Today’s class was opened with a general description of the course along with a brief introduction of class members. Next, a few depictions of urbanization as both problems and solutions were displayed in regards to changing environmental conditions such as increasing energy usage and carbon dioxide emissions.

Most of the class was spent on examining semantics of terms, in particular, terms such as “urban,” “rural,” “urban ecology,” and “forest.” It was shown that these concepts are dynamic, with definitions varying in terms of specified quantifications and qualifications, from nation to nation, and from one discipline to another (i.e. from an environmental perspective or an urban planning background.) It was also shown that in different countries, varying socioeconomic factors influenced the definition of “urban” and “rural”. Consequently, models to project growth rate of cities, or populations in cities, can only be so accurate.

Building off these concepts, we discussed the conclusions made in the Hutyra and Seto 2012 paper that used factors such as population growth rates, local infrastructure, and natural terrain to project detailed probabilities in worldwide urban expansion by the year 2030. With our understanding of the challenges of making such projections, we debated whether or not one could use such thoughtful, science-based, yet inherently flawed models to make policy affecting people, wildlife, and the environment.

Next, ecosystem ecology was discussed, and factors required to build a habitable terrestrial landscape were examined. Areas of discussion were the sources of these necessary essential elements and nutrients in both natural and urban settings, as well as how certain urban conditions can modify the available levels of these substances.

Finally, the term urban ecology was put into a visual perspective with a discussion of central park, and of invasive species such as the Tree of Heaven (Ailanthus altissima). In particular, the topic of the benefits and costs of removing an invasive species like this was further explored. The class was ended with a discussion of which habitat would be better for a particular tree: a natural forested habitat west of Boston, or a spot directly in the middle of the BU campus. The discussion required us to challenge our kneejerk reaction of “natural is better;” while the natural habitat may provide less disturbance and pollution, the urban habitat may provide higher levels of nutrients or protection from natural enemies which would allow the tree to thrive. Indeed, as we examined graphically, at intermediate levels of disturbance, there is often higher biodiversity. Thus, we must be open to new ideas, as our perceptions of urban ecology, and in fact of the very word “urban,” will be challenged and informed in the coming semester.


Evan Kuras - Semantics play an important role in how we conceptualize urban ecological problems. In class, we discussed the goods and evils associated with Ailanthus altissima, the Tree of Heaven. This non-native tree grows (and provides ecosystem services) where other plants do not. The lecture slides also noted that the tree is "known as the ‘Ghetto Palm’ or the ‘tree of hell’ and smells of urine & is not especially attractive." I was taken aback by these descriptions - I always thought the tree smelled more like peanut butter and I found the compound leaves an attractive part of the cityscape. Was I dead wrong?
The first time I appreciated the global connectedness of cities was when I saw Ailanthus growing on the side of a road in Jerusalem, Israel. A Chinese tree in origin, Ailanthus is as out of place in Jerusalem as it is in Brooklyn or Boston. Yet I found this sight moving and inspiring. To Dr. Hutyra and other urban ecologists, Ailanthus may smell like urine and represent all that is wrong with the state of urban nature, or to others it may smell like peanut butter and be a symbol of just how connected we really are. The question from class remains, "Is it better to remove this invasive or leave it in place to provide the ecosystem services?" And the answer: semantics.

Steve Decina - Ailanthus is a subject very dear to my heart; I feel unequivocal and unapologetic reverence for this tree. It is perhaps the most charismatic (plants can be charismatic!) of what Peter Del Tredici calls "spontaneous urban plants." In Del Tredici's 2010 field guide, Wild Urban Plants of the Northeast, he makes an interesting connection between our attitudes towards Ailanthus and the misguided effort in New York City to plant a million trees: "When the mayor of New York City promised in 2007 to plant a million trees to fight global warming, he failed to realize that if the Ailanthus trees already growing throughout the city were counted he would be halfway towards his goal without doing anything" (Del Tredici 2010). And why were they not counted in the street tree inventory of New York City? They were not counted because, according to Del Tredici, no one planted them. If this is not a vestige of warped, man vs. nature hubris, I don't know what is.
I agree with Evan - I find Ailanthus beautiful. In fact, according to this loving, emotional, and historical account by Shiu Ying Hu, Ailanthus was actually cultivated in France and England for its beauty, and despite that it had been classified in the Rhus genus (now Toxicodendron), the same genus that houses poision ivy and poison sumac (Hu 1979), which it easily mistaken for when it is young. Hu goes on to detail the ways that Ailanthus has been and could be used by people to better their lives and their cities; anyone interested in this tree at all should give the chapter a read.
The point, for me, is that this tree symbolizes our perverse attitude towards spontaneous urban plants. Despite the services they provide to us and to all of the non-human parts of the ecosystem (if I can be un-anthropocentric for a moment), we see them as nuisance species, and fight their arrogance of self-subsistence and self-propagation with herbicides, finicky ornamentals, and pavement.
I will close with this - I taught in Newark, NJ for many years, and spontaneous urban plants were the only kinds of plants that were growing in the neighborhoods where my kids laid their heads at night. There was not space, nor good enough soil, nor enough governmental care to plant the fancy, high-maintenance ornamentals or the water-guzzling, wasteful lawns of my own suburban hometown. So these plants, with Ailanthus at the forefront, lived among my kids, cleaned the air they breathe, slowed the runoff that would otherwise cause their sewage to overflow, and made verdant and serene the places that were marred by the twisted, burned metal and concrete of the 1967 riots. In Newark, Ailanthus is a gift. In the words of Peter Del Tredici: "Indeed, if one were to ask whether our cities would be better or worse without Ailanthus, the answer would clearly be the latter, given that the tree typically grows where few other plants can survive." I would like to think that Dr. Del Tredici was not only talking about the strict environmental benefits that this tree confers, but the inextricably-linked socio-economic ones as well.

