When Urban Pollinator Gardens Meet Native Plant Communities

Public concern about the state of bees and other pollinating insects has led to increased interest in pollinator gardens. Planting a pollinator garden is often promoted as an excellent way for the average person to help protect pollinators. And it is! However, as with anything in life, there can be downsides.

In many urban areas, populations of native plants remain on undeveloped or abandoned land, in parks or reserves, or simply as part of the developed landscape. Urban areas may also share borders with natural areas, the edges of which are particularly prone to invasions by non-native plants. Due to human activity and habitat fragmentation, many native plant populations are now threatened. Urban areas are home to the last remaining populations of some of these plants.

Concern for native plant populations in and around urban areas prompted researchers at University of Pittsburgh to review some of the impacts that urban pollinator gardens may have and to develop a “roadmap for research” going forward. Their report was published earlier this year in New Phytologist.

Planting a wildflower seed mix is a simple way to establish a pollinator garden, and such mixes are sold commercially for this purpose. Governmental and non-governmental organizations also issue recommendations for wildflower, pollinator, or meadow seed mixes. With this in mind, the researchers selected 30 seed mixes “targeted for urban settings in the northeastern or mid-Atlantic USA” to determine what species are being recommended for or commonly planted in pollinator gardens in this region. They also developed a “species impact index” to assess “the likelihood a species would impact remnant wild urban plant populations.”

A total of 230 species were represented in the 30 seed mixes. The researchers selected the 45 most common species for evaluation. Most of these species (75%) have generalized pollination systems, suggesting that there is potential for sharing pollinators with remnant native plants. Two-thirds of the species had native ranges that overlapped with the targeted region; however, the remaining one-third originated from Europe or western North America. The native species all had “generalized pollination systems, strong dispersal and colonization ability, and broad environmental tolerances,” all traits that could have “high impacts” either directly or indirectly on remnant native plants. Other species were found to have either high dispersal ability but low chance of survival or low dispersal ability but high chance of survival.

This led the researchers to conclude that “the majority of planted wildflower species have a high potential to interact with native species via pollinators but also have the ability to disperse and survive outside of the garden.” Sharing pollinators is especially likely due to super-generalists like the honeybee, which “utilizes flowers from many habitat types.” Considering this, the researchers outlined “four pollinator-mediated interactions that can affect remnant native plants and their communities,” including how these interactions can be exacerbated when wildflower species escape gardens and invade remnant plant communities.

photo credit: wikimedia commons

The first interaction involves the quantity of pollinator visits. The concern is that native plants may be “outcompeted for pollinators” due to the “dense, high-resource displays” of pollinator gardens. Whether pollinator visits will increase or decrease depends on many things, including the location of the gardens and their proximity to native plant communities. Pollinator sharing between the two has been observed; however, “the consequences of this for effective pollination of natives are not yet understood.”

The second interaction involves the quality of pollinator visits. Because pollinators are shared between native plant communities and pollinator gardens, there is a risk that the pollen from one species will be transferred to another species. High quantities of this “heterospecific pollen” can result in reduced seed production. “Low-quality pollination in terms of heterospecific pollen from wildflower plantings may be especially detrimental for wild remnant species.”

The third interaction involves gene flow between pollinator gardens and native plant communities. Pollen that is transferred from closely related species (or even individuals of the same species but from a different location) can have undesired consequences. In some cases, it can increase genetic variation and help address problems associated with inbreeding depression. In other cases, it can introduce traits that are detrimental to native plant populations, particularly traits that disrupt adaptations that are beneficial to surviving in urban environments, like seed dispersal and flowering time. Whether gene flow between the two groups will be positive or negative is difficult to predict, and “the likelihood of genetic extinction versus genetic rescue will depend on remnant population size, genetic diversity, and degree of urban adaptation relative to the planted wildflowers.”

The fourth interaction involves pathogen transmission via shared pollinators. “Both bacterial and viral pathogens can be transmitted via pollen, and bacterial pathogens can be passed from one pollinator to another.” In this way, pollinators can act as “hubs for pathogen exchange,” which is especially concerning when the diseases being transmitted are ones for which the native plants have not adapted defenses.

photo credit: wikimedia commons

All of these interactions become more direct once wildflowers escape gardens and establish themselves among the native plants. And because the species in wildflower seed mixes are selected for their tolerance of urban conditions, “they may be particularly strong competitors with wild remnant populations,” outcompeting them for space and resources. On the other hand, the authors note that, depending on the species, they may also “provide biotic resistance to more noxious invaders.”

