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Global warming modulates the spatial and temporal occurrence of insect outbreaks, leading to as-yet-unknown effects on forests ecosystems. Warmer trends may favour the upward and northward expansion of pests, albeit increased exposure to heat events and droughts may also hamper insect growth and development. Thus far, further research is needed about the balance of climate warming on pine processionary moth (PPM) (Thaumetopoea pityocampa) development stages, especially at broader scales, despite being the main conifer-defoliating insect in the Mediterranean area. This research analyses the relationships of PPM with the climatic conditions during its most vulnerable development phases in Spain to provide base-information for forest managers. We hypothesize that warmer winter temperatures will increase PPM growth at their larval feeding stage, whereas summer-heat events will reduce PPM rates from egg and early larval stages, leading to counterbalanced effects of climate warming. Furthermore, we expect dry springs will allow an earlier development of PPM and higher incidence of outbreaks. To analyse climate effects on PPM populations in Andalusia, Castilla-La Mancha, and Navarre (37 to 42°N), we compiled information from the Regional Forest Services comprising up to 26 years of monitoring data from 2465 forest stands dominated by Pinus nigra and Pinus sylvestris. We fitted Cumulative Link Mixed Models (CLMM) to test the climate effects on four PPM defoliation severity levels. Our results support higher PPM larvae survival and incidence due to warmer winter conditions, but also the reduction of PPM population size under summer heat conditions. Particularly, the increasing incidence associated to warmer winters during the larval defoliating stage is counterbalanced by the decreasing population at earlier life stages during summer heat events. Spring drought also plays an important role on PPM incidence rates, but its effect is idiosyncratic to each region, suggesting an

Defoliating insects’ outbreaks play a critical role in trees’ carbon cycle. The pine processionary moth (PPM; Thaumetopoea pityocampa) is the major defoliating insect of Mediterranean coniferous forests. The frequency and intensity of PPM outbreaks is projected to increase as winter temperatures become milder due to climate warming. An accurate evaluation of this projection requires a wide spatial baseline of the historical PPM incidence. PPM outbreaks affect tree secondary growth leading to narrow rings, providing a tree level signal. However, PPM defoliation rings can be confounded with drought rings, the most frequent cause of narrow rings in Mediterranean environments. Thus, an accurate identification of PPM rings demands the consideration of additional tree ring traits. Here, we introduce a multiproxy approach to identify and distinguish PPM and drought events. We sampled four Pinus nigra (3) and P. sylvestris (1) stands in Spain. We identified and verified years of PPM defoliation using remote sensing analysis and field observations of Regional Forest Service. We identified drought events through the combination of climatic data with radial growth reductions. We considered climate growth residuals, among-trees growth variability, latewood percentage (%LW), intrinsic water-use efficiency (iWUE) and minimum blue intensity (BI) to discern between droughts and PPM outbreaks. In comparison with drought rings, PPM rings showed 1) more negative residuals in climate growth models, 2) higher secondary growth variance, 3) higher percentage of latewood and 4) lower iWUE. Minimum BI did not differ between drought and PPM rings, but was lower than in the rest of the rings. The combination of these traits provides a signature to identify PPM rings, opening the opportunity to reconstruct PPM incidence on a broad spatio-temporal scale.

Little is known about how much continuous landscape transformation might affect the most vulnerable elements of biodiversity. In this study, we quantified changes in the normalized difference vegetation index (NDVI) over the past 35 years across locations with threatened plants and in Natura 2000 (N2000) protected areas, in an environmentally heterogeneous region of Southern Europe. First, we estimated the intensity and duration of NDVI gains and losses based on Landsat time series using the LandTrendr algorithm in Google Earth Engine. Then, we tested: 1) whether populations of threatened plants were located in more stable sites than non-threatened plants (i.e., lower NDVI changes); 2) whether NDVI changes around populations of threatened plants differed across habitats and inside/outside N2000 areas, and 3) whether lower NDVI changes occurred in N2000 areas than unprotected areas, thereby indicating their effectiveness at preserving biodiversity. Threatened plants tended to be concentrated in sites with less change irrespective of the habitat where they occurred and their location within protected areas. Occurrence in stable sites also reduced the risk associated with small-sized populations. N2000 areas were in line with the overall greening trend but they experienced less loss events than the unprotected areas, thereby supporting their role in slowing down human-induced land cover changes. Our approach demonstrates how long-term remote sensing monitoring can help to assess the effects of both slow processes and drastic landscape transformation events on priority plants in a comprehensive and rapid manner. This method can identify hidden patterns in extensive regions and guide effective conservation management.

In the present scenario of climatic change, climatic refugia will be of paramount importance for species persistence. Topography can generate a considerable climatic heterogeneity over short distances, which is often disregarded in macroclimatic predictive models. Here we investigate the role of rocky habitats as microclimatic refugia by combining two different analyses: exploring a thermal mechanism whereby rocky habitats might serve as refugia, and examining if the biogeographic pattern shows a high abundance of relict, endemic and peripheral species. The thermal profile of two populations of relict and endemic plant species occurring in Pyrenean cliffs was investigated by infrared images and in situ temperature data-loggers. Despite occurring in crevices of a south oriented slope, Androsace cylindrica showed a narrower daily range of temperature than the surrounding matrix, thereby avoiding extreme high temperatures. Borderea chouardii, of tropical ancestors, also occurred in patches where temperatures were buffered during the growth season, experiencing lower mean temperatures than the surrounding matrix and nearby areas during the warmer part of the day, and similar temperatures during the colder. The rocky habitats of both species, therefore, reduced temperature ranges and exposition to extreme climatic events. Compared to other habitats, the rocky ones also harboured a very high fraction of both endemics and peripheral plant populations according to the largest vegetation dataset available in the Pyrenees (18,800 plant inventories and 400,000 records). Our results suggest an association between the habitats of relicts, endemics and species at their distribution limit, driven by a stabilizing effect of rocky habitats on extreme temperatures. Given the important role of rocky habitats as hotspots of singular and unique plants, their characterization seems a sensible first step to identify potential refugia in the context of climate change.