Module 1: Trees Topics addressed in this module include: introducing general tree anatomy and functions, identifying key characteristics of healthy and sick trembling aspen, understanding the nutrient and water cycles of trembling aspen, and understanding the various threats to, and their impacts on, trembling aspen. Updated Nov. 4, 2019 TREE: Module 1: Trees Page 2 Table of Contents Section 1.1: ....................................................................................................................................3 What Makes up a Tree? ......................................................................................................................................... 4 What Makes up Tree Roots on the Cellular Level? ................................................................................................ 5 How do Trees Drink and Gather Nutrients? .......................................................................................................... 6 What are the Main Parts of a Tree Trunk? ............................................................................................................ 6 What Makes up a Tree Trunk on the Cellular Level? ............................................................................................. 7 How do Trees Grow? ............................................................................................................................................. 8 How do Tree Rings Form? ...................................................................................................................................... 8 What Makes up a Tree Leaf on the Cellular Level? ............................................................................................... 8 What is Transpiration and Capillary Action? ....................................................................................................... 10 Section 1.2: Trembling Aspen 101.................................................................................................. 11 Trembling Aspen .................................................................................................................................................. 13 Other Poplar Species ........................................................................................................................................... 13 How to Say “Aspen” in Various Indigenous Languages ....................................................................................... 14 How to Identify Trembling Aspen ........................................................................................................................ 15 How do Trembling Aspen Reproduce? ................................................................................................................ 16 Where do Trembling Aspen Grow? ..................................................................................................................... 17 Additional Information about Clonal Aspen Stands ............................................................................................ 18 Section 1.3: Aspen Health ............................................................................................................ 29 Do Trees Get Sick? ............................................................................................................................................... 30 Signs & Symptoms of Unhealthy Trees ................................................................................................................ 30 What Threatens a Trembling Aspen? .................................................................................................................. 31 The Most Common Trembling Aspen Threat....................................................................................................... 32 Section 1.4: The Water Cycle ......................................................................................................... 35 What is the Water Cycle? .................................................................................................................................... 36 Water Cycle Processes ......................................................................................................................................... 37 Section 1.5: The Nutrient Cycle ..................................................................................................... 39 What is the Nutrient Cycle? ................................................................................................................................. 40 Nutrient Cycle Process ......................................................................................................................................... 40 What Elements are Found in the Nutrient Cycle? ............................................................................................... 41 What Factors Influence the Nutrient Cycle?........................................................................................................ 41 What Disturbs the Nutrient Cycle? ...................................................................................................................... 42 Glossary ....................................................................................................................................... 43 TREE: Module 1: Trees Page 3 Section 1.1: Tree Anatomy & Functions Image by cristi21tgv TREE: Module 1: Trees Page 4 Section Overview Outcomes Students will: • Identify and describe the main parts of a tree (roots, trunk, and canopy). • Analyze the characteristics of cells in tree roots, trunk, and leaves. • Understand the structural and functional relationships among cells and tissues, including how cells and tissues contribute to the growth and health of the tree. • Comprehend how tree rings form annually, including how the size of each tree ring differs due to environmental conditions. Key Terms Adhesion Exodermis Parenchyma Cells Transpiration Capillary Action Heartwood Pericycle Tree Ring Chlorophyll Inner Bark Phloem Vascular Bundle Cohesion Late Wood Photosynthesis Vascular Cambium Early Wood Mesophyll Pith Layer Endodermis Outer Bark Sapwood Vascular Tissue Epidermis Osmosis Stoma Xylem What Makes up a Tree? Trees are the largest plants on the planet. They provide us with oxygen, help stabilize the soil, and give life to the world’s wildlife. Trees are key members of the ecosystem and they are an excellent source of information about the environment. Through the TREE Program, you will get to investigate and find out what stories’ trees have to share, specifically looking at trembling aspen trees. For now, we start by looking at what trees are composed of. They can be divided into three main parts: the roots, the trunk, and the canopy. • Roots Refers to all the tree parts below ground although roots can occasionally be above ground. Roots spread throughout the ground to anchor the tree in place and to gather water and nutrients. Roots also serve to store food for the tree throughout the winter. With some species, trees reproduce through their roots, creating what are known as clone trees. • Trunk Refers to the large column(s) of wood above ground but below the canopy. The trunk supports and elevates the canopy, as well as transports water and nutrients throughout the tree. • Canopy Refers to the leaves and branches of the tree. The canopy positions the leaves in full view of the sun, allowing for photosynthesis, transpiration, and hormone production in the tree. TREE: Module 1: Trees Page 5 What Makes up Tree Roots on the Cellular Level? Tree roots are not only the anchor for the tree but essential in providing the tree with life. They soak up the necessary nutrients and water from the soil, feeding the growth cycle of the tree. Tree roots are composed of a complex and intertwined network of cells with two main types of structures: root hairs and lateral roots. Root hairs are a small outgrowth stemming off the lateral roots. Root hairs are continually being created and typically last 2-3 weeks before they die off and their nutrients are taken up by the roots. Root hairs provide a lot of surface area to absorb water and nutrients into the root. Lateral roots are the other main root structure and are much bigger than the root hairs. The lateral roots contain larger amounts of tissue, called vascular tissue, to transport nutrients and water throughout the tree. When roots are cross sectioned, we can see that they have five main types of cells: the epidermis, the exodermis, the cortex, the endodermis, and the vascular tissue (as shown in the figure below). The term tissue in this context refers to when cells are bundled together. Figure 1 shows a cross-section of the cellular structure of roots. Image by CNX OpenStax. Types of Tree Root Tissue • Epidermis The epidermis is the outermost tissue that is a physical barrier providing protection, insulation, as well as moisture and gas control. The epidermis also absorbs some nutrients and water. As the epidermis wears away and dies off, it is continually replaced by cells from the exodermis. • Exodermis The exodermis tissue is right underneath the epidermis and it replaces epidermis tissue as it wears away and dies off. This is very similar to how the inner bark replenishes the outer bark on the trunk which is explained in upcoming sections. TREE: Module 1: Trees Page 6 • Cortex The cortex is a layer of cells that lies directly below the exodermis. The cortex transfers nutrients