Food production vs. biodiversity: comparing organic and conventional agriculture

Gabriel et al. 2013. Journal of Applied Ecology 50(2): 355-364. DOI:10.1111/1365-2664.12035. Food production vs. biodiversity: comparing organic and conventional agriculture

Technically, this is a bumble bee, and so it's appropriate.

What do you mean, wrong kind of bumble bee?

Jennifer Banfield-Zanin

Jennifer Banfield-Zanin

Ladies and gentlemen of the jury, I must confess that I’m not really sure where to start on this one. It’s an interesting piece of work, the aim of which was to quantify the trade-off between agricultural yield and biodiversity in organic and conventional farming systems, in terms of costs to yield and benefits to biodiversity.

The main finding of the study seemed to be that there was an overall negative relationship between biodiversity on farmland and yield, and that when results were controlled for yield it didn’t matter whether the system was conventional or organic. Now that’s a neat little result likely to ruffle a few feathers right there! Basically, to quote the authors, “higher biodiversity levels in organic compared with conventional farming… may simply reflect the lower production levels”. The question it raises, I think, is: if wildlife benefits are limited under high-intensity organic farming, then is it worth it? Why not stick with the conventional system? I can see this causing some debate between the proponents of both agricultural systems.

The suggestion made by the authors is that in highly productive landscapes, conservation efforts should centre round conventional high-yield farms with ‘spared’ land managed for wildlife – things like field margins, hedgerows, as well as potentially larger parcels of lands. In fact, such schemes are already in place in the U.K., with Environmental Stewardship schemes run through the government. In low-productivity landscapes, concentrating organic farms into hotspots would give the best biodiversity benefit. It seems to make sense, but I have to question why you would put a low-productivity system somewhere were productivity is already low. Might this not serve to suppress yield further, or am I missing something key here? Feedback on this would be greatly appreciated!

Moving on. This might just be me griping, but my main sticking point was that there seemed to be no real assessment on the impact of crop pests in the system. Insect pests are not mentioned at all, nor are they factored into the analysis. Aphids, for one, have the potential to reduce crop yield, both through direct effects on plants and also because they can transmit various viruses while feeding, and this may affect the results observed in such studies. I would have liked to see some thought given to how the two systems, or to how these attempts at conserving biodiversity, would impact pest fauna.

Following from there, what about other functional classes of insects? Natural enemies beyond hoverflies, which can help suppress insect pests and therefore support yield and reduce the need for pesticide inputs as well as contribute to biodiversity? What about other Dipteran pollinators? While it is true that a lot of current focus seems to centre round bees, butterflies (the entomological equivalent of ‘big fuzzies’) and birds, there are other invertebrate groups that play equally important roles in any agricultural system and landscape. All are important, and all can help modulate yield while contributing towards biodiversity.

There was also no real consideration of integrated, or low-input conventional approaches – conventional farming doesn’t have to mean pack as much fertiliser in as you can, spray whenever you see something you don’t want and as much as you can until the problem is gone. Environmentally sensitive crop management in conventional systems is becoming increasingly popular, or so I am led to believe. Such systems have the potential to maintain high yields while improving biodiversity, even on high-intensity conventional farms.

Despite the above, I really do think it was an interesting article, which highlighted the complexity of agricultural systems, and the importance of striking a balance. They highlighted the over-arching importance of scale and landscape, and I believe added more evidence to support the need for habitat variability on multiple scales in agricultural systems. A worthwhile read, and a welcome break from my usual reading fare.

Mark Ramsden

Mark Ramsden

Forecasts of an increasing world population are a common theme in the introduction to a lot of articles these days, and while this was no exception, it was refreshing in its scrutiny of current farming practices. Organic farming is widely sold as the more environmentally friendly side of agriculture, and it’s marketing often relies on its image as being ‘better’ in order to succeed. Here, the evidence suggests that the environment may benefit as much from a willingness to accept lower yields as it is from reduced chemical applications. This hits at the crux of an ongoing stalemate in agriculture. The current mosaic of organic and conventional farms works because we can still tolerate lower yields in some land, but for how much longer? Solitary bees, bumble bees and butterflies did not fare well in high yield landscapes, but careful habitat management around the fields can be effective in boosting numbers. In an associated study the authors published a few years earlier, nature reserves out performed any kind of farming for these pollinators. One interesting case was the Hoverflies, which responded positively to increased yield. Most of these belonged to species with predatory larvae, which help to manage pest aphids in cereals and other crops. At first, this sounds great: more yield, more beneficial insect predators. But the increased hoverfly abundance would suggest greater pest abundance, and furthermore, cereal aphids could benefit much more from increased yield than their predators, which need a greater range of resources.

I really liked this study, because it was thorough in its methods, both in its design and the range of biodiversity that it covers. It can be pretty tricky to compare different systems over such a large area, given how much the local landscape can affect the abundance of flora and fauna, but despite this, the results are quite clear and well presented. The arguments around sparing land versus sharing land with wildlife were well covered, and it raises some interesting questions about how agriculture will cope in the future demands for higher yields.

Laura Vickers

Laura Vickers

I have to admit when this paper was suggested I found the title rather intriguing. You hear people generally quoting that organic farming has greater benefits for biodiversity than intensive agriculture as though it is the accepted norm. The message comes from everywhere, particularly the big supermarkets looking for the best marketing angle for their new product, so this paper made quite a refreshing read.

At the beginning of the paper the authors introduce two concepts; land sharing and land sparing. The land sharing scenario is where available land is under low intensity agriculture, the decrease in intensity of cultivation allows biodiversity to be conserved, making up for the increase in land needed for production. The land sparing scenario is where land is subdivided into areas specialised for intensive agricultural production and areas for maintaining biodiversity.

