Nandina: A Berry Interesting Problem

Oh, nandina, nandina, you trouble my heart!  You are so beautiful all winter with your green foliage and bright red berries, but you are an invasive plant.  What is a good naturalist to do?

Nandina, AKA heavenly bamboo.

Invasive species (species = type of organism) are a problem in Tennessee, and in the rest of the world as well.  They are currently the #2 cause of extinction of other species, just after habitat destruction.   Invasive species are non-native organisms that grow like crazy and take over.  Non-native organisms are moved from one part of the world to another, mostly by humans.  This is usually not a problem, except that for some non-native species, the new habitat has none of their usual diseases and predators, and the habitat seems to fit just right.  In that case....they can take over and crowd out the habitat of other organisms.  Nandina is native in Asia - from Japan west to India.  It is a beloved plant there, also used in landscaping like we use it here. 

Poisonous beauty: these berries contain nandina seeds and cyanide!

In Tennessee, some of our most harmful invasives are bush honeysuckle and kudzu.  Bush honeysuckle uses up habitat for other plants.  Also, birds that nest in it are more likely to get eaten (not sure why).  Kudzu simply crowds out every living organism where it grows.  Nandina is not that bad!  It is usually only found growing wild near where humans have intentionally planted it.  The Tennessee organization that helps keep invasive plants under control (TN-EPPC)  wants more information about nandina in order to keep tabs on the problem.  If you are ever out hiking in the wild (not in a landscaped yard) and you see a nandina, TN-EPPC would like to know about it.  You can report an escaped nandina at the TN-EPPC website: http://www.tneppc.org/

A nandina draws your gaze from behind a sedimentary rock.

Biologists worry about invasive species because they cause the total number of species to decrease.  The loss of a species, or extinction, causes the loss of a participant in an ecosystem.  For example, when a bird species dies out, an ecosystem might lose a seed-disperser.  If honeybees died out, there would be way fewer pollinators and thus way fewer fruits and seeds.  If a type of beetle died out, we might lose a soil recycler. 

Nandina is guilty of taking up a tiny bit habitat that would otherwise be used by native species, though it doesn't appear extremely aggressive.  It has another problem, though.  Nandina berries contain a toxin called cyanide.  Birds in the US haven't figured out how to deal with the poison, and some cedar waxwing birds have died from eating lots of the berries.  The berries can be toxic to any other animal too, so don't eat them. (It probably takes a lot of berries to hurt a large animal such as a human...still...don't eat them.)

Back to the original question: what's a good naturalist to do?  That depends on who you ask.  Some will say to never plant nandinas.  Others say plant them but clip off the berries this time of year when birds start foraging.  Others say don't worry about it - eventually the other species will adapt and nandina will become another important part of our ecosystem.  The only problem with this last option is that adaptation takes hundreds to thousands of years, so we won't find out how nandinas mesh with our Middle Tenneessee ecosystem for a looooonnnngggg time!  What do you think we should do?

American Chestnut Trees

Here's something you don't see every day...

American chestnut (Castanea dentata) leaves.

 ....an American Chestnut tree!  My parents are growing American Chestnuts (Castanea dentata) on their property to help bring this great American tree species back to prominence.  Mom learned about the American Chestnut and wanted to get involved, and Dad was game to help Mom put in the work needed to plant and protect these trees as they try to survive.  They are both pleased with their American Chestnuts.

Dad with an American Chestnut on Father's Day.

Eastern forests in the United States were once dominated by this tree species.   If you think about how prevalent oak trees are in the Eastern forests of this country, it gives you a sense of the size of the American Chestnut's niche.  Its nuts provided great quantities of seriously delicious food for people, deer, bears, squirrels and many other animals.  It is a fast-growing member of the oak plant family (Fagaceae), and its wood is strong and particularly resistant to decay, so it was an extremely useful lumber-producing tree.

