Afforestation in Denver?

What the heck is Afforestation?

The AP recently reported on some upcoming research that will suggest the best way to sequester carbon is by planting a trillion trees. That’s 125 trees for every human being on earth, or 3k trees for every American. It’s 30% more trees than exist in the world today. The estimated ground cover for new forests would be equivalent to all the land in the US.

This led to some reading on afforestation, which I suppose is the name we have made up to describe the process of growing new forest. In nature, this takes between 600 and 1000 years, but humans have been able to speed this process up to around 100 years, and new techniques yield pretty spectacular results in only 10 years. In 100m^2 it’s possible to grow around 600 trees, which would mean you’d need 1.6B m^2 or 160k hectares. The publication in Science claims a need for a billion hectares of additional forest. That’s a tremendous amount of land but I doubt that’s for a maximized process.

Anyways, the Afforest foundation was created by a former Toyota engineer to optimize growing conditions for new forests. They apply a technique where they loosen the soil over a large area, add natural fertilizers to kick-start the growth process, and perform a very dense planting of trees over a small area, with local species selected that comprise canopy trees, mid-level trees, and shrubs. In tropical environments they’ve seen pretty rapid growth in just a couple of years. The claim is that the loose and fertile soil allows the trees to grow strong roots, and the dense planting compels the trees to compete for light, absorbing nutrients and turning them into biomass with higher efficiency. After a few years, 100% of the rainfall on the plot is absorbed by the layers of humus and roots that have accumulated underneath the forest.

Afforestation in Temperate Climates?

It’s a pretty bold claim and their work is primarily focused in India, but a couple of projects have been done in the US, closer to the Mississippi river and the midwest, where rainfall and climate are amenable to forest growth, and one project was done in the Netherlands.

A different afforestation project was undertaken by Israel starting in 1948, as a part of their national forest service’s mandate. They have planted around 250 million trees in a temperate climate, with special techniques implemented to help grow trees in areas with reduced rainfall. In particular, they discuss how runoff on angled slopes helps to provide trees with a higher effective rainfall amount than they would get otherwise.

So it’s promising then that an afforestation project could be undertaken in Denver. Looking at long-term climate trends, there seems to be a consensus among models that temperatures will rise over the next 50 years, while precipitation will stay about the same. Denver in particular sees around 15" of precipitation annually, with most of that concentrated in the spring and summer months. Average annual temperature is around 10F cooler than the Israeli environments - 50F versus 60F.

Colorado has a lot of native trees, but native forests are in my experience primarily dense pine forests or aspen colonies. I have not seen a forest in CO that is like any of the forests from back east, and certainly not anything like the jungles that the afforest project has been growing in India.

It doesn’t seem like doing this in Denver is impossible, but it might not be cost-effective. I would be interested in knowing whether Denver’s soil and rainfall totals could support any sort of rapidly growing forest, and interested in knowing the impact that large swaths of new forest might have on the microclimate here. At some point, the impact to the local system of increased forest coverage will have an impact on the whole system, and that sort of impact is difficult to predict. If carbon capture is carbon capture, regardless of the location, then it makes sense to do something like this in places amenable to growing trees quickly. But there are additional localized benefits to biodiversity, pollinators, and community awareness that shouldn’t be overlooked.

More Questions than Answers

  • Is it cost-effective to do this in Denver?
  • How does the presence of a forest impact rainfall totals in an arid climate?
  • w/r/t the above, especially when considered at massive scale?
  • Could a large humus be built up in CO or is it too arid here?
  • What is the total amount of carbon sequestered in a single young tree?
  • How much CO2 is sequestered annually per 100m2 of mature forest?
  • Would large-scale afforestation tie into a water rights discussion?
  • Will climate change allow Denver to develop a more biodiverse or faster growing “non-native” forest?
  • Would afforestation projects lead to pest population problems?
  • What are the barriers to doing this cost-effectively?
  • How fast would the global rate of afforestation need to be in order to offset growth in carbon emissions?
  • Same as above, but what about sequestering all the carbon from 1800-present?

References