Every urban area is bound to have its share of vacant lots. These are sites that for whatever reason have been left undeveloped or were at one point developed but whose structures have since been removed. The maintenance on these lots can vary depending on who has ownership of them. Some are regularly mowed and/or treated with herbicide, while others go untouched for long periods of time. Even when there is some weed management occurring, vacant lots are locations where the urban wild flora dominates. Typically no one is coming in and removing weeds in an effort to cultivate something else, and so weeds run the show.
As with any piece of land populated by a diverse suite of wild plants, vacant lots are dynamic ecosystems, which you can read all about in the book Natural History of Vacant Lots by Matthew Vessel and Herbert Wong. The impact of humans can be seen in pretty much any ecosystem, but there are few places where that impact is more apparent than in a vacant lot. In lots located in bustling urban centers, human activity is constant. As Vessel and Wong write, “numerous ecosystem interactions are affected when humans intervene by spraying herbicides or insecticides, by trampling, by physically altering the area, or by depositing garbage and waste products.” These activities “can abruptly alter the availability and types of small habitats; this will in turn affect animal as well as plant diversity and population dynamics.” The dynamic nature of these sites is a reason why vacant lots are excellent places to familiarize yourself with the wild urban flora.
On our morning walks, Kōura and I have been visiting a small vacant lot on West Kootenai Street. We have watched as early spring weeds have come and gone, summer weeds have sprouted and taken off, perennial weeds have woken up for the year, and grass (much of which appears to have been intentionally planted) has grown tall and then been mowed with some regularity. Someone besides us is looking after this vacant lot, and it’s interesting to see how the plant community is responding. As Vessel and Wong note, “attempts to control weedy plants by mowing, cultivating, or spraying often initiate the beginning of a new cycle of growth.” For plants that are adapted to regular disturbance, measly attempts by humans to keep them in check are only minor setbacks in their path to ultimate dominance.
What follows are a few photos of some of the plants we’ve seen at the vacant lot on Kootenai Street, as well as an inventory of what can be found there. This list is not exhaustive and, as with other Weeds of Boise posts, will continue to be updated as I identify more species at this location.
Bromus tectorum (cheatgrass)
Capsella bursa-pastoris (shepherd’s purse)
Ceratocephala testiculata (bur buttercup)
Descurainia sophia (flixweed)
Draba verna (spring draba)
Erodium cicutarium (redstem filaree)
Geum urbanum (wood avens)
Holosteum umbellatum (jagged chickweed)
Hordeum murinum (wild barley)
Lactuca serriola (prickly lettuce)
Lamium amplexicaule (henbit)
Lathyrus latifolius (perennial sweet pea)
Lepidium sp. (whitetop)
Malva neglecta (dwarf mallow)
Muscari armeniacum (grape hyacinth)
Plantago lanceolata (narrowleaf plantain)
Plantago major (broadleaf plantain)
Poa bulbosa (bulbous bluegrass)
Poa pratensis (Kentucky bluegrass)
Rumex crispus (curly dock)
Taraxacum officinale (dandelion)
Tragopogon dubius (salsify)
Trifolium repens (white clover)
Veronica sp. (speedwell)
If you live in an urban area, chances are good there is a vacant lot near you. What have you found growing in your neighborhood vacant lot? Feel free to share in the comment section below.
In part one and part two of this series, I introduced you to at least 23 plant-themed and plant-related podcasts. But wait, there’s more. As podcasts continue to be such a popular medium for entertainment and education, plant podcasts proliferate. You won’t see me complaining. I’m always happy to check out more botanical content. What follows are mini-reviews of a few more of the plant shows I’ve been listening to lately.
Plants Grow Here – Based in Australia, this is a horticulture and gardening podcast hosted by Daniel Fuller (and the occasional guest host). What separates it from other horticulture-related podcasts is the heavy focus on ecology and conservation. As Daniel says in the introductory episode, “there’s no point in talking about plants at any length without acknowledging that they exist within a wider web.” Daniel interviews plant experts, professionals, and enthusiasts from various parts of the globe, and while much of the focus is on horticulture topics, specifically related to gardening in Australia, there are several episodes that focus solely on the plants themselves and their place in the natural world.