All of these interactions require further investigation. In their conclusion, the authors affirm, “While there is a clear potential for positive effects of urban wildflower plantings on remnant plant biodiversity, there is also a strong likelihood for unintended consequences.” They then suggest future research topics that will help us answer many of these questions. In the meantime, pollinator gardens should not be discouraged, but the plants (and their origins) should be carefully considered. One place to start is with wildflower seed mixes, which can be ‘fine-tuned’ so that they benefit our urban pollinators as well as our remnant native plants. Read more about plant selection for pollinators here.

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The Agents That Shape the Floral Traits of Sunflowers

Flowers come in a wide array of shapes, sizes, colors, and scents. Their diversity is downright astounding. Each individual species of flowering plant has its own lengthy story to tell detailing how it came to look and act the way it does. This is its evolutionary history. Unraveling this history is a nearly insurmountable task, but one that scientists continue to chip away at piece by piece.

In the case of floral traits – particularly for flowers that rely on pollinators to produce seeds – it is safe to say that millennia of interactions with floral visitors have helped shape not only the way the flower looks, but also the nature of its nectar and pollen. However, flowers are “expensive” to make and maintain, so even though they are necessary for reproduction, plants must find a balance between that and allocating resources for defense – against both herbivory and disease – and growth. This balance can differ depending on a plant’s life history – whether it is annual or perennial. An annual plant has one shot at reproduction, so it can afford to funnel much of its energy there. If a perennial is unsuccessful at reproduction one year, there is always next year, as long as it has allocated sufficient resources towards staying alive.

Where a plant exists in the world also influences how it looks. Abiotic factors like temperature, soil type, nutrient availability, sun exposure, and precipitation patterns help shape, through natural selection, many aspects of a plant’s anatomy and physiology, including the structure and composition of its flowers. Additional biotic agents like nectar robbersflorivores, and pathogens can also influence certain floral traits.

This is the background that researchers from the University of Central Florida and University of Georgia drew from when they set out to investigate the reasons for the diverse floral morphologies in the genus Helianthus. Commonly known as sunflowers, Helianthus is a familiar genus consisting of more than 50 species, most of which are found across North America. The genus includes both annuals and perennials, and all but one species rely on cross-pollination to produce viable seeds. Pollination is mainly carried out by generalist bees.

Maximilian sunflower (Helianthus maximiliani)

Helianthus species are found in diverse habitats, including deserts, wetlands, prairies, rock outcrops, and sand dunes. Their inflorescences – characteristic of plants in the family Asteraceae – consist of a collection of small disc florets surrounded by a series of ray florets, which as a unit are casually referred to as a single flower. In Helianthus, ray florets are completely sterile and serve only to attract pollinators. Producing large and numerous ray florets takes resources away from the production of fertile disc florets, and sunflower species vary in the amount of resources they allocate for each floret form.

In a paper published in the July 2017 issue of Plant Ecology and Evolution, researchers selected 27 Helianthus species and one Phoebanthus species (a closely related genus) to investigate “the evolution of floral trait variation” by examining “the role of environmental variation, plant life history, and flowering phenology.” Seeds from multiple populations of each species were obtained, with populations being carefully selected so that there would be representations of each species from across their geographic ranges. The seeds were then grown out in a controlled environment, and a series of morphological and physiological data were recorded for the flowers of each plant. Climate data and soil characteristics were obtained for each of the population sites, and flowering period for each species was collected from various sources.

The researchers found “all floral traits” of the sunflower species to be “highly evolutionarily labile.” Flower size was found to be larger in regions with greater soil fertility, consistent with the resource-cost hypothesis which “predicts that larger and more conspicuous flowers should be selected against in resource-poor environments.” However, larger flower size had also repeatedly evolved in drier environments, which goes against this prediction. Apart from producing smaller flowers in dry habitats, flowering plants have other strategies to conserve water such as opening their flowers at night or flowering for a short period of time. Sunflowers do neither of these things. As the researchers state, “this inconsistency warrants consideration.”

