Natural Notes: Our Essential Oaks
This blog post consists of my notes from a presentation on oak ecosystems of the Greater Chicago Area. The presenter was Kim Blaszcak, Resource Management Project Manager with the Forest Preserves of Cook County. The presentation was delivered on October 6, 2016 at Sand Ridge Nature Center in South Holland, Illinois.
Oaks as a keystone species
Oaks (Quercus spp.) are a keystone species in the Chicago Region. They support many organisms and ecosystem functions. Oaks are important to wildlife through acorn production and habitat. Oaks exhibit a periodic massive yield of acorns known as a mast year that compensated for periods of scarcity. Oak germination and timing of acorn production are important factors. Red oak acorns are produced in the fall and germinate the following spring. white oak acorns produce acorns which germinate in a single season (in the spring).
Oaks are a critical food source for wildlife in North America: 96 % of wildlife species nationwide eat oaks. In Illinois alone, 45% of wildlife species eat oaks (acorns, leaves, bark, etc.).
Oak trees also provide homes and shelter for cavity-dwelling fauna such as cavity nesting birds. Many species of oak trees have leaves that persist through the winter, a phenomena known as marcescence. Fallen oak trees and their leaves help form critical habitat for endangered resources such as wild lupine (Lupinus spp.) and the associated Karner blue butterfly (Plebejus melissa samuelis). Blue-spotted salamanders (Ambystoma laterale) need wet areas with ample fallen branches from oaks such as Swamp White Oaks (Q. bicolor) or other wet-tolerant oaks. Oaks are also important for many invertebrates that live on the trees or amongst the leaf litter. For example, certain species of Lepidopterans, scales, weevils, gall wasps, leaf hoppers, borers, and even walking sticks rely on oak trees in some fashion or another. The leaf litter also provides habitat for certain types of spiders, springtails, and mites.
Certain varieties of fungi are decomposers of fallen oak logs, which in turn helps create cavities for wildlife habitat. Specific types of root fungi, known as ectomycorrhiza, form a sheath on the outside of oak tree roots and assist with nutrient intake. Oaks also have plant associates, including Penn Sedge (Carex pennsylvanica), cream gentian (Gentia alba), and wild coffee (G. sp.? ).
Oak Ecology
Oaks are play an important role in providing or maintaining special abiotic factors, such as light and canopy cover, stormwater absorption and mitigation, soil stabilization, inputs of organic matter, producing clean air, and carbon sequestration.
Oaks are a disturbance-adapted group of trees, especially of fire. In Cook County, oak communities can be classified based upon the intensity and frequency of wildfires:
____________
Hottest
Open Savanna (0-10 % canopy cover)
Savanna (10/20% canopy cover)
Woodland (25-60 % canopy cover)
Forest (60-100 % canopy cover)
Coolest
____________
The variability of oak communities relative to their wildfire frequency and intensity is related to the glacial geologic history of Cook County. Lowland areas dominated the landscape of Cook County, a product of glaciation and the recession of ice and melt-water. Pre-colonial vegetation in Cook County was 73% prairie, with woodland areas near lakes and rivers. Woodland areas were primarily located on the east side of rivers and lakes that were protected from westward wind-driven fires (see below).
Threats to Oak Ecosystems
There are numerous threats to Cook County's oak ecosystems. Only about 5% of Cook County remains as an oak ecosystem today. In current oak stands, there is a lack of age diversity, and the introduction of non-native invasive plants and the development of a mesophytic plant community are replacing oak ecosystems. Other confounding factors include herbivory - especially by deer -habitat fragmentation, and perhaps the extinction of the Passenger Pigeon (Ectopistes migratorius).
Oak regeneration has become suppressed, and new oak growth can remain stuck in the seedling stage for 20 years or more as they build up root and energy reserves for more rapid growth when enough sunlight can reach them. Invasive shrubs can block out sunlight, preventing seedlings from developing. Some invasive shrubs are allelopathic and can kill off the mycorrhiza fungi needed for oak growth and development.
Even earthworms, which are not native to cook county, are contributing to a decline in oaks, as they disrupt soil composition and eat mycorrhiza fungi.
Establishment of shade-tolerant, fire sensitive plants has altered oak communities into more mesophytic (middle-moisture) vegetation such as cherries and maples. For example, fire suppression has allowed for an astonishing 4,119% increase in maple trees in Illinois between 1962-1985!
Deer can eat 6 pounds of tree buds each winter, and they love oaks!
Oak Ecosystem Restoration
Restoring oak ecosystems in Cook County involves removal of invasive brush, canopy thinning, cut-stump herbiciding of invasive woody plants, prescribed burns, and follow-up herbicide applications. Figure 2 represents an example of a restoration procedure, which can be established in concert with priority sights identified in a natural resource management plan, such as the one for Cook County.
