DOI: 10.5061/dryad.2ngf1vhsn
title: The dominant plant species Solidago canadensis structures multiple trophic levels in an old-field ecosystem

description: Dominant plant species are locally abundant and have large impacts on
 ecological communities via a variety of mechanisms. However, few studies
 have evaluated the influence of a dominant plant species both within and
 among trophic levels and on key ecosystem functions such as productivity.
 In this study, we evaluated the effect of the dominant plant species
 Solidago canadensis on plant and arthropod communities in an old-field
 ecosystem in southeastern Michigan. We found that S. canadensis negatively
 correlated with the richness and combined biomass of all other plant
 species in the community, likely by reducing light availability. In turn,
 less biomass of all other plant species led to lower arthropod abundance.
 Specifically, detritivore and predator arthropod abundance was lower with
 less biomass of all plant species excluding S. canadensis, but herbivore
 and omnivore abundance was unaffected. Our results highlight the
 significant role of dominant plants in determining plant diversity and
 ecosystem function, and further suggest that the effect of a dominant
 plant species on a community is observed at higher trophic levels.
description: Site
 description We conducted this study in August 2021 in an old
 field at Matthaei Botanical Garden in Ann Arbor, Michigan (42.30° N,
 83.66° W). Local average monthly temperature ranges from -4.6 ℃ in January
 to 22.6 ℃ in July (ClimateData 2021). Average annual precipitation is 954
 mm (U.S. Climate 2021). The old field we worked in is typically mowed
 annually and burned semi-annually, maintaining it in an early-successional
 state. The most abundant plant species at the site is S. canadensis, a
 perennial, clonal herbaceous species common in the northeastern and
 midwestern United States. At this site, S. canadensis constitutes, on
 average, ~ 50% of above-ground plant biomass (Eckberg, unpublished data).
 Other than S. canadensis, the four most abundant plant species include
 Monarda fistulosa, Vitus riparia, Vicia tetrasperma, and Toxicodendron
 rydbergii (Table S1).  Solidago canadensis impact on plant
 community At the site, we placed 24 1-m2 quadrats in a grid.
 Quadrats were at least six meters apart, and we mowed paths among quadrats
 approximately monthly. To evaluate the effect of S. canadensis on light
 availability, we estimated light intensity above the tallest plants in
 each quadrat and 50 cm above the ground prior to removing all S.
 canadensis stems from each quadrat. We made five light intensity
 measurements above the canopy created by S. canadensis and five below
 using the iOS app Lux Light Meter Pro version 2.1.1 (Polyanskaya 2021).
 Then, for each quadrat, we calculated the average light intensity above
 and below the canopy. We calculated light availability as the proportion
 of light above the canopy that penetrated to 50 cm above the
 soil. To
 evaluate the effect of S. canadensis on the plant community, we first
 estimated biomass of S. canadensis in each quadrat by clipping all of the
 S. canadensis stems at ground level. We then dried the S. canadensis stems
 in each 1-m2 quadrat for 72 hours at 60℃ and weighed them. After the S.
 canadensis stems were removed from each quadrat we estimated plant species
 richness in each 1-m2 quadrat. We then clipped, dried, and weighed those
 other plant species from each 1-m2 quadrat as described
 above. Solidago canadensis impact on other trophic
 groups To
 evaluate the effect of S. canadensis on the ground-foraging arthropod
 community, we buried one 50mL centrifuge tube pitfall trap flush with the
 soil surface in the center of each quadrat after S. canadensis was
 removed, but before we removed other plants. We partially filled each
 pitfall trap with a mixture of water and unscented dish soap. We left
 traps in place for 72 hours and immediately counted and stored arthropods
 in ethanol upon removing pitfall traps. Using a dissecting microscope in
 the lab, we identified arthropods to the lowest possible taxonomic level
 and categorized them by trophic level (herbivore, predator, detritivore,
 omnivore, parasite, or pollinator) using published sources and online
 guides. The most common arthropod families identified were the Formicidae
 (ants) and Armadillidiidae (pillbugs). We collected arthropods once to
 limit damage to the plant community caused by arthropod sampling.
 Additionally, sampling arthropods multiple times may have negatively
 affected arthropod populations and impeded our ability to study how
 arthropods affect, and are affected by, the plant community in this and
 future studies.