Shrub and Herbaceous Plants at Sherburne National Wildlife Refuge

Plants across Control, Thin, ThinBurn and ThinBurnGraze treatments

Drew Pearson

Background

Yantes et al. abstract (2023)

Comparing Shrubs and Herbs using NMDS ordination

Focus:

  • Plant species composition

  • Shrub abundance

  • Herb abundance

Treatments

  • No Management

  • Tree Thinning

  • Tree Thinning + Burning

  • Tree Thinning + Burning + Cattle Grazing

Data

  • Shrubs: 55 species (242 plots)

  • Herbs: 54 species (242 plots)

Treatment Plots
Control 34
Thin 70
ThinBurn 68
ThinBurnGraze 70

Methods

Data Setup

  • Sites grouped by treatment: Control, Thin, ThinBurn, ThinBurnGraze
  • Split data into
    • Shrubs (55 species)
    • Herbs (54 species)

Ordination

Ran NMDS for each plant group using Bray-Curtis distance on abundance:

  • Shrubs: 2 dimensions, stress = 0.183
  • Herbs: 3 dimensions, stress = 0.198

Stress has to be lower then 0.2

Analysis

Used envfit to regress each species onto NMDS space.

Filtered meaningful variables(p< 0.05).

Filtered arrows for plotting based on R² thresholds:

  • Shrub > 0.05
  • Herb > 0.25

R² thresholds were somewhat arbitrary but kept to retain variables with ecological meaning and interpretive value.

Shrub NMDS Biplot

  • Each point is one of the 242 plots.

  • Lots of overlap between treatments due to the large abundance of different species of Shrubs.

  • Strongest shrub species: American Hazelnut, Blackberry Raspberry, Red Maple.

Herb NMDS Biplot

  • Some overlap between treatments, some distinct groups

  • ThinBurn plots are concentrated in the upper-left and center of the chart, near the Hogpeanut and Sedge arrows.

  • Thin is spread out, most on right side.

envfit test

  • Tests each species against the NMDS ordination (R² and permutation p-value).

  • Species with higher R² are concentrated in plots that are similar to each other.

  • Low R² means the species is scattered across plots with no clear pattern.

Shrub

Variable R2 p_value
American Hazelnut 0.649 0.001
Blackberry Raspberry 0.552 0.001
Red Maple 0.144 0.001
Northern Red Oak 0.139 0.001
Bur Oak 0.093 0.001
Black Chokeberry 0.060 0.004
Poplar Aspen 0.060 0.004
Black Cherry 0.052 0.003

Herb

Variable R2 p_value
Virginia Creeper 0.411 0.001
American Hogpeanut 0.350 0.001
Pointed leaved Tick Trefoil 0.326 0.001
Pennsylvania Sedge 0.325 0.001
Western Poison Ivy 0.310 0.001
Canada Mayflower 0.275 0.001

Significant Shrub variables

  • American Hazelnut increases in abundance as more disturbances happen

  • Red Maple, Northern Red Oak, Bur Oak are mostly in Control and near zero in treated plots

  • Black Chokeberry is present in only a few plots, so its pattern isn’t visible in the boxplot

Significant Herb variables

  • Hogpeanut, Tick Trefoil, Sedge peak at ThinBurn

  • Virginia Creeper and Poison Ivy have a ThinBurn median of 0, while the other treatments are around 2–3

  • Canada Mayflower has a Thin median around 2, and ThinBurnGraze is flat at zero.

Summary

  • Treatment plots showed differences in species composition for both shrubs and herbs.

  • Shrubs differentiate the plots more than herbs. Their strongest species have higher R², the treatment differences are clearer, and herb treatments overlap heavily.

  • Shrubs showed higher abundance of American Hazelnut in ThinBurnGraze and Blackberry/Raspberry in Thin, while Red Maple, Northern Red Oak and Bur Oak were more abundant in Control.

  • Herbs showed higher abundance of American Hogpeanut, Pointed-leaved Tick Trefoil and Pennsylvania Sedge in ThinBurn, and Canada Mayflower in Thin.