesn’t.
Most interesting is how some species seem to thrive even when the dominant species is doing its best to wipe them out. They do so by providing something the dominant species needs. Mycorrhizal fungi flourish on the roots of pine trees. They provide nutrients to the pines which are locked up in the soil until the fungi release them. They are examples of complementary diversity and discussed in more detail in our book.
Like all species in nature, pine trees get their comeuppance if they grow too big for their britches. When pine trees dominate a landscape too thoroughly, they provide the perfect environment for species like white pine blister rust, southern pine beetles, and mountain pine beetles. These species love to destroy homogenouse stands of pine. A vast increase in diversity then follows.
Pine and other allelopathic species keep trying to create a world fit only for their species. Nature always puts them in their place.
Man in his hubris should learn some lessons. Though all species will try to perpetuate their own kind, the most resilient will embrace diversity–at least as long as it is complementary.