Studying our orchards can help POP better understand the different ways in which community orchards support our neighbors, understanding they already bring people together, provide food, and keep our city beautiful. Yet the environmental benefits or urban orchards, especially for climate, remain less understood.

This led POP, over the past year, to partner with researchers from the University of Pennsylvania to understand how much carbon our orchards could capture via sequestration and/or reduce via localized production. POP has long talked about this ‘double carbon impact’, but we wanted to see if it was possible to begin to quantify it.

Our collaboration focused on measuring carbon sequestration, the process by which trees pull CO2 and store it in their woody mass —their trunks, branches, and roots. Much of the existing literature on carbon sequestration focuses on trees growing in forests or commercial farms. Our collaboration explored the possibilities of sequestering carbon at a smaller urban scale, a calculation we hope could be replicated by other orchards throughout the country.

Measurement of DBH being taken, which involves measuring the circumference of a tree 4.5 feet above the ground (Photos: Benjamin Stahl)

How we Collected Data

To explore how much carbon our orchards store, we surveyed 165 trees through six POP supported orchards in North and West Philly. We used iTree, a free software developed by the United States Forest Service, to conduct some of our calculations. iTree has become a standard tool for researchers to study the potential environmental impacts of trees, due to the abundance of tree measurements and calculations embedded in the software.

At each orchard, we measured five key features for each tree: diameter at breast height (DBH), canopy width, tree height, base height, and canopy height. To calculate DBH, the circumference of the tree was measured 4.5 feet above the ground, then divided by pi. The base height is the height below the first tree fork, the area where the tree begins to split into different branches, while the canopy height measures the height above the first tree fork.

Simultaneously, while we were collecting data at the different POP-supported orchards, the research team also built a model to study the carbon offset of local food production, the amount of carbon saved by growing locally instead of importing food from greater distances. Four fruits—cherries, figs, peaches, and plums—were chosen, due to their planting across POP orchards and abundance at supermarkets throughout the region.

Using R, a free statistical computing software, the team compared packaging, transportation, and other differences between locally produced and commercially imported fruits, to better understand their carbon impacts.

What We Found at the Orchards

After information on each tree survey was entered into iTree, figs were shown to have sequestered the most carbon.  (Graph: Benjamin Stahl)

After completing our tree measurements at the various orchards, we were impressed by how well the orchards performed sequestering carbon, sequestering nearly 1,679 pounds of carbon annually and storing around 30 tons of carbon each year. Even the smallest orchard measured, at Monumental Baptist Church in West Philly, was able to sequester nearly 4 tons of carbon across six trees.

Within each orchard, certain tree species performed better at sequestering carbon than others. For example, Paw Paws were abundant throughout orchards, but performed poorly, likely due to their young age and corresponding smaller size.

Sweet almonds and figs, interestingly, were not the most abundant trees measured across orchards but performed the best at sequestering and storing carbon. This is not to say that orchards should prioritize planting particular trees only for their carbon benefits; rather, planting a diverse set of trees and woody shrubs generally produces the greatest set of ecological benefits, including carbon, water, fruit, shade, cooling, soil health, habitat, and other important effects.  

What we Found with Transportation

Through the statistical model, we were able to document substantial benefits to producing food locally that help avoid emissions from long-distance food travel. The analysis showed carbon use of only 30-40% of commercial counterparts for all four fruits studied. POP already harvests its own food and does not require plastic packaging to transport fruits, reducing the use of non-biodegradable packaging found throughout commercial crop transport. Locally grown fruits do not require intense refrigeration that is necessary to preserve fruits over long distances. Fruits like peaches and figs travel the greatest distances to reach Philadelphia supermarkets, often from places like Turkey or Chile when they are off season locally. Overall, growing locally poses greater environmental benefits for the climate and the community.

Going Forward

Orchards help to offset emissions from long-distance travel and sequester large amounts of carbon locally. Understanding these carbon effects is important for appreciating orchards’ contributions to climate adaptation, even as carbon effects are just part of a larger set of ecological benefits of urban orchards.

While most POP-supported orchards may be small in scale, they provide impactful environmental resources for communities in greater Philadelphia. Urban orchards can be a powerful small-scale solution to climate change, something that can grow with the community. We’re excited to play our part in helping sequester carbon locally and learn more about the many impacts of orchards with our volunteers and neighbors who come join us.  

A more formal report from Penn’s Kleinman Center will be produced soon, which we will share at a later date.

This POP Blog was written by Ben Stahl

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