Most people would assume that any tree, even a few, would make a good place for wildlife. A couple of trees around the roads and gardens should provide habitats, right? Well technically that is true, however on more occasions it is inadequate. Trees in towns and cities are important for many birds, but it is unlikely that different varieties will colonize these trees because there simply isn’t enough territory and food to sustain them.
The example above is a common picture, with many areas of woodland being removed for roads, and conurbations. Trees that are then planted to balance the removal of the forest usually result in a discontinuity in habitat and therefore a reduction in diversity. It may look nice in and around towns, but they provide few homes for our wildlife. Don’t get me wrong, trees need replacing if removed as it breaks up our urban jungle. An example of this problem was at a recent conservation event that took place in a reserve near an airport. Ash trees planted to replace trees removed seemed a blessing (there was a protection rim around the tree’s trunk), but they are extremely fast growing and prevalent self seeders. There were ash trees all around that had grown naturally too, yet this area near the airport had a policy: remove one tree and plant two. This on the outset sounds great, however the trees needn’t be planted, well at least not this species. Most likely they were the cheapest, fastest growing and the original reserve management thought it was a good idea. It makes it look like your implementing a green alternative for wildlife on a large scale construction project when it really has no benefits for wildlife.
Species diversification is an important element for any healthy woodland reserve. Where there is a lack of variation the woodlands become devoid of wildlife. If, dominated with one particular species such as silver birch, then there is a reduction in the number of habitats available for wildlife. The silver birch is good for some insects, some nesting birds like flycatchers and wood warblers, but few others. It self-seeds and grows very quickly, similar to ash, as well as growing tightly together creating thick impenetrable vegetation. The problem is that it makes it difficult for other tree species to seed and grow, as well as mammals and birds to colonise and find food. Blue tits rely on the spring growth of oak trees due to the high concentration of grubs and caterpillars that oaks support. With a lack of oaks in a particular area blue tits cannot rely on them for food and can sometimes move elsewhere.
Species variety is also important to prevent distribution of disease. Forests dominated with elm trees, for example, would result in the disease quickly spreading because there closely connected. The mix of species creates natural breaks in woodland as well as different habitats like grasslands in a well-managed space, that prevent the spreading of the disease.
Another important but similar issue to diversification is that of non-native species. The assumption of any tree or shrub being beneficial to wildlife is again false and in fact does the opposite. Rhododendrons are a case that seems beneficial for wildlife, growing fast and flowering, yet they take over a woodland reserve. They dominate heathland areas and reduce the biodiversity rapidly growing faster than the heather. No other ground dwelling plants can compete, heather and wild flowers die and the nectar they produce can also affect bees and other insects.
Woodlands that have differing structural height give the best habitats for wildlife. When there is mix woodland, grasslands and small bushy areas wildlife can thrive in huge numbers. Heathland, for example, often has patches of bracken, small trees, giving a mixed habitat, which creates a greater concentration of different species. Coal tits, chaffinch as well as buzzards and other birds of prey are found in heathland and grasslands because of the variety of food. Examples with a lack of diversity includes pine forest, growing high and blanketing the forest floor. Personally I find pines, particularly Scots pine, magnificent, growing to such heights and having such an amazing aroma. The main issue with these tall trees is the lack of sunlight and warmth that reaches the ground. However, if we mix pines, oaks and other trees this creates different shapes and geometry, leaving areas of the ground exposed for shrubs and grasses to grow.
This sounds slightly trivial but it is important for any woodland. Obviously I’m not referring to human rubbish, instead natural waste like leaves, branches and dead trees. The leaves are important for the bottom of the food chain, the fungus, and the mushrooms that feed on the rotting material. These then provide a source of food for smaller mammals and invertebrates. This then leads on to providing food for foxes, badgers and birds of prey. Dead tree stumps are a perfect home for great spotted woodpeckers as well as perches for buzzards. However, the increase in health and safety procedures and the rapid removal of deteriorating trees make this convenient home disappear before it can be used. The added benefit of trees either pulled down in storms or weakened by disease could open up a large patch of forest to sunlight creating new habitats scattered within woodland.
All trees are not equal, different varieties are essential to create a diverse wildlife environment. Before planting a tree, think about what is its purpose, what wildlife are you trying to attract… To attract birds, insects, mammals and other wildlife the easy response of planting trees never fulfils the brief of a wildlife reserve. A combination of woodland, heathland, grassland and wild flowers create the most diverse habitats providing food and homes. Basically trees themselves aren’t enough, where wildlife thrives across the UK it is directly because of this natural mix.
It all links back to the topic of rewilding. If we want to reintroduce species such as lynx we need a healthy ecosystem to sustain them. If we want to reintroduce extinct mammals then we need to restore and rewild the countryside with this mix of habitats.
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