Drought as a Disturbance in Forests

by

Rafael Poyatos, Enrique Doblas-Miranda

• LAST REVIEWED: 29 October 2021
• LAST MODIFIED: 26 July 2017
• DOI: 10.1093/obo/9780199830060-0187

Introduction

Drought is a situation of water deficit of a system, compared to normal conditions. Operational definitions of drought (i.e., those used to identify specific drought events) change depending upon the system under consideration, but they have been historically restricted to climatic, agricultural, hydrologic, and socioeconomic systems. From an ecologic point of view, the literature on drought-related impacts on ecosystems has grown dramatically only in recent years, prompted by our need to predict such impacts under the drier conditions projected for many areas of the Earth as a result of climate change. This article provides a guide to the literature addressing the role of drought as an agent of change in of ecosystem structure and function mediated by vegetation responses. The study of drought responses in plants has traditionally been led by agronomists and plant ecophysiologists, with an emphasis on the understanding of physiological stress or plastic responses. Here we will focus not on mild stress, but on extreme functional responses and drought-related persistent changes in terrestrial, natural, and seminatural ecosystems, considering that agricultural or freshwater ecosystems merit their own review and are beyond the scope of this article. Because of the increasing interest in the causes and consequences of drought-induced vegetation dieback since the early 21st century, many of the references included in this article are relatively recent. This large body of research has been mostly developed for woody communities, and the majority of studies selected here are hence based on woodlands. Nevertheless, we recommend the “Drought” section in the Oxford Bibliography on the “Grassland Biome” for further information.

Definitions

Disturbance is defined as “a relatively discrete event in time that disrupts the ecosystem, community or population structure and changes the resources, substrate availability or physical environment” (p. 407) (original definition by P. S. White and S. T. A. Pickett, quoted in White and Jentsch 2001). Disturbances are viewed as inherent features of ecosystems, as they are major drivers of biotic diversity and spatial heterogeneity and are tightly linked to human activity. The aggregate outcome of the disturbances occurring in a given ecosystem is called a disturbance regime, and it is shaped by the magnitude, temporal characteristics and spatial extent of individual disturbances (White and Jentsch 2001). A definition for “ecological drought” would be an appropriate starting point to characterize drought-driven disturbances, but this definition is absent from current drought typologies because drought has been frequently seen only from meteorological, hydrological, or agricultural perspectives (Mishra and Singh 2010). Indeed, the ecological- and forestry-related literature has not started to consider drought as a disturbance until very recently (Peters, et al. 2011).

• Mishra, Ashok K., and Vijay P. Singh. 2010. A review of drought concepts. Journal of Hydrology 391.1–2: 202–216.

  DOI: 10.1016/j.jhydrol.2010.07.012

  This paper outlines the main motivation for drought-related research, summarizing recent societal and economic impacts across the globe. It also summarizes current classifications of drought and drought indexes, but it does not include yet an “ecological drought” typology.

• Peters, Debra P. C., Ariel E. Lugo, F. Stuart Chapin, et al. 2011. Cross-system comparisons elucidate disturbance complexities and generalities. Ecosphere 2.7: 1–26.

  DOI: 10.1890/ES11-00115.1

  Presents a conceptual framework in which disturbances are disaggregated into different components, to aid in comparisons across different natural systems. Compared to earlier conceptual works on disturbance theory, drought is discussed intensively.

• White, Peter S., and Anke Jentsch. 2001. The search for generality in studies of disturbance and ecosystem dynamics. In Progress in botany. Edited by Karl Esser, Ulrich Lüttge, Joachim W. Kadereit, and Wolfram Beyschlag, 399–450. Progress in Botany 62. Berlin and Heidelberg, Germany: Springer.

  DOI: 10.1007/978-3-642-56849-7_17

  This book makes the case for a generalization of the understanding of ecological disturbances. It summarizes the challenges posed by ecological heterogeneity and scaling issues and proposes different approaches to deal with them. It includes a section on various definitions associated with disturbance and disturbance regimes.