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Scotland's Native Trees and Shrubs
Rich assortments of species are efficient
Darwin observed 150 years ago that ecosystems with a rich assortment of species work better than ecosystems with fewer species. Rich assortments of species growing together with different shaped and positioned leaves make more efficient use of sunlight and nutrients and consequently make more growth. The root systems of different species also reach down to different depths, drawing in different resources of water and nutrients. This explains how and why trees prefer to grow in intimate relationships with one another, why inter-cropping in agriculture brings benefits in total yield and why agronomists mix tall and short growth amenity grass species together and legumes with fodder species.
As landscape designers, we need to learn more about these natural woodland systems for they have an enormous potential to enrich our new landscape with self-perpetuating life and energy. They have the additional advantage of being more robust and less vulnerable to damage when conditions change. In the long term this could become relevant in the light of climate change. In the meantime, it could reduce the incidence of wind-throw.
It is evident from observation that pine, birch and rowan like to form close relationships with one another. The three species grow well together as one container grown unit. This one is surviving, without protection, despite the rabbits having free access. Look closely at the birch. Insects find them irresistible.
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It is all too easy to cast non-native species in the 'bad for nature conservation mould'. This is not necessarily so. This Spanish chestnut (Castanea sativa) in a mixed woodland has been selected by the lesser-spotted woodpecker as its 'drumming post'. Can you spot the drumming position? | Trees are gregarious. They prefer to grow with companions, living together in communities for mutual benefit. | Multi-species unit of pine and oak planted on the A9 in Tayside. Oak and pine may seem odd bedfellows, but they seem to enhance each other's performance and make optimum use of ground space. Is it because as the roots of the oak penetrate deep down to the substrate the soil above is improved for the shallow spreading root of the pine? |
As has been described, the selection of species is made by firstly determining the appropriate National Vegetation Classification / NVC community. W18, for example, in its simplistic form is basically Scots pine, silver birch, downy birch, rowan and common juniper.
The NVC can be used as a basis for the relative abundance and average percentage cover of different species to be used in a planting scheme and can give details of the final dominating influences in the vegetation, as well as a comprehensive species list. However, the NVC cannot be used to understand the small-scale geographical clumping and species associations that often occur in woodland and scrub situations and give that woodland its particular local landscape character.
Often these patterns are related to local environmental conditions, for example, clumps of even aged ash are frequently found in areas where a large canopy tree has fallen in the past and full sunlight and higher temperature has allowed a group of ash seedlings to germinate and grow at the same time. These details can only be accurately surveyed by visiting the site. For the uninitiated this exercise can be a revelation. These locally distinctive characteristics will demonstrate how to use natural characteristics in planting design. It could, for example, illustrate a particular variation of randomness in species, spaces and assemblages, as the road passes from one landscape character zone to another.
All too often this ecological and landscape character survey information is compiled during the planning stages of a scheme and not translated with enough attention to detail by the landscape designers at the detailed design stage. This practice must change. In future, landscape architects preparing planting schemes for the Scottish Executive will be required to demonstrate that they have undertaken and recorded the findings of a detailed site investigation and that they have taken these into account in their design.
The same attention to detail that is afforded to prestigious urban ornamental planting designs will in future be required for new planting in the countryside.
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Designs from nature: Some of the land within the corridor of the proposed M74 extension south of Glasgow is contaminated by chromium waste. A desk-based discussion could not resolve what trees would grow in such conditions. A visit to the site gave us the answer. | Honeysuckle planted as a companion plant with oak. |
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