Barriers To Root Growth
Sidewalks, driveways, pavement, dense rock layers, poor drainage, soil compaction, toxins (herbicides, insecticides, fertilizers, road salt, tap water), pockets of wet areas between sidewalks and curbs, malnutrition and other societal practices are barriers to optimal root development. Combine this with lack of recognition of these problems, denial and refusal to take corrective actions, then trees in urban-suburban landscaped areas will continue to fall down at a higher and increasing rate than trees in other settings. The impediments to healthy root growth harm roots all around the tree. It is already known that when roots on just one side of a healthy tree are damaged or stunted, that this one factor significantly weakens the tree and its stability. Urban-suburban trees experience several factors that weaken them. These are some of the major barriers and major influences on tree root development. This causes trees in urban and suburban environments to be unhealthy and fall at a higher rate during storms than trees in the same geographic area, but growing in natural conditions.Tree Roots In General
1. As it is with all research on any topic, there are wide variances of findings and interpretations regarding tree root development. Some studies say tree root depth is mostly limited by water availability or subsoil characteristics, while others say trees can grow roots well beyond the subsoil and into the weathered bedrock and/or maintain active roots below the average soil water level. 2. Tree roots can extend 1 to 2.5 times the radius of the branches (canopy, drip line, branch spread). 3. Although soil compaction is an impediment to root growth, however in the long run, root depth does not appear to be affected by soil type. Roots will grow faster in less compacted soils, if all other needs for healthy tree growth are present. 4. Root systems are usually not uniformly distributed around a tree due to variations in conditions around the tree. 5. Depths at which any type of plant has 50% or 95% of their root biomass, are significantly deeper in drier than in humid environments. 6. Genetics, physiological needs, external physical factors and biochemical factors influence root development. Due to the adaptability of genetics, root development of each tree species varies from optimal to suboptimal in response to the overall set of conditions each tree and each species experience. 7. Global models of root distribution in forests show root distribution and root depth are driven by climate variables. 8. Globally, the rooting depths of trees is 23 feet to 26 feet. 9. Some articles say root depth is limited when roots reach soil that has no oxygen and that plants have evolved to grow their roots near the soil surface. I suspect this is only partially true under certain conditions. Oxygen must be able to be transported to roots where there is not enough oxygen in the same way nutrients are transported around the plant's circulatory system. Trees in low oxygen soil can adapt just as trees growing in water have figured out a way to get oxygen to their underwater roots.Tree Root Development In Natural Environments, Open Environments, Forest Environments
Trunk diameter is about as good as it gets for estimating root spread of unobstructed trees. Small young trees have a much wider root spread than we realize. The ratio of trunk diameter to root spread decreases with age. In general, older trees spend a greater proportion of their resources on tree maintenance and growing very small absorbing roots. Root depth of first year Scotch pine trees reached 5.7 feet. Pecan trees root depth in Georgia rarely exceeds 5 feet. Oak trees in Nebraska were found to not only have lateral roots that were 2 to 4 times the branch spread, but also had deep roots that reached 14 feet. In evergreen tropical forests, a number of tree species have deep root systems greater than 26 feet. I suspect this is true for evergreens growing in temperate zones, that they also have deeper root systems than deciduous trees because evergreens do not have a dormant period and must be able to access water year round. In tropical rainforests where humidity is high, the first six to eight inches of soil is a compost of decaying organic matter. To tap this resource, trees are shallow rooted; however another study says that taller trees in a mature rainforest develop deep roots while shorter trees in the understorey develop shallower roots. This is what agroforestry somewhat mimics by combining agriculture and tree conservation, thus agroforestry is known to promote deeper rooting of trees compared with monoculture agriculture or monoculture tree farms. This again highlights the adaptive response (plastic, plasticity) in trees and other plants that allows them to grow deeper roots when other soil vegetation is occupying topmost soil layers. Rooting depths of tropical trees can reach or exceed depths of 23 feet.Most tree roots outside of tropics extend more than 5 feet.
