## 4 Discussion
### Threshold-Based Early Warning System  
Detecting thresholds for early warning bridges statistical modeling with practical application, enabling the development of threshold-based early warning systems for ghost forest formation. Collectively, these thresholds define an empirical \"vulnerability envelope\", a zone within which the likelihood of rapid forest decline and ghost forest formation is significantly elevated.  
Our threshold values of 2.23 cm for GWT, 3.07 for LAI, 1.27 g C m\({}^{-2}\) d\({}^{-1}\) for NEE, and 167.54 W m\({}^{-2}\) for Rn correspond with earlier studies that highlight how increasing groundwater levels and declining canopy cover contribute to forest dieback, especially in coastal and lowland regions experiencing sea level rise and saltwater intrusion [5; 13]. For example, groundwater levels above 2 cm have been linked to tree stress and mortality in saturated environments, while LAI thresholds below 3 have been associated with reduced photosynthetic capacity and carbon assimilation [77]. Similarly, low NEE values reflect a decline in net carbon uptake, a known precursor to ecological tipping points [78]. Rn, as a proxy for available energy, plays a role in modulating evapotranspiration and plant stress responses [79; 80]. However, we advise that these results be interpreted with appropriate caution, as they may not be universally applicable without careful site-specific verification and local validation.  
Prolonged flooding elevates tree mortality in wetlands, especially during leaf-out and active growth when root oxygen demand is high. Elevated groundwater tables (GWTs) during these periods hinder root respiration and carbon allocation, increasing stress susceptibility [81; 82]. Leaf area index (LAI) peaks in spring-summer, enhancing transpiration, but excessive GWT can suppress it due to root hypoxia, limiting stomatal conductance and exacerbating inundation stress [60; 63]. Increasing solar radiation in spring-summer boosts evapotranspiration and photosynthetic demand, but in waterlogged soils, limited oxygen intensifies physiological strain and reduces carbon assimilation [83]. Seasonal NEE is driven by LAI, radiation, and hydrology, with high GWTs promoting anaerobic soils that reduce both decomposition and root activity [84; 85]. Persistent inundation lowers ecosystem respiration but also limits carbon uptake, shifting NEE toward a net carbon source. Chronic waterlogging may lead to carbon starvation and long-term tree decline [46; 86].  
Importantly, these thresholds are not fixed. They may shift with ongoing climate change, vegetation succession, and land-use interventions. However, their identification provides a critical step toward building dynamic, data-driven early warning systems for forest vulnerability. Combined with field-based tools like groundwater monitoring wells, remote sensing technologies such as satellite-derived LAI, and eddy covariance towers measuring NEE, these threshold values can facilitate proactive landscape-scale management and focused targeted intervention strategies.  
Such analytical approaches are increasingly necessary as ecosystems undergo critical transitions as a function of intensifying climate pressures. By combining mechanistic understanding with statistical rigor, threshold-based frameworks can serve as the backbone of adaptive monitoring strategies, helping land managers anticipate and respond to ecological tipping points before irreversible damage occurs [11; 71; 87].