Deforestation is one of the primary global threats to biodiversity. Forests improve our air and water quality, and support diverse ecosystems. But growing a forest requires more than just planting trees. To grow forest like a pro, you’ll need to think like a forester.
Steps to grow a forest
During my time as a professional forester, I would grow hundreds of acres of new forest each year. But even if you only have half an acre, following these steps will ensure you end up with a healthy mature forest on your property.
1. Site-preparation
One of the biggest mistakes you can make when creating a forest is to just start planting trees. This can lead to damage to the trees and other common mistakes like over-mulching and root compaction. But it’s easy to avoid this mistake by considering what your trees need to grow.
Trees grow if they get a combination of sunlight, water, nutrients, and air. That’s all. Air is probably not going to be a limiting factor for your trees, so let’s talk about the other three: sunlight, water, and nutrients. Sunlight comes from above. But plants get water and nutrients from below, in the soil.
So, competition above (older trees) will restrict a tree’s access to sunlight. And competition below (smaller plants and younger trees) will restrict access to water and nutrients.
Set your forest up for success
Site-prep is the method foresters use to increase access sunlight, water, and nutrients just before planting trees. Unfortunately, in the world of commercial forestry this often involves spraying herbicides and plowing soil. Burning debris or existing vegetation is also considered a site-prep technique, and is appropriate in some cases.
Site-prep is an issue of scale. If you are planting a few individual trees for a mini-forest, you can site prep by hand in the area immediately surrounding them. But, if you want to convert a 10-acre field to a forest, you might need a tractor.
It’s important to use the right site-prep technique for your project to avoid unnecessary damage to the environment. Common forestry site-prep techniques include:
- Chemical herbicide use
- Broadcast or debris burning
- Raking and piling
- Plowing or bedding
- Disking/harrowing
- Chopping
Some of these techniques only affect vegetation, while others move around debris or the soil. For converting grass, surface-level tilling to break up the grass root-mat is a good technique. If the area is small enough, covering the tilled soil with newspaper or cardboard can prevent erosion and keep weeds down.
How to pick the right site prep technique
Answering a few questions can help you figure out what kind of site prep to use.
Is there debris on the site that will make it hard to plant trees? If so, you will need to either clear it away or speed up the decomposition process by burning it. You don’t need to clear all of it, though, because your trees will need some space between them. We’ll revisit this idea in the planting step.
Is there woody competition? For seedlings of most tree species, dense woody vegetation is a major problem. You will need to kill or clear away some of the existing vegetation to create space for your trees. The more competition you kill, the more sunlight, water, and nutrients are available for your trees. But it comes with a financial cost and environmental impact.
Are there nonnative invasive plants on the site? This is when chemical herbicide can start to look like a good idea for some sites. Nonnative invasive plants can do irreparable harm to a forest if left unchecked.
Some other considerations that will impact your choice of site prep technique include
- cost
- timing
- need for future actions (e.g. burning more than once may be needed)
- equipment and labor availability
- a need to manipulate the water table (this is only common along the coast)
- a need to break through a rock or hard-pan layer
The best site-prep technique for mini-forests and lawns
If you’re growing a mini-forest or converting your lawn to a forest, this is the best site-prep technique. Use this technique at least 3 weeks up to 3 months before planting.
- Till the top 2 inches of soil using a roto-tiller or farm tractor to disturb the grass’s root-mat across your planting area
- Cover the exposed soil with cardboard, newspaper, or another biodegradable material
- Wet thoroughly
- Optional: add mulch or topsoil to hold everything down
2. Planting
Planting trees is a crucial step in establishing your forest, for obvious reasons. But, some forest regeneration can happen naturally if nearby trees drop fruit and nuts into the area. Planting offers a few advantages over natural regeneration, such as:
- control over tree spacing (to manage competition and get even coverage)
- control over genetic stock
- a head start after site-prep
Natural regeneration is made more difficult due to the prevalence of nonnative invasive species today. And even strictly managed forests are prone to invasive plants, except in the most remote locations.
Logistics
Planting is, like site-prep, an issue of scale. If you are planting 10 or 20 acres, it is doable by hand or with a tractor. If you are planting 200 or 1,000 acres, you will need professional help that can be expensive and hard to find.