Completely Arbortrary – Relatively new to the scene but an instant classic. Completely Arbortrary is hosted by Casey Clapp, a tree expert, and Alex Crowson, a tree agnostic. In each episode, Casey introduces Alex to a new tree species. After learning all about the tree, they each give it a rating (from zero to ten Golden Cones of Honor!). Sometimes the ratings will surprise you (Alex gave Bradford pear 9.1 Golden Cones of Honor). As the show has gone on, additional segments have been introduced, like Trick or Tree and listener questions. This is easily one of the best plant podcasts around, not just because you’ll learn something about trees (and who doesn’t love trees?), but because you will have a delightful time doing so with a couple of the friendliest and goofiest podcast hosts around.
Naturistic– In the same vein as Completely Arbortrary, Naturistic features host, Nash Turley, telling his co-host friend, Hamilton Boyce, about a natural history topic. At the time of this posting, there are only a handful of episodes available, and not all are plant-focused (most are about animals), but I assume more plant ones are in the works. Either way, each episode is well worth a listen. The topics are well-researched and presented in an amiable and approachable manner. There are also some nicely done videos that accompany some of the episodes.
Flora and Friends – A plant podcast based in Sweden and hosted by Judith, who is also a member of The Plant Book Club. Generally, Judith spends a few episodes with several guests diving deep into a single plant, group of plants, or plant-related topic. So far, there are series of episodes about nasturtiums, Pelargonium, Fritillaria, and forests. Sometimes the episodes are in Swedish, and when that’s the case, Judith refers listeners to a summary in English on the podcast’s website. Each episode is a casual and pleasant chat – or in other words a “botanical tea break” – about the topic at hand, which explains why Judith refers to the podcast as “your botanical cup of tea.”
Field, Lab, Earth – “A podcast all about past and present advances in the fields of agronomy, crop, soil, and environmental sciences.” Produced by a group of three professional societies – American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America – and hosted by Abby Morrison. In each episode, Abby talks with a guest or guests about a research topic, often having to do with agriculture, but sometimes having to do with other aspects of plant and soil science. Listeners get behind the scenes information about how the research was conducted, as well as in depth discussions on the findings. You don’t necessarily need a background in plant and soil science to listen, as many of the basic concepts are well-explained along the way. Also, if you’re a Certified Crop Adviser or Certified Professional Soil Scientist, you can earn Continuing Education Credits by listening to each episode and taking a quiz. Major Bonus!
Backyard Ecology – An urban ecology podcast hosted by Shannon Trimboli. Nature isn’t just some far off place, it’s right outside our doors as well. With a little effort, we can make our yards and other urban spaces more biodiverse and create quality habitat for all sorts of wildlife. Plants are the foundation of our urban habitats, as is the case practically anywhere else, so even when episodes of this podcast are focused on animals, you can be sure that plants are at the heart of the conversation. Join Shannon as she, through conversations with other experts and nature enthusiasts, “ignites our curiosity and natural wonder, explores our yards and communities, and improves our local pollinator and wildlife habitat”
Talking Biotech – This is a long-running podcast hosted by Dr. Kevin Folta that aims to help people better understand the science behind genetic engineering. Folta’s university research supports plant breeding efforts, and many of the episodes of his podcast focus on plant breeding using both traditional methods and genetic engineering. A variety of other aspects and uses of biotechnology are also explored on the podcast. Folta has a passion for science communication and is adamant about debunking misinformation and sharing with the world the promise that new technologies offer us in our efforts to feed the world, improve human health, and address environmental threats. Even if you’re not generally interested in plant breeding, the discussions about the plants and the research is always very interesting and thought-provoking.
War Against Weeds – There is so much more to plants than meets the eye, and what group of plants demonstrates this better than weeds? They are our constant companions, and they are continually outwitting us. Their “craftiness” is one of the reasons I find them so intriguing. Controlling weeds is a constant battle, and few know that battle better than those who work in agriculture. After all, their livelihoods depend on it. War Against Weeds is hosted by three weed scientists whose job it is to help farmers successfully manage weeds. Each episode is a peek into what it takes to do the job. The war may never be won, and the strategies must be diverse – hence the podcast’s tagline, “silver bullets are for werewolves” – and so the conversation will continue. Luckily, we get to listen in.
