A comparison of the biodiversity friendliness of crops

A comparison of the biodiversity friendliness of crops with special reference to hemp (Cannabis sativa L.)

P.O. Box 228, Alcove, Quebec JOX 1AO, Canada
e-mail: <smontford@hotmail.com> fax: +1 (819) 459-1495

Eastern Cereal and Oilseed Research Centre, Research Branch, Agriculture and Agri-Food Canada,
Central Experimental Farm, Ottawa, ON K1A OC6, Canada
e-mail: <smalle@em.agr.ca> phone: +1 (613) 759-1370, fax: 613-759-1599

Montford, Suzanne and Ernest Small 1999. A comparison of the biodiversity friendliness of crops with special reference to hemp (Cannabis sativa L.) Journal of the International Hemp Association 6(2): 53-63. Since the dawn of agriculture, some 10,000 years ago, crops have been chosen for the benefit of humans, not the environment or biodiversity. Agriculture today is dominated by the cultivation of very large monocrops, and little attention has been focused on whether or not certain of these are significantly more ecologically friendly than others. Information on the subject of the comparative ecological virtues of crops is limited. Although there are various studies of the comparative sustainability of monocrops, as a rule these are anthropocentric, i.e. emphasis is on economic success rather than preservation of biodiversity. Recently, this issue has been highlighted by enthusiastic claims that hemp (Cannabis sativa L.) is exceptionally compatible with the environment and biodiversity. This paper compares the ecological friendliness of hemp and major monocrops on the basis of numerous crop characteristics that relate to biodiversity and/or the environment upon which biodiversity depends.

The primary objectives of this paper are to propose a method to compare the biodiversity friendliness of crops, and to employ this to evaluate the widespread claim of the superior biodiversity/environmental friendliness of hemp. Ideally, rigorous ecological-economic analysis of crops should be conducted to assess their comparative biodiversity and environmental merit. However, criteria for conducting this exercise have not been adequately examined to date, and for most crops (including hemp) there are insufficient data available to carry out this exercise with precision. Accordingly, we undertook to develop a preliminary set of criteria for gauging the biodiversity/environmental friendliness of crops, and to examine (albeit in a crude fashion) major monocrops, along with Cannabis, within this framework.

"Ecological friendliness" of cultivated crops is not a simple concept, as there are numerous parameters that are indicative of negative and positive effects on biodiversity and/or the environment. We attempted to base our assessment of crops on the basis of the predominant manner of their cultivation. Certainly there is some flexibility in regard to how a crop is grown with respect to its biodiversity-friendliness. Thus, dry land rice would score higher than paddy rice in terms of water consumption (currently, 55% of the world's rice areas rely on irrigation). Growing coffee in the traditional manner, with shade trees, provides habitat for birds and other wildlife including invertebrates, but dense open plantations reduce these benefits for biodiversity. In the absence of agreement on the relative importance of factors that bear on the problem, and since factors tend to differ in importance depending on local circumstances, we have attempted to conceptualize as many criteria as possible, and to weight these equally. The twenty-six criteria that we formulated for assessing biodiversity/environmental friendliness of crops are given in Table 1, along with some explanation. The criteria are not all mutually exclusive. Criteria were assessed as ordered three-state values, i.e. they were assigned values of -1, 0 or 1, where -1 indicates that the crop is relatively undesirable with respect to the criterion for biodiversity, 0 indicates that the crop has an average or undetermined impact, and 1 indicates that the crop is relatively desirable with respect to the criterion. Simple averaging was used to calculate a mean score, with a higher positive score indicating that the crop is more ecologically friendly. (See Sneath and Sokal 1973 for information on character conceptualization, weighting, and mathematical methods of comparing scores.) Hemp could, in theory, be compared to any of the hundreds of crop species that have been cultivated. We have chosen to compare fibre and oilseed hemp with a number of important fibre and food crops that dominate world agriculture and, therefore, have an extremely high impact on biodiversity. Later, we point out weaknesses of our methodology (see Evaluation).

