Detecting treeline dynamics in response to climate warming using forest stand maps and Landsat data in a temperate forest

Abstract

Background: Treeline dynamics have inevitable impacts on the forest treeline structure and composition. The present research sought to estimate treeline movement and structural shifts in response to recent warming in Cehennemdere, Turkey. After implementing an atmospheric correction, the geo-shifting of images was performed to match images together for a per pixel trend analysis. We developed a new approach based on the NDVI, LST (land surface temperature) data, air temperature data, and forest stand maps for a 43-year period. The forest treeline border was mapped on the forest stand maps for 1970, 1992, 2002, and 2013 to identify shifts in the treeline altitudes, and then profile statistics were calculated for each period. Twenty sample plots (10 × 10 pixels) were selected to estimate the NDVI and LST shifts across the forest timberline using per-pixel trend analysis and non-parametric Spearman's correlation analysis. In addition, the spatial and temporal shifts in treeline tree species were computed within the selected plots for four time periods on the forest stand maps to determine the pioneer tree species. Results: A statistically significant increasing trend in all climate variables was observed, with the highest slope in the monthly average mean July temperature (tau = 0.62, ρ < 0.00). The resultant forest stand maps showed a geographical expansion of the treeline in both the highest altitudes (22 m-45 m) and the lowest altitudes (20 m-105 m) from 1970 to 2013. The per pixel trend analysis indicated an increasing trend in the NDVI and LST values within the selected plots. Moreover, increases in the LST were highly correlated with increases in the NDVI between 1984 and 2017 (r = 0.75, ρ < 0.05). Cedrus libani and Juniperus communis spp. were two pioneer tree species that expanded and grew consistently on open lands, primarily on rocks and soil-covered areas, from 1970 to 2013. Conclusion: The present study illustrated that forest treeline dynamics and treeline structural changes can be detected using two data sources. Additionally, the results will have a significant contribution to and implication for treeline movement studies and forest landscape change investigations attempting to project climate change impacts on tree species in response to climate warming. The results will assist forest managers in establishing some developmental adaptation strategies for forest treeline ecotones.

Sensitivity of Vegetation on Alpine and Subalpine Timberline in Qinling Mountains to Temperature Change

“…Maliheh Arekhi developed a new approach based on the NDVI, LST (land surface temperature) data, air temperature data, and forest stand maps over a 43-year period. The results show that during 1970-2013, the two pioneer tree species continued to expand and grow on open land, mainly in areas covered by rock and soil [36].…”

Comparative Evaluation of the Spectral and Spatial Consistency of Sentinel-2 and Landsat-8 OLI Data for Igneada Longos Forest

“…This alignment is reduced and eliminated by performing the geoshift code with "geoshift" function on images before the pixels were overlaid exactly for further comparison of the two data sets for all investigated variables (B1, B2, B3, B4, B5, NDVI, NDWI and EVI). To explain, performing geo shifting process completely omits the errors caused by the image to image misregistration and images' misalignment with a shift of 15 m to the west (x-direction) and 16 m to the north (y-direction) [45][46][47]. It is worth mentioning that Sentinel images were resampled to 30 meters and shifted to overlay the Landsat-8 OLI images, including B1, B2, B3, B4, B5, NDVI, NDWI and EVI, which are considered to be base images.…”

Impacts of Global Change on the Spatial Dynamics of Treeline in Venezuelan Andes

“…This migration rate appears to be related to an estimated shift of the permafrost limit by +240 m during the last 50 years; they considered the climate warming a primary cause of the observed upward migration of high mountain plants. In a study of the treeline dynamics in response to climate warming in the Mediterranean region of Cehennemdere, Turkey, Arekhi et al (2018) found the geographical expansion of the treeline, with a migration rate of 20-40 m each decade, and the treeline altitude increased to 2,442 m from 2,335 m. In a study based on the supervised classification of historical (1953) and current (2015) aerial photographs on the spatial dynamics of the ecotone of alpine trees in the French Pyrenees, Feuillet et al (2020) observed an upward displacement of the tree line by ∼ 45 m on average, with at an overall rate of 0.73 m year −1 . Furthermore, during the study period, the minimum mean air temperatures increased by 0.6 • C, and the maximum mean air temperatures increased very slightly by 0.14 • C. Telwala et al (2013) surveyed historical (1849-1850) and the recent (2007)(2008)(2009)(2010) data on temperature and endemic species in elevational ranges at the alpine Sikkim Himalaya region and recorded a mean upward displacement rate of 27.53 ± 22.04 m per decade, which make to the montane floras, in particular, highly sensitive to climate change.…”