Arthro-Pod – Just as the name implies, this is an entomology podcast. Insects and plants share an intimate relationship, so I consider this enough of a plant-related podcast to be included here. Plus I really like it. It came to me highly recommended by Idaho Plant Doctor, who is also really into plants and bugs. Hosted by three professional entomologists that all work in extension, Arthro-Pod is a bit like War Against Weeds, but is geared more towards the layperson than the professional. The hosts are humorous and clearly love what they do, which is why, apart from the fascinating discussions about insects, this is such a delight to listen to.
Chances are there will be a part four to this series. If you’re aware of a plant podcast that I haven’t covered yet, please let me know in the comment section below or by sending me a message via the Contact page.
Nearly a year has passed since Sierra and I took a trip to Ketchum, Idaho and I reported on some of thesnagswe encounteredthere. After months without a break, we finally had the chance to get away for a few days, and since we were desperate for some time off and a change of scenery, we couldn’t turn it down. Plus, we were heading back to Ketchum, so I knew I’d get to check out a few more snags. I was stoked.
I’m obsessed with trees, and my preference is for live ones (generally speaking), but dead trees are certainly gaining in popularity. After all, a dead tree isn’t truly dead. As its corpse slowly rots, it continues to harbor and support life inside and out in a substantial way. Forests need dead trees just as much as they need live trees. Plus, ecology aside, dead trees are no less photogenic than any other tree.
Death isn’t all bad. New life springs from decay. Given our current state of affairs, we need this reminder, and snags offer it in spades. As Sierra and I pulled up to the Apollo Creek trailhead, we looked out onto a section of forest that had clearly been ravaged by fire in the not too distant past. Acres of standing and fallen burned out trees bore witness to this fact. Yet among the dead, life flourished, as dozens of songbirds actively foraged on and around the charred trees. They were there for the insects that were feeding on the dead wood, fueling themselves for fall migration. In the spring, when the birds return, some of them may even nest in the cavities of the dead trees. They will feed again on the insects and raise up a new generation of songbirds that will do the same. In and among snags there are myriad examples just like this, showing us the countless ways in which death supports new life.
What follows is a small sampling of the snags we encountered this time around on our trip to Ketchum.
post-fire snag among many other snags
a series of cavities in a post-fire snag
snag surrounded by live trees
three new snags
new tree emerging from a nurse stump
not a snag, but one of many lupines we saw flowering along Apollo Creek Trail
Gyroscopes are entertaining toys and incredibly useful tools. They retain their balance and resist changes to their orientation as long as their flywheel is spinning. As the flywheel slows or stops, the gyroscope wobbles out of control and ultimately quits. Considering their design and function, it’s easy to find parallels between gyroscopes and living systems. Consistent energy inputs keep living things alive. Changes can bring imbalance; major disruptions can lead to death. There is a reason we often describe the natural world as a sort of balancing act. It is the work of an ecologist to make sense of this balancing act. The better we understand it, the more equipped we are to protect it and operate responsibly within it.
It is through this lens that David Parrish writes about the biological world in The Gyroscope of Life, a book that Parrish refers to as “a love song to the field of biology.” Parrish has spent much of his life observing and studying the natural world and, as professor emeritus of Crop and Soil Environmental Sciences at Virginia Tech, undoubtedly shared much of what he presents in his book with countless students over the years. The Gyroscope of Life reads like part memoir and part last lecture, and is the work of someone who has an obvious passion for science and nature.
Parrish spends the first few chapters of his book writing mostly about his life and how he came to be a biologist. He acknowledges his privelege – “born male, white, and American in an era where each of those attributes provided me major advantages” – having essentially been placed on third base from the start, “well down the third base line.” An aspiring zoologist turned botanist, he spent his early years in graduate school studying seeds and seed dormancy. It’s a topic that obviously interests him, as several pages of the book are spent considering what’s going on inside of a seed. “Seeds provide the widest-spread examples of suspended life,” Parrish says. Are they alive or dead or neither?
