Human Flower Project

Science

Friday, June 06, 2008

A Flower for the Pleiades—Matariki

It’s the Maori New Year, observed across New Zealand with the making and presentation of harakeke flowers.

A flower made from woven flax is the traditional gift of New Zealand’s New Year, in early June
Photo: Ali Brown

Thursday, on the final dog walk of the night, we spotted the head and claws of Scorpio coming over a neighbor’s house. Summer is here.

Or winter if you live in New Zealand. And in the early mornings, Taurus the bull rises with the sun. In his horns you can see the twinkling Seven Sisters – the Pleiades. In Maori they’re known “Matariki,” and their appearance both marks and names the Maori New Year (in 2008, it fell on June 5th).

An old custom of Matariki is the weaving of kites and flowers out of a native plant called harakeke (Phormium tenax) – or New Zealand flax. From pictures, it looks like a cross between palm and agave.

Harakeke seems to have been THE basis of Maori material culture: “The long strap-like leaves were ideal for plaiting into mats, containers, shoes and even shelters. …Strong flexible fibre could also be extracted from the leaves for weaving into clothing, or for making rope and fishing nets.”

Phormium tenax varieties growing at Landcare Research in New Zealand
Photo: Warwick Harris, via Fernwood Nursery

Among “observant” Maori there is a quite extensive protocol both for gathering the leaves and for working them into objects. To wit:

“A prayer of thanks or karakia may be said before cutting.  Flax is not cut at night or in the rain or snow.
 Only enough flax is cut to complete the weaving project.
 Flax is not cut by women who are menstruating, although 
they are able to weave.”

…the very sorts of requirements and prohibitions that indicate sacredness. So do these woven flowers, because the first putiputi (or flower) made from flax at the New Year must be presented to someone as a gift.

A flax “lily” by Sema
Photo:  Flax Flowers by Sema

As one would expect, there are now crafts specialists who make flax flowers to sell, both for special local occasions and as New Zealand souvenirs. Today schoolchildren make putiputi at the New Year, too. Like so many human-flower traditions, the Maori custom has taken on a secular, nationalistic, and commercial flavor. If you have some New Zealand flax (or a similar plant on hand) you might ask a blessing and then try weaving your own New Year’s flower with these instructions. Now, don’t forget to give it away!

We’d be negligent if we didn’t show you the flowers harakeke can make all by itself. They’ll bloom six months from now, in December – the height of New Zealand summer. We understand they’re used to sweeten foods and drinks.

The Maori are just one of many cultures that have marveled at the Pleiades, and considered them divinely creative. Count contemporary scientists among these stars’ most awed admirers.

The Pleiades, in the constellation Taurus: a planet incubator?
Photo: Space Spin

“Rocky terrestrial planets, perhaps like Earth, Mars or Venus, appear to be forming or to have recently formed around a star in the Pleiades ("seven sisters") star cluster, the result of ‘monster collisions’ of planets or planetary embryos,” according to astronomers at Gemini Observatory in Hawaii. “This is the first clear evidence for planet formation in the Pleiades,” says Joseph Rhee, an astronomer from UCLA. “The results we are presenting may well be the first observational evidence that terrestrial planets like those in our solar system are quite common.”

A happy, humbling thought for the New Year.

Friday, May 09, 2008

Warm the Cacti, Cool the Computers

An Indiana city saves on heating, while the university pays less to chill its super computers. Kiss your brain!

Computer scientist 
Paul Brenner of Notre Dame explains how the university’s computers and the city’s desert plants will make beautiful climate together.
Photo: University of Notre Dame

Better than a stroke of genius, here’s a spike of conservation brilliance.

The University of Notre Dame’s computer experts have teamed up with botanists of South Bend, Indiana, to save energy. They’re moving several of the university’s 400-pound computer processors into the city’s Arizona Desert Dome.

