The Planting Design Handbook by Nick Robinson

Author:Nick Robinson [Robinson, Nick]
Language: eng
Format: azw3, pdf
ISBN: 9781317021247
Publisher: Taylor and Francis
Published: 2016-06-17T04:00:00+00:00

Competition and Coexistence

Plants in any wild community or designed assemblage interact. If we observe, we can see two types of interaction. Competition, in which the success of one species leads to the suppression or demise of another, is a familiar concept in ecology. But plants also benefit from or even depend upon other plants and animals, and it is this web of different kinds of relationships within a habitat that forms the basis of a functioning ecosystem. An obvious example of a beneficial relationship would be the dependence of an epiphyte on its host – the epiphyte (perching lily, vireya rhododendron or orchid for example) has adapted to the opportunity of higher light levels provided by the supporting trees. The trees that support the epiphytes also create the shade, shelter and humidity that allows the growth of shade loving understorey species that could not survive in the open. An example of a mutually beneficial relationship between organisms in plant communities is the mycorrhizal relationships many plants have with fungi in order to provide them with inorganic compounds and trace elements.

Another example of plant coexistence is provided by research into the patterns of growth of three herbaceous species in a roadside plant community in Southern England for a period of over thirty five years. This investigation (summarized in Dunnett, 2004) followed the annual growth of three species, Chamaenerion angustifolium (rosebay willow herb), Arrhenatherum elatius (tall oat grass) and Stachys sylvatica (hedge woundwort), measuring their height and biomass production. An interesting observation to emerge from the data was the different kind of relationships between the three species and how the success of one affected the others. Chamaenerion and the Arrhenatherum appeared to be in direct competition; the height and biomass production of one species was more or less inversely related to that of the other – as one grew more dominant the other declined. The growth and productivity of the Stachys, however, mirrored that of the Chamaenerion, increasing as it spread and decreasing as it declined. This is because the woundwort is adapted to the partly shaded niche that exists in the spaces immediately adjacent to the willowherb and has effectively formed a kind of ‘alliance’ with that species.

So it is helpful for designers to understand the both the competitive and the beneficial relationships likely to exist between plants grown in close proximity. We should aim to avoid planting the most aggressive species where they would exclude others and also to combine species that can coexist in related niches. To do this we need to be aware of just how the more competitive species achieve their typical dominance in a community and whether they leave opportunities for other plants to coexist in close proximity. Some trees, shrubs and herbs are capable of very rapid extension of the foliage canopy – they ‘forage’ for light, searching it out and shading nearby plants in the process; these competitive species need to be located to ensure that they do not suppress slower-growing and shade-intolerant neighbours.

Shrubs

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