RESEARCH

Blooming warning

THE JACARANDAS (Jacaranda mimosifolia), which were primarily planted during the 19th century as a source of timber for the Gold Rush, are in full bloom during spring time in the cities of Johannesburg and Pretoria.

For Witsies the blossoms signal final exams are not far away.

A study by Dr Jennifer Fitchett (BSc Hons 2012, MSc 2013, PhD 2015) and Andile Fani (BSc 2017, BSc Hons 2018, MSc 2021) has found that gradually over the decades, the date of bloom has advanced through October to the early weeks of September.

This is referred to as a phenological shift and is being observed across a range of species because of climate change. The strongest climatic driver of the phenological advance of the jacarandas was found to be increased daily maximum temperatures during the month of June – the dormant period of the trees. Phenological shifts represent an adaptation strategy for the trees, but this cannot happen indefinitely. As temperatures continue to increase, the risk of heat stress to the trees is heightened. This could mean that the years of purple spring seasons in Gauteng are limited.