Just as the forests around the Pisa were cut down to make way for urban structures, so too are the forests of today. Put simply, deforestation is “the result of clearing trees for a change to a non-forest landuse.” (NRCAN, 2008). This can include a variety of land-uses including for urban expansion or for agriculture. Generally, mass deforestation causes a loss in biodiversity and accelerates climate change (Chakravarty et al., 2012). The threat of climate change has led some to revisit one of man’s oldest materials.
Compared to wood, compression material such as concrete consumes 20% more energy, emits 29% more green house gases, discharges 12% more airborne pollutants, and produces 225% waterborne pollutants. (NRCAN 2017). Wood also environmentally outperforms steel across those same categories. Proponents of steel & concrete construction are quick to point out that the recyclability, resilience, and strength of both materials make them superior to wood. While the recyclability of wood is less versatile than that of steel, wood can still be reused in products such as particleboard, paper, or even as burned as a fuel source. And while traditionally, the strength of wood has constrained its applications in architecture, the strength of manufactured wood products such as mass timber is redefining the possibilities in wooden architecture.
Michael Green of Michael Green Architects is a major proponent for tall wood buildings. A movement that is controversial not only because are these architectural typologies are normally built from steel and concrete, but also in that Green suggests the we should actually be harvesting more wood to build these wooden structures. Green and Karsh addresses these concerns in his treatise The Case for Tall Wood Buildings (2012) by stating that ubiquitous Tall Wood buildings can only become a reality when strict regulation of sustainably managed forests is properly enforced (Green and Karsh 2012, 15). Green’s firm has redefined what’s possible in wood construction with the “FFTT” structural system – “Finding the Forest Through The Trees” (ibid., 1). This structural system is made possible due to mass timber products/systems: cross laminated timber, laminated strand lumber, and laminated veneer lumber. The manufacturing process of these products have either mitigated or nearly-eliminated the weaknesses of natural wood. Mass timber has fire resistance, insect resistance, and high structural performance – both in tension and compression.
The importance of wood and therefore deforestation on the future of green construction cannot be understated. Wood is not only more energy efficient than steel and concrete, wood also sequesters carbon. This means that using wood as a construction material stores carbon emissions in the walls and floors of the building. Old evidence even suggests that burning biomass for fuel is carbon neutral so long as there are enough trees to re-sequester the released carbon dioxide. However, much more recent evidence with a more nuanced approach to the carbon cycle suggest that carbon-zero biomass is not entirely true (Brack 2017). This only further suggests that wood ought to be used primarily in construction rather than as fuel and, as Green writes, requires a predetermined plan for how to recycle wood architecture at the end of its life cycle (Green and Karsh 2012, 27).
The absence of wood however, doesn’t necessarily mean that builders might turn towards concrete and steel once again. Alternatives to wood products such as bamboo are becoming increasingly popular (Fairs 2014). At the same time, locals might also towards their architectural history and revisit the ancient vernacular of the area. In the semi-arid areas of Africa, the Nubian Vault Association has led a revival of mud bricks houses (Cooke 2017). This comes as a response to the lack of bush timber due to climate change and deforestation. The ancient techniques of rammed-earth construction have also began to trend in the industry (Dobson 2000). This method uses materials equally as sustainable as wood construction: earth, chalk and lime.
Urban & Landscape
It is known that forests are partially responsible for the local movement of precipitation, it’s specifically theorized this is done through a method called biotic pumping (Robbins, 2015). This theory posits that a low-pressure system is created above forests which pumping in moisture from the sea. This low-pressure system would be degraded from mass deforestation. Certain evidence shows that the impact deforestation has on the hydrological cycle could cause destruction of forests hundreds of miles away. Researchers have shown a relationship between deforestation in the Amazon and droughts along the western United States (Kelly, 2013). Evidence shows that in just six years of drought, California has lost 102 million trees (Chow, 2016). While academics wait until more evidence corroborates the link, what should be noted is that range and magnitude of consequences that deforestation can produce. In contrast to drought, deforestation can also cause flooding. Flooding can occur when the lack of trees allow for the soil to become fully saturated with water earlier in the season that results in additional precipitation to run off (Chakravarty et. Al, 16). Deforestation also increases flood risk is by causing soil compaction which makes the soil more impervious to rain (Chakravarty et. Al). Increased risk of flooding puts many urban water-adjacent properties at risk. Increased chance of regional drought puts entire regions at risk. The response to flooding and scarcity has renewed and inspired interest in Water Sensitive Urban Design.
Innovative projects such as Bjarke Ingels’ New York Dryline and theoretical projects such as Baharash’s Water Boulevards are already shaping the city and the discussion in how water is best integrated and managed in modern cities.
While the effects local deforestation has across continents and oceans are not entirely clear, what is for certain is that local deforestation directly destroys local habitat. This not only leads to a decline in wildlife population, but also – in some cases – causes species to migrate closer towards urban centres. Professor Stan Gehrt from Ohio State University is the principal investigator of the Urban Coyote Research program. The program has documented the growth of coyotes living in the urban core. Across the pond, London has seen a spike in red foxes in the urban sphere (Mahoney, 2012). Even habitats that are preserved might still be degraded due to fragmentation. One effect of fragmented habitats is the increased frequency of contact between animals and humans. For example, the rate of human-elephant conflict in the northern West Bengal of India has risen due to deforestation. This has resulted in the deaths of around 50 persons and 20 elephants annually (Chakravarty et. Al, 17). If left unmanaged, migration and habitat shifts places humans and animals in direct conflict in our cities. Some planners address fragmentation by joining habitats via green corridors or through careful zoning of forested areas. Greenbelts – such as the one in Ottawa – has been a popular choice for a few cities. However, the use of greenbelts and other means of continuous green corridors are also criticized for increasing urban sprawl.
Deforestation demands a response by urban planners and policy maker. To the benefit of city dwellers, the U.N. has called for an increase in urban forests as part of their efforts to address climate change. Adopted in 1992, Chapter 11 of Agenda 21 – titled ‘Combatting Deforestation’ – has a provision which calls for increasing the development of urban forests. Vegetation in the city as an urban feature dates all the way back to antiquity. The increase in urban trees parks has the added effects of improving urban air quality and mitigating the urban heat island effect. One could even argue that if humans feel greater stewardship over the things they control, then society will exercise greater stewardship and care over urban trees rather than distant forests.
What should be noted then is that deforestation has had and will continue to have an effect on the design and construction of our buildings and cities. In the process of examining the impacts of deforestation on architecture and cities, one should also examine the effects of continuous deforestation (i.e. the loss of harvestable material) and the changes in built-design in response to deforestation. For while the effects of deforestation may be dire, the response to deforestation might result in an architecture and urbanism that bridges the urban-nature divide. However, such a claim cannot be merely substantiated on the increased interest in urban forestry, water-sensitive cities, and wooden architecture. Such a claim requires further research into the response ancient cities had to climate change as well as the economic viability of managing more complex urban systems.