Ragweed in the City: Part 1

This is the first of three blog posts I will be writing about my current research on the causes and consequences of disparities ragweed pollen in urban areas. Read on!

Why ragweed!?

As an urban ecologist, I am interested in how urban environments shape the distribution and traits of plants and animals. When I began my PhD in 2013, I spent a few weeks walking around Minneapolis identifying different species and observing urban habitats. I quickly noticed that there were a few plants that thrived. One of these plants was ragweed (Ambrosia artemisiifolia), the bane of many allergy sufferers. Ragweed produces a prolific amount of pollen, causing allergies in approximately 15-20% of Americans, and triggering asthma in some individuals. If you have allergies in late summer or fall, you are probably allergic to ragweed!

Ragweed living that city life in an alley in Minneapolis

Curious observations

I found ragweed just about everywhere: along bike paths, railroads, and riverbanks and in sidewalk cracks, lawns, parks and vacant lots. I also noticed that ragweed wasn’t evenly distributed across Minneapolis. Some residential neighbourhoods had lawns and boulevards with few ragweed plants and lots of trees. Others had more vacant lots and recently disturbed areas, fewer trees, and more ragweed plants. These two observations (ragweed growing in lots of different habitats, ragweed distributed unevenly across the city), led me to focus my dissertation on studying how selection in response environmental variation at different spatial scales (within a city, between urban and rural areas, and across latitude) can shape the evolution and adaptation of plants.

As my research took me to other U.S. cities (St.Louis, New Orleans, and others), I continued to observe differences among neighbourhoods in the abundance of ragweed plants. Was this a real pattern or simply an observation? Why might some neighbourhoods have more ragweed than others? And does this lead to differences in the amount of allergenic pollen across neighbourhoods? My dissertation research went in one direction, and these questions were left percolating in the back of my mind.

Is ragweed pollen in urban areas an environmental justice issue?

Fast forward to 2018: I was writing a research proposal for the Grand Challenges Postdoctoral Fellowship. The goal of this fellowship is to encourage interdisciplinary research that contributes to addressing major societal challenges identified by the University of Minnesota. My observations about the disparities in the abundance of ragweed in cities seemed like a good fit because I was increasingly realizing that it might be an environmental equity issue.

Tree canopy coverage and greenspace in the city

By now I had learned that most cities only have a single pollen count, but in New York and Detroit, the amount of pollen produced by trees and weeds can vary at scales of 1-10 km. This indicates that wind-dispersed pollen like ragweed may not move as far in urban areas as expected. Single pollen counts may not be representative of the actual pollen levels in different neighbourhoods. Ragweed is also more abundant in vacant lots in Detroit, and vacant lots are more common in lower income neighbourhoods Furthermore, wealthier neighbourhoods tend to have more trees or canopy coverage, which likely reduces the available habitat for weedy species like ragweed that tend to thrive in recently disturbed areas.

I decided to step out of my comfort zone and proposed to study the environmental and societal causes of inequality in urban plant allergens by diving into the fields of mathematical biology, public health, and environmental policy. I was fortunate to find three mentors (Dr. Allison Shaw, Dr. Bonnie Keeler and Dr. Jesse Berman), who were equally enthusiastic about these questions. In 2019 I was awarded the Grand Challenges Postdoctoral Fellowship for 2019-2021 to pursue this research.

Up next: pollen traps, field surveys and lots of ragweed

In the coming weeks I will be writing updates for two components of this research I’ve started working on in 2020:

1) Measuring ragweed pollen at small spatial scales in Minneapolis using pollen traps

2) Assessing the abundance of ragweed plants and green amenities using field surveys.

Stay tuned! 

Field season is almost over…updates soon!

Unfortunately, this field season, I haven’t been updating my research blog regularly. I’ve been traveling so much for my latitudinal reciprocal transplant experiment, I haven’t had much time to spare! To give you an idea, every month since May, my field work schedule has been as follows:

Let’s just say, I know where are the best donut spots are between Minneapolis and St.Louis.