Different species of trees are planted with different spacing and techniques. And site conditions can also dictate which technique is appropriate. But the most important factor for choosing a planting technique is definitely the cost.
Planting trees is expensive! Hand planting pine trees will cost at least $50 per acre (with higher costs for smaller jobs), if you can even find anyone to do the difficult labor. Planting machines can be used on some sites for improved survival and more accurate spacing. But they are more expensive.
If you want to plant the trees yourself to save money, expect to cover less than an acre per day until you get the hang of it. You’ll need a tool like a dibble bar or a hoedad (or just a shovel) to open and close your planting holes. Tree roots need to be kept wet or they’ll die off, killing the tree.
If you don’t have the budget to pay for planting over your whole project area and can’t do it yourself, you might want to consider natural regeneration. You can always supplement with a few older seedlings, especially if you aren’t trying to grow timber.
How to make natural regeneration work
To grow a forest while planting no (or just a few) trees, you need two things to happen. One is a seed source. Often a nearby forest can drop or blow in seeds, and sometimes seeds can remain dormant in soil for decades. So, if your land was formerly a forest, you might luck out. But if your future forest is located somewhere with no trees and no seeds, natural regeneration might not be right. Spreading purchased or collected seeds to grow a forest might work, but it will probably take a lot of babysitting, weeding, and luck.
The second requirement for natural regeneration is competition management. In the natural process of forest development, forests colonize grassland very slowly. A gradual shift in light levels and soil makeup allows tree species to move into an area in stages. To speed this process up (to happen in less than a human lifetime), you’ll need to control competition.
Controlling competition
Controlling your trees’ competition is important whether you are planting or using natural regeneration. First, you need to be able to identify and decide which plants are competition and which ones are trees. But not all trees are “trees.” If 3 trees pop up within a few inches of each other, only one of those is considered a tree, and the others are its competition and should be removed. And you may want to select for desired species. So, marking your “crop trees” early on is a good idea.
Culling the weeds
Next, you should apply control techniques to individuals or groups of competing plants. The correct control technique will vary depending on the type of competition. For example, if invasive tree species are competing with your crop trees, using the “hack-and-squirt” method to apply herbicide will kill them without impacting other plants. But if fast growing vines are climbing your trees, herbicide would do more harm than good. Using clippers or loppers to cut and manually remove the vines would be more effective. Herbaceous plants competing for water and soil (space and nutrients) can be mowed or trampled.
On larger and more remote tracts, fire might be an effective tool for managing competition, if your crop trees can survive a low-intensity burn. But use caution! Fire is dangerous, and some species are not adapted to fire and will die. Bush hogging is also effective for covering a lot of ground, but your crop trees are at risk of accidental chopping. Common techniques for controlling competition are:
- selective herbicide use
- prescribed fire (for some species)
- bush hogging
- mowing
- mulching/debris spreading
- trampling/crushing
- manual removal using machetes or other tools
Thankfully, you don’t need to be very diligent about controlling competition, especially if you did site prep. For the first year, you will want to check your crop trees and “release” them from competition once in the spring and again in fall. The second year, repeat your spring and fall evaluation and release treatments. For the greatest survival and growth, continue to evaluate and release your trees for the first five years.
3. Maturation
As your forest grows taller than you, your role in keeping it healthy shrinks. But there are still some situations that can call for intervention to keep your forest healthy. Specifically, there are threats to mitigate and opportunities to seize.
Threats to your forest
Your trees are always vulnerable to individual diseases, pests, and weather. But your forest should be able to survive the loss of a few individuals thanks to the natural resistances it has to these threats. Trees tend to be most resistant to these dangerous forces when they are growing vigorously.
Most mortality will happen when one stressor causes growth to slow down, then another comes in for the kill. The clearest example is during a drought or flood, when trees are vulnerable to insects or pathogenic fungi. The stress caused by having too much or too little water forces your trees to lower their defenses, and a beetle infestation or root rot finishes them off.
Defending your forest
You can’t do much to protect your forest from bad weather. Choosing native species that are well suited to your site and using good planting techniques gives your forest the best chance of surviving. So, plan accordingly. Don’t plant a dry-site species in a swampy area, or vice-versa.
