# Monitoring Forest Phenology in a Changing World
## 3 Emerging Technological Advancements
### Molecular Methods for Understanding Phenology  
New molecular tools are being developed to monitor phenology and will become integrated within larger scale monitoring frameworks in the coming years [89]. Molecular phenology works through the quantification of gene expression from plant samples using qPCR, microarray and RNA-sequencing methods, creating high-resolution molecular phenology data [168]. For example, flowering phenology can be forecast by examining the regulatory expression dynamics of flowering genes [169]. This allows the immediate detection of 'invisible' plant phenological changes, rather than the delayed detection that is gained from monitoring just the end phenology such as the presence of flowers [89; 168].  
Molecular techniques are expensive and require physical samples to be extracted from individual plants, meaning they are unlikely to be widely applied for basic monitoring of phenology. One approach may be using eDNA or eRNA sampling to collect molecular information on phenology from the soil or air surrounding plants. eDNA sampling has become widespread in ecology, with sample kits becoming relatively inexpensive in recent years [170], and although RNA degrades faster in the environment, eRNA sampling kits are being refined [171]. Therefore, eRNA could be used as a means for larger scale molecular monitoring by sampling population level gene expression related to phenological change.  
Where in situ molecular monitoring is not feasible, but collection of plant reproductive material is, provenance trials--the process of taking seeds of species from different areas and planting them together in an experiment--may offer a solution. Provenance trials allow molecular monitoring to take place in controlled, easily accessible environments where they can also help us understand and mitigate the effects of climate change on species whose phenology put them at risk [172]. They can do this by providing experimental information on which genotypes may be able to survive the changing climate and how different phenological forms can arise due to variable responses to climate change [173; 172]. In regions where tree species span vast areas of climate, provenance trials have been used to examine the variation in phenological forms [173; 172], although to date this approach has largely been restricted to temperate species.  
We expect, however, that the strength of molecular methods is their promise to provide much clearer insight into the physiological processes driving phenology, rather than as a direct contribution to directly monitoring phenology. These insights will be central to providing the data needed to develop predictive models examining the abiotic and biotic cues driving phenological events. Such understanding, will, in turn, be needed to allow us to predict the evolutionary responses of phenological patterns as a result of environmental change [89; 168]. The higher accuracy and greater responsiveness of molecular phenological data means it can be used to parameterise models with only one or two years of data where more traditional, non-molecular methods may require decades of data [168; 169]. The construction of phenological models based on this molecular understanding has potential to then inform other monitoring activities. For example, by building more accurate predictive models, we can better direct expensive, high-resolution satellite remote sensing towards locations that are expected to have change at a particular location and time, saving both money and researcher time.