Types of Forest Plantations: Stand Structure, Canopy Layers, and Species Mixes

libre

July 24, 2015 1 reads

Forest stands are described and classified by foresters using a small set of consistent traits: how many canopy layers they form, which tree species are mixed together, and the overall age of the trees. Imagine standing in a forest as a forester, tasked with describing the types of forest stands and giving each a profile.

Types of forest plantings — At first glance the sheer number of trees can be overwhelming — different species, trees of every size, some crowns rising above others in what looks like complete confusion. Once you settle and start noticing patterns, the apparent chaos resolves into clear categories.

What is the forest canopy and how are layers identified?

The forest canopy is the layer formed by tree crowns sitting at roughly the same height, and counting these layers is the first step in classifying a stand. Look closely and you may see that the tallest trees are spruces, their crowns aligned on one level to form a single canopy. A little lower, aspens look stressed beneath the spruce canopy — clearly cramped and short of light — forming a second canopy of their own.

Aspen and birch typically appear beneath spruce only during a transition of species. These layering signs are exactly what foresters use to tell stand types apart:

When a single canopy rises above the ground, the stand has a simple, single-storey form.
When a second storey grows beneath the first, the stand has a complex, multi-storey form.

How do tree species differences define a stand?

The mix of tree species determines whether a stand is called mixed or pure. Where aspen, spruce, birch and linden all grow intermingled, the species blended together are termed mixed stands. Cross a quietly murmuring stream into a grove of nothing but pines, and that community is a pure, single-storey stand.

Complex multi-storey stands form naturally because trees grow at different rates — even within one species and one age class, some grow faster and others more slowly. This difference in growth speed is the engine behind layering. The way it plays out depends on the species present:

In mixed (non-pure) stands, fast-growing species such as birch, larch or aspen outpace the shade-tolerant slow growers and build an upper canopy above them — sometimes even two.
In broadleaf-spruce stands the first storey is usually formed by light-demanding species — aspen or birch.
In three-storey oak woods the structure is more intricate: the first storey usually holds oak and ash, the second is built by linden, Norway maple and elm species, and the third by field maple and, again, linden.

Birch forest belt — In practice, complex mixed stands tend to be more stable than simple ones — they make better use of light, heat, moisture and soil, and are more wind-resistant. Complex storeys made of a single species do occur, but only rarely. They arise from trees of different ages: old trees occupy the upper storey while younger trees fill the second and third.

How is the age of a forest stand determined?

The age of a forest stand is judged from the prevailing part of the tree layer, because a stand contains trees of many different ages. When a stand is complex and multi-storey, the age is determined separately for each storey. Getting this right matters for any practical use of the forest.

Foresters use specific terms for age classes — words like mature, ripening and pole stands. Tree layers are conventionally divided by age:

Pole stands — the tree crowns have already closed together.
Young growth — saplings whose crowns have not yet closed.
Middle-aged stands — defined by a different quality: fruiting begins and growth increment is at its best.
Ripening stands — trees are starting to slow their growth.
Mature stands — growth has almost stopped.
Overmature stands — likewise give almost no increment.

Overmature stands also carry a large number of diseased and damaged trees. Accounting for all of these qualities is very important in the practical management of forests.

Why do complex stand forms occur?

Complex stand forms are never accidental — they follow consistent ecological rules, with a cause behind every structure. Light-demanding species, because they thin out early, always tend to form complex, multi-storey, mixed stands. Oak, forming the upper storey, allows ash, maple and elm to settle beneath it.

Pine also loves light, so it is inclined to form complex stands. It can be found together with various species — with spruce, fir, beech, birch and so on. On the other hand, it also forms pure pine groves (more on this: what types of forest exist). It all depends on soil quality, since not every species is as undemanding as pine.

Multi-storey forest stands are built by species with differing shade tolerance and, therefore, differing growth rates. Much depends on this, and once you understand these relationships between trees, it is no surprise that spruce can form a second storey beneath pine, while pine cannot do the same beneath spruce — owing to its need for light (more on this: how a pine forest comes to be).

Frequently Asked Questions

What are the types of forest plantations?

Forest plantations are classified by structure and species composition. By structure they are simple (single-tiered) with one canopy layer, or complex (multi-tiered) with two or more layers. By species they are pure stands, made of a single tree species, or mixed stands containing several different species growing together.

What is a simple versus a complex forest stand?

A simple, single-tiered stand has only one canopy layer rising above the ground. A complex, multi-tiered stand has additional layers beneath the first, such as two- or three-tiered structures where shorter trees grow under taller ones.

What is the difference between pure and mixed forest stands?

A pure stand consists of a single tree species, like a forest of only pines. A mixed stand contains multiple species growing together, such as spruce, aspen, birch, and linden intermingling within the same area.

How do complex multi-tiered stands form naturally?

They form because trees grow at different rates. In mixed stands, fast-growing, light-loving species like birch, larch, or aspen outpace slow-growing, shade-tolerant species, forming an upper canopy above them and sometimes a second layer below.

What is a forest canopy?

A forest canopy is the layer formed by tree crowns at roughly the same height. When trees of similar height align their crowns, they create one canopy level; multiple species at different heights can create several stacked canopy layers.

What species form the layers in a three-tiered oak forest?

In three-tiered oak forests, the first tier typically holds oak and ash, the second tier consists of linden, Norway maple, and elm species, and the third tier contains field maple and linden.