Extent change of protected mangrove forest and its relation to wave power exposure on Aldabra Atoll

Mangrove forests, vital for the conservation of biodiversity, protection of coastlines, and carbon capture, are decreasing globally at a rate higher than most other tropical forests. They are threatened by sea level rise, drought and storm surge, especially on low-lying islands where forests are directly exposed to the elements and have limited land area. We investigated changes in the spatial extent of mangroves on Aldabra Atoll, Seychelles – a protected area without direct human pressures, over 21 years using Landsat images. Over the 21-year study period, mean mangrove extent was 1283 ha with an overall net increase of 60 ha (0.23% year-1). The majority of extent changes were small (<2 ha) and contiguous to the existing mangrove extent. We then assessed the relation of mangrove cover change along the lagoon coastline with wave power (rate of energy transfer by waves), using fetch measures and local wind data. We found lower wave power values for stable mangrove areas than for areas that had gained or lost mangroves from 1997 to 2018. We identified wave power thresholds of 2.3 W m-1 for stable mangrove and 7.1 W m-1 for mangrove occurrence. These thresholds might be valuable for assessing threats and sites with the greatest potential for mangrove restoration across similar areas worldwide. Our results highlight the importance of quantifying mangrove extent changes at a local scale to assist with planning for the protection and restoration of this ecologically important habitat, given its vulnerability to the pressures associated with climate change

Increasing Arctic Tundra Flooding Threatens Wildlife Habitat and Survival: Impacts on the Critically Endangered Siberian Crane (Grus leucogeranus)

Climate change is causing Arctic temperatures to increase at least twice as fast as the planet on average. Temperature and precipitation are predicted to continue increasing, such that flooding might become more prevalent in the new Arctic. Increased flooding frequency and extreme flooding events may pose new threats to Arctic biodiversity through habitat disturbance and decreased survival. We used the Siberian crane (Grus leucogeranus) as a model organism to investigate how flooding influences nesting habitat availability and juvenile counts. When spring flooding destroys eggs, adults either do not raise any chicks or have reduced time to prepare them for their long migration to China, thus years with extensive flooding could negatively impact future crane generations. We used nest site observation data from 14 surveys between 1995 and 2019, habitat mapping based on Landsat 8 imagery, and species distribution modeling to predict Siberian crane potential nesting habitat. Nesting habitat loss due to extreme flooding was calculated by overlaying this potential nesting habitat with Global Surface Water data. The percent of potential flooded nest sites varied between 6.7–55% across years, with a significant increase between 2001 and 2018. Extreme flood events, as experienced in 2017 and 2018, eliminated almost half of the potential nesting habitat. Importantly, we found that the percentage of flooded nest sites across years was negatively correlated with the number of observed juveniles. The Arctic lowlands are exposed to seasonal water level fluctuations that species have evolved with and adapted to. Siberian cranes and other species depending on Arctic ecosystems are expected to continue adapting to changing flood conditions, but extreme flood events further threaten the long-term survival of critically endangered species. It is imperative to assess how ecosystems and species respond to climatic extremes to support Arctic conservation strategies

Extensive fires in southeastern Siberian permafrost linked to preceding Arctic Oscillation

Carbon release through boreal fires could considerably accelerate Arctic warming; however, boreal fire occurrence mechanisms and dynamics remain largely unknown. Here, we analyze fire activity and relevant large-scale atmospheric conditions over southeastern Siberia, which has the largest burned area fraction in the circumboreal and high-level carbon emissions due to high-density peatlands. It is found that the annual burned area increased when a positive Arctic Oscillation (AO) takes place in early months of the year, despite peak fire season occurring 1 to 2 months later. A local high-pressure system linked to the AO drives a high- temperature anomaly in late winter, causing premature snowmelt. This causes earlier ground surface exposure and drier ground in spring due to enhanced evaporation, promoting fire spreading. Recently, southeastern Siberia has experienced warming and snow retreat; therefore, southeastern Siberia requires appropriate fire management strategies to prevent massive carbon release and accelerated global warming.11Ysciescopu

Mid-summer snow-free albedo across the Arctic tundra was mostly stable or increased over the past two decades