**Table 1.** In the text, we discuss 13 of the 25 parameters that we adopted to evaluate the ecological friendliness of crops. These are reviewed in some detail either because they are relatively important for understanding the comparative ecological friendliness of crops in general, or at least hemp in particular. Brief descriptions of the other 12 parameters 14 through 25 are found below.
Criterion	Effect on biodiversity and/or environment	Example of environmentally/ biodiversity friendly crop	Example of environmentally/ biodiversity unfriendly crop	Evaluation of Cannabis sativa	Score Fibre Oil
Large monocrop or not	Large monocrops tend to eliminate habitat	Many herbs are grown in small areas (e.g., ginsing)	Most important crops are grown as large monocrops	hemp is grown as a large monocrop	-1	-1
State of domestication	Wilder plants tend to require fewer agricultural inputs	Relatively undomesticated plants like timber trees and pasture plants require comparatively little care	Floral crops and cereals are so weakened by domestication they require huge agricultural inputs	Hemp is relatively little domesticated	1	1
Crop spares wild species from harvest. Saves wild plants or animals	Jojoba (Simmondsia chinensis) oil substitutes for sperm whale oil	Not applicable	Hemp has potential to reduce harvest of forest trees		1	1
Crop produces environmentally friendly (or unfriendly) manufactured products	Promotes or depresses environmental quality	Fuel plants (clean-burning ethanol from corn, biodiesel from rape) reduce traffic in oil tankers and probability of spills; natural plant pesticides (e.g., parthenolide) are friendlier than synthetics	Most products manufactured from plants are good for the environment, or innocuous	Hemp is useful for producing insulation products and biofuels, which reduce energy use; textiles and paper from hemp are longer-lasting and recyclable	1	1
Crop attracts subsidies & tariffs that indirectly harm biodiversity	Subsidies tend to promote cultivation in unsuitable areas & impact negatively on environment and biodiversity	Many minor crops (e.g., many culinary and medicinal herbs) are not controlled by subsidies and tariffs	Most important crops attract subsidies & tariffs (e.g., wheat, canola, soybean) which promotes their cultivation in marginally suitable areas	Hemp is often stigmatized because of the notoriety of marijuana, and this lowers subsidation	0	0
Irrigation	Energy required to irrigate; possible soil salinization; run-off may carry pollutants and may eutrophy surrounding ecosystems	Dryland farming (by definition) conserves scarce water resources	paddy rice consumes a large proportion of water resources	Hemp can be grown both with and without irrigation, depending on location, season & climate	0	0
Biocides (herbicides, fungicides, bactericides, rodenticides, etc.)	Reduces soil organism biodiversity; spill-over kills non-targeted wild organisms and threatens survival or some species	Low or no need for biocides; pasture forages & fodders (e.g., clover, alfalfa, timothy)	Potato (one of the most chemically-intensive crops grown, because of susceptibility to insects and diseases)	Has relatively limited need of any biocides (although intensive cultivation will probably reveal additional needs)	1	1
Fertilizers	Reduces soil organism biodiversity; spill-over results in eutrophication of waterways and consequent reduction of biodiversity	Many culinary and medicinal herbs develop more attractive chemical profiles under limited fertilization; legumes require little or no nitrogen fertilization	Most major annual monocrops require high input of fertilizers	Hemp has need for nitrogen to grow well, but this can be satisfied by manure, which is environmentally advantageous where there is a surplus of manure	1	1
Energy to produce crop	Mining fuels (e.g., coal, oil, lumber) may degrade environment; fossil fuel consumption generates atmospheric gases, changes climate	Crops that are necessarily hand-harvested (e.g., many berry crops, saffron) reduce energy use	In Western countries, cereals, field crops are planted and harvested by motorized machinery	Hemp can be grown and harvested either by energy-consuming machinery or by hand-labor	-1	-1
Energy to process crop	Some harvested crops are consumed directly; others require processing that may consume fuels and generate pollution, and some require energy to store (e.g., for refrigeration)	Many food crops are consumed directly	Textile crops require extensive machinery-driven processing; oilseeds in western countries require extraction machinery	Hemp fibre and oilseeds can be processed either by hand labor or be machinery	-1	-1
Proportion of crop used	Crops harvested for just one portion waste energy and decrease efficiency of land use	Oilseed flax straw, left after harvest, is used for fibre products	Most annual crops are harvested for just one product (e.g., sunflower seeds), leaving much residue	The residue from oilseed hemp is useful for building materials, etc.	1	1
Urban vs. rural crops	Urban crops reduce pressure to usurp land occupied by natural biodiversity in rural areas	Many vegetables and some small fruit-bearing crops are ideal for urban cultivation	Most crops grown only as large monocultures are unsuitable for urban areas (e.g., cereals)	Oilseeds & fibre hemp are rural crops	-1	-1