Two additional, major life events play a prominent role in the arc of Parrish’s book. One being his break from organized religion and the other his battle with advanced prostate cancer. He grew up in an orthodox Christian home with a very literal understanding of the Bible. His education put him at odds with what he was taught growing up about (among other things) the age of the earth and its creation. Eventually he came to understand that science and religion “exist in separate non-overlapping spheres – the physical and the metaphysical.” He doesn’t necessarily see science and religion as being inherently at odds with each other, but his understanding of science makes it difficult to “find resonance in religion” due to the “cacophony of dissonance” it offers.
In addressing his prostate cancer, Parrish underwent an operation that gave him a newfound perspective on gender. Freed from “testosterone poisoning,” he was able to more fully consider sex and gender from a biological perspective, which he says he had been doing for decades prior to the operation. He spends a good portion of the book “demystifying sex and gender.” One compelling example he offers involves avocado flowers, which actually change gender over time, a phenomenon known as synchronous dichogamy.
Over the course of its pages, The Gyroscope of Life covers a significant number of topics in the fields of biology and ecology. It’s a relatively short book, but as it careens through such wide-ranging material, it does so in an approachable and suprisingly succint manner. Parrish’s sense of humor, which doesn’t waver despite how bleak the discussion sometimes gets, helps carry the story along and keeps things interesting. Parrish covers evolution (“[Biologists] argue that, if evolution didn’t happen, it should.”), taxonomy (“the name for naming things”) and sytematics, ecological niches (“[humans] are essentially living niche-free and ecosystemless”), domestication, and so much more. The last chapter is spent discussing agroecosystems (“the organisms and abiotic environment that interact in a human-managed agricultural setting”), a topic he spent much of his career studying.
The underlying message of this book, as I see it, is a simultaneous celebration for life on earth and a concern for the direction things are going considering how humans have managed things. Parrish has some admonition for humans in light of how we’ve treated our home planet, but he isn’t too heavy-handed about it. Overall, reading the book felt like sitting in on a lecture given by a friendly and dynamic professor who has obviously given a lot of thought to what he has to say.
Check out the following video to see David Parrish describe the book in his own words.
A couple of weeks ago, Sierra and I were in Ketchum, Idaho taking a much needed mid-October vacation. The weather was great, and the fall color was incredible, so heading out on multiple hikes was a no-brainer. On our hikes, I found myself increasingly drawn to all of the snags. Forested areas like those found in the Sawtooth National Forestare bound to have a significant amount of standing dead trees. After all, trees don’t live forever; just like any other living being, they die – some of old age, some of disease or lightning strike or any number of other reasons. But death for a tree does not spell the end of its life giving powers. In the case of snags, it’s really just the beginning.
Death might come quick for a tree, but its rate of decomposition is slow. Fungi move in to begin the process and are joined by myriad insects, mosses, lichens, and bacteria. The insects provide food for birds, like woodpeckers and sapsuckers who hammer out holes in the standing trunk. As primary cavity nesters, they also nest in some of these holes. Secondary cavity nesters make a home in these holes as well. This includes a whole suite of birds, mammals, amphibians, and reptiles. Without the habitat provided by snags, many of these animals would disappear from the forest.
Eventually snags fall, and as the rotting continues, so does the dead tree’s contribution to new life. It’s at this point that snags become nurse logs or nurse stumps, providing habitat and nutrients for all sorts of plants, fungi, and other organisms.
Unfortunately I can’t bring a you a complete representation of the many snags of Sawtooth National Forest. You’ll have to visit sometime to see them all for yourself. Instead, what follows is a small sampling of a few of the snags we saw near Ketchum and Stanley.
new cavities in new snag
old cavities in old snag
knobby snag with lichens
lone snag on hillside
snags are more alive than you might think
just look at those cavities
For more snag and nurse log fun, check out the following episodes of Boise Biophilia:
This will be the last post for a few weeks as I will be taking a break to finish working on a related project. I hope to be back sometime in December with more posts, as well as the unveiling of what I have been working on. In the meantime, you can stay updated by following Awkward Botany on Twitter or Facebook.
