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Disturbance theory

Ecology 7. Disturbing News for Bowling Clubs

In 1988, Grime, Hodgson and Hunt published their study called “Comparative Plant Ecology – A functional approach to common British species”, which on the face of it sounds like ideal bed time reading for insomniacs. However, the work these scientists carried out might make you sit up in bed and take notice when you realise how relevant it could be to the performance of your bowling green.

In this work, the authors state that vegetation that develops in a place at a particular time is governed by environmental pressures. These pressures may be categorised as stress, disturbance and competition (S, R and C) and that these vary in their relative intensities. Individual species develop their own growth strategies in order to deal with their own environmental pressures.

In Performance Bowling Greens, I introduced the concept of Disturbance Theory which is simply a way of thinking about and defining the growth strategies of each of the fine grass species we aim to grow on our bowling greens. Furthermore, by relating this Disturbance Theory to our greenkeeping calendar we can develop programs and strategies to help us create the environmental conditions that favour the species we know will produce the finest bowling surface. In the UK these are the bent and fescue grasses, but Disturbance Theory holds up for any environment, including the warm season areas of the world.

In a nutshell, Disturbance Theory encapsulates the main themes of the previous 6 articles (imaginatively labelled Ecology1 to 6) on bowling green ecology and attempts to become the go to tool for greenkeepers to help them manage their greens in a manner that heeds the importance of ecology in bowling green maintenance. In particular it should help give lay people an understanding of how to manage the bowling green in favour of a dominance of the finer grasses. If allowed to develop, the bent and fescue grasses will provide improved playing qualities and reduced vulnerabilities compared to annual meadow-grass.

To be able to manage your bowling green eco-system correctly it is necessary to understand the nature of the pressures.

■ Stress (S) is defined as the environmental constraints to growth. This may include soil moisture (too much or too little), poor fertility (too low or too high), low temperatures, soil acidity and/or salinity.

■ Disturbance (R) is the physical damage occurring within the environment. This is particularly important for bowling greens due to our reliance on regular mowing as the main route to preparing the green for play. Regular disturbance imposes what ecologists call “selection pressure” on the environment.

■ Competition (C) is the struggle between plants to survive and assume dominance within the environment. Some plants have evolved to naturally assume dominance given the right conditions. The continual removal of leaf tissue by mowing would seem to stack the odds against our fine grasses, but these species have developed naturally in closely grazed environments, like we see on the Machair.

Of course as we’ve increasingly become aware of over this series on ecology, environmental pressures rarely act alone. There is invariably a combination of factors and stresses at work in our greens and this is largely what dictates the nature of the growing environment.

Each species has strengths and weaknesses depending on which environment they evolved to survive in. The bents and fescues are considered to be C-S-R strategists as they do not welcome too much disturbance pressure but will put up with some stresses such as mowing quite well. Poa annua (annual meadowgrass) is considered an R strategist that thrives under disturbance but does not welcome too much stress. It is quick to establish in space but struggles to get a hold in a tight knit turf of finer grass. This gives us a strong indication that what we need to do to ensure our greens favour the finer grasses is to minimise the level of disturbance and use stress as a beneficial selection pressure against the annual meadow-grass.

To set the correct environment we need to be able to play with the pressures.

Next time we will investigate further what the greenkeeper can do to influence the level of environmental pressure on the bowling green and how we can harness the effects of ecology to our benefit.

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