The computers shed heat, which is just dandy with the cacti and other Southwestern plants, and air circulating through the 26,000-square-foot greenhouse will help cool the machines. Big computers like these are very expensive to keep cool. “According to The South Bend Tribune, the plan will save the university about $100,000 in utility costs, even after the university pays for the electricity to power the processors.” Nobody knows yet how much the computers’ warmth will save the city, but last year South Bend’s parks department spent $70,000 to heat the desert dome and other conservatories.

According to Kathleen, a South Bend blogger and conservationist, this region of Indiana “relies heavily on coal-powered generators for electricity,” so this Desert Dome/Computer partnership should reduce emissions from burning coal, heating the desert greenhouse while cutting down on greenhouse gases.

This forward-thinking human flower project grew out of the city of South Bend’s commitment to climate protection. Last month, South Bend became one of 800 Cool Cities dedicated to reducing the causes of global warming.

With amaryllis looking on inside the Potawatomi Park Greenhouse, Mayor Stephen Luecke (right) is honored by Christine Fiordalis and Steve Francis of the Sierra Club. South Bend became a “Cool City.”
Photo: Kathleen, If We Only Connect

“This Green computing initiative proves that global challenges can bring out the best of our creativity,” said Mayor Stephen Luecke, “especially when the public and private sector join together to find solutions. It is only the latest of a history of ventures by the City of South Bend to reduce our carbon footprint and make a real difference for the future of our planet.”

Couldn’t such a climate partnership work between any botanical garden (or private business) with greenhouses to heat and any company or institution with computers to keep cool? Congratulations to scientists of Notre Dame and the city of South Bend. May your initiative spike others into collaboration.

Friday, April 25, 2008

A Tall Order—Large Stature Trees

What lengths would you go to for shade, good drainage, and year ‘round beauty? Urban arborist Georgia Silvera Seamans explains the benefits of tall trees and ways to plant these giants successfully in cities. Thank you, Georgia.

Cycle path, Lincoln Parkway, Buffalo
Source: Heartland

By Georgia Silvera Seamans

The “Right Tree in the Right Place” (RTRP) concept encourages municipalities, NGOs, and homeowners to plant trees shorter than 25 feet under overhead utility lines. The crowns of large stature trees, encroaching on wires, can cause a number of problems: downed branches that interrupt utility service, tree trimmers’ perilous contact with live wires, and the conventional pruning of tree crowns into U-shapes (these tend to be structurally unsound and are nearly always unattractive).

Consequently, following RTRP along roads and in neighborhoods with overhead wires yields a short canopy. Redbud, purpleleaf plum, crape myrtle, “flowering” cherry, crabapple, Japanese lilac, and trident and hedge maples, these small stature trees both look and function differently than do streetscapes of large trees like elm, London plane tree, sweet gum, tulip tree, ginkgo, oak, and linden.

Let’s consider some of those differences.

Setback trees on private property create sidewalk shade.  Berkeley, CA.
Photo: Georgia Silvera Seamans

The aesthetic contribution of short stature trees tends to be limited to their flowering season, while the arching canopy effect of larger stature trees is a year-round feature. Also, short canopies, while beneficial to wildlife, produce smaller ecosystem benefits.  (See “Street Trees: Let’s Think Outside the Wires.” Short stature trees have tremendous habitat and food value.  Take urban birds.  They utilize different layers of the urban forest canopy. As Julie Zickefoose writes in Natural Gardening for Birds, short stature hawthorns provide berries, while larger stature ashes and locusts provide nesting.)

Here are other benefits provided by larger stature trees:

• They provide more shade for infrastructure like streets: “shade on the street segment with large-stature trees will reduce costs for repaving by $2,900 (58%) over the 30-year period compared to the unshaded street. Shade from the small-stature trees is projected to save only $829 (17%)” (From Why Shade Streets? by the Center for Urban Forest Research, 2006).

• In terms of air pollution, “the annual net reductions for pollutants range from 10.1 lbs for a 40-year-old large tree to 0.7 lbs for a 40-year-old small tree. And values range from $64 for a 40-year-old large tree to $1.62 for a 40-year-old small tree” (Center for Urban Forest Research, newsletter, January 2005).

To learn more, here are three good resources (al pdf files): the CUFR’s 2003 newsletter “The case for the large tree”; 2001 Factsheet #1 about the benefits of large front yard trees; and Dr. Greg McPherson’s 2003 article, “A benefit–cost analysis of ten street tree species in Modesto, California, U.S.,” published in the Journal of Arboriculture.

Another deficit of the Right Tree for the Right Place formulation is its ignorance of design factors.  Street trees are typically planted at the street edge of the sidewalk.  Wires are generally sited towards the edge of the sidewalk, too.  With this inevitable conflict for over space, streets with overhead wires are usually planted with short stature trees.  But, street trees could be planted on the building side of the sidewalk or in front yards (preferably through an easement so that the city has some oversight about removals).  There are actually several such “setback” programs in the U.S.  The City of Boston Parks Department sponsors one, (and is enabled to do so according to Massachusetts General Law).  Public trees can be planted on private property as long as they are within 15 feet of the public right of way.  EarthWorks Projects in Boston, MA, initiated the Setback Trees Project in 2007, self-described as planting “trees on private property for the common good.”

Bumpout (note this bumpout is not connected to the sidewalk) – tree is just outside overhead wires.  Berkeley, CA
Photo: Georgia Silvera Seamans

There are other design possibilities.  Trees could be planted in bump-outs located beyond overhead wires, in traffic circles at neighborhood intersections, or in the center of neighborhood blocks (see photo below).  (Traffic calming is one co-benefit of planting trees in the center of the roadway or at an intersection.)

And overhead wires could be buried.  This is an expensive proposition; according to The Seattle Times, the cost to the city of burying utility wires for a local project was $350-$400 per linear foot.  In another Washington community, the cost of burying electric, phone, and cable wires was estimated at $2500 per foot.

However, tall urban street canopies provide considerable benefits long-term.  The conflict between large stature trees and overhead wires is not new.  In his fascinating book, Republic of Shade, about the American elm (Ulmus americana) in New England, Thomas J. Campanella describes anti-elm sentiments expressed in an 1853 article from the New York Times:

“Most American cities were in urgent need of a pruning.  Larger, ‘weedy’ species should be removed at once, (the Times writer) argued, and replaced with smaller trees ‘of a character that can be trained around the wires.’ Elms, very big and very weedy, must be sacrificed to appease the goddess of electricity.”

Appeasing the gods of electricity: large trees pruned into u’s under wires on Old Brownsboro Road, Louisville, KY
Photo: Human Flower Project

Campanella also notes that changes in road technology affected trees.  Street surfaces before 1890 did not restrict “the passage of water, nutrients, or oxygen to the roots of adjacent trees,” but asphalt and concrete paving “virtually sealed the surface of the street,” depriving trees of all three. 

Another dimension of “Right Tree in the Right Place” is to select species according to the size of the growing area—most often the square foot of the sidewalk cutout or width of the tree lawn (the grass strip located within the sidewalk).  This is a very reasonable concept.  Healthy trees depend on adequate root systems, which requires sufficient area to grow.  Often, according to landscape architect and arborist James Urban, we look up at tree crowns and ignore what’s happening below ground.

Different cities have different standards.  In the City of Boston, the minimum tree well area is 24 square feet, often a 3x8 foot or 4x6 foot sidewalk cutout.  One East Bay, California city’s minimum standard is 2x2 feet or 4 square feet!  Generally speaking, a foot of root area supports an inch of trunk diameter.  Accordingly, at only four inches in diameter at breast height, a tree with a well area of 4 square feet has maximized the initial growing area for its root system.  This tree will seek additional space either within the sidewalk (made visible by buckling) or in someone’s front yard.

A small cutout clearly will restrict the size of the tree that can be planted initially.  For example, a 2x2 foot area cannot adequately accommodate a tree that is two inches in diameter whose root ball is two feet in diameter.  On average, for every diameter inch at planting, a tree needs a year to establish.  So, a two inch tree will take two years to establish.  Although, a 15-gallon tree (the size frequently planted in a 2x2 foot cutout) will establish faster, its aesthetic and functional presence is less significant than a larger diameter tree.