The researchers speculate that “the evolution of larger flowers in drier environments” may be a result of fewer pollinators in these habitats “strongly favoring larger display sizes in self-incompatible species.” The flowers are big because they have to attract a limited number of pollinating insects. Conversely, flowers may be smaller in wetter environments because there is greater risk of pests and diseases. This is supported by the enemy-escape hypothesis – smaller flowers are predicted in places where there is increased potential for florivory and pathogens. Researchers found that lower disc water content had also evolved in wetter environments, which supports the idea that the plants may be defending themselves against flower-eating pests.

Seed heads of Maximilian sunflower (Helianthus maximiliani)

Another interesting finding is that, unlike other genera, annual and perennial sunflower species allocate a similar amount of resources towards reproduction. On average, flower size was not found to be different between annual and perennial species. Perhaps annuals instead produce more flowers compared to perennials, or maybe they flower for longer periods. This is something the researchers did not investigate.

Finally, abiotic factors were not found to have any influence on the relative investment of ray to disc florets or the color of disc florets. Variations in these traits may be influenced instead by pollinators, the “biotic factor” that is considered “the classic driver of floral evolution.” This is something that will require further investigation. As the researchers conclude, “determining the exact drivers of floral trait evolution is a complex endeavor;” however, their study found “reasonable support for the role of aridity and soil fertility in the evolution of floral size and water content.” Yet another important piece to the puzzle as we learn to tell the evolutionary history of sunflowers.

Highlights from the Alaska Invasive Species Workshop

This October 24-26th I was in Anchorage, Alaska for the 18th annual Alaska Invasive Species Workshop. The workshop is organized by the Committee for Noxious and Invasive Pests Management and University of Alaska Fairbanks Cooperative Extension. It is a chance for people involved in invasive species management in Alaska – or just interested in the topic – to learn about the latest science, policies, and management efforts within the state and beyond. I am not an Alaska resident – nor had I ever been there until this trip – but my sister lives there, and I was planning a trip to visit her and her family, so why not stop in to see what’s happening with invasive species while I’m at it?

What follows are a few highlights from each of the three days.

Day One

The theme of the workshop was “The Legacy of Biological Invasions.” Ecosystems are shaped by biotic and abiotic events that occurred in the past, both recent and distant. This is their legacy. Events that take place in the present can alter ecosystem legacies. Invasive species, as one speaker said in the introduction, can “break the legacy locks of an ecosystem,” changing population dynamics of native species and altering ecosystem functions for the foreseeable future. Alaska is one of the few places on earth that is relatively pristine, with comparably little human disturbance and few introduced species. Since they are at an early stage in the invasion curve for most things, Alaska is in a unique position to eradicate or contain many invasive species and prevent future introductions. Coming together to address invasive species issues and protect ecosystem legacies will be part of the human legacy in Alaska.

The keynote address was delivered by Jamie Reaser, Executive Director of the National Invasive Species Council and author of several books. She spoke about the Arctic and its vulnerability to invasive species due to increased human activity, climate change, and scant research. To address this and other issues in the Arctic, the Arctic Council put together the Arctic Biodiversity Assessment, and out of that came the Arctic Invasive Alien Species Strategy and Action Plan. Reaser shared some thoughts about how government agencies and conservation groups can come together to share information and how they can work with commercial industries to address the threat of invasive species. She stressed that Alaska can and should play a leadership role in these efforts.

Later, Reaser gave a presentation about the National Invasive Species Council, including its formation and some of the work that it is currently doing. She emphasized that invasive species are a “people issue” – in that the actions and decisions we make both create the problem and address the problem – and by working together “we can do this.”

Day Two

Most of the morning was spent discussing Elodea, Alaska’s first invasive, submerged, freshwater, aquatic plant. While it has likely been in the state for a while, it was only recognized as a problem within the last decade. It is a popular aquarium plant that has been carelessly dumped into lakes and streams. It grows quickly and tolerates very cold temperatures, photosynthesizing under ice and snow. It propagates vegetatively and is spread to new sites by attaching itself to boats and float planes. Its dense growth can crowd out native vegetation and threaten fish habitat, as well as make navigating by boat difficult and landing float planes dangerous. Detailed reports were given about how organizations across the state have been monitoring and managing Elodea populations, including updates on how treatments have worked so far and what is being planned for the future. A bioeconomic risk analysis conducted by Tobias Schwörer was a featured topic of discussion.