Luxury vs. essential crops	Crops that are non-essential for human survival use scarce resources better used for essential crops	Crops that provide food, shelter, clothing, and medicine are essential for human survival	Plants used for tobacco, perfume, ornament	Cannabis is basically a food and fibre plant	1	1
Crop produces beneficial products for wildlife	Supplies food for wildlife: e.g., for pollinators, ducks	Birds love sunflower seeds (either "stolen" or in wild bird feed)	Many crops provide no benefit to wildlife, and some drug crops are poisonous	Hemp seeds are a common component of wild bird feeds	-1	1
High value/acre	Crops with high value/acre increase local wealth, and tend to decrease pressure to exploit local biodiversity	Ginseng and saffron produce huge value/acre	Cereals have comparatively low value/acre	Fibre and oilseed crops appear competitive with other crops	0	0
Crops used for meat production	Crops eaten by livestock produce food much less efficiently than crops eaten directly by humans	Crops grown primarily for human consumption, such as most vegetables and fruits, consume less energy for production than meat; some crops (e.g., soybean) are as nutritious as meat, but healthier	Crops dedicated to meat production (e.g., alfalfa) exemplify inefficient transfer of food energy to humans	Oilseed Cannabis is useful primarily as a human food, although also useful for feeding poultry and wild birds	0	1
Possibility of cultivated crop exterminating wild gene pools by interbreeding	Crops that interbreed with wild ancestors can hybridize with the wild plants, and exterminate their unique genes	Many cultivated crops no longer have wild ancestors that can be threatened by growing cultivated crops nearby	Most major cereals have extant ancestors that are threatened by growth of domesticated relatives	Cannabis debatably has extant wild ancestors ("wild" plants seem to be weedy forms)	1	1
Suitability in crop rotations	Crops grown in rotation reduce pest and disease accumulation and therefore need for agrochemicals; however, some crops are much more beneficial than others in the rotation	Legume crops are excellent contributors to crop rotation, improving the soil through nitrogen fixation	Potato exemplifies a poor contributor to crop rotations, and is grown principally as the primary crop in rotation	Hemp is an excellent rotational crop, useful in many different crop combinations	1	1
Continuity of plant cover	Annual crops (in contrast to perennials) reduce period of soil cover and result in decreased residues which in turn decrease soil biodiversity	Plantations of long-lived crops, especially legume forage crops like alfalfa and clover, often coexist with appreciable levels of soil biodiversity	The majority of food crops are grown as annuals (even if perennial), maximizing productivity but reducing biodiversity	Cannabis is an annual	-1	-1
Woody perennial plants vs. herbaceous plants	Woody plants (trees and shrubs) provide excellent habitats for many animals	Tree crops such as apples and sugar maple, provide considerable sites for nesting of birds, mammals and insects	Herbaceous plants do not provide year-round above-ground habitats, and are usually more intensively cultivated, providing fewer habitats for animals	Cannabis is basically herbaceous	-1	-1
Impact of root system	Crops with deeply penetrating roots that decay rapidly provide aeration and fertilization to soil upon decay	Alfalfa roots are deeply penetrating and decay quickly	Corn roots decay slowly, and are considered a poor soil conditioner	Hemp roots are deeply penetrating and decay before next planting season	1	1
Soil compaction through use of machinery	Crops adapted to use of heavy machinery in field tend to compact soil and reduce soil biodiversity	Crops that are planted, tended, and harvested by hand do not compact soil (e.g., many berry crops)	Most field crops (e.g., cereals) involve heavy machinery in field, resulting in soil compaction	Cannabis is planted & harvested in western countries with heavy machinery, but there is little requirement for machinery in the interim	0	0
Crop produces damaging (escaping) weeds	Weeds reduce biodiversity	Most highly domesticated crops cannot survive outside of cultivation, and so do not produce weeds	Cultivated sunflowers and alfalfa escape easily to the wild and compete with indigenous plants	Hemp is rather weedy in nature, and escapes easily	-1	-1
Toxic soil residues from crop itself	Reduces soil biodiversity (decay microorganisms and invertebrates necessary for soil mixing and fertilization)	Most plants are not thought to produce significant toxins that affect soil biodiversity	Black walnut produces toxic residues that inhibit growth of other organisms	Toxic residues are known to accumulate during water-retting of hemp in fibre production; it is possible that these toxins affect soil biodiversity	0	1
Toxic atmospheric products from crop itself	Atmospheric pollution	Most crops are not known to produce significant levels of atmospheric gases	Canola (rapeseed) is said to produce significant levels of sulfer dioxide; opium poppy fields produce intoxicating gases; coniferous trees have been alleged to produce significant harmful gases	As with resinous trees, much of the resin produced by Cannabis evaporates; the effects are unknown	0	0
Total score					2	6