Eric Bullock - While I agree with what was said in class and among the other blog posts that Ailanthus altissima, or Tree of Heaven, is an often beautiful plant hidden among concrete and buildings, my opinion about how to approach the species could not be more different. In my honest opinion, keeping the Ailanthus among the streets of Boston (or any city) is making a a similar ecological mistake that has been made time and time again. That mistake is viewing an ecological system as independent, or disconnected from the larger ecosystem as a whole. While at a small-scale, the Ailanthus has plenty of benefits in terms of urban ecology. That being said, can we really ignore the impacts of urban species on species outside of the urban setting? Is that not the mindset that has caused environmental degradation for years? In my opinion, a key part of protecting an urban environment to minimize its impacts on less developed ecosystems.
Having worked for months at killing the Tree of Heaven, I have seen the devastating effects it can have to an ecosystem. The plant can quickly take over any wet, disturbed areas, causing numerous negative affects such as water level declines in riparian areas and native species loss. In addition, the term 'disturbed areas' does not merely mean areas developed by humans. This also includes natural disturbances such as fires or storms. It is widely regarded as one of the most invasive plant species in the country. So much so, that some parks are contemplating introducing a non-native fungus, just because it is known that the fungus is detrimental to the health of the Tree of Heaven. In one of the pictures of the tree from class, it was on the edge of a train track. In addition, most the trees are found along side walks. In my experience with invasive species, shoes and modes of transportation (trains included) are among the most common way nonnative seeds are spread. The train could easily spread the seeds to pristine, untouched areas. By allowing the existence of the species to exist in the urban environment we are ignoring the interconnectivity of the ecosystems around the world. In my opinion, while it is nice to be reminded of the natural world when walking around a city, it does not make it worth the risk of the impact the species can have on on the true, untouched nature found around the country.

Lucy Hutyra - A question for Eric and everyone else: Do we have 'pristine, untouched areas'? I think human activities influence ALL ecosystems through phenomena like climate change, long distance dust transport, increasing CO2 and nutrient inputs (fertilization/eutrophication), etc. Is it useful to think about pristine, untouched ecosystems?

Eric Bullock - I think my use of the word 'untouched' was wrong to use. I think 'less direct human impact' would be better. Or basically any less-developed area. An example of this would be as followed: In LA, a large portion of the city's clean air supply comes directly west from the Santa Monica Mountains (where I used to work killing Ailanthus). I would in no way say that the mountains were 'untouched', but they are substantially less touched than inside the city limits. Invasives were spread through the park primarily by hikers/backpackers coming from the city. The reason we cared so much about Ailanthus was that it had devastating effects to water levels and riparian habitats. The decrease in water made perfect riparian habitat for Conium maculatum (Poison hemlock) - a plant made famous for killing Socrates and also for killing uninformed hikers and scavengers. We saw that killing Ailanthus and also non-native (but not invasive) Eucalyptus trees was a much more effective way of controlling the Conium than directly killing it. The cycle of invasives, perpetuated by the exploration of city-dwellers, created an ecosystem problem constantly threatening to limit the city's clean air supply (native animals couldn't eat these plants, the hemlock would destroy biodiversity while having relatively small biomass blah blah blah I won't dive into this but you get the point) and also limit the river's ecologic benefits by the decrease in water levels and the poisonous 'buffer' of hemlock. I know this is just one example, but my point is that the Ailanthus is a perfect example of how urban environments can interact with suburban or even 'natural' environments (no matter how untouched it is they still serve the same ecological purposes) and how those impacts can directly relate back to the urban environment.

Sravya- Perception is everything when it comes to determining how we conceptualize and assess the world around us. The semantical variance of terms such as “urban,” and “rural” is fittingly the manifestation of different perceptions regarding these concepts. As a suburban resident of a small Western Massachusetts town (my hometown actually has a 2 mile radius), I had a very different perception of what “urban” was. To me, the term urban had always implied city, particularly large cities and therefore I never paid any consideration to “urban ecology” in my setting. My definition of urban, and urban ecology was simply a perception relative to my setting. Similarly, the disparate definitions of “urban” as displayed by this list compiled by the United Nations shows that the concept of urban ecology varies from place to place, and is certainly influenced by our perceptions.

