September 3, 2019

New Zelkova Trees in Washington Square Park Thriving in Sandy Loam Soil

When Washington Square Park underwent a major reconstruction in the 2000s, large Japanese pagoda trees (Styphnolobium japonicum) circling the fountain were removed. The new design for the fountain plaza included seven Zelkova (Zelkova serrata) trees. Four of the original seven died and were replaced several times. I happened to be in the park on April 24, 2018 to observe the most recent replacement of Zelkovas. I watched various phases of the excavation and planting process, and more importantly spoke with the NYC Parks project manager about the death and life of the fountain Zelkovas.

The Zelkovas that were planted were during the reconstruction project were larger in diameter than typically specified. I suspect that NYC Parks sourced larger trees for two reasons. The first reason was to mitigate the loss of the large Japanese pagoda trees with new trees of a large diameter than typically specified. New street and park trees range in size of 2.5 to 3.5-inch in caliper where caliper is measured at 6-12 inches from the base of the tree. (Parks requires that caliper be measured 6 inches from the base of the tree.) The Zelkovas planted in Washington Square Park circa 2005 were 11 inches in diameter at breast height aka DBH which is measured at 4.5 feet above the ground. The second reason for planting larger than usual trees was to provide more shade. A larger diameter tree has a larger canopy at the time of planting. The fountain plaza is an expansive hardscape that not only heats up quickly but retains the heat so shading this area in the summer is important.

Tree diameter has a critical relationship with soil volume. For every 1 inch of diameter, the recommended root ball size is 10 inches. An 11 inch diameter tree would come with a 110-inch or 9-foot root ball. If you look at the diameter of the openings in the fountain plaza where the Zelkovas area growing you can see that the openings are not 9 feet across. The original Zelkovas were planted first and then the fountain hardscape installed around and over the root balls. To replace the Zelkovas that subsequently died, NYC Parks did not rip up the plaza. The agency specified smaller caliper trees with root balls that could be planted into the openings in the plaza. Although smaller trees establish faster and grow more quickly after planting than larger diameter trees, the newer, smaller Zelkovas also died.

The replacement trees died because of the soil. The initial trees were grown in a nursery with clay soil. Most of the replacement trees were sourced from the this same nursery. Clay soil does not drain well. In a nursery situation or even on a construction site while a tree might linger in sub-optimal conditions before planting, slow draining soil might not be problematic but in a landscape setting such as the fountain plaza in Washington Square Park, the roots suffocated. According to the project manager, when a tree is being replaced, the NYC Parks standard is to remove 18 to 24 inches of existing soil and replace it with new soil. Even if this standard was met when the first round of Zelkovas died and were placed, there was a significant volume of clay soil left in each of the planting areas. New trees were being planted in a clay bowl. Remember, the original root balls were big. Each was 9 feet in diameter, and I'm estimating that the height/depth of each root ball was 5.5 feet (per American Standard for Nursery Stock, 2004: "Balls with diameters of 20 inches and up - depth not less than 60% of the diameter of the ball").

Soil is a critical factor in tree health. The newest round of Zelkova trees planted in 2018 were sourced from a nursery with sandy loam soil. The trees have sandy loam root balls. In addition, during the 2018 replacement, most of the remaining clay soil was removed and replaced with sandy loam. The four new trees planted in 2018 have full, healthy-looking canopies. It appears that the right soil made the difference.

August 26, 2019

People-Plant Relationships

On May 10 2019, I gave a talk about the relationships between plants and people at the Weedy Resistance Salon on Networks. This blog post is an edited version of the talk. I spoke about the benefits of people-plant relationships. I am familiar with scholarship on tree benefits (and disservices) from my dissertation on the mainstreaming of the ecological benefits of urban trees. There are many social and health benefits that accrue to people from their relationship with plants. Benefits also accrue to plants. The focus of my presentation was on three sets of benefits. One, social ties and empowerment benefits accrue people from being in the presence of and stewardship plants. Two, purposefully planted urban tree have a greater survival rate when cared for by local people. Three, the production of knowledge about trees and other plants benefits people, and through our directed attention on them, plants also benefit. Given the weedy nature of the host, I concluded my remarks with musings about a “nature ethic” for weeds.

“The Nature Fix”

Being in the presence of and interacting with nature also has physiological and emotional benefits. The latest research about the benefits of human exposure to nature are chronicled in The Nature Fix: Why Nature Makes Us Happier, Healthier, and More Creative by Florence Williams. For a quick introduction to Williams's book, watch her video summary.

