Prof. Meelis Pärtel, University of Tartu
Dr. Aveliina Helm, University of Tartu
Prof. Markus Fischer, University of Bern, Switzerland
Habitat loss and fragmentation are one of the greatest threats to biodiversity in the modern world. We used Estonian alvar grasslands, which have gone through a major area loss over the last century as a model system to investigate plant species responses to habitat fragmentation. We found that alvar grasslands in northern Estonia had lost almost 30% of their former habitat specialist species richness and that plant populations in the western Estonian alvars also showed notable responses to past landscape changes. Species and trait responses revealed susceptibility to habitat connectivity loss, which hinders seed dispersal and pollen movement between sites and can lower the genetic diversity and site species richness. Moderate human impact is necessary for the persistence of these semi-natural grasslands and their specialist species. Our results confirmed that moderate human impact supported population performance of the species more susceptible to landscape changes. At the same time, overly intensive human impact lowered population genetic diversity.
Genetic diversity, plant trait responses and population performance all showed a time-lag in their response to landscape changes, similarly to a delay in species richness recorded in many communities around the world. It is necessary to recognise that the current state of populations is transitory and that populations are still in progress of responding to landscape changes that occurred decades ago. This time-lag makes plant populations more resilient to changes on the on one hand, but at the same time cautions us to take it into consideration when making long-term conservation decisions.