The Mainz Sand Dunes landscape is a nature reserve in the northwest of the city of Mainz. The flora here is considered a relict of post-ice age steppe landscapes that covered large expanses of Central Europe about 9,000 years ago. It is the only area in Central Europe that has been able to retain this character thanks to the particular local conditions. It is thus of supraregional significance.
A dry and cold climate dominated the Rhenish Hesse region during the late phase of the last ice age some 18,000 years ago so that only the sparse vegetation similar to what is now found in the tundra could survive here. Due to the lack of plant development and the dryness at this time, large amounts of the calcareous sand deposited in the bed of the Rhine were transported by the wind to the northern slopes of the Rhenish Hesse plateau. This process continued with interruptions until around 10,000 years ago and, as a result, an expansive region of sand dunes developed in the area between Ingelheim and Mainz that extended southwards as far as Darmstadt and Heidelberg.
The Scots pine (Pinus sylvestris) was the first tree species to reestablish itself in our region with the gradual warming of the climate in the later phase of the ice age, approximately 12,000 years ago. The termination of the ice age 10,000 years ago was followed by a period with dry, warm summers and cold winters. It was at this time that steppe plants from Southeastern Europe and Western Asia spread far into Central Europe. As the warming continued, plants from the Mediterranean region followed. Some 8,000 years ago the climate then became more moist, allowing other tree species to return to Central Europe. First to develop were mixed oak forests until the European beech (Fagus sylvatica) arrived around 5,000 years ago and became the dominant tree species. As forest cover became increasingly extensive, the steppe plants were forced out of Central Europe. They were only able to survive here in just a few locations.
There were two factors that promoted the survival of the steppe grasslands in the sandy regions between Mainz and Ingelheim: The warm, dry climate prevented the growth of most species of trees on sandy soils with their poor water retention properties. In addition, humans kept these sandy areas open by using them extensively for grazing over a longer period. The Mainz Sand region was further used for military exercises until the end of World War II. These activities also inhibited the development of plant growth here. Today, extensive preservation work, mainly carried out by volunteers, is required to maintain the steppe vegetation character of the area. Since 2002, the Botanic Garden has participated annually in the preservation program in the nature reserve.
In addition to Eastern European steppe plants such as feather grasses (Stipa capillata and Stipa joannis), the rare purple goldendrop (Onosma arenaria), and the fastigiate gypsophila (Gypsophila fastigiata), there are also plants that migrated here from the Mediterranean region. These include honewort (Trinia glauca), the sprawling needle sunrose (Fumana procumbens), and the field eryngo (Eryngium campestre). This combination of Mediterranean and continental floral elements can only be found in the Mainz Sand reserve.
Ever since its foundation, the Botanic Garden of Johannes Gutenberg University Mainz has maintained a display for the plants of the Mainzer Sand region to be viewed and studied. This display was originally positioned opposite the Alpinum at the Anselm-Franz-von-Bentzel-Weg entry. When the Botanic Garden was expanded in 1982, it was possible to create a large new site that reproduced the conditions in the Mainz Sand Dunes nature reserve. The sand for this recreation was taken from the excavation pit of the Budenheim glass foundry in the Gonsenheim Forest. As part of the redesign of the JGU Botanic Garden, the Mainz Sand site was relocated to the core area of the garden in April 2006.
The plants of the Mainzer Sand Dunes reserve, some of which are very rare, can thus be bred and preserved in the JGU Botanic Garden. Due to the high number of visitors from all age and population groups, the Botanic Garden is an ideal location for promoting awareness of the significance of this nature reserve.