Guilds: Collaborative Associations of Plants
Guilds are made up of a close association of species clustered around a central element (plant or animal). This assembly acts in relation to the element to assists its health, aid in management, or buffer adverse environmental effects.
We have long recognized companion planting in gardens, and crop mixes of various species in agriculture that do well together. Hence the concept of guilds which rely on composition and placement of species which benefit (or at least do not adversely affect) each other. Benefits can include:
- Reducing root competition
- Providing physical shelter
- Providing nutrients
- Assisting in pest control by providing chemical deterrents (Tagetes marigolds fumigate the soil of certain types of nematodes); hosting insect predators (umbelliferous plants such as dill, carrot, and fennel); and using animal foragers such as chickens to clean up fallen fruit.
Pest Control Through Guilds
Umbelliferous and composite plants such as dill, fennel, daisies, and marigolds placed around the garden attract predator insects (insects that feed on parasite pests). Ponds in the garden attract insect-eating frogs. Suitable nest-boxes or thorny shrubs provide a habitat for insectivorous birds. Fungi and beneficial bacteria or nematodes have also been used to control insects, and many plants provide insect control or nematode control.
Of great importance in crop mixtures are pest interactions and functions of the plant species involved:
- Insectary plant: the plant acts as a host (a food plant) for predatory insects which prey on the crop pests.
- Sacrificial plant: pests attack this plant preferentially, which nevertheless does not prevent it setting seed. Other plants nearby escape severe predation.
- All-season host: pests overwinter or live in this type of plant, enabling them to build up larger populations (e.g. pests of citrus are hosted off-season by oleanders).
- Predator or pollinator attractor plant: the crop or hedgerow species provides flowers to feed the adult predators (e.g. buckwheat in or near a strawberry crop).
- trap crops: some crops can attract or kill pests, or the pests can be caught or destroyed on those crops.
These important functions are served by trees, shrubs, flowers, and vines, so that any farmer who carefully selects hedgerow species to be in one or more of the above categories has substantial pest control capabilities.
If we have a system with diverse plant and animal species, habitats, and microclimate, the chance of a bad pest situation arising is reduced. Plants scattered amongst others make it difficult for pests to go quickly from one food plant to another. However, once pests do breed on any one tree, insect predators perceive this as a concentrated food source and will congregate to take advantage of it. In the monocultural situation the food for pests is concentrated; in a polyculture, the pest itself is a concentration of food for predators.