Rhododendron ponticum – you love it or you hate it

While working in the South-West of England in nature conservation, I came across the plant Rhododendron ponticum quite often. In England, it is grown in many gardens for its beautiful flowers. Unfortunately, it has the nasty habit of escaping and invading the surrounding native woodlands. Once there, the species seeds itself in large amounts, and creates deep shade, outcompeting the native woodland flora. Conservationists are therefore fighting what seems a never-ending battle with this plant and even include sinister practices like chemical warfare (stem injection).

A plant that survived the ice-ages

In Strandja, however, it is a different story. The plant grows here naturally and the Strandja Mountains are one of the few places where it survives; not the war with mankind, but the battle with the ice-ages!

Rhododendron ponticum is here known as Strandja Rhododendron or Zelenika. It is the official symbol of the Strandja Nature Park and the most characteristic species of the area. The people in Strandja adore rhododendron. They are so fond of it that they organise a whole festival around it every year: the Zelenike festival!

Flagship species in Strandja

Strandja Rhododendron is also a flagship species for a whole host of other plants that are now only found in this remote corner of Europe (for example as Caucasian Whortleberry and Double Lilac Primrose). All these plant species started to evolve about 65 million years ago, during the Tertiary. This was the time when the age of the dinosaurs had ended and mammals were emerging as the dominant species on the planet. The worldwide climate was warm and wet; tropical conditions prevailed, that gradually became cooler over millions of years, culminating in the last ice ages that started about 1.8 million years ago.

The vegetation that had developed during the warmer and wetter conditions was pushed right back South, and only managed to survive in a few climatic mild and wet pockets. One of these areas is the Strandja Mountains. Land ice never reached this region, but in addition the area remained relatively warm and wet under influence of the Black Sea, the Aegean Sea and the Marmora Sea. Strandja’s terrain also played a role. Sea winds push humid air further inland through the deep river valleys, which keeps conditions wetter here. Morning mist in the valleys is a very common sight in the East part of Strandja. So at the end of the ice ages, these Tertiary plant communities only survived in a few areas. They are still here now and form windows to the vegetation of the past.

Evolutionary survival tactics

Nowadays, the climate is once again relatively mild and wet in a few places in Europe, like the South-West of England. The species does not occur in the UK naturally, because glaciations made it impossible for the species to survive. But the beauty of the flowers has persuaded people to once again bring it to their gardens in other parts of Europe, and from there it is colonizing long-lost territory. Certainly an interesting evolutionary survival strategy! However, if you want to see the ponticum rhododendron, and many other beautiful relicts in their natural habitat, a visit to Strandja Park is a must!