What Defines a Healthy Forest in North America?

Learn about the importance and definition of maintaining healthy forests in today’s world

When most of us think of a healthy forest, we probably envision a beautiful forested landscape with mature, stately trees. You know – the kind you can’t wait to go explore on a beautiful fall day. And you probably wouldn’t be wrong about that. But what exactly does “healthy” mean in the context of a forest?

To kick things off, we need to define what we mean by the term “healthy” as it can mean many things to different people. The dictionary has several definitions, including being free of disease, showing physical well-being, or even a state of flourishing or thriving. How do we know when a particular forest stand is showing those signs?

Healthy forests are diverse forests

Like humans, forests do better and are more resilient when they are diverse—in fact, that’s when they thrive. A range of age classes (e.g., young, mature, old-growth), structures/heights (e.g., large canopy trees, understory trees, etc.), and species are all needed. A diverse forest is often described as a “mosaic” in that it supports more plant and animal life across the board. Think of an ornate and artistic mosaic—each individual piece is a minor part of the whole, but it’s important all the same. The finished pattern would look pretty boring if it consisted of the same piece of glass repeated over and over. The same can be said about landscapes. Monocultures (such as pine plantations) are usually on the opposite end of the spectrum, and unsurprisingly, can often be biological deserts. There just isn’t enough variety of ages, sizes, or species to support much life. But a forest mosaic of different species, structures, and ages often supports many other species and natural processes. In that sense, a high level of biodiversity could be described as a state of flourishing.

What do healthy forests do?

Besides look pretty for hikers or hunters, what exactly is it that healthy forests do for us? It might seem strange that forests actually provide services for us, but it’s true. In fact, it’s estimated that forests provide trillions of dollars’ worth of ecosystem services for us each year, just by existing (Holzman 2012). A few of these services include habitat for wildlife, carbon capture, oxygen production, water quality improvements, flood regulation, and actual forest products we use for shelter, heat, and food. Here’s a deeper dive into some of these critical services.

Improved wildlife habitat

Healthy forests are obviously important because they provide habitat to wildlife. As hunters, we care deeply about the conservation and sustainability of wildlife populations, and this is where many of us start looking into forest management. But looking far beyond just our favorite game birds here, forests support 80 percent of the world’s terrestrial plant and animal species (World Wildlife Fund). That’s an incredible figure to understand. The vast majority of the world’s land-based biodiversity is tied to healthy forests, so we have a responsibility to make sure these forests stay healthy.

Different wildlife species require various habitats throughout their life cycle. For example, ruffed grouse are a species of forest grouse. But diving deeper, they require a forest mosaic of different age classes, structures, and plant species to survive through a single year. Without a diversity of those features, grouse have a hard time thriving. And as Aldo Leopold once said, “…subtract the grouse and the whole thing is dead.” A big part of what makes a forest healthy is the overall biodiversity of plant and animal life.

Forests improve air quality

Healthy forests improve air quality in a few important ways. First, they convert our carbon dioxide emissions into oxygen, which we obviously need to survive. As trees grow, they store or sequester this carbon in their biomass (e.g., trunks, branches, leaves, etc.). Carbon is slowly released back into the atmosphere when the tree dies and decomposes on the forest floor. On the other hand, when wood is burned (e.g., wildfires, firewood, etc.), the carbon is quickly released back to the atmosphere. This contributes to greenhouse gas emissions, which has been shown to increase the effects of climate change. This is one of the major concerns about global deforestation, particularly in tropical rainforests.

When the trees absorb more carbon than they are releasing, it’s referred to as a carbon sink. In other words, when a forest is growing and expanding without a significant permanent loss of trees, they are storing more carbon than they are releasing. Trees absorb different amounts of carbon at different rates throughout their lifetime. For example, younger or immature trees tend to absorb the highest rates of carbon dioxide per year because they are growing quickly and adding a lot of biomass. The U.S. Forest Service estimates that all combined U.S. forests sequestered as much as 309 million tons of carbon per year from 1952 to 1992 (Urban Forestry Network). Trees also absorb other airborne pollutants and greenhouse gases, such as ozone, sulfur dioxide, nitrogen oxides, and particulate matter.

