Author’s Biography: Trevor Gibson is a semi-retired agricultural consultant currently residing in Chiang Mai, Thailand. He began his consulting work in Chiang Mai in 1972 and has worked in several Asian countries since. He originally specialized in forage research but then expanded to consult on general smallholder livestock and agricultural production.
I read David Price’s concerns about promoting invasive forage plants in Asia Note #25 [Eds’ Note: AN #25 was written in response to AN #23] and would like to respond based on my own experience and observations.
My reply will be based on the following principles:
- It is moral to help poor farmers as much as practicable.
- The primary aim of human activity is the betterment of the human condition. Thus, preservation of the natural environment is NOT necessarily the primary aim of development activities.
I have been promoting the use and expansion of all of the species listed by David to smallholder farmers for, in some cases, the last 45 years. I wish to address the concerns David has for each of the species listed in Asia Note #25. I live in northern Thailand now, so I will use local examples, but the comments should apply equally as well to most of the humid and sub-humid tropics.
Panicum maximum: Guinea Grass
Guinea grass is truly a very invasive species, found growing wild in most of the moist, tropical world. But it is also a species of great benefit to the ruminant livestock of smallholder farmers. It readily produces a large amount of good quality forage with, in some cases, negligible input by the smallholder. Guinea grass, particularly a giant variety, grows along the roadsides and wastelands in northern Thailand. One can often see poor villagers harvesting this free, good quality forage and carting it back to their houses to feed their animals. It is immoral, in my view, to wish that poor farmers not have this opportunity. Guinea grass no doubt displaces some local plant species, but I do not see how this is a harm to the poor farmer. The plants it displaces are inferior forages and poor farmers would be worse off if they had to rely only on native species.
Simply because guinea grass produces more growth than native species, it probably constitutes a greater fire hazard. But that doesn’t seem to have stopped regeneration of the forests in northern Thailand after a ban on forest fires was successfully implemented in the last 20 years. Like any plant in an unwanted location, Guinea grass can be a weed, but I am not aware of any instance where Guinea grass is a significant constraint to crop production. In any case, Guinea grass is so widespread and so successfully invasive, it would be pointless to try to suppress its expansion. If farmers wish to grow Guinea grass for their livestock, then, in my opinion, they should be encouraged to do so.
In NE Thailand, poor farmers have made a lot of money from growing well-fertilized guinea grass in the lowlands to sell for commercial and non-commercial livestock. Guinea grass has been widely promoted and grown in Thailand for animal production (the popular commercial variety in Thailand is known as purple Guinea), but it is being replaced by other cultivars and species that have better forage characteristics (faster growth, better feed quality, etc.).
Brachiaria species hybrids
David says that Brachiaria hybrids ‘Mulato II’ and ‘Cayman’ are closely related to Guinea grass. I don’t tend to think so: they are very different genera in appearance and adaptability. Guinea grass has a much more open and branched seed head than the brachiarias, and the seeds are very different in shape and size (Figure 1).
‘Mulato II’ is very palatable for ruminant animals and of high nutritive quality. If it is invasive in places, I have not seen it. ‘Cayman’ is a notoriously poor seed producer. I doubt whether either type could become invasive; even if they did, I don’t think this would be a serious problem, as both are very good forage grasses and readily eaten by animals.
Other Brachiaria species have invaded parts of northern Thailand. One, probably B. brizantha or B. decumbens, can be found along the roadside on parts of Doi Inthanon. B. ruziziensis (Ruzi grass) has been widely propagated in Thailand and has invaded parts of NE Thailand, but I don’t think it is particularly troublesome for cultivation farmers. The brachiarias (there are many of them) are all good forage species in their adaptive situations, and Ruzi grass is well-utilized by the livestock of poor smallholder farmers in SE Asia in general. The Thai Livestock Department has encouraged the production of Ruzi grass for many years now and poor farmers have made a lot of money from seed production. Ruzi grass is also propagated for poor farmers in Laos, Malaysia, and elsewhere in SE Asia. I very highly recommend that the brachiarias be extended for use as forage for the livestock of smallholder farmers in SE Asia.
P. atratum and P. plicatulum have very different agronomic characteristics and are not usually confused by forage agronomists. P. plicatulum was sown to some extent in NE Thailand as a cut forage species, but it quickly loses its quality and has been replaced by other better-quality forage grasses. P. plicatulum has persisted well on infertile soils in northern Laos, but to my knowledge is in no way troublesome to cropping. One of David’s suggested analogues for this species, vetiver (Chrysopogon zizanioides), is a very poor forage species; it is highly indigestible even when young, compared to P. atratum. Animals will not favor vetiver at any stage of growth, but livestock readily eat young leaves of P. atratum. Vetiver is not comparable to the paspalums; one doesn’t grow vetiver for forage.
Pennisetum purpureum: Elephant Grass, or Napier Grass
From my observation, a somewhat invasive cultivar of Napier grass can be found in specialized niches in Thailand, but I cannot see how it could seriously interfere with cropping land. Napier cultivars are the mainstay of many smallholder dairy and beef farms in Thailand, and of livestock rearing in general in much of SE Asia and other parts of the tropical world. In my view, it would be immoral to prevent poor farmers from growing Napier.
