They Can’t See the Trees for the Forest?
A review of The Hidden Life of Trees
I can’t help myself, I see trees in a forest. I ask which ones are “keepers,” i.e. crop trees, and which should go to reduce competition with them. Species, form, defects, apparent growth rate, but especially likelihood of making a saleable tree in the future factor in. That’s how I was trained in the 1960’s. Since then foresters have learned to think of forests more holistically. We leave standing deadwood to feed and shelter wildlife. We manage other vegetation to do likewise and control erosion. And, we struggle to control invasive species. But still, we focus on what we can see above ground in the context of a site classification. After all, exposure to sunlight determines what happens there. Below ground is considered primarily with regard to moisture availability and nutrient deficiencies on some sites. Is there more down there that foresters ignore at our peril?
Foresters’ fundamental beliefs are challenged by the segment of society that sees forests, not individual trees. Harvesting trees to them is like the amputation of a body part. They view trees for their contribution to the forest as a whole. Some go further by anthropomorphizing trees. Peter Wohlleben, a German forester is one of “those people,” reflected in The Hidden Life of Trees: What They Feel, How They Communicate: Discoveries from a Secret World, Greystone Books, Vancouver/Berkeley, 2015, 272 p. The book was featured on the 30 percent off display at my local independent bookstore, a place I love. If you’re a Purdue grad you know it, Von’s Shops in the Village. I like being challenged intellectually, and this title was a slap upside my head. Surely no forester believes that trees are like people, at least not in scientific terms, philosophically maybe. The author’s hypotheses are based primarily on his observations in the beech-oak forest he manages in the Eifel Mountains of Germany. It also includes commercial coniferous plantations. He also draws on some peer-reviewed research, but his intended audience is a non-scientist.
Wohlleben’s analogies to humans is rooted in his conclusion that trees communicate. He doesn’t hear trees talking, although they may scream. He focuses on the release of chemicals by one picked up by another. Tordon flashback is an example. Root grafts transfer it from the treated tree to others. Gases transferred through the air are another mechanism. The roles of pheromones are well documented, including our own mating. He cites the example of acacia trees in Africa that produce toxic substances when giraffes are dining on them. They release ethylene that is sensed by nearby trees. They respond by also producing the toxic substances. Giraffes have adapted by moving to trees far enough away to not have received the signal.
He contends that trees support each other in other ways, essentially organisms. The book opens with a description of the living part of a dead tree. He found a moss covered section of a “dead” beech tree. He couldn’t pick it up because it was attached to the ground. Looking further he identified the “gnarled remains of an enormous ancient tree stump” without any sprouts. Sections of it were alive under the moss. This was a result of surrounding live trees transferring nutrients to the remnants of the “dead” tree. This occurs by interconnecting fungal networks around root tips, or root grafts. He also discusses the fungal connections, an underground web of mycelium.
Trees are sex—that is, they come as male and female on the same tree or single-sex trees. All living organisms reproduce, but is the reproductive mechanism of trees analogous to humans? He compares coniferous and deciduous species. Conifers produce large quantities of seed every year consumed by animals to a limited extent. Deciduous trees produce large quantities every few years. Their large seeds are a primary food source for many animals. Lean years are a control on animal populations, which increases the likelihood of seedlings developing. He also discusses inbreeding controlled by male and female flowers on the same tree opening at different times.
The next chapter deals with the tree lottery, how trees balance growth and reproduction. Both require large quantities of carbohydrates from photosynthesis, and in temperate climates, enough energy must be stored over the winter to restart growth and flowering. He also discusses the relationship between rate of growth and exposure to light. Little light means little energy, little growth and no seed output. Tree etiquette has to do with the form trees take is dependent on the species and growing conditions.
The author refers to real-time adaptations to rapid micro-environment changes as “tree school,”—that is, trees learn and call on learned knowledge when needed. His examples include adaptation to soil moisture. For example, species that evolved for moist sites can grow elsewhere by reducing water intake. Other species, such as spruce, do not adjust. He also discusses how trees physically support each other, reflected by the shape of their crowns. If an opening occurs the “pain” from bending in the wind causes an adjustment in where new wood is laid down, especially thickening of the truck instead of the previous growth rate in height. Drought causes some species to “scream” at an ultrasonic level, recorded by the Swiss Federal Institute of Forest, Snow and Landscape Research. The sound is generated by vibrations when the flow of water in the trunk is interrupted. He also cites a study of a sensitive plant that can be studied in detail in the lab. Mimosas, a tropical creeping herb, learns how to respond appropriately to precipitation levels. When they first experience steady drops of water they close their leaves, but then do not after “learning” that the drops of water will not hurt them. He never provides an explanation of how trees store the learned responses cited.
The other chapters are an overview of tree physiology in laymen’s terms. He discusses water flow within the tree, bark thickness related to susceptibility to fire damage, reduced growth rate of suppressed trees in uneven-aged stands and the ability to respond when exposed to more sunlight, gaseous exchanges in leaves, filtering of particulate matter in air, carbon capture, and changes in species’ ranges which he refers to as movement.
I highly recommend this book for those who don’t understand foresters’ fascination with trees and forests. After they read it we can discuss with them the relevancy of the analogies the author makes to humans. It can help us understand the perspective of those against any harvesting. From a forest science perspective, I came to the conclusion that forestry research has not provided the findings needed to relate the impact from stand manipulations to the complex web of life underground. Soil science needs to go beyond structure, nutrients, and moisture. Increased understanding of the “biology of soil” is needed.
Bill Hoover is a professor Emeritus of Forestry, Purdue Univesity. During his tenure, Bill was a leader and nationally known expert in the application of the federal income and estate tax laws to family forest owners. He expertly guided thousands of landowners all over the U.S. through his publications, web sites, regular tax columns and workshop presentations on forest economics. One of the department’s most popular publications was the “Indiana Forest Products Price Report and Trend Analysis” which Bill published from 1976 through 2013, spanning his 37-year extension appointment with Purdue University.