Friday, February 24, 2012

Plant Quiz Solved! Black Locust, Robinia pseudo-acacia

Good call, A.L.! It is Robinia pseudo-acacia, Black Locust. This is an impressive looking tree when it matures, but it is said to have nitrogen-fixing bacteria in root nodules and as a result, it inhibits the growth of many other plants (Google "Allelopathy"). Young trees (and young branches on older trees) have small but very sharp spines. The lower bark on mature trees is VERY deeply furrowed and distinctive (see below). This is why the lower trunk was cropped away from the plant quiz photo!
Can you identify this tree just by its distinctive shape? Good luck! Please feel free to ID the tree or just take a guess. Photographed in St. Joe County, Indiana.


Marianne, aka Ranger Anna said...

I'm stumped, but the hubby is guessing Sassafras.

Keith said...

That is a very good guess because Sassafras has unusual branching patterns similar to this, but this tree is not Sassafras.

Daricia said...

is it sourwood? love that halloweeny branching!

Keith said...

Wow, this is a Halloween-style tree, good observation! However, it is not Sourwood. Good try though!

WisconsinWildMan said...

Kentucky Coffee Tree?

A.L. Gibson said...

appears to be a Robinia pseudoacacia to me! I believe I still see some legume pods on the lower right branches.

Keith said...

Nope, not Kentucky Coffee Tree, and YEP, it is Black Locust, Robinia pseudo-acacia! Good call A.L.!

Nick said...

John Muir recounted how the black locust helped steer him towards botanical study.

Keith said...

I forgot to mention that the flowers smell like Concord grapes - very nice, but overall this is still an undesirable tree.

Anonymous said...

Undesirable throughout its range? It is native to the US.

Keith said...

Just my opinion, but its allelopathic effect on the soil makes for a very weedy and depauperate undergrowth, and it can spread to form thickets. In my view, some native plants are indeed undesirable. Typha latifolia, for example, our native Cattail, can form solid stands in wet areas just like non-native cattails, along with the North American native Phragmites australis var. americana. I wouldn't promote their extermination, of course, but I must admit that if Poison Ivy suddenly became rare I wouldn't shed a tear.

Scott Namestnik said...

It all depends on your interpretation of "undesirable," I think. When botanizing, I agree that I wouldn't be too keen on spending a lot of time in a Robinia pseudoacacia forest. According to Doug Tallamy's research, however, Robinia pseudoacacia is a host plant for 72 Lepidopteran species (67 native). In parts of the country, it is in fact native, though it often serves as a pioneer species, providing early woody cover (and presumably nitrogen fixation services) in disturbed areas. I would easily agree that it is not a conservative species by any means, as it will grow under a variety of conditions and in areas of heavy anthropogenic disturbance. I bet that many would agree that it is "undesirable," but it certainly also has its benefits.

Regarding Typha latifolia, unfortunately this native plant is being displaced from many areas around the Great Lakes by the non-native T. angustifolia and the aggressive hybrid between the two (T. x glauca). I believe there will be a time soon enough when T. latifolia is tracked as a species of concern in some states. I've never seen dense colonies (to the exclusion of other species) of Phragmites australis var. americana. In fact, that's one of the ways to distinguish it from the non-native variety... the native variety doesn't grow as densely and doesn't exclude other species. I know that there are many, many people that feel the same way as Keith does about Toxicodendron radicans, but can you imagine how its extirpation would affect bird populations that rely on it as a major food source?

I feel the same way about Populus deltoides and Salix spp. Regulatory agencies try to exclude these species (along with Acer saccharinum) from mitigation wetlands, at least in Indiana. These species are thought of as "undesirable," yet in a mitigation setting they are the pioneer species that do the dirty work and prepare a site for the later successional species. In addition, Doug Tallamy's research shows that of woody genera, only Quercus and Prunus support more lepidopteran species than Salix, and Populus comes in fifth in the ranking of woody genera with regards to number of Lepidopteran species supported. These "undesirable" trees not only serve a successional niche, but also provide habitat for the caterpillars that are eaten by the songbirds that are eaten by the raptors that are eaten by the foxes (and so on). Thus, there is an arguement that they are, in fact, desirable, in some sense.

Keith said...

