Measuring Agroforests

In agroforests, more than 40 tons of food per hectare per year can be produced. This high productivity is possible, among other factors, because of the diversified production on the same piece of land. It is a myth, therefore, to think that agroforests produce little. This myth is sustained by the illusion that high productivity is only possible by controlling nature with heavy machinery, chemical fertilizers, and pesticides.

Moreover, unlike conventional agriculture, which usually produces much less per area, agroforests also produce biodiversity, increase soil fertility, and remove carbon dioxide from the atmosphere—not elsewhere, but in the same productive area.

To get an idea of how much carbon agroforests are removing from the atmosphere, a study was conducted between 2011 and 2012 on sixteen agroforests, with ages ranging from 1 to 15 years, with areas between 0.3 and 2.0 hectares, and managed by different families associated with Cooperafloresta. In each of these agroforests, five plots (10 x 10 meters) were established, within which all plants taller than 1.5 meters were identified, and their heights and diameters were measured, mapping out the position of each one within the plot.

The first conclusions of this study showed the effectiveness of agroforests in conserving and increasing biodiversity: 194 species of shrubs and trees were identified in the sixteen agroforests studied, with the majority (89%) of species being common to the Atlantic Forest biome. On average, 37 species were identified per agroforest. Most of the plants in these agroforests were planted (61%), while the rest (39%) came from natural regeneration, which is maintained and stimulated. Since the planting is quite dense, the plant density in agroforests is 7,231 plants per hectare.

With this high diversity of species and plant density, the farming families who practice agroforestry have contributed to the increase in biodiversity not only in their own areas but also through the pollination of flowers and seeds for the recovery of other areas in the region, partnering with a wide variety of insects, birds, bats, and rodents that transport this plant biodiversity.

And How to Measure Carbon Fixation?

With the data on all the plants measured in the survey, it was possible to identify which ones appear most frequently in gardens and which ones contribute the most, collectively, with the greatest area of aboveground biomass and trunks. To study carbon fixation in agroforests, the 30 species that showed the highest combination of these characteristics (called the Importance Value Index) were initially selected. An adult plant (with a trunk diameter greater than 5 cm) of each of these 30 species was then cut down to determine how much each one weighed in its biomass. For banana trees, for example, one of the species with the highest importance value, 15 plants from each of the agroforests were cut down for an average calculation. Knowing the biomass and diameter values and the height of all measured plants, it was possible to create equations to estimate the biomass of the aboveground part (trunk, branches, and leaves) of the agroforests as a whole.

For this study, plants with a trunk diameter smaller than 5 cm were used. Ten 10 m² plots were established in different agroforests. In addition to being cut, these species of plants that did not reach this diameter were also dried and weighed to estimate the aboveground biomass. It was known that in the studied area, the ratio between the biomass with seeds and the biomass with trunks and branches was 1.0 for planted species. Thus, it was known how much woody biomass was stored in an agroforest by its age. However, the biomass of living plants is not the only form of carbon storage in agroforests. Pruning branches and trees is a very frequent practice in these areas. Part of the carbon in this material is incorporated into the soil through the action of soil microorganisms. According to studies by researchers at the Federal University of Rio Grande do Sul, conducted over eleven years in no-till areas, this ratio is 0.146. This means that for every ton of branches and leaves deposited on the soil in no-till areas, the amount of carbon from this material is incorporated into the soil through soil microorganisms.

How Much Carbon Dioxide Do Agroforests Remove from the Atmosphere?

The results indicated that, considering only the aboveground part (trunk, branches, and leaves) of plants with a trunk diameter greater than 5 cm, young agroforests (3 to 5 years old) store an average of 2.8 tons of carbon per hectare. Agroforests aged 4 to 9 years store 11.6 tons of carbon in the aboveground part of their plants. The trunks, branches, and leaves of plants in older agroforests (10 to 15 years old) store an average of 31.4 tons of carbon per hectare.

For the aboveground part of plants with a trunk diameter of less than 5 cm, the average carbon stock was 4.5 tons per hectare.

Combining these data with the estimated biomass of the roots (20% of the aboveground biomass), it was possible to determine the amount of carbon stored in the biomass of all plants in the agroforests:

Carbon Stock in the Plants of Agroforests of Farmers Associated with Cooperafloresta:

Age of Agroforests (years) and Carbon Stock (tons per hectare):

• 1 to 3: 8,8 t/ha

• 4 to 9: 19.4 t/ha

• 10 to 15: 43.0 t/ha

When pruned and collected, the weight of the pruned material, as well as the percentage of carbon in the collected material, were evaluated. Only the dry weight of the pruned material was included in the calculation of carbon quantity in the soil, because the carbon in the foliar part decomposes rapidly and is re-emitted as CO2. Therefore, the pruned material incorporated only 0.6 tons of carbon per hectare in older agroforests (10 to 15 years old).

Due to this pruning, that is, from the microbial degradation of the pruned material, in agroforests aged 1 to 3 years, only 1.6 tons of carbon per hectare were incorporated into the soil. In agroforests aged 4 to 9 years, this amount was 3.5 tons of carbon, and in agroforests aged 10 to 15 years, 2.6 tons of carbon in average were incorporated into the soil.

These results show how the practice of pruning helps not only the regrowth of pruned plants and the entry of light for shorter plants and trees, but also the strengthening of the soil.

Adding the carbon stock in the aboveground part of the plants to the carbon stock in the soil, it was possible to affirm that in 15 years, agroforests associated with Cooperafloresta removed 60.5 tons of carbon per hectare from the atmosphere.

Annual Increase in Carbon in the Agroforests of Farmers Associated with Cooperafloresta:

Age of Agroforests (years):

• 1 to 3: 4.5 t/ha

• 4 to 9: 6.7 t/ha

• 10 to 15: 6.5 t/ha

Many plants in younger agroforests (1 to 3 years old) are still growing rapidly and, therefore, removing a lot of carbon from the atmosphere. The same occurs with agroforests aged 4 to 9 years. In older agroforests (10 to 15 years old), the increase in carbon stock was smaller than in the first 10 years. Nevertheless, it was still considerable, with an average of 6.6 tons of carbon per hectare incremented annually.

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