Alert farmers watch carefully for signs of heat stress in their herds: faster breathing, grazing less, drinking more and moving slower. Because cows graze less and use more energy when it’s hot, heat stress is known to cause billions of dollars’ worth of losses to meat and milk production globally. The economic impact of heat stress on cows is projected to become more severe due to climate warming.
Tree establishment to provide shade in pastoral livestock farming holds a lot of potential as a nature-based adaptation tool to reduce cattle heat stress. To establish trees in the best way to help cows, we must answer a complicated mix of questions – what type/s of tree, planted where, and in what densities? And what are the likely financial benefits of increasing on-farm shade on future milk and meat yields?
Researchers led by Dr Dan Richards at Manaaki Whenua have now developed a general model for the impact of trees on cattle heat stress, carefully piecing together the effects of various climatic elements including air temperature, wind speed and humidity with tree characteristics such as height and leaf density. They have added high- resolution mapping of over 400,000 farm management units to estimate the amount of shade currently available to the beef and dairy herds across New Zealand, and used all this information to model milk and meat production under future climate scenarios at varying scales. The work neatly links to other work currently being done at Manaaki Whenua on the potential benefits of planting mosaics of trees in pastoral landscapes for carbon capture.
The modelling shows that existing tree cover already brings impressive economic benefits to New Zealand. The simulated current contribution of trees to national milk yields is in the order of 500 million extra litres of milk to the overall total of around 20 billion litres per year, which conservatively works out at an additional US$200 million of revenue per year based on 2017 milk prices. For meat production, the contribution of trees is around 8000 tonnes of meat to an annual national total of around 110,000 tonnes – an extra US$37 million of revenue.
Adding more shade trees to pastures could bring even bigger economic returns. The maps in the model estimated that tree shade is currently (as of 2020) not available to around 3 in 10 cows in New Zealand’s dairy herd and to around 1 in 5 of the beef herd. If additional trees were established to ensure universal access to shade for cattle and minimise the risk of heat stress, the modelling showed that by 2070-2080 there could be an increase in national milk yields of an average of 350,000 litres per year and an increase in meat yields of an average 2500 tonnes per year, within a range of yields depending on the degree of future climate change.
This big-model approach to nature- based adaptations provides powerful evidence to benefit New Zealand’s future farmers, and Dan – an ecologist by training – has learned a lot about cow physiology and behaviour in the process. “We know that the effects of trees on keeping cows comfortable and productive are context-dependent and multi-dimensional, varying with wind speed, solar radiation, cloudiness, tree species and leaf density, as well as dominance within herds and cow breed,” he says. “In the future we will refine these parameters and customise the model so that it can zoom in and predict what trees will do across a region or even at the farm scale, so that we can make specific, evidence-based recommendations to farmers around what to plant and where.”
