In this post we will explore the carbon calculation tool ‘Pathfinder’ created specifically for Landscape Architects. This was created by Pamela Conrad in the USA at Climate Positive Design. Pathfinder was a major inspiration in the creation of Carbon Positive Landscapes.
Link:
- With current standard landscape practices (significant paved areas with concrete block paving), Most schemes won’t be carbon positive for at least 50 years.
- More greenery and tree planting will be essential for carbon sequestration, (let alone other benefits)
- It is essential to begin calculating the impact of our schemes now to beat the back-industry. Waiting for suppliers to reach net zero will be too late.
DOWN TO IT
Pathfinder works on the basis of calculating the embodied carbon of the various site elements (Paving, fencing, furniture, aggregates), and the sequestration abilities of different types of vegetation.
This input is based on spatial measurements - m2 / dimensions / weight / volume.
Once the embodied carbon is weighed against the sequestered carbon, then a timeframe to ‘carbon positive’ is shown with a clear graphic to illustrate this.
It is extremely intuitive and that speaks to it’s success in the States. It is heavily weighted to US terminology but bespoke elements can be created and used. IE if there was a specific paving from Marshalls, the embodied carbon can be calculated and therefore would be UK specific.
I’d recommend you explore the app yourself. It’s based in browser and is completely free.
For now we will explore some typical scenarios base on a site area of 1000m2. This is a nice round number and allows us to compare easy ratios of hard to soft to simply understand the impact of our schemes at a simple level.
- For reference an adult football field (100m x 70m) is 7000m2. 1000m2 is about the size of Euston Square. You know - the bit outside with the Pret and where it’s always raining.
- 1000m2 = 31 x 31m approx.
Also for good reference when thinking about these things :
- A Typical middle class Brit has a carbon footprint of 10 tonnes carbon annually.
- A return flight to Hong Kong is 3.5 Tonnes of carbon
A SMALL FIELD
1000m2 of Field with 15 trees on a 7m grid
Large specimens
Perennial grassland below
No hard landscape at all
5 hours maintenance every 2 weeks with an electric lawnmower
Results: 47 Tonnes of carbon sequestered over 50 years. 0.165 Tonnes of carbon used. That’s 13 return flights to Hong Kong
A PUBLIC SQUARE
1000m2 of concrete paving (eg Marshalls Fusion)
150mm aggregate base
15 Large Trees in ground
No allowance made for below ground soils, assume they are in recycled crates (we’ll tackle this another day)
Results: Over 50 years a net emission of 43.4 Tonnes of carbon. Not carbon positive until 255 years later… (the 23rd century basically.)
Let’s triple this and say the public square and trees survive for 150 years. This would result in
52.8 - (50 years of sequestration x 3)
52.8 - (9.3 x 3) = 24.9 Tonnes emitted over 150 years
That’s not looking good for this public space. But let’s give it a break, it’s only theoretical.
What about if we triple the number of trees (quite tight but let’s run with it…)
A PUBLIC SQUARE with 45 trees
1000m2 of concrete paving (eg Marshalls Fusion)
150mm aggregate base
45 Large Trees in ground
No allowance made for below ground soils, assume they are in recycled crates (we’ll tackle this another day)
Results: Over 50 years a net emission of 24.8 Tonnes of carbon. Obviously the same as waiting another 100 years. Carbon positive in 2112.
So this isn’t good enough to pave over everything with concrete blocks.. Let’s look at different ratios.
30:70 PAVING / GREEN STUFF
300m2 of concrete paving (eg Marshalls Fusion)
150mm aggregate base
25 Large Trees in ground
350m2 of Herbaceous Perennials
350m2 of moderately maintained lawn
Results: Carbon positive by roughly 2050. 12 Tonnes sequestered by 50 years later.
This is interesting - This is quite a good result and possibly down to the 350m2 of perennials.
PAVING : LAWN
If we alter all the green area to a lawn, this worsens and will be carbon positive about 53 years later. (A BIT LATE?)
Also interesting is the operational carbon of paving - much higher than lawn. Not sure how this figure has been generated.
MOSTLY GREEN : 15% PAVED
150m2 of concrete paving (eg Marshalls Fusion)
150mm aggregate base
25 Large Trees in ground
10 Smaller Trees
300m2 of Herbaceous Perennials
300m2 of Lawn
250m2 of Wetlands (I’m not clear on exactly what this is defined as. Mangroves will be better at sequestering than ponds i think..)
Results: Carbon positive in 8 years, and 49.5 Tonnes of Carbon absorbed in 50 years.
Very good. This is where we should be aiming for
What isn’t included in any of these scenarios are:
- Site furniture
- Lighting
- Underground Drainage
- Fencing or Boundary Treatments
- Any recycled materials - of course this will make a huge difference to the available hard landscape budget’
Further strengthening the argument for using SUDs, as little underground infrastructure as possible and considering sequestered carbon in timber for furniture.
THOUGHTS
To achieve a carbon positive landscape in 20 years with current typical landscape practices, it’s evident approximately 85% of the site needs to be green, and much of that full of carbon sequestering planting.
Whilst it may seem obvious to some, I believe this is a stark contrast to most schemes practices within the UK are familiar with. Of course this can be balanced with lower carbon hard materials, but having not factored in any furniture, fencing, soils, drainage etc. it’s clear there needs to be a rapid shift away from expanses of paving and hard surfaces.
Furthermore, in future many of these hard materials will ideally have a MUCH lower embodied carbon and a ‘net zero’ taget can be reached for the materials. This would allow for a greater proportion of hard to soft. But until net zero is legit, this isn’t a good idea. Plus given what we know about the benefits of green space, shading, climate adaptation and biodiversity…is this a future we want to progress?
I think the need to carbon positivity now will reshape the pattern of the typical design we will see in the coming years. Much more greenery please, and a lot less pixelated paving patterns.
Future posts will explore Pathfinder further, along with calculators from Sasaki and others. I’m intrigued to see how furniture and imported soils will affect the timeframe to positive. We’ll also be exploring the current LCA process - what relevance does Landscape schemes play? and how this compares to Pathfinder. I have a feeling it won’t be as interesting as the excellent work by Climate Positive Design.
If you think this is interesting, please let me know and I’d welcome any thoughts you have.
To achieve a carbon-positive landscape within 20 years using current typical landscape practices, it is evident that approximately 85% of the site needs to be green, with much of it filled with carbon-sequestering planting.
While this may seem obvious to some, I believe it is a stark contrast to most schemes practiced within the UK. Of course, this can be balanced with lower-carbon hard materials, but without factoring in furniture, fencing, soils, drainage, etc., it is clear that there needs to be a rapid shift away from expanses of paving and hard surfaces.
Furthermore, in the future, many of these hard materials will ideally have a much lower embodied carbon, and a "net zero" target can be reached for the materials. This would allow for a greater proportion of hard to soft. However, until net zero is legitimate, this approach is not advisable. Additionally, given what we know about the benefits of green space, shading, climate adaptation, and biodiversity, is this the future we want to progress towards?
I believe the need for carbon positivity will now reshape the typical design pattern we will see in the coming years. More greenery and a lot less pixelated paving patterns, please.
Future posts will explore Pathfinder further, along with calculators from Sasaki and others. I am intrigued to see how furniture and imported soils will affect the timeframe to carbon positivity. We will also be examining the current life cycle assessment process- what relevance does landscape schemes have? How does this compare to Pathfinder? I have a feeling it won't be as interesting as the excellent work by Climate Positive Design.
If you find this interesting, please let me know, and I would welcome any thoughts you have.