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Remote Sensing of Tropical Montane Ecosystems and Elevation Gradients

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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Environmental Remote Sensing".

Deadline for manuscript submissions: closed (1 May 2022) | Viewed by 20685

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Special Issue Editors

Dr. Eileen H. Helmer

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Guest Editor

International Institute of Tropical Forestry, Forest Service, United States Department of Agriculture, 1201 Calle Ceiba, Jardín Botánico Sur, San Juan, PR 00926-1119, USA
Interests: tropical forest ecology; remote sensing; montane tropical ecosystems; land use

Patrick J. Comer

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Guest Editor

NatureServe, Science Division, Boulder, CO 80303, USA
Interests: biodiversity conservation; terrestrial ecosystem mapping; status and trend assessment of ecosystem condition; climate change vulnerability and adaptation; systematic conservation planning
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Dr. David Gwenzi

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Guest Editor

Department of Environmental Science and Management, Humboldt State University, Arcata, CA, USA
Interests: remote sensing of vegetation structure and function; spatial decision support tools; spatial statistics; vegetation phenology

Dr. Wan Shafrina Wan Mohd Jaafar

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Guest Editor

Earth Observation Centre, Institute of Climate Change, National University of Malaysia (UKM), Selangor, Malaysia
Interests: LiDAR remote sensing; tropical forests; forest ecology; remote sensing; GIS

Dr. Xiaolin Zhu

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Guest Editor

Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hong Kong 999077, China
Interests: remote sensing; spatial data analysis; data fusion; vegetation phenology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

This Special Issue focuses on patterns, applications, conservation, and remote sensing methods related to tropical montane ecosystems and elevation gradients.

Dear Colleagues,

We invite you to join us in developing a Special Issue dedicated to remote sensing of tropical montane ecosystems and elevation gradients. Tropical mountain environments are undergoing significant changes in climate, land-use, biogeochemistry, and water resources. Moreover, they support large human populations, are the headwaters for important rivers, and are biodiversity hotspots.

Remote sensing is crucial to monitoring and understanding tropical mountain systems, but these landscapes pose unique challenges. Steep topography affects remote sensing responses, and clouds are persistent. Climate stations, stream gauges, forest inventories, and other environmental samples are sparse relative to the steep environmental gradients. Natural vegetation is easy to confuse with managed or grazed lands in remotely sensed data.

Examples of research topics for this Special Issue on montane tropical ecosystems and elevation gradients include but are not limited to applications on the following topics:

Remote sensing of tropical montane ecosystems
- Characterizing elevation gradients (e.g., vegetation traits, nutrient cycles)
- Characterizing other gradients in species composition, diversity, or distribution
- Quantifying and mapping aboveground biomass
- Mapping other aspects of ecosystem structure, distribution, processes, and services
- Characterizing fog, clouds, cloud base heights, temperature, rainfall
- Using remotely sensed land-cover data to scope ecosystem restoration and recovery

Remote sensing and change in tropical montane landscapes
- Land-use and land-cover change in tropical montane forests, grasslands, and shrublands (e.g., afforestation, deforestation, woody encroachment, grazing, etc.)
- Effects of land use on mountain landscapes
- Changes in snow, ice, surface waters, wetlands, fog, and clouds
- Thermophilization and other changes in species or ecosystem distributions
- Changes due to earth movement, hurricanes, typhoons, and fire

Methods and challenges in tropical montane environments
- Accounting for topography in remote sensing and mapping, for example, with topographic correction, including change detection and mapping of environmental gradients
- Inventory and sample design and intensification
- Cloud screening and addressing the lack of cloud-free imagery
- Airborne laser scanning for modelling forest structural heterogeneity

Dr. Eileen H. Helmer
Mr. Patrick J. Comer
Dr. David Gwenzi
Dr. Wan Shafrina Wan Mohd Jaafar
Dr. Xiaolin Zhu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

tropical forest
cloud forest
páramo
montane shrublands
montane forest
alpine
lidar
biodiversity
species migration
altitudinal gradient
fog
climate change
topographic correction
topographic shadow
cloud detection and removal
spatiotemporal fusion
natural hazards
ecosystem classification

Published Papers (6 papers)

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Research

21 pages, 11674 KiB

Open AccessArticle

Analyzing Canopy Height Patterns and Environmental Landscape Drivers in Tropical Forests Using NASA’s GEDI Spaceborne LiDAR

by Esmaeel Adrah, Wan Shafrina Wan Mohd Jaafar, Hamdan Omar, Shaurya Bajaj, Rodrigo Vieira Leite, Siti Munirah Mazlan, Carlos Alberto Silva, Maggie Chel Gee Ooi, Mohd Nizam Mohd Said, Khairul Nizam Abdul Maulud, Adrián Cardil and Midhun Mohan

Remote Sens. 2022, 14(13), 3172; https://doi.org/10.3390/rs14133172 - 1 Jul 2022

Cited by 8 | Viewed by 3557

Abstract

Canopy height is a fundamental parameter for determining forest ecosystem functions such as biodiversity and above-ground biomass. Previous studies examining the underlying patterns of the complex relationship between canopy height and its environmental and climatic determinants suffered from the scarcity of accurate canopy height measurements at large scales. NASA’s mission, the Global Ecosystem Dynamic Investigation (GEDI), has provided sampled observations of the forest vertical structure at near global scale since late 2018. The availability of such unprecedented measurements allows for examining the vertical structure of vegetation spatially and temporally. Herein, we explore the most influential climatic and environmental drivers of the canopy height in tropical forests. We examined different resampling resolutions of GEDI-based canopy height to approximate maximum canopy height over tropical forests across all of Malaysia. Moreover, we attempted to interpret the dynamics underlining the bivariate and multivariate relationships between canopy height and its climatic and topographic predictors including world climate data and topographic data. The approaches to analyzing these interactions included machine learning algorithms, namely, generalized linear regression, random forest and extreme gradient boosting with tree and Dart implementations. Water availability, represented as the difference between precipitation and potential evapotranspiration, annual mean temperature and elevation gradients were found to be the most influential determinants of canopy height in Malaysia’s tropical forest landscape. The patterns observed are in line with the reported global patterns and support the hydraulic limitation hypothesis and the previously reported negative trend for excessive water supply. Nevertheless, different breaking points for excessive water supply and elevation were identified in this study, and the canopy height relationship with water availability observed to be less significant for the mountainous forest on altitudes higher than 1000 m. This study provides insights into the influential factors of tree height and helps with better comprehending the variation in canopy height in tropical forests based on GEDI measurements, thereby supporting the development and interpretation of ecosystem modeling, forest management practices and monitoring forest response to climatic changes in montane forests. Full article

(This article belongs to the Special Issue Remote Sensing of Tropical Montane Ecosystems and Elevation Gradients)

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23 pages, 2478 KiB

Open AccessArticle

Demand for Ecosystem Services Drive Large-Scale Shifts in Land-Use in Tropical Mountainous Watersheds Prone to Landslides

by Francisco Javier Álvarez-Vargas, María Angélica Villa Castaño and Carla Restrepo

Remote Sens. 2022, 14(13), 3097; https://doi.org/10.3390/rs14133097 - 27 Jun 2022

Cited by 3 | Viewed by 1612

Abstract

An increasing frequency of extreme atmospheric events is challenging our basic knowledge about the resilience mechanisms that mediate the response of small mountainous watersheds (SMW) to landslides, including production of water-derived ecosystem services (WES). We hypothesized that the demand for WES increases the connectivity between lowland and upland regions, and decreases the heterogeneity of SMW. Focusing on four watersheds in the Central Andes of Colombia and combining “site-specific knowledge”, historic land cover maps (1970s and 1980s), and open, analysis-ready remotely sensed data (GLAD Landsat ARD; 1990–2000), we addressed three questions. Over roughly 120 years, the site-specific data revealed an increasing demand for diverse WES, as well as variation among the watersheds in the supply of WES. At watershed-scales, variation in the water balances—a surrogate for water-derived ES flows—exhibited complex relationships with forest cover. Fractional forest cover (p_i) and forest aggregation (AI_i) varied between the historic and current data sets, but in general showed non-linear relationships with elevation and slope. In the current data set (1990–2000), differences in the number of significant, linear models explaining variation in p_i with time, suggest that slope may play a more important role than elevation in land cover change. We found ample evidence for a combined effect of slope and elevation on the two land cover metrics, which would be consistent with strategies directed to mitigate site-specific landslide-associated risks. Overall, our work shows strong feedbacks between lowland and upland areas, raising questions about the sustainable production of WES. Full article

(This article belongs to the Special Issue Remote Sensing of Tropical Montane Ecosystems and Elevation Gradients)

