# Monitoring Forest Phenology in a Changing World
## 2 Monitoring Phenology
### A Brief Description of Phenological Monitoring Methods
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Moonitoring Method**}} & \multirow{2}{*}{**Measurement**} & \multicolumn{2}{c}{**Spatial Resolution**} & \multicolumn{2}{c}{**Temporal Resolution**} & \multicolumn{2}{c}{**Lagrangian Cost per km\({}^{2}\) (s)**} & \multicolumn{2}{c}{**Acquisition**} & \multicolumn{2}{c}{**Quantity Dumbility**} & \multicolumn{2}{c}{**Adaquisition**} & \multicolumn{2}{c}{**Data Frequency**} & \multicolumn{2}{c}{**Frequency**} & \multicolumn{2}{c}{**Frequency**} \\  & & & **(nm)** & & **(h)** & & **km\({}^{2}\) (s)** & & **(s)** & & **(s)** & & **(s)** & & **(s)** \\ \hline \multirow{4}{*}{**Moonitoring Method**} & Direct & 0.10-40 & 0.1-24 & 60 & 60 & High & Low & Medium & NA & High & Low & \begin{tabular}{c} Direct \\ measure/ \\ \end{tabular} & \begin{tabular}{c} Direct \\ lime \\ \end{tabular} \\  & \begin{tabular}{c} Indirect– \\ Mass \\ Pruy \\ \end{tabular} & 1-2 & 24 & 220k; 60 & NA & NA & NA & Low & Low & Low & Medium & \begin{tabular}{c} High \\ Indirect \\ peaky \\ \end{tabular} & \begin{tabular}{c} High \\ Indirect \\ peaky \\ \end{tabular} & \begin{tabular}{c} High \\ Indirect \\ peaky \\ \end{tabular} & \begin{tabular}{c} High \\ Experimental \\ degree in \\ processing \\ \end{tabular} & \\ \hline \multirow{4}{*}{**Moonitoring Method**} & Indirect– \\ \cline{2-10}  & Wood & 0.5-10 & 0.5-24 & 2-30,000 & NA & NA & NA & Low & High & High & High & High & \begin{tabular}{c} The characteristics/ \\ Rogitives \\ high \\ quantities \\ \end{tabular} \\  & \
\begin{tabular}{c} Direct \\ lime \\ \end{tabular} & 1-2 & 24 & 50k; 60 & NA & NA & Medium & Low & Medium & Medium &
\begin{tabular}{c} Inexpensive/ \\ Large labour \\ cost \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cont. through time as phenophases such as leaf flush or leaf senescence cause variations in these chromatic coordinate values [42; 106]. The third category consists of approaches that measure direct or indirect proxies of phenology. Collection traps exist in many forms but generally consist of a net raised above the ground under trees or plants that are being monitored [107]. They work by collecting any fallen material from a focal tree, which is then weighed or counted to estimate the quantity of phenology in the canopy. Collection traps have been used in a range of environments to assess leaf phenology [108; 109], fruit and seed phenology [107; 110; 111; 112], and their connections to other aspects of ecosystem function such as carbon fluxes [108]. Accelerometers, dendrometers, and micro-coring approaches monitor phenological activity through the approximation of tree mass or growth at a given time [26; 29; 46]. Accelerometers and dendrometers attach to trees and record movement and growth which can be used to approximate the presence of a phenological change [26; 29]. Leaf emergence and leaf drop alter the aboveground tree mass, resulting in a change that is detectable by the accelerometer or dendrometer [29]. Such measures correlate closely with visual assessment of leaf emergence phenology, but to date have failed to accurately detect leaf loss events [29]. Micro-coring consists of taking samples to measure xylem development which is shown to correlate with leaf flush events [26; 46]. Alternatively, eddy covariance flux towers measure CO\({}_{2}\) fluxes to calculate gross primary productivity (GPP) [113], which can indicate the phenological start and end of season dates [27; 114; 115]. Fluxes recorded from eddy covariance towers have also be used to validate satellite-based monitoring of phenology [115].