Current market forces tend to pressure farmers to narrow the spectra of crops and livestock produced. Modern agriculture and plantation forestry are highly-productive, but constitute artificial, low-diversity ecosystems. Today, much of the world is occupied by monocultures, particularly cereals (notably wheat, barley, oats, rice, corn, millet, and sorghum). Cereals have been the principal basis of civilization ever since agriculture commenced. Indeed, continuous growth of the human population for millennia has been possible only because of the extremely high productivity of high-yielding cereal cultivars. Unfortunately this dependence on cereals has been a Faustian bargain. The benefit of feeding and sustaining a huge population has been achieved at the cost of having to grow large monocrops that are so very highly domesticated that they require heavy inputs of energy and agrochemicals, and are therefore rather environmentally-unfriendly. Also, such systems are very susceptible to climate variations and outbreaks of pests and pathogens.

In 1991, food production occupied about 37% of the world's land area: crop lands occupied about 11% and permanent pastures about 26% (World Resources Institute 1994). Two dozen crops account for 90% of the plant calories consumed by humans, with wheat, rice, maize (corn) and potatoes alone accounting for half of this (Harlan 1975, Prescott-Allen and Prescott-Allen 1990). Of the world's 30 most important food crops, cereals represent about 80% of the total production by weight (Harlan 1992). Most of the world's cropland is used to produce grain, of which humans consume about 50% directly and the other 50% indirectly as livestock products (Brown et al. 1998). Cereals dominate the human diet, and it does not seem feasible that environmentally more friendly crops can replace them to any appreciable extent, despite surplus production in some regions. This is a sobering "reality check" to those who advocate a conversion of all agriculture to low-input systems. This does not mean that cereal production cannot be made friendlier to the environment by adopting new cultivars and appropriate management techniques that improve sustainability. It simply means that, as long as human population growth and wasteful mass consumption patterns continue, the diversification of monocrops with environmentally more friendly alternatives is only a partial solution. (Small 1997 discusses major issues that agriculture needs to address in order to co-exist harmoniously with the world's biodiversity.)

Another discouraging consideration is population growth. As human population increases, inevitably monocultures increase, and the natural world decreases. Population control is the critical issue of our time, and human food security is the principal threat to the environment and biodiversity. To feed the 80 million more people that are currently added to the planet each year requires expanding the cereal harvest by 26 million tons, or 71,000 tons/day (Brown et al. 1998). Abundant harvest from cultivated land is important for preserving habitat for biodiversity, but prospects for land productivity increases are very limited. Feeding the expanding population of the world appears possible only by sacrificing more of the natural world (or by some revolutionary technological advance). Moreover, there is general agreement that such factors as water scarcity, conversion of cropland, soil erosion, rangeland deterioration, air pollution, climate change, and the increased demand associated with rising affluence in some parts of the developing world, will greatly exacerbate food scarcity, and that "the world is on an economic and demographic path that is environmentally unsustainable" (Brown et al. 1998).

To be economically justified with respect to the principal products of hemp (i.e., fibre and oilseed), relatively large-scale cultivation is required. That is, hemp is a large-scale monocrop. However, such cultivation is very unlikely to displace natural ecosystems. This is because most first-class agricultural land is already occupied by crops, and hemp requires excellent arable land to be grown well. Thus, hemp will have to compete with established crops for available arable land, but is unlikely to compete with wild lands.

There is a correlation between the degree of domestication of a crop and its degree of environmental friendliness. The wilder (less domesticated) a plant is, the less likely it is to require special inputs of fertilizer, biocides, irrigation and cultivation, and hence the greater the environmental/biodiversity friendliness. As plants are domesticated from their wild progenitors, they become more susceptible to diseases, pests, weeds and climatic extremes, and in general, the more domesticated the greater the susceptibility. Modern cereals, for example, are very highly domesticated and require enormous agronomic inputs. By contrast, fodder and pasture species (such as many clovers and grasses) are generally much less domesticated and once planted will survive for at least several years without inputs.

Cannabis exists both as a broad range of cultivars and as wild, weedy forms, and while some of the advanced (fibre) cultivars require high inputs and attentive management, fairly undomesticated forms have been usefully cultivated in the past. It is the utility of the less-domesticated forms of Cannabis that deserves special notice, since these are naturally more competitive, and even in today's circumstances conceivably could be grown for some purposes (e.g., biomass). The genetics of Cannabis are of special interest in the context of environmental/biodiversity friendliness. This is because Cannabis evolved as a "camp follower," i.e. a species that became naturally adapted to human habitation, rather than through human selection (Small 1979). Camp followers have retained the large degree of genetic variability characteristic of wild plants, and thus lend themselves to low-input agriculture. By contrast, most crops are the result of very strong selection that has drastically narrowed their genetic base with the result that high inputs are necessary to compensate for their acquired weaknesses. The high-yield grains of the "Green Revolution" epitomize the modern agricultural dilemma of breeding extraordinarily productive crops that can be maintained only at considerable cost of natural resources.

