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The Complete Lifecycle Of A Tree
Trees are among the world’s oldest living things. The Great Basin Bristlecone Pine is a species of pine tree that grows mostly in the western United States. One of these ancient trees was discovered to be 5,065 years old! According to Arizona State University, this tree is the oldest living non-clonal organism on Earth.
Yet trees have a life cycle just like any other organism: from conception (seed), to birth (sprout), to infancy (seedling), to juvenile (sapling), to adult (mature), to elderly (decline), and finally to death (snag/rotting log).
For the tree’s life cycle to not be interrupted prematurely, a number of external and internal conditions must be favorable for the tree. These include sunlight, water, nutrients, and room to grow.
Even under optimal circumstances, however, a tree can weaken and die due to various stressors like insects, diseases, injuries, competition from other plants, and weather.
Some tree seeds have a protective shell like a nut. Other seeds are contained in fleshy fruits. Certain maples and sycamores have helicopter-like seeds that twirl to the ground called “samaras.”
Over millennia, seeds have evolved into different types and shapes so they can be dispersed by wind, water or animals. Each seed has all the resources it needs to survive until it reaches a favorable place to sprout and grow.
If certain environmental conditions are met, germination of the embryo contained in the seed can occur. The embryo depends on the supply of food stored in the seed for the energy necessary to grow, expand, and break through the seed coat.
The root grows down into the soil to search for water and nutrients, while the sprout pushes upward seeking sunlight. If the sprout succeeds, the leaves will develop and allow the tree to create its own food through photosynthesis.
The sprout grows and gradually takes on woody characteristics. The soft stem begins to harden, change from green to gray or brown, and develop a thin bark. More leaves or needles sprout from newly formed branches seeking light.
The tree roots also continue to grow and branch out. The majority of the tree’s roots are near the surface of the soil, in order to absorb available water and nutrients and to breathe, as roots also require oxygen.
It is at this stage when trees are most vulnerable to disease, insects, extreme weather conditions, or grazing animals like deer.
According to the Texas A&M Forest Service, a tree is generally considered to be in the sapling stage when it is between 1 and 4 inches in diameter at 4.5 feet. This is the standard height where a tree’s diameter is measured, known as the “DBH” or “diameter at breast height.”
This is typically the size of a small tree when you purchase it in a commercial nursery and transplant it to your yard. It is in the juvenile stage of its life, when it is yet unable to produce fruit or flowers. The length of this stage depends on the species of tree, and trees with longer overall lifespans will generally be saplings for a longer period.
A tree becomes mature when it starts producing fruits or flowers, and can begin the reproductive process of dispersing seeds. Again, how long it remains in this productive stage will depend on the species.
The Woodland Trust states that a typical English oak tree begins producing acorns at around 40 years old, and peaks in productivity at around 80-120 years. In general, oaks can be productive for 300 years, then rest for 300 years before they begin to decline.
During this stage in the life cycle, a tree will grow as much as its species and site conditions will permit.
You can recognize an ancient tree by gaps appearing in the canopy, a reduced crown, a wide trunk which might be hollow, and heavy limbs which could be covered in short sprouts. At this stage, it will become a host for a variety of insects, animals, and fungi.
Its survival will be determined more by external stresses, such as insects, diseases and competition from other plants, than by its own vigor.
To keep an ancient tree in good health, regularly prune away dead wood, and watch for insect infestations and diseases that may cause added stress. Your tree could continue to live on for decades in this state of gradual decline.
Many factors can contribute to the death of trees. Usually it is a combination of conditions, such as injury, drought, disease, rot, and insects, to name a few.
Yet, this is not necessarily the final stage in a tree’s life. A standing dead tree, also called a snag, can provide a habitat for wildlife and insects, and the insects become a food source for birds and small mammals. The snag slowly breaks down and returns nutrients to the soil, which in turn is taken up by other trees, and the life cycle begins anew.
If you would like to see a visual demonstration of how trees grow, take a look at this fascinating video.
What Can Affect A Tree’s Growth Rate?
While tree growth is partly determined by its species, environmental factors play a big role in how trees grow.
Oregon State University claims that most issues affecting plant growth are caused by environmental stress, either directly or indirectly. Trees can be directly damaged by too little water, for example, or they can be indirectly damaged by environmental stress which can make them more susceptible to disease or insect attack.
Here are some things to consider so that your trees encounter as little stress as possible, and have a better chance of growing to their maximum yearly capacity.
Plant Hardiness Zone
Weather and temperature variations can have a large impact on growing plants. A tree will have a better chance of growing to its full potential if it is planted in the proper “plant hardiness zone.”
A zone is designated by the average annual minimum winter temperature, and each zone has a range of 10 degrees Fahrenheit. There are also half-zones with a 5-degree temperature variation. For example, Zone 1 ranges from -60 to -50 degrees F, while Zone 1a ranges from -60 to -55, and Zone 1b is -55 to -50 degrees F.
