What are Weeds?

A quick definition

There are many definitions for weeds, but in reality they are simply plants that are growing in places where they are not wanted. They may have a negative impact on the plants, animals, landscape or physical processes that occur where the weed has established itself. In New Zealand weeds are becoming a significant issue for both conservation managers, farmers and urban householders. Most weeds in New Zealand are introduced species that have readily adapted to our unique climate, landscape and ecosystems. Many weed species can be best be described as “transformers” or “environmental pioneers” because they transform the original environment they have invaded into habitats that suit their reproduction and resource use traits through their dominance. They also transform and alter the physical processes such as water movement or sediment flow that were present before their arrival.

What Makes a Weed?

Weeds have specific characteristics that often distinguish themselves from other plants in terms of their reproduction, growth and the resources they use to survive. When weeds are introduced into a new environment they often rapidly grow and invade that new environment more effectively than the native species that would be normally be found growing there. Weed species often share similar characteristics that make them successful invasive plants in new habitats.

Reproductive Strategy	·Vegetative reproduction ·Production of large amounts of viable seed ·Non-specialist pollination & dispersal mechanisms ·Sexual & asexual reproduction
Phenology	·Early maturity ·Perennial vs. annual ·Fast growth to compete life cycle ·Phenotypic plasticity (adaptation to environmental stress)
Resource Use	·Allocates resources toward reproduction and seed production ·Allocates resources towards growth ·Broad niche user ·Rapid response to resource (space, water, nutrients) utilisation  as they become available

 How do Weeds Affect Wetlands?

Without weed control wetlands like Waihola and Waipori will continue to be choked by Willow, Alder and Glyceria. This will affect water movement, water quality, siltation of the channels and eventually displace the native vegetation that supports fish, bird and invertebrate species. The result is the gradual degradation of the catchment that will spoil the recreational activities people are used to enjoying in the area, as well as displacing the plants, fish and bird species that have become an integral part of the life of the area.The risks to the long term management of the Waihola Waipori area are actually greater without weed control. The siltation of the lakes caused by the trapping of sediment in willows will gradually mean the lakes will become shallower and smaller.