The present paper reports the assessment of the vegetation occupancy rate of the roadside, through analysis of aerial photographs. Using such value the potential of these areas to be employed as carbon (C) sinks was also assessed. Moreover, for the areas suitable for afforestation, the potential for carbon sequestration was estimated considering different species of vegetation, both native (scenario 1) and exotic (formed by
One of the most significant challenges of 21st century is reducing the impact of climate change by developing effective ways of adaptation (
One way to mitigate excessive GHG is by promoting carbon (C) sequestration and storage through increasing C sinks (
Roadsides are a land segment that can be used as a C sink, and which may be considered in afforestation activities, as well as in other ecological functions. Roadsides are areas outside the paved or traveled ways (
In Brazil, for single lane roads, the roadside vegetation is considered an “area for permanent preservation” of 60 meters width, and 100 meters for double track. Additionally, there is the “no built-up” zone where construction of any kind is prohibited, including urban, suburban, and rural expansion, that spans 15 meters on each side of the roadside, as prescribed in the Brazilian Federal Law no. 6766 of 19 Dec 1979 (
According to Brazilian Agency of Terrestrial Transport (
Plants sequester and store C. Moreover, forests have the ability to sequester C for decades, stored in the wood and other organic matter (
The faster growth of forest biomass in the tropics, due to higher temperatures and regular rain (
These facts indicate a viability and success of the proposed project for the generation and sale of C credits. However, carrying out a project for this purpose would require the formulation of specific methodologies, or determining the adequacy of existing ones, to be developed to meet the C credit market rules.
The issue of vegetation along roadsides has been discussed recently in Brazilians organizations, such as National Department of Infra-structure of Transports (DNIT) and São Paulo State’s Department of Roads (DER-SP). It was the target of the 2007 law project no. 623, which concerned “afforestation of roadside”. There is, however, a lack of specific information in the literature regarding the benefits and problems caused by the presence of vegetation, or concrete data on the occupancy of roadsides (
The aim of this study was to evaluate the density of vegetative cover along roadsides for two locations, and to use this data to estimate the potential for these areas to be used as C sinks. In addition, for areas with significant potential to be afforested, we compared the potential for C sequestration using different species of vegetation, both native and exotic.
Two areas were studied, one was a stretch of highway SP-280 (Castello Branco Highway) between the 85 and 95 kilometer markers. The other area was located in the city of Borborema, on highway SP-304 (Highway Deputy Leonidas Pacheco Ferreira) between the 77 and 87 kilometer markers. These areas were selected because they present different kinds of land use and have available updated digital aerial images (
Two sets of aerial photographs were used in this study, both taken in 2006 and available from Escola Superior de Agricultura Luiz de Queiroz - São Paulo University. Photos had 1.0 meter resolution, and were georeferenced, ortho-rectified and mosaiced (
The photos were exported to ArcGIS 9.0 software (
In the extension located in the region of Sorocaba (SP-280), a two-lane highway stretch was analyzed and in a second one, located in the region of Borborema (SP-304), a single lane highway stretch was analyzed, due to the characteristics of the highways. For comparison, the area between the two lanes of Sorocaba stretch was disregarded,
After, we delimited the beginning and end of the 10 kilometers stretch of land areas in both regions. Subsequently, we analyzed the land cover and classified in the domain area according to one of the three categories listed below:
By checking the land cover from photography, we digitalized the polygons according to visual interpretation and after, each polygon was classified according to one of category described above.
Once the study area (roadside) is fifteen meters wide on each side of the road,
where
The occupancy rate of each region was obtained by the following equations (
where
Considering that it was used the same extent of land areas analyzed in two sections, the occupancy rate of the roadside (
In order to compare the amount of C stored in the areas of the State of São Paulo, two different scenarios were analyzed, each one covered by a different type of vegetation. The Scenario 1 was constructed considering native species from the Atlantic Rain Forest (Brazilian Southeastern region). Scenario 2 was constructed considering exotic species commonly used in reforestation activities, represented essentially by species of
The estimation of the amount of fixed C was established considering a period from 2 to 10 years for the two different types of vegetation here considered. This period was established according to bibliographical reference used (
The amount of fixed C by each type of vegetation over the mentioned period was estimated by the average of the increase of C, considering the species studied by Britez et al. (
Afterwords, in order to calculate the amount of stored C during the period 2 to 10 years, it was calculated the average accumulated C by all species in each period. Such calculated value was multiplied by the corresponding period. Then, we summed the values obtained for each one of the two mentioned periods, in order to obtain the total increase of C within the specified period.
The same procedure was carried out for quantifying the accumulation of C by exotic species and considering the same considered period. Thus, considering whole above-ground biomass, we consider that the amount of accumulated C was 12.63 tons of C per hectare for native species and 63.09 tons of C per hectare for exotic species.
The coefficients of variation computed for the native species, in periods from 2 to 5 years and 5 to 10 years were 1.54 and 1.31, respectively. For exotic species, the coefficients were 0.56 and 0.36, respectively. These situations show expressive variation in stored C between the species used, particularly for native species.