Preserving, creating, and using vegetated spaces provides social benefits. One type of benefit is the development of bonding ties, or links between people who are the same. Rebecca Coley et al. (1997), Frances Kuo et al. (1998), and Andrea Taylor et al. (1998) have documented instances bonding tie formation in green spaces.
  • Coley et al. (1997) compared the presence of people and the presence of trees in two different public housing communities in Chicago and found that people were more likely to be present in spaces with trees than in spaces without trees, areas with more trees attracted more people, and more young people and mixed groups of youth and adults occurred in areas with trees.
  • Kuo et al. (1998) found that greenness, which they defined as the amount of trees and grass, in the courtyards of public housing neighborhoods, is an important indicator of the use of space. “The more vegetation associated with a resident’s apartment and building, the more she socialized with neighbors, the more familiar with nearby neighbors she was, and the greater her sense of community” (839).
  • Children and their play and access to adults also benefit from access to green spaces. Taylor et al. (1998) found that more child’s play occurred in greener spaces. Twice as many children played in areas with trees than in areas with lower tree cover. Also, children played more creatively in areas with more trees than in areas with fewer trees. Finally, adults and children not only jointly used spaces that were greener, but adult attention was also higher in highly vegetated spaces.
Another way in which green space is good for you is its effect on empowerment. Lynne Westphal (2003) found that individuals felt a sense of accomplishment after planting trees. Organizations and communities can also benefit from tree planting; individuals bond to the organization and to each other during the work of planting trees.

Related Link - The Nature Fix by Florence Williams

Trees are More Successful When They are Stewarded

Exposure to nature provides many benefits to humans. One type of exposure to nature is through physical stewardship and conservation efforts. Looking at the specific case of street trees, researchers have quantitatively shown that trees in the public right of way have a higher survival rate when cared for by community groups.
  • Steve Boyce, president of the Friends of Greenwich Street in Tribeca, found that consistent and active volunteer stewardship as well as institutional resources led to a significant reduction in the mortality of recently planted and established trees. In addition, “observational stewardship” defined as observing trees and reporting threats that were rapidly resolved, also led to substantial reductions in mortality rates.
  • Emily Jack-Scott et al. (2013) research in New Haven looked at the effect of a community group’s characteristics on tree success. The researchers found that group longevity (the number of years the group has been planting trees) and experience level (the number of trees the group has planted) were positively related to tree survival and growth.
  • Lara Roman et al. (2015) found annual survivorship rates of of 99.4% in East Palo Alto, CA and 98.4% and 95.4% within six years after planting in two different neighborhoods in Philadelphia. The authors noted that these “outcomes are among the highest establishment survival ever reported” and could be attributed to many factors but stewardship, planting, and maintenance practices ranked highly.
  • Jessica Vogt et al. (2015) found that “people [and their planting and stewardship choices] influence the survival and growth of trees.” One stewardship choice is collective watering, and in a related study, Mincey and Vogt (2014) observed that trees in a neighborhood with a collective watering approach had higher survival rates than street trees watered by individual residents (in neighborhoods without signed agreements, monitoring, or reminders among neighbors).
  • Jacqueline Lu and colleagues at NYC Parks and the US Forest Service Urban Field Station in NY examined the roles of biological, stewardship, and urban design factors in street tree mortality. They designed a stewardship index based on explicit signs of tree care at the tree pit, building, and streetscape levels. At the tree pit level, “active, direct tree stewardship is a positive indicator or predictor of street tree survival.” The direct actions included planting in the tree pit, mulching, weeding, and the presence of signage.

Producing Ecological Knowledge

Humans derive benefits from spending time in and caring for nature. Nature benefits from the latter activity as the above examples about street tree stewardship show. We also create another benefit stream through our study of nature. We derive pleasure from learning about nature, and certainly nature benefits from our interest. As Robert Michael Pyle wrote in The Thunder Tree, “people who care conserve; people who don’t know don’t care.” So if we observe, study, and come to know a plant (or any species), we are more likely to care for and conserve that plant, a situation that is beneficial to the plant. But this is not necessarily an active human-passive plant scenario. In The Botany of Desire, Michael Pollan challenged the traditional view of a one-way relationship between people and plants. Humans are not the only agent in the people-plant relationship. Pollan’s writing encouraged us to see the ways in which plants were active participants in domestication by "satisfying our desire" for certain traits.