When I haven’t been out of state, I’ve been collecting data for my precipitation manipulation experiment at Scooterville.

Anyways – 6+ months and +12,000 miles later, field season is almost over! I finished data collection for the precipitation manipulation experiment and at my MN, IA and IL field sites in October. I am traveling down to MO for final data collection Nov 10-13, and then it will finally be over!

I’ll write a summary of the field season and maybe even put up some graphs with data (!) sometime around American Thanksgiving*

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*Canadian Thanksgiving occurs in Oct.

 

 

Bring on the rain! (but not too much)

The precipitation experiment is in full swing! Woohoo! So is my latitudinal reciprocal transplant experiment…but more on that another day when I finish field work early.

The experiment was planted at the beginning of June (yes…this is a late blog post), with 30 plots total. There are 10 control plots, 10 addition plots, and 10 reduction plots. Each plot has seeds from 26 populations I collected from Minnesota to Louisiana in 2014 and 2015. Depending on which is your favourite BIOCLIM variable to look at, these populations span a gradient of precipitation, with populations from Minnesota experiencing drier climates than those from Louisiana.

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The location of the 26 populations included in the precipitation experiment

Annual precipitation, with lighter green corresponding to lower rainfall. Image taken from BONAP climate maps.

Annual precipitation, with lighter green corresponding to lower rainfall. Image taken from BONAP climate maps.

 

 

 

 

 

 

 

 

 

 

 

Plots after planting and before the start of the treatments

Plots after planting and before the start of the treatments

Over of the course of the growing season (July-Oct), I am reducing precipitation by 30% and increasing precipitation by 30% for the reduction and addition plots, respectively. To do this, I’m employing event based rain exclosures, which basically means I’ve become a storm chaser!

One of the reduction plots, complete with rainout shelter and barrel for rainwater collection.

One of the reduction plots, complete with rainout shelter and barrel for rainwater collection.

For certain rain events, I am covering the reduction plots with rainout shelters I constructed out of PVC pipes and overwintering plastic. I made these structures with the help of another graduate student at the University of Minnesota, Anna Peschel, who is also conducting a precipitation experiment at the same field site, focusing on the partridge pea, Chamaecrista fasciculata (a much cuter plant than ragweed).

For the addition plots, on the days we deploy the rainout shelters,  I am recording the amount of rain that fell at the field site with rain gauges, then adding that volume of water to the addition plots with watering cans.

We started the precipitation treatments at the beginning of July, which is very exciting! The tricky part is if the storm is going to be too severe (crazy wind, hail, etc), we can’t put them out because the structures will be destroyed. Basically we are hoping for lots of mild rain storms over the course of the season! Fingers crossed.

Rainout shelters deployed!

Rainout shelters deployed!

Broken bones, furious data collection and next steps: the end is nigh!

I’m in the final throes of collecting data on my experiment! I’m definitely ready to be finished, but there is much to do before the first frost hits.

Broken finger x-ray!

Broken finger x-ray!

Unfortunately for me, my dog broke the 4th finger on my left hand two weeks ago (leash wrapped around finger+ cat = dog excitement + broken finger). I’m left handed, so it’s been challenging to collect data. But with some sweet “buddy tape” though, I’m making it work!

Shamed (but still cute) dog.

Shamed (but still cute) dog.

Data collection at River Terrace (rural field site)

Data collection at River Terrace (rural field site). 

I’m currently in the process of counting male female reproductive parts to get estimates of male and female fitness. By “parts” I mean the stalks with the male inflorescences (see the previous post on ragweed flowering) and the fruit. This is fairly time consuming, as you can imagine, especially since some of plants are well over 1 m tall!

The plants are starting to get pretty crispy and brown, which is to be expected as the summer season comes to an end. Plus the first frost in Minneapolis normally occurs in early October. It’s a race against time to finish data collection before they get zapped!

