Data from: Groundwater salinisation intensifies drought impacts in forests and reduces refuge capacity

1. Shallow groundwater aquifers regularly support drought refuges for
water-dependent ecosystems. However, many aquifers are impacted by
over-extraction and pollution, potentially degrading their ability to
support groundwater-fed drought refuges. 2. We investigated the response
of groundwater-connected riverine forests to a drought considered
equivalent in intensity to those predicted under severe climate change for
2030. The drought's impact was investigated in an area where shallow
groundwater resources are heavily exploited and polluted by salinization.
3. We used remotely sensed vegetation productivity (enhanced vegetation
index) data from a long-term data set (2000–2011) at 475 riverine forest
sites in the Campaspe catchment, south-eastern Australia. Generalized
additive mixed models and boosted regression trees were used to model the
relationship between groundwater and other environmental covariates with
forest change during drought. 4. Models explained up to 44% of the
variation in forest change during drought. Forests underwent the greatest
declines in areas of high salinity (>6000 μS cm−1) associated with
shallow groundwater depths (0–5 m). Conversely, forests in areas of lowest
salinity (<2000 μS cm−1) and groundwater depths of more than 7·5 m
showed the least decline during drought. 5. In landscapes where
groundwater quality is not compromised, previous studies have shown that
shallow groundwater provides important drought refuges and refugia. Here,
we show that when groundwater salinization has occurred, forests connected
to shallow groundwater are more vulnerable to drought. In effect,
salinization reduces the capacity of groundwater-connected habitats to
function as drought refuges. 6. Synthesis and applications. Currently,
there is an emphasis on managing environmental flows to support freshwater
ecosystems and associated forests under water stress. However, delivery of
environmental water is restricted to areas within a linear stream network
and there is often limited capacity to deliver environmental flows during
drought. Alternatively, a focus on drought refuges and refugia and
processes important for maintaining groundwater quality (e.g. catchment
revegetation to reduce shallow groundwater salinization) may better allow
drought effects to be managed across a catchment, without directly
focusing on highly contested surface water resources.