After lunch I took a short break from the conference to walk around downtown Anchorage, so I missed a series of talks about environmental DNA. I returned in time to hear an interesting talk about bird vetch (Vicia cracca). Introduced to Alaska as a forage crop, bird vetch has become a problematic weed on farms, orchards, and gardens as well as in natural areas. It is a perennial vine that grows quickly, produces copious seeds, and spreads rhizomatously. Researchers at University of Alaska Fairbanks found that compared to five native legume species, bird vetch produced twice the amount of biomass in the presence of both native and non-native soil microbes, suggesting that bird vetch is superior when it comes to nitrogen fixation. Further investigation found that, using only native nitrogen-fixing bacteria, bird vetch produced significantly more root nodules than a native legume species, indicating that it is highly effective at forming relationships with native soil microbes. Additional studies found that the ability of bird vetch to climb up other plants, thereby gaining access to more sunlight and smothering host plants, contributed to its success as an invasive plant.

 Seed pods of bird vetch (Vicia cracca) in Fairbanks, Alaska

Day Three

The final day of the workshop was a veritable cornucopia of topics, including risk assessments for invasive species, profiles of new invasive species, updates on invasive species control projects, discussions about early detection and rapid response (EDRR), and talks about citizen science and community involvement. My head was swimming with impressions and questions. Clearly there are no easy answers when it comes to invasive species, and like other complex, global issues (made more challenging as more players are involved), the increasingly deep well of issues and concerns to resolve is not likely to ever run dry.

Future posts will dig further into some of the discussions that were had on day three. For now, here are a few resources that I gathered throughout the workshop:

Interpretive sign at Alaska Botanical Garden in Anchorage, Alaska

Is There a Place for Weeds in Urban Ecosystems?

Highly urbanized areas have a long history of disturbance. They are a far cry from the natural areas they once displaced, bearing little resemblance to what was there before. In this sense, they are a brand new thing. During the urbanization process, virtually everything is altered – temperatures, soils, wind patterns, hydrology, carbon dioxide levels, humidity, light availability, nutrients. Add to that a changing climate and increased levels of pollution, and the hope of ever seeing such a site return to its original state – whatever that might mean – is crushed.

What then should we consider the natural flora of an ecosystem like this? Certainly it is not the native flora that once stood on the site before it was developed; virtually none of the conditions are the same anymore. If we are defining “natural” as existing with minimal human intervention, then the natural urban flora would be whatever grows wild outside of our manicured landscapes and managed, remnant natural areas. It would be a cosmopolitan mixture of plants that have joined us in our migrations with and without our permission, along with a collection of species that are either extant to the site or have been brought in by wildlife. In many ways it would mirror the human populations of our modern cities – an assortment of residents from around the globe with diverse backgrounds and cultural histories.

In Wild Urban Plants of the Northeast, Peter Del Tredici classifies urban land into three general categories based on their ecological functions: native, remnant landscapes; managed, constructed landscapes; and ruderal, adaptive landscapes. Native, remnant landscapes are generally small areas within city limits that have never been developed. They contain a portion of the native plants that once populated the area, and they require vigilant and regular maintenance to keep non-native plants from invading and to control those that already have. Managed, constructed landscapes include all of the parks and gardens that have been designed and intentionally planted. They require regular maintenance of varying intensity in order to keep them looking the way they are intended to look. Ruderal, adaptive landscapes are abandoned or neglected sites that are populated by plants that have arrived on their own and that maintain themselves with virtually no human intervention. This is where the true, wild urban flora resides.

Prickly lettuce (Lactuca serriola) growing in an abandoned lot.

Many of the plants that make up our wild urban flora are what we commonly refer to as weeds. These weedy plants appear in landscapes throughout our cities, but are generally removed or controlled in all landscapes except the abandoned ones. It is in these neglected sites that weeds have the greatest potential to provide vital ecosystem services, performing ecological functions that are beneficial to urban life.

