Lessons learned from a long‐term irrigation experiment in a dry Scots pine forest: Impacts on traits and functioning

Abstract

Climate change exposes ecosystems to strong and rapid changes in their environmental boundary conditions mainly due to the altered temperature and precipitation patterns. It is still poorly understood how fast interlinked ecosystem processes respond to altered environmental conditions, if these responses occur gradually or suddenly when thresholds are exceeded, and if the patterns of the responses will reach a stable state. We conducted an irrigation experiment in the Pfynwald, Switzerland from 2003-2018. A naturally dry Scots pine (Pinus sylvestris L.) forest was irrigated with amounts that doubled natural precipitation, thus releasing the forest stand from water limitation.The aim of this study was to provide a quantitative understanding on how different traits and functions of individual trees and the whole ecosystem responded to increased water availability, and how the patterns and magnitudes of these responses developed over time. We found that the response magnitude, the temporal trajectory of responses, and the length of initial lag period prior to significant response largely varied across traits. We detected rapid and stronger responses from aboveground tree traits (e.g., tree-ring width, needle length, and crown transparency) compared to belowground tree traits (e.g., fine-root biomass). The altered aboveground traits during the initial years of irrigation increased the water demand and trees adjusted by increasing root biomass during the later years of irrigation, resulting in an increased survival rate of Scots pine trees in irrigated plots. The irrigation also stimulated ecosystem-level foliar decomposition rate, fungal fruit body biomass, and regeneration abundances of broadleaved tree species. However, irrigation did Arun K. Bose and Andreas Rigling contributed equally to this work.

Photosynthetic acclimation and sensitivity to short- and long-term environmental changes in a drought-prone forest

“…In a Scots pine-dominated fore t i o e of witzer a d' drie t areas, we conducted leaf-level gas exchange measurements in a long-term irrigation experiment covering multiple years. Scots pine in this region is growing at the dry edge of its distribution, pushing the species to be highly drought-selected (Bose et al, 2022). Previous studies within this long-term irrigation experiment showed significant structural adjustments of the trees in response to long-term irrigation, in the form of increased leaf area and growth (Fig.…”

Temporal and spatial dynamics in soil acoustics and their relation to soil animal diversity

“…The study was set up within the irrigation experiment initiated in 2003 by the Swiss Federal Research Institute for Forest, Snow, and Landscape Research WSL [37] (Fig 1), targeted at obtaining a high spatial variability in soil microclimatic conditions. Every year between April and October, half of the plots (irrigation treatment) were irrigated by a sprinkler system providing an additional 700 mm of water annually, and the other half served as control.…”

Soil Respiration Response to Simulated Precipitation Change Depends on Ecosystem Type and Study Duration

“…Intriguingly, there is evidence of this relationship between OCS and ecosystem acclimation: in a long‐term grassland irrigation experiment, which was not included in our data set, the long‐term increased precipitation treatment had the highest respiration rates (higher than short‐term increased precipitation) and increased soil labile C content (Broderick et al., 2022). Additionally, in a dry Scots pine forest irrigated for 17 years, tree responses typically took 4 years to reach a peak value and then stabilized or decreased (Bose et al., 2022). These responses included increased belowground C inputs.…”