The calculation of total increment of C was performed by multiplying the content of fixed C for each scenario of areas considered as not employed. This rate was defined as (1-O.R.A),
where
In order to demonstrate the potential of study area for incrementing and storing of C, we calculated the amount of C fixed in both scenarios (natural forest and exotic species) per kilometer of road. For this, it was determined how many meters of road were required to have an amount of one hectare of land areas, considering its width, or 15 meters to each side of the highway, using the following
where
This means that, approximately for each 0.3 kilometers of highway, we have 1 hectare of land areas. Or, at 1 km of highway, we have approximately 3 ha of land areas. Based on these calculated values in
where
Considering that one ton of C equals 3.67 tons of CO2 (
where
Finally, for demonstrating the roadside’s potential already explored in the areas examined, it was calculated the total area vegetated, and their percentage in relation to the total area with potential for that purpose.
It was observed that crossroads and ramp highways occupy most of the roadside. Shops, gas stations, motels, hotels, industries, among others, are located outside the range area. However the occupation of the roadside occurs through their access.
It was observed different degrees of urbanization. Consequently, an expressive difference between occupancy rates of the roadside was expected. However, this difference was approximately 6%. This means that, although in most urbanized areas there are a greater number of occupations, in the less urbanized there is a larger number of small farms, culminating in a larger number of interchanges and access to cut the roadside.
It was also found that areas that were included in the category forested areas were located with a wide prevalence in permanent preservation areas (riparian vegetation). These areas are along the rivers that passed under the bridges. In the studied areas (out of permanent preservation areas), only a few trees showed up along the entire stretch, and in the two regions, whose areas were not considered. The estimated value of vegetated area in Borborema was 0.11 ha and in Sorocaba region was 0.05 ha.
The values, estimated using the average value of increment of C from the species contained here, present some uncertainties. This is justified by the large difference of fixed C among different species, as evidenced by the variation index, which reached 1.54. The increment value of one species among all considered for the calculation of increment of C in Scenario 1, can be moderately different from the average.
Forests composed predominantly by exotic species, for this case composed basically by
Taking into account the occurrence values for the vegetated area, the areas with potential of forestation, and besides of the potential to act as C sinks, equivalent to 56.71 ha and the average of the vegetated areas two parts is equal to 0.08 ha, the use of this potential is, on average, only 0.3%. This shows how far the areas are for an ideal situation of vegetation cover and how much remains to be done in this the area in a specific occupancy (roads).
Finally, we should consider that the database estimated and presented here reflects a typical situation for São Paulo State. São Paulo State is the Brazilian state that encompasses high rates of deforestation and high highway density. Comparing São Paulo State with whole Brazilian territory, we know that Brazil has many differences of land cover and many biomass (Atlantic forest, savanna -
So, values regarding the amount of fixed C by each type of vegetation should be estimated specifically for each region. The method employed here (the sequence of equations) and the potential of use of
It is important mention that the proposal described here does not have the intention of considering forest products generated by trees, as resin, wood, fruits and oil, only the ecological service fixing C. Thus, the trees planted in pre-established places would remain there until they dead naturally, even in cases of exotic species. This scenario (
Regardless of urbanization level of the region, there was a large difference between the occupancy rates of the roadside.
We have to consider that if the activity of revegetation prioritizes the avoid future climatically driven catastrophes, it is recommend the use of
Taking into account the approximate 131 tons of CO2 km-1 highway to native species, 655 tons of CO2 km-1 of highway for exotic species and the entire grid road in the State, we can observe that there is an opportunity for a feasibility study for this project in order to generate C credits.
The tracks represent an area of enormous potential for sequestration and C storage, and very little of this is explored. Whereas global warming and all the conflicts that revolve around this, these areas should be studied and exploited, can contribute significantly to this end.
For the Campus of UNESP Sorocaba, granted by the framework to develop the project. To “Escola Superior de Agricultura Luiz de Queiroz - USP” for available the aerial photography collection for developing the study. To Dr Dianne Stott (National Soil Erosion Research Laboratory - West Lafayette, IN, USA) by English revision.
Localization of São Paulo State in Brazilian territory (smaller map) and both cities in São Paulo State map.
Illustration of a stretch of highway of Borborema region (single lane).
Illustration of a stretch of highway of Sorocaba region (two lanes).
Characteristics of the Borborema and Sorocaba urban areas. Source: IBGE (
Characteristics | Borborema | Sorocaba |
---|---|---|
Neighboring Counties | Novo Horizonte,Itápolis,Ibitinga,Itajobi | Porto Feliz,Votorantim,Mairinque,Itu,Araçoiaba da Serra,Salto de Pirapora,Iperó |
Distance (km) from Capital | 390 | 90 |
City area (km2) | 553 | 449 |
Population (n inhabitants) | 14 376 | 576 312 |
Human density (n. hab. km-2) | ~ 25 | ~ 1 263 |
Altimetry (m a.s.l.) | 429 | 601 |
Biome | Atlantic forest | Atlantic forest |
Climate | Subtropical Aw | Subtropical |
Occupancy rates for vegetation in the two study areas.
Study Site | Occupancy Rate (%) |
---|---|
O.R.B - Borborema | 0.055 |
O.R.S - Sorocaba | 0.059 |
O.R.A - Mean | 0.057 |
Simulations using both scenarios.
Parameters | scenario 1 | scenario 2 |
---|---|---|
Fixed C in the roadside - CF (tons of C ha-1) | 11.91 | 59.51 |
Fixed C in the roadside per km of road - CFD (tons of C ha-1) | 35.74 | 178.54 |
Amount of CO2 sequestered from the atmosphere per hectare of roadside - CO2F (tons of CO2 ha-1) | 43.72 | 218.41 |
Amount of CO2 sequestered from the atmosphere per km of roadside - CO2FD (tons CO2 km-1) | 131.18 | 655.24 |