Tuesday, December 23, 2008

Landscape - Horticultural Ecosystems IX

This is a continuation of the series taken from a presentation that I give on sustainable landscapes as horticultural ecosystems.

In a balanced horticultural ecosystem, plants will for the most part be healthy. However, undue stress from abiotic (environmental) factors and biotic stressors (such as pests) can upset the balance. The goal in any horticultural ecosystem is to create and maintain a healthy environment. Landscape maintenance activities should be designed to maintain plant health.

Abiotic or environmental stress factors include drought/water stress, flooding, high temperatures, low temperatures, wind dessication, physical damage, salt injury, and nutrient deficiencies. Plant health can be negatively affected if these stress factors are excessive. However, moderate stress is normal and a healthy landscape can tolerate many stresses and actually will benefit in some ways. Understanding when you should intervene to reduce stress (such as with water during a drought) is key. Other stresses can be avoided by prudent landscape maintenance activities (no damage to landscape plants for example).

Biotic stress factors in the horticultural ecosystem include the common pests - insects, mites, slugs, weeds, diseases (fungi, bacteria, nematodes), rodents, and other animal pests. Many times our pests become an issue because of a lack of diversity in landscape, improper plant selection or use of poorly adapted plants, having excess environmental stress that predisposes plants to pests, or improper landscape maintenance activities that favor pests.

As stated before, the goal is to reduce plant stress. Use of organic amendments can go a long way to reducing water and nutrient stress. Proper pruning and thinning can reduce diseases by lowering humidity around plants. Providing proper drainage can reduce the incidence of root rots. It is important when considering methods to reduce stress not to upset the balance in the horticultural ecosystem. For example, excess nitrogen fertilizer can push plants to produce too much growth. This excess growth is often more susceptible to plant diseases.

To be continued.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County

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