There seems to be a bias towards funding charismatic megafauna research and conservation, and there are good reasons to focus on charismatic species. But what are the options for engaging with everyday plants and plants? Many people dismiss everyday birds such as pigeons but there are some who embrace the species and have formed tight relationships with pigeons. Weedy plants have had a harder time being embraced widely. Inspired by my work in Washington Square Park generating "small data" about birds and wildlife, I sought out other small data folks, in the weedy plant arena specifically, engaged in grassroots production of ecological knowledge.

Related Link - Grassroots Citizen Science in Urban Spontaneous Vegetation

What I have observed in my research is artists, designers, and academic scientists asking questions about the benefits of weeds, though legacy language about weeds remains. Weeds may be in a position analogous to where urban trees were prior to the late 1980s, before the creation of modeling tools to quantify the ecosystem services provided by urban trees and assign an extrinsic monetary value to them. Measuring the performance of urban trees was a necessary strategy to conserve and expand urban forests as urban planning and funding became increasingly evidence-based and data driven.

A “Nature Ethic” for Weeds

I am curious about the emergence of nature ethics that could positively incorporate weeds and the assemblages and habitats they form. Weeds don’t have a place in the wilderness or pristine nature ethic. Nor do they have a place in our traditional garden ethic. We weed our gardens; and when we talk about transitioning vacant lots or post-industrial sites to more productive ecological and social uses we talk about clearing out the weeds. Emma Marris’s concept of a “rambunctious garden” might be a fitting perspective. The wilderness that the Dutch encountered on Manhattan in 1609 was land managed by native peoples. With the rolling out of climate change, human impact on landscapes is both intensive and extensive. Admittedly spaces of weeds are a novel ecosystem different than remnant habitats but we could think about managing weedy plant communities as an early successional stage in a temperate forest system (disclaimer: I live in New York).

While I am enthusiastic about this new direction in the discourse about weeds, at least in some quarters, I wonder about other aspects of this resource narrative. Who is valorizing weedy landscapes? Why? What are the potential consequences of giving advantage to weeds as "the flora of the future"?

I’d love to hear about your relationship with plants. Please let me know in the comments.

August 9, 2019

Impact of Soil Mounding in Washington Square Park Woodland

The largest lawn in the northwest corner of Washington Square Park is being restored. Much of the lawn has been spray seeded. Sod was installed in the sunny southeast nook.This area of the park is also the largest wooded area in the park. I am concerned about the grade changes in this area of the park. Most of the trees in this section of the park are large ranging in diameter from 15 inches to 40 inches. I contacted the NYC Parks Administrator for Washington Square Park (wearing my Washington Square Park Eco Projects hat) and expressed my concern about the volume of soil placed within the critical root zones of the trees in the northwest woodland.

The critical root zone (CRZ) of a tree is the circular area of tree roots that are most sensitive to disturbance. A rapid calculation for CRZ is the area below a tree's drip line equivalent to the outer limits of its canopy spread. Another method to calculate CRZ is a diameter:ground ratio. NYC Parks requires a CRZ ratio ranging "from ½ foot per one inch DBH (diameter at breast height) to 1½ foot per one inch DBH. If the species tolerance is unknown, then the 1½ foot per one inch DBH standard is assumed" (NYC Parks Parks Tree Preservation Protocols, 2009). The CRZ for a 20 inch diameter tree, for example, can range from 10 to 22.5 feet radius from the trunk. A tree's roots extend beyond the drip line or CRZ but using either measure provides the minimum protection to a tree's root zone. Disturbance in the CRZ should be limited to none. In NYC parks, "In general, no encroachment of the CRZ shall occur without the written permission of the Agency, and without the on-site presence of the Agency’s representative or an approved arborist" (NYC Parks Parks Tree Preservation Protocols, 2009).

Disturbance includes grade changes. Changing the grade by removing or adding soil can negatively impact the feeder roots of a tree. "Many tree roots occur within the top six to eight inches of the soil" (NYC Parks Parks Tree Preservation Protocols, 2009). Adding soil above a tree's roots alters the oxygen and water exchange and movement. The degree of grade change, the type of soil (clay vs sandy loam), and the tree species contribute to the response that a tree will have to a grade change. Per the NYC Parks Parks Tree Preservation Protocols (2009),
Fill of up to three (3) inches additional depth may be permitted with the written approval of the Agency. Fill exceeding three inches shall not occur without the prior installation of an aeration system or other detail approved by the Agency, such as a tree well, retaining wall, terracing, or other such mechanism.
I don't know the specifics of the plan submitted to NYC Parks for this public project because the agency has not posted any signs at the project site nor is there information about the project on the agency's website.

Let's take a look at one of the trees impacted by grade change in the northwest lawn. The Japanese pagoda tree (Styphnolobium japonicum) closest to the Arch is 20 inches in diameter. The tree's CRZ is at least a 20 foot radius from the trunk. The new mound adjacent to the tree sits within the CRZ. The mound, which peaks at 2.5 feet in height, starts at 5.5 feet from the tree's trunk. The numbers presented here are estimates. The project site is not accessible and the agency has not posted information at the site.

I don't know how the Japanese pagoda tree will tolerate this grade change within its drip line. There are several other instances of grade change within the drip lines of trees in the northwest lawn. Oaks and lindens, which are fill intolerant species, are growing in the lawn.

Often tree decline occurs years after the initial disturbance. Because of the lag time between disturbance and decline, the triggering event is often not tagged as the cause of the tree's demise. Here are symptoms of grade change disturbance:
Symptoms of damage from grade changes can appear as a progressive decline of the crown occurring over a period of several months to several years. Initial symptoms generally include delayed budbreak, reduced growth, stunted light green to yellow leaves, crown thinness, and premature fall coloration and leaf abscission. Epicormic sprouts might form on the trunk and large limbs and twig dieback may occur. This may be followed by dieback of large branches and entire leaders and finally, tree death. (Preventing Grade Change Damage to Trees by E.Thomas Smiley, PhD, Urban Forestry, for Bartlett Tree Experts)
I will visually monitor the trees in this section of the park for these symptoms.

 Update: I had a walk-through with the Washington Square Park Administrator, George Vellonakis, on August 16th. He told me that the grade change was made with fill and not soil. To my concern about drainage within the drip line, he said that fill would permit drainage to the underlying soil. However, I have read - I am no longer a certified arborist - that even fill should not be placed within the drip line of a tree, especially a mature tree. Many of the trees in the northwest lawn could be considered mature trees. The new contours of the NW lawn have created a "swale" in the center of the lawn to capture rain and prevent runoff unto the hardscape. However, some of the large trees sit within this "swale." The water regime of these large trees will be different in the presence of the swale. There will be more water pooling around their trunks and within their drip line. This can create a situation that is similar to overwatering from irrigation systems. In addition, if the lawn area is irrigated for lawn health (shallow and more often) vs. tree health (deeper and less frequently), overwatering can also occur. Too much water in the soil reduces air exchange. Water is essential for trees but so is root access to oxygen.

August 6, 2019

Women Who Steward Urban Wildlife Habitat

BIRDLINK (Anina Gerchick, artist/landscape architect), Sara D. Roosevelt Park, New York NY

There is a long history of greening our cities from Boston's Emerald Necklace to the Chicago Wilderness, from 19-century boulevards to "million tree" planting initiatives, from Victory Gardens to community gardens. We have preserved remnants of "natural areas", restored landscapes to a preferred ecology, and made parks and gardens. Urban greening encompasses many different institutions and actors, policies and practices, and benefits. In this post, I highlight women who have spearheaded wildlife habitat projects. These women are stewarding natural resources where stewardship is defined as "consisting of six functions: conservation, management, education, advocacy, monitoring, and transformation" (STEW-MAP). This broad definition of stewardship is inclusive of the many ways in which people positively engage with the nature of cities.

The six women are:
  • Anina Gerschick - BIRDLINK (NYC)
  • Marni Majorelle - Kingsland Wildflowers (NYC)
  • Jane Martin - Plant*SF (San Francisco)
  • Amber Hasselbring - Garden for the Birds at the Sangati Center (San Francisco)
  • Sarah Bergmann - The Pollinator Pathway (Seattle)
  • Megan Draheim - District Coyote Project (Washington, DC) 

BIRDLINK (Anina Gerchick, artist/landscape architect), Sara D. Roosevelt Park, New York NY

Anina Gerschick - BIRDLINK (NYC)

Anina Gerschick is a painter and landscape architect. She is also the founder of BIRDLINK, a modular native bird habitat. Because she's an artist, the habitat installation is aesthetically pleasing. I met Anina last year when she was finalizing details to install BIRDLINK at Sara D. Roosevelt Park (SDR). The eco-art sculpture was planted in early June, and has gotten lots of press coverage. One of favorite pieces, This Art Project Could Help Make Cities More Habitable for Birds, was written by Bryony Angell for ABC Birds. Anina's long-term goal for the project is to create a BIRDLINK network that will expand habitat in urban sections of American flyways by infilling the mid-canopy layer. If you live in New York, visit the SDR BIRDLINK on Houston Street.

Marni Majorelle - Kingsland Wildflowers (NYC)

Marni Majorelle, owner of the green roof company Alive Structures, envisioned transforming warehouse roof space into bird and insect habitat. She collaborated with NYC Audubon and the owner of the Broadway Stages warehouse to submit a proposal to the Greenpoint Community Environmental Fund which was established with a $25 million settlement from an Exxon Mobil oil spill. Kingsland Wildflower was funded at $971,782 and opened at 520 Kingsland Avenue in September 2016. The plant palette includes native grasses and flowers. NYC Audubon monitors bird, insect and bat populations.

Related Link - Women Who Speak for Urban Trees and Plants

Sarah Bergmann - The Pollinator Pathway (Seattle)

The original Pollinator Pathway is a one-mile corridor of mostly bio-regional native plants growing in sidewalk planting strips connecting two pollinator-friendly fragments in Seattle. "A pathway is the goal," writes Bergmann. The pathway connects two existing habitat fragments. From this first design project, founder Sarah Bergmann has conceptualized reintegrating ecological function in cities including a design kit for anyone to design a pollinator pathway.

Plant*SF garden at Harrison and 23rd, San Francisco

Jane Martin - Plant*SF 
Amber Hasselbring - Garden for the Birds at the Sangati Center (San Francisco)

I wrote about the projects spearheaded by Jane Martin and Amber Hasselbring about 10 years ago. I was exploring nature-making or designing with ecological intent to support ecosystem functions and improve environmental quality. Creating networks of gardens for stormwater management and plant habitat as well as wildlife corridors in urban sidewalks fit into my typology. I hope you'll follow the links above to read more about these urban ecology projects.

Megan Draheim - District Coyote Project (Washington, DC)

The District Coyote Project educates the public about coyotes and conducts research about coyote ecology and human-coyote interactions. The project is a departure from the other greening projects in several ways. One, the project does not vegetate landscapes. Two, it focuses on a single species, the coyote. Three, the physical scope of the project is much larger than the others, covering an entire metropolitan area. Four, citizen science is integral to the project. Coyote observations by people in the DC metro area are used in the project's research program.

The scope of these six projects is inspiring. I know there are other women managing our urban landscapes to benefit wildlife. Nominate yourself or tag a woman steward you know.

July 9, 2019

Washington Square Park Red-tailed Hawk Nest

The 2019 Red-tailed Hawk nesting and fledgling season in Washington Square Park was emotional. Sadie (Aurora) laid three eggs all of which hatched then Bobby disappeared from the territory. He is presumed dead. A new male entered the territory before the chicks fledged. He appeared antagonistic towards the first fledge when the bird was perched on a building ledge and apparently catalyzed the fledging of the second and third chicks. There was more drama. Two of the fledges were rescued and fortunately one of them has been released in the park. If you have concerns about the safety of a WSP hawk, Roger Paw recommends contacting WINOOR or the NYC Urban Park Rangers.

Note: this post was originally published in March 2018 and has been updated.

Image: Washington Square Park Red-tailed Hawk Nest, March 27, 2018, 11:45 AM

Red-tailed Hawks lay one brood or set of eggs each season. The number of eggs in the brood ranges from one to five. The WSP hawks have laid between two and three eggs annually since 2011. Red-tailed Hawks are monogamous, mating for life. The male hawk (named Bobby) has not changed since the mating pair formed, but there have been three female hawks.

Violet, the first female hawk, laid three eggs in 2011 but only one survived to be named Pip. (Pip is an ornithological term referring to the hole in the egg made by the hatchling's egg tooth.) Violet died at the end of 2011. During her rehabilitation off the nest, a female hawk, eventually named Rosie, arrived in the territory and paired up with Bobby.

Rosie laid two eggs in 2012. The eggs hatched and fledging was successful. In 2013, she laid three eggs and all of them hatched. Rosie laid two eggs in 2014 both of which hatched. Rosie left the territory in the fall of that year.

By February of 2015, Bobby had a new mate, Sadie (aka Aurora). The pair incubated three eggs but only two hatched and fledged. Sadie again laid three eggs in 2016.  However, only one hatched. That chick fledged in June. 2017 marked the third consecutive year that Sadie laid three eggs. Despite successfully incubating two of the three eggs, one of the hatchlings died. The third egg never hatched. It's safe to say that hawk watchers are delighted by and anxious about this nesting cycle.

The male and female hawks share nest-building duties. The male also participates in incubating the eggs but this task is mostly done by the female hawk. Incubation begins with the first egg and lasts anywhere from 28 to 35 days. Chicks are nestled for a period of up to 46 days.

The traditional location of a Red-tailed Hawk's is in a tall tree with a fairly sweeping view of the surrounding landscape. Red-tailed Hawks also nest on cliff ledges and on human-made structures such as window ledges. In the case of the Washington Square Park Red-tailed Hawks, the nest is on a ledge of the Bobst NYU Library. The ledge is quite deep and affords a view of the almost 10-acre park. Within the hawks' territory are many tall buildings that provide advantageous perches. The hawks have used the same nest each season which is typical of this species. They repair it annually. I have seen them collecting and arranging nesting material. The nest extends beyond the width of the window ledge; you can see it if you look up while standing on West Fourth Street.

Related Link: Natural and Artificial Materials in Bird Nests

To follow the nest happenings, watch the hawk cam. For off-camera hawk life in Washington Square Park, I recommend two blogs: Roger Paw and Urban Hawks.

Nest information provided in this post sourced from All About Birds here and here.

June 14, 2019

10 Trees Removed in 2 Years in Washington Square Park

10 Trees Cut Down in Washington Square Park, 2017-2019

Since 2017, 10 trees have been cut down in Washington Square Park and none have been replaced. Additional trees have been removed from the park in this time period specifically the Zelkova serrata around the fountain but those trees have been replanted. In this post, I will describe each of the 10 trees and the context of its removal.

Four large trees were removed in 2017. The first of the four was a 29-inch diameter London plane tree (Platanus x acerifolia) in the "big kid" playground in the northeast section of the park. Two similar-sized London plane trees remain in the playground. I assume that the work was completed by NYC Parks and or its contractor. The other three large trees removed in 2017 include a 28-inch pin oak (Quercus palustris), a 47-inch London plane tree, and a 25-inch green ash (Fraxinus pennsylvanica) all of which were removed by a contractor. All three trees were compromised by fungal disease, cracks, rot, root damage, and cavities. In the case of the pin oak in the northwest section of the park, WSP Eco Projects first reported the presence of oak bracket to NYC 311 and NYC Parks. I believe this observation precipitated the removal of this oak. The poor health of the plane tree and ash were discovered by Emerald Tree and Shrub Care Company, the arboriculture firm contracted to prune 270 shade trees in the park.

Two trees were cut down in 2018. One was a dead paper birch (Betula papyrifera) in the northeast corner of the park. The birch was planted in memoriam to actor Spalding Gray. I did not see the removal so I don't know who performed the work. Damage from an early snowstorm in November 2018 was given as the reason for the removal of the second tree, a dawn redwood (Metasequoia glyptostroboides). The WSP Conservancy determined that the dawn redwood near the Thompson Street entrance had sustained irreparable damage to its leader and cut down the tree.

So far in 2019, four trees have been removed. A deodar cedar (Cedrus deodar) was removed by NYC Parks in the early part of the year. The tree began to lean after its root zone was compromised by a extensive rat burrow. The other three trees were removed this month.  It is likely that their removal was precipitated by a falling limb of a different tree that critically injured a park visitor in May. A 23-inch diameter Northern red oak (Quercus rubra) south of Holley Plaza and a 33-inch diameter American sycamore (Platanus occidentalis) in the southwest corner were cut down. The third tree was 30-inch diameter Ailanthus altissima. Can you believe there was such a big tree-of-heaven growing in the park?! Among the trees, the health issues ranged from extensive rot and and cavities to cracks and large dead limbs. The removal of these four trees adds up to a loss of 86 inches of tree diameter.

None of the 10 trees mentioned in this post have been replaced. It makes sense that the trees removed this year have not yet been replaced. The area that hosted the dawn redwood has been replanted with herbaceous perennials as too has the spot in the southwest that hosted the plane tree. The big north lawn will undergo a major repair soon so I don't expect that the pin oak in the northwest will be replaced until that the lawn work is completed. The paper birch has not been replaced. A river birch would be a great addition to the park. The green ash location has not been replanted. Due to the presence of emerald ash border, NYC Parks is no longer planting ash trees. Beyond species selection, I'm assuming that a tree will not be replanted in that location because of heavy foot traffic from the "webs" play feature. Finally, a replacement tree hasn't been planted in the larger playground.

New York City has been a strong proponent of increasing urban tree cover as evidenced by various policy instruments including Million Trees NYC. Yet, small parks such as Washington Square Park are underrepresented in these grand visions of nature in the city. In my role with WSP Eco Projects, I have been advocating for a small parks ecology initiative to assess the environmental benefits provided by small parks as well as to actively manage for succession in this park type. Eco Projects is preparing a draft tree plan for Washington Square Park. Several guiding questions are: Which tree species will thrive in our climate-affected city? Which trees and other plants will provide the optimal habitat for birds and other animal wild life? How should we diversify and enrich our canopy cover?

Washington Square Park looks well canopied. Looking at an aerial image, approximately 66% of the park is covered by tree canopy, so the removal of 10 trees might seem insignificant. However, the four trees cut down in 2017 alone equaled approximately 211 inches of tree lost from the park. If a 20" plane tree is estimated to be 33 years old* then the 29" and 47" plane trees were likely 47 and 77 years old respectively. The 28" pin oak was likely over 46 years old, and the 25" green ash could have been 83 years old. These four trees accounted for an estimated 253 years of tree growth. It is critical that we begin to plan for regrowing the canopy in the park as trees, especially big ones, are removed because of death and/or potential hazards.

* Tree age estimates were taken from "Estimated Age of Urban Trees by Species and Diameter (DBH)" by City Parks Foundation.

June 12, 2019

Deadwood Trees for Wildlife in Small Urban Parks

Snags, standing dead or dying trees, are commonplace features of rural forests and can also be observed in inaccessible areas of forested areas in urban settings. Despite their wildlife value, snags are rarely tolerated in small urban parks. Risk exposure increases with proximity to people and property. However, a variation of the swag, what I am calling the deadwood tree, is a safe approach to maintaining dead trees in small urban parks.

If a tree needs to be removed, and it does not contain a pest or disease of concern and the trunk is relatively stable, then the tree should not be cut to the stump. Large limbs should be removed and the bole at least 4 feet above ground could be left standing. An example of this treatment is pictured above. This deadwood tree is located along a path in Washington Square Park in New York City.

There are three reasons to leave deadwood trees in small urban parks. A deadwood tree provides similar benefits as a snag. Dying and dead wood re extremely productive for wildlife. A snag provides habitat and food, serves as a perch and shelter, and a fallen snag or "nurse log"* becomes a nursery for seedlings. Small urban parks support year-round and migrating wildlife. Migratory birds, for example, rest and refuel in small urban parks. Deadwood trees would enhance the regulating ecosystem services of small urban parks.

The second reason to maintain deadwood trees is to provide natural markers of environmental change. Although a plant feature such as a tree would not be a permanent fixture in the landscape, a deadwood tree could potentially last longer and would be more visible than the typical stump which is easy to overlook a stump hidden in a lawn or among herbs and forbs. Deadwood trees would commemorate tree losses in the canopies of our small urban parks.

Finally, the third reason to leave deadwood trees in small urban parks is to foster people-plant relationships. A deadwood tree could be an engaging counter to plant-blindness, a lack of knowledge and awareness of plants in one's local environment. The outstanding nature of a deadwood tree would spark questions. In addition, parkgoers could follow the cycles of life associated with dead wood.

While it might not be feasible or desirable to leave a deadwood tree in every case of a tree removal, a strategic plan to manage the urban forests of small urban parks should include a provision to identify trees that would be suitable candidates as deadwood trees based on criteria such as species, age, and location within the park.

*Regarding logs, the deadwood tree could be left in a horizontal position if the local parks department would like to further reduce its risk exposure.