You will need:
To be in an outdoor area with many different kinds of trees.
A tree identification book
Read the book The Giving Tree by Shel Silverstein
Establish Sacred Space
Imagine you are a little seed hanging high on the branch of a tall tree until a strong wind comes by and knocks you down to the ground. You fall into the soft bed of leaves your mother and father and all of their brothers and sisters left for you on the ground and you lay there for a time. The sun shines, and the moon shines in turn. Sometimes it is warm, and sometimes it rains. Before long winter comes, covering you in a blanket of soft, cold snow. It is dark, and very quiet. Many days go by like this.
Before too long, the days grow longer and warmer and the snow melts to water which softens your hard outer shell and a little seedling breaks through and you spread two little green leaves up joyfully toward the sun. And you grow little roots, thin as hairs at first, that dig down into the soil drinking up nutrients left by your mother's decaying leaves. You stand there, in your little patch of sun, surrounded by your kin, reveling in the warm sun and the cool earth and you are, just what you are.
You grow slowly, but every year you are a bit taller, your trunk is a bit thicker, your roots dig a bit deeper and your branches spread out a bit wider. Every autumn your leaves fall to replenish what you have taken from the Earth to nourish yourself and every spring new leaves appear to drink in sunlight, which you turn into the energy you need to grow. You absorb carbon dioxide given off by animals and in turn you release the oxygen that animals need to live.
One spring, after several years, you flower, and the flowers draw insects until one day the flowers turn into seeds, or fruit, or nuts. These may feed many types of animals and some of these will sprout into new baby trees.
And so the years will pass and around you the forest will change. Some trees will fall, and others will grow and still you will grow taller and thicker, and your roots will dig deeper and your branches will spread farther. And birds and animals will make homes in your branches and line their winter dens with the leaves that you drop in autumn. And when you grow old and hollow, some will make dens right inside of you and you will protect their young as they grow and help them store food and stay safe and warm through long, cold winters.
And one day you will die. Maybe a strong wind will blow you over, or you'll be struck by lightening. Maybe you will die standing tall and remain standing for many years after. Either way you will continue to provide food and shelter to many other forms of life for many years after your death.
And now your soul has left the tree and returned to the body of a human. You are here, listening to my voice, sitting in this spot. But you remember, what it's like to be a tree.
Have everyone discuss their experience as a tree. Then have each participant get up and find a tree that they particularly like. Have them sit by the tree and observe it. Touch it, smell it, look at it and see how it serves other life forms. What sort of tree is it? Have them write in their journal about their tree. Identify it using your tree identification book.
Homework: Each person is to go home and research a particular type of tree.
You can have them study the tree they chose, or they can draw leaves or names on pieces of paper.