Why am I speaking in the past tense?  Because this tree species is now mostly gone due to the chestnut blight.  Chestnut blight (Cryphonectria parasitica) is a fungal disease that evolved in Asia and was accidentally brought to the U. S. in the late 1800's, probably on furniture, lumber or nuts.  Chinese Chestnut trees evolved with the disease, so they are resistant to it, but our trees were not resistant, and they succumbed to the disease as quickly as Native Americans died from European diseases introduced by the first European settlers of this land.  The disease was discovered in 1904, and by 1950, almost all the American chestnut trees were dead, with only small shrubby root sprouts left surviving.

Chestnut catkins (flowers).  The narrow ones have only male flowers, the upper one has some pollinated female flowers, which will produce nuts.

Several organizations, including the American Chestnut Foundation, are trying to breed blight-resistant chestnuts and repopulate our forests with this missing foundation species.  Chestnut-lovers are using existing trees to search for blight resistance.  They are also breeding Chinese Chestnut trees with American chestnut trees, eliminating those that don't survive the blight, and crossing the offspring back with American Chestnuts to result in trees that are mostly American but with the Chinese blight-resistance genes.  Right now, there exist trees that are 98% American with 2% Chinese genes.  These mostly American Chestnuts are responding well to blight exposure.  Nothing against Chinese Chestnut trees - they are great, but they're adapted to Chinese ecosystems.  Chestnut-lovers and ecologists want to maintain both species - with the American Chestnut trees back in the ecosystems here.  In the mean time, many people have planted Chinese or European Chestnuts in their yards in order to have some chestnuts to eat in the fall. 

Chestnut catkins with pollinated female flowers that have become burs, and male flowers above them.

Chestnuts have either all male flowers or male and female flowers.  Mom and Dad obtained dozens of chestnuts from the American Chestnut Foundation so they would have many trees and guarantee that they could have cross-pollination between the trees.  Chestnuts cannot self-pollinate.  This time of year,  pollinated female flowers are enlarging into burs.  Burs are spiky fruits that contain chestnut seeds.  In the fall, the seeds will be mature, the fruits will crack open, and the whole bur will fall to the ground.  As soon as the burs crack open, the seeds are mature and ready to overwinter and grow into new trees or to be eaten.

There are a few remaining adult American Chestnuts in North America.  Many of the surviving ones are outside the former range for American Chestnut trees, so the blight hasn't spread easily to them.  Also, there are different climactic conditions outside our chestnut's normal range, which cause the blight fungus to be weaker, or hypovirulent.  Mom and Dad's chestnut trees are outside the normal range, so they may survive longer than other American Chestnuts.  Of the original seeds they planted, about half remain.  Their trees probably didn't die due to blight, but to non-ideal climactic conditions.  Blight tends to affect teenage trees, and these trees are younger.  It is likely that all my parents' trees will eventually die, unfortunately.  Still, they may have a resistant tree, and their trees help maintain living tissue, help educate people about the trees, and help scientists learn more about what these trees need to survive.  With so many people working to solve this ecological tragedy, it appears likely that American Chestnuts will eventually recover.  I'm so proud of my parents for helping the American Chestnut!

Little Green Farm Workers

With the greens of the farm plants fading, two bright green animals brought themselves to our attention on the farm this week.  Both of them are welcome creatures that help us keep the numbers of pest insects low. 

The first green creature of the week, a rough green snake, was hanging out in the barn.  I found him in a basket I was about to use for eggplants.  We quickly caught him and put him in this jar (with air holes), so that the farm owner's son could see him too.  These little green snakes are a rare sight on the farm, and they hold a special place in the hearts of this farm family.  We marveled and the bright emerald luminescent color of this sleek, friendly snake.

Rough Green Snake with grass- we released him quickly!

Rough green snakes don't get large.  They can grow to almost 3 feet long, but they always stay skinny.  They are great climbers and spend their time hunting insects and spiders in any kind of vegetation from grass to trees, but they prefer to be higher up rather than on the ground.  Green snakes are well camouflaged for their preferred habitat, and I've probably seen dozens of them without realizing it.  They coil up in branches to sleep at night, and in the cooler weather, they seek refuge under logs or other debris.  This may be why our green snake ventured into the barn.  He probably thought he found a good place to overwinter.

