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Serving small woodland owners and managers in the Willamette Valley and northwest Oregon
Updated: 6 hours 1 min ago
By Amy Grotta and Brad Withrow-Robinson, OSU Forestry & Natural Resources ExtensionThrough a creative and carefully planned harvest, this mature forest has undergone a structural diversity makeover.
Continuing our series, we’ll now look at steps that woodland owners can take to enhance structural diversity in their forests. Recall that “structural diversity” refers to the amount of three-dimensional variation in the forest. In other words, a structurally diverse forest has trees of different sizes arranged in uneven patterns across the site.
Why do we care about structural diversity? Structural diversity is important to creating an “older” or “natural” forest look that many people want on their property.
Structural diversity is also a very important part of wildlife habitat. By creating variation in the tree canopy, and creating layers of vegetation at many levels within a forest, you are creating micro-environments. These micro-environments, each with its own set of light, temperature and moisture conditions, allow different sets of plants and animals to flourish. You are setting the stage for biological diversity to develop. Raptors may perch in the upper branches of the tallest trees, while small birds that nest in thickets may find a home lower down. Light-loving shrubs will fill in the sunny openings, while mosses and lichen will be happy in the cool shade of taller trees.
To create structural diversity, we rely on all the same tools in our forest management toolbox that we use to achieve other things in our woods: planting, thinning, harvesting. We just apply them a little differently to produce a different outcome. Many of the opportunities described below and illustrated in the graphic at the right will be familiar from our last post, since structural and species diversity often go hand in hand.
Preparing to grow a new forest: don’t clean it up too much
After a timber harvest, there will be a lot left behind: limbs and treetops (slash), and sometimes logs with too little value to take to the mill. Part of site preparation involves getting these residues out of the way to make room to plant new trees. Often slash is piled and burned, but leaving those logs and even a few of these piles creates instant structure. They will decompose over decades, providing a shelter for critters and slowly evolving into a substrate for new plants. Check out this article for some great how-to’s and cautions.
Planting a new forest
Since a diversity of tree and shrub species can also greatly enhance future structural diversity by creating different textures or layers in the forest, the steps at planting outlined in our previous post can do double duty.
Tending a developing forest: thin early, thin often and change it up
While a diverse forest is an appealing image to many small woodland owners, what they often actually have is a uniform forest of trees roughly the same size and spacing. In these situations, thinning is the best opportunity to enhance structural diversity.From top to bottom, examples of young, intermediate and mature conifer forests with low structural diversity
You can use thinning early in the life of a forest to create both horizontal and vertical structure (recall the cookie metaphor for definitions). Some specific ideas for making your forest more structurally diverse through thinning include:
- Thin early to promote layers of plants on the forest floor.
- Mix it up with a variable density (rather than uniform) thinning strategy:
- Leave some areas dense or even unthinned.
- Thin some other areas heavily to grow big trees and promote regeneration of new trees.
- Be messy. Leave snags and dead wood behind.
Opportunities in an older, maturing forest are to create gaps and leave legacies. If you find a group of young, shade-tolerant trees coming up on the forest floor, you can create a small gap to give them room to grow. Or you can cut a patch and plant it with shade tolerant species such as western hemlock or grand fir to create another canopy layer. Both of these things could be part of a regularly planned thinning harvest.
Any harvest is a chance to enhance the structural diversity of the future forest. Leaving dead wood (both standing and down) is particularly beneficial for wildlife. If doing a clearcut harvest, you can also leave some live trees, in groups or islands when possible. Good candidates include trees that are hard to access, have defects, or are intermixed with snags you wish to protect. Even if they blow down, the downed wood is another important structural legacy.
We hope this series has given you some new ideas about how to enhance your woodland diversity and enrich your experience as a landowner. There is lots more information out there to help you work out the details. Here are a few:
This is an excellent publication from WSU Extension, Diversifying Forest Structure to Promote Wildlife Biodiversity in Western Washington Forests (written for our neighbors to the north, but just as applicable to western Oregon).
Wildlife in Managed Forests: Oregon Forests as Habitat published by Oregon Forest Resources Institute
Alternative Forest Management series in the OSU Extension Catalog
The post Growing a Diverse Forest: Steps to a Structural Diversity “Forest Makeover” appeared first on TreeTopics.
By Amy Grotta and Brad Withrow-Robinson, OSU Forestry & Natural Resources Extension
Our previous installment of this series introduced the key elements of forest diversity. Species diversity (a.k.a. compositional or biological diversity) is one of those elements. So how do you achieve it, especially if what you are starting out with is a plantation forest with only a few species? The transition to an older forest with many plant species will not happen quickly. However, at every stage in a forest’s life cycle, there are opportunities and choices one can make to move the needle to a more species-rich forest.
The rest of this article and the accompanying infographic takes us through these choices, stage by stage.