By the turn of the century, 3 billion people may live in areas where wood is cut faster than it grows or where fuelwood is extremely scarce" (World Commission on Environment and Development 1987). "Since mid-century, lumber use has tripled, paper use has increased six-fold, and firewood use has soared as Third World populations have multiplied" (Brown et al. 1998). The most widespread claim for the environmental friendliness of hemp is that it has the potential to save trees that otherwise would be harvested for production of lumber and pulp. However, Wong (1998) notes evidence that in the southern US, hemp would produce only twice as much pulp as does a pine plantation, and current newsprint technology produces paper from trees far more cheaply than seems possible from hemp. On the other hand, for the production of construction materials, several factors appear to favor increased use of wood substitutes, especially agricultural fibres such as hemp. Deforestation, particularly the destruction of old growth forests, and the world's decreasing supply of wild timber resources are today major ecological concerns. Agroforestry using tree species is one useful response, but nevertheless sacrifices wild lands and biodiversity, and is less preferable than sustainable wild land forestry. The use of agricultural residues (e.g., straw bale construction) is an especially environmentally friendly solution to sparing trees, but material limitations restrict use.

There is growing enthusiasm for the deliberate cultivation of annual crops specifically as primary sources of agricultural fibres (in contrast to salvaging fibres from crop waste) to replace forestry products. One chief advantage of annual fibre crops is that they satisfy a market specifically for long fibres that cannot be supplied by trees or agricultural residues (Bolton 1995). Because of favorable characteristics of particular species (such as tear resistance and wet strength in Cannabis), several annual fibre species have established markets for a variety of specialty papers, such as high-quality printing and writing papers, filter papers, cigarette paper, cardboard and packaging products (Nova Institute 1995). Hemp's long fibres also make paper more recyclable. Since virgin pulp is required for added strength in the recycling of paper, hemp pulp would allow for at least twice as many cycles as wood pulp. Another chief advantage of several annual fibre crops over forestry crops is the former's relative productivity, annual fibre crops producing of the order of four times as much per unit of land, in some locations. Still another important advantage is the precise control over production quantities and schedule that is possible with annual crops. In many parts of the world, tree crops are simply not a viable alternative. Insofar 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 fibre demand while trees reach their ideal maturation. In developing countries where fuelwood is becoming increasingly scarce and food security is a concern, the introduction of a dual-purpose crop such as hempseed to meet food, shelter and fuel needs may contribute significantly to preserving biodiversity (Montford 1996).

We have noted the following objection to the value of growing hemp as a replacement for harvesting forest trees (see "Why the greens should rethink their policy on forests" by P. Moore; originally published in Canberra Times, July 14, 1997; available at http://www.nafi.com.au/issues/).

"The environmentalist agenda for wood use reduction is two-pronged. First, they want us to stop making paper from trees and use 'non-wood fibres' to make 'tree-free paper'... The second prong of their agenda is to reduce wood use as a building material and substitute it with so-called 'environmentally appropriate alternatives'. This may sound good at first but there is a serious problem. Where will we grow all these exotic, annual, monoculture farm crops, enough to provide 300 million tons of paper per year?"

As noted above, we advocate sustainable use of forest resources, but in places where demand exceeds the renewable supply, it is appropriate to consider annual fibre crops as a supplemental source of pulp and wood products. Of course, where suitable agricultural land is unavailable or better utilized with other crops, annual fibre crops are inappropriate.

The textile use of hemp plummeted in the 19th century as softer fabrics took over the clothing market. Traditionally manufactured hemp cloth was quite coarse (its durability made it popular). Nevertheless, there is renewed interest in using hemp for clothing, and there has been considerable improvement in the quality, texture, and wearing comfort of apparel made with hemp blends. Fashion designers have recently featured hemp clothing, and the counterculture image of hemp suits, shirts, hats, and accessories is highly attractive to a segment of the market. From an environmental point of view, the durability of hemp fabrics represents an outstanding advantage. Hemp cloth was used in sails and cordage because of its resistance to water and saline damage, but this very tough material is also resistant to abrasion. Further, hemp fabric makes excellent paper and so is highly recyclable. Although the manufacturing of a product is a source of pollution and energy consumption, hemp is comparable in these respects to the manufacturing of other vegetable fabrics (cotton, linen, etc.). Synthetic textiles (e.g. acrylic, nylon, orlon, polyester) are considerably more consumptive of energy and productive of pollution, and often use non-renewable resources like petroleum, so that the environmental advantages of hemp and other vegetable fibres should not be overlooked. Textile manufacturing is a risky enterprise, with large investments in infrastructure, intense competition, and market volatility, but with the possibility of short-term high profits based on fashion trends. By comparison, the products mentioned below seem less speculative.