Many forage agronomists recommend that Napier be replaced by other forage species of better quality. However, the recommended replacement species are also listed by David as being invasive. ‘Pak Chong,’ the Napier currently promoted in Thailand, is a hybrid and not invasive as far as I know. Compared to traditional Napier cultivars, it has superior dry matter production but inferior nutritive qualities. I would not recommend promoting the ‘Pak Chong’ cultivar just on its perceived lack of invasiveness. I would promote the forage type that would most benefit the smallholder farmer, which will depend on the farmer’s cultural and environmental contexts.
Stylosanthes guianensis: Common Stylo
I have not seen Stylosanthes guianensis become invasive anywhere. In fact, some complain that it is not persistent enough, and forage agronomists would like a more persistent variety. S. hamata has been widely spread in Thailand, often by helicopter; it has persisted well in certain environments and is often found on the roadsides in northern Thailand, especially in NE Thailand where the climate seems to suit it. In such environments, I think it is persistent rather than invasive. However, it is not favored by poor farmers, as it produces less than forage grasses and is of poor forage quality. David claims in AN #25 that stylo increases soil acidity and increases erosion. I tested the effect of forage legumes on soil pH in NE Thailand and did not find that any legume, including S. hamata, increased soil acidity. I have also not observed stylos increasing soil erosion.
Arachis pintoi: Pinto Peanut
David likes this species because it is not invasive. Unfortunately, smallholder farmers don’t seem to think much of it as a forage plant. Though it has been promoted in SE Asia, I am not sure that any farmer has adopted it for animal feeding - it produces too little forage. However, it is used as a permanent cover crop and as an ornamental.
Leucaena is an invasive, persistent, high quality, very productive forage tree legume. It grows wild in the lowlands of northern Thailand on soils that are not too acidic (it doesn’t like soils of pH less than 5.5). Leucaena is very underutilized, because people believe it is toxic to livestock. However, when animals are introduced gradually to leucaena, very high animal production can occur. In fact, leucaena is the best tropical forage legume available for cattle; an individual animal can gain more than 1 kg live-weight per day when eating only leucaena.
The claim that leucaena is allelopathic (leaches plant compounds that hinder the growth and/or development of other living things) is inconsistent with the SALT (Sloping Agriculture Land Technology) philosophy and with experience with leucaena - leucaena cuttings are used to PROMOTE additional crop growth, not restrict it. Leucaena doesn’t necessarily reduce land available for cropping: it has been promoted as an improver of shifting cultivation areas. Therefore, I most highly recommend that leucaena be promoted for animal feed in SE Asia.
I have never seen gliricidia spread invasively. However, if an environment is suitable for leucaena, I would recommend leucaena over gliricidia because the former is a higher quality feed.
David shared concerns about invasive plants in AN #25, stating that in many situations the benefits of potentially invasive forages1 outweigh the costs. I think this is true in all the cases that David has listed. All of these cultivars have been well-tried and tested in many parts of the world, including SE Asia. We do not need to test these species again. We know, from many years of experience, what they can do, both positively and negatively.
I have long observed the benefits of introduced forages (as animal feed) compared to local forages. Compared to the best introduced forages, the local forages invariably, from my observations, have inferior growth (less dry matter production per year or per season) and/or inferior quality (less digestibility usually related to increased steminess, earlier flowering, or later seasonal regrowth).
Introduced forages have been selected, and sometimes bred, from many tens of thousands of plants in order to find better forages than the local ones. In my view, it would be a waste of limited resources to try to find local species that are better forages than a suitably introduced forage. It will help poor farmers most if we use the information and experience available now, and current information and experience strongly suggest that we promote all of the forages that David has listed.
David seems to imply that preserving native plants and native ecosystems in all situations is good in itself. I would certainly disagree. Do we recommend to lowland rice farmers to abandon monoculture rice in their paddies, and allow the naturally occurring rainforest to come back? Or suggest that maize farmers allow native weeds to grow amongst their maize crops2? Would such actions be to the benefit of the poor farmer? The same argument applies to forages. If it benefits poor farmers to replace local species and ecosystems with introduced ones, then it is morally responsible to do so. Maintaining biodiversity does not always benefit the poor farmer; if wasteland and un-cropped areas are invaded by an introduced species that benefits poor farmers, then it is moral to accept and promote that invasion.
This is not to say we should not keep some native plants and native ecosystems. We should, but when such preservation is not to the benefit of the poor farmer, then such preservations should be made in specially designated areas (e.g. national parks, bio-conservation areas, etc.). There are advantages in keeping such native areas (e.g. for maintaining genetic diversity that may be utilized for human benefit in the future, and for recreational, historical, ascetic and sentimental reasons).
I hope my reasoning somewhat reassures David, ECHO, and others who may be involved with promoting introduced forages for poor farmers. Of the tried and tested forages that David listed, I don’t think we have much to fear from promoting these forages, and poor livestock farmers will be better off if we do.
1I prefer to use the term ‘forages’ for the species under discussion, rather than ‘forage crops’ because ‘crops’ implies a species involved in more intensive cultivation than that normally applied to forages. Invasive forages are often just spread on uncultivated or poorly cultivated land, in which case they would not qualify as ‘crops.’
2ECHO has suggested elsewhere https://www.echocommunity.org/en/resources/e72b6545-9cb7-49f6-a8e1-2bde4d582ccb, that Mexican farmers use the weeds in their maize fields, but I doubt whether any Asian farmer would prefer to have weeds in their maize fields rather than no weeds. Of course, use the weeds if you have to put up with them, but remove them if you want maximum maize production.