Changes in floristic composition and physiognomy are decoupled along elevation gradients in central Argentina

Abstract

Questions Most vegetation descriptions tacitly assume that floristic composition and physiognomy are tightly linked. However, the two vegetation properties may not respond in a similar way to environmental and disturbance gradients, leading to uninformed management planning and difficulties when attempting to restore degraded ecosystems. In this context, we addressed two main questions: (1) how close are relations between floristic and physiognomic types as defined by numerical vegetation classification in mountain ecosystems; and (2) how are floristic and physiognomic types distributed along the elevation gradient? Location Central mountains of Argentina, between 500 and 1700 m a.s.l. Methods We selected 437 sites where we performed complete floristic and physiognomic relevés. We classified eight physiognomic and eight floristic types. We tested the relationship between the two classifications through a chi square analysis. We tested the association between elevation and each physiognomic and floristic type with random permutations. Results In general, floristic types were significantly and positively associated with more than one physiognomic type and vice versa. Physiognomic and floristic types responded differently to the elevation gradient. Floristic types were restricted to different sections of the gradient, although having large overlap among them. In contrast, seven out of the eight physiognomic types did not show elevation restriction, being distributed along the complete elevation gradient. The open low woodland with shrubs was the only restricted physiognomy, significantly absent from the upper part of the gradient. Conclusions We highlight the importance of considering the two vegetation properties independently when characterizing vegetation patterns in heterogeneous systems, since they show decoupled responses to environmental gradients. We note that the assumption of a direct link between floristic composition and physiognomy may induce bias into the understanding of vegetation patterns and processes. Hence, we encourage managers and restoration practitioners to consider the complete range of possible physiognomic types under each floristic type.

A 55‐year‐old natural experiment gives evidence of the effects of changes in fire frequency on ecosystem properties in a seasonal subtropical dry forest

“…Species richness was higher in HF than in LF. This pattern is common in many ecosystems of the world, particularly in dry Mediterranean woodlands (Bond & van Wilgen, 1996;Giorgis et al, 2013Giorgis et al, , 2017Guo, 2001), where richness was found to increase mainly in the first decade after the recurrent fires and to decrease when the forest canopy began to close (Tessler, Wittenberg, & Greenbaum, 2016).…”

“…Woody native species have been found to support fires through different mechanisms: Small or young individuals can resprout from the base, whereas large or mature individuals are more susceptible to fire, but they can escape from fires occurring at the understory level (Gurvich et al, 2005). The pristine condition of the region is still not very well understood (Giorgis et al, 2017). Nonetheless, simulations showed that the region could have been almost completely covered by dry forest (Cingolani, Renison, Tecco, Gurvich, & Cabido, 2008).…”

The role of frugivorous birds in fruit removal and seed germination of the invasive alien Cotoneaster franchetii in central Argentina

“…, ; Giorgis et al . ). The alien shrub Cotoneaster franchetii (Rosaceae, Maloideae) spreads markedly in the region (Tecco ; Giorgis et al .…”

Post‐burning germination responses of woody invaders in a fire‐prone ecosystem

“…The dominant vegetation includes Lithraea molleoides, Schinopsis marginata and other woody species in the forests, Vachellia caven (ex Acacia caven ) in the shrublands and Festuca hieronimy in the grasslands ( see Giorgis et al . and Cabido et al . for full description of the floristic and physiognomic classification of the ecosystem).…”

“…), fire, grazing and the recent advance of woody exotic species are the major drivers of vegetation change in the mountains of the region, transforming the landscape into a complex mosaic of degraded native forests, monospecific stands of woody exotics, shrublands and grasslands (Hoyos et al ; Giorgis et al . , , ; Furey et al . ; Zeballos et al .…”