Once the reciprocal transplant experiment wraps up, I will embarking on a road trip in October/November to collect seeds from a whole bunch of populations in both urban and rural locations from Minneapolis to St.Louis to Dallas. These seeds will be used for an experiment next summer where I will be looking at continental-wide patterns of population divergence and adaptation in common ragweed as well as testing for evidence of convergent evolution in phenotype to urban environments.

Blue skies in rural MN

Blue skies in rural MN

I’m going to write some regular posts about my collection trip (if anything just to post some photos of delicious t-ravs in St.Louis), but for now, here is a teaser photo I took out by one of of my Minnesota rural collection locales last week!

Ragweed flower anatomy and updates from the field!

Today we got rained out from our regular day of field work, so I thought I would post an update!

CBS undergraduates Eric Holton and Liz Sampson collecting data at the River Terrace field site

CBS undergraduates Eric Holton and Liz Sampson collecting flowering data at the River Terrace field site (rural location)

All the ragweed plants seem to have finally passed peak male and female flowering – data collection was pretty crazy for awhile. They are producing a huge amount of pollen, which is not surprising given that it’s a wind-pollinated plant and a major source of hay fever! Luckily, neither Eric nor I are allergic (yet).

A. artemisiifolia involucres. In the lower right is a single male flower, with two marks along a ruler indicating a length of 1 mm. Image taken from www.backyardnature.net

A. artemisiifolia involucres or “hats” as I call them. In the lower right is a single male flower, with two marks along a ruler indicating a length of 1 mm. Image taken from http://www.backyardnature.net

Common ragweed is a member of the Asteraceae, which is a large family of flowering plants that includes sunflowers and daisies (among many others!). Like other Asteraceae, common ragweed has composite flowers. The male flowers of common ragweed are clustered into little green upside-down bowl-like structures known as involucres, each of which is a single inflorescence. Multiple inflorescences are found along elongated spikes or stalks, and these stalks are found all over the plant! This means a single plant can have thousand of male flowers, each of which is releasing pollen into the air. Hello allergies!

A. artemisiifolia female flowers at the junction of a leaf and the main stem. Image by Graham Calow, taken from www.naturespot.org.uk

A. artemisiifolia female flowers at the junction of a leaf and the main stem. Image by Graham Calow, taken from www.naturespot.org.uk

The female flowers are a little bit harder to spot – they are generally located on stalks below the male inflorescences or at the junction of a leaf and the stem of the plant. Initially all you can see are tiny protruding stigmas (see picture to the left!), which then develop into a single seed.

In my experiment this summer, there are also some really neat all female plants that don’t have a single male flower on them! They are already starting to develop mature fruit as well. I’ll try to include a picture of one of these plants in a future blog post.

Sad, wilted ragweed plants at Scooterville on August 4th, 2015.

Sad, wilted ragweed plants at Scooterville on August 4th, 2015.

The past two weeks were pretty hot in Minneapolis – there were a few 35 C days and it didn’t rain for over a week. I was a bit of a scared that a significant number of plants at the Scooterville site (urban location) were going to die, but I resisted the temptation to water them. I am looking for differences in adaptation between populations after all!

Nevertheless, I am pretty happy that it rained today.

Until next time, fellow ragweed enthusiasts!

Insects and other animal friends (or enemies?) in the field

It’s been quite a while since I last posted – it’s been a busy few weeks in the field full of data collection (height! leaf numbers! male flowers! female flowers! exciting!), mosquito bites, and sunburns (only one so far).

Death by rabbits - a murder most foul

Death by rabbits – a murder most foul

Earlier this month I had to build a fence at the Scooterville site to keep rabbits out – or I think it’s rabbits. They seem to get a kick out of completely decimating a plant by removing the majority of the leaves, and yet, not eating a single one. I think I’ll put rabbits in the “enemy” column for now.

I’ve been trying to snap some photos here and there of various insects and other animals we have come across during field site visits and data collection. Here is a collection of some of those!

I have tried to identify them,  but despite my love of all creatures great and small, I’m not particularly good at identification. Please feel free to correct me!