For a little over a year now, I’ve been doing a tiny radio show with a friend of mine named Casey O’leary. The show is called Boise Biophilia and airs weekly on Radio Boise. On the show we each take about a minute to talk about something biology or ecology related that listeners in our local area can relate to. Our goal is to encourage listeners to get outside and explore the natural world. It’s fascinating after all! After the shows air, I post them on our website and Soundcloud page for all to hear.
We are not professional broadcasters by any means. Heck, I’m not a huge fan of talking in general, much less when a microphone is involved and a recording is being made. But Casey and I both love spreading the word about nerdy nature topics, and Casey’s enthusiasm for the project helps keep me involved. We’ve recorded nearly 70 episodes so far and are thrilled to know that they are out there in the world for people to experience. What follows is a sampling of some of the episodes we have recorded over the last 16 months. Some of our topics and comments are inside baseball for people living in the Treasure Valley, but there’s plenty there for outsiders to enjoy as well.
Something you will surely note upon your first listen is the scattering of interesting sound effects and off the wall edits in each of the episodes. Those come thanks to Speedy of Radio Boise who helps us edit our show. Without Speedy, the show wouldn’t be nearly as fun to listen to, so we are grateful for the work he does.
Boise Biophilia logo designed by Sierra Laverty
In this episode, Casey and I explore the world of leaf litter. Where do all the leaves go after they fall? Who are the players involved in decomposition, and what are they up to out there?
In this episode, Casey gets into our region’s complicated system of water rights, while I dive into something equally complex and intense – life inside of a sagebrush gall.
In this episode, I talk about dead bees and other insects trapped and dangling from milkweed flowers, and Casey discusses goatheads (a.k.a. puncture vine or Tribulus terrestris) in honor of Boise’s nascent summer celebration, Goathead Fest.
As much as I love plants, I have to admit that some of our best episodes are insect themed. Their lives are so dramatic, and this episode illustrates that.
The insect drama continues in this episode in which I describe how ant lions capture and consume their prey. Since we recorded this around Halloween, Casey offers a particularly spooky bit about garlic.
If you follow Awkward Botany, you know that one of my favorite topics is weeds. In this episode, I cover tumbleweeds, an iconic western weed that has been known to do some real damage. Casey introduces us to Canada geese, which are similar to weeds in their, at times, overabundance and ability to spawn strong opinions in the people they share space with.
In this episode, I explain the phenomenon of marcescence, and Casey gives some great advice about growing onions from seed.
And finally, in the spring you can’t get by without talking about bulbs at some point. This episode is an introduction to geophytes. Casey breaks down the basics, while I list some specific geophytes native to our Boise Foothills.
I love music for its ability to conjure up emotions, create a mood, and inspire action. The music of Laura Veirs has always inspired me to get out into nature and be more observant of the wild things around me. Her music is rich with emotions, and I feel those, too. However, when I think of her music, I can’t escape images of the natural world and the creatures that inhabit it.
Found within her nature-centric lyrics are, of course, numerous botanical references. After all, plants and their actions make excellent subject matter for all types of art. And with that in mind, Veirs asks rhetorically in the song Rapture, “Doesn’t the tree write great poetry?”
When it comes to botanical references, the song that jumps first to mind is Lonely Angel Dust, starting off right away with these lyrics: “The rose is not afraid to blossom / though it knows its petals must fall / and with its petals fall seeds into soil / Why toil to contain it all? / Why toil at all?” Plants produce seeds in abundance, as mentioned in Shadow Blues: “Thousand seeds from a flower blowing through the night.” And, as in Where Are You Driving?, they’re seeking a suitable spot to plant themselves: “Through clouds of dandelions / seeds sailing out on the wind / hoping you’ll be the one to plant yourself on in.”
Flowers come up often in the songs of Laura Veirs. In White Cherry, “cherry trees take to bloom.” In Nightingale, “her heart a field in bloom.” In Make Something Good, “an organ pipe in a cathedral / that stays in tune through a thousand blooms.” In Sun is King, “innocent as a summer flower.” In Cast a Hook, “with watery cheeks down flowered lanes.” In Life Is Good Blues, “Messages you sent to Mars came from a crown of flowers.” Grass and weeds get a few mentions, too. In Summer Is the Champion, “let’s get dizzy in the grass.” In Life Is Good Blues, “tender green like the shoots of spring / unfurling on the lawn.”