The 2x2 foot area is the minimum, so presumably a larger growing area will be provided if the sidewalk can accommodate it.  Although a 3x8 or 4x6 space is significantly larger, it can only support a 24-inch diameter tree within the original cutout.  Ideally, street trees would be given larger growing areas for their root systems.  However, if the sidewalk is space constrained (Americans with Disabilities law requires four feet of clearance for accessibility), what are the options? 

Annie’s Oak, Berkeley, CA
Photo: Georgia Silvera Seamans

One option is to install structural soil beneath the sidewalk.  Structural soil is an engineered medium that supports root growth while simultaneously satisfying engineering load-bearing requirements.  The most well known structural soil recipe was developed by Cornell University’s Urban Horticulture Institute.  An older version of structural soil is sand-based, also known as Amsterdam structural soil.  The most significant difference is that CU soils can achieve a greater level of compaction (important for load bearing) and still sustain root systems than can the Amsterdam soil – 95% versus 85-90%.  The installation of structural soils could be undertaken as sidewalks are repaired, redone, or created.  Like the burying of overhead utility wires, this solution is costly, but again, the potential benefits to a city, its trees, streets and people are significant. 

Thursday, April 10, 2008

Street Trees: Let’s Think Outside the Wires

Local Ecology’s Georgia Silvera Seamans explains why, in choosing a city’s trees, there’s a lot more to consider than power lines.

Hawthorn tree in bloom: short, showy, and nectar rich
So why isn’t it a choice of Oakland’s city foresters?
Photo: Georgia Silvera Seamans

In urban settings, human tensions arise over the selection of large stature or small stature street trees.  The “Right Tree in the Right Place” planting policy recommends that short stature trees – 25 feet or less – should be planted beneath utility lines because the canopies of these trees do not interfere with overhead wires.  But emphasis on height alone neglects larger issues—of ecosystem value. 

Large stature trees—like red oak, London plane tree, or sweetgum—do interfere with overhead wires, but they also provide greater ecosystem benefits than do small stature trees: they sequester (store) more carbon, filter more particulate matter from the air, and intercept more rainfall via leaves, trunk, and soil (and slow runoff into storm drains). And, because of their larger crown spread and evapotranspiration capacity, larger trees cool larger areas of surrounding air (cooling nearby infrastructure and buildings, too).

In a study of Berkeley’s street tree canopy conducted by the USDA Forest Service Center for Urban Forest Research (CUFR), researchers found that city trees saved $12.58 per tree in annual electricity costs. As for capturing stormwater runoff, the average street tree intercepted 1,478 gallons, a value of $5.91 per tree annually. The researchers also found that, overall, larger stature trees provided the most benefits: the average small, medium, and large deciduous street tree produced annual benefits totaling $32, $79, and $96, respectively. (Note: Author Georgia Silvera Seamans, assisted by Qingfu Xiao, research scientist at UC Davis, obtained this information as part of a research grant with Urban Releaf.)

Ginkgo (Ginkgo biloba): as with many large trees, its flowers aren’t showy
Photo: Georgia Silvera Seamans

Though not all short stature trees have showy floral displays, they tend to have larger, more conspicuous flowers. Most people think of herbaceous perennials as the plants that attract bees and butterflies, but flowering trees are definitely popular with wildlife too. As cities make tree selections, they should consider the “wildlife-value” of species that produce fruits, seeds, nuts, catkins, and acorns.  A tree’s wildlife-value in the larger ecosystem, something not usually quantified, involves its floral services for small, highly mobile species like butterflies and bees and some birds.  Hummingbirds, for example, utilize showy flowers for nectar.  As well, floral displays attract insects on which non-nectar eating birds rely.  Not only are the showy flowers of shorter stature trees attractive to birds and bees, their exuberant flowering draws “oohs” and “aahs” from us humans.  I have never visited Washington, D.C., in the spring, but I have heard the buzz about the mass blossoming of the Mall’s 3,000 cherries.  (At this year’s San Francisco Flower & Garden Show, the USDA Forest Service created an urban forest garden.  The sign below the coast live oak, interestingly enough, listed the aesthetic monetary value of the oak over 40 years as $5,210.)

