For the functional diversity study, field data was performed in two different ecosystems during the growing season. Field samples were collected from these locations approximately every two weeks. From the tropical location, 3 grass, 3 tree, and 3 vine species were sampled. From the temperate location only one species of tree was collected, from three different heights. Specific leaf area, leaf dry matter content, and total chlorophyll content were derived. These were used to derive four FD indices. A time series was created for each of these indices for each location. Changes were compared among the two ecosystems and looked at in terms of species diversity and abiotic differences. For the plot-scale study on drought effects, the same field and lab data was used as in the functional diversity study, with the addition of carotenoid analysis. Standard precipitation index (SPI) was calculated spanning 2017 to 2019. Times series of traits were examined with drought level to determine response to drought. For the landscape-scale drought study, the goal was to determine how the temperate forest responded to drought on a larger spatial scale in terms of resilience and resistance capabilities. The studied section of forest in the Netherlands covered 3,300 ha and primarily Douglas Fir. The duration of the drought was determined for this area by calculating SPI values spanning 2018 to 2020. Sentinel images of the study area from each month were downloaded and processed for particular traits and indices. Changes and patterns were analyzed in relation to the SPI time series. All time series of functional diversity indices in both locations showed significant changes throughout the season. The non-diverse site showed increasing correlation and uniformity of trait values. The species diverse area showed no indication of directionality and had relatively more normal distributions and independence of trait values. Overall, this shows that the species diversity provides more consistency in functional trait dynamics over the growing season. In the plot-scale drought study, chlorophyll and carotenoids had the largest responses to the drought in ways that indicated plant stress. Though Douglas Fir has been considered drought resistant, this study reveals that the intensity of the 2018 drought had an impact on its traits and its resilience without sufficient soil moisture relief in the following year. SPI in the study area indicated that 2017 ended in a drought which became a severe drought in 2018 and never fully recovered to “normal” in 2019. This points to the larger problem of ecosystems persisting in a chronic state of drought and the rapid change in precipitation regime. Normalized difference Vegetation Index dropped a small amount each year, showing a general resistance to drought. Leaf area index and fractional vegetation cover responded with a highly fluctuated pattern indicating weak resistance. Some results from the first two objectives have been disseminated in conferences (European Geophysical Union 2019 and 2020). Data has been shared with another Horizon 2020 project (MULTIPLY). Overall it can be concluded from this research that species diversity provides more consistency in FD dynamics over the growing season; and that it is not necessarily an extreme event that can irreparably damage an ecosystem, but rather these events paired with a lack of adequate recovery conditions that push ecosystems past their tipping point. These studies paint a picture of a temperate forest being pushed to its limits – a common situation for natural systems around the world. Tracking these systems’ response to stress gives insight into whether, how and into what they may transition. Mortality and transitioning to a more xeric ecosystem are likely outcomes for this forest if the below average precipitation pattern is to persist into the future.
