Introduction to Occupy Trees

Attention, Protesters!

We live in troubled times. During times like these, we must express our dissatisfaction by taking to the streets. We must march, we must picket, we must occupy. But we also need to be aware of the ecology of our surroundings.Trees provide demonstrators with protection from the elements, cans of tear gas, and angry insults from counter-protesters. They also provide the powers that be — a.k.a., “the Man” — with excuses to break up our demonstrations. “Park cleaning” and “property damage” are both justifications that public officials might use to send us home. When we damage the greenery that surrounds us, we damage our own cause.

So whether you’re occupying a public area or camping out in a private park, it’s important to take care of your protest space. The following pages were written to help you do just that…

The Science of Trees

Basic Tree Biology: How do They Work?

Trees and other plants have often been called factories because they convert light energy into chemical energy. Through the process of photosynthesis, leaves capture solar energy by converting carbon, hydrogen, and oxygen into complex  sugars. One of these complex sugars is cellulose, the main ingredient of wood fiber. Although a complete knowledge of photosynthesis is not essential to understanding how trees grow, it is important to realize that, in theory, the faster and more efficiently a tree carries on photosynthesis, the faster it will grow. Availability of light and water are two factors that can be controlled by harvesting.

When a portion of the growing stock is removed, the photosynthetic material is reallocated to the remaining trees. In a young stand, it is usually only a matter of 5 to 10 years before the crowns of residual trees grow into the spaces left by those taken out. Trees are principally composed of four main parts: roots, stem, branches, and leaves. Other specialized structures, like flowers and seeds, develop periodically for purposes of reproduction. However, virtually all of the important physiological processes in trees involve one or more of the four main parts.


About 20% of the mass of a forest-grown tree is devoted to roots. In addition to anchoring the tree, roots gather mineral nutrients, take up water, and store the products of photosynthesis. Forest tree roots are much more extensive than they appear. For example, the root system of a sugar maple may extend as much as 2 to 5 times beyond the spread of its crown. Most of these roots, known as fine or feeder roots, are within a few inches of the soil surface.  Though the fine roots may account for only 14% of the total root mass, 80% of the total root length is in fine roots. Consequently, roots are everywhere in the forest and the ones that are most sensitive to damage are also the most susceptible.


The main stem usually makes up about 60% of a tree’s weight. It supports the branches and leaves and serves as the main plumbing system, with vessels to transport water and nutrients up to the leaves and with other cells to transport photosynthesis sugars to living tissue throughout the tree. The growing portion is only a thin layer of cells surrounding the main stem. Each year this thin sheath of cells puts down a new layer of sapwood. The rate at which it does this determines how fast a tree grows in girth.

Branches & Leaves

A tree’s branches support leaves in a configuration that maximizes light availability or that protects them from excessive exposure on harsh sites. Branches also serve as the second-order plumbing of the main stem. The leaves carry on photosynthesis and exchange important gasses, such as oxygen and carbon dioxide, with the atmosphere. Combined, branches and leaves make up about 20% of the tree’s total weight. Although all trees have roots, stems, branches, and leaves, the form of each of these components differ among species – and within a species in some cases.  Some characteristics, such as the size and shape of leaves from the top of the crown versus those on shaded lower branches, even differ on the same tree. For this reason, leaf size and shape are said to be plastic because they are characteristics that mold themselves to the circumstances. This is one of the reasons why learning trees solely by their leaves is so unreliable and frustrating.

Environmental Factors

Although many of the obvious differences among trees within a species are random, some are not. Important differences in a tree’s form and function may be caused by environmental factors. For example, the root systems of most trees tend to be more extensive on drier sites. Another example: open-grown trees tend to have short stems and wide, deep crowns, while forest-grown trees of the same species, in their struggle to obtain crown space, tend to have long stems and short, irregular crowns that fit the available space in the canopy. Important genetic differences between species have evolved over millions of years.

Although not all structural differences are due to adaptations that make one species a better competitor than another on a given site, many of them are. For example, many conifers have adapted to become better competitors on dry sites than most hardwood species. Though most conifers will do well on better sites, their natural habitat is defined by the limits of tolerance of other species. White pine is a good example. It grows extremely well on moist, protected, “hardwood” sites, but it is nearly impossible to get a new stand of pine started using natural regeneration.  Hardwood species, such as sugar maple and yellow birch, are much better competitors in the understory.

On a drier site, the reverse may be true – white pine can compete more effectively than most hardwoods. Each species has a range of environments in which it will grow. These extend from circumstances where it is a minor component, poorly formed and slow growing, to situations where the tree is able to take full advantage of a site and grow to its maximum biological potential. One of the most common silvicultural errors in forest management is trying to grow a species on a site where it can achieve only a fraction of its growth potential.

Source: Northwest Illinois Forestry Association 1995

What To Do and What Not To Do

What “To Do” and “Not To Do” During an Occupation
DO NOT – Walk on the Tree Beds

Trees absorb water through their “fine roots”, located deep beneath the top of the soil. Foot traffic on the tree beds causing soil compaction which prevents water from properly traveling through the soil to the tree’s fine roots.

DO NOT – Urinate on the Tree Beds

Human Urine, in small doses, can actually be beneficial for the trees due to it’s high nitrogen content. But if a lot of people are urinating in the same spot, an overload of nitrogen/acidity can occur, causing long-term damage to the tree. In large occupations, it may be hard to keep track of the number of people urinating in each spot – therefore we recommend to prohibit such activity. Salting of the soil?

DO NOT – Let Dogs Urinate on the Tree Beds

Dog urine contains particularly high levels of salt, which removes moister from the tree leaves and roots and kills beneficial soil microorganisms. Dog urination on tree beds should be strictly prohibited.

DO NOT – Break Branches and Leaves off the Trees!

DO NOT – Carve Your Name or Anything Else on the Trees!

By carving in the tree you are damaging the protective layer of the tree, making it more susceptible to disease. It may also inhibit movement of water and vital nutrients.

DO NOT – Tie Tents, Lock your Bike, or Wrap anything around the Trees!

Tying things around a tree or Locking your bike to a tree can damage the protective bark and the cambium (inner skin), which transports sap, what trees need to live! It can also leave permanent scars, leaving an opening for parasites and fungus. You could also get a fine!

DO – Put Up Signs!

Help prevent people from walking on the tree beds, and urination on the tree beds, by putting signs up around the tree. Ideally, these signs would contain information about the potential hazards of these actions to help inform the occupiers and better serve the long-life of the tree.

DO – Get Certified to be and Urban Tree Pruner!

Find out how to get certified in your city and you can legally prune the trees.

DO – Spread the Word!

Tell other occupiers what you know about trees and encourage people to be aware and respectful of the trees.


In case this handy dandy website doesn’t answer all your questions or you feel like talking to a real live person about trees, here are some resources:

Davis, California

Boston, MA

New York, NY

Chicago, IL

Seattle, WA

Washington DC