Written by Kelaine Vargas | 05 April 2010

Energy conservation is perhaps the most valuable of the ecosystem services that trees provide. Why? Because it has trickle-down effects that amplify other benefits, like air quality improvement and carbon sequestration. But we’ll get to those later this week. For now, let’s talk about how trees help save energy.

Trees help reduce energy used for cooling in three main ways:

• Shading reduces the amount of heat that reaches buildings.
• Shading of heat-absorbing surfaces like parking lots, roads, roofs, and sidewalks helps reduce the “urban heat island” effect. These manmade surfaces can increase city temperatures as much as 8-10° above the surrounding natural areas.
• As trees take in and give off water (evapotranspiration), they use up solar energy that would otherwise heat the air. Over large areas of trees, this effect can be substantial.

Trees also help reduce energy used for heating:

• Reducing windspeed reduces the movement of colder outside air into buildings.

What kinds of impacts can we expect in San Francisco?

In all honesty, the energy conservation benefits of trees in San Francisco will likely be lower than just about anywhere else! Why? Mainly because of our very mild climate. Few San Francisco buildings even have air conditioners, so there aren’t so many opportunities to reduce air conditioning use, and it’s rarely cold enough to require heat.

A 2003 study [PDF] on the street trees of San Francisco estimated that the average tree here reduces energy consumption by only about $1. Compare that with the results of a similar study in Berkeley [PDF], where warmer temperatures and bigger trees yieled energy benefits that were 15 times higher.

Still, there are a lot of ways we can plant trees with energy conservation in mind. In a future post, we’ll talk about how to get the most out of your trees with special emphasis on the unusual circumstances of San Francisco. And remember, one of the coolest things about the Urban Forest Map is that it will help estimate how much energy the trees of San Francisco are conserving. Once you've added a tree (with its trunk diameter and species), we'll calculate the energy benefits and add them to the city total.

For more information on how trees help conserve energy and how and what to plant to maximize benefits, visit the Center for Urban Forest Research’s website and check out these two research summaries [PDFs]:

Written by Kelaine Vargas | 15 March 2010

There’s a pretty good chance that any reader of this page likes trees. And we like them for all sorts of reasons: for supporting the tree houses of our childhoods, for housing the birds that sing us awake in the morning, for giving our children a place to swing, for the memories that are attached to them, for their cool shade on brutal summer days, or the shelter from an unexpected rain shower.

But we might not always appreciate just how much work trees are doing to improve our environment. They help clean the air of pollutants, reduce our energy consumption, filter stormwater before it reaches the Bay, and reduce atmospheric carbon dioxide to help fight climate change. In other words, they provide valuable services that help the ecosystem function properly.

Scientists at the US Forest Service’s Center for Urban Forest Research (my former employer!) have been working for decades to quantify these ecosystem services, so that we can have hard data to back up our intuition that trees are awesome (and to help policy makers understand their value). We’re making use of their research to provide what I think is one of the coolest features of the Urban Forest Map—its calculations of these ecosystem services––so you can see how hard the trees in your backyard or in your neighborhood or across San Francisco are working. 

So, consider this an introductory post. For the rest of the week, I’ll tackle each of those four aspects I mentioned above, explain how trees do what they are doing and give some numbers from a recent study of San Francisco done by the Center for Urban Forest Research. In the future, we’ll talk more about less tangible benefits (like wildlife habitat, effects on health, sense of place) too.

Written by Kelaine Vargas | 09 March 2010

Written by The Urban Forest Map | 15 February 2010

Since this is a collaborative project, we could use some collaboration! We’re looking for a short and sweet motto to feature on our home page in bold letters.

Here’s the basic mission of the project:

The Urban Forest Map is a collaborative project among city agencies, tree advocacy groups, and you -- the citizen foresters and nature lovers of San Francisco -- to build an inventory of San Francisco’s urban forest one tree at a time. Just log in online, click the map, and add the trees near you! For each tree added, we’ll calculate the environmental benefits its providing -- how many pounds of air pollutants it’s capturing, how much energy it’s helping conserve, how many gallons of stormwater it’s filtering, and how much carbon dioxide it’s removing from the atmosphere. As we build an inventory together, the information will help planners, city arborists, ecologists, tree advocates, and residents protect and grow the urban forest.

Here are a few thoughts for a motto that we had to help get the ball rolling:

• Tree by tree
• What trees are your neighbors?
• One tree at a time
• Turning gray into green!
• Map your urban forest!

So what do you think? Add your motto in the comments here, or on our Facebook Page, and we’ll take it into consideration! Thanks!