Tree Roots In Urban-Suburban Areas, Built Environments & Commercial Tree Farms , Fruit Farms, Nut Farms
Many trees in urban-suburban areas do not allow nowhere near normal root development. For fruit trees grown on an experimental farm, the greatest amount of roots appeared in the upper 3 feet while some roots penetrated to 9 feet. It is uncommon for landscape trees to have roots deeper than 6 feet, although some really small roots of only a few millimeters thickness can extend to 15 feet or more. 90% of all roots are located in the upper 2 feet of soil. Under good conditions, 50 percent of roots are in the top 1 foot of soil and 40 to 45 percent is in the next 2 feet. Root spread is typically 2 to 3 times tree height or branch spread.In compacted soils, roots will be shallower with a wider spread. Most landscape-trees are not strongly taprooted. When it comes to commonly known trees in urban-suburban environments, some of them, such as oak, hickory, walnut, and pine that normally develop deep taproots up to 8 foot in natural settings; only grow taproots of no more than a few feet in urban-suburban areas, with most roots appearing in the upper 1 foot to 3 feet of soil. 99% of urban-suburban tree roots are located in the top 3 feet. In loose deep soils, deeper roots do occur.
Summary
We are not trying to specifically determine how wide or deep tree roots grow. It is enough to understand that tree roots grow deeper and wider in natural settings. Our main goal is to understand a little better why trees fall down on a regular basis in urban-suburban areas when the wind blows strongly. Simply put it is due to the perfect storm of human events and superhuman events. Many urban-suburban trees in parkways and in yards and other landscaped places, will most likely have stunted damaged root systems due to numerous inappropriate cultural practices that are not conducive to healthy trees. Humans fail to understand, respect and live in harmony with the ecosystem, thus we run around giving little to no consideration to the workings of the natural world, except in the most immature of climate change ways. This message and UC#2182 linked above, came about as the result of hearing a weatherchannel segment say that due to the shallow roots of trees, combined with water saturated soils in a strong windy environment, that these are the main factors responsible for trees falling down. The news program said most tree roots are in the top 2 feet of soil and showed a graphic of a tree with a root system smaller or equal to the branch spread.One of the problems with that news report was that it was talking about trees in urban-suburban environments but this was not specified. Neither did the report state that trees suffer due to many types of human practices. I sent an email to the weatherchannel and they corrected the report sufficiently enough for what it was intended to accomplish; however I had more questions. It is misleading to say trees fall down in heavy winds due to waterlogged rain saturated soil and shallow narrow root systems and then leave the impression that these root systems are normal for trees in general. This blames nature's design for the pandemic and pandemonium of trees falling down on houses, cars, utility lines, roads, people and so on.
If nature was to blame, then what we should see is more trees falling in open areas and at the edge of forests and on large streets and highways. Truth is, the main cause of trees falling is human culture being enormously out of sync with the ecosystem to the point of repeatedly carrying out a lot of small, medium and large behaviors that work against ecosystem health, soil health, tree health, human health. Trees, other plants, animals, insects, other organisms, above and below ground rocks and layers of soil, all support each other by forming an interlocking network of sharing.
We know a primary function of roots is to anchor the plant, anchor the person.
If tree roots fail to strongly anchor a tree in various sets of conditions, then very suboptimal conditions must exist.
If roots fail to strongly anchor a person in various sets of conditions, then very suboptimal conditions must exist. Therefore then, to overcome this weakness and grow healthier, either genetics must evolve or conditions must change or both. Both is what is taking place via multiple interconnected forms of environmental change.
Trees are falling, submerging. Trees are rising, emerging.
It is the best of times and worst of times, the age of wisdom and foolishness, the epoch of belief and incredulity, the season of Light and Darkness, the spring of hope and winter of despair… (from a tale of two cities)