Some other threats to your trees include:
- damage from wildlife (especially deer)
- invasive nonnative insects and diseases
- severe storms including ice and wind
- wildfire
You should expect your forest to experience some tree mortality, even when everything goes smoothly. The reason for this is straightforward: older trees take up more space than younger trees. So, as your trees age they will start to bump into one another and compete for sunlight and resources. Individuals that grow slower or are in a worse spot will become suppressed and lose out on vital resources and eventually die. Culling diseased or suppressed trees is called thinning.
Thinning
Thinning is one of the most effective tools at your disposal for growing a healthy forest. It promotes increased growth of the remaining trees, and reduces the overall susceptibility of your forest to threats like insects and fire.
It may seem counterintuitive to cut trees down to benefit the forest. But if you want your forest to reach a mature state, you’ll have to see plenty of trees die along the way. Deciding which ones will take the hit and beating nature to it is a powerful strategy.
Speeding up selection
Part of the reason thinning works so well is because of the pattern of growth that forests exhibit. To summarize: young forests have lots of little stems, old forests have a few big stems. If all of the trees in the forest are the same age or age-class, then a few of them will die over the years to make space for the remaining ones to grow larger. If the forest is grown with two or more age classes, then a few of the older trees will die every few years to make room for younger trees to grow. Of course, some of the younger trees may also die before reaching maturity.
Thinning is a way to speed up the process by identifying individual trees that are unlikely to survive long enough to meet your goals – whether that means sexual maturity for a self-sustaining forest habitat or commercial viability as timber. Removing these trees at the correct time keeps your crop trees growing vigorously and reduces competition. This can be enough of a leg-up to protect them from diseases and droughts.
4. Age-class establishment
In the world of forestry, research time and money tends to go towards one particular goal: growing as much timber as possible as quickly as possible. To that end, most commercial forests are usually made up of one cohort of trees. All the trees are planted within a few days of one another, thinned once or twice as they mature, and then clearcut when they have grown large enough to do so. The process is then repeated.
Forest forever
I’m going to assume that some readers will have different goals in mind from the timber industry. How can you sustain the forest you grow so that it will always be a forest? If individual trees die off over time, where does that leave your forest long-term? To remain sustainable in a forested state, your forest will need diverse cohorts (groups of around the same age) of trees. This is called uneven-aged management.
In an uneven-aged stand, you will have lots of small stems, AND a few big stems. So, parts of your forest appear young, and other parts appear old. Of course, these terms are relative. Your forest doesn’t need to always have trees in the 0-3 years age-class. Generally speaking, having cohorts separated by 10 or 20 years is sufficient to achieve a sustainable population. But it can depend on the species and site.
Achieving an uneven-aged state is tricky. Younger cohorts are shaded by older cohorts, and they are usually isolated in dense, small groups. So, they can be vulnerable to threats. And planting trees in the middle of a forest is much more labor-intensive, because site-prep may not be possible.
Creating an uneven-aged forest
To get your forest in a state that will support multiple cohorts, you’ll need to cut trees selectively. Thinning is one type of selective cut. But select cuts can be dangerous for the forest. And irresponsible select cutting has led to major problems for the timber industry across much of the Eastern U.S. High-grading is the practice of removing only the largest and most valuable trees. This practice allows loggers to extract the most value from a forest, but it can jeopardize the future of the forest. High-grading removes the best genetic material for future generations. The trees that are left tend to be slower growing and more susceptible to pests and diseases. Not the best genetic stock for the next cohort.
The opposite approach is usually the most desirable in terms of forest health. By removing ONLY the diseased and slow-growing trees, so-called “thinning from below” creates space for the offspring of the best trees to sprout. But, as usual, some degree of compromise is typically needed to make the project worthwhile for a logger while also improving the overall health and genetics of the forest.
Other types of select cut
Select cutting does not necessarily need to be a form of thinning, though. Other approaches, such as the patch or group clearcut and shelterwood, can be effective methods for growing multiple cohorts. But the bottom line is that you’ll need to remove some of your older trees to make room for younger trees. Some sunlight needs to reach the forest floor for seedlings to grow.
5. Long term management
Finally, we need to put it all together. Your forest should outlive you, and your kids, and your grandkids, unless someone along the way decides to cut it down. Those crucial early years get a lot of attention. And it’s hard to overstate the importance of starting your forest off on the right foot. But long-term management of the forest is just as important for keeping your forest healthy and sustainable over decades or even centuries.
