PART THREE: Climate Resiliency of Prairies and Oak Ecosystems
Using Historical Oak Savannas as a Model for the Future Climate of Minnetonka Prairies and oak ecosystems are more resilient to extreme heat, droughts, and fluctuating temperatures than cool, damp closed canopy forests. The deep-rooted prairie-like vegetation creates a vast network of fibrous roots that help build soil organic matter and are the conduit between the plant and soil microorganisms and fungi that help facilitate the exchange of sugar, water, and nutrients. With projections of the future Minnetonka climate becoming similar to the state of Kansas in terms of average precipitation and temperature, oak savannas will be more tolerant to extremes in heat and drought and likely easier to manage and maintain due to the adaptability of these ecosystems to withstand stress.
Carbon Sequestration These grassland systems have been shown to sequester more tons of carbon per acre than forests, storing the majority of carbon permanently in the soil, rather than in aboveground vegetation or trees as would occur in a forest. This aboveground storage in trees is temporary; when the tree dies and starts to decompose, the stored carbon is re-released into the atmosphere.
There are two primary ways in which prairies and oak ecosystems store carbon in the soil.
Sixty to eighty percent of the biomass of grassland plants occurs belowground and about one-third of the extensive belowground root system dies every year. The carbon in this plant tissue remains belowground, sequestered in the soil.
During photosynthesis, plants use energy from the sun to convert atmospheric carbon dioxide and water (atmospheric and soil) into carbohydrates (sugars) and oxygen. Excess sugars are secreted from the plant roots into the soil which feed soil microorganisms that, in return, provide the plants minerals and water.
Soil Conservation Soil disturbance and erosion can result in the oxidation of soil carbon and its release back into the atmosphere. The dense ground layer vegetation of prairies and oak ecosystems not only builds soil organic carbon but it also helps prevent soil erosion. In contrast, dense, shaded forests have very low ground layer plant diversity and the leaf litter is readily consumed by non-native earthworms. This can result in large areas of bare soil that are susceptible to soil erosion.
Oak ecosystems that become invaded by fire-intolerant trees are also more susceptible to invasion by invasive plant species. When a full invasion occurs, the system deviates from its stable state and shifts to an unstable state. This deviation continues to compound, resulting in a self-reinforcing feedback loop.
Biodiversity, Ecosystem Stability, and Resiliency Oak savannas (plant communities with scattered bur and white oak trees and a prairie-like ground layer vegetation) are some of the most biodiverse ecosystems, hosting a significant number of plant, animal, bird, and insect species. This diversity helps ensure that the plant community remains adaptable if a disturbance occurs, or as the climate continues to get warmer. In contrast, the mixed, closed canopy forests one observes in Minnetonka’s parks or open spaces today, may be high in tree diversity, but are low in overall plant diversity (and biodiversity).
Consequently, oak ecosystems that become invaded by fire-intolerant trees are also more susceptible to invasion by invasive plants such as European buckthorn and garlic mustard. When this occurs, the system deviates from its stable state and the resulting shift to instability compounds and becomes a self-reinforcing feedback loop. With the use of fire and other restoration management tools, oak ecosystems can sustain a fluctuating (prairie to oak woodland continuum) but stable state, and the system is inherently more resilient.