Detection of susceptible Norway spruce to bark beetle attack using PlanetScope multispectral imagery

Climate change-related acute or long-term drought stress can weaken forest ecosystems and result in widespread bark beetle infestations. Eurasian spruce bark beetle (Ips typographus L.) infestations have been occurring in Norway spruce [Picea abies (L.) Karst.]-dominated forests in central Europe including the Czechia. These infestations appear regularly, especially in homogeneous spruce stands, and the impact varies with the climate-induced water stress conditions. The removal of infected trees before the beetles leave the bark is an important step in forest pest management. Early identification of susceptible trees to infestations is also very important but quite challenging since stressed tree-tops show no sign of discolouration in the visible spectrum. We investigated if individual spectral bandwidths or developed spectral vegetation indices (SVIs), can be used to differentiate non-attacked trees, assumed to be healthy, from trees susceptible to attacks in the later stages of a growing season. And, how the temporal-scale patterns of individual bands and developed SVIs of susceptible trees to attacks, driven by changes in spectral characteristics of trees, behave differently than those patterns observed for healthy trees. The multispectral imagery from the PlanetScope satellite coupled with field data were used to statistically test the competency of the individual band and/or developed SVIs to differentiate two designated classes of healthy and susceptible trees. We found significant differences between SVIs of the susceptible and healthy spruce forests using the Enhanced Vegetation Index (EVI) and Visible Atmospherically Resistant Index (VARI). The accuracy for both indices ranged from 0.7 to 0.78; the highest among all examined indices. The results indicated that the spectral differences between the healthy and susceptible trees were present at the beginning of the growing season before the attacks. The existing spectral differences, likely caused by water-stress stimuli such as droughts, may be a key to detecting forests susceptible to early infestations. Our introduced methodology can also be applied in future research, using new generations of the PlanetScope imagery, to assess forests susceptibility to bark beetle infestations early in the growing season

The Last Trees Standing: Climate modulates tree survival factors during a prolonged bark beetle outbreak in Europe

Plant traits are an expression of strategic tradeoffs in plant performance that determine variation in allocation of finite resources to alternate physiological functions. Climate factors interact with plant traits to mediate tree survival. This study investigated survival dynamics in Norway spruce (Picea abies) in relation to tree-level morphological traits during a prolonged multi-year outbreak of the bark beetle, Ips typographus, in Central Europe. We acquired datasets describing the trait attributes of individual spruce using remote sensing and field surveys. We used nonlinear regression in a hypothesis-driven framework to quantify survival probability as a function of tree size, crown morphology, intraspecific competition and a growing season water balance. Extant spruce trees that persisted through the outbreak were spatially clustered, suggesting that survival was a nonrandom process. Larger diameter trees were more susceptible to bark beetles, reflecting either life history tradeoffs or a dynamic interaction between defense capacity and insect aggregation behavior. Competition had a strong negative effect on survival, presumably through resource limitation. Trees with more extensive crowns were buffered against bark beetles, ostensibly by a more robust photosynthetic capability and greater carbon reserves. The outbreak spanned a warming trend and conditions of anomalous aridity. Sustained water limitation during this period amplified the consequences of other factors, rendering even smaller trees vulnerable to colonization by insects. Our results are in agreement with prior research indicating that climate change has the potential to intensify bark beetle activity. However, forest outcomes will depend on complex cross-scale interactions between global climate trends and tree-level trait factors, as well as feedback effects associated with landscape patterns of stand structural diversity

Alaska Mean Monthly Precipitation in 2010

The folder includes the 2010 average monthly precipitation across the state of Alaska as a raster image file. The spatial resolution is 60-m and the geographic projection is NAD 1983 Alaska Albers.Ye

Alaska National Land Cover Data 2011

The NLCD 2011 map of Alaska is a raster image file that includes different land cover types. The spatial resolution is 30-m and the geographic projection is NAD 1983 Alaska Albers.Ye

Alaska Slope Map

We prepared a slope map of Alaska at 60-m spatial resolution using the Alaskan Digital Elevation Model (DEM). The geographic projection was set at NAD 1983 Alaska Albers.Ye

Alaska Map of Distance to Towns

The Alaska map of distance to towns is a raster image file that includes Euclidean distance value from the Alaska towns and cities. We prepared the map at 60-m spatial resolution using a vector map of the Alaska towns and cities. The geographic projection was set at NAD 1983 Alaska Albers.Ye

Alaska Map of Bark Beetle Pseudo-Absence

We created a shapefile of 5000 pseudo-absence points, with a minimum Euclidean distance from each other of 1-km across Alaska, as a background dataset with which to compare bark beetle presences. The 5000 random point locations were generated in ArcMap 10.4 (ESRI Inc., Redlands, CA), with the geographic projection of NAD 1983 Alaska Albers.Ye

Alaska Map of Bark Beetle Presence in 2016 and 2017

A shapefile of 68 species locations, surveyed by the USFS from 2016 to 2017, includes 3 bark beetle species. The geographic projection of the map was set at NAD 1983 Alaska Albers.Ye

Alaska Map of Distance to Main Roads

The Alaska map of distance to main roads is a raster image file that includes Euclidean distance value from the Alaska main roads. We prepared the map at 60-m spatial resolution using a vector map of the Alaska main roads. The geographic projection was set at NAD 1983 Alaska Albers.Ye

Alaska Map of Distance to Coastline

The distance to coastline map of Alaska is a raster image file that includes Euclidean distance value from the Alaska coastline. We prepared the map at 60-m spatial resolution using a vector map of the Alaska coastline. The geographic projection was set at NAD 1983 Alaska Albers.Ye