Pest outbreaks often occur when large numbers of immigrant pests, inhibited populations of beneficial insects, favourable weather and vulnerable crop stages happen simultaneously. The depletion of soil organic matter has also reduced the food supply of soil organisms leading to less diversity of soil life, and therefore less natural control on potential pest problems.
Due to the high demand of certain nutrients in the soil by certain species has meant fertilisers are required to maintain soil fertility. This is expensive and can pollute surrounding groundwater due to leaching. When rich nitrates reach the rivers, lakes etc. they cause eutrophication.
Hedgerows have been a part of farmland since Anglo-Saxon times to mark boundaries and enclose livestock. Since the Second World War much hedgerow has been removed because of many reasons. Mixed farms have been converted to arable farms so hedgerows are not needed to contain animals. Hedgerows reduce space available for planted crops and their roots compete for nutrients in the soil; inter specific competition. Hedgerows harbour pests and are a reservoir for disease and weeds. The hedgerows also have to be maintained which costs money and takes time.
Diverse hedgerows provide habitats for at least 30 species of trees and shrubs, 65 species of nesting birds, 1500 species of insects and 600 species of wildflowers. These in turn provide food for small mammals; they also act as corridors, allowing animals to move safely between woodlands. Moreover, some of the animals they shelter are predators of plant pests; so they may reduce pests, not increase them.
Hedgerows are efficient windbreaks, providing shelter for animals and plants, and reducing soil erosion. During storms in recent years large amounts of topsoil was blown away from large unsheltered fields. The topsoil of the ground is the most fertile part of the soil. Therefore loss of topsoil causes loss of valuable nutrients. The hedgerows provide habitats for pollinating insects; so removing them can indirectly reduce the populations of other local plant species.
Conclusion
The importance of hedgerows is now being recognised, and farmers can now receive grants to plant hedgerows. However it takes hundreds of years for new hedgerows to mature and develop the same diversity as the old ones.
Some farmers are now returning to traditional crop rotations, where different crops are grown in a field each year. This breaks the life cycles of pests (since their host is changing); improves soil texture (since different crops have different root structures and methods of cultivation); and can increase soil nitrogen (by planting nitrogen-fixing legumes).
Diversity of crops above ground as well as diversity of soil life below ground provide protection against the weather, as well as outbreaks of diseases or insect pests.
