Functional and ecological xylem anatomy

Published Date
Perspectives in Plant Ecology, Evolution and Systematics
2001, Vol.4(2):97–115, doi:10.1078/1433-8319-00017

Abstract 

Cohesion-tension transport of water is an energetically efficient way to carry large amounts of water from the roots up to the leaves. However, the cohesion-tension mechanism places the xylem water under negative hydrostatic pressure (P_x), rendering it susceptible to cavitation. There are conflicts among the structural requirements for minimizing cavitation on the one hand vs maximizing efficiency of transport and construction on the other. Cavitation by freeze-thaw events is triggered by in situ air bubble formation and is much more likely to occur as conduit diameter increases, creating a direct conflict between conducting efficiency and sensitivity to freezing induced xylem failure. Temperate ring-porous trees and vines with wide diameter conduits tend to have a shorter growing season than conifers and diffuse-porous trees with narrow conduits. Cavitation by water stress occurs by air seeding at interconduit pit membranes. Pit membrane structure is at least partially uncoupled from conduit size, leading to a much less pronounced trade-off between conducting efficiency and cavitation by drought than by freezing. Although wider conduits are generally more susceptible to drought-induced cavitation within an organ, across organs or species this trend is very weak. Different trade-offs become apparent at the level of the pit membranes that interconnect neighbouring conduits. Increasing porosity of pit membranes should enhance conductance but also make conduits more susceptible to air seeding. Increasing the size or number of pit membranes would also enhance conductance, but may weaken the strength of the conduit wall against implosion. The need to avoid conduit collapse under negative pressure creates a significant trade-off between cavitation resistance and xylem construction cost, as revealed by relationships between conduit wall strength, wood density and cavitation pressure. Trade-offs involving cavitation resistance may explain the correlations between wood anatomy, cavitation resistance, and the physiological range of negative pressure experienced by species in their native habitats.

Key words

cavitation

drought stress

ecological wood anatomy

freezing stress

stomatal control

wood density

xylem structure

corresponding author

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http://www.sciencedirect.com/science/article/pii/S1433831904700426

Wood decay under the microscope

Published Date
November 2007, Vol.21(4):133–170, doi:10.1016/j.fbr.2007.09.001
Review 

Author 

• Francis W.M.R. Schwarze ^a,b,,

• aSwiss Federal Laboratories for Materials Testing and Research (EMPA), Wood Laboratory, Lerchenfeldstr. 5, CH-9014 St. Gallen, Switzerland
• bProfessur für Forstbotanik, Albert-Ludwigs-Universität Freiburg, Bertoldstrasse 17, D-79085 Freiburg i.Brsg., Germany

Available online 26 November 2007.

Abstract

Many aspects of the interactions between host wood structure and fungal activity can be revealed by high resolution light microscopy, and this technique has provided much of the information discussed here. A wide range of different types of decay can result from permutations of host species, fungal species and conditions within wood. Within this spectrum, three main types are commonly recognised: brown rot, white rot and soft rot. The present review explores parts of the range of variation that each of these encompasses and emphasizes that degradation modes appear to reflect a co-evolutionary adaptation of decay fungi to different wood species or the lignin composition within more primitive and advanced wood cell types. One objective of this review is to provide evidence that the terms brown rot, white rot and soft rot may not be obsolete, but rigid definitions for fungi that are placed into these categories may be less appropriate than thought previously. Detailed knowledge of decomposition processes does not only aid prognosis of decay development in living trees for hazard assessment but also allows the identification of wood decay fungi that can be used for biotechnology processes in the wood industry. In contrast to bacteria or commercial enzymes, hyphae can completely ramify through solid wood. In this review evidence is provided that wood decay fungi can effectively induce permeability changes in gymnospermous heartwood or can be applied to facilitate the identification of tree rings in diffuse porous wood of angiosperms. The specificity of their enzymes and the mild conditions under which degradation proceeds is partly detrimental for trees, but also make wood decay fungi potentially efficient biotechnological tools.

Keywords

Co-evolutionary adaptation

Host fungus interactions

Light microscopy

Lignin composition

Tree risk assessment

Wood decay

---

 Table 1

Table 1.

 Table 2

Table 2.

Figs. 1–4.

Figs. 5–8.

Fig. 9.

Fig. 10–13.

Fig. 14–19.

Fig. 20.

Fig. 21–24.

Fig. 25–30.

Fig. 31.

Fig. 32.

Figs. 33–37.

Figs. 38–44.

Figs. 45–50.

Fig. 51.

Figs. 52–57.

 Table 3

Table 3.

Figs. 58–63.

Fig. 64.

Figs. 65–70.

Figs. 71–76.

Fig. 77.

Fig. 78.

• ☆
  Dedicated to Alex L. Shigo.

• ∗ 
  Swiss Federal Laboratories for Materials Testing and Research (EMPA), Wood Laboratory, Lerchenfeldstr. 5, CH-9014 St. Gallen, Switzerland. Tel.: +41 71 2747274; fax: +41 71 274 7694.

