Fields with trees are cooler and possibly more profitable

‘Drones to detect heat stress in livestock’ was a headline on the Dutch news channel NOS on 18 June this year. Such checks are increasingly needed, says the Netherlands Food and Consumer Product Safety Authority (NVWA). It is mandatory for farmers to provide enough shelter for their cows, sheep, pigs and horses to prevent the animals from suffering from the heat. In previous inspections, the NVWA found that many farmers were indeed providing sufficient cover for their livestock, but some still had a lot of cows exposed to the burning sun and without enough drinking water. 

Brigitte de Bruijn, an animal welfare and health researcher at Wageningen University & Research, notes that dairy cows in particular suffer problems due to heat stress. ‘If they get hot, they start eating less, are more susceptible to diseases and their milk production declines by up to 35 per cent.’ Cows start to experience adverse health and welfare effects at just 21 degrees Celsius and high humidity. The hotter it is and the higher the humidity, the greater the impact on the cow. The phase in the cow’s lifecycle also has an effect. ‘Cows that have just calved are particularly susceptible as they are still recovering from giving birth and are also producing a lot of milk. Milk production costs a lot of energy — you have to be in peak condition.’

The situation was never easy for them, but now dairy cows are increasingly facing extreme conditions. ‘Fifteen years ago, many farmers had the attitude that they did need to protect their cows, but fortunately there were only a few really hot days,’ says De Bruijn. That is no longer the case: the risk of heat stress has increased in the past few years because of climate change. The summers are hotter and heatwaves last longer. ‘Lengthy periods of hot weather with warm nights make conditions more difficult for cows as they are unable to cool down in between.’

Farmers are now taking more mitigating measures, both indoors and outside. They are installing cooling systems with ventilators and nebulizers in their barns. Cooled cubicle stalls are also available, even if they are not widely used yet. De Bruijn would like to do more research on the efficacy of these systems. At present, most of the knowledge about them comes from abroad, where conditions are often different — less humid, for example. More research would let Dutch farmers take the right measures in their barns, based on the scientific evidence. De Bruijn: ‘It would also be nice to give the cows a choice, letting them go indoors or outdoors whenever they want.’ For instance, they could spend the nights in the field and rest in the shade during the day.

If you want more shade in a field, that usually means planting trees and bushes. It is not only cows that benefit from that: insects and birds also get food, shelter and places to build their nests. What is more, the trees and bushes keep the moisture in the soil. Andrew Dawson is a researcher in agroecology and business economics at WUR who specialises in this form of agriculture, known as agroforestry. ‘If you have just a single tree in a field that was deliberately planted to provide shade, that counts as agroforestry. You can also use the trees to produce crops or animal feed, or to enhance biodiversity. Livestock farmers are increasingly practising agroforestry for a combination of those reasons.’

There is fierce competition for the scarce shade in some fields these days, but things were different in the past. Fields used to have far more trees and bushes. ‘They formed hedges that were originally intended to keep the cows in the field but also provided shelter,’ explains Dawson. 

However, farmers replaced the rows of hawthorns or alders with barbed wire, as that was less work and created more space. Mowing was also easier without the trees. ‘We’ve lost more than 200,000 kilometres of hedges and brushwood banks,’ estimates Dawson. Some farmers now want to plant trees again, but they are sometimes prevented from doing so by municipal regulations. ‘It can be difficult to get a permit,’ says De Bruijn. ‘Even my colleague who studies this policy has called it complex. If a field doesn’t yet have trees in it, that is by no means always the farmer’s fault.’

Any farmer who does manage to plant trees for shade will reap other benefits too. ‘Farmers who go about this in a smart way can increase their income,’ says Dawson, who researches agroforestry for both arable and livestock farmers. ‘It’s true that crop yields can be lower in the first few metres around a tree, but they can then be higher further away. The trick is to make sure there is enough light for the plants.’

Only a handful of studies have been carried out on how this works for grass and other crops. In a German study, trees boosted sugar beet yields by 25 per cent. ‘And grass can cope better with partial shade than many other crops,’ explains Dawson. ‘A Dutch trial showed 30 per cent higher yields from grass in the first few years. However, yields declined again as the trees grew bigger.'  

That’s still the sticking point. Heleen van Kernebeek, a researcher into animal production systems, explains why: ‘Trees and grass compete for water, light and nutrients. At the same time, trees create a more aerated soil and improve water retention. We’re very keen to find out exactly how that affects grass growth.’ Until then, the fear that the grass will grow more slowly may deter farmers from adopting agroforestry. But Van Kernebeek believes that farmers will weigh up their options differently in the future. ‘If we no longer have the protection of trees in the landscape, how productive will the landscape still be? Climate change is going to force us to make some very urgent choices.’

Dawson has noticed that farmers who want to start now often opt for species that their cows can nibble on. Hedges of such trees can offer cows different nutrients than they get from the grass and introduce more variety in their diet. Cows sometimes seem to go for specific plants, such as willows because of the pain-killing effect of salicin. Other plants contain tannins, which help the animals get rid of parasites or worms. ‘A hedge with trees the cows can feed on is the most straightforward option. You can plant it in the field or on the path the cows take to the field. Farmers often opt for a solution that is a good fits for their type of farm.’

The cows benefit from the natural shelter and a varied diet, but farmers may be interested in more direct economic advantages, for example from fruit trees. Arable farmers are already showing an interest in walnut and hazelnut trees. Dawson thinks nuts could be a useful source of extra income for livestock farmers as well. ‘They don’t require much manual labour. Farmers can harvest the nuts efficiently using machinery and store them for sale. In the end, it’s not just about what’s feasible but also about what’s profitable. That’s the challenge.’ The researchers therefore intend to set up a study involving nut trees in the coming years to answer that question.

Whether farmers can make a profit will determine where we will see agroforestry being adopted in the future. Dawson certainly sees opportunities in the vicinity of nature areas, in part thanks to Dutch and EU nature policies. That is because brushwood and wooded banks help achieve the nature objectives — they capture ammonia, a nitrogen compound, from the air, store carbon and improve water quality and biodiversity.

All these objectives are important in the environs of Natura2000 areas. Dawson: ‘Farmers in the proposed buffer zones of 500 to 1,000 metres around the Natura2000 areas will be subject to policies discouraging intensive agriculture. That obviously raises questions about how they can still make a profit. Cultivating alternative crops such as nuts could be an interesting option for livestock farmers. Agroforestry is a particularly promising business model for this group of farmers.’