Insulation to regulate temperature is an extremely important way of reducing energy consumption, and thereby limit damage to the environment and biodiversity. Inorganic fibres such as rock wool and fiberglass presently dominate the insulation market, although recycled paper and plant fibres are also used. In building applications, hemp straw can replace several layers of conventional building materials: bricks or cement, vapor barrier, insulation, and plaster board. As an insulation material, natural fibres are especially energy efficient (e.g., homes stay cool in the summer and retain more heat during winter). Waste portions of hemp stems have been combined with lime to create an insulating plaster for the remodeling of older buildings. The resulting mix resembles cement and like cement, the substance becomes resistant to molds and insects, and is fire retardant. This mix is lighter than cement and offers a combination of thermal and sonic insulation which can be used to construct floors and walls. (See Nova Institute 1995 for information related to this paragraph.)

Hempseed is believed to be a more efficient producer of the popular nutritional supplement gamma-linolenic acid than presently grown sources. Accordingly, hempseed as a crop has the potential of lessening demand for crop land (although not in a major way). Hemp oil can substitute for non-renewable petrochemicals in many applications, such as paints and printing inks. Oilseed hemp is useful not only for the seed crop, but because of their high fibre content, the remainder of the plants following seed harvest can be used to prepare such biodiversity-friendly commodities as insulation and composite natural building materials. Seeds from hemp are extremely attractive to wild birds. The oil cake remaining after oil is expressed from the seeds is also a very nutritious feed supplement for livestock, and for production of a high-protein flour.

Subsidies and tariffs, by changing relative prices, are means of encouraging the cultivation of some crops over others. Virtually all countries subsidize particular home-grown crops and tax many imported crops for social, cultural, political, and security reasons. Crops that attract either tariffs or subsidies tend to be harmful for the environment and biodiversity. Both practices distort market conditions and result in artificial competitive advantages for subsidized crops. Such crops are often grown in sub-optimal regions, hence productivity is lower and more land and resources need to be sacrificed. However, subsidies can be good for biodiversity, such as policies that promote low-input agriculture.

Subsidies are particularly significant in considering hemp. The European Union (EU) has subsidized hemp production in recent years by as much as US$761.00/ha. However, there is currently an effort underway to reduce EU subsidies for hemp. In Canada, subsidies are not provided for hemp, although back in the 17th and 18th centuries, both subsidies and awards were used to encourage hemp production.

Hemp products compete most evidently with tree products. The price of tree products (lumber, pulp) is frequently artificially low because of government subsidies. Timber companies that harvest wild trees from public lands generally have far lower production costs than agro-forestry firms which must cover the costs of land and production, just like farmers. With the increasing scarcity of wild tree resources and concomitant increasing cost of tree products, as well as concern over associated biodiversity destruction, shifting subsidies to production of substitute annual crops such as hemp may be desirable.

Irrigation greatly alters ecosystems, and is a key consideration of the extent to which a crop can be considered environmentally-friendly or not. Agriculture uses an astonishing 63% of the world's fresh water consumption (Heywood 1995). In recent years, irrigation has been associated with a dramatic increase in food production, but unfortunately irrigated areas are detrimental to indigenous species that are adapted to dry areas. Accordingly, crops requiring limited or no irrigation are, at least in this respect, beneficial to biodiversity. Because of the increasing scarcity and cost of water, it is certain that drought-resistant crops will become more important in the future, and so relatively limited need for water is a probable way that environmental friendliness of crops can be enhanced. As noted in Table 1, Cannabis benefits considerably from adequate water availability in early development, but on the whole is neither notably consumptive or sparing of water by comparison with other crops. Of course, whether this species requires irrigation or not depends on local climate.

Agriculture makes heavy use of biocides (pesticides, fungicides, herbicides), which can be extremely detrimental to biodiversity. Although conscientious attempts are generally made to localize application, accidental drift of biocides can be harmful (for example, to fish in nearby streams), and soil organisms in the area of application cannot escape exposure, nor can visiting pollinators, birds, and other foragers. Although various techniques (most importantly organic agriculture, integrated pest management IPM and genetic engineering) offer means of decreasing biocide use, most monocrops are dependent on heavy use of biocides, notably of pesticides and herbicides. Crops that are naturally resistant to attacking organisms are therefore very important in reducing damage to biodiversity. Cannabis is known to be significantly resistant to pests. Indeed, a concentrated search for biocontrol agents to eliminate marijuana plants has been unsuccessful to date. Nevertheless, the resistance of hemp to attacking organisms has been greatly exaggerated, as various insects and fungi are known to specialize on hemp.

Although Cannabis is a weed, seedlings of this species are somewhat susceptible to being crowded out by weeds, and so herbicides are used in some circumstances to clear fields for planting. However, once established, little weeding is required, especially for growth of fibre plants, which are crowded to the point that they shade out competing weeds.