Not all plants are suited for this role. Spontaneous urban vegetation is particularly suited due to its ability to thrive in highly modified, urban environments without external management. Regardless of provenance, this suite of plants, as Del Tredici points out, seem to be “preadapted” to urban conditions and “are among the toughest on the planet.” A long list of traits has been identified for plants in this category, ranging from seed dispersal and viability to speed of growth and reproduction to tolerance of harsh conditions. Del Tredici summarizes by stating, “a successful urban plant needs to be flexible in all aspects of its life history from seed germination through flowering and fruiting, opportunistic in its ability to take advantage of locally abundant resources that may be available for only a short time, and tolerant of the stressful growing conditions caused by an abundance of pavement and a paucity of soil.”

Abandoned lots flush with weeds, overgrown roadsides and railways, and neglected alleyways colonized by enterprising plants are generally seen as ugly, unsightly eyesores – products of neglect and decline. Some of the plants found in such locations are valued in a garden setting or prized as part of the native landscape in a natural area, but growing wildly among trash and decaying urban infrastructure they, too, are refuse. As Richard Mabey has written: “If plants sprout through garbage they become a kind of litter themselves. Vegetable trash.”

Abandoned chicken coop overtaken by tree of heaven saplings (Ailanthus altissima).

Despite how we feel about these plants or the aesthetics of the locations they find themselves in, they are performing valuable services. Apart from adding to the biodiversity on the site as well as producing oxygen and sequestering carbon – services that virtually all plants offer – they may be preventing soil erosion, stabilizing waterways, absorbing excess nutrients, reducing the urban heat island effect, mitigating pollution, building soil, and/or providing food and habitat for urban wildlife. While cultivated and managed landscapes can achieve similar things, these neglected sites are doing so without resource or labor inputs. They are sustainable in the sense that their ability to provide these services is ongoing without reliance on outside maintenance.

Sites like these should be further investigated to determine the full extent of the services that they may or may not be offering, and in the event that they are doing more good than harm, they should be conserved and encouraged. One service that is receiving more attention, as Del Tredici writes, is phytoremediation – “the ability of some plants to clean up contaminated sites by selectively absorbing and storing high concentrations of heavy metals such as cadmium, lead, copper, zinc, chromium, and nickel in their tissues.” Weed species with this ability include prickly lettuce (Lactuca serriola), lambsquarters (Chenopodium album), and mugwort (Artemisia vulgaris). In an article in Places Journal, Del Tredici gives the example of the often despised, introduced plant, common reed (Phragmites australis) cleaning up the New Jersey Meadowlands by “absorbing abundant excess nitrogen and phosphorous throughout this highly contaminated site.”

In the book, Weeds: In Defense of Nature’s Most Unloved Plants, Richard Mabey writes: “As we survey our long love-hate relationship with [weeds], it may be revealing to ponder where weeds belong in the ecological scheme of things. They seem, even from the most cursory of looks, to have evolved to grow in unsettled earth and damaged landscapes, and that may be a less malign role than we give them credit for.” Perhaps, seeing them in this worthy role, will temper our knee-jerk inclination to demonize them at every turn.

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See Also: Our Urban Planet and Wild Urban Plants of Boise.

Seagrass Meadows and Their Role in Healthy Marine Ecosystems

Seagrass meadows are found along soft-bottomed, shallow, marine coastlines of every continent except Antartica. Their abundance and the important roles they play earn them the title of third most valuable ecosystem on the planet after estuaries and wetlands. These extensive meadows are made up of a group of flowering plants that are unique in their ability to thrive submerged in salty seawater. Tossed about by the tides, they feed and harbor an incredibly diverse world of marine life and help protect neighboring ecosystems by stabilizing sediments and mitigating pollution.

Seagrasses are often confused with seaweed, but they are very different organisms. Seaweed is algae. Seagrasses are plants that at one point in their evolutionary history lived on land but then retreated back into the waters of their ancient ancestors. They are rooted in the sediment of the sea floor and, depending on the species, can reproduce both sexually (submerged flowers are pollinated with the help of moving water) and/or asexually (via rhizomes). Although many of them have a grass-like appearance, none of them are in the grass family (Poaceae); instead, the approximately 72 different species belong to one of four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae, or Cymodoceaceae).

