Natural grasslands are Uruguay’s main natural ecosystem in terms of size, biological diversity and ecosystem contribution. Except for fishing, almost all of the country's productive development has taken place at the expense of this ecosystem, with transformation processes initially driven by extensive agriculture more than a century ago.
Since then many research projects have investigated the functioning of natural grasslands, including analyses of changes in vegetation composition after being transformed by agricultural production such as cattle grazing or rotation for agricultural crops. This natural ecological succession is very well known and, some years after the last crop, native species return to form a vegetation type similar – but not the same – to the original, the so-called re-established grassland. Because industrial forestry is more recent in the country, dating back to around 30 years ago, fewer studies analyse this impact on grasslands used for afforestation.
Taking the research initiative
“At UPM we wanted to address this critical issue scientifically, providing local knowledge for responsible forestry production,” says Iván Grela, Biodiversity Coordinator at UPM Uruguay.
In collaboration with the Faculty of Agronomy at the University of the Republic (UDELAR), UPM began by monitoring seven farms – five in the western part of the country and two in the northeastern Department of Tacuarembó. This resulted in a decade-long cooperation between UPM and UDELAR, reinforced with two Master’s theses on vegetation and on soil seed banking (natural storage of seeds in soil).
“The project examined various afforestation scenarios to evaluate how vegetation evolves in areas once planted with eucalyptus or pine species. These studies monitored sites and compared regenerated areas with adjacent untouched natural grasslands,” Grela explains.
High regeneration capacity
The results revealed that, beyond the characteristics of each farm, all show a tendency for the herbaceous vegetation to regenerate in a different way to that of a re-established natural grassland’s vegetation after agricultural intervention.
In the case of agriculture it was observed that, initially, annual weeds predominate. This is followed by short-lived perennial species and, over time, by long-lived perennial grass species that indicate the final recovery towards a natural grassland similar to its pre-transformation status – a re-established grassland.
In contrast in afforestation a faster increase in the richness, diversity and cover of native perennial grass species was observed after harvesting, with a low presence of weeds, indicating a quicker recovery compared to agriculture.
When comparing re-established, i.e. previously forested, natural grasslands with untouched plots, there are similarities in the amount and diversity of plants, although differences in what types of plants are present. Studies show that these differences tend to decrease over time.
Reinforcing sustainable forestry
In conclusion, the studies indicate that a re-establishment of natural grassland is possible after at least two rounds of tree plantations for pulpwood (i.e. 20 to 22 years) – without the need for special management measures after harvesting, just cattle grazing.
“These results underscore the potential for balance between productive forestry and ecological restoration. The natural grassland’s capacity to regenerate shows that productive land use and biodiversity can go hand in hand,” Grela concludes.