Trees are the real stars, though. Veirs makes frequent references to trees and their various parts. This makes sense, as trees are real forces of nature. So much happens in, on, and around them, and images of the natural world can feel barren without them. First there is their enormousness, as in Black Butterfly, “evergreen boughs above me tower / were singing quiet stories about forgiveness, ” and Don’t Lose Yourself, “we slept in the shadow of a cedar tree.” Then there is their old age, as in Where Are You Driving?, “tangled up in the gnarled tree,” and When You Give Your Heart, “falling through the old oak tree.” There is also their utility, mentioned in Make Something Good, “I wanted to make something sweet / the blood inside a maple tree / the sunlight trapped inside the wood / make something good.” And then, of course, there is the fruit they bear, as in July Flame, “sweet summer peach / high up in the branch / just out of my reach,” and then in Wandering Kind, “a strange July / a storm came down / from the North and pulled out the salt / and it tore out the leaves from the pear tree / my canopy.”
Many of Veirs songs create scenes and tell stories of being in the wilderness among rivers, lakes, mountains, and caves. Chimney Sweeping Man, for example, is a “forest resident” who “walks[s] quiet through the forest like a tiny, quiet forest mouse.” In Snow Camping, Veirs tells a story about sleeping in a snow cave in the forest, where “a thousand snowflakes hovered,” “a distant songbird [was] singing,” and “the weighted trees” were her “only home.” But sometimes those forests burn, which is captured in Drink Deep: “Now the raging of the forest fires end / and all the mammals fled / I smell in the charred darkness / a little green / a little red.” Later in the song: “the fire closed his eyes / tipped his flame hat and slipped through the dire rye / we wandered romantic / we scattered dark branches / with singing green stars as our guide.”
Nature can also be empowering, and Veirs often refers to things in the natural world as metaphors or similes for the human experience. In Cast a Hook, Veirs adamantly asserts, “I’m not dead, not numb, not withering / like a fallen leaf who keeps her green.” This line comes up again in Saltbreakers: “You cannot burn me up / I’m a fallen leaf who keeps her green.” In Lake Swimming, Veirs addresses change and how some of life’s changes may wound us but we can still shine – “shucking free our deadened selves / like snakes and corn do / … / Old butterfly / I’ll dance with you / though our wings may crumble / we can float like ash / broken but the edges still shine.”
The botanical references Veirs makes in her songs are not the only things that excite me. Birds, insects, mammals, fish, and worms all find a place in Veirs’ lyrics. This is why, after more than a decade of listening to her songs, I find myself coming back to them again and again. There is a sort of kinship we feel for each other when we share in common a love of the natural world. I find that in the music of Laura Veirs.
One of the biggest threats to wetland ecosystems is, of course, invasive species. In last week’s postI shared a selection of videos that were produced by a variety of organizations to inform the public about invasive species. Many such videos specifically address invasives in wetlands and waterways. Here are a few of those videos.
Generally speaking, individual plants produce an enormous amount of seeds. This may seem like a huge waste of resources, but the reality is that while each seed has the potential to grow into an adult plant that will one day produce seeds of its own, relatively few may achieve this. Some seeds will be eaten before they get a chance to germinate. Others germinate and soon die from lack of water, disease, or herbivory. Those that make it past the seedling stage continue to face similar pressures. Reaching adulthood, then, is a remarkable achievement.
Antelope bitterbrush is a shrub that produces hundreds of seeds per individual. Each seed is about the size of an apple seed. Some seeds may be eaten right away. Others fall to the ground and are ignored. But a large number are collected by rodents and either stored in burrows (larder hoarding) or in shallow depressions in the soil (scatter hoarding). It is through cachingthat antelope bitterbrush seeds are best dispersed. When rodents fail to return to caches during the winter, the seeds are free to sprout in the spring. Some of the seedlings will dry out and others will be eaten, but a few will survive, making the effort to produce all those seeds worth it in the end.
