EMN July 2024 Update

The tables and figures below summarize Ecological Monitoring Network (EMN) progress and patterns in the data being collected, as plots are installed and surveyed across Minnesota. Regular resurveys in the future will document long-term change, or stability, in vegetation in the monitoring plots. The patterns highlighted below relate to several of EMN’s basic objectives: for example tracking trends in invasive species and detecting change in measures of forest health. These highlights represent just a small fraction of the information and patterns that can be extracted from data that will be collected over time at EMN plots.

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.

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.

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.