Climate and landscape variation shapes the water balance of piñon pine-juniper woodlands

Abstract

• Piñon pine-juniper woodlands are strongly influenced by water balance (WB) variation. • Southern Nevada woodlands are a model for future hot and dry conditions regionally. • WB magnitude was driven by climate; partitioning was shaped by landscape factors. • Tree transpiration partitioning and magnitude declined at moderate woodland densities. • Climate conditions and stand characteristics impart meaningful WB variation. Piñon pine-juniper woodlands are strongly influenced by water balance variation imparted by variation in climate, landscape attributes, and tree stand characteristics. To elucidate how these multiple factors shape woodland ecohydrology, we simulated the water balance of woodlands in the Spring (higher precipitation (PPT), higher potential evapotranspiration (PET)) and Sheep (lower PPT, lower PET) mountains of southern Nevada, USA. Simulations included: (1) elevation and climate (2000, 2200 and 2400 m; 3 scenarios); (2) low and moderate adult tree density (2 scenarios); and (3) south-facing, neutral, and north-facing aspects (3 scenarios; 18 scenarios in each mountain range). Due to the interplay between PPT and PET, the lower PPT Sheep mountains were atmospherically less dry (PPT – PET) than the Spring mountains. Following this, the Sheep mountains had higher transpiration partitioning into evapotranspiration (T/ET), whereas transpiration magnitude was higher in the Spring mountains. In both mountain ranges, soil moisture and tree transpiration were highest in winter and spring, and low in summer. T/ET was maximized at 12–15 m 2 ha − 1 basal area, illustrating the increasing influence of interception at higher tree densities. Thus, the water balance of these woodlands was driven by PPT, yet partitioning was shaped by PET and tree stand density. Interplay between soil moisture, tree transpiration, evaporation and interception is a defining characteristic of woodlands in southern Nevada, and may be influenced at broader and finer spatial scales. Better understanding of climatic, landscape, and tree stand factors may help to explain high water balance variation observed in woodlands across the western US, and improve understanding of how future change to piñon pine-juniper ecosystems may be realized.