Stem girth changes in response to soil water potential in lowland dipterocarp forest in Borneo: An individualistic time-series analysis

PLoS One. 2022 Jun 30;17(6):e0270140. doi: 10.1371/journal.pone.0270140. eCollection 2022.

Abstract

Time-series data offer a way of investigating the causes driving ecological processes as phenomena. To test for possible differences in water relations between species of different forest structural guilds at Danum (Sabah, NE Borneo), daily stem girth increments (gthi), of 18 trees across six species were regressed individually on soil moisture potential (SMP) and temperature (TEMP), accounting for temporal autocorrelation (in GLS-arima models), and compared between a wet and a dry period. The best-fitting significant variables were SMP the day before and TEMP the same day. The first resulted in a mix of positive and negative coefficients, the second largely positive ones. An adjustment for dry-period showers was applied. Interactions were stronger in dry than wet period. Negative relationships for overstorey trees can be interpreted in a reversed causal sense: fast transporting stems depleted soil water and lowered SMP. Positive relationships for understorey trees meant they took up most water at high SMP. The unexpected negative relationships for these small trees may have been due to their roots accessing deeper water supplies (if SMP was inversely related to that of the surface layer), and this was influenced by competition with larger neighbour trees. A tree-soil flux dynamics manifold may have been operating. Patterns of mean diurnal girth variation were more consistent among species, and time-series coefficients were negatively related to their maxima. Expected differences in response to SMP in the wet and dry periods did not clearly support a previous hypothesis differentiating drought and non-drought tolerant understorey guilds. Trees within species showed highly individual responses when tree size was standardized. Data on individual root systems and SMP at several depths are needed to get closer to the mechanisms that underlie the tree-soil water phenomena in these tropical forests. Neighborhood stochasticity importantly creates varying local environments experienced by individual trees.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Borneo
  • Droughts
  • Forests*
  • Soil*
  • Trees / physiology
  • Tropical Climate

Substances

  • Soil

Grants and funding

The dendroband field work was supported by the Swiss National Science Foundation (Grant 31003A-110250, 2006-2010) to D. M. Newbery, and the subsequent data analysis by the Chair for Vegetation Ecology (DMN), Bern. Comparative tree growth data used in this paper came from previous research also supported by the SNSF (Grant 3100-59088) also to D. M. Newbery. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.