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Feeling The Heat – Fruit Trees Are Having A Hard Time

Fruit Trees Are Having A Hard Time

Shiny, red apples like Red Delicious are a must have for any Indian fruit platter. They may taste mealy and past their prime, but as fruit that can only be grown in the foothills of the Himalayas they remain as much a luxury as mangos or pineapples might be in the UK.

Red Apples

In spring, hillsides in the lower regions of the northern states of Himachal Pradesh and Uttarakhand are tinted white and pink by apple blossoms. Apple growing used to be a major income source for farmers in these areas. That was thirty years ago, today orchards at an altitude of about 1,500 m are all but gone and the processing plants have closed down. A 2013 study found that due to warmer temperatures and less snowfall apple production had decreased by 77% between 1981 and 2007. For the farmers there was nothing they could do but switch to other crops.

It’s not the summer heat that causes the problem, apples, like many other fruit and nut trees need ‘chill hours’, a certain number of hours during winter in which temperatures are below a certain temperature – not hard frost but cool temperatures between 1,5° C and 7° C.  It’s the time in which the tree rests, a peach farmer told me. If winters aren’t cool enough the trees get not enough rest and behave in spring like us when we have had too little sleep or woke up too often: they get grumpy and nothing goes right. With too few chill hours many of the tree’s flower buds won’t open in spring or they might open at hugely different times, too early or too late to coincide with the presence of the right pollinators, and the tree’s production of leaves may be delayed too. If the tree produces fruit at all they are often small and prone to disease. How many chill hours an apple tree needs depends on the variety – anything between 100 and 1100 hours[1]. Pears want 800 – 1100 chill hours, peaches 400 – 1050 and, cherry trees over 1000 hours.

In Europe and North America the main issue is unseasonal frosts, and fruit growers have come up with ingenious (though not exactly environmentally friendly) ways of protecting their trees from frost – from giant fans to actual heaters. But there is no way to provide chill hours which is why apple orchards in India have moved up the mountains. If Rudyard Kipling’s Kim were to visit the hamlet of Chitkul at the far end of the Sangla valley today he would have made his way through apple orchards at an altitude of 3,000 m and above!

Growing apples at altitude

But moving up the mountains isn’t an option everywhere. In Germany, just south of Stuttgart, Jörg Geiger produces alcoholic and non-alcoholic sparkling wines from heritage apple and pear varieties as well as stone fruit. The landscape is beautiful but there isn’t much fertile soil on the slopes of the Swabian Alps. Traditionally farmers used such marginal land just for grazing, they planted a few trees to provide shade for the sheep in summer and fruit in autumn. The trees can grow 15 m tall and often get over 100 years old. But climate change is taking its toll. In particular cherry trees don’t get enough chill hours, the trees produce very small fruits and in summer it can be so hot that they dry on the tree like raisins. Jörg Geiger has planted new trees higher up on the slopes, but that won’t be an option much longer – the mountains are not that high. He hopes that some of the apple and pear varieties may be able to adapt to the changing conditions. Unlike trees in commercial orchards meadow fruit trees are grafted onto strong rootstock, the trees grow enormous crowns and the roots reach deep. It takes up to 10 years until they start producing fruit, but their longevity also gives the trees a better chance of survival though adaptation.

Leaving the survival of fruit trees to nature is not our only option. What’s desperately needed is investment into plant breeding. Most of the commercially available apples have a very narrow genetic base, they were all bred from a handful of varieties and ‘share’ the same ancestors, selected for criteria like high yield, crispness, sweetness and (red) colour. How long will they cope with fewer and fewer chill hours? Developing a new fruit variety takes decades, which may be one reason why few breeders do it. Those who still work on finding tomorrow’s bestselling apple should not just look for taste and yield but add other criteria too – like needing fewer chill hours.

[1] Figures from Laura Lengnick: Resilient Agriculture.