Later in the week, we were working in the greenhouse, and we found two gigantic praying mantises, both the brightest of green.  One of the mantises was half brown and the other was all green.  I wrote a little about mantids earlier, but here's some more information about them.

In Tennessee, our most noticeable mantids come in three color variations: green, brown, and green plus brown.  The green ones are European mantids, the brown are Carolina mantids, and the green plus brown are Chinese mantids.  Only the Carolina ones are native, and the other two were introduced to the US to help control garden pests.  These introduced species do not appear to be particularly invasive, though they can reduce numbers of helpful organisms like wolf spiders.  People generally regard them as welcome workers in farms and gardens.   There are several other mantis species that are illegal to import because they pose a threat to native ecosystems.  They can probably reproduce very quickly and overeat beneficial insects.

European mantis, about 6" long.

Female mantises are disconcertingly large this time of year.  They grow big from hunting all season, and their abdomens are filled with eggs.  Now they are laying their egg cases on vegetation.  The egg cases look like brown trilobytes - they are oblong with ridges and about 1-2" long.  They are eggs encased in a foamy mass that hardens after it is laid.  The eggs overwinter to hatch in the spring, releasing hundreds of tiny, springy green mantises into the area.  The tiny, thin mantises need to disperse fast, because their siblings pose a significant predation threat.

Japanese Beetles Put their Thumbs on the Scales

The stability of any ecosystem depends on having a multitude of species playing different roles in that ecosystem.  Some are producers, some are decomposers, some are predators, and no one gets out of hand.  The predators don't take over because there are bigger predators, disease organisms, and competitors for food and other limiting factors. 

Invasive species are the newcomer species that upset the fine balance, altering ecosystems and even causing extinctions.  For example, entire food chains have collapsed in the Great Lakes due to the invasion and overgrowth of the zebra mussel.  The zebra mussel eats all available algae, and other species starve.

Invasive species arrive in many ways - sometimes by expanding their range but usually because they have been carried from one place to another by humans.  Our species of the day, the Japanese beetle (Popilla japonica) (picture), was accidentally brought into the United States from Japan as grubs in soil of ornamental plants.  The new species was detected in New Jersey in 1917 and quickly traced to a plant nursery in the area.

Because invasive species are new to an ecosystem, they are neighbors with other species to which they have not evolved.  That means their neighbors have not had a chance to adapt to eating the invasive species, or competing with it or infecting it.  That's how you end up with entire mountains covered in kudzu.  Or the entire eastern United States covered in Japanese beetles (range map), despite massive federal, state and private efforts to destroy this aggressive farm pest.

But even invasive species are fascinating.  Japanese beetles are beautiful, metallic beetles.  Also, they might just be the only insect capable of growing one body part at a time, according to Dr. Hans-Willi Honegger, an entomologist who also works on the farm.  Dr. H thinks they might be able to grow their jaws, which would make sense since they are such voracious feeders.  Japanese beetles' life cycles are also very interesting.  They emerge in late spring, feed like crazy on leaves of their favorite plants, mate and lay their eggs in the soil.  Most of the adults die off by late August, but the larvae are just starting to get busy.  They burrow in the upper layers of soil throughout the fall, eating roots and organic matter in the soil.  When the temperatures start to drop, the beetles burrow deeper and deeper to stay warm only to come back up when the spring thaw comes again.

On the farm, the beetles are just starting to emerge.  According to the farm owner, the beetles have gotten a little worse over the past few years as their range has expanded.  Now that they are here, they are probably already laying eggs here for next year, and their numbers may increase.  Once beetles establish themselves, they are really impossible to get rid of, but several strategies can help.  A soil drought during early larval stages can kill many larvae; parasitic wasps, worms or bacteria can be released into the area to help kill beetles; traps do attract beetles, but they don't seem to help the overall problem; and insecticides are of course used on non-organic farms.  A surefire way to control Japanese beetles would be to simply wait around long enough for evolution to take its course.  All those Japanese beetles are a great food source for any animal that could evolve to eat them.  Given the rate of evolution, we might only have to wait about 20,000 years for Japanese beetles to become a part of our balanced ecosystem.