Hemp is nevertheless exceptionally suitable for organic agriculture, and is remarkably less "ecotoxic" in comparison to most other crops. Figure right presents a comparison of the ecological friendliness of Hemp crops (fiber, oilseed, and narcotics) and 21 of the world's major crops, based on 26 criteria used by Montford and Small (1999a) to compare the ecological friendliness of crops.
The most widespread claim for environmental friendliness of hemp is that it has the potential to save trees that otherwise would be harvested for production of lumber and pulp. In so far as hemp reduces the need to harvest trees for building materials or other products, its use as a wood substitute will tend to contribute to preserving biodiversity. Hemp may also enhance forestry management by responding to short-term fiber demand while trees reach their ideal maturation.
The most valid claims to environmental friendliness of hemp are with respect to agricultural biocides (pesticides, fungicides, herbicides). Hemp is known to be exceptionally resistant to pests, although, the degree of immunity to attacking organisms has been greatly exaggerated, with several insects and fungi specializing on hemp. Despite this, use of pesticides and fungicides on hemp is usually unnecessary, although introduction of hemp to regions should be expected to generate local problems. Cannabis sativa is also relatively resistant to weeds, and so usually requires relatively little herbicide. Fields intended for hemp use are still frequently normally cleared of weeds using herbicides, but so long as hemp is thickly seeded (as is always done when hemp is grown for fiber), the rapidly developing young plants normally shade out competing weeds.