Ecological Monitoring with Spy Satellite Images—The Case of Red Wood Ants in Romania

Abstract

Dynamics of habitat conditions drive important changes in distribution and abundance of animal species making monitoring an important but also a challenging task when data from the past are scarce. We compared the distribution of ant mounds in the 1960s with recent inventories (2018), looking at changes in canopy cover over time, in a managed forest. Both historical and recent sources of information were used. Habitat suitability at present was determined using a Normalized Difference Vegetation Index (NDVI) image as a proxy for stand canopy cover. The NDVI product was obtained using Google Earth Engine and Sentinel 2 repository. For past conditions (no spectral information available), presence of edges and more open canopies was assessed on a Corona spy-satellite image and based on information from old forest management plans. A threshold distance of 30 m was used to assess location of ant nests compared to favorable habitats. Both old and new information sources showed that ants prefer intermediate canopy cover conditions in their vicinity. Nests remained clustered because of the heterogeneous habitat conditions, but spatial distribution has changed due to canopy alteration along time. The analysis on the NDVI was effective for 82% of cases (i.e., nests occurred within 30 m from favorable habitats). For all the remaining nests (18%), the Google Earth high resolution satellite image revealed in their vicinity the presence of small canopy gaps (undetected by the NDVI). These results show that historical satellite images are very useful for explaining the long-term dynamics of ant colonies. In addition, the use of modern remote sensing techniques provides a reliable and expedite method in determining the presence of favorable small-scale habitat, offering a very useful tool for ecological monitoring across large landscapes and in very different areas, especially in the context of ecosystem dynamics driven and exacerbated by climate change.

The potential of historical spy-satellite imagery to support research in ecology and conservation

“…For example, philopatric steppe marmots ( Marmota bobak ) responded with a 50-year time lag to historical habitat disturbance (Munteanu et al 2020 ), whereas the capercaillie ( Tetrao urogallus ) recolonized historically disturbed forest patches relatively quickly (Stăncioiu et al 2021 ). Similarly, mound-building red wood ants ( Formica rufa ) responded immediately to changes in canopy openness, relocating mounds since the 1960s along forest edges both in historical and recent time periods (Klimetzek et al 2021 ).…”

A Re-Inventory After 12 Years – Increase in Red Wood Ant Nests and Woodpecker Cavities in Nests in the West Eifel Volcanic Field Despite Climatic Changes

“…In our mapping approach it is these small nests that are mapped because of their importance for understanding population dynamics in a study area and for evaluating spatial distribution and tectonic patterns (Berberich et al 2022a,b;2016a,c). 3) Inappropriate selection of a mapping method: our approach produces more accurate results in contrast to imperfect detection and underdetection of small NH classes by using random sampling, transects (at 20-50 m intervals), or the use of satellite imagery with a 30 m threshold spacing without the ability to identify start-ups and short nests (e.g., Sondeij et al 2018;Klimetzek et al 2021;Reimann 2021;Véle and Frouz 2023). 4) Incorrect documentation of mapping results: We have learned from working with lay observers that they rarely record nests digitally with GPS and only vaguely record the data collected from memory on analog maps and not using geographical information systems (GIS).…”

“…6) Short time intervals for re-inventories: This is the most critical aspect of re-inventories. Recent studies conducted after several decades show a mixed picture: stable RWA nest counts in England and Romania (two decades), a pressure situation in Belgium (three decades), and both decreases and increases in RWA nest counts in The Netherlands (six decades (Robinson and Robinson 2008;Dekoninck et al 2010;Mabelis and Korczyńska 2016;Van Buggenum 2021;Klimetzek et al 2021). The results of re-inventories after several decades should be viewed critically, because a time interval of more than 20 years seems much too long to document population dynamics.…”

Forest Habitat Fragmentation in Mountain Protected Areas Using Historical Corona KH-9 and Sentinel-2 Satellite Imagery

“…An increasing potential in forested landscape change analysis is represented by the declassified data of former spy satellites [53,54] with photogrammetric sensors and panchromatic imagery such as CORONA KH, HEXAGON, etc., e.g., Rendenieks et al [55] in the Baltic states and Munteanu et al [56] in the Romanian Carpathians. Although these data archives are free, their preparation for analysis and mapping needs typical photogrammet-ric processing for orthophoto production and spatial accuracy assessment in order to adapt them to recent date imagery [57][58][59]. This is one of the directions of our current approach in the context of forest fragmentation multidate modelling in a representative protected area in the Romanian Carpathians.…”