Demonstratively, the tree Ailanthus altissima, displays the power of perception. Ailanthus is known by a wide variety of names: ranging from Tree of Heaven to “ghetto palm.” In China, this tree was valued for its medicinal properties and because it is home to the ailanthus silkmoth, and silk was a valued commodity. However, when brought to the United States, this species revealed its less heavenly attributes such as its foul order, and its capability of vegetative propagation, and soon became an invasive species earning the disdainful nicknames "ghetto palm," "stink tree," and "tree of Hell,” demonstrating that what is valued in once palace is loathed in another.

Interestingly, the removal of this invasive species is not a black and white solution. Ecologists are reevaluating the environmental contributions of this plant in urban settings. As displayed by the image on Ailanthus growing through pavement alongside a building, this plant can thrive in seemingly impossible conditions. I personally this this tree is amazing, standing as a lone survivor where no other plant can grow, so from that perspective I would support the decision to leave the tree because it provides environmental services other plant could in such a setting. However, I am sure the people who live near this tree, whose water is constantly backed up, see otherwise and would support the removal of the tree. The answer to whether or not a species like this should be preserved or removed requires the analysis of factors such as fiscal expenses of preserving the tree in relation to ecosystem benefits or costs, as well as sentimental attachment. While the preservation of a lone tree may not be problematic, I am sure, as Eric stated, that on a large scale, the presence of this plant could have a devastating impact. However, it may also be possible, that Ailanthus has a found a new niche that may not be so taxing on other native plants.

On a side note, in response to Professor Hutyra’s question, I believe there are very few “pristine” areas remaining (which would have to be significantly isolated for the matter), and even such, they are likely to be indirectly affected by human activity. For example, in the arctic regions where human presence is minimal, the overall excess of anthropogenic pollutants, and activities such as over fishing is causing the ice caps to melt at faster rates and has changed the existing trophic dynamics. However, I believe that it is useful to consider pristine environments, so that we can appreciate nature and make greater efforts to conserve ecosystems, as well as to serve as a reminder to be more cognizant about leaving the environment we interact with as unaltered as possible.

Amanda Gallinat- I have no personal connection to Ailanthus—in fact, after meeting it last year, I’m still not totally sure I could pick it out of a lineup* (unless only one tree in the lineup is growing out of a sewage pipe). But my 2 cents is that ecological communities (even urban plant communities) differ A LOT, and it seems worth determining at least the following two things for any given ecosystem before deciding whether or not to attempt eradication:

1) Is it actually occupying a niche that native species, or any other species for that matter, would occupy? It seems like long-term records would be very useful for determining whether Ailanthus is, in fact, displacing any local species, and whether that may result in extirpation. If there is no risk to the diversity of the local plant community, it may not be worth prioritizing its eradication
2) If Ailanthus is displacing other species, what are the indirect effects of that displacement? For instance, are there specialist insects whose hosts are displaced by Ailanthus, or birds that rely on nesting materials from a plant that is displaced by Ailanthus? Aside from effects like increased carbon uptake and slowed runoff, what are the effects on species diversity beyond the plant community?

What I do feel pretty strongly about is the mention of ‘pristine’ ecosystems. I’d like to suggest that in addition to being unrealistic, the concept of pristine ecosystems is also pretty dangerous.

Why unrealistic?
Human impacts like deforestation and habitat fragmentation are very visible, and make it tempting to draw boundaries between people and nature (making national parks off-limits to developers, for instance). But in the last decade, there has been increasing recognition of some of the less visible phenomena that Prof. Hutyra listed above (increased CO2 emissions, nutrient inputs, climate change, etc). Range and phenology shifts resulting from climate change lead to local extinctions in developed areas like Concord, MA, but surprisingly the same amount of species loss is happening in Acadia National Park, which is considered relatively pristine (MacKenzie in press). There’s a growing body of evidence that we are in fact influencing systems that were previously considered free from human impacts. So I think we can safelyreplace the concept of pristine ecosystems with a spectrum of human impact.

And why dangerous?
If we believe there are pristine ecosystems out there, there are some frightening potential consequences. The thought that nature exists separately may allow us to feel we have carte blanche, as long as we’re emitting carbon dioxide or dumping nitrogen fertilizers, for instance, on “our side of the fence.” If we are separate from the natural world, we can behave as though we operate inside a bubble. I know this is a less commonly held assumption now, but it was surprisingly popular for a long time and still seems to have a place in many old people’s hearts. Separating ourselves from nature, even in a vague and semantic way, also somehow ignores all the important (and often arbitrary) ecological interventions in which people take part. We decide which species are protected, re-established, and weeded out all the time, and not just in our backyards! We are inseparable from the natural world, whether we’re talking about urban or rural ecosystems, or even ecosystems on which humans have never set foot. There exists a spectrum of human disturbance, but it seems ‘pristine’ is not an option.

*edit: apparently the idea of an invasive species lineup is not original!: