The term “temperate rainforest,” or “Celtic rainforest,” has been rapidly gaining public attention in the UK recently.
In February 2023, the British insurance company, Aviva, provided £38 million in funding for the restoration of these rainforests. These restoration efforts have even caught the interest of Prince William, who has announced plans to double the size of Wistman’s Wood, an iconic piece of ancient woodland on his Dartmoor estate.
Britain was once covered in trees. But for thousands of years, the ancient forests in the wetter parts of the west of the country have been cleared and turned into pastures for sheep and cattle. At the turn of the 20th century, Britain and Ireland became the least forested region in Europe, with only small patches remaining on the west coast of the rainforest zone in both countries.
But how much of this forest is actually considered rainforest? The complex diversity of different forest types makes it difficult to classify them as rainforest or non-rainforest. And while Britain and Ireland’s climate is wetter than southern and eastern Europe, the question remains: How wet is wet enough to support a rainforest?
To understand if an area can support a rainforest, it is important to consider not only the average annual rainfall, but also the rainfall throughout the seasons. Other areas of the Mediterranean basin may receive the same amount of annual rainfall as parts of Great Britain. But this rain is concentrated in the winter, and long periods of drought during the summer prevent the formation of a recognizable rainforest.
In Britain and Ireland, the climate is characterized by low rainfall seasonality, with dry summers being the exception rather than the rule. However, most climate models predict that this will change in the future, meaning that very few areas of these islands will be able to support rainforests.
But rainfall alone does not determine the presence of rainforests. Groundwater availability, which is influenced by factors such as soil depth, texture and organic matter content, plays an important role in supporting rainforest trees. Even in areas with high rainfall, thin soils can lead to drought-prone conditions.
So this leaves us with a problem: How do you see a rainforest in Britain and Ireland?
1. Characteristic plant type
The most iconic plant types characteristic of temperate rainforests are epiphytes. These are plants that grow above the ground and attach themselves to the trunks of trees or shrubs.
Epiphytes, including orchids, are an important part of the biodiversity of tropical rainforests. In contrast, most epiphytes in temperate rainforests are “lower plants,” such as ferns and plants that lack vascular systems to move water within them, such as mosses, liverworts and lichens.
2. Horizontal rain
Epiphytes get some of their moisture from water that runs down tree trunks during heavy rains (a process called “stem flow”). But these plants are not only dependent on rain.
In mountainous or coastal environments, where soil or fog is common, another important source of moisture for epiphytes is horizontal rain (water droplets suspended in clouds). This source of moisture is especially important for epiphytes that are most susceptible to drought, such as filmy ferns and some mosses and lichens.
3. Tree climbers
The UK’s temperate rainforests have many other features reminiscent of their tropical counterparts. One such feature is woody climbers (or lianas) that use trees to climb up into the forest canopy. Classic examples of these plants in Britain and Ireland are ivy, clematis and honeysuckle.
However, the presence of tree climbers alone is not indicative of a temperate rainforest. While ivy, for example, is most abundant in wetter forests, these three liana species are found in a variety of woodlands in Britain and Ireland, even in the drier eastern regions.
4. Tree structure
Tree species found in the rainforests of Britain and Ireland are not good indicators of their rainforest status. The dominant canopy tree is mostly the sessile oak, which is the only species that dominates many of the forests that produce high-quality straight oak trees in northern France.
What better distinguishes a rainforest in Britain or Ireland is the structural characteristics of the trees. In rainforests near the west coast, such as Dartmoor, trees tend to be short, with leaning trunks and low branches.
However, this less tree structure may not be a direct result of high rainfall. Canopy trees in temperate rainforests in the wetter coastal areas of Oregon, Washington State and British Columbia in North America reach at least twice that height (40 meters or more). The distinctive short stature of Britain’s rainforest trees is probably influenced by a combination of factors, including exposure to strong winds and uncultivated thin soils, both characteristic of the Atlantic coast and mountains of western Britain and Ireland.
The temperate rainforests of Britain and Ireland are fast gaining iconic status, creating a vivid image of mist, moss and tangled trees.
But these groves are more than visually appealing—they’re unique habitats important for many endangered species, especially epiphytes. Unfortunately, they are also vulnerable to the effects of climate change. This makes them an appropriate focus for new initiatives aimed at their restoration.
Provided by Bangor University
Citation: How to recognize a temperate rainforest in Britain and Ireland when you see one (2023, July 13) retrieved on 14 July 2023 from https://phys.org/news/2023-07-temperate-rainforest -britain-ireland.html
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