Watch for weeds
Keeping nonnative invasive plants at bay is a constant battle in many forests. The earlier you spot and eradicate an infestation of these noxious weeds, the cheaper and more effective your treatment will be. Full eradication of invasive weeds is often a multi-year project (if it’s possible at all) once they get established in a forest. So walk your forest often and be ruthless with these pests.
Grow your soil
Growing a forest is more than growing some trees together. A rich soil ecology can support and enhance the health of your forest. Healthy soil will also sequester carbon from the atmosphere and improve the water quality of nearby streams and rivers. Avoid soil compaction by limiting heaving equipment use, especially during wet weather. And prevent erosion by following your state’s best management practices (BMPs) for any silvicultural management. Having a healthy O-layer (organic layer) on your soil’s surface will help your soil grow, hold more nutrients, and resist floods and droughts. Thankfully, you don’t need to add compost to create an O-layer. Just let leaves, twigs, needles, and roots decompose without too much disturbance.
Advanced regeneration
As you walk your forest, keep an eye out for the future generations of trees. Try not to trample the knee-high saplings that appear when an older tree dies and a new patch of sunlight appears on the forest floor. And try not to trample the ankle-high sprouts that grow in the shade of mature trees. These seedlings are the offspring of your oldest trees, and are poised to spring up if an older tree dies. In fact, scientists have found that the mother tree will often send nutrients to its offspring through their shared root network during times of stress.
Don’t panic
Listen: bugs happen. Floods happen. Ice storms, tornadoes, droughts, and fires can all seriously harm your forest. But growing a forest often requires you to step back and be patient. See how your forest responds to these disturbances over the following growing season or two. Often, these types of disturbances end up significantly improving the long-term health of your forest. They not only create opportunities for new cohorts to spring up, they also cull the weakest members of the gene pool. Of course, if you’re only interested in timber value, the best response to a major event might be to salvage harvest and start over.
What kind of forest should you grow?
Forests come in all shapes and sizes. Your site is going to determine what kinds of forest are feasible on your property, but your vision and goals will ultimately determine what kind of forest you grow.
What are your priorities?
Are you growing a forest for financial gain? For scenic beauty? For wildlife habitat? Write down your priorities to help guide your forest planning. You will need to research forest issues in your state or region. If you’re interested in selling timber, find out what mills are near you and what species they accept. If you’re going for wildlife habitat, find out what kinds of forest habitat are disappearing from your area.
Types of forest
Forests are grown in a few broad categories. Deciduous forest is more prevalent in the temperate Eastern U.S. and in some wetlands. But conifers dominate in more extreme climates, both cold and hot. The deep south is excellent pine habitat. Pines also thrive in the high altitudes of the rocky mountains. In central and eastern Canada and the lake states, spruce performs well, although deciduous forests also make an appearance. Along the west coast, unique forests types like redwood and sequoias, as well as western hemlock (all conifers) find their niche.
The U.S. is also home to several temperate rainforests. The Great Smoky Mountains area of Tennessee and North Carolina, and the Olympic peninsula in Washington are home to rainforests.
Conifer forests
Conifers evolved earlier than their deciduous cousins, and they behave a little differently. Conifers will generally grow straight and narrow in an effort to occupy the highest spot in the canopy. Many conifers also develop a taproot – a wide, tough root that penetrates straight down to seek the water table. Conifers are typically “soft” wood (as opposed to hardwoods). Additionally, conifers tend to grow needles instead of broad leaves. On pine trees, these needles fall off periodically, but never all at once, causing the soil pH to slightly decrease (become more acidic).
Conifer forests can be dense, like the Black Forest in Germany. They can also be very sparse, like the longleaf pine savannas in Florida. Softwood conifers dominate the timber market in much of North America, but most of that timber comes from commercial plantations. Conifer forests are on average less diverse than deciduous forests.
Deciduous forests
Deciduous forests are made up of trees that lose their leaves during the dormant season. There are conifers which aren’t evergreen, and there are broadleaf species that retain their leaves (like Magnolias). So, there is some overlap. However, deciduous forests are generally composed of a diverse mix of species working together.
