1Water resources and their management present social, economic and environmental 2 challenges, with demand for human consumptive, industrial and environmental uses 3 increasing globally. However environmental water requirements, that is, the allocation of 4 water to the maintenance of ecosystem health, are often neglected or poorly quantified. Further, transpiration by trees is commonly a major determinant of the hydrological balance 6 of woodlands but recognition of the role of groundwater in hydrological balances of 7 woodlands remains inadequate, particularly in mesic climates. 8In this study we measured rates of tree water use and sapwood 13 C discrimination in a 9 mesic, temperate Eucalypt woodland along a naturally-occurring gradient of depth-to-10 groundwater (DGW), to examine daily, seasonal and annual patterns of transpiration. We We conclude that even in mesic environments groundwater can be utilised by trees. We 1 further conclude that these forests are facultatively groundwater dependent when 2 groundwater depth is < 9 m and suggest that during drier-than-average years the 3 contribution of groundwater to stand transpiration is likely to increase significantly at the 4 two shallowest groundwater sites.5

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Groundwater-dependent ecosystems (GDEs) are threatened by over-extraction of groundwater for human needs across the world. A fundamental understanding of relationships between naturally occurring gradients in depth-to-groundwater (DGW) across landscapes and the ecological properties of vegetation assemblages is essential for effective management of the impacts of groundwater extraction. Little is known, however, about relationships between DGW and the ecology of mesic woodlands in GDEs. Here, we investigated relationships between a naturally occurring DGW gradient and plant species composition, richness and abundance in mesic Eucalyptus woodlands of eastern Australia. Across 16 sites varying in DGW from 2.4 m to 43.7 m, we found that plant species composition varied significantly in relation to DGW, independently of a range of 14 physical and chemical attributes of the environment. Nine understorey species, representing only 7% of the pool of 131 plant species, were identified as contributing to up to 50% of variation in species composition among the study sites. We suggest this dominant pattern driver in the understorey is explained by differential abilities among understorey species in their ability either to tolerate extended dry conditions at deeper DGW sites during periods of low rainfall, or to withstand periodically waterlogged conditions at shallow sites. Plant species richness and total plant abundance (a measure of plant productivity) were not significantly and independently related to DGW or any of the other 14 environmental attributes. Our finding for a direct relationship between DGW and plant species composition provides important reference information on the ecological condition of these mesic woodlands in the absence of groundwater extraction. Such information is vital for setting ecological thresholds that ensure sustainable extraction of groundwater.

Fire trails provide access into vegetation for controlled burns in fire-prone regions of the world. We examined the