The nutrient relations of crops are important to biodiversity, since natural efficiency means a lowered need to add supplements, and less depletion of the fertility and quality of the soil. Runoff from fertilization can eutrophy streams and lakes, and thereby drastically alter natural vegetation. Unfortunately, alleged differences in nutrient uptake and return by different crops grown as monocultural annuals have been insufficiently quantified under comparable conditions. While there do seem to be differences in the ability of crops to extract and return nutrients to the soil (Reichert 1994), on the whole, monocultural, annual crops are generally nutrient-depleting of soils and except for nitrogen-fixing leguminous crops, may not differ sufficiently to be important in terms of ecological friendliness to the soil. Cannabis has a reputation as a nitrophile, i.e. it thrives on high levels of nitrogen in the soil, and indeed grows poorly otherwise. It responds especially well to manure, and therefore would seem to be an ideal crop to use up surplus manure. This applies, for example, in the Netherlands, a country which has an alarmingly high surplus of manure, and a growing interest in hemp cultivation. Study is required of the extent to which hemp can benefit from manure, especially in comparison to other crops. Runoff from manure can be as damaging to biodiversity as runoff from inorganic fertilizers, so that the use of manure is not problem-free.

Some crops, either during the cultivation, harvest or manufacturing stages, are especially wasteful of energy or, conversely, require limited energy expenditure. Hemp pulping has been alleged to require lower energy and chemical input than conventional softwood pulping (Nova Institute 1995), although this claim has been disputed (D. Marcus, personal communication). Because hemp seeds (once toasted or ground) and hemp oil can be prone to rancidity, refrigeration may be required, which requires energy. Much of the energy expenditure of agriculture is concerned with the manufacture and application of herbicides, pesticides, fungicides, and chemical fertilizers. As noted elsewhere, Cannabis crops require lower use of these agrochemicals than most other crops, and this factor tends to lower energy consumption costs.

There is concern over the depleting supply of fossil fuels (coal, oil, peat), as well as the environmental degradation associated with mining and transportation damage (e.g., strip mines, oil tanker spills), and the atmospheric pollution generated. Plants that generate biomass that can be used as fuel, in some cases, may be preferable (although burning wood from trees is probably not a wise alternative). Hemp is considered a good choice for biomass production. Also, hempseed oil combined with 15% methanol provides a diesel fuel substitute that burns 70% cleaner in particulate production than petroleum diesel (McNulty 1995).

An interesting aspect of the problem of evaluating the ecological friendliness of a given crop is the extent to which that crop encourages hand labor as opposed to the use of energy-consuming machinery. Advanced farming is very heavily based on machinery, which depletes fossil fuels and produces greenhouse gases. By contrast, labor intensive farming does not have these adverse effects on the environment. Some crops (e.g., strawberries, ginseng, saffron) are naturally labor-intensive, despite the efforts to develop harvesting machines, and so in at least this limited respect are friendly to the environment and biodiversity. What is the situation for hemp? For the last several decades, hemp has been produced in countries with large pools of low-cost labor, such as China, Romania, the USSR and Spain. However, it is probable that should hemp become a major crop in Europe and North America, countries in these areas would only grow the crop competitively with specialized harvesting and processing machinery.

A relatively small part of most annual crop plants is usually harvested (e.g., tomatoes, carrots), and although the remaining organic material is always recycled eventually, unused material decreases production efficiency of land, and therefore increases pressure to usurp wild land used by biodiversity. Crop residues after harvest provide nutrient return to the soil, but this is a difficult issue since residues are sometimes considered undesirable (because of delivery of diseases to the soil or of slowly degrading material that interferes with subsequent planting). Where a substantial proportion of residues are removed (for example, where cereal residues are used as a pulp source), it is possible that the humus level will be excessively reduced, degrading soil quality and structure. Cannabis is unusual in having the capability of providing double harvests from the same crop (seeds for oil and stem fibre), and although crops grown specifically for the production of highest-quality fibre are not used for commercial harvests of seeds for industrial use, many dual-purpose cultivars can provide both a good seed crop and a good fibre crop. Although seed varieties produce inferior quantities of fibre for textile purposes, the stems and branches remaining after the seeds are collected are excellent for other purposes, particularly for building materials.

