## 3 Results
### WUE\({}_{\rm s}\) at Different Canopy Heights of Larch Forest
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Leaf Anatomical Properties**} & \multicolumn{3}{c}{**Canopy**} \\ \cline{2-4}  & **Upper** & **Middle** & **Lower** \\ \hline LMA (g/m\({}^{-2}\)) & 30.84 \(\pm\) 2.05 A & 19.15 \(\pm\) 1.22 B & 18.44 \(\pm\) 1.01 B \\ LT (\(\upmu\)m) & 364.00 \(\pm\) 15.06 A & 352.98 \(\pm\) 15.47 A & 345.79 \(\pm\) 13.05 A \\ Upper ET (\(\upmu\)m) & 8.76 \(\pm\) 0.44 A & 10.24 \(\pm\) 0.57 A & 12.93 \(\pm\) 0.91 A \\ SD in upper epidermis (mm\({}^{-2}\)) & 68 \(\pm\) 5 B & 78 \(\pm\) 6 B & 94 \(\pm\) 4 A \\ SL in upper epidermis (\(\upmu\)m) & 26.89 \(\pm\) 1.38 A & 24.93 \(\pm\) 0.39 A & 21.69 \(\pm\) 2.49 A \\ SW in Upper epidermis (\(\upmu\)m) & 9.65 \(\pm\) 0.81 A & 7.89 \(\pm\) 1.39 A & 6.85 \(\pm\) 2.26 A \\ GCA in upper epidermis (\(\upmu\)m\({}^{-2}\)) & 538.2 \(\pm\) 22.52 A & 419.25 \(\pm\) 17.02 B & 363.28 \(\pm\) 12.51 C \\ lower ET (\(\upmu\)m) & 7.34 \(\pm\) 1.48 A & 8.06 \(\pm\) 1.44 A & 9.51 \(\pm\) 0.17 A \\ SD in lower epidermis (mm\({}^{-2}\)) & 107 \(\pm\) 3 B & 110 \(\pm\) 4 B & 140 \(\pm\) 4 A \\ SL in lower epidermis (\(\upmu\)m) & 33.00 \(\pm\) 3.14 A & 29.96 \(\pm\) 1.14 A & 27.37 \(\pm\) 2.68 A \\ SW in Lower epidermis (\(\upmu\)m) & 12.57 \(\pm\) 0.48 A & 10.94 \(\pm\) 1.71 A & 8.32 \(\pm\) 1.75 A \\ GCA in lower epidermis (\(\upmu\)m\({}^{-2}\)) & 637.8 \(\pm\) 21.07 A & 487.52 \(\pm\) 19.2 B & 444.03 \(\pm\) 21.46 C \\ \hline \end{tabular}  
* Notes: Stand mean \(\pm\) within-standard standard deviation; different capital letters in the same column meant significant difference at 0.01 level. LMA is leaf mass per unit area, SD is stomatal density, LT is leaf thickness, ET is epidermis thickness, SL is stomatal length, SW is stomata width and GCA is guard cell area. Different capital letters in the same column mean significant difference at 0.05 level.  
\end{table} 
Table 5: Leaf anatomical characteristics at different height canopies of the larch forest. As can be seen from Table 6, \(\rm WUE_{s}\) of different canopies were significantly negatively correlated with SD (\(p<0.05\)), significantly positively correlated with LMA (\(p<0.05\)) and not significantly correlated with other structural indicators (\(p>0.05\)) except for the upper ET and SL. Therefore, SD and LMA had a strong influence on \(\rm WUE_{s}\) while other indicators had relatively less effect. Random Forest Analysis of Leaf WUE\({}_{s}\) and Influencing Factors at Different Canopy Heights of Larch Forest  
To analyze the extent to which each influencing factor contributes to the \(\rm WUE_{s}\) of larch forests at different canopy heights, we conducted a weighted random forest analysis of 10 influencing factors that have significant or highly significant effects on \(\rm WUE_{s}\), including meteorological factors, photosynthetic parameters and leaf structure (Figure 5). The analysis showed that all 10 factors contributed to the \(\rm WUE_{s}\) of the leaves at different heights but with different degrees. The middle and lower influencing factors have the same rules but are not consistent with the upper canopy. It can also be seen that VPD is the main influencing factor causing the variation of leaf \(\rm WUE_{s}\) in each canopy. In addition, RH and Pn also play an important role in the variation of leaf \(\rm WUE_{s}\) in each canopy. PAR has a higher influence on leaf \(\rm WUE_{s}\) in the upper canopy than in the middle and lower canopy; Ta is an important factor affecting leaf \(\rm WUE_{s}\) in the middle and lower canopy, while LMA and SD contribute relatively less to leaf \(\rm WUE_{s}\).