Summer Branch Drop

Several areas of the Botanic Garden are roped off. A sign explains that is to protect visitors from the risk of falling branches as a result of Summer Branch Drop. That can occur when trees are drought stressed, and when they take up water after a period of drought. It is unpredictable, and not related to other indicators of tree health.

The Drought FAQ page of the Botanic Garden website mentions that branch drop can affect any tree but is particularly known to affect cedars, pines, oaks, beeches, chestnuts and poplars, as well as old trees.

Rain taken up by branches after drought can weaken them to the point that branch drop can occur – usually six to eight hours after heavy rain.

While some trees are sacrificing branches, others such as this Yoshino cherry, are curling up their leaves to limit transpiration.

Meanwhile, no real rain for almost a month.

Osage Orange 2022

I’ve been looking out for the fruiting bodies of the Osage Orange (see the post from last year) and today I spotted the first one. There may be others on the tree, but this is the only one I saw. It is about two inches (five cm) in diameter. And as you can see it is covered in these hairs.

Osage Orange fruiting body

July Heat and Drought

In March at the Cambridge University Botanic Garden, the Yoshino Cherry (Prunus x yedoensis) was flowering. The flowers of the Yoshino Cherry are white when they are fully open, but tinged with pink when the buds are closed or just opening.

Now in late July the flowers have gone, but the leaves are bright. and the tree stands out against the pale buff of the dry grass.

The grass is pale buff because it hasn’t rained since the end of May, and even that was just a light shower. How long can grass do without rain before it is too late for it to recover?

There were two long days of record breaking heat a few days ago, with a high of 37°c. The forecast is that it will rain today and tomorrow, and after that there is no rain forecast for the next two weeks. The question is how much will it rain today and tomorrow? The grass especially, needs hours and days of steady rain.