The post provided by Zahed Shakeri, Daniel Simberloff, Markus Bernhardt-Römermann and Rolf Lutz Eckstein
This post refers to the article The impact of livestock grazing and canopy gaps on species pool and functional diversity of ground flora in the Caspian beech forests of Iran by Shakeri et al., published in Applied Vegetation Science (https://doi.org/10.1111/avsc.12592)
Many European countries banned livestock grazing in forests due to conflicts between commercial forestry and livestock grazing during the 19th century. However, despite forest grazing interdictions, domestic ungulates continue to graze commercial forests in many developing countries, such as Iran. Historically, there has been a conflict between the forest service and forest dwellers in Iran because of the high dependence of local communities on livestock husbandry on the one hand and the scarcity of forest resources on the other. Iran’s Caspian Forest (also known as the Hyrcanian) consists of two million hectares of commercial forest, and it is a UNESCO World Heritage Site since July 2019.
For millennia, the traditional transhumance livestock husbandry system has remained unchanged in the Caspian region, with domestic cattle roaming freely in the forest during daytime and returning to cowsheds at night without human assistance. Most often, dogs accompany cows in order to protect them from predators and to bring them back to camp. During the year, cow herders move their herds along an elevational gradient to take advantage of free forage and to exploit appropriate weather conditions. The domestic cattle (Bos taurus) are the closest descendants of the aurochs (Bos primigenius) that originally grazed in Europe and Asia. In areas where megaherbivores are absent, the local cattle act as substitutes for native species.
Despite a long tradition of animal husbandry in forests throughout the Caspian region, commercial forestry is relatively recent. Shelterwood and strip cutting have been used in this area since 1959. Often, forestry plans fail to ensure that target species regenerate after the final cut in the face of the high pressure of cattle grazing. As a result of the inability to exclude cattle from the forest and the regeneration failure of target species, the Iranian forest service introduced close-to-nature silvicultural techniques in 1980 that avoid creating large openings in the forest, and the service encourages single-tree and group-tree selections. Nevertheless, the Iranian Forest Administration considers forest logging and livestock grazing the most important factors in deforestation and biodiversity loss. Therefore, late in 2017, the Iranian Forest Administration decided to end all logging projects and prohibited forest exploitation for ten years to protect commercial species and biodiversity, which sparked several debates between supporters and opponents of this action.
The cattle grazing, harvesting, and canopy gaps are spatially patchy in the Caspian forests. We examined the effects of these disturbances on species pools, single traits, and functional diversity by analyzing the vegetation and environmental variables of Fagus orientalis-dominated stands in northern Iran. Based on grazing and light intensity (altered by harvesting and canopy gaps), we classified our sites into four groups based on relative light and grazing intensity: low light-low grazing, low light-high grazing, high light-low grazing, and high light-high grazing. We showed that both light and grazing intensities significantly affected species pools, single traits, and functional divergence. By encouraging early-successional plants, sites with higher light intensity have a larger species pool and higher beta diversity in the Caspian beech forests; however, they have lower functional diversity than low-light sites mainly because of trait convergence.
Early successional species inside the gaps (e.g. raspberry, bluegrass, and wood sedge) can provide abundant and attractive forage for cattle, so cattle prefer to graze in such open areas of the forest. Therefore, by reducing the abundance of dominant plants, grazing may assist plants with different functional traits and enhance functional diversity.
Silvicultural methods such as single-tree and group-tree selection have been practised in Iranian Caspian forests since 1980, and livestock grazing has also been practised for a long time. As part of a strict conservation measure to protect biodiversity in these forest ecosystems, the Iranian forest administration prohibited cattle grazing in 1967 and harvesting in 2017. Nevertheless, our empirical data demonstrated that traditional cattle grazing could not only maintain species diversity and increase functional diversity in Caspian Oriental beech forests but also allow sustainable forest management.