Immediate and carry‐over effects of insect outbreaks on vegetation growth in West Greenland assessed from cells to satellite

Abstract

Aim Tundra ecosystems are highly vulnerable to climate change, and climate–growth responses of Arctic shrubs are variable and altered by microsite environmental conditions and biotic factors. With warming and drought during the growing season, insect‐driven defoliation is expected to increase in frequency and severity with potential broad‐scale impacts on tundra ecosystem functioning. Here we provide the first broad‐scale reconstruction of spatio‐temporal dynamics of past insect outbreaks by assessing their effects on shrub growth along a typical Greenlandic fjord climate gradient from the inland ice to the sea. Location Nuuk Fjord (64°30′N/51°23′W) and adjacent areas, West Greenland. Taxa Great brocade (Eurois occulta L.) and grey willow (Salix glauca L.). Methods We combined dendro‐anatomical and remote sensing analyses. Time series of ring width (RW) and wood‐anatomical traits were obtained from chronologies of >40 years established from 153 individuals of S. glauca collected at nine sites. We detected anomalies in satellite‐based Normalized Difference Vegetation Index (NDVI) related to defoliation and reconstructed past changes in photosynthetic activity across the region. Results We identified outbreaks as distinctive years with reduced RW, cell‐wall thickness and vessel size, without being directly related to climate but matching with years of parallel reduction in NDVI. The two subsequent years after the defoliation showed a significant increase in RW. The reconstructed spatio‐temporal dynamics of these events indicate substantial regional variation in outbreak intensity linked to the climate variability across the fjord system. Main conclusions Our results highlight the ability of S. glauca to cope with severe insect defoliation by changing carbon investment and xylem conductivity leading to high resilience and rapid recovery after the disturbance. Our multiproxy approach allows us to pinpoint biotic drivers of narrow ring formation and to provide new broad‐scale insight on the C‐budget and vegetation productivity of shrub communities in a widespread arctic ecosystem.

Divergence of Arctic shrub growth associated with sea ice decline

“…The implications of increasing heterogeneity of Arctic shrub growth trajectories to sea ice-induced changes in regional climate might be widespread, including permafrost degradation and heat flux alteration in response to changes in vegetation cover and albedo ( 45 ), increased wildfire risk ( 53 ), and susceptibility to insect outbreaks ( 54 ). Furthermore, the declining growth response revealed for decreasers might be indicative of more limited woody biomass production and reduced carbon sequestration in a pool (i.e., wood) with a long mean residence time.…”

“…We acquired both published and unpublished deciduous shrub-ring chronologies that were distributed throughout the Arctic region [ SI Appendix , Table S1 , and the Dryad Digital Repository: https://doi.org/10.5061/dryad.kh1893248 ( 57 )] and covered, if possible, the entire 40-y-long period of passive microwave satellite-based estimates of Arctic SIE (1979 to the present). In order to perform a comparable study at the biome level, our synthesis focused on two shrub genera of commonly studied ( 21 – 25 , 33 , 45 , 48 , 54 ) and widespread deciduous shrubs: Betula and Salix . We analyzed both shrub-ring chronologies and shrub-ring series from individual shrubs.…”

Annual air temperature variability and biotic interactions explain tundra shrub species abundance

“…These points further stress the importance of in situ measurements of abiotic conditions for predicting tundra species distributions (Lembrechts et al, 2019). In addition, future studies should consider biotic interactions across trophic levels such as browsing (Olofsson et al, 2009;Vowles et al, 2017) or insect herbivory (Prendin et al, 2019), and temporal dynamics, for instance, to include different successional stages and abundance changes, as well as effects of intra-specific trait variation on the outcome of biotic interactions among shrubs (e.g., Violle et al, 2012;Westerband et al, 2021). Addressing these knowledge gaps could further improve understanding of long-term tundra shrub responses to changing abiotic and biotic environments.…”

Pine Looper Bupalus piniaria (L.) Outbreaks Reconstruction: A Case Study for Southern Siberia

“…The impact of needles loss (in terms of improvement of the model) is comparatively small. The advantage of including the defoliation factor in our model is commensurate with [42] and far less than in [41,43]. Nevertheless, the statistical significance of the differences between climate only and climate/defoliation models is very high for all three sites.…”