Fruits forming on antelope bitterbrush (Purshia tridentata)
Antelope bitterbrush (Purshia tridentata) is in the rose family and is often simply referred to as bitterbrush. It occurs in grasslands, shrub steppes, and dry woodlands throughout large sections of western North America. It is a deciduous shrub that generally reaches between three and nine feet tall but can grow up to twelve feet. It has wedge-shaped leaves that are green on top, grayish on bottom, and three-lobed. Flowers are yellow, strongly fragrant, and similar in appearance to others in the rose family. Flowering occurs mid-spring to early summer. Fruits are achenes – single seeds surrounded by papery or leathery coverings. The covering must rot away or be removed by animals before the seed can germinate.
Bitterbrush is an important species for wildlife. It is browsed by mule deer, pronghorn antelope, bighorn sheep, and other ungulates, including livestock. It provides cover for birds, rodents, reptiles, and ungulates. Its seeds are collected by harvester antsand rodents, its foliage is consumed by tent caterpillars and other insects, and its flowers are visited by a suite of pollinators. For all that it offers to the animal kingdom, it also relies on it for pollination and seed dispersal. The flowers of bitterbrush are self-incompatible, and if it wasn’t for ants and rodents, the heavy seeds – left to rely on wind and gravity – would have trouble getting any further than just a few feet from the parent plant.
Antelope bitterbrush (Purshia tridentata) in full bloom – photo credit: wikimedia commons
In a study published in The American Naturalist (February 1993), Stephen Vander Wall reported that yellow pine chipmunks were the primary dispersal agents of bitterbrush seeds in his Sierra Nevada study area. The optimal depth for seedling establishment was between 10-30 millimeters. Seeds that are cached too near the surface risk being pushed out of the ground during freeze and thaw cycles where they can desiccate upon germination. Cached bitterbrush seeds benefit when there are several seeds per cache because, as Vander Wall notes, “clumps of seedlings are better able to push through the soil and can establish from greater depths than single seedlings.”
Another study by Vander Wall, published inEcology (October 1994), reiterated the importance of seed caching by yellow pine chipmunks in the establishment of bitterbrush seedlings. Seed caches, which consisted of anywhere from two to over a hundred seeds, were located as far as 25 meters from the parent plant. Cached seeds are occasionally moved to another location, but Vander Wall found that even these secondary caches produce seedlings. Of course, not all of the seedlings that sprout grow to maturity. Vander Wall states, “attrition over the years gradually reduces the number of seedlings within clumps.” Yet, more than half of the mature shrubs he observed in his study consisted of two or more individuals, leading him to conclude that “they arose from rodent caches.”
A study published in the Journal of Range Management (January 1996) looked at the herbivory of bitterbrush seedlings by rodents. In the introduction the authors discuss how “rodents [may] not only benefit from antelope bitterbrush seed caches as a future seed source, but also benefit from the sprouting of their caches as they return to graze the cotyledons of germinating seeds.” In this study, Ord’s kangaroo rats, deer mice, and Great Basin pocket mice were all observed consuming bitterbrush seedlings, preferring them even when millet was offered as an alternative. The two species of mice also dug up seedlings, possibly searching for ungerminated seeds. Despite seed dispersal via caching, an overabundance of rodents can result in few bitterbrush seedlings reaching maturity.
A cluster of antelope bitterbrush seedlings that has been browsed. “Succulent, young seedlings are thought to be important in the diets of rodents during early spring because of the nutrients and water they contain.” — Vander Wall (1994)
Photos of antelope bitterbrush seedling clusters were taken at Idaho Botanical Garden, where numerous clusters are presently on display along the pathways of the native plant gardens and the adjoining natural areas.
