The study by researchers from the “Phytoremediation and Environmental Mitigation” (Fitorimedio e mitigazione ambientale) group at IBE-CNR analyzes the ecological footprint of plants used in the design of a structure in Italy, whose design and construction involved the integration of 182 trees of 36 species, 1,749 plants of an evergreen hedge known as Ligustrum Japonicum, 3,906 shrubs, and a 7,491 m2 public lawn in a low-environmental-impact residential complex, also equipped with photovoltaic panels.

In total, the vegetation present in three-quarters of a hectare leads to the sequestration of 30.55 tons of CO2, the release of 20.1 tons of oxygen, and the removal of 43.4 kilograms of pollutants (gaseous and particulate pollutants – ozone, nitrogen dioxide, sulfur dioxide, PM10, and PM2.5), and the emission of 51.7 kilograms of volatile organic compounds (VOCs). They also reduce surface runoff of rainwater by 4 m3/year.

Analysis by vegetation type

The 182 trees belonging to 36 species have the capacity to sequester 2.3 tons of CO2 from the atmosphere each year and release 1.7 tons of oxygen (O2).

“These plants also perform the important function of purifying the air by removing 8 kg of pollutants from the atmosphere each year, most of which is ozone (O3, 6.5 kg), which is very harmful to the health and well-being of the environment and people,” reads the group’s report.

In total, the trees are capable of reducing surface runoff from rainfall by 0.7 m3/year and emitting 14.3 kg of volatile organic compounds (VOCs) annually, which are volatile hydrocarbons that can improve air quality by reducing atmospheric ozone levels.

In addition to these benefits, there are also those associated with the 1,749 Ligustrum Japonicum plants.

“The 1,749 plants are capable of sequestering 11.2 tons of CO2 from the atmosphere each year and releasing 7.7 tons of O2. The same plants have already accumulated 31 tons of CO2 in their biomass and remove 8.9 kg of pollutants from the atmosphere each year, most of which is O3 (6.9 kg),” the report states.

The 1,749 plants also emit 25.4 kg of VOCs annually and are capable of reducing surface runoff of rainwater by 1.1 m3.

The 3,906 shrubs sequester 14.5 tons of CO2 from the atmosphere each year,
produce 10.7 kg of oxygen, and have accumulated 43.1 tons of CO2 in their biomass.

The shrubs remove 26.5 kg of pollutants from the atmosphere each year, most of which is O3 (21.6 kg).

Each year, the shrub species emit 12 kg of VOCs and help reduce surface runoff of rainwater by 2.2 m3.

As for lawns, the study estimates that the Ecovillage’s public lawn, which covers an area of 7,491 m2 and is composed of a mixture of crabgrass, fescue, and clover, sequesters approximately 2.55 t/year of CO2.

Analysis by tree and shrub species

The study also reports on the ecosystem services provided by the various plants used in the structure.

The alder (Alnus x spaethii) contributes to CO2 sequestration with approximately 404 kg and an accumulation of approximately 6,918 kg, followed by the poplar (Populus alba) with 394 kg and 6,044 kg of accumulated CO2. These are followed by elm, cherry, aspen, curly maple, southern ash, and downy oak.

Alder (Alnus x spaethii) removes approximately 3 kg of pollutants annually and poplar (Populus alba) 2.1 kg, ranking in the top two positions for pollutant sequestration as well.

Of the 36 tree species, 13 do not emit volatile organic compounds (VOCs), the most abundant of which are ash and lime trees, while the species that contribute most to isoprene emissions are poplar (Populus alba) and cork oak (Quercus suber), and alder for monoterpenes (Alnus x spaethii).

Moving on to shrub species, Abelia edward goucker sequesters 1,446 kg of CO2 annually, followed by Rosa double knock out with 1,033 kg.

The species that remove the most pollutants annually are Ligustrum ovalifolium (1.9 kg), Viburnum opulus sterile (1.8 kg), Spiraea x vanhouttei *basitona (1.7 kg), Rosa chinensis “mutabilis” (1.7 kg), Viburnum opulus (approx. 1.6 kg), Rhyncospermum jasminoides (1.5 kg), Rosa aspirin (1.3 kg), Rosa double knock out (1.3 kg), and Rosa pink double knock out (approx. 1.2 kg).

Moving on to VOCs, dogwood (Cornus sanguinea) is the largest emitter of monoterpenes.

Methodology

The project, known as the Montale Ecovillage, is located in Castelnuovo Rangone, in the province of Modena, in northern Italy. The working group estimated the main ecosystem services provided by the plants present, such as: the accumulation and sequestration of carbon dioxide (CO2) and atmospheric pollutants, the production of oxygen, the reduction of surface runoff of rainwater, and the emission of volatile organic compounds. The study provides both an estimate of these benefits and a methodology for the estimate itself.

The study uses data on the sequestration and accumulation of CO2 and pollutants, as well as the emission of volatile organic compounds, from the i-Tree database. Eco v 6.0.37, implemented and updated by the Forest Service of the United States Department of Agriculture (USDA) with the support of the IBE-CNR research group.

To evaluate the ecosystem benefits offered by the green area that makes up the Ecovillage structure, the researchers’ analyses are based on data processed by the “Phytoremediation and Environmental Mitigation” group of the IBE-CNR.

This database does not report the systemic benefits of the Gaura and Gaura nana shrub species. The database also provides a calculation model that uses various algorithms that consider structural data, air pollution data, and local micro-meteorological conditions. Meteorological data and air quality data are acquired independently by the i-Tree Eco model.