Vegetation

• Assess current and long-term trends in vegetation composition, structure and condition within native grasslands, wetlands and forests.
• Track long-term trends in magnitude and extent of browse on vegetation.
• Document status and trends in non-native invasive plant species presence and cover.
• Document plant community change by assigning plots to Minnesota native plant community types in the field and assess quality and condition of native plant communities over time.
• Document status and trends in forest structure.
• Track long-term trends in forest succession by tracking height and diameter (DBH) and by documenting tree mortality and regeneration.
• Determine status and trends in the volume of coarse woody debris.
• Track changes in canopy cover in forest stands.

Landscape Context

• Determine relationships between landscape context (e.g., size of surrounding natural area and proximity of anthropogenic land use) and changes in native grassland, wetland, and forest vegetation.

Soils

• Assess soil type and health in order to relate it to trends in grasslands, wetlands, and forests.
  • Qualitatively assess topographic position, aspect, and soil type at the onset of monitoring.
• In upland forests, assess forest floor condition and compaction by documenting litter type and depth and amount of exposed bare soil. In addition, using a rapid assessment method, track impacts of earthworms using visual indicators to understand potential effects on vegetation or soil compaction.
• In peatlands, document organic soil depth and depth to mineral soil and track status and trends in substrate as it relates to peat type, hummock height, and dominant bryophytes.

Hydrology

• Assess hydrology and its relationships to trends in wetland vegetation.
  • Document long-term changes in hydrology in select sites that represent a spectrum of wetland types.
  • Assess status and trends of pH in wetland vegetation.

Pollinators and Other Wildlife

• Collect baseline surveys of select groups of pollinating insect species occurring in targeted vegetation types.
• Document high priority vegetation characteristics related to wildlife habitat (e.g. snags and depth of leaf litter).

Pests and Pathogens

• Assess the extent and degree of known pest and pathogen outbreaks.  

Current proportions of EMN monitoring plots

Objective: Track effects of browsing on vegetation

Heavy browsing by herbivores such as white-tailed deer can negatively impact forest vegetation. Deer eat tree seedlings and saplings and can suppress regeneration of the species that would otherwise form the future tree canopy. This can lead to shifts in forest composition and structure. Over-browsing of forests can also lead to reduced deer populations long-term and reduce other ecosystem benefits provided by healthy forests.

• EMN evaluates the effect of deer browsing on woody vegetation less than two meters from the forest floor.
• Browse pressure is measured as a ratio of browsed to total branches of all woody species in the plot.
• EMN forest plots in southern Minnesota appear to be experiencing consistently higher browse pressure than plots in northern Minnesota.

Figure 4. Levels of browse pressure within individual EMN plots (ratio of browsed:total branches). Larger dot size represents higher browse pressure by deer. Click to enlarge

Objective: Document status and trends in non-native invasive plant species

Initial Work and Observations

• Non-native species cover is the ratio between the sum of non-native species cover compared to total species cover in a plot.
• EMN plots installed in prairies have higher relative non-native species cover than plots installed in forests. This difference is likely driven by two invasive grasses, Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis), that occur largely in non-forested habitats.
• EMN plots installed in southern communities have higher relative non-native species cover than plots installed in northern communities.

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Figure 7. Ratios of non-native species cover to the total species cover at each EMN plot. Larger cylinders represent higher relative non-native species cover. Plots are categorized into four groups by ecological classification system: Fire Dependent Forest (red), Mesic Hardwood Forest (green), Upland Prairie (yellow), and Wet Prairie (orange). There appears to be a spatial pattern of increases in relative non-native species cover from north to south and east to west. In addition, upland and wet prairie systems appear to have high relative non-native species cover than fire dependent and mesic hardwood forests.

Ratios of non-native species cover to total species cover in northern vs. southern floristic regions in four Ecological Systems. Overall, plots in the southern floristic regions of each system appear to have higher cover of non-native species compared to their northern counterparts. The prairie systems have noticeably larger invasive species cover than the forest systems.

Objective: Determine status and trends in volume of coarse woody debris

Coarse woody debris (CWD) is the large dead wood present in the forest. CWD includes both snags (standing dead trees) and fallen logs. CWD plays a major role in natural forest processes, including providing habitat (e.g., small mammals, invertebrates), cycling nutrients, and storing carbon.

• Map View
• Table View

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Initial Work and Observations

• EMN staff measure the diameter of all downed woody debris (and strongly leaning snags) ≥ 7.5cm in diameter that intersects the 45-meter-long center lines of EMN plot transects.
• From these measurements, volume is estimated for the amount of CWD that would occur in a full hectare ( m^3/ha )

Objective: Assess multiple factors impacting forest floor conditions

Under natural conditions in forests, leaf litter breaks down slowly leaving the forest floor layered with organic matter in various stages of decomposition, from intact leaves to finely decomposed particles. Several native forest plant species are adapted to this slow layering process, requiring finely decomposed leaf litter, called duff and humus, to survive. Invasive earthworms, transported into Minnesota by human activity since the 1700s, are rapidly removing duff and humus layers in forests throughout many parts of Minnesota. Measurements of leaf litter and humus are collected in forested EMN plots to assess the presence and impact of invasive earthworms.

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Initial Work and Observations

• EMN uses the Invasive Earthworm Rapid Assessment Tool (IERAT) to evaluate depletion of leaf litter on forest floors by earthworms. IERAT scores range from 1 in plots with intact, unfragmented litter, duff, and humus layers (i.e., no worm effects), to 5 in plots characterized by bare mineral soil with abundant earthworm casts and middens (i.e., high worm effects).
• IERAT was developed for mesic hardwood forest systems, like sugar maple and basswood dominated communities.
• EMN plots show higher levels of invasive earthworm impacts in mesic forests in the southern half of the state relative to the northern half.