Leafcutter Ant Nests Inhibit Low-Intensity Fire Spread in the Understory of Transitional Forests at the Amazon's Forest-Savanna Boundary

Abstract

Leaf-cutter ants (Atta spp.) remove leaf litter and woody debris-potential fuels-in and around their nests and foraging trails. We conducted single and three annual experimental fires to determine the effects of this leaf-cutter ant activity on the behavior of low-intensity, slow-moving fires. In a transitional forest, where the southern Amazon forest meets the Brazilian savanna, we tested whether leaf-cutter ant nests and trails (i) inhibit fire spread due to a lack of fuels, and (ii), thereby, reduce the total burned area during these experimental low-intensity fires, particularly at forest edges where leaf-cutter ant abundance was higher. Finemedium fuel mass increased with an increase in distance from ant nest, and the mean area of bare soil was greater on nests than on the forest floor. Between 60 to 90 percent of the unburned area was within 30 m of ant nests, and burned area significantly increased with increasing distance to ant nests. In addition, the number of ant nests declined with increasing distance from the forest edge, and, with exception of the first experimental fire, burned area also increased with increasing distance from the edge. The present study provides new insight to fire ecology in Amazon environments.

Forest edge orientation influences leaf‐cutting ant abundance and plant drought stress in the Brazilian Atlantic forest

“…A distance‐related pattern that appears to be highly consistent, however, is the edge‐induced proliferation of LCA colony density. The increased LCA colony density in the first 50‐m edge zone compared with farther edge distances (>150 m) conforms well with previous studies reporting a strong and persistent (Wirth et al ., ; Meyer et al ., ; Dohm et al ., ; Carvalho et al ., ; Barrera et al ., ) negative relationship between LCA abundance and edge distance. In addition to edge distance, LCA colony density is also under the influence of edge orientation, as demonstrated by the higher LCA colony density in north‐facing edges.…”

“…This group of winner species combines a set of morphophysiological characteristics that in turn influence the patterns of plant–herbivore relationships along forest edges, resulting in the proliferation of generalist herbivores worldwide from boreal to tropical, dry to wet, and evergreen to deciduous forests (Wirth et al ., ). Leaf‐cutting ants (LCA; Formicidae: Attini) are a prime example of such edge‐induced herbivores given their drastic (up to 20‐fold) increase in colony density along the edges of neotropical wet forests and savannas (Rao et al ., ; Terborgh, ; Wirth et al ., ; Dohm et al ., ; Carvalho et al ., ; Rao, ; Barrera et al ., ). Three key mechanisms (not mutually exclusive) have been proposed to explain this pattern.…”

The Multiple Impacts of Leaf‐Cutting Ants and Their Novel Ecological Role in Human‐Modified Neotropical Forests

“…, Carvalho et al . ). Together with the fact that these colonies harvest equal amounts of biomass, smaller foraging areas ( e.g ., 0.9 vs. 2.3 ha/col/yr, Urbas et al .…”

Could biodiversity loss have increased Australia's bushfire threat?

“…Herbivory is well documented as affecting fire regimes by removing fuel on plants and fuel that can fall as leaf litter (Leonard, Kirkpatrick & Marsden‐Smedley, ; Ingram, Doran & Nader, ). Bioperturbating species, such as bower birds and lyrebirds, alter litter volume and distribution, and thereby reduce fire likelihood (Mikami et al ., ; Carvalho et al ., ; Nugent et al ., ). Here, we aimed to determine whether the extinction of members of Australia's critical weight range mammal fauna (Burbidge & McKenzie, ) has led to an increased accumulation of fuel that would potentially affect the rate of fire spread.…”