Seagrass meadow in Wakaya, Fiji (photo credit: wikimedia commons)

Seagrass meadows can be composed of a single seagrass species or multiple species, with some meadows consisting of a dozen species or more. Seagrasses depend on light for photosynthesis, so they generally occur in shallow areas. How far seagrass meadows extend out into the ocean depends on light availability and the shade tolerance of the seagrass species. Their presence at the shoreline is limited naturally by how exposed they become at low tide, the frequency and strength of waves and associated turbidity, and low salinity from incoming fresh water.

Seagrass meadows benefit life on earth in many ways. As ecosystem engineers they create habitat and produce food for countless species, sequester a remarkable amount of carbon, and help maintain the health of neighboring estuaries, mangroves, coral reefs, and other ecosystems. They are home to commercial fisheries, which provide food for billions of people. Like many ecosystems on the planet, they are threatened by human activity. Pollution, development, recreation, and climate change jeopardize the health and existence of seagrass meadows. Thus, it is imperative that we learn as much as we can about them so that we are better equipped to protect them.

Turtle grass (Thalassia testudinum) growing in an estuary on the coast of San Salvador Island, Bahamas (photo credit: wikimedia commons)

In a report published in a February 2017 issue of Science, researchers examined the ability of seagrass meadows in Indonesia to remove microbial pathogens deposited into the sea via wastewater. When levels of the bacterial pathogen Enterococcus were compared between seagrass meadows and control sites, a three-fold difference was detected, with the seagrass meadows harboring the lowest levels. When other potential disease-causing bacteria were considered, the researchers found that “the relative abundance of bacterial pathogens in seawater” was 50% lower in both the intertidal flat and the coral reefs found within and adjacent to the seagrass meadows compared to control sites.

This has implications for the health of both humans and coral reefs, the latter of which face many threats including bacterial diseases. Two important coral reef diseases, white syndrome and black band disease, as well as signs of mortality associated with bleaching and sediment deposition “were significantly less on reefs adjacent to seagrass meadows compared to paired reefs,” according to the report.

Cushion sea star in seagrass meadow (photo credit: wikimedia commons)

The researchers note that “seagrasses are valued for nutrient cycling, sediment stabilization, reducing the effects of carbon dioxide elevation, and providing nursery habitat for fisheries.” The results of this study demonstrate the potential for seagrass meadows to “significantly reduce bacterial loads,” benefiting “both humans and other organisms in the environment.” Yet another reason to care about and conserve this vital ecosystem.

Additional Resources on Seagrass and Seagrass Conservation:

And if that’s not enough, check out this fun YouTube video:

When Sunflowers Follow the Sun

Tropisms are widely studied biological phenomena that involve the growth of an organism in response to environmental stimuli. Phototropism is the growth and development of plants in response to light. Heliotropism, a specific form of phototropism, describes growth in response to the sun. Discussions of heliotropism frequently include sunflowers and their ability to “track the sun.” This conjures up images of a field of sunflowers in full bloom following the sun across the sky. However cool this might sound, it simply doesn’t happen. Young sunflowers, before they bloom, track the sun. At maturity and in bloom, the plants hold still.

What is happening in these plants is still pretty cool though, and a report published in an August 2016 issue of Science sheds some light on the heliotropic movements of young sunflowers. They begin the morning facing east. As the sun progresses across the sky, the plants follow, ending the evening facing west. Over night, they reorient themselves to face east again. As they reach maturity, this movement slows, and most of the flowers bloom facing east. Over a series of experiments, researchers were able to determine the cellular and genetic mechanisms involved in this spectacular instance of solar tracking.

Helianthus annuus (common sunflower) is a native of North America, sharing this distinction with dozens of other members of this recognizable genus. It is commonly cultivated for its edible seeds (and the oil produced from them) as well as for its ornamental value. It is a highly variable species and hybridizes readily. Wild populations often cross with cultivated ones, and in many instances the common sunflower is considered a pesky weed. Whether crop, wildflower, or weed, its phototropic movements are easy to detect, making it an excellent subject of study.