Given the dual appeal of short stature trees, I was curious to see which varieties municipal urban forestry departments selected.  A natural choice for a case was the City of Oakland.  I am an intern of urban forestry issues for the City of Oakland Mayor’s Office.  Oakland’s street trees are managed by its public works agency.  The city’s Official Tree Species List, as of November 2007, has a limited palette of small stature trees.  The list contains seven species: Strawberry tree (Arbutus unedo), Eastern redbud (Cercis canadensis), Crape myrtle (Lagerstroemia indica), Photinia (Photinia fraseri), purple leaf plum (Prunus cerasifera ‘Thundercloud’), Evergreen pear (Pyrus kawakamii), African sumac (Rhus lancea), and Water gum (Tristania laurina ‘Elegant’).  Many of Oakland’s residential streets are lined with overhead utility wires, so I expected a longer list of short stature trees.

Of these seven species on Oakland’s approved street tree species list, four have documented wildlife value.  According to the USDA Forest Service Silvics Manual of North America (1990), the eastern redbud nectar is used for honey production (and the fruit is eaten by cardinals, bobwhites, ring-necked pheasants, rose-breasted grosbeaks, white-tailed deer, and gray squirrels).  The crape myrtle attracts “beneficial insects” according to the UC Davis Arboretum plant database, but it does not give a list of insect species.  Water gum or Tristania laurina provides nectar to honey bees; these bees are common to very common visitors of the water gum flowers.  The UC Berkeley Urban Bee Garden project also observes that water gum flowers occasionally attracts small, native bees.

A powerline-centric view of urban tree selection
Image: Pacific Gas & Electric

As mentioned previously the primary limiting factors in planting the right tree in the right place with regards to overhead utility lines is height; trees should be twenty five feet or less in height at maturity.  Of the seven species listed by the City of Oakland as “small,” two can attain thirty feet in height: the crape myrtle and the purple leaf plum.  Two of the species categorized as “medium” are listed with heights of twenty feet: the bronze loquat (Eriobotrya deflexa) and the Saint Mary magnolia (Magnolia grandiflora ‘Saint Mary’).  In general, magnolias are medium-sized trees, but I gather that the Saint Mary variety is typically twenty feet at maturity.  The flower of the loquat attracts bees (and birds eat the summer fruit). 

The City of Oakland does not list the hawthorn.  I have noticed bees buzzing around and landing on hawthorn (Crataegus species) flowers in my Berkeley neighborhood.  My casual observation is supported by the UC Berkeley Bee Garden project.  Crataegus laevigata attracts five to nine honey bees every three minutes for pollen and nectar, while C. phaenopyrum (Washington hawthorn) attracts five to nine honey bees every three minutes and occasionally attracts small and medium bees for nectar.

Of course, wildlife value is not limited to short stature, showy, flowering trees, and flowers are not the only source of value.  Linden trees (Tilia species) attract bees in great numbers according to observations made by the Cornell University Arboretum.  The valley oak (Quercus lobata), according to the UC Davis Arboretum plant database, attracts butterflies, beneficial insects, and birds.  But, the valley oak does not make a good street tree.  Urban sidewalks are not designed to accommodate this large, broad-crowned California native that requires “deep soils where it can tap groundwater.”

A coast live oak in its namesake city, Oakland, California
Photo: Georgia Silvera Seamans, Local Ecology

Actually, the City of Oakland is named for the oaks that used to cover its land area.  The coast live oak (Quercus agrifolia) is conspicuously absent from the city’s list of large tree species.  This species would require a large growing area and the majority of residential sidewalks in Oakland are six feet wide; a four-foot right of way is required by the Americans with Disabilities Act.  To see an urban mature coast live oak (and its optimal growing space), visit Oakland’s City Hall Plaza.