Dirty field hands and a furry friend. Yellow wooly bear, Spilosoma virginica.

Dirty field hands and a furry friend. Yellow wooly bear, Spilosoma virginica.

Eric Holton (CBS undergraduate) with a garter snake at the River Terrace field site back when we were transplanting

Eric Holton (CBS undergraduate) with a garter snake at the River Terrace field site back when we were transplanting

Tiny frog (I think). Not sure of the species

Tiny frog (I think). Species unknown!

A little bit blurry, but Calligrapha leaf beetle. Not sure which species.

A little bit blurry, but Calligrapha leaf beetle. Not sure which species.

Cute little Eight-spotted Forester (Alypia octomaculata)

Cute little Eight-spotted Forester (Alypia octomaculata)

The elusive Euaresta bella (Tephritidae) has been difficult to photograph – this is a a specialist on common ragweed. The larvae develop in the  fruit and bore their way out. I’ve seen the adults all over the place but they are speedy. It’s a pretty neat species interaction and the flies are beautiful! Here’s a picture of an adult (not mine, taken from bugguide.net). Hopefully I’ll capture a good picture soon!

Euaresta bella. Such neat wings!

Euaresta bella. Such neat wings!

6 weeks and growing!

First of all – Happy Canada to all! If I ever get around to it, I’m going to make a page with amusing Canadian items, like the Long John Service Index of Canada.

The ragweed plants are happily growing and are getting huge! Last week I visited all my field sites to do some growth measurements on the plants at 6 weeks. There is a lot of variation in size of plants between the four field sites – the plants at the St.Paul site (urban garden) appear to be the largest, and those at the River Terrace site (rural garden) appear to be the smallest. I don’t know what is driving these size differences, however I have a feeling it might be due to soil differences between the sites. This gives me further motivation to do some sort of follow-up greenhouse experiment with the soil from these field sites to determine whether it is affecting plant growth and fitness.

Ragweed plants at St.Paul field site (6 weeks old!)

Ragweed plants at the St.Paul field site (6 weeks, urban location)

Ragweed plants at the River Terrace field site (6 weeks, rural location)

Ragweed plants at the River Terrace field site (6 weeks, rural location)

The beginning of flower development on a ragweed plant at the Scooterville field site.

The beginning of flower development on a ragweed plant at the Scooterville field site.

The plants have also started to initiate flower development! I was surprised to see this as A. artemisiifolia doesn’t  normally start to flower until late July or early August. I will be tracking and recording the emergence of both the male and female flowers as the season progresses with plastic party swords – I have to keep data collection exciting, right?

Adaptation to urban and rural environments – Germination + Transplanting!

It’s a little late, but finally a post about the experiment I’m doing this summer!

In Fall 2014, I collected seeds from multiple common ragweed (Ambrosia artemisiifolia) populations within urban Minneapolis and in the surrounding rural area. This summer, I am conducting an urban-rural reciprocal transplant experiment using those seeds to determine whether ragweed populations have adapted in response to the selection pressures present in urban and rural environments.

I have four field sites – two located in urban Minneapolis (called St.Paul and Scooterville), and two located in rural locations outside of the Twin Cities (called River Terrace and Rosemount). The Scooterville site is located on the University of Minnesota East Bank Campus and is part of the UMN Living Labs program.

Tilling Scooterville

Eric Holton (UMN undergraduate in EEB), tilling the Scooterville field site

In mid-May, I germinated the seeds in the greenhouse at the UMN and I prepared the sites for planting. This included lots of tilling, which is basically like using a giant lawnmower, but scarier.  In early June, I transplanted the ragweed seedlings out into the four field sites (with the help of others, of course). Overall, the transplanting was a success and most of the plants survived! Hurray!

I’ll be collecting data on these plants over the course of the summer, and I’ll try to post an update now and then with some pictures too! Stay tuned for more on everyone’s favourite plant, ragweed.

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Ragweed germinants successfully transplanted

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The Rosemount field site after transplanting