At Maine Treekeepers LLC, we care for trees with an understanding that goes far beyond pruning and maintenance. Trees are not just individual organisms- they are entire ecosystems, in fact modern ecology and arboriculture teach us that trees function as holobionts (or super organisms), hosting trillions of microbes and fungi that sustain their health and connect them to the larger forest around them.
In this blog, we’ll explore the study of ecology and how it connects to arboriculture practices like pruning, tree care, and soil health. We’ll also share what we learned from a recent ecology and pruning class at the Coastal Maine Botanical Garden in Boothbay, where we studied European pruning methods and the role of microbial communities in tree health.
What is Ecology?
Ecology is the branch of biology that deals with the relationships of organisms to one another in their physical surroundings. For trees, this means their relationship with soil microbes, fungi, insects, wildlife, and the forest ecosystem as a whole. Understanding ecology allows arborists to care for trees in ways that preserve not only the tree itself but also its role in the broader environment.
European Pruning Specifications
Across Europe, arboriculture is guided by standardized pruning specifications. These aim to create consistent, science-based practices for pruning, planting, and tree assessment. Some specialized techniques include
* Pollarding– a pruning method where the upper branches of a tree are cut back regularly to promote dense growth of new shoots. Traditionally used for wood production, it can also help manage tree size and shape.
* Espalier pruning– the training and pruning of trees to grow flat against a structure such as a wall or trellis. This method maximizes sunlight exposure in a small space eRiciently while producing fruit or decorative growth.
* Vista Pruning– a selective pruning technique used to create or preserve scenic views, while maintaining the health and structure of a tree.
In our class at the Boothbay Botanical Gardens, we learned how these pruning techniques not only manage tree growth but also produce wood that can be reused in garden beds and around trees to enrich soil with micro fungi.
Trees are Holobionts
A tree is more than just bark, leaves, and wood. It is a holobiont- a host organism plus the bacteria, fungi, and other microorganisms that live on and within it. Collectively, they’re combined genetic material is called hologenome.
The concept challenges the old idea of a tree as a single organism. Instead, trees function like humans do with gut bacteria: they depend on symbiotic microbial communities for their physiology, immunity and even evolution.
Microbial Communities Inside Trees
Almost every part of a tree contains fungi and bacteria. In fact, a tree may host over one trillion microbes. These microbial communities vary by tree species and by part of the tree:
* Heartwood (dead center) – Specialized microbial groups adapted to low- nutrient conditions.
* Sapwood (outer living wood) – Rich in microbes that influence water flow in nutrient cycling.
Types of Microorganisms
Bacteria– The most abundant microbe in trees, some of which play roles in nutrient cycling.
Fungi– Often responsible for breaking down wood but also crucial for symbiosis with roots and defense against pathogens.
Functions of Tree Microbiomes
- Nutrient cycling– Microorganisms in trees act as internal recyclers. Certain bacteria and fungi break down complex organic matter, releasing essential elements like nitrogen, phosphorus, and carbon back into forms that the tree can use. For example, fungi are often responsible for breaking down lignin and cellulose in woody tissue, making nutrients accessible. This constant nutrient cycling helps sustain the tree’s metabolism, even in poor soils. In forest systems, these microbial processes also enrich the soil when deadwood and leaf litter decompose creating healthier ecosystems for surrounding plants.
- Gas production– Microbial activity within trees also influences the gases present inside woody tissue. Some microbes produce methane and carbon dioxide as byproducts of metabolism, while others help regulate oxygen levels. This internal “gas balance” can affect how well water moves through the Xylem (tissue responsible for transporting water) and even influence the formation of internal cavities. In fact, scientists studying tree gases have found that these microbial processes may play a role in global carbon cycling, linking individual trees helped to the climate system.
- Species- Specific Roles– Each tree species hosts a unique microbial community, almost like a fingerprint. For instance, and Maple trees, you can often find “ sugar eating” bacteria that metabolize SAP sugars. In oak trees, microbes may specialize in breaking down tannins, while in conifers, fungal partners often assist with resin breakdown in nutrient exchange. These species-specific roles not only support the individual trees but also influence what insects, fungi, and wildlife are drawn to. This specialization explains why some trees thrive in particular environments and why certain species are keystone hosts for biodiversity.
Together these microbial functions ensure that a tree is more than just wood and leaves; it’s a dynamic, living ecosystem supporting cycles of nutrients, gases, and life that ripple outward and surrounding environments.
Just like probiotics support human health, veteran wood (older wood rich in microbial life) can be added to your garden beds to help protect against soil pathogens and increase beneficial fungi.
It is also possible to introduce beneficial fungi directly to your trees; you can purchase fertilizers that contain microfungi to support newly transplanted or stressed trees. Another natural method is to collect soil from beneath a veteranized tree of the same species in the woods and create a slurry. Pouring the slurry over your tree’s root structure can introduce a thriving community of fungi, boosting resilience helping your tree establish stronger ecological connections.
How to Support Veteran Trees
To help your trees develop strong micro fungi communities, arborist recommend
- Removing large, deadwood safely.
- Bracing the crown to reduce stress.
- Reducing the tree to its retrenchment point.
- Reducing weight without lion tailing (over thinning branches).
It is important to allow natural features like snags, bark tears, and hollows to remain when they aren’t hazardous. These imperfections create homes for birds, insects, and small animals, boosting biodiversity.
Old Trees and the Mycorrhizal Network
The older the tree, the more biodiversity it supports. Veteran trees are deeply connected to the Mycorrhizal Network – the underground fungal web that links tree roots together. Through this network, trees can share nutrients with neighbors, even across species.
The Mycorrhizal Network is often called the “Wood Wide Web” Because it allows trees and plants to “communicate” through fungal hyphae. These microscopic threads wrap around or even enter the roots, creating a partnership where:
- The fungi supply nutrients and water (especially phosphorus and nitrogen) that the tree’s roots cannot easily access on their own.
- The tree supplies the fungi with sugars (carbohydrates made during photosynthesis) as an energy source.
Benefits of Mycorrhizal Network
- Resource sharing- Trees in distress can receive nutrients and water from healthier neighbors. For example, a large oak may share with younger saplings in shaded areas.
- Increased resilience- Trees connected to strong fungal networks often show better resistance to drought, disease, and pests.
- Cross- Species Support- The network isn’t limited to one type of tree. A pine may pass resources to a nearby Birch, or a Maple may support a struggling beech.
- Soil health improvement- Fungi improves soil structure, increased nutrient availability, and helps retain moisture.
While the network is strongest in natural forests (where leaf litter and fallen logs enrich the soil), homeowners can mimic it by allowing wood to decompose naturally and by creating habitat piles. These piles look neat while providing shelter for insects, birds, and small mammals.
In short, the Mycorrhizal Network turns individual trees into part of a cooperative forest community- one where strength and survival are shared through underground fungal connections.
The Cycle of Tree Decline: The Demon of D
Eventually, all trees go through the natural decline:
- Depletion –Running out of energy.
- Dysfunction- Processes within the tree beginning to fail.
- Disruption- The tree falls apart.
Even in death, trees provide immense ecological value:
- Home for insects (food for birds).
- Nesting spots for birds.
- Shelters for mammals.
- Nutrient recycling once they decompose.
Ecology in Action: Growing Plants for Insects, Insects for Birds
In ecology every plant you grow plays a role in the food web. You grow plants for insects, and you grow insects for birds. Some of the best trees for supporting wildlife in Maine include:
- Oak, Willow, Maple, Birch, Black Cherry, Basswood & Crab Apple
These trees provide exudates- seeds, fruits, pollen, and nectar- that sustain herbivores and decomposers, which in turn feed larger animals.
Closing Thoughts
At Maine Treekeepers LLC, our motto is ” Caring for the Earth, one tree at a time.” By blending ecology and arboriculture, we aim to not only care for trees but also preserve the ecosystems they sustain.
Whether it’s reusing veteran wood for soil health, practicing European pruning methods, or allowing old trees to serve as wildlife habitats, every action we take shapes the web of life around us.
