Redwood Reader

88. Succession, Renewal, Biodiversity and Glomalin
Little material available discusses old growth forests as ongoing operations in the prime of their operational capacity. It has been far more profitablre to believe trees are either growing or failing without regard to how they are the driving force in forests. If forests were in decline that needed our attention they wouldn’t have survived hundreds of millions of years. It is our picture of what a healthy forest is that needs changing.
Several articles recently pointed this out to me. The first is the first forest based glomalin study I am aware of, done in Chile. As in a most of these studies, I feel the researcher is fumbling around the edges of the iss8ue. We will take the evidence presented and interpret it according to our own perspective as outlined earlier in this blog.
In the Chilean study, glomalin in the top several inches of soil around trees was measured. Glomalin was shown to be older at the trunk and younger as samples came from further away. One interpretation would be that glomalin is associated with new growth, and most production is in the topsoil, and that the glomalin in an area is associated with a single above ground species and few fungal species. This is the snapshot approach of studying dynamic systems and people can claim it is good science. If we look at the system in a particular area over a period of time we see the dynamics much more clearly.
Mycorhizzial fungi are widespread in forests. Some are specific to tree hosts and some are universal. While some are well known, many fruit below ground in the form of truffles, false truffles, and rhizopogons. As plants inhabit an area, a succession of mycorhizzia occurs, by species as well as over time as conditions change. So we have one set for disturbed ground (morels), seedlings associates, then truffles and other hypogenous appear in young forests as the canopy closes in, and finally chanterelles appearing in mature forests. Each of these species has to infect a portion of root hair, and extends hyphae to gather nutrients when it does. In the extension of hyphae is the physical need of the plant to produce the glomalin, sealing the hyphae against loss in either direction. The glomalin binds local soil particles into a porous water holding soil. Root hairs have been found with seven species of fungus in a half centimeter of root hair. Glomalin is made from excess carbon products the tree produces from CO2 and water.
The stated life span of glomalin allows the original glomalin production to condition the soil until the canopy normally closes in. It seems likely underground fruiting fungi evolved to await canopy closure so they didn’t just wash out. As a piece of ground matures, the hyphae continually search for nutrients, depositing glomalin in a continual process. The results of this process are the water holding capacity of forest soils. The process continues as new trees and especially age appropriate associated plants appear in the understory. New mycorhizzia grows back over the same lands already conditioned, further increasing the water holding capacity of the soil. New trees reintroduce the succession fungi to established areas. Weather caused canopy openings allow for more regeneration and biodiversity.
Many forest trees are associated with ectomycorhizzial fungi. These tend to coat the root hair and turn it into an absorbent sponge. With this in mind we can expect newer, fresher glomalin at the drip line and older glomalin closer to the origins. We also expect glomalin to be produced deeper in the soil as the roots grow out and down. Eventually the glomalin “dies” and reverts to CO2 after fifty or so years but the forest is thriving by then and production far outweighs loss.
We should expect mature trees to live a busy life as adults, and glomalin production for water storage and nutrient gathering would be primary activities. As a by product we have water stored in the soil keeping rivers flowing year round and trees emitting gases that cause raindrops to develop. Staying on short rotations means the soil is depleted and not allowed to recondition itself. Water storage drops and production in the dry season becomes an issue in the streams. This is the local difference between industry managed lands and lands managed for reasons other than timber cutting. The need to reduce rising carbon dioxide levels is becoming apparent to many but this simple fact of how the world works is ignored in forestry, but not agriculture. We are learning to connect the dots representing highlights of reductionist science, but the implications are not industry friendly at this time. Even so, the need to act on rising CO2, as well as the understanding to use that information to repair past damage will justify long term forest protection.