Symptoms of Sudden Oak Death on Rhododendron leaves in California caused by the introduced fungus, Phytophthora ramorum. Photo credit: Joseph OBrien, USDA Forest Service, Bugwood.org
Symptoms of Oak Wilt caused by the oak wilt fungus Ceratocystis fagacearum look similar to sudden oak death. The fungus is spread to an oak tree by underground root grafts between trees or infected beetles feeding on leaves or sap. Photo: Fred Baker, Utah State University, Bugwood.org.
The oak silhouette is so distinctive! In the UK oaks watched over Druid worship, and gave their wood for the British ships that sailed the world. Its leaves and acorns are the emblem of the National Trust.
The Major Oak is said to be the UK's largest oak. Standing in Sherwood Forest legend has it that Robin Hood and his band of Merry Men camped under it. It is thought to be 800-1000 years old. How magnificent!
This champion White Oak in Maryland's Wye Oak State Park was thought to be 500 years old when it was felled by a summer storm in 2002. Photo: Davey Tree Service Blog
Browsing the UK...
I recently picked up some back issues of BBC Gardener’s World for some relaxing reading during the polar vortex. Minus 50⁰ weather guaranteed I needed something green and plant-related to help take my mind off the frigid, bone-grinding temperatures we’ve experienced recently. Getting cozy with some hot tea and a group of magazines with colorful covers was just the thing to while away a bitterly cold Saturday afternoon…
Gardener’s World is a popular gardening magazine in the UK (England, Scotland, Wales and Northern Ireland) I was struck by how the themes of some of the articles were similar to here. It was interesting reading about them from a UK perspective! Here’s a brief sampling…
Long Term Oak Survival
Fears are growing about the long-term survival of oaks in the UK. Whereas most of the threats to our oaks here in the Great Lake region seem to stem primarily from invasive species and lack of controlled burn management, oaks in the UK are facing pests and diseases such as sudden oak death caused by a plant pathogen Phytophthora ramorum, acute oak decline, and problematic insects. It turns out the U.S. has also seen devastating tree loss in California and Oregon due to sudden oak death (which kills other tree and shrub species too) though this pathogen has not yet been seen elsewhere in the country.
On the other hand, oak wilt which presents similar syptoms is seen throughout Illinois. It is caused by a fungus that invades and subsequently restricts the upward flow of water and nutrients from the tree’s roots to the leaves. Species in the red oak group such as red and black oaks are the most susceptible followed by those in the white oak group.
Oaks as a Keystone Species
As here in Illinois, oaks in the UK are highly valued as a cultural icon and a critically important keystone species. According to the UK website, Action Oak, oaks support approximately 2,200 species. Ours are likely to support similar numbers when the more than 530 moth and butterfly species published by Doug Tallamy are supplemented with the many other invertebrate, bird and other mammal species that are dependent on this genus . Here in Chicago, the Chicago Region Trees Initiative (CRTI) is beginning to lead the formation of oak woodland recovery groups under the Oak Ecosystem Recovery Project. To learn more click here. Oak Keepers of McHenry County, a program of the Land Conservancy of McHenry County, is leading a program with similar objectives.
Returning Natives to UK Gardens
In one article, Monty Don, a well-known garden writer and television host, writes about bringing natives back to UK gardens after more than a century of assigning greater value to introductions. I chuckled that such an article just happened to be in an issue I randomly picked up.
Writes Monty, “…For the past 150 years or so, we have taken it as read that a garden with the greatest number of unusual and interesting plants is best for this diversity…” After all, the UK began searching the world for unusual and interesting plants as far back as the early 1820s at the behest of what is now the Royal Horticultural Society. However, the RHS recently reported the results of a new study titled Native and Non-Native Plants for Plant-Dwelling Invertebrates . Doesn’t the title of the report just sound very British?
As you would think, the UK’s much longer history of invasion and settlement makes defining native more challenging. The importance of co-evolution is recognized however, “…the longer a plant has grown in a geographical location, the better it is for the “local” invertebrates…” I felt quite at home reading similar recommendations to those we see on this side of the Atlantic.
- Plant mostly UK-native plants
- Gardens planted with exotic species support about 20% fewer invertebrate species
- A more densely planted garden supports a higher invertebrate population
- Be tolerant of chewed leaves and allow dead plant material to accumulate
It is interesting that a list of UK natives includes several of our invasive species: Wild Privet (the UK common name): Ligustrum vulgare, Purging Buckthorn (again the UK common name and most apt!): (Rhamnus cathartica), Common Teasel: Dipacus fullonum, Creeping Thistle: Cirsium arvense, and Purple Loosestrife: Lythrum salicaria. Also interesting is that our own common milkweed (Asclepias syriaca) is listed in the UK as an invasive plant.) Some UK natives such as English Primrose: Primula vulgaris, Bloody Cranesbill: Geranium sanguineum, Ox-eye daisy: Leucanthemum vulgare and Sweet Violet: Viola odorata are also familiar ornamentals in our gardens.
As the RHS report says, “…An abundance of bugs of all types equates to healthy garden ecology …”
I just love the Brits!