Filter water and prevent erosion

Forests obviously need water to grow well and survive, but they also have a tremendous impact on water quantity and quality. A tree’s canopy, the accumulated leaves on the forest floor (i.e., duff or leaf litter), and the root system itself reduces the force of rainfall and helps hold soil in place during intense rain events, which allows the water to slowly filter through the soil into groundwater or nearby stream systems. This process regulates how fast water can pass through an ecosystem, and even filters the water of sediment or some pollutants. Amazingly, it’s estimated that a single 100-foot-tall tree can absorb 11,000 gallons of water in a single growing season (American Forests). If trees aren’t there to absorb and slow the water, it flows off the surface quicker to run downstream, drying out the once-forested land and causing potential floods downstream.

Without forests to prevent or minimize erosion, soil can be quickly transported to water systems, which causes sedimentation and pollution issues downstream. Getting back to the wildlife perspective, sediment in the water affects aquatic ecosystems in a few ways. Fine sediment can affect aquatic plants, aquatic insect larvae (prey for many fish species), native mussels/shellfish, or fish and amphibians, and it may reduce the dissolved oxygen levels as well. Salmonid species are particularly affected as they deposit their eggs on gravel substrates, and rely on the water flow to keep sediment off of them (American Fisheries Society). Over time, this loss of topsoil and nutrients also hurts the previously forested landscape and makes it harder for other plants to germinate or thrive.

On the positive side, forests also help produce soils. Over long time periods, leaves and woody debris naturally decompose to produce a soft, spongy layer on the forest floor, which also absorbs and holds water for longer time periods. This organic duff layer is great for germinating new tree and shrub seedlings, and supports many species of insects, fungi (like truffles), and plants. These invertebrates and fungi help break the duff down even further into humus and eventually soil. Without the forests, those species would also struggle to persist, and soil wouldn’t be made nearly as efficiently.

Healthy forests support local products and industry with working forests

I’m sure you recognize many different forest products that we all use regularly. Lumber, firewood, paper, medicine, turpentine, Christmas trees, and food products (e.g., fruit, nuts, etc.) are all examples. These forest products are collected, harvested, refined, and produced by us, which creates plenty of economic opportunities as well. It’s estimated that almost one quarter of the world’s population relies on forests for their livelihoods (IUCN 2021). In essence, forest management is still a very necessary aspect of our lives. It might sound like we’re preaching “no forest cutting” above, but that’s not true. Sound forest management, when done sustainably, is not the same thing as deforestation (i.e., permanent loss of forest). Forest stands can be harvested and managed sustainably for generations, which provides jobs and products for us, habitat for wildlife, and ecosystem services for the world.

What about the forest products we don’t know about yet? When we maintain healthy, diverse forests, we increase the chance that one day we will find something else, such as a new pharmaceutical that cures a disease. If we let global forest health decline, we reduce our options of discovering something in the future.

How healthy forests can help combat climate change effects

After all of the discussion above, why does this truly matter to you? Why are we talking about this right now? Ultimately, healthy and diverse forests are more resilient to impacts. Things like insect infestations, non-native and invasive species, disease outbreaks, and climate change all have the ability to negatively impact forest ecosystems. Climate change alone is expected to continue influencing weather events to get worse. For example, higher temperatures and droughts will lead to more wildfires, which destroys more forests. Extreme rain events on sites that have already been deforested may lead to more sedimentation and flooding at downstream communities. It’s one big and dangerous feedback loop.

Diverse, healthy forests are the solution. Healthy forests have several levels of different species, structures, and age classes, which increases the chance that they can manage the stresses put on them. Due to their diversity, they are more flexible and resilient. For example, a few native tree species may exist in a forest community as a minor component currently. When conditions change over time, they may be better adapted to survive than the current dominant species, and will essentially take over. The forest community may change, but it has the ability to do so without a sudden strain on the ecosystem.

Another reason this matters is because of all the symbiotic relationships and ecosystem services discussed above. If we don’t manage forests to maintain a healthy state, we risk putting many other species (plant and animal) and ecosystem processes in jeopardy. And frankly, there’s just no way that we can replace those species or processes on our own. As the current stewards of and participants in the natural world, we need to do our part to maintain healthy forests for future generations.