How climate, topography, soils, herbivores, and fire control forest–grassland coexistence in the Eurasian forest‐steppe

Abstract

Recent advances in ecology and biogeography demonstrate the importance of fire and large herbivoresand challenge the primacy of climateto our understanding of the distribution, stability, and antiquity of forests and grasslands. Among grassland ecologists, particularly those working in savannas of the seasonally dry tropics, an emerging fire-herbivore paradigm is generally accepted to explain grass dominance in climates and on soils that would otherwise permit development of closed-canopy forests. By contrast, adherents of the climate-soil paradigm, particularly foresters working in the humid tropics or temperate latitudes, tend to view fire and herbivores as disturbances, often human-caused, which damage forests and reset succession. Towards integration of these two paradigms, we developed a series of conceptual models to explain the existence of an extensive temperate forest-grassland mosaic that occurs within a 4.7 million km 2 belt spanning from central Europe through eastern Asia. The Eurasian forest-steppe is reminiscent of many regions globally where forests and grasslands occur side-by-side with stark boundaries. Our conceptual models illustrate that if mean climate was the only factor, forests should dominate in humid continental regions and grasslands should prevail in semi-arid regions, but that extensive mosaics would not occur. By contrast, conceptual models that also integrate climate variability, soils, topography, herbivores, and fire depict how these factors collectively expand suitable conditions for forests and grasslands, such that grasslands may occur in more humid regions and forests in more arid regions than predicted by mean climate alone. Furthermore, boundaries between forests and grasslands are reinforced by vegetation-fire, vegetationherbivore, and vegetation-microclimate feedbacks, which limit tree establishment in grasslands and promote tree survival in forests. Such feedbacks suggest that forests and grasslands of the Eurasian forest-steppe are governed by ecological dynamics that are similar to those hypothesised to maintain boundaries between tropical forests and savannas. Unfortunately, the grasslands of the Eurasian forest-steppe are sometimes misinterpreted as deforested or otherwise degraded vegetation. In fact, the grasslands of this region provide valuable ecosystem services, support a high diversity of plants and animals, and offer critical habitat for endangered large herbivores. We suggest that a better understanding of the fundamental ecological controls that permit forest-grassland coexistence could help us prioritise conservation and restoration of the Eurasian forest-steppe for biodiversity, climate adaptation, and pastoral livelihoods. Currently, these

Relationship between extreme species richness and Holocene persistence of forest-steppe grasslands in Transylvania, Romania

“…The results of recent studies suggest that both views can be reconciled if we take into consideration all major factors driving forests-steppe development, i.e. climate, topography, soil and disturbance regime (Chytrý, et al 2022; Erdős et al, 2022). The synthesis of Feurdean et al (2018), based in part on case studies from the Transylvanian Basin, proposed a general model of Holocene grassland persistence in the East-Central European lowlands.…”

“…The occurrence of open and semi-open ecosystems in potentially forested landscapes raises questions about their origin and long-term dynamics. In addition to climate, other possible driving factors such as topography and especially the disturbance regime come to the fore (Chytrý et al, 2022; Erdős et al, 2022; Sümegi et al, 2012).…”

Plant functional traits couple with range size and shape in European trees

“…Similarly, the extensive European forest‐steppe region harbours several deciduous tree species characterized by relatively higher resource‐acquisitive strategies, including Tilia cordata , Ulmus glabra and Populus tremula (Erdős et al., 2018). Hence, the wider distribution of these species could be linked to their relatively faster growth rate favoured by milder climatic conditions characterizing the Eurasian forest‐steppe mosaics (Erdős et al., 2022) compared, for example, to the drier Mediterranean climate.…”

Multifunctionality of angiosperm floral bracts: a review

“…(5) Protection from fire Fire has a significant impact on various aspects of plant performance and functioning, prompting plants to evolve diverse traits for adaptation, particularly in environments prone to frequent fire, such as grass-dominated habitats (He, Lamont & Pausas, 2019;Erd} os et al, 2022). Recent research conducted by Simpson et al (2021) has demonstrated that awns of grass play a crucial role in fire protection through their ability to enhance seed burial.…”

“…Fire has a significant impact on various aspects of plant performance and functioning, prompting plants to evolve diverse traits for adaptation, particularly in environments prone to frequent fire, such as grass‐dominated habitats (He, Lamont & Pausas, 2019; Erdős et al ., 2022). Recent research conducted by Simpson et al .…”