When thinking about forests, the average European citizen will picture an ecosystem that has been shaped by human activity for hundreds of years. In fact, today, more than 70% of European forests are used for timber harvesting. Only a small percentage of all extant European forests have remained in a relatively natural state, where biodiversity and ecosystem processes have been able to develop in an undisturbed way. If you have ever visited such a pristine forest, you will know the difference.
The Białowieża Primeval Forest in Eastern Poland (Puszcza Białowieska), is the last pristine forest ecosystem of the European lowland. The 625 km2 of forest in Poland consists of a mosaic of patches of with different intensities of forestry activities. The special thing about the forest is that potentially an area of about 45 km2 has never been commercially logged. This core area has thus been a realm where forest flora and fauna have developed in a natural way since the last ice age. Therefore, the Białowieża Forest represents a unique reference site to study how the fragmentation and conversion of continuous old-growth forest ecosystems to secondary habitats alters the structure of ecological communities and associated ecosystem processes.
In our study, we worked in this unique forest ecosystem to investigate the effects of forest fragmentation on plant-frugivore interactions and seed dispersal processes. We investigated the characteristics that determine a species’ response to fragmentation, and how this relates to effects on seed dispersal processes. Our results are based on more than 2,000 observation hours of fruit-eating animals on nine fleshy-fruited plant species in Białowieża Forest.
We found that forest dependent and large-bodied fruit-eating birds and mammals were less common in fragments than in continuous forests. However, species with a loose dependency on forests as well as small-bodied species maintained seed dispersal services even in small forest fragments.
Our findings from a temperate forest contrast with the high vulnerability of seed dispersal processes reported for most tropical forests. They highlight, that despite the absence of certain vulnerable species, seed dispersal can still be maintained in fragmented forests. Thus, species communities may to some degree be able to tolerate processes like forest fragmentation. Yet, the loss of vulnerable species may have unforeseen consequences, e.g. by decreasing chances for rare long-distance dispersal by large-bodied frugivores, which is crucial for the persistence in a fragmented landscape and even for range shifts at large spatial scales.
In future studies, we aim at investigating the consequences of species loss on other aspects of seed dispersal, such as spatial patterns of dispersal, seed germination and plant regeneration. We want to achieve a better understanding of how human activities impact important ecosystem processes and how natural dynamics in forest ecosystems can be conserved in our human-dominated European landscape.
Nina Farwig, Philipps-University Marburg, Germany