Rapid warming accelerates tree growth decline in semi‐arid forests of Inner Asia

Abstract

Forests around the world are subject to risk of high rates of tree growth decline and increased tree mortality from combinations of climate warming and drought, notably in semi-arid settings. Here, we assess how climate warming has affected tree growth in one of the world's most extensive zones of semi-arid forests, in Inner Asia, a region where lack of data limits our understanding of how climate change may impact forests. We show that pervasive tree growth declines since 1994 in Inner Asia have been confined to semi-arid forests, where growing season water stress has been rising due to warming-induced increases in atmospheric moisture demand. A causal link between increasing drought and declining growth at semi-arid sites is corroborated by correlation analyses comparing annual climate data to records of tree-ring widths. These ring-width records tend to be substantially more sensitive to drought variability at semi-arid sites than at semi-humid sites. Fire occurrence and insect/pathogen attacks have increased in tandem with the most recent (2007-2009) documented episode of tree mortality. If warming in Inner Asia continues, further increases in forest stress and tree mortality could be expected, potentially driving the eventual regional loss of current semi-arid forests.

Biome changes and their inferred climatic drivers in northern and eastern continental Asia at selected times since 40 cal ka bp

“…For example, 20th century warming caused shrub expansion ("arctic greening") in northern Siberia (Sturm et al 2001;Frost and Epstein 2014), whereas forest cover was reduced in central Yakutia from 1982 to 2005 due to permafrost degradation (Lloyd et al 2011). In the semi-arid forests of inner Asia, tree growth has declined since 1994 due to a temperature-induced reduction in effective moisture (Liu et al 2013). However, an increase in vegetation cover occurred between 1991 and 2000 on the Loess Plateau, especially in hilly regions (belonging to the semi-arid region), mainly as a result of ecological restoration (Sun et al 2015).…”

Climate effects on vegetation vitality at the treeline of boreal forests of Mongolia

“…Forests in the taiga receive generally more precipitation and thus have developed higher stand densities and are also home to more water-demanding dark taiga tree species like Abies sibirica and Pinus sibirica (Dulamsuren, 2004;Dulamsuren et al, 2010a). Reports of increased drought stress, reduced stemwood formation, reduced forest regeneration and increased tree mortality, especially in the Larix sibirica-dominated forest-steppe ecotones of inner Asia, support this conclusion (Dulamsuren et al, 2010a(Dulamsuren et al, , b, 2013Liu et al, 2013).…”

Species- and Elevation-Dependent Growth Responses to Climate Warming of Mountain Forests in the Qinling Mountains, Central China

“…It has been reported that forests are subjected to an increasing risk of growth decline, canopy dieback, and mortality under warming-induced drought stress in semi-arid areas [3][4][5][6], but on the other hand, climate warming has increased tree growth and recruitment in cold biomes [7,8]. However, the climate-growth relationship seems to be more complex in humid and sub-humid mountainous areas [9][10][11], where forest dieback and mortality episodes have been also recorded [2].…”