Stemflow metazoan transport from common urban tree species (São Paulo, Brazil)

Abstract

For precipitation to reach the surface of vegetated ecosystems, it must first pass through the canopy. A portion of precipitation, stemflow, drains down branches to the stem. This stemflow may wash canopy-dwelling animals (metazoans) into the litter and soils below; however, stemflow metazoans transport has typically been ignored in past research. In fact, the visual presence of metazoans in stemflow collection bins was reported as "contamination" in past research. Thus, we know little about these organisms' transfer from plant canopies to the surface. To investigate this topic, we monitored metazoan concentrations and composition within stemflow that drained from eight urban tree species (n = 3 per species) over 12 months. Annual (±SE) stemflow recorded from all 24 sampled trees was 19.6 (±3.3) mm (2.3% rainfall). Analysis of 288 samples found 1,307 individuals distributed into seven classes (16 orders) and one organism at phylum level. Considering all trees (n = 24), the annual mean metazoan density in stemflow was 8.6 individuals L À1 . Among tree species, there were considerable variations, ranging from 1.0 to 17 individuals L À1 .Annual metazoan transport per tree ranged from 20 to 376 individuals m À2 y À1 . The most common taxa observed in stemflow from this site included Arachnida (10%), Collembola (33%) and Insecta (56%). Variability in metazoan density within and across species was high, but individual trees with the highest metazoan stemflow density and flux were those with large diameter and exfoliating bark structure. This study demonstrates that stemflow can transport a substantial and diverse meso-and macro-fauna to the surface of urban forests. Future work may be merited on the fate and/or role of these metazoans in litter and soil systems.