Researchers began by tying plants to stakes so that they couldn’t move. Other plants were grown in pots and turned to face west in the morning. The growth of these plants was significantly stunted compared to plants that were not manipulated in these ways, suggesting that solar tracking promotes growth.

The researchers wondered if a circadian system was involved in the movements, and so they took sunflowers that had been growing in pots in a field and placed them indoors beneath a fixed overhead light source. For several days, the plants continued their east to west and back again movements. Over time, the movements became less detectable. This and other experiments led the researchers to conclude that a “circadian clock guides solar tracking in sunflowers.”

Another series of experiments helped the researchers determine what was happening at a cellular level that was causing the eastern side of the stem to grow during the day and the western side to grow during the night. Gene expression and growth hormone levels differed on either side of the stem depending on what time of day it was. In an online article published by University of California Berkeley, Andy Fell summarizes the findings: “[T]here appear to be two growth mechanisms at work in the sunflower stem. The first sets a basic rate of growth for the plant, based on available light. The second, controlled by the circadian clock and influenced by the direction of light, causes the stem to grow more on one side than another, and therefore sway east to west during the day.”

The researchers observed that as the plants reach maturity, they move towards the west less and less. This results in most of the flowers opening in an eastward facing direction. This led them to ask if this behavior offers any sort of ecological advantage. Because flowers are warmer when they are facing the sun, they wondered if they might see an increase in pollinator visits during morning hours on flowers facing east versus those facing west. Indeed, they did: “pollinators visited east-facing heads fivefold more often than west-facing heads.” When west-facing flowers where warmed with a heater in the morning, they received more pollinator visits than west-facing flowers that were not artificially warmed, “albeit [still] fewer than east-facing flowers.” However, increased pollinator visits may be only part of the story, so further investigations are necessary.

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I’m writing a book about weeds, and you can help. For more information, check out my Weeds Poll.

Concluding the Summer of Weeds

“Most weeds suffer from a bad rap. Quite a few of the weeds in your garden are probably edible or even medicinal. Some invasive plants, including horsetail and nettle, are rich in minerals and can be harvested and used as fertilizer teas. Weeds with deep taproots, such as dandelions, cultivate the soil and pull minerals up to the surface. … Weeds are nature’s way to cover bare soil. After all, weeds prevent erosion by holding soil and minerals in place. Get to know the weeds in your area so you can put them to use for rather than against you.” — Gayla Trail, You Grow Girl

Great Piece of Turf by Albrecht Dürer (photo credit: wikimedia commons)

With summer drawing to a close, it is time to conclude the Summer of Weeds. That does not mean that my interest in weeds has waned, or that posts about weeds will cease. Quite the opposite, actually. I am just as fascinated, if not more so, with the topic of weeds as I was when this whole thing started. So, for better or worse, I will much have more to say on the subject.

In fact, I am writing a book. It is something I have been considering doing for a long time now. With so many of my thoughts focused on weeds lately, it is becoming easier to envision just what a book about weeds might look like. I want to tell the story of weeds from many different angles, highlighting both their positive and negative aspects. There is much we can learn from weeds, and not just how best to eliminate them. Regardless of how you feel about weeds, I hope that by learning their story we can all become better connected with the natural world, and perhaps more appreciative of things we casually dismiss as useless, less quick to jump to conclusions or render harsh judgments about things we don’t fully understand, and more inclined to investigate more deeply the stories about nature near and far.

Of course, I can’t do this all by myself. I will need your help. If you or someone you know works for or against weeds in any capacity, please put us in touch. I am interested in talking to weed scientists, invasive species biologists, agriculturists and horticulturists, edible weed enthusiasts, plant taxonomists, natural historians, urban ecologists, gardeners of all skill levels, and anyone else who has a strong opinion about or history of working with weeds. Please get in touch with me in one of several ways: contact page, Facebook, Twitter, Tumblr, or by commenting below.

Another way you can help is by answering the following poll. If there is more than one topic you feel particularly passionate about, feel free to answer the poll as many times as you would like; just wait 24 hours between each response. Thank you for your help! And I hope you have enjoyed the Summer of Weeds.

Quick Guide to the Summer of Weeds: