Evidence of vegetation greening at alpine treeline ecotones: three decades of Landsat spectral trends informed by lidar-derived vertical structure
Monitoring changes in vegetation at high-latitude and alpine treeline ecotones is critical for characterizing changes to carbon and energy budgets, plant species richness, and habitat suitability and is often considered a bellwether of a changing climate. Herein, we used transects of airborne laser...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2018-01-01
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| Series: | Environmental Research Letters |
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| Online Access: | https://doi.org/10.1088/1748-9326/aad5d2 |
| _version_ | 1797748172667224064 |
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| author | Douglas K Bolton Nicholas C Coops Txomin Hermosilla Michael A Wulder Joanne C White |
| author_facet | Douglas K Bolton Nicholas C Coops Txomin Hermosilla Michael A Wulder Joanne C White |
| author_sort | Douglas K Bolton |
| collection | DOAJ |
| description | Monitoring changes in vegetation at high-latitude and alpine treeline ecotones is critical for characterizing changes to carbon and energy budgets, plant species richness, and habitat suitability and is often considered a bellwether of a changing climate. Herein, we used transects of airborne laser scanning (ALS) data to identify alpine treeline ecotones in the Yukon Territory of Canada, and assessed changes in vegetation greenness using a time-series of Landsat imagery over a 30 year period from 1985 to 2015. Specifically, we calculated the enhanced vegetation index (EVI) from annual Landsat composites and assessed temporal trends within 500 m of detected forest-lines (i.e., transition point from continuous forest into treeline ecotones) using Theil–Sen’s nonparametric regression. Across 74 detected treeline ecotones, 27.5% of Landsat pixels displayed a significant positive trend in EVI and 5.6% of pixels displayed a significant negative trend ( p < 0.05). By using ALS data to determine vegetation structural class, we found that non-treed pixels had the highest percentage of significant positive trends in vegetation greenness (40.8%), followed by shrubs (30.5%), with lower percentages in sparse forests (18.9%) and open/dense forests (13.3%). These results suggest herbaceous and shrub vegetation types are undergoing the most significant changes in greenness, likely due to increases in shrub cover and herbaceous biomass in areas associated with these alpine treeline ecotones. The limited increases in EVI in forests likely indicates that vegetation cover is changing less rapidly in forests than in shrub and herbaceous vegetation types. Moreover, EVI may not be capturing increased height growth in forests near the treeline. Combining ALS data and Landsat time-series data provides a useful approach to locate and characterize alpine treeline ecotones, and enables the direct assessment of which vegetation structural classes are experiencing the greatest greening trends, thereby providing new insights to ecosystem change. |
| first_indexed | 2024-03-12T16:02:07Z |
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| institution | Directory Open Access Journal |
| issn | 1748-9326 |
| language | English |
| last_indexed | 2024-03-12T16:02:07Z |
| publishDate | 2018-01-01 |
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| series | Environmental Research Letters |
| spelling | doaj.art-efeb56fa31e24ba08905fb726a2eca6b2023-08-09T14:36:46ZengIOP PublishingEnvironmental Research Letters1748-93262018-01-0113808402210.1088/1748-9326/aad5d2Evidence of vegetation greening at alpine treeline ecotones: three decades of Landsat spectral trends informed by lidar-derived vertical structureDouglas K Bolton0https://orcid.org/0000-0002-4365-2039Nicholas C Coops1https://orcid.org/0000-0002-0151-9037Txomin Hermosilla2https://orcid.org/0000-0002-5445-0360Michael A Wulder3https://orcid.org/0000-0002-6942-1896Joanne C White4https://orcid.org/0000-0003-4674-0373Integrated Remote Sensing Studio, Department of Forest Resources Management, University of British Columbia , 2424 Main Mall, Vancouver BC, V6T1Z4, CanadaIntegrated Remote Sensing Studio, Department of Forest Resources Management, University of British Columbia , 2424 Main Mall, Vancouver BC, V6T1Z4, CanadaIntegrated Remote Sensing Studio, Department of Forest Resources Management, University of British Columbia , 2424 Main Mall, Vancouver BC, V6T1Z4, CanadaCanadian Forest Service (Pacific Forestry Centre), Natural Resources Canada, 506 West Burnside Road, Victoria, BC, V8Z1M5, CanadaCanadian Forest Service (Pacific Forestry Centre), Natural Resources Canada, 506 West Burnside Road, Victoria, BC, V8Z1M5, CanadaMonitoring changes in vegetation at high-latitude and alpine treeline ecotones is critical for characterizing changes to carbon and energy budgets, plant species richness, and habitat suitability and is often considered a bellwether of a changing climate. Herein, we used transects of airborne laser scanning (ALS) data to identify alpine treeline ecotones in the Yukon Territory of Canada, and assessed changes in vegetation greenness using a time-series of Landsat imagery over a 30 year period from 1985 to 2015. Specifically, we calculated the enhanced vegetation index (EVI) from annual Landsat composites and assessed temporal trends within 500 m of detected forest-lines (i.e., transition point from continuous forest into treeline ecotones) using Theil–Sen’s nonparametric regression. Across 74 detected treeline ecotones, 27.5% of Landsat pixels displayed a significant positive trend in EVI and 5.6% of pixels displayed a significant negative trend ( p < 0.05). By using ALS data to determine vegetation structural class, we found that non-treed pixels had the highest percentage of significant positive trends in vegetation greenness (40.8%), followed by shrubs (30.5%), with lower percentages in sparse forests (18.9%) and open/dense forests (13.3%). These results suggest herbaceous and shrub vegetation types are undergoing the most significant changes in greenness, likely due to increases in shrub cover and herbaceous biomass in areas associated with these alpine treeline ecotones. The limited increases in EVI in forests likely indicates that vegetation cover is changing less rapidly in forests than in shrub and herbaceous vegetation types. Moreover, EVI may not be capturing increased height growth in forests near the treeline. Combining ALS data and Landsat time-series data provides a useful approach to locate and characterize alpine treeline ecotones, and enables the direct assessment of which vegetation structural classes are experiencing the greatest greening trends, thereby providing new insights to ecosystem change.https://doi.org/10.1088/1748-9326/aad5d2remote sensingforest structuretundraclimate changetime-series |
| spellingShingle | Douglas K Bolton Nicholas C Coops Txomin Hermosilla Michael A Wulder Joanne C White Evidence of vegetation greening at alpine treeline ecotones: three decades of Landsat spectral trends informed by lidar-derived vertical structure Environmental Research Letters remote sensing forest structure tundra climate change time-series |
| title | Evidence of vegetation greening at alpine treeline ecotones: three decades of Landsat spectral trends informed by lidar-derived vertical structure |
| title_full | Evidence of vegetation greening at alpine treeline ecotones: three decades of Landsat spectral trends informed by lidar-derived vertical structure |
| title_fullStr | Evidence of vegetation greening at alpine treeline ecotones: three decades of Landsat spectral trends informed by lidar-derived vertical structure |
| title_full_unstemmed | Evidence of vegetation greening at alpine treeline ecotones: three decades of Landsat spectral trends informed by lidar-derived vertical structure |
| title_short | Evidence of vegetation greening at alpine treeline ecotones: three decades of Landsat spectral trends informed by lidar-derived vertical structure |
| title_sort | evidence of vegetation greening at alpine treeline ecotones three decades of landsat spectral trends informed by lidar derived vertical structure |
| topic | remote sensing forest structure tundra climate change time-series |
| url | https://doi.org/10.1088/1748-9326/aad5d2 |
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