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17 pages, 8366 KiB

Open AccessArticle

Conserving Ecosystem Diversity in the Tropical Andes

by Patrick J. Comer, Jose Valdez, Henrique M. Pereira, Cristina Acosta-Muñoz, Felipe Campos, Francisco Javier Bonet García, Xavier Claros, Lucia Castro, Franciscio Dallmeier, Enrique Yure Domic Rivadeneira, Mike Gill, Carmen Josse, Indyra Lafuente Cartagena, Roberto Langstroth, Daniel Larrea-Alcázar, Annett Masur, Gustavo Morejon Jaramillo, Laetitia Navarro, Sidney Novoa, Francisco Prieto-Albuja, Gustavo Rey Ortíz, Marcos F. Teran, Carlos Zambrana-Torrelio and Miguel Fernandez Show full author list Hide full author list

Remote Sens. 2022, 14(12), 2847; https://doi.org/10.3390/rs14122847 - 14 Jun 2022

Cited by 8 | Viewed by 6782

Abstract

Documenting temporal trends in the extent of ecosystems is essential to monitoring their status but combining this information with the degree of protection helps us assess the effectiveness of societal actions for conserving ecosystem diversity and related ecosystem services. We demonstrated indicators in the Tropical Andes using both potential (pre-industrial) and recent (~2010) distribution maps of terrestrial ecosystem types. We measured long-term ecosystem loss, representation of ecosystem types within the current protected areas, quantifying the additional representation offered by protecting Key Biodiversity Areas. Six (4.8%) ecosystem types (i.e., measured as 126 distinct vegetation macrogroups) have lost >50% in extent across four Andean countries since pre-industrial times. For ecosystem type representation within protected areas, regarding the pre-industrial extent of each type, a total of 32 types (25%) had higher representation (>30%) than the post-2020 Convention on Biological Diversity (CBD) draft target in existing protected areas. Just 5 of 95 types (5.2%) within the montane Tropical Andes hotspot are currently represented with >30% within the protected areas. Thirty-nine types (31%) within these countries could cross the 30% CBD 2030 target with the addition of Key Biodiversity Areas. This indicator is based on the Essential Biodiversity Variables (EBV) and responds directly to the needs expressed by the users of these countries. Full article

(This article belongs to the Special Issue Remote Sensing of Tropical Montane Ecosystems and Elevation Gradients)

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21 pages, 13314 KiB

Open AccessArticle

Characterization of Dry-Season Phenology in Tropical Forests by Reconstructing Cloud-Free Landsat Time Series

by Xiaolin Zhu, Eileen H. Helmer, David Gwenzi, Melissa Collin, Sean Fleming, Jiaqi Tian, Humfredo Marcano-Vega, Elvia J. Meléndez-Ackerman and Jess K. Zimmerman

Remote Sens. 2021, 13(23), 4736; https://doi.org/10.3390/rs13234736 - 23 Nov 2021

Cited by 11 | Viewed by 2367

Abstract

Fine-resolution satellite imagery is needed for characterizing dry-season phenology in tropical forests since many tropical forests are very spatially heterogeneous due to their diverse species and environmental background. However, fine-resolution satellite imagery, such as Landsat, has a 16-day revisit cycle that makes it hard to obtain a high-quality vegetation index time series due to persistent clouds in tropical regions. To solve this challenge, this study explored the feasibility of employing a series of advanced technologies for reconstructing a high-quality Landsat time series from 2005 to 2009 for detecting dry-season phenology in tropical forests; Puerto Rico was selected as a testbed. We combined bidirectional reflectance distribution function (BRDF) correction, cloud and shadow screening, and contaminated pixel interpolation to process the raw Landsat time series and developed a thresholding method to extract 15 phenology metrics. The cloud-masked and gap-filled reconstructed images were tested with simulated clouds. In addition, the derived phenology metrics for grassland and forest in the tropical dry forest zone of Puerto Rico were evaluated with ground observations from PhenoCam data and field plots. Results show that clouds and cloud shadows are more accurately detected than the Landsat cloud quality assessment (QA) band, and that data gaps resulting from those clouds and shadows can be accurately reconstructed (R² = 0.89). In the tropical dry forest zone, the detected phenology dates (such as greenup, browndown, and dry-season length) generally agree with the PhenoCam observations (R² = 0.69), and Landsat-based phenology is better than MODIS-based phenology for modeling aboveground biomass and leaf area index collected in field plots (plot size is roughly equivalent to a 3 × 3 Landsat pixels). This study suggests that the Landsat time series can be used to characterize the dry-season phenology of tropical forests after careful processing, which will help to improve our understanding of vegetation–climate interactions at fine scales in tropical forests. Full article

(This article belongs to the Special Issue Remote Sensing of Tropical Montane Ecosystems and Elevation Gradients)