Giving your trees adequate amounts of water, particularly during the growing season, can make a big difference in helping them reach their full size at maturity. We recommend using a slow irrigation system to provide your tree’s roots with the appropriate amount of deep watering, without drowning them.
The soil should be damp but not soggy, and you should allow for short periods between waterings to ensure that enough oxygen is able to reach the roots.
Adding fertilizer to your soil, especially in the first stages of tree growth, will help them grow faster, taller, and fuller. Fertilizer helps incorporate essential nutrients into the soil to support growth and photosynthesis. Fertilizers contain varying amounts of nitrogen, phosphorus, and potassium, which are like vitamins for your trees.
Phosphorus, for example, helps your trees develop chlorophyll, which allows them to turn solar energy into chemical energy, promoting growth. Different tree species will require different compositions of fertilizer, so it’s a good idea to consult with one of our tree care professionals before you begin feeding your trees.
A layer of organic mulch around your tree can provide many benefits that will support its growth. Mulch helps trees retain water, regulates temperature, and adds nutrients to the soil as it decomposes. It will also restrict weeds, which compete with your tree for water and nutrients.
The layer should be only one to two inches thick, to ensure that the root system isn’t smothered. And always leave 3 to 10 inches of space around the base of the tree, as this is a vulnerable area and subject to decay if not kept dry.
If your tree is planted in a location where it might be damaged by vehicles, lawn equipment, or animals — especially if it’s still a sapling — it’s a good idea to provide some protection.
Posts, fencing, or plastic cylindrical tubes around any parts of the tree that may be exposed to injury will help keep your trees safe. Healing from a wound requires extra energy, and will inhibit your tree’s growth.
Can You Tell The Age Of A Tree Without Seeing Its Rings?
We all were taught how to count the rings on a tree stump to determine the age of the tree, but can you know a tree’s age without cutting it down?
While we can’t know for sure exactly how old a tree is, forestry experts will generally use the following 4 step process for estimating its age.
Determine what species of tree you have. If you don’t know, try asking your neighbors. You could also look it up in this handy guide.
Next, find the circumference. Remember the DBH (Diameter at Breast Height) we mentioned above? To calculate the diameter, first we have to know the circumference. Take a measuring tape and measure the circumference of the trunk 4.5′ feet from the ground.
Now we can figure out the diameter. This requires a little math.
Diameter = Circumference divided by 3.14 (Pi).
If the circumference of your tree was 100 inches, the diameter is 31.4 inches.
Find the growth factor. If you know the species of your tree, you now can look up the growth factor. This table lists the growth factors for several trees. There are many resources online if you don’t see the growth factor for your particular tree.
Diameter X Growth Factor = Approximate Tree Age
The growth factor of a Big Leaf Maple is 4.7. If the diameter is 31.4 inches, we can estimate the age to be around 148 years.
If you prefer to skip the math, here is a website that will do the calculation for you!
Do Trees Stop Growing? How Can You Tell?
Have you ever wondered if trees stop growing? If trees continue to add rings year after year, they must certainly be getting wider. But, for all practical purposes, trees do stop growing in height.
You may have noticed that trees of the same species in the forest will be of a similar height, even if the width of their trunks may vary widely.
Trees grow more slowly as they age. After a certain age, they essentially stop gaining height. A mountain ash, for example, may grow seven to 10 feet every year.
But after it reaches around 90 years of age, its growth will slow to about a foot and a half. By the time it reaches 150-years-old, growth in height will have virtually stopped.
Why do trees stop growing? Some scientists suggest that tree cells are like animal cells.
They have to stop growing after a certain number of divisions. If a tree’s cells stop dividing, then it stops getting taller. However, there is no conclusive evidence to back this theory.
Another idea is that a tree’s height is limited by the way it transports water from its roots to its leaves. Water moves upward because it is pulled towards the leaves, where it evaporates into the air through tiny pores called stomata.
The cells inside the leaves and stems are inflated with water, like air in a bike tire.
This pressure is called “turgor” and is necessary for cells to expand and grow. Some scientists hypothesize that when a tree gets very old, and therefore tall, it becomes difficult for the tree to pull the water all the way to the top.
Gravity’s pull reduces turgor, and that may be why trees stop growing at a certain height.
Can A Tree Professional Help Identify A Tree’s Growth Stage?
A tree care professional will take many factors into consideration in determining the life stage of a tree. These factors might include:
- Thickness of trunk
- Estimated age
- Whether the tree is producing flowers and fruit
- Density of foliage
- Color of tree leaves
- Integrity and surface of bark
- Presence of decay or dead wood
- Thickness of branches
Understanding the life stage of a tree is important in evaluating its overall health. An arborist will also take a tree’s life stage into consideration in deciding how best to care for it in terms of watering, fertilizing, pruning, and treating diseases or insect infestations.
Feel free to contact one of our certified arborists if you have any questions about your trees.