Post-fire consequences for leaf breakdown in a tropical stream

Consequências do pós-fogo para a decomposição foliar em riachos tropicais

Abstract

Aim  Wildfire is a natural pulsed disturbance in landscapes of the Savannah Biome. This study evaluates short-term post-fire effects on leaf litter breakdown, the invertebrate community and fungal biomass of litter from three different vegetal species in a tropical stream.

Methods  Senescent leaves of Inga laurina, Protium spruceanum and Rircheria grandis (2 ± 0.1 g dry mass) were individually placed in litter bags (30 × 30 cm: 10 mm coarse mesh and 0.5 mm fine mesh) and submerged in the study stream before and after fire. Replicate bags (n = 4; individually for each species, sampling time, fire event and mesh size) were then retrieved after 20 and 40 days and washed to separate the invertebrates before fire event and again immediately after fire. Disks were cut from leaves to determine ash-free dry mass, while the remaining material was oven-dried to determine dry mass.

Results  The pre-fire mean decomposition coefficient (k = -0.012 day^-1) was intermediate compared to that reported for other savannah streams, but post-fire it was lower (k = -0.007 day^-1), due to decreased allochthonous litter input and increased autochthones production. Intermediate k values for all qualities of litter post-fire may indicate that fire is equalizing litter quality in the stream ecosystem. The abundance of scrapers was found to be more important than fungal biomass or shredder abundance, probably due to their functioning in leaf fragmentation while consuming periphyton growing on leaf litter.

Conclusions  Theses results indicate that fire can modify the relationships within decomposer communities in tropical stream ecosystems.

Keywords:  litter decomposition; indirect fire effects; allochthonous litter; short-time scale