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La Cigarra Café Entry Pavilion

To create the structure's organically shaped skin from thousands of elm strips, Spanish architect Tomás Amat worked side by side with artist Manolo Garcia.

By TIMOTHY A. SCHULER

David Frutos

Every spring, artisans in Valencia, Spain, sculpt giant caricatures of historical and mythical figures—and then set them ablaze. The tradition is part of Las Fallas, a week-long festival that coincides with St. Joseph's Day, named after the patron saint of carpenters in the Catholic Church. Several years ago, Tomás Amat, founding principal at Tomás Amat Estudio de Arquitectura, recruited renowned wood-falla artist Manolo Garcia for a new café project in his hometown of Alicante, a port city on the country’s Mediterranean coast. The two had met through an earlier project and Amat considered Garcia to be the only person to execute his design.

The café occupies a small plaza among a collection of red-tile-roofed warehouses that operated as tobacco factories for most of the 20th century. In 2010, to preserve the site’s heritage, the facilities were converted into Las Cigarreras Cultural Center, a museum and performing arts venue. Inspired by Barbarela Studio’s nearby Jardin Vertical, Amat envisioned the freestanding 2,600-square-foot café as an insect in a garden. He designed a long, low structure split into three parts: “head” (kitchen), “body” (seating area), and “tail” (entry pavilion). A pair of tall steel beams bent like a cricket’s hind legs flank the structure, completing the allusion.

David FrutosThe structure was designed as three parts (r to l): the “head” (kitchen), “body” (seating area), and “tail” (entry pavilion). A pair of bent steel beams complete the allusion to a cricket.

Designed for Alicante’s mild winters and hot summers, the 600-square-foot tail is covered by a free-form wood shell, crafted by Garcia. “There’s nobody [in] the world who could make it like him,” Amat says. Garcia began by sculpting a 1.5-foot-long plaster model based on a digital mock-up by Amat. As the basis for everything else, the model had to be perfect, the Spanish architect says. He and Garcia even tweaked the curves and wrinkles by hand, creating a piece that looks like an insect’s molted skin, scrunched up and discarded. (Amat’s affinity for curvaceous forms perhaps stems from the two years he spent at Zaha Hadid Architects.)

Garcia then blended digital fabrication technology with traditional craftsmanship in a process that Amat claims is years ahead of the mainstream architectural profession. The plaster model was digitally scanned and then transversely sliced into a series of sections, which were then exported to CNC-milling machines. “The people in Valencia have developed really complex methods to make these shapes,” Amat says. “To scan in 3D now is very common, but they [were] using it eight, nine years ago.” The CNC machines cut five transverse frames and 48 longitudinal purlins that serve as the pavilion's base structure. Made from pine and measuring each roughly 1 inch wide, 4.5 inches deep, and 32 feet long, the purlins are spaced every 10 inches and are screwed directly into the transverse frames.

Entry pavilion diagram

This wooden skeleton is then wrapped in approximately 10-foot-long strands of unfinished elm, each of which is 0.5-inch wide and 0.1-inch thick and submerged in water for an hour before being stapled to the wood frame. The shape of the swirling skin follows the contours of the underlying structure, but each strand is placed "sobre la march," Garcia says—or "on the fly." He along with nearly a dozen laborers built the pavilion in four sections in a Valencia warehouse and then erected the pavilion on-site. The shell is protected with a spray-applied polyurethane finish.

The café opened in 2015 and is now known as La Cigarra (The Cicada), a name coined by the local politicians that stuck due to its resemblance to las cigarreras—a term that also applies to the women who work in tobacco factories, rolling cigars. Despite its modest size, the project, undertaken by Alicante's city government, took more than four years to complete, primarily due to funding issues.

Amat says what began as a €200,000 (about $225,000) budget quickly dwindled to just 1/10 of that. “[The city] keeps calling me until they say, ‘Tomás, listen, we have €20,000,’” he recalls. Initially, Amat suggested half-jokingly that they buy some Coca-Cola, some Heineken, and a few chairs, because “for €20,000, we cannot do anything.” But Amat eventually proposed a public-private partnership and secured donations from local companies—DuPont Corian, Finstral, and Tecnocemento, among others—whose logos now adorn the head and body of the building.

Unlike the rest of the café, the tail is unbranded except for a series of inconspicuous, laser-cut wooden tags running down the side of one of the pavilion’s many folds. These tags display only two names: Manolo Garcia and Tomás Amat Estudio de Arquitectura.

David Frutos

David Frutos

David Frutos

ABOUT THE AUTHOR

Timothy A. Schuler

Timothy A. Schuler is a contributing editor at Landscape Architecture Magazineand writes about architecture, landscape architecture, and urban design for a variety of national and international publications. Based in Honolulu, he is a graduate of Kansas State University. Follow him on Twitter or visit timothyschuler.com. 

