Zomer, M. A. | bioRxiv Science

bioRxiv2020

The impact of fire intensity on plant growth forms in high-altitude Andean grassland

Fires in the paramo grasslands of the tropical northern Andes vary in intensity at the landscape scale. Fire suppression strategies, intended to conserve biodiversity and paramo ecosystem integrity and function, could lead to the accumulation of high fuel loads and ultimately fires of higher intensity. Yet the impact of fire intensity on paramos is not well studied or understood. 5[1/2] years after a fire, we measured plant growth form composition, light transmission to the ground and soil temperature in plots representing very high, high, medium, and low fire intensities, plus a "control" that had been unburned for at least 40 years. We also assessed Espeletia rosette diameters, heights, population density, and mortality. The low intensity plot, with a closed canopy of vegetation and lower growth form diversity, contrasted with the very high intensity plot, with patchy vegetation cover and higher growth form diversity. The high intensity plot had shorter Espeletia plants with smaller rosettes. Light transmission to the ground increased with fire intensity, as did soil temperatures. We demonstrate that the same fire can produce different microenvironmental conditions, plant communities, and population structures in different parts of the same fire event. In future, fire suppression could provoke more intense fires with consequences for ecosystem function and service provision. Since intensity is determined by a complex interaction of factors, we advocate a field programme of experimental fires for a better understanding of paramo fire ecology and to guide effective paramo conservation strategies.

ecology↗

bioRxiv2020

Post-fire changes in plant growth form composition in Andean paramo grassland

QuestionsFire suppression policies have been widely adopted in the paramo grasslands of the northern Andes to protect their biodiversity and ecosystem services. Paramos have been regularly burned for many years, and it is not clear how paramo vegetation will respond to significant changes in their fire regimes. This study investigates differences in plant growth form composition, light levels and soil temperatures in paramo plots representing a range of recovery times since the last fire. LocationReserva Ecologica El Angel and La Bretana Nature Reserve, Carchi, Northern Ecuador. MethodsWe assessed the frequency of ten paramo growth forms, vegetation height, soil temperature, and light intensity in fifteen fire sites with historical records of fire (<1 - 15 years since fire), and one recently unburned site (at least 40 years since fire). A chronosquence of sites was used to assess potential changes in plant community composition in post-fire succession of paramo. ResultsThe recovery of paramo vegetation after fire comprised three phases: initial recruitment with high growth form diversity, followed by reduced diversity, light and soil temperatures in dense tussock vegetation, and ultimately canopy height stratification with a return of diversity. All but one plant growth forms were represented in each of the three phases, and the changes reflected differences in relative abundance. ConclusionsPost-fire paramo succession is characterized by clear shifts in the relative abundance of plant growth forms, ending with (co-)dominance of upright shrubs. The long-term consequences of such shifts for biodiversity and ecosystem function, given the widespread adoption of fire suppression policies in the paramo need careful, evidence-based consideration.

ecology↗