## 3 Results
### i-Tree Canopy Results  
The MCN cover area, estimated by means of the assessed 803 points, is mainly represented by the 29% trees planted over pervious grounds (TP), 23% impervious area where trees are impractical (IN) and 17% agricultural land (AG) (Table 3).  
The area currently covered by trees within the MCN boundaries was identified in 251 points (TP and TI) and was estimated at 367.26 square kilometres. The area for the potential planting of new trees was identified in 128 points (IP and PP), equal to about 187.28 square kilometres (16% of the entire MCN area), which represents a potential increment of 51% in green spaces. The estimated area needed to plant one million is 80 square kilometres of forests [61]. Thus, around 240 square kilometres would be required to achieve the goal of planting three million trees, which is 30% larger than the identified available area. The analysis performed in this work suggests a current availability for plantations equal to around 2.34 million trees.  
The i-Tree Canopy tool considers a linear correlation between the presence of trees and the functions they provide. In so doing, considering that all available areas will actually be used for tree plantation, the potential scenario presents an estimated 51% increment in terms of benefits related to air pollution absorption (Figure 2a) and carbon sequestrated and stored during trees' lifetime (Figure 2b). A 51% of increment is also estimated for avoided runoff (113 megalitres of water per year) and the hydrological cycle (219,273 megalitres of water per year) of the photosynthesis steps (evaporation, interception, transpiration, potential evaporation, and potential evapotranspiration) (Table 4).  
\begin{table}
\begin{tabular}{l c c} \hline \hline \multirow{2}{*}{**Benefits**} & \multicolumn{2}{c}{**Amount (MI)**} \\ \cline{2-3}  & **Present** & **Potential** \\ \hline AVRO & 221,81 & 334.92 \\ E & 5485.22 & 8282.46 \\ I & 5491.00 & 8291.20 \\ T & 39,447.51 & 59,564.16 \\ PE & 200,226.75 & 302,334.42 \\ PET & 179,330.20 & 270,781.45 \\ Total & 430,202.49 & 649,588.61 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Hydrological benefits from tree coverage in megalitres (MI).  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Cover Class** & **N\({}^{\circ}\) of Points** & **Area (km\({}^{\text{2}}\))** & \(\pm\)**SE (km\({}^{\text{2}}\))** & **\% Cover** \\ \hline TP & 230 & 336.53 & 29.08 & 29\% \\ IN & 187 & 273.61 & 17.50 & 23\% \\ AG & 136 & 198.99 & 15.51 & 17\% \\ IP & 70 & 102.42 & 11.75 & 9\% \\ PP & 58 & 84.86 & 10.70 & 7\% \\ SB & 46 & 67.31 & 9.63 & 6\% \\ GH & 30 & 43.90 & 7.86 & 4\% \\ TI & 21 & 30.73 & 9.64 & 3\% \\ PN & 13 & 19.02 & 5.28 & 2\% \\ WT & 9 & 13.17 & 4.35 & 1\% \\ OT & 3 & 4.39 & 2.61 & 0\% \\ \hline Total Area & 803 & 1174.93 & 30 & 100\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Number of points assessed and estimated area for each cover class.  
Figure 2: Tree benefits: (**a**) amount of air pollution absorbed expressed in carbon monoxide (CO), nitrogen dioxide (NO\({}_{2}\)), Ozone (O\({}_{3}\)), particulate matter (PM10 and PM2.5) and sulfuric dioxide (SO\({}_{2}\)); (**b**) carbon annually sequestrated and carbon stored in trees’ lifetime.  
The increment of the annual economic benefits is more than USD 12.4 million per year, going from almost USD 24.5 million to nearly USD 36.9 million (Table 5); 87% of this value is due to the carbon sequestrated annually by trees. Considering the amount of carbon stored in trees during their lifetime (4261 kt), the final economic value increases by more than USD 270 million, from about USD 530 million in the present scenario to more than USD 800 million in the potential scenario.