Oaks as a keystone species
Oaks (Quercus spp.) are a keystone species in the Chicago Region. They support many organisms and ecosystem functions. Oaks are important to wildlife through acorn production and habitat. Oaks exhibit a periodic massive yield of acorns known as a mast year that compensated for periods of scarcity. Oak germination and timing of acorn production are important factors. Red oak acorns are produced in the fall and germinate the following spring. white oak acorns produce acorns which germinate in a single season (in the spring).
Oaks are a critical food source for wildlife in North America: 96 % of wildlife species nationwide eat oaks. In Illinois alone, 45% of wildlife species eat oaks (acorns, leaves, bark, etc.).
Oak trees also provide homes and shelter for cavity-dwelling fauna such as cavity nesting birds. Many species of oak trees have leaves that persist through the winter, a phenomena known as marcescence. Fallen oak trees and their leaves help form critical habitat for endangered resources such as wild lupine (Lupinus spp.) and the associated Karner blue butterfly (Plebejus melissa samuelis). Blue-spotted salamanders (Ambystoma laterale) need wet areas with ample fallen branches from oaks such as Swamp White Oaks (Q. bicolor) or other wet-tolerant oaks. Oaks are also important for many invertebrates that live on the trees or amongst the leaf litter. For example, certain species of Lepidopterans, scales, weevils, gall wasps, leaf hoppers, borers, and even walking sticks rely on oak trees in some fashion or another. The leaf litter also provides habitat for certain types of spiders, springtails, and mites.
Certain varieties of fungi are decomposers of fallen oak logs, which in turn helps create cavities for wildlife habitat. Specific types of root fungi, known as ectomycorrhiza, form a sheath on the outside of oak tree roots and assist with nutrient intake. Oaks also have plant associates, including Penn Sedge (Carex pennsylvanica), cream gentian (Gentia alba), and wild coffee (G. sp.? ).
Oak Ecology
Oaks are play an important role in providing or maintaining special abiotic factors, such as light and canopy cover, stormwater absorption and mitigation, soil stabilization, inputs of organic matter, producing clean air, and carbon sequestration.
Oaks are a disturbance-adapted group of trees, especially of fire. In Cook County, oak communities can be classified based upon the intensity and frequency of wildfires:
____________
Hottest
Open Savanna (0-10 % canopy cover)
Savanna (10/20% canopy cover)
Woodland (25-60 % canopy cover)
Forest (60-100 % canopy cover)
Coolest
____________
The variability of oak communities relative to their wildfire frequency and intensity is related to the glacial geologic history of Cook County. Lowland areas dominated the landscape of Cook County, a product of glaciation and the recession of ice and melt-water. Pre-colonial vegetation in Cook County was 73% prairie, with woodland areas near lakes and rivers. Woodland areas were primarily located on the east side of rivers and lakes that were protected from westward wind-driven fires (see below).
 |
| Figure 1: More densely wooded areas with less fires were historically found in areas of Cook County that were east of a body of water where fire could not pass through. |
Threats to Oak Ecosystems
There are numerous threats to Cook County's oak ecosystems. Only about 5% of Cook County remains as an oak ecosystem today. In current oak stands, there is a lack of age diversity, and the introduction of non-native invasive plants and the development of a mesophytic plant community are replacing oak ecosystems. Other confounding factors include herbivory - especially by deer -habitat fragmentation, and perhaps the extinction of the Passenger Pigeon (Ectopistes migratorius).
Oak regeneration has become suppressed, and new oak growth can remain stuck in the seedling stage for 20 years or more as they build up root and energy reserves for more rapid growth when enough sunlight can reach them. Invasive shrubs can block out sunlight, preventing seedlings from developing. Some invasive shrubs are allelopathic and can kill off the mycorrhiza fungi needed for oak growth and development.
Even earthworms, which are not native to cook county, are contributing to a decline in oaks, as they disrupt soil composition and eat mycorrhiza fungi.
Establishment of shade-tolerant, fire sensitive plants has altered oak communities into more mesophytic (middle-moisture) vegetation such as cherries and maples. For example, fire suppression has allowed for an astonishing 4,119% increase in maple trees in Illinois between 1962-1985!
Deer can eat 6 pounds of tree buds each winter, and they love oaks!
Oak Ecosystem Restoration
Restoring oak ecosystems in Cook County involves removal of invasive brush, canopy thinning, cut-stump herbiciding of invasive woody plants, prescribed burns, and follow-up herbicide applications. Figure 2 represents an example of a restoration procedure, which can be established in concert with priority sights identified in a natural resource management plan, such as the one for Cook County.
 |
| Figure 2: Example oak ecosystem restoration process. |
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