Arctic vegetation changes, such as increasing shrub-cover, are expected to accelerate climate warming through increased absorption of incoming radiation and corresponding decrease in summer shortwave albedo. Here we analyze mid-summer shortwave land-surface albedo and its change across the pan-Arctic region based on MODIS satellite observations over the past two decades (2000-2021). In contrast to expectations, we show that terrestrial mid-summer shortwave albedo has not significantly changed in 82% of the pan-Arctic region, while 14% show an increase and 4% a decrease. The total median significant change was 0.014 cumulative over the past 22 years. By analyzing the visible and near-/shortwave-infrared range separately, we demonstrate that the slight increase arises from an albedo increase in the near-/shortwave infrared domain while being partly compensated by a decrease in visible albedo. A similar response was found across different tundra vegetation types. We argue that this increase in reflectance is typical with increasing biomass as a result of increased multiple reflection in the canopy. However, CMIP6 global climate model albedo predictions showed the opposite sign and different spatial patterns of snow-free summer albedo change compared to satellite-derived results. We suggest that a more sophisticated vegetation parametrization might reduce this discrepancy, and provide albedo estimates per vegetation type

Extensive fires in southeastern Siberian permafrost linked to preceding Arctic Oscillation

Carbon release through boreal fires could considerably accelerate Arctic warming; however, boreal fire occurrence mechanisms and dynamics remain largely unknown. Here, we analyze fire activity and relevant large-scale atmospheric conditions over southeastern Siberia, which has the largest burned area fraction in the circumboreal and high-level carbon emissions due to high-density peatlands. It is found that the annual burned area increased when a positive Arctic Oscillation (AO) takes place in early months of the year, despite peak fire season occurring 1 to 2 months later. A local high-pressure system linked to the AO drives a high-temperature anomaly in late winter, causing premature snowmelt. This causes earlier ground surface exposure and drier ground in spring due to enhanced evaporation, promoting fire spreading. Recently, southeastern Siberia has experienced warming and snow retreat; therefore, southeastern Siberia requires appropriate fire management strategies to prevent massive carbon release and accelerated global warming

CEOS WGCV Land Product Validation (LPV) Sub-Group: Current and Potential Roles in Future Decadal Survey Missions

The goals and objectives of the sub group are: To foster and coordinate quantitative validation of higher level global land products derive d from remotely sensed data, in a traceable way, and to relay results so they are relevant to users. and to increase the quality and effi ciency of global satellite product validation by developing and promo ting international standards and protocols for: (1) Field sampling (2) Scaling techniques (3) Accuracy reporting (4) Data / information exchange also to provide feedback to international structures (GEOSS ) for: (1) Requirements on product accuracy and quality assurance (QA 4EO) (2) Terrestrial ECV measurement standards (3) Definitions for f uture mission

Soil nutrient content and water level variation drive mangrove forest aboveground biomass in the lagoonal ecosystem of Aldabra Atoll

Lagoonal mangrove ecosystems are vital for carbon capture, protection of coastlines and conservation of biodiversity. Yet, they are decreasing globally at a higher rate than other mangrove ecosystems. In addition to human drivers, local environmental factors influence the functioning of lagoonal mangrove ecosystems, but their importance and combined effects are relatively unknown. Here, we investigate the drivers of mangrove functioning, approximated by mangrove aboveground biomass (AGB), in a protected lagoonal mangrove ecosystem on Aldabra Atoll, Seychelles. Based on a survey of the mangrove forest structure in 54 plots, we estimated that the mean mangrove forest AGB was 82 ± 13 Mg ha−1. The total AGB of the mangrove area (1720 ha) was nearly 140,600 Mg, equivalent to about 66,100 Mg of carbon stored in the standing biomass on Aldabra. To assess the direct and indirect effects of soil nutrient content, water level variation and soil salinity on mangrove AGB, we used a structural equation model. Our structural equation model explained 82 % of the variation in mangrove AGB. The soil nutrient content (concentration of essential macronutrients in the soil column) had the greatest influence on mangrove AGB variation. Additionally, high variation in water level (change in water depth covering a location) increased mangrove AGB by increasing nutrient content levels. Our results highlight the important contribution of Aldabra's lagoonal ecosystem to Seychelles' carbon storage and the role of hydroperiod as a regulator controlling the availability of crucial nutrients needed for the functioning of mangroves within lagoonal systems. We suggest conservation managers worldwide focus on a holistic ecosystem-level perspective for successful mangrove conservation, including the protection and maintenance of nutrient cycling and hydrological processes