Land that is used intensively for human activities more or less limits natural biodiversity. This includes areas used for dwellings, buildings in general, and similarly highly-developed areas. Plants often occupy considerable proportions of the urbanized landscape for such purposes as shade and ornament. Most significantly, food plants are often grown in urban settings. In Western society, food plants are typically grown in home gardens merely as a supplement to the food budget; by contrast, in developing countries home gardens may constitute a critical source of food, and even rooftops may be used efficiently. "An estimated 200 million city dwellers worldwide now practice urban agriculture, supplying part of the food needs of some 800 million people" (Brown et al. 1998). Greenhouses can be positioned in urban settings for production of high-value and out-of-season crops. Crops that lend themselves to urban culture represent a significant means of reducing the pressure to use land now occupied by natural biodiversity. Obviously, major monocultural crops are inappropriate for urban settings, while, herbs, vegetables and small fruit shrubs and trees are ideal. Insofar as cultivation of fibre and oilseed forms of hemp, it may be noted that as with all fibre and oilseed crops, a rural setting is necessary.

Some crops are grown simply for aesthetics, for example plants grown for the floral and perfume markets (a very small amount of Cannabis is currently used for the production of essential oil). The flower trade involves large transportation costs and tends to be environmentally detrimental, and the perfume trade involves extensive chemical processing that creates polluting wastes. Recreational inebriants like tobacco, snuff, and alcoholic beverages, are also "luxury crops" that are often extremely expensive in energy usage. While such non-essential crops are economically important, their occupation of land that could otherwise support natural biodiversity is less morally justified than those that humans must have for survival (food, shelter, clothing, medicine). Cannabis notably provides products that meet all of these basic human needs.

Table 1 reports scores for 25 parameters that assess relative ecological friendliness of Cannabis sativa as a fibre and oilseed crop. In Figure 1, we compare the biodiversity friendliness of the two Cannabis crops types with 21 of the world's major crops. (Scores for the 25 parameters for these 21 crops are not reported here, but can be obtained by e-mail from the authors.) Oilseed hemp scored slightly higher than fibre hemp. Alfalfa was the most biodiversity-friendly of all of the crops that we evaluated, and timber trees ranked next in this regard. Most of the world's important crops that were examined, including the cereals, sugar cane, potato, sunflower, cotton, rapeseeed, soybean, and tobacco, ranked low in terms of environmental friendliness. We do not claim, where it is indicated that a crop is relatively friendly, that it is actually good for biodiversity, since virtually all crops impact at least somewhat negatively on natural biodiversity.

We are not aware of a previous assessment of the comparative biodiversity-friendliness of crops, such as is attempted here, and we note the following weaknesses of our analysis so that readers will not be misled regarding the significance of the rankings. We do regard the very high rank achieved by fibre and oilseed hemp as indicative that these crops are indeed significantly biodiversity-friendly. However, the precise rankings of the crops analyzed should not be interpreted as actually measuring precisely their comparative degree of biodiversity-friendliness. This is because of the following problems:

1) The criteria chosen for evaluating comparative biodiversity-friendliness of crops were defined based on our personal familiarity with the subject; others, depending on their fields of specialization and expertise, might well choose a different set. Reviewers of this paper suggested adding the following criteria: a) competition with wild pollinators (i.e., crops might damage biodiversity by disrupting natural pollination patterns); b) whether annual or perennial (perennials save energy by avoiding the need to reseed); c) presence of genetically engineered traits that in some manner threaten natural biodiversity.

2) Our expertise on the large range of crops and criteria examined is limited; such an enterprise would best be conducted by a multidisciplinary team of experts.

3) Depending on local situation, some criteria may deserve to be more heavily weighted than others (e.g., irrigation may be more important where there is a great scarcity of water).

The primary goals of this paper were to create a method for comparing the biodiversity friendliness of crops, and employ this to evaluate the widespread claim of superior biodiversity/environmental friendliness of hemp. Based on averaged scores for the 26 criteria we adopted, hemp was found to be superior to most major monocrops in terms of limiting damage to biodiversity. If some crops, such as hemp, are indeed more environmentally-friendly than others, what are the implications? Certainly it would be desirable from an ecological viewpoint to preferentially grow environmentally-friendly crops. However, socio-economic considerations, i.e., the profitability and agricultural suitability of crops, predominantly determine which are grown. In this pragmatic world, environmental/biodiversity evaluation of crops cannot be separated from their social and economic values. Nothing is more illustrative of this than the inescapable fact that key cereals and potatoes provide most human food; it is academic that they many food crops may be rather unfriendly to biodiversity since without them the planet could not sustain more than a fraction of the present human population. With the growing awareness that the sustainability of agriculture and the welfare of society depend on the health of the planet's biodiversity, criteria such as the comparative environmental-friendliness of crops may receive more consideration. What is needed is a comparative analysis of crops giving appropriate weight not only to ecological considerations, but also to regional economic and socio-political realities. We are confident that hemp will be playing an increasingly important role in meeting the evolving needs of the world.

We thank the editor and reviewers for constructive comments in order to adapt this paper for the Journal of the International Hemp Association.

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