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

Abstract

Fire frequency has been highlighted as an important component of fire effects on ecosystems; nevertheless, there is scarce information about how fire modulates changes in ecosystem properties, particularly for subtropical dry forests. A long‐term natural experiment and a multiscale approach were used to analyze changes in ecosystem properties in a subtropical dry forest subjected to contrasting fire regimes. Measurements were taken in two adjacent sites that had contrasting fire regimes (low/high fire frequency), and vegetation and soil analyses were combined with dendrochronological methods. Ten plots (20 × 20 m) were established in each site and soil (depth, chemical, and biological properties), and vegetation (species composition and growth of the dominant tree, Lithraea molleoides) variables were measured. Fire scars in L. molleoides were useful in determining fire history. Shrubs and grasses were more abundant in the high fire frequency site, with a high cover of the exotic grass Melinis repens, whereas trees and vines were more abundant in the low fire frequency site. Soil of the high fire frequency site tended to have lower C and nutrient content as well a significant lower depth than those of the low fire frequency site. Growth of L. molleoides individuals was lower in the high fire frequency site. Our results suggest that the long‐term effects of high fire frequency probably increase both soil loss and fire frequency in the future due to changes in plant composition, indicating that frequent burning is not a sustainable management option for this seasonal subtropical dry forest.

A global synthesis of fire effects on pollinators

“…The fire interval in these studies ranged from 10 to 12 years ( SD = 5–7 years between fires), and they largely corresponded to wildfires (69%) in extratropical biomes. That is, under non‐tropical environments these short fire intervals tend to be detrimental for pollinators, as for other organisms (Kowaljow et al, ; Kral et al, ). However, we cannot disentangle whether this reduction of pollinators is due to reduced flowering (i.e., immaturity risk under short fire intervals) or to a direct negative effect on pollinators, and thus a disruption of the pollination interaction (Kowaljow et al, ; Vieira et al, ).…”

“…In addition, prescribed fires may be often performed in already open communities, or in understorey of woodlands, and thus the changes in structure are low. In contrast, unmanaged wildfires likely cause more drastic changes in vegetation structure and composition (Carbone, Aguirre‐Acosta, Tavella, & Aguilar, ; Kowaljow et al, ; Pellegrini et al, ) allowing a more significant change (increase) in floral resources for pollinators. The importance of changes in community structure is also evident given that the case studies with the highest positive effect sizes were all temperate forests subject to crown fires (e.g., Bogusch, Blažej, Trýzna, & Heneberg, ; Moretti et al, ; Taylor & Catling, ).…”

“…The fire interval in these studies ranged from 10 to 12 years (SD = 5-7 years between fires), and they largely corresponded to wildfires (69%) in extratropical biomes. That is, under non-tropical environments these short fire intervals tend to be detrimental for pollinators, as for other organisms (Kowaljow et al, 2018;Kral et al, 2017).…”

“…However, we cannot disentangle whether this reduction of pollinators is due to reduced flowering (i.e., immaturity risk under short fire intervals) or to a direct negative effect on pollinators, and thus a disruption of the pollination interaction (Kowaljow et al, 2018;Vieira et al, 2013).…”

Top-down and bottom-up controls on soil carbon and nitrogen cycling with repeated burning across four ecosystems

“…The responses of soil C and N stocks to fire are in part regulated by total plant biomass responses, with larger fire-driven reductions in plant biomass expected to lead to larger reductions in soil C and N (Pellegrini et al 2014, Kowaljow et al 2018). Within fire-influenced landscapes, heterogeneity in soil C and N can result from the local enrichment under individual trees, which can have higher soil C and N concentrations and faster decomposition than areas away from tree canopies (Belsky et al 1989, Ludwig et al 2004, Dijkstra et al 2006).…”