In 1946, North American beavers were introduced to the archipelago of Tierra del Fuego at the tip of South America in an attempt to start an industry based on beaver fur. Although this industry has not thrived, beavers have multiplied enormously. By cutting trees and building dams, they have transformed forests into meadows and also fostered the spread of introduced ground cover plants. Now numbering in the tens of thousands in both Chilean and Argentinian parts of the archipelago, beavers are the target of a binational campaign to prevent them from spreading to the mainland of these two nations. — Invasive Species: What Everyone Should Knowby Daniel Simberloff
Beavers in South America are just one example of the series of effects a species can have when it is placed in a new environment. Prior to the arrival of beavers, there were no species in the area that were functionally equivalent. Thus, through their felling of trees and damning of streams, the beavers introduced novel disturbances that have, among other things, aided the spread of non-native plant species. Ecologists call this an invasional meltdown, wherein invasion by one organism aids the invasion of another, making restoration that much more difficult.
Complicated interactions like this are explored by David Wardle and Duane Peltzer in a paper published last month in Biological Invasions. Organisms from all walks of life have been introduced to forests around the world, and while many introductions have had no discernable impact, others have had significant effects both above and below ground.
The authors selected forest ecosystems for their investigation because “the imprint of different invaders on long-lived tree species can often be observed directly,” even when the invading organisms are doing their work below ground. Moreover, a greater understanding of “the causes and consequences of invasions is essential for reliably predicting large-scale and long-term changes” in forest ecosystems. Forests do not regenerate quickly, so protecting them from major disturbances is important. Learning how forests respond to invasions can teach us how best to address the situation when it occurs.
The authors begin by introducing the various groups of organisms that invade forests and the potential impacts they can have. This is summarized in the graphic below. One main takeaway is that the effects of introduced species vary dramatically depending on their specific attributes or traits and where they fall within the food chain. If, like the beaver, a novel trait is introduced, “interactions between the various aboveground and belowground components, and ultimately the functioning of the ecosystem” can be significantly altered.
After highlighting some of the impacts that invasive species can have above and below ground, the authors discuss basic tenets of invasion biology as they relate to forest ecosystems. Certain ecosystems are more vulnerable to invasions than others, and it is important to understand why. One hypothesis is that ecosystems with a high level of species diversity are more resistant to invasion than those with low species diversity. This is called biotic resistance. When it comes to introduced plants, soil properties and other environmental factors come in to play. One species of plant may be highly invasive in one forested ecosystem, but completely unsuccessful in another. The combination of factors that help determine this are worth further exploration.
When it comes to restoring invaded forests, simply eliminating invasive species is not always enough. Because of the ecological impacts they can have above and below ground, “invader legacy effects” may persist. As the authors write, this requires “additional interventions to reduce or remove [an invader’s] legacy.” Care also has to be taken to avoid secondary invasions, because as one invasive species is removed another can take its place.
Nitrogen-fixing plants (which, as the authors explain, “feature disproportionately in invasive floras”) offer a prime example of invader legacy effects. Introducing them to forest ecosystems that lack plants with nitrogen fixing capabilities “leads to substantially greater inputs of nitrogen … and enhanced soil fertility.” Native organisms – decomposer and producer alike – are affected. Simply removing the nitrogen fixing plants does not at once remove the legacy they have left. Examples include Morella faya invasions of forest understories in Hawaii and invasions by Acacia species in South Africa and beyond.
“It has been shown that co-invasion by earthworms enhances the effects that the invasive nitrogen fixing shrub Morella faya has on nitrogen accretion and cycling in a Hawaiian forest, by enhancing burial of nitrogen-rich litter.” – D.A. Wardle and D.A. Peltzer (2017) – photo credit: wikimedia commons
The authors conclude with a list of “unresolved issues” for future research. A common theme among at least a couple of their issues is the need for observing invasive species and invaded environments over a long period. Impacts of invasive species tend to “vary across both time and space,” and it is important to be able to predict “whether impacts are likely to amplify or dampen over time.” In short, “focus should shift from resolving the effects of individual invasive species to a broader consideration of their longer term ecosystem effects.”
This paper does not introduce new findings, but it is a decent overview of invasion biology and is worth reading if you are interested in familiarizing yourself with some of the general concepts and hypotheses. It’s also open access, which is a plus. One thing that is clear after reading this is that despite our growing awareness of the impacts of invasive species, there is still much to be learned, particularly regarding how best to respond to them.
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