How much forest does biodiversity need in cultivated landscapes?

Lacandonon Jungle in southeastern Mexico: The one hectare forest in the middle h

Lacandonon Jungle in southeastern Mexico: The one hectare forest in the middle has tall trees that serve as nesting places for rare macaw parrots. Photo: Victor Arroyo-Rodriguez

Research team with Göttingen participation develops concepts to promote biodiversity

Forests, especially in the tropics, are home to the world’s greatest biodiversity, but are threatened by increasing land use. An international research team with participation of the University of Göttingen has investigated how high the proportion of forest in cultivated landscapes must be in order to protect the greatest number of animal and plant species that depend on this habitat. The proportion of forest must be at least 40 percent: around ten percent in large protected areas and 30 percent scattered across the countryside. The fragments of forest should preferably be surrounded by a landscape with small-scale, structure-rich, managed land to reduce the probability of population extinction. The results have been published in the journal Ecology Letters.

The researchers, led by Dr Victor Arroyo-Rodriguez at the National Autonomous University of Mexico, evaluated literature for the study and presented approaches for the design of cultivated landscapes that are suitable for the sustainable protection of forest flora and fauna, whether specialist or generalist species. This requires large forested areas. In Brazil, for example, this was already known and led to the Brazilian Forest Code, a law dating from 1965, according to which farms in the Amazon region must designate up to 80 percent of their land as protected forest areas.

However, protecting forests isn-t just about looking after large forests, but also about small patches of forest, which need to be distributed over the whole landscape or region in order to provide maximum protection for habitat diversity and biodiversity. Cultivated landscapes that are small in structure and have a high proportion of agroforestry systems, or crops such as fruit trees, promote the preservation of the biodiversity typical of forests. Areas of ecological succession (where plants and animals typical for the site return following disturbance of the habitat), riparian zones (strips of natural vegetation alongside a stream or river) and forest corridors all reduce the probability of animals and plants becoming extinct.

"All interventions which increase nature conservation in cultivated landscapes are most efficient when they bring about a significant improvement. This is shown to be the case in landscapes that have already suffered severe habitat loss, but not in landscapes which were already diverse," emphasises Professor Teja Tscharntke, Head of the Agroecology Group at the University of Göttingen and co-author. "However, the priority in nature conservation must be to preserve the remaining large, old forest landscapes, especially in the tropics".

Original publication: Victor Arroyo-Rodriguez et al.: Designing optimal human-modified landscapes for forest biodiversity conservation. Ecology Letters.

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