Stemflow metazoan transport from common urban tree species of varying
canopy structure
Abstract
The stemflow may wash canopy-dwelling metazoans to the litter and soils
below; however, metazoans transported by stemflow have been typically
ignored in past research. In fact, the visual presence of metazoans in
stemflow collection bins was reported as “contamination.” 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 8 urban tree species
over 12 months. Metazoan concentration and composition in stemflow were
also analyzed with respect to tree canopy and bark traits to assess
whether, or to what extent, canopy metazoan dispersal was affected by
canopy structure. Tree structural traits studied here, include bark
texture, stem diameter at breast height (D) and canopy height-to-width
ratio (H:W). These traits were sorted into three classes: (1) furrowed-,
flaky/exfoliating- and smooth-bark texture; (2) <10, 10-20 and
>20cm D; and (3) <1, 1-2 and >2 H:W.
Analysis of 288 samples found 1,307 individuals distributed into 7
classes (16 orders), and one organism at phylum level. There were
considerable variations in metazoans’ density [ind L
-1] in stemflow, ranging from 1.0 to 16.9 ind.L
stemflow −1. Variability across individual trees was
high across species, but individual trees with the highest metazoan
stemflow density and flux were flaky-exfoliating-barked individuals in
the largest D size class with moderate-to-high canopy. On the other
hand, based on trait groups across all individuals, higher stemflow
metazoan density and flux was generally observed in smooth-bark trees in
largest D and H:W classes.