Management Methods: Physical Methods

Introduction

Management methods that use manual or mechanical means to remove, kill, injure, or alter growing conditions for unwanted plants are termed physical methods. Such methods are relatively expensive and labor intensive, and may need to be used repeatedly or in combination with other management methods. However, for socially sensitive sites and sites with high ecological value, highly selective physical methods may be desirable because of their minimal environmental impact.

The physical methods that may be applied to invasive plants in terrestrial and aquatic environments are many and varied. They vary in the type of injury or stress they inflict, their selectivity and potential for nontarget impacts, and the procedures, skills, equipment, labor, and funds they require.

Ever since people began to prefer certain assemblages of vegetation over others, they have manipulated plants in the environment. Vegetation management in its earliest form used simple physical methods—removing some plants and adding or sustaining others.

Over time, the physical methods and tools used in agriculture—that is, in growing crops and removing unwanted plants—were adapted for other situations, such as gardens, pastures, roadsides, and wildlands.

Physical Methods for Terrestrial Habitats
Mowing common reed (Phragmites australis) at Rachel Carson NWR in Maine. Photo credit: USFWS
Pulling	remove the plant from the soil; requires only a pair of work gloves; pulling tools may be used for large plants, shrubs, or trees
Hoeing	scrape seedlings from the soil or cut off small plants just below the soil level; a variety of hand-held tools may be used
Tilling	break, cut, or uproot plants from the soil and alter soil environment; use equipment such as plows, blade plows, harrows, and cultivators
Mowing	cut or shred aboveground vegetation; mechanical mowers may be used, or hand-held sickles, scythes, or machetes
Cutting	lop off plants at ground level; saws, axes, and loppers are used
Stabbing	damage the underground carbohydrate storage structure (e.g., taproot, root corm, or rhizome); spade, pruning saw, or knife is pushed into the storage structure
Girdling	cut away a strip of bark several inches wide around trunks of trees or woody vines to interrupt the flow of nutrients to leaves and active growing points (meristematic tissue); cuts are made with a knife, ax, or saw
Chaining	drag a heavy chain between two tractors to crush or uproot shrubs or trees
Mulching	physically impede plant growth and exclude light from germinating plants; mulches may be organic such as straw, sawdust, or crop residues, or synthetic such as woven plastic or nylon
Soil solarization	cover damp soil to trap heat and increase soil temperatures to levels that are lethal to plants and seeds; use clear or black plastic
Flooding	cover an area with water deep enough to completely submerge plants, altering oxygen levels available for plant respiration

Physical Methods for Aquatic Habitats
Mechanical harvester collecting floating water chestnut plants (Trapa natans) in Silvio O. Conte NFWR. Photo credit: USFWS
Harvesting	use mechanical harvesters to cut a wide band of vegetation from 5 to 10 feet below the water surface, then collect the biomass and deposit it on upland sites
Diver dredging	divers remove entire plants including the sediment in which they grow; floating plant fragments are collected at the water surface and removed to prevent re-establishment
Benthic barriers	pin or weight groundcover cloth or erosion control material to the lake or river bottom to smother aquatic plants
Water drawdown	use a water control mechanism to lower lake, reservoir, or river water levels below the depth of targeted aquatic species

A benefit of physical methods is that volunteers can participate in management efforts without special licenses, equipment, or training. Photo credit: J Jeffrey/USFWS

Physical methods typically employ simple, readily available tools and equipment. However, the effectiveness, impacts, and expense of physical methods can vary greatly depending on the type of method used and the characteristics of the infestation.

Some physical methods can be quite labor intensive and therefore expensive, but these usually have low environmental impact and are therefore appropriate for small, localized infestations or infestations in ecologically or socially sensitive areas. Physical methods that can be applied more easily over larger areas, may have more significant nontarget effects.