These are all good points and I don't want to argue with any of them. I'll have to admit that I have a personal bias against this tree. I just think there a lot of trees that would be more desirable in any situation and probably support as many Lepidopterans, if not more. Just a few minutes' searching revealed the following quotes:
From the National Park Servce:
Black locust poses a serious threat to native vegetation in dry and sand prairies, oak savannas and upland forest edges, outside of its historic North American range. Native North American prairie and savanna ecosystems have been greatly reduced in size and are now represented by endangered ecosystem fragments. Once introduced to an area, black locust expands readily into areas where their shade reduces competition from other (sun-loving) plants. Dense clones of locust create shaded islands with little ground vegetation. Lack of ground fuel limits the use of fire in natural disturbance regimes. The large, fragrant blossoms of black locust compete with native plants for pollinating bees.

From the Missouri Dept. of Conservation (the tree is native in the Ozarks):
Black locust invades dry or moist open woodlands, stream valleys, pastures, thickets and roadsides. It can be found in upland forest natural areas where it becomes established along ridge-top logging roads, at old homesites, or in openings following natural tree fall. Eroded areas along streams also provide potential habitat for seedling establishment.

From the Wisconsin Dept. of Natural Resources:
Because dense clonal stands shade out most understory vegetation, such tree groves can be detrimental to native vegetation.

From “A Brief Guide to Kentucky’s Non-Native, Invasive Species, Common Weeds, and other Unwanted Plants (the tree is native in Kentucky)
It has become invasive, displacing native
species and adversely impacting ecosystems and
several endangered native bird species that depend on
other plants for food, as well as several endangered
plant species.

Scott Namestnik said...

There is nothing wrong with personal biases, and I certainly have my own (not a fan of Leersia or Bidens in the fall!). Also, I do not support planting black locust outside of its native range, and would comepletely agree that it should be removed to restore native plant communities in places it is not native, so long as native species are present or are at least being planted to replace the removed trees that provide food and habitat.

To add to the Lepidopteran note, Dr. Tallamy's research shows that Robinia ranks 36th of 206 woody genera in terms of number of Lepidopteran species supported; looking only at the native woody species included in Dr. Tallamy's research, Robinia ranks 34th of 132 woody genera. So yes, there are species that support more Lepidopterans, but many that also support less.

To comment on each of the quotes you found during your quick search:

NPS - it states that black locust poses a serious threat to native vegetation outside of its historic North American range. Agreed.

MDC - every one of the habitats and situations they mention, with the exception of dry or moist open woodlands, is a disturbed site. Black locust therefore is filling the niche in its native range as a pioneer species. Several sources state that it is a fast-growing, short-lived species; these are other characteristics of pioneer species.

WDNR - I agree it does not belong in Wisconsin, where it is not native.

A Brief Guide to Kentucky's... - Adding the rest of the paragraph for context... "A plant is considered exotic, (alien, foreign, non-indigenous, non-native), when it has been introduced by humans to a location outside its native or natural range. Most invasive, exotic plants have escaped cultivation or have spread from its origin and have become a problem or a potential problem in natural biological communities.
For example, black locust, a tree that is native to the southern Appalachian region and portions of Indiana, Illinois, and Missouri, was planted throughout the U.S. for living fences, erosion control, and other uses for many years. Black locust is considered exotic outside its natural native range because it got to these places by human introduction rather than by natural dispersion. It has become invasive, displacing native species and adversely impacting ecosystems and several endangered native bird species that depend on other plants for food, as well as several endangered plant species." The map at shows that its native range only included primarily the eastern third of Kentucky (with a few small outliers scattered about the state). I would venture to guess that within its native range, it acted as it does in the Ozarks, mentioned above. This is what is sometimes scary about native landscaping... you take a species that is native to a particular region within a state, consider it native to the entire state, and plant it in widespread monocultures, and look what can happen.

sternfeldt said...

I know Black locust is invasive, which is a problem that needs to be addressed, but at that same time - the tree got such good potential. It can replace hardwood from rainforest, which is such a great trait. It is not easy to find wood with such qualities as the wood from black locust, if not in tropical areas and we have exploited rainforests far too much. If we could come to terms with the invasive trait, which we must for sure deal with, it could be a tree that could provide us with valuable timber and biomass energy at the same time.