For further information log on website :
http://www.architectmagazine.com/technology/detail/la-cigarra-cafe-entry-pavilion_o

The Reclaimed Circular Pavilion

Cyrus Cornut/Matignon21.10.2015. Le Pavillon Circulaire, Hotel de Ville. fait de materiaux essentiellement recupérés. Arch: Encore heureux

The Circular Pavilion is anything but round, with the exception of its nearly 180 doorknobs. The skin of the 750-square-foot polygonal cafe and event space in Paris comprises a bevy of reclaimed doors, salvaged from a public housing project in the city’s 19th arrondissement, to the northeast. Designed by local firm Encore Heureux and erected in front of City Hall, the temporary structure is named for the aspirational circularity of the lifecycles of its building components.

Reclaimed materials from projects throughout the city make up 80 percent of the open, stick-framed pavilion with a sawtooth roofline and 20-foot-high ceilings. It is a statement about global sustainability, yes—the pavilion was on display during the Paris Climate Agreement talks last December—but it is also an experiment in allowing found materials to drive the design process and to create networks between the building industry and public services. “We are not making trash architecture,” says firm partner Nicola Delon. “It’s very different to take a bunch of trash, put it together, and say, ‘You see?’ ”

The project emerged from Encore Heureux’s 2014 exhibition “Matiere Grise”(“Grey Matter”), which explored the often invisible impacts of a building, such as waste. Partnering with the city, which helped sponsor the exhibition, the firm engaged municipal personnel into realizing the pavilion. Maintenance workers and garbage collectors, for instance, helped divert wooden chairs from the city’s curbside furniture pick-up service.

In the pavilion, architecture acts as a literal intervention, disrupting the everyday waste collection and deposition processes and restricting the architects to design with what could be salvaged. “When we started, we had no idea what kind of material we would have,” Delon says. Insulation came from a supermarket renovation. Baseboards were surplus from Rudy Ricciotti’s MuCEM building, in Marseille. And light fixtures were exhumed from a warehouse owned by Evesa, the company in charge of Paris’ city lighting.

And then there’s the envelope of doors. In May 2015, three months away from the pavilion’s scheduled opening, Encore Heureux got a call from the city: It was removing 400 wooden doors from a 1936 housing project. Immediately, Delon went to see the doors. “Wow,” he said. “They’re perfect.”

His team returned to the studio and began mocking up geometric configurations using pieces of wood cut to match the doors’ proportions. Eventually, they devised a herringbone pattern, with each door angled 45 degrees. They scrapped their initial concept for the pavilion—a tent-like structure made from aluminum panels salvaged from a former high school—and drew a new building with a trapezoidal floor plan and jagged roof punctuated with east-facing skylights. The salvaged doors dictated essentially everything about the structure, Delon says. “It’s impossible to design this building without the doors.”

Cyrus Cornut/Matignon21.10.2015. Le Pavillon Circulaire, Hotel de Ville. fait de materiaux essentiellement recupérés. Arch: Encore heureux

Encore Heureux worked with the city to time the housing project’s deconstruction with that of the pavilion’s construction, arriving onsite on the day the doors were removed. “We tried to be at the bottom of the building and take them at that time because if you wait, they’re just stuck somewhere or put in the trash,” Delon says. The doors were trucked to a city facility, stripped of hinges and locks, and then shipped to the pavilion site.

To build the structure, the firm again tapped city workers. An open call generated too much interest so the firm developed a rotation system, where laborers cycled on and off the job. Cruard Charpente, the only other private company involved in the project, served as the main timber contractor.

user

The wood-frame structure sits on steel footings with 4-inch-wide, 10-inch-deep Douglas fir posts and floor joists every 10 feet. The reclaimed doors are screwed to 2-inch-wide wood slats spaced at 2 feet. Behind the doors is a layer of waterproofing membrane on 0.35-inch-thick OSB sheathing, and mineral wool insulation. With the doors coated in 70 years of varnish, and the waterproofing membrane, an exterior finish on the wood was unnecessary. Inside, the walls are finished with 3-foot-by-8-foot painted wood panels, reclaimed from several city buildings.

To account for variances in the sizes of the doors, some of which were significantly warped, the designers left a 0.75-inch joint between doors, filling the gaps with scrap wood painted to match. “The people from the city are good at making the right color because most of the time they work with historical buildings,” Delon says. The angled doors on the upper half of the pavilion were hung first and then trimmed in order to ensure perfect alignment.

Later this year, the pavilion will be deconstructed and moved to its new home along the Petite Ceinture, a former railway that encircles the city inside its once-fortified walls and is being reimagined as a public open space, à la the High Line. Delon hopes the structure and its repurposing of waste have left an impression on the city and people involved. “When you find ways to not waste, you find positive energy,” he says. “Two centuries ago, we’d go to the forest. Now, we go to the city. It’s a change in paradigm.”

Cyrus Cornut/Matignon

ABOUT THE AUTHOR

Timothy A. Schuler

Timothy A. Schuler is a contributing editor at Landscape Architecture Magazineand writes about architecture, landscape architecture, and urban design for a variety of national and international publications. Based in Honolulu, he is a graduate of Kansas State University. Follow him on Twitter or visit timothyschuler.com. 

For further information log on website :
http://www.architectmagazine.com/technology/detail/the-reclaimed-circular-pavilion_o