Drought, fog and vegetation resilience: Potential tipping points of forests in semiarid coastal basins of central Chile.

Semi-arid forests are becoming increasingly vulnerable to climate change as drier conditions are more frequent. In the coastal basins of semi-arid Chile, that are disconnected from the Andes, snow and rainfall contribute little to forest water supply. Instead, fog can provide an important moisture subsidy that helps sustain forest function and persistence, potentially increasing drought tolerance. Since 2010, however, the co-occurrence of stronger drought conditions and a decline in fog frequency have raised concern about the possibility of large-scale forest collapse.

Here we evaluate forest resilience and ask whether these forests are moving toward bifurcation-driven tipping points across a 4,067 km² coastal landscape. Using satellite time series spanning 1984–2024, we reconstructed land-surface phenology and identified post-2010 anomalies to quantify the magnitude and spatial extent of drought impacts. We then combined multiple satellite-derived indices in a multivariate framework to describe vegetation states associated with drought stress, explicitly contrasting the pre-2010 period with the subsequent drought years. From this analysis, we selected pixels showing the strongest evidence of potential state change and examined them with univariate time-series methods. We computed early warning signals (EWS) and critical slowing down (CSD) metrics, including variance, lag-1 autocorrelation (AR1), and the restoring rate (λ), using rolling ten-year windows to track changes in stability through time.

Results show that the extreme 2019 drought affected 82% of the forest area. Despite this widespread impact, forest patches were generally more resilient than adjacent shrublands: across the landscape, many forests remained stable and some showed signals consistent with recovery even under high drought severity. Univariate EWS analyses indicate that drought is increasingly constraining forest states; however, CSD metrics do not yet provide consistent evidence that the system has crossed a tipping point. Even so, continued extreme drought combined with further reductions in fog could erode buffering capacity and raise collapse risk. Overall, the relative stability of forests compared with shrublands supports the idea that fog-inundated forests persist with a higher resilience under progressive drying in this region.