Preparing to grow a new forest: have more than zero tolerance for shrubs
One of your best chances to grow a more diverse mature forest is on a just-logged site, even before you plant any new trees. This is (perhaps ironically) often one of the most diverse stages in forest development, when many sun-loving leafy plants show up. They provide important food and cover for many birds and other animals. The trick is to balance this vegetation with the needs of growing tree seedlings. You’ll still need to establish a stand of young trees successfully to meet Forest Practices rules. We’ll look at this stage again later in another article.
After logging, there are typically still native shrubs left behind. Sure, they may have taken a beating, but most will rebound if given the chance. So as you prepare the site for planting, whether with herbicides or machinery, you can intentionally save (choose to keep) some of these shrubs to meet your diversity objectives. Some specific strategies:
- Identify and mark the shrubs you want to preserve. Consider keeping them in scattered clumps and “sacrificing” the space they occupy, rather than planting trees there.
- Be selective in the species that you preserve, choosing those that won’t quickly outgrow planted trees. For example, Oregon-grape, cascara, and oceanspray grow slowly, while salmonberry and thimbleberry spread quickly. Bigleaf maple clumps are too competitive for most objectives/situations and should be controlled.
- Use spot sprays of herbicide instead of a broadcast spray.
- Evaluate what vegetation is growing on the site, and choose an herbicide strategy that targets the worst competitors while leaving desired vegetation. For example, you could select an herbicide that controls grasses, thistles and other non-woody weeds but is easier on shrubs. Consult product labels and the PNW Weed Management Handbook for guidance.
- Keep a close eye on things, and quickly take steps to correct a situation if things look like they are getting out of hand.
Establishing a new forest: species and spacing choices
Planting multiple species of trees may seem like an obvious strategy to increase species diversity. Yet it’s not as simple as mixing up the seedlings across your planting site if you want to keep that diversity long-term. Trees all have different growth habits and growth rates. When trees of different growth habits are closely mingled, the faster growing tree tends to win out. Red alder and Douglas-fir are a good example (see illustration). Plant clumps of individual species rather than an intimate mixture to reduce competition, make subsequent tending of the stand easier, and keep diversity longer. If one of your motivations for having a diverse forest is to have a resilient forest, then keeping a mix of species in the canopy may be important.Fast-growing alder will overtop and kill neighboring Douglas-fir (top). Instead, plant these species in groups (bottom)
Work with, not against, your site, and use microsites as a “palette” on which to paint your species choices. For example, plant wet areas to cedar, alder, or even ash.
The other planting decision you can use to enhance diversity is tree spacing. By planting trees further apart (say at 12-foot instead of 10-foot), you are giving more room and time for shrubs to re-establish. You can also resist the urge to come back in and replant spots where seedlings did not make it (as long as you’ve met Forest Practices Act reforestation requirements). Instead, allow hardwoods to fill in small gaps.
Tending a young forest: stay proactive
Your job of growing diversity is not done after planting. Invasive weeds and crowding are two things to keep an eye on. Some specific tips:
- Stay on top of invasive weeds before the canopy closes. Resist the temptation to leave blackberries or scotch broom to get shaded out once tree crowns touch. Unfortunately, shade is not a particularly selective form of weed control: by the time the weeds get shaded out, so will many of the understory plants you desire.
- Extend the life of your understory by thinning early and often.
- Thinning also is an opportunity to diversify the tree canopy, by choosing to leave behind “underrepresented” species. Thin around and release oaks, madrone, true firs, and any other minor species, as long as they are vigorous. (Don’t try to release suppressed trees that won’t respond to thinning.)
Harvest: leave a legacy
A mature forest can have many kinds of plants growing in the understory that you want to keep. When it comes time to do a timber sale, how can you carry that diversity into the next-generation forest? This is your opportunity to leave legacies.
- Retain some hardwood trees. Better to leave a single-stemmed bigleaf maple than to cut it and deal with the inevitable stump sprouts.
- Mark and protect clumps of native shrubs.
The bottom line with all of this is that growing a multi-species forest does not have to be a revolutionary form of forest management. As illustrated above, you can be opportunistic, make proactive decisions, and even small tweaks to your management practices to maintain and enhance species diversity according to your interests. This article provides some ideas, which you can tailor for your own forest. You might want to talk with a professional forester, including your local Extension agent, to design a site-specific strategy.
The next post in this series will look at structural diversity (the other major aspect of forest diversity), and ways to achieve it.
The post Opportunities to enhance species diversity in small woodlands appeared first on TreeTopics.
Brad Withrow-Robinson and Amy Grotta, OSU Forestry & Natural Resources Extension.
Many landowners are interested in growing a diverse forest as discussed in the previous post. Their reasons may include having an attractive woodland retreat, providing habitat for wildlife or having a more resilient forest. Whatever the reason, knowing what different parts of forest diversity look like is a key step towards getting it.
