Land Clearing Impacts
Anonymous May 27, 2019 at 11:42 pm
I have just watched the recording of your lecture on life cycle design. It was very informative and interesting – especially to see that there are people who do care about the real impact of our building and not just ticking ‘environmental’ boxes. However, I see a major omission in your accounting for Life Cycle Design.
And that is of the trees that the house footprint, and in fact usually the whole house block, is replacing.
There would be a formula for working out how much carbon the trees that were replaced by the house would have taken from the atmosphere every year. This balance needs to be added to the houses overall score rating. It would mean that a house would never have a zero rating (unless built in the desert?) and this is true – while a house takes up land from a forest or bushland it should never have a zero rating. Facing this very real fact could also help us come up with solutions to this problem. Could specified planting in other areas offset this problem for instance?
I believe if we continue to ignore this very real fact population growth will increase our carbon output every year. In Australia alone we have to house around 200,000 new people every year, which means huge land clearance rates to accommodate this. We should not be giving these new houses zero carbon ratings when they have replaced bushland and forest as the impact of not having those trees take carbon from the atmosphere is ongoing and could be accounted for in a yearly style. What do you think?
Thank you very much for caring and bringing hope to those who are so frustrated by what is happening.
Thank you for a great question. Certainly, land clearing is normally omitted from an eToolLCD Life Cycle Assessment. We follow the guidance of EN15978 which does not include this in scope, but you raise a very important point that is worth exploring.
We have included Land Clearing in some previous assessments where it was specifically requested. In these situations we used FullCAM software to conduct these calculations of stored carbon in the land. To give you some idea of how the stored carbon compares to the impacts of a building I will provide an example below.
In Perth Australia FullCAM told us that the carbon stored per Ha was approximately 43t Carbon which when released as Carbon Dioxide equates to 158tCO2e/ha. This figure seems quite small given that one mature tree alone can store upwards of 5tCO2e, however FullCAM is a fairly well reviewed program and accounts for a large array of factors such as biomass density, natural carbon cycles, species diversity etc.
For the purposes of the example let’s make the following assumptions:
– The building site for a home is 500m2 (above average for Perth now)
– The building site was native Acacia forest prior to construction
– The vegetation was all immediately burnt (carbon released in it’s entirely)
– No vegetation was replanted (or retained) on the site
The biogenic carbon lost would equate to 7.88tCO2e. A typical detached home in Australia emits approximately 500tCO2e over a 40 year life span. So the biogenic carbon lost would be somewhere between 1 and 2% of the life cycle carbon footprint of a typical home.
This contribution would deviate depending on the location and characteristics of the building. In a location like Tasmania the impacts for a residential plot and home may increase to 5-10% due to a higher density natural vegetation rate and much lower carbon intensity of energy supply. For commercial buildings the impact would be far lower due to the higher energy intensity per m2 of these buildings.
Biodiversity offsets and native tree planting are definitely worth considering, as are the building design and landscaping plan for the plot. An example of what would be possible by re-imagining our plot and density designs in Perth is the Underwood bushland site. There is some debate about this land that the University of Western Australia are planning develop as a housing development. The first phase is 25ha with reasonably low density yielding only 300 dwellings with most of the site cleared. The site is particularly contentious as it’s an important habitat for the endangered carnaby’s black cockatoo. If a high density residential tower was instead built on the site the land clearing impact to provide 300 dwellings could be minimised to less than a hectare thereby preserving 95% of the bush (indeed, with a tower like Pinnacle at Duxton in Singapore you could building upwards of 1000 dwellings on a hectare of land).
eTool have logged land use carbon as a feature on our backlog and depending on demand it may be prioritised and developed. There are other features that are currently out of scope in eToolLCD which we would also like to bring in scope such as:
– Occupant Transport over the life of the building
– Occupant Goods, Food and Services consumption
– Occupant waste generation
All of these factors are potentially very significant Greenhouse gas contributors and can be influenced by the design of the buildings and / or town planning.
Thanks again for the question, I hope that shed some light on the topic.
One other thing we should mention on this topic is that once vegetation is mature it reaches a fairly stable level of sequestered carbon (that is, it doesn’t continue to uptake more and more carbon over time once mature). So the main benefit associated with biogenic carbon uptake in trees is while they are growing, and the main impact is when they are felled (and burnt). In fact, the largest short term deviation in atmospheric carbon is due to the annual seasonal release and uptake of carbon by deciduous forests. See detailed info on this here. If timber is harvested and used for construction products that will be locked up in a building for 50 years or more then the impact of felling the trees is relatively minor. Even better if new trees are replanted. The other biogenic carbon store is soil carbon which is very complex.
Outside of Greenhouse Gas management, biodiversity is a different environmental that (in my opinion) needs due consideration as well. Native forests need to be preserved as they are habitat for species (including threatened species which need no further pressure).
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