Communities and lime-loving plants

The area surveyed was an area of chalk grassland which is managed in three different ways. Chalk grasslands are characterised by shallow soil which is lime rich and overlies limestone rocks such as chalk. The grasslands are home to a wide range of plant communities and lime-loving plants are abundant in the huge variety of flora, many of whom are considered rare (UK Biodiversity Plan, 1998).

This richness of flora species supports diverse invertebrate species and provides feeding or breeding habitat for a wide range of birds. Because of the huge amount of diversity supported in these areas it is important to understand the plants strategies such as the habitat requirements of the young plants and seeds, in order to manage the grasslands appropriately (Rorison and Hunt, 1980). These plants competing for space and light above ground and nutrients and water underground develop tall with high biomass and a reduction in this competition intensity can be limited by stress and disturbance (Rorison and Hunt, 1980).

Stress includes the factors which restrict production such as a lack of essential water, light and nutrients and disturbance includes partial or semi-destruction of plants by such outside factors as man, herbivores or weather related causes (Rorison and Hunt, 1980). Many forms of stress come from the vegetation itself and disturbance at low intensities can work to reduce this stress by reducing competition and it is this idea which shall be explored for this report.

To this end, a survey was made of an area of chalk grassland which had three different management techniques. These were an area fenced off and grazed by sheep, an area mowed twice yearly and an area of abandonment. The abandoned area has been left to its own devices and it is probable this area has higher biomass and taller plants but as dominant plants would succeed in out-competing lesser able ones, this area perhaps would have the least plant biodiversity. It is necessary to compare the differences in success of the grazed and mown areas, which it is thought would have higher diversity due to the disturbance which is modifying competition.

Mowing and grazing has the effect of causing tall competitors to be displaced and allow the typical grassland stunted species to flourish close to the ground surface (Rorison and Hunt, 1980). It has been hypothesised that the areas which have been traditionally managed by grazing would provide more of an opportunity for plant diversity and the abandoned area with least diversity and dominance by taller species. It is the purpose of this report to investigate whether a return from non-management (abandonment) to mowing the grasslands would suffice as an alternative management technique and indeed which technique of the three is most successful for supporting as high diversity as is possible in the chalk grassland area.

8 quadrats were surveyed in each of the three different areas of management. In all of the randomly chosen quadrats the heights of the 4 tallest plants and the height of the smallest were recorded. The percentage cover of ground taken up by bare ground, litter, moss, grass, forbs and woody species was estimated. The number of species and open flowers were recorded to try estimate the amount of biodiversity in the area.

Results

Figure 1 above shows the mean heights of the 4 highest and 1 smallest piece of vegetation that was recorded in the samples of each of the three areas. It is possible to see clearly from this diagram that the area which has been left wild has had the most height, with the grazed area with the least height. These results were to be expected given that sheep in the grazed area would be continuously grazing down the vegetation here, so it would have little chance to reach the heights achieved by those left to grow wild. Mown vegetation is kept in check with bi-annual mowing so it is at an intermediary stage.

Figure 2 Sample mean number of species and open flowers Keeping this information in mind, it is now possible to view the number of vegetative species which were recorded in the three sites. The grazed area had the highest number of species recorded with the wild areas having the least. The results for number of species reflect the contrasting heights which were recorded. The areas with the most height had the least species because it is in this area that one or a small number of dominant species took hold, out-competing the other species for resources such as light, water and air.

In all three areas the percentage ground cover was estimated and the means of these data are recorded below. In these three areas bare ground, moss and woody species made up the smallest percentages of cover with some areas with none of the above. Woody species were most visible in the wild area, suggesting these species are dominant species which will flourish when abandoned, although they were also visible in the grazed area.

Hawthorn were absent from the mown area so perhaps the trees were purposefully removed. Although the Hawthorn was taking over the wild area, in the grazed area their numbers were at a more suitable level. It is important that the Hawthorn are managed well so that the land is still available for livestock and humans to use, but also so there are trees which provide an important nesting and food sources for birds.

Moss was found in the abandoned and to a higher extend in the mown area, but was absent from the grazed area. Moss can be found in all types of habitats but the majority of its lifecycle occurs when the plants are wet (Simon et al, 1977), suggesting that the high density of litter and taller plants were creating an atmosphere suitable for moss growth underneath but perhaps this moss growth is restricting the water availability also.

In terms of biodiversity, the wild area had the lowest recorded plant species variety which is due to the high stress in terms of plant height and the lack of disturbance. The lack of disturbance has resulted in high productivity, which has as a result produced high amounts of litter which add stress to the short competitors. However this high amount of litter and taller species may provide small mammals and birds with areas for nesting and shelter, thus increasing the faunal biodiversity here. The high productivity above ground would support a large amount of invertebrates who are acting as decomposers.

The grazed area had the highest number of plant species which were mainly made up of forbs and grasses, but no open flowers were recorded. Heights were low here and it was found that those that made up the height we hawthorn offspring who were beginning to develop. This type of management supports a higher variety of plants species but the plants were also perhaps grazed too much, not allowing much growth or flowering to develop and thus not supporting much faunal diversity.

The mown area had a middling range of diversity but the small differences in recorded value are not enough to support this. It had the most open flowers and from surveying the area more species of insects were supported in this area. In terms of ease of access for walking by people the grazed area was the most accessible but the mown area was also quite accessible. The abandoned area was not user friendly from a human perspective.

The methods and inexperience of the surveyors should also be considered here, and although data may support the findings, it has been beneficial to put this information together with thoughts which were gathered on the day. It was difficult to count the number of species and although similar numbers of species were recorded, many of the species were of very different variety in all three areas. Some species could be visible in just one of the areas for example. In managing the plant community it is necessary to take into account all those who are dependant on it, such as the farmers, walkers, birds, mammals and insects, so a suitable technique can be found to suit this complex mix of users. It would also be essential to consider which plants are most rare and how to support these.

In conclusion I would recommend a combination of management techniques as this seems to be working well, if anything I would reduce the amount of areas which were abandoned, but ensure the preservation of hedgerows and large shrubs. I think if the whole area was open to being grazed it would cut out the need for mowing and would allow for plants to grow if smaller herds of sheep were employed.

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