There are several key parts to diversity: those things that grow and live in a forest, how those things are arranged and when those things happen. Each is shaped or influenced by the physical environment (like soils or elevation) and natural processes (like competition, storms or fire). Many kinds of diversity can also be enriched by us.
Probably the first thing people think about as diversity is the number and types of plants and animals in the forest. Certainly, what is growing in the forest (the species composition) is an important part of diversity. A mix of trees which includes cedar and maple along with Douglas-fir is more diverse than monocrop of Douglas-fir alone in the forest canopy. You can think of the different kinds of plants as the building blocks of a forest, or maybe better, ingredients in a recipe. An oatmeal raisin cookie is more diverse than an oatmeal cookie. But not twice as much. There are many ingredients in cookies that go unobserved or unseen. While trees are the most obvious and the defining elements of the forest (like the oatmeal and raisins), understory plants, soil microorganisms, fungi, and other elements play less glamorous but essential roles (like the flour, sugar and baking powder) in making the cookie a cookie.
Another easily observed feature of diversity is the forest’s structure, or how things are arranged. Looking up and down you may see one or more layers of vegetation from the tree canopy to the leafy plants growing on the forest floor. Looking at these layers, you are looking at the vertical diversity. An Oreo cookie has more of it than our oatmeal cookie does. This structure affects how the woods look, but also how things work. Having more vertical diversity can be visually appealing. And because different animals use different parts of this vertical forest structure to forage, roost or nest, it may mean more types of animals using your woods too.
Likewise, looking side to side we can see the texture of the forest (its horizontal diversity). The woods may be quite uniform throughout, with little difference from place to place. Or the woods may be uneven, with groups or patches of different things scattered about. These could be areas with different ages, sizes or species of trees. To picture this horizontal diversity, let’s think about cookies with a similar variety of ingredients but different horizontal structure: chocolate and chocolate chip. Chocolate cookies are uniform throughout, but chocolate chip cookies are patchy, and more diverse. Like vertical structure, this horizontal structure provides different conditions that may be visually appealing or suit different animals.
Perhaps the least obvious part of woodland diversity is time, or perhaps better, processes that take time. It may be cheating a bit to include time as part of diversity, but as an observer of nature and care-taker of a woodland, it is important for you to recognize its impact on the different parts of diversity. Some kinds of diversity can happen quickly, others just take time to develop. Cookie dough is great, but it is not a cookie until it has spent some time in the oven.
Imagine a riparian restoration plantation along a stream. You can quickly create species diversity by planting a mix of species, and horizontal diversity by planting patches of different trees or shrubs rather than blending them together. However, to get vertical diversity with layers including large trees (desired to shade more of the stream longer and/or have large logs to fall in the steam), you need decades, maybe even a century or more for that to fully develop.
As a landowner, you have many opportunities (such as planting, controlling invasives or thinning) to shape your woodland property. Each is a choice between paths that take you to different destinations, with different outcomes, depending on the recipe you pick. We hope this introduction will help you choose a path to your destination. Coming up in our next article: specific steps you can take to enhance your woodland’s diversity according to you objectives.
But now, it is time for a cup of coffee. And a cookie!
Brad Withrow-Robinson and Amy Grotta, OSU Forestry & Natural Resources Extension.
We often hear from landowners that that they want a diverse, natural-looking forest. Their reasons vary. Some folks are aware of the many ecological benefits that diversity brings to a woodland property, while others may have been inspired by the beauty of an old growth forest.Old growth forest at HJ Andrews Experimental Forest, Blue River OR
Of course, it takes centuries for an old growth forest to develop and many of our readers have young stands planted within the last decade or two that may look more like this:Young D-fir plantation in foothills of the Coast Range
So how do you move from one situation to another?
Happily, a landowner has many ways to influence and encourage diversity in their woodlands. Even if you have just bought some recently cut-over land, it does not have to remain a simple timber plantation if you do not want it to be. You can grow a diverse forest. And it can be done within decades rather than centuries. No, it will not be old growth, but it may help reach many of the diversity-related objectives landowners commonly mention, including an attractive forest setting, better habitat for a variety of animals and a resilient forest.A network of paths leads from any starting point in a woodland’s development. Each crossing is an event or decision that leads in a different direction and towards a different woodland condition.
In this series, we will be exploring the pathways to a diverse forest in western Oregon. These ideas also apply to an oak woodland, a riparian forest as well as an upland conifer-dominated forest. In our next post we look at what makes a forest diverse and why it matters. In later posts we will consider turns you can take throughout the life of the forest to restore, enhance and maintain woodland diversity to match your particular objectives.Another view of pathways, incorporating competitive zones leading to certain outcomes.