Forest thinning: Helping trees and wildlife thrive

Supporting more resilient forests in state parks 

What is forest thinning 

To put it simply, forest thinning is the practice of strategically removing trees from a forested area to improve the forest’s overall health. 

When there is less competition for available resources – things like light, food, space and water – the remaining trees are able to grow healthier and more resilient. So, when there are disturbances like wildfire or bark beetle outbreaks, the forest is more likely to recover. 

Think of it this way: What happens when you put too many cookies on a tray and try to bake it? The cookies don’t bake evenly, they squish into each other, some aren’t able to rise, some burn and some don’t cook at all. 

The same can be said about our forests. 

When we have overcrowded forests, there are a number of things that can happen: 

• Trees grow taller, skinnier and less strong as they try and reach for the sunlight through the crowded canopy 
• Densely growing trees of the same species don’t leave space for other trees to come in, so there is often less species diversity 
• Less species diversity means if there is a disease that impacts the dominant type of tree, the whole forest is at greater risk of disease or death 
• Dense tree canopies block sunlight from reaching the forest floor and prevent understory plants and grasses from growing 
• Wildlife have limited options for food and habitat because there are fewer species of trees, less layers of vegetation from the ground up to the canopy, and limited understory growth for food and shelter. 
• Wildfire risk increases because fires have more fuel to burn in a denser forest 

Giving trees in our forests a little bit of space to grow helps them build strength, leaves space for new species to populate the area and provides wildlife with a more complex neighborhood to live in.  

Why we like our forests complex 

When we say we love a complex forest, what we’re really saying is we love to see a forest with a variety of tree ages, species, densities, places with gaps in the tree canopy and good spacing. 

A forest community, just like any community, needs these complexities to function effectively. A healthy mix of tree ages means as older trees die, there are mature trees there to take their place and young trees growing right behind them. Species diversity provides food and habitat for different insects and animals. It also protects the forest against wipeout from species-specific disease.  

Densities, gaps in the tree canopy and spacing all support sunlight, the understory and the availability of resources. While it is good to have some areas of dense forest, there still needs to be areas where sunlight can break through to the ground. 

Forest thinning for forest health vs. timber production 

When we thin the forest to remove trees, we may be able to cut them and leave them onsite. But, if there are enough trees or if there are big trees that can quickly make a big mess, leaving them can make problems like wildfire risk much worse.  

Instead, we often choose to harvest the trees that are cut and send them to a mill. This form of timber harvesting (aka logging) is not the same as harvesting for timber production. What separates the two is the overarching goal: 

• Forest thinning for forest health aims to create healthier, more resilient ecosystems and the choice of which trees to cut and how many to leave behind are different.   
• Forest thinning for timber production generally aims to generate revenue or put the forest on a pathway toward a future harvest that generates revenue. At State Parks our forests are never expected to generate revenue through timber harvesting.   

Bark beetles: What happens when there’s too much of a good thing 

Making sure we have healthy, resilient forests is especially important in the fight against bark beetles.  We say fight, but these tiny insects aren’t typically invasive species, and they do perform an important function in our forests when present in the right amounts.  

In overcrowded forests, though, they can lay waste to the ecosystem, killing large numbers of trees that we don’t want to lose and increase the amount of wildfire fuels. 

Healthy trees can withstand the attack of a few bark beetles. However, they like to prey on stressed, diseased and dying trees. 

If our forests are overcrowded, they’re already weakened by competition for water and light. These underlying stressors make forests susceptible to outbreaks of native and non-native insect pests and diseases, which can quickly become too much of a good thing in an already stressed-out forest.   

The bark beetle way 

Bark beetles attack a tree by burrowing through its bark to create tunnels and lay eggs. Their tunnels wind their way through the tree’s vascular system, which is responsible for transporting its sugars, nutrients, water and sap. Eventually, the tree starves and dies.  

The forest after thinning  

Forests after forest thinning look different, especially immediately after.  

While you may be used to visiting your local state park and seeing a dense stand of forest, visiting after forest thinning might be a different experience.  

Right after thinning is completed, there may be a lot of disturbance left by the equipment and people used to do the work. There may be churned up soil and tire marks or ruts from heavy equipment. There may be slash (the cut and broken limbs and tops of trees) left scattered or made into “slash piles” on the ground.   

Most of the impacts of the work are short-term and fade naturally with time, but sometimes we have clean-up work to do.    

Sometimes exposed soils need to be reseeded, and ruts need to be smoothed out. Slash piles are often burned, processed through a woodchipper or hauled out.  

And don’t forget about baby trees!  Sometimes we need to replant with seedlings to introduce new species back into the forest.    

The forest may look a little drab after a forest thinning. It has likely been a while since it had any sunlight and there were just crews and machinery working in the area.  

Give it time.  

With a little sunlight and rain, you will be amazed at how quickly it will rebound with grasses and flowers.