DOI: 10.5061/dryad.dbrv15f38
title: Data from: Woody plant secondary chemicals increase in response to abundant deer and arrival of invasive plants in suburban forests

description: Plants in suburban forests of eastern North America face the dual
 stressors of high white-tailed deer density and invasion by nonindigenous
 plants. The combination of chronic deer herbivory and strong competition
 from invasive plants could alter a plant’s stress- and defense-related
 secondary chemistry, especially for long-lived juvenile trees in the
 understory, but this has not been studied. We measured foliar total
 antioxidants,  phenolics, and flavonoids in juveniles of two
 native trees, Fraxinus pennsylvanica (green ash) and Fagus grandifolia
 (American beech), growing in six forests in the suburban landscape of
 central New Jersey, USA. The trees grew in experimental plots that had
 been subject for 2.5 years to factorial treatments of deer
 access/exclosure X addition/no addition of the nonindigenous invasive
 grass Microstegium vimineum (Japanese stiltgrass). As other hypothesized
 drivers of plant secondary chemistry, we also measured non-stiltgrass herb
 layer cover, light levels, and water availability. Univariate mixed model
 analysis of the deer and stiltgrass effects and multivariate structural
 equation modeling (SEM) of all variables showed that both greater
 stiltgrass cover and greater deer pressure induced antioxidants,
 phenolics, and flavonoids, with some variation between species. Deer were
 generally the stronger factor, and stiltgrass effects were most apparent
 at high stiltgrass density. SEM also revealed that soil dryness directly
 increased the chemicals; deer had additional positive, but indirect,
 effects via influence on the soil; in beech PAR positively affected
 flavonoids; and herb layer cover had no effect. Juvenile trees’ chemical
 defense/stress responses to deer and invasive plants can be protective,
 but also could have a physiological cost, with negative consequences for
 recruitment to the canopy. Ecological implications for species and their
 communities will depend on costs and benefits of stress/defense chemistry
 in the specific environmental context, particularly with respect to
 invasive plant competitiveness, extent of invasion, local deer density,
 and deer browse preferences.
description: Data were collected in six suburban forests in central New
 Jersey, USA, within 16 m<sup>2</sup> plots, with half fenced
 to exclude deer. Variables measured for this study were:
 - Proportion cover of all plants in the herb layer, scored in 10%
 intervals and measured in 16 0.25 m<sup>2</sup> subplots per
 plot - Ground-level photosynthetically active radiation
 (PAR), measured as the percent of full sun PAR, using five measurements
 per plot made with an AccuPAR ceptometer - Soil water
 potential measured on two samples per plot with a benchtop WP4
 meter - A deer browse index for each plot, set to zero
 for fenced plots and assigned to one common value for all unfenced plots
 within one forest, based on the proportion of deer-browsed individuals in
 unfenced plots of five native plant taxa: <em>Carya spp., F.
 grandifolia, Fraxinus pennsylvanica, Acer rubrum</em>, and
 <em>Rubus allegheniensis</em>. These were included because
 they were sufficiently common in the forests’ understories to allow for
 one index applicable to all of the forests and because they were, in our
 sites, neither the most browsed species nor completely avoided by
 deer-browsed In these same plots, leaf tissue was
 collected from Fagus grandifolia and Fraxinus pennsylvanica, dried at 50
 deg C and used in chemical analysis of total antioxidants, total
 phenolics, and total flavonoids.  All data were entered
 and managed in Excel data files, and statistical analysis was done in SAS
 for mixed model analysis and in R (piecewiseSEM package) for structural
 equation modeling
description: A ReadMe file is included with detailed information.