 |
| An oak branch in the white oak group |
Oaks
Most oaks (Quercus spp.) are hardwood trees and have been used by people over the ages for building structures and boats. The oak fruit is a true nut with a hard shell and a cap, called the cupule, which protects the kernel. The kernel, which consists of two fatty seed leaves, called cotyledons, which surround a small embryo. This is an important food for wildlife and for early humans once they learned how to remove the bitter tannins.
Oaks are divided into two major groups. The white oaks are those with rounded lobes on their leaves and the acorns mature within one season and are less bitter. The red oaks generally have pointed lobes or sharp lobes on their leaves and their acorns stay on the trees for two seasons, so their acorns have more tannins and are therefore more bitter.
 |
| The supply of acorns affects the local ecosystem. |
Every 2 to 5 years oaks produce many more acorns than normal; these are called mast years. Many ecologists think that this is to ensure that enough acorns are able to grow into trees. If the production was the same each year then the birds and other wildlife would expand to consume most of the acorns every year. But if most years are lean, then the wildlife populations would be trimmed to the numbers that could be supported by that number of acorns. On the mast years the consumers would not be enough to eat all of the nuts, so greater number would survive to become trees.
Oaks are often large sturdy trees with large root systems, which means that they play an out-sized role in their local ecosystems by creating more habitat, soaking up more water from the soil and therefore releasing more water into the air through transpiration. This process where water shifts from a liquid in the leaves to a gas, water vapor, will actually cool the air. Also putting more water vapor in the air means that more will be carried in the to distant places and help to offset droughts. For more details on this, read "Transpiration: Forests' most important service" and "The value of trees."
 |
| Four live oaks (Quercus virginiana) growing as one canopy & providing deep shade and cooling in a North Florida yard. |
Florida's oaks
Oaks (Quercus spp.) occur naturally in all of Florida and according to the Plant Atlas of Florida, there are 26 species of oaks and 16 naturally occuring hybrids that are all native to Florida. (Here is the link to their Quercus page which includes a key to identify the species.)
The Florida Native Plant Society lists 24 of the oak species on their native plants page, which generally indicates that they are likely to be available from native plant vendors.
FNPS lists four oaks as favorites. Click on the links for their plant profiles for more information, more photos, and a link to native plant vendors that have them in stock.
- Live oak (Q. virginiana)
- Sand live oak (Q. geminata)
- Sand laurel oak (Q. hemispherica)
- Shumard oak (Q. shumardii)
 |
| A live oak hammock in Central Florida. Note all the epiphytes on the spreading branches including resurrection ferns and Spanish moss. |
Two live oaks
1) Live oak (Q. virginiana) is the iconic oak with large speading, almost horizontal branches. When many people think of oaks, this is the one that comes to mind. It lives for centuries; is wind tolerant, salt tolerant, drought tolerant, and fire resistant. It provides habitat for other plants, insects, birds, and other wildlife. (See Doug Tallamy's take on oaks below.) In addition, its graceful shape is an asset in the landscape.
2) And then there is a live oak on the opposite spectrum: Dwarf live oak (Q. minima), which is basically a ground cover.
 |
 |
| Dwarf live oak (Q. minima) is the smallest of Florida's oaks. | Dwarf live oak often acts as a ground cover, but its acorns are important food for the Florida endemic Scrub Jay (Aphelocoma coerulescens). |
 |
| The worldwide range of oaks. |
Oaks around the world
Oaks (Quercus spp.) occur naturally across the world, but are notably absent south of the tropics. Except in South Africa and New Zealand where they've been introduced and have escaped cultivation. According to Kew Gardens, there are 147 accepted oak species.
 |
| The cork oak (Q. suber) is Portugal's national tree . |
The bark is stripped away by hand and these workers are highly skilled & highly paid. Care must be taken, so that the cambium layer, the growing region (the xylem and phloem) under the bark is not disturbed during the process. The first two harvests, starting when the oak is 20 to 25 years old, (virgin and secundeira) are not used for wine corks because the cork tissue is too hard and too irregular, but it has other uses. Starting with its third harvest where the tissue is more uniform, is used for corks for wine bottles and more. A good cork oak tree might provide 10 to 17 harvests (every 8 to 12 years) over its lifetime and under favorable conditions.
Doug Tallamy & oaks
Doug Tallamy, an entomology professor at the University of Delaware changed the whole narrative of why native plants are important and that even small stands of native plants can make a real difference for birds. His message to gardeners is, "Your garden needs to be more than just pretty, it needs to be part of the local ecosystem."
One of the key factors in a bird-friendly native landscape is its production of caterpillars. Tallamy's years-long research has shown that one pair of chickadees requires 6,000 to 9,000 caterpillars to raise one clutch of young. So after the 5 or 6 eggs hatch, the parents need to find that many caterpillars until those baby birds are able to fly away and be on their own. And most caterpillars are supported on native trees, and of those, the oaks support the most caterpillars. While he's been talking and writing about this for years, his latest book finally focuses on oaks.
 |
 |
| Doug Tallamy has been talking about the importance of caterpillars for birds and other wildlife for many years. | Order Tallamy's new book from the Homegrown Park website. |
Link to Talllamy's oak video
Link to my article on Tallamy
More resources:
Green Gardening Matters,
Ginny Stibolt
No comments:
Post a Comment