## 2 Methodology
### Sampling Sites  
Several forest sites have been sampled between 2008 and 2014 to build significant sample sets of different ecosystems, from temperate to tropical forests (Table 4). Our first airborne lidar measurement was conducted over the Landes forest, located in the southwest of France (44\({}^{\circ}\)N, 1\({}^{\circ}\)W) and mainly composed of maritime pines. The second experiments were carried out, during both winter and summer season, above the Fontainebleau forest in the southeast of Paris (48\({}^{\circ}\)N, 2\({}^{\circ}\)E), which is a temperate deciduous forest composed of evergreen and broadleaf trees. Forests of white oaks and a plantation of poplars in and close to the OHP (Observatoire de Haute-Provence, 44\({}^{\circ}\)N, 6\({}^{\circ}\)E) were also sampled during spring 2012. Recently, airborne lidar measurements were conducted in May 2014 over several tropical forest sites of Reunion Island (21\({}^{\circ}\)S, 55\({}^{\circ}\)E), including rain and montane cloud forests. The tree species included in the sampled sites of temperate forests constitute about 70% of the ones encountered in the western European forests (distribution maps of tree species are available from the European Forest Genetic Resources Programme website: [61]). Temperate forests significantly impact the atmospheric chemistry and mainly the ozone concentration in the troposphere, especially at regional \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Forest Sites** & **Land Cover1** & **Main Tree Species** & **Location** & \begin{tabular}{c} **Sampling** \\ **Date** \\ \end{tabular} & \
\begin{tabular}{c} **Sampling** \\ **Area** \\ \end{tabular} &
\begin{tabular}{c} **Laser** \\ **Shots** \\ \end{tabular} \\ \hline Landes & Temp.Conf. & Maritime pins & 44\({}^{\circ}\)9\({}^{\circ}\)N, 1\({}^{\circ}\)9\({}^{\circ}\)W & September 2008 & 170 ha & 62.3 \(\times\) 10\({}^{3}\) \\  & Temp.Deci. & Oaks, Sylvester pines, & & & November 2010 & 25 ha & 86.9 \(\times\) 10\({}^{3}\) \\ Fontainebleau & Temp.Deci. & Hornbeams and & 2\({}^{\circ}\)38\({}^{\circ}\)E & June 2012 & 4000 ha & 1.2 \(\times\) 10\({}^{6}\) \\  & & Becches & & March 2013 & 5 ha & 41.8 \(\times\) 10\({}^{3}\) \\ OHP2 Region & Temp.Deci. & White oaks & 43\({}^{\circ}\)49\({}^{\circ}\)N, 1\({}^{\circ}\)9\({}^{\circ}\)W & May 2012 & 10 ha & 29.5 \(\times\) 10\({}^{3}\) \\  & Plantation & Poplars & 5\({}^{\circ}\)49\({}^{\circ}\)E & May 2014 & 5 ha & 12 \(\times\) 10\({}^{3}\) \\  & & Labourdonnaisia & 21\({}^{\circ}\)4\({}^{\circ}\)S, 1\({}^{\circ}\)5\({}^{\circ}\)30\({}^{\circ}\)E & May 2014 & 420 ha & 48.4 \(\times\)10\({}^{3}\) \\  & & & & & & \\  & Trop.montane & & 21\({}^{\circ}\)21\({}^{\circ}\)S, 1\({}^{\circ}\)5\({}^{\circ}\)44\({}^{\circ}\)E & May 2014 & 420 ha & 48.4 \(\times\)10\({}^{3}\) \\ \hline \hline \end{tabular}  
* Temp.: temperate, Conf.: conifer, Deci.: Deciduous, Trop.: tropical; 2 OHP: Observatoire de Haute Provence.  
\end{table} 
Table 4: Description of the sites sampled with the airborne lidar ULICE between 2008 and 2014.  
scales [2]. Although composed of small trees, the rainforests of the Reunion Island are representative of many tropical forest areas in terms of density [62]. For the boreal forests, the lidar budget is easier to be built because they are less dense. If the lidar-derived information is reliable for the low-/mid-latitude (tropical/temperate) forests, it will also be reliable for the higher latitudes. Nine plots of \(\sim\)5 ha were studied, representing different biomes.