Tag Archives: nature

Are there tipping points in pest management?

Tipping points are common in nature. When systems are disturbed beyond a certain point – a tipping point – they may undergo irreversible or hardly reversible changes that provoke shifts towards undesirable system states. It is often difficult to get systems back from this new ‘stable’ yet undesirable situation. Examples are many. A classical one comes from the work of Marten Scheffer in The Netherlands. He studied the dynamics of shallow lakes as they undergo phases of turbidity as influenced by nutrient loads or pollution. You can find out more about his work here.

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How about agricultural systems subject to high pesticide pressure? 

Synthetic pesticide applications are standard practice in conventional farming systems because they are simple to use, cheap, and usually effective in providing short-term reduction in pest densities. Yet, their effectiveness as a long-term sustainable pest management strategy is debated. This debate has been fuelled by the introduction of recent technologies, such as neonicotinoids seed coatings and herbicide tolerant GMO crops, with uncertain outcomes for biodiversity and resistance development.

Historic cases show that the use of pesticides can set off a positive feedback process whereby natural enemy populations are decimated and pesticides become the only pest management option left. The positive feedback between pesticide use and natural enemy mortality suggests the possibility of tipping point dynamics where the system can “tip” from a biocontrol dominated state to a pesticide dominated state. Tipping the system back from the pesticide dominated state to the biological control state could be challenging and require persistent efforts to allow a recovery process of natural enemy populations. Such transition may depend on landscape context and involve complex interactions between human actors and the agro-ecological environment.

The question remains: is there evidence for such tipping points? This will be the central question to be addressed during the debate that will bring Felix Bianchi, Dave Mortensen, Doug Landis and me together at a workshop organised by the PE&RC Graduate School of Wageningen University.

MORE INFORMATION: Poster-Tipping points in pest management

Agriculture, nature and the yellow press

In my current job coordinating a natural resources and environment program in Argentina I often come across complex issues labelled as ‘conflict’ between agriculture and nature conservation. The presumed damaged caused by wild animals to agriculture and livestock is a particularly tough one. From wild herbivores such as guanacos or deer competing for grass against sheep and cattle, to grain-eating birds shopping through mature grain crops, or pumas and foxes dining on tender lambs or chicks, such cases make it repeatedly to the national and local press and cause agitation amongst farmers. This has been the case of, for example, the poor mourning dove.

Slide1 The mourning dove became a new ‘plague’ to the sunflower crop. And how does our cultural wisdom deal with plagues? Control them! Poison them! Shoot them! Part-time hunters are always ready to jump at any opportunity to justify their shooting (and their polluting the place with lead and noise); much better still when this can be done in the name of ‘nature management’. This is exactly what happened with the poor mourning dove.


Granted, mourning doves are perhaps not your favourite wild bird, they are not what you may call emblematic biodiversity, but they do have their ecological function, their place in nature. Other bird species, such as local parrots or the migratory cauquén, experienced a similar fate. (The cauquén, which lands on agricultural fields in big flocks, was even accused of generating soil compaction! Later on research showed that this was total nonsense).

Who eats what… and how much?

What’s the best way to deal with this kind of conflict? Let’s recur to science, to knowledge, to information, I would say. Or, as Julieta von Thungen, responsible for this line of work in our program puts it: “we should do what we know best; and we do know how to count”. And counting they did. Jaime Bernardos, Sonia Canavelli and their teams monitored mourning doves, their temporal and spatial dynamics during the cropping season, their presence, distribution and feeding patterns in sunflower fields and the level of damage they caused, expressed as a percentage of the harvest that was lost to the birds. And what did they find? See for yourself:

Slide3In short, lots of fields with insignificant damage, with less than 1% of the harvest lost, and a few fields with about 30% harvest losses. Does this justify going out to shoot mourning doves or poison them, creating risks for other species as well?

Such a pattern in the reaction of farmers and the civil society is common to most agriculture-nature conflicts and it is largely driven by perceptions. Once an animal species is perceived to be a plague there is no way of stopping this type of behaviour.

Science to the rescue?

Here again science has a crucial role to play by providing hard evidence, knowledge and information. Not just about leves of economic damage; there is also evidence that choosing the right species of trees to plant around fields, such as deciduous species that grow less than 15 m tall, can reduce the population of potentially damaging birds such as doves and parrots. By contrast, it seems that evergreen species like Eucalyptus and Pines are very attractive for their nesting.

Unfortunately the funding necessary for the type of field work necessary to monitor presence, incidence and damage – which in the case of mourning doves involves just a field car, fuel and man-hours, whereas for the puma it would involve installing a large number of sensor infrared cameras, and a lot of patience – comes only after the problem started, often too late to prevent it.

Moreover, such basic research may also be discouraged through insufficient academic reward, as the results are not always attractive to the editors of high impact journals due to lack of scientific novelty. And, as we scientist know all too well, poor publication records translate into even less funding. Who should be doing this kind of less-rewarding, basic, but extremely useful research?

I have no immediate answer to this. But one possibility is to establish what is known as ‘observatories’ of sustainability, similar to those used to monitor the impact of tourism. Imagine a portion of a landscape or territory under human use in which all the basic environmental and biodiversity monitoring research is done over sufficiently long periods of time, generating the necessary data to inform discussions and decisions. Some examples of this already exist. Let me investigate a bit more and come to that in another post.

Meanwhile, when it comes to agriculture-nature conflicts, let us please stay away from the yellow press.