One particular feature I really liked in the paper was how the authors clearly identified the scientific questions they are asking in their study. This is the first paper I have read that clearly states questions at the beginning of the paper, and it is certainly something that I would like to see more often. Table 1 was simple to understand and clearly set out the summary data for crop yield and species density for the different farmland taxa in the conventional and organic fields. It included detail on the method of sampling for each taxa, which was particularly useful for quickly referencing methods.

The discussion and conclusion were easy to follow and the main conclusions of the study were that farmland biodiversity is typically negatively related to crop yield for both conventional and organic farming. The paper concluded that the modest biodiversity gains from organic production can not clearly be justified by the substantial reductions in food production. It suggested that organic farming should be mainly encouraged in low productivity, mosaic landscapes. The results of the paper indicate that there is no single solution to the debate of land sparing vs. sharing, instead suggesting that the solution may differ depending on the species group and the landscape.

Overall, the authors presented a solid data set, with data collected from a total of 165 fields from 29 farms over 2 years. The language, style and detail presented in the paper made it an easy to follow study, and the conclusions of the authors highlighted some important points with regards to balancing the need for increasing food production and maintaining biodiversity.

Lynsey McInnes

Lynsey McInnes

Well, this was a bit of a foray into the unknown for Will and I. Applied Ecology? Ouf.

I found the paper to be well-presented and well-written, investigating the trade-off between provisioning for biodiversity and for higher crop yields is affected by conventional and organic agricultural practices (OK, this might not have been the exact aim but it was the part I was most interested in). The authors more or less find that organic practices do not do better than conventional practices in provisioning for biodiversity (which a lot of hippy dippies, including myself, might have thought they did).

I appreciated the time the authors spent on the caveats of their study and share their concern over the perhaps truncated variation they found because their study design meant that the conventional and organic sites were paired (close by) and unpaired fields (of either type) might exhibiit more extreme results. More ancedotal checks could be done to see if this really is the case, I guess.

Two thoughts that came to my mind. First, although they mentioned it, the authors seemed to shy away from the more social/economic issues surrounding conventional vs. organic practices. These days, surely part of the tradeoff comes from what people are willing to pay for the crops/crop products? On both sides, many members of the public have entrenched opinions on whether they want to eat conventional or organic foodstuffs. How would incorporating ‘people’ affect the conclusions?

Second, could this study contribute (maybe it is already), to a larger-scale study looking at agricultural practices over broader spatial scales and different crops? What generalities emerge?

Apologies for the fairly superficial comment above, and thanks to Fran & Co. for given me plenty of food for thought.


About will.pearse
Ecology / evolutionary biologist

3 Responses to Food production vs. biodiversity: comparing organic and conventional agriculture

  1. seantuck12 says:

    I have caught this post a little on the late side, but why not comment anyway. I don’t consider this specific area to be ‘what I do’, but nevertheless I have found myself these last few months working on a project very much related to this (will be submitting any day now).

    I just have a few comments, some of which will echo what has been said already. The first and most obvious point is that, as well as biodiversity, evaluation of organic farming in relation to crop yields should account for the effects of farming practice on wider environmental factors. It is already mentioned above that impact of crop pests in the system is not assessed. As another example, nitrogen and phosphate pollution caused by leaching from intensively managed fields is still a major problem in many countries.

    It is probably also worth mentioning, if organic systems support higher biodiversity, the evidence is mounting that crop yields in organic systems may be more stable over time, and less vulnerable to collapse with changing environmental conditions. Intensively-farmed monoculture crops may be more susceptible to infectious disease.

    This study was based on cereal crops in Southern England, but there is still some controversy on whether this yield-diversity trade-off is more prominent in developed countries. We have an incredibly Euro-centric view of organic farming.

    I’ll finish with a more general (hopefully not too simplified) and controversial thought. Yes, it looks like we are faced with future demands on food production that would cripple current supply. But rather than focus only on population growth, much of this is a product of Western consumption. Let’s consider also that the agricultural landscape is a very important resource for European species. Maybe, then, when we are enjoying our high-calorie diet we should think more about the consequences it has for biodiversity in our agricultural landscape and beyond.

    • will.pearse says:

      I agree. I often wonder (and I think there is a fair bit of work on this) whether, given the intensity of demand we’re about to place on agricultural systems, maybe we’re better off not worrying about surroundings areas at all. Perhaps we should just draw a fence around some areas, write them off in terms of biodiversity, and then focus on keeping other areas pristine. That’s a bit extreme, but I do fear that having a lot of areas that are friendly to wildlife is not quite the same as having lots of areas that are exactly what natural wildlife needs.

      • seantuck12 says:

        The old land sharing vs land sparing debate. You’re right in thinking there has been work on this. The discussion has got a bit more intricate though, as it seems the most appropriate management is contingent on how complex the surrounding landscape is, and how high the potential yield is for that farm.

        Organic farming is essentially a land sharing option. The extreme perspective you mention is land sparing. Let’s just think about Europe for a minute. Agricultural land takes up a massive proportion of the European landscape. If we took a full throttle land sparing approach tomorrow, personally, I highly doubt we would see much land being ‘given over to nature’. Plenty of species have done well in extensively-managed farmland and are threatened by intensification. Also, it seems clear to me that some organisms are necessary on the farm to support pollination and pest control, which contribute to yield. We know too that the effects of maximising yield at any expense would not stop at the fence surrounding our pristine area, but have a much wider impact than the farm it was applied on – neonicotinoids being a current example. Add in that we can’t guarantee the long-term safety of pristine areas anyway, and I start coming down on the land sharing side of the debate.

        As I said, it’s more detailed than that: instead of thinking about converting all farmland one way or the other, it needs to be what’s best on a case by case basis. My two cents on the whole thing anyway, for what it’s worth.

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