# Characterizing Growing Season Length of Subtropical Coniferous Forests with a Phenological Model
## 3 Results
### Inter-Annual Climate Control Factors for Ecosystem-Scale Phenological Processes  
Ecosystem-scale phenological processes (SOS, EOS, and LOS) showed different sensitivities to annual weather variables by site (Table 4). At the mesic site, SOS was sensitive to PAR in early spring (January to March) and showed a significant negative correlation, i.e., with the increase in PAR in early spring, SOS was significantly advanced (\(p<0.01\)), and then the growing season was significantly extended (\(p<0.05\)). EOS has a significant positive correlation with annual precipitation (\(p<0.05\)), i.e., as the annual precipitation increases, EOS appears to be significantly delayed.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline  & & & \multicolumn{3}{c}{**Fire Year**} & \multicolumn{3}{c}{**Non-Fire Year**} \\ \hline
**Time Scale** & **Climate Variable** & **SOS** & **EOS** & **LOS** & **SOS** & **EOS** & **LOS** \\ \hline Annual & \(T_{a}\) anomaly & \(-0.33\) & \(0.05\) & \(0.25\) & \(0.06\) & \(0.35\) & \(0.04\) \\  & Precipitation anomaly & \(0.31\) & \(0.11\) & \(-0.23\) & \(-0.11\) & \(-0.30\) & \(0.04\) \\  & PAR anomaly & \(-0.30\) & \(0.05\) & \(0.28\) & \(-0.05\) & \(-0.34\) & \(-0.13\) \\ March & PAR & \(\mathbf{-0.62}\)* & \(0.36\) & \(\mathbf{0.59}\)* & \(-0.29\) & \(-0.17\) & \(0.13\) \\  & \(T_{a}\) & \(0.09\) & \(-0.21\) & \(-0.15\) & \(-0.07\) & \(\mathbf{0.51}\)** & \(0.28\) \\  & Precipitation & \(0.39\) & \(-0.13\) & \(-0.35\) & \(0.10\) & \(-0.17\) & \(-0.08\) \\ Early spring & PAR & \(-0.38\) & \(0.3\) & \(0.4\) & \(-0.11\) & \(-0.34\) & \(-0.08\) \\  & \(T_{a}\) & \(\mathbf{-0.50}\)* & \(\mathbf{0.56}\)** & \(\mathbf{0.57}\)** & \(-0.10\) & \(\mathbf{0.53}\)** & \(0.32\) \\  & Precipitation & \(0.06\) & \(0.21\) & \(0.02\) & \(-0.17\) & \(-0.47\) & \(-0.01\) \\ \hline \end{tabular} Bold fonts represent significant relationships, * \(p<0.05\); ** \(p<0.01\).  
\end{table}
Table 3: Spearman correlation coefficients relating start of growing season (SOS), end of growing season (EOS) and LOS (length of growing season) to interannual, March, and early spring (January to March) air temperature (\(T_{a}\)), PAR and cumulative precipitation anomalies by site. \(T_{a}\) (\({}^{\circ}\)C) and PAR (\(\mu\)mol m\({}^{-2}\) s\({}^{-1}\)) were estimated as averages, precipitation as cumulative, for years with and without prescribed fire.  
At the intermediate site, SOS was sensitive to annual precipitation and spring PAR (March), i.e., as annual precipitation increased, SOS was significantly delayed (\(p<0.05\)), but as early spring PAR increased, SOS was significantly advanced (\(p<0.01\)). EOS was sensitive to the precipitation at late autumn (October to November). As the precipitation at late autumn increased, EOS was advanced. LOS was also sensitive to precipitation (annual and late autumn) and spring PAR. As precipitation increased, LOS was shortened (\(p<0.01\)), and as spring PAR increased, LOS was extended (\(p<0.01\)).  
At the xeric site, SOS, EOS, and LOS were all sensitive to the air temperature, i.e., as the air temperature warmed, SOS was significantly advanced and EOS was significantly delayed (\(p<0.01\)), thereby significantly extending the growing season (\(p<0.05\)). However, similar to the intermediate site, precipitation had a significant positive correlation with SOS (\(p<0.05\)) and a significant negative correlation with LOS (\(p<0.01\)), i.e., as annual and late autumn precipitation increased, SOS was significantly delayed and EOS was significantly advanced, thus significantly shorten the growing season (\(p<0.05\)).  
In general, we believed that the phenology process of mesic and intermediate sites was more sensitive to PAR in spring, while the xeric site was more controlled by air temperature. More annual precipitation was beneficial to the mesic site, but excess precipitation in late autumn may have a negative impact on xeric and intermediate sites.