Deciduous trees differ from conifers in that they will often spread their canopy horizontally at the top, rather than forming a Christmas-tree shape. Their roots will also spread horizontally under the soil surface, rather than penetrating straight downward. Because of this characteristic, hardwood forests tend to have an upper limit on stem density. They can still be very dense, though. Layers of vegetation under the canopy are usually full of shade-happy shrubs and trees.
Because of the high level of diversity in a deciduous forest, they are prone to changing cover types over time. For example, across the Eastern U.S. white oak forests are in decline. The reason for this is that shade-happy maples make up most of the understory in existing white oak forests, and slowly replace the oaks as individuals die out.
Species composition
Forests are largely defined by the dominant species in the overstory. The forest canopy and its characteristics can often define what other plants grow there and how the forest functions as a habitat. Some desirable species compositions, or forest types, include:
- oak-hickory
- spruce-fir
- longleaf-slash pine
- oak-gum-cypress
- aspen-birch
There are many other types of forest native to the U.S. like pinyon-juniper and maple. No forest type is “bad,” but they all have different characteristics. Forests that are dominated by mast-producing species like hickories will support more and different types of wildlife than those that don’t, like maple.
Visit local forests and see what appeals to you and your priorities.
How many trees make a forest?
Where is the line between a grove of trees and a forest? Does it have to do with acreage or the number of trees? Some forests have as few as 10 adult trees per acre, while others can have hundreds.
There is probably some academic, research-based way to make a distinction between a group of trees and a forest. But for the purposes of an average landowner, it isn’t about size or the number of trees. The characteristic that defines a forest (in my mind at least) is that nature shapes a forest. While groves are intensively managed with pruning, mowing, fertilizing, and irrigation, forests are mostly left alone.
Don’t get me wrong – foresters frequently use techniques like fertilization, pruning, and passive irrigation in different parts of the world. But human intervention in forests is limited. In a given year, a forest might be burned and fertilized, resulting in obvious signs of human activity. But that activity takes place in an environment that is largely shaped by nature. In a grove, offending branches are removed. Infrastructure is built to support and enhance the purpose of the grove. Humans are needed to keep the system working. Not so in a forest.
Mini-forests
Because forests are defined more by their character than their size, the concept of mini-forests is often asked about. The invention and spread of Miyawaki Forests is redefining how human society sees forests. Many of these forests are a few hundred square meters or less.
Of course, a mini-forest lacks some of the benefits of a larger forest. Generally speaking, connections between good habitat are incredibly important ecologically. When a forest is larger, it is much easier to chart connections between the ideal habitat for a given species within that area and nearby forests. If a mini-forest is isolated from other habitat, its effect is limited.
Can you grow an old-growth forest?
Ask any forester about old-growth forests and you’ll probably get an eye-roll and a long explanation. Old-growth forests are some of the most important and rare resources on the planet, but misconceptions and myths about them abound.
Old-growth forest is a “climax community,” meaning it is a stable ecological state. This means that the forest will not undergo significant changes to its species composition or its ecological function unless some outside force causes a change.
Trees still die in an old-growth forest, and so young trees still sprout to keep the system stable. An old-growth forest is not just old trees. It is also many young and middle-aged trees, plus (usually) plenty of shrubs and herbaceous plants. So, if you want to grow an old-growth forest, you will need to plan carefully and get the right species composition.
How not to grow an old-growth forest
Many environmentalists I know believe that if landowners would just leave forests alone for a long time, it would result in plentiful old-growth forest. This is true, if by “a long time” they mean 500 years or longer. But because of introduced pests, many of the tree species that dominated old-growth forests when North America was re-discovered by Europeans are now extinct or in decline.
Since we cannot reproduce the old-growth that previously grew in America, we will need a different approach to growing forests if our goal is to create stable systems. Forests need to be evaluated regularly, and when problems arise they should be addressed. Leaving forests alone can result in overcrowding and homogenization, leaving the forest less stable. It can also invite unintended species composition shifts, as shade-tolerant species become dominant and prevent sunlight from reaching the forest floor.
Grow a forest at home
Even if you don’t have a few hundred acres in the country to play around with, you can still grow a forest. Start with a small planting, following The Unlawning Guide. Getting neighbors involved can expand your forest across property lines. And if your property backs up to stream or existing forest, the ecological benefits of planting trees will be enhanced.