Washington, July 4 : Scientists have demonstrated that natural disturbances such as flooding and animal diseases are very important for the diversity of natural areas.
For research into the matter, Dutch Rubicon laureate Chris Smit investigated a large number of blackthorn seedlings between five and ten years old in the Junner Koeland, a 100 ha, species-rich natural area along the Overijsselse Vecht river in The Netherlands, which has been grazed extensively for centuries.
Young blackthorns have scarcely been spotted there over the past 30 years.
These observations coincided with a considerable reduction in the rabbit population since the end of the 1990s, caused by the disease viral haemorrhagic septicaemia (VHS).
The establishment of scrub is an important process that leads to greater variation and diversity in a landscape.
Prickly shrubs such as blackthorn and hawthorn provide a valuable safe haven for many plant and animal species. The thorns protect these plants and animals from grazing by large mammals.
Smit's experiments show that blackthorn seeds under the scrub are quickly eaten by small mammals such as mice. Thorns provide no protection against this.
However, Smit discovered that the young plants in the Junner Koeland frequently grew in recently flooded sections among high vegetation that was inedible for grazers.
Blackthorn seeds in the inedible vegetation have better chances of survival.
Thus, large and small grazers together limit the spread of blackthorn, with the influence of the small grazers seeming to be the greater.
Current nature management policies will need to take more account of the importance of small mammals and natural disturbances when it comes to the diversity of natural grasslands.
Large grazers have now been introduced on a wide scale in Dutch natural areas.
One of the main aims of this introduction is to promote greater natural diversity in the landscape, as greater diversity leads to more plant and animal species.