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29 pages, 8691 KiB

Open AccessArticle

Vertical Differences in the Long-Term Trends and Breakpoints of NDVI and Climate Factors in Taiwan

by Hui Ping Tsai, Geng-Gui Wang and Zhong-Han Zhuang

Remote Sens. 2021, 13(22), 4707; https://doi.org/10.3390/rs13224707 - 21 Nov 2021

Viewed by 2414

Abstract

This study explored the long-term trends and breakpoints of vegetation, rainfall, and temperature in Taiwan from overall and regional perspectives in terms of vertical differences from 1982 to 2012. With time-series Advanced Very-High-Resolution Radiometer (AVHRR) normalized difference vegetation index (NDVI) data and Taiwan Climate Change Estimate and Information Platform (TCCIP) gridded monthly climatic data, their vertical dynamics were investigated by employing the Breaks for Additive Seasonal and Trend (BFAST) algorithm, Pearson’s correlation analysis, and the Durbin–Watson test. The vertical differences in NDVI values presented three breakpoints and a consistent trend from positive (1982 to 1989) to negative at varied rates, and then gradually increased after 2000. In addition, a positive rainfall trend was discovered. Average and maximum temperature had similar increasing trends, while minimum temperature showed variations, especially at higher altitudes. In terms of regional variations, the vegetation growth was stable in the north but worse in the central region. Higher elevations revealed larger variations in the NDVI and temperature datasets. NDVI, along with average and minimum temperature, showed their largest changes earlier in higher altitude areas. Specifically, the increasing minimum temperature direction was more prominent in the mid-to-high-altitude areas in the eastern and central regions. Seasonal variations were observed for each region. The difference between the dry and wet seasons is becoming larger, with the smallest difference in the northern region and the largest difference in the southern region. Taiwan’s NDVI and climatic factors have a significant negative correlation (p < 0.05), but the maximum and minimum temperatures have significant positive effects at low altitudes below 500 m. The northern and central regions reveal similar responses, while the south and east display different feedbacks. The results illuminate climate change evidence from assessment of the long-term dynamics of vegetation and climatic factors, providing valuable references for establishing correspondent climate-adaptive strategies in Taiwan. Full article

(This article belongs to the Special Issue Remote Sensing of Tropical Montane Ecosystems and Elevation Gradients)

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15 pages, 4968 KiB

Open AccessArticle

Elevation and Distribution of Freshwater and Sewage Canals Regulate Canopy Structure and Differentiate Hurricane Damages to a Basin Mangrove Forest

by Qiong Gao and Mei Yu

Remote Sens. 2021, 13(17), 3387; https://doi.org/10.3390/rs13173387 - 26 Aug 2021

Cited by 3 | Viewed by 2048

Abstract

The coastal mangrove forest bears important ecosystem functions and services, including the protection of shorelines and coastal communities. While coastal mangroves often suffer severe damage during storms, understanding the vulnerability and resistance of mangroves to the damage at a landscape scale is crucial for coastal mangrove management and conservation. In September 2017, two consecutive major hurricanes caused tremendous damage to the coastal mangroves in the Caribbean. By utilizing LiDAR data taken before and after the hurricanes in a basin mangrove forest in Northeast Puerto Rico, we analyzed the spatial variation of a canopy structure before the hurricanes and hurricane-induced canopy height reduction and explored possible drivers by means of spatial regressions. Regarding the canopy structure, we found that the pre-hurricane canopy height of the mangrove forest decreased with elevation and distance to the freshwater/sewage canals within the forest, and these two drivers explained 82% of variations in the mangrove canopy height. The model, thus, implies that freshwater and nutrient inputs brought by the canals tend to promote the canopy height, and mangrove trees at lower elevation are especially more advantageous. Similarly, tree densities decreased with the canopy height but increased with the elevation and the distance to the canals. We also found that this mangrove forest suffered on average a 53% canopy height reduction, reflecting mostly heavy crown defoliation and the rupture of branches. The regression, which explains 88% of spatial variation in the canopy height reduction, showed that mangroves with a higher canopy or lower density, or growing in lower elevation, or being closer to the canals suffered more damage. Our findings indicate that delivered freshwater/sewage by means of human-made canals has a strong impact on the canopy structure as well as its resistance to tropical storms. Freshwater and sewage tend to release the salinity stress and nutrient deficit and, thus, to promote the mangrove canopy height. However, the addition of freshwater and nutrients might also increase the risk of mangrove damage during the storms probably because of an altered allometry of assimilates. Full article

(This article belongs to the Special Issue Remote Sensing of Tropical Montane Ecosystems and Elevation Gradients)

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