Coping With Extreme Events: Growth and Water‐Use Efficiency of Trees in Western Mexico During the Driest and Wettest Periods of the Past One Hundred Sixty Years

Abstract

Understanding how trees respond to extreme events is important to predict how climate change will impact forests in the future. In this study, we report changes in radial growth and tree-ring carbon (δ 13 C) and oxygen (δ 18 O) stable isotope ratios of Pseudotsuga menziesii (Douglas-fir) in western Mexico. Tree growth was compared with δ 13 C and δ 18 O ratios recorded during dry and wet periods caused by El Niño-Southern Oscillation since 1850. The three driest and three wettest events during the studied period caused tree growth decline of up to 50% followed by 6-10 years of slow recovery until baseline growth was regained. Wet events resulted in up to 17% growth increase, a positive effect that persisted for no more than 3-5 years. Stable isotope ratios recorded physiological adjustments that in some cases correlated significantly with tree growth. Excursions in tree-ring Δ 13 C and δ 18 O isotope ratios suggest that trees cope with dry and wet periods with proportional but divergent adjustments in photosynthesis versus stomatal conductance. Notably, the intrinsic water-use efficiency-that is, the ratio between carbon assimilation and water loss through transpiration-was positively correlated with tree basal growth only during dry periods. We found no significant correlations between growth and intrinsic water-use efficiency during wet periods. Contrary to expectations, rising CO 2 levels over the past~160 years did not affect tree growth response to precipitation variability.

Climate-induced reversal of tree growth patterns at a tropical treeline

“…Contrary to expectations, we did not find clear growth signals of El Niño–Southern Oscillation events, which have been recorded in other montane forests in the region ( 40 ). We lack historical climate data before the 1960s, when the local instrumental record begins, but our growth data indicate a persistent trend from favorable to increasingly adverse conditions on SFS and increasingly favorable conditions on NFS.…”

“…In other systems, these buffering effects have resulted in lagged responses of plant community composition and productivity to climate change (51). In montane forests of central Mexico, this buffering effect influenced tree response to the driest and wettest events since 1850, manifested as a 3-to 10-year lag in BAI growth responses accompanied in some cases by iWUE and  18 O excursions (40). In recent decades, glaciers in the volcanoes of central Mexico have almost disappeared.…”

A record of vapour pressure deficit preserved in wood and soil across biomes

“…These sites and other low-VPD (< ~ 0.6 kPa) sites are among the most favorable locations to preserve cellulose because the preservation of cellulose requires exceptional taphonomic conditions that suppress decay 65 . This almost always requires rapid burial in an aqueous medium, and therefore the resulting mummified or coalified wood is likely to occur in low-VPD settings where δ 13 C and δ 18 O ratios may be decoupled 66 . Such low VPD sites include Histosol paleosols, like the Eocene Metasequoia wood sites used here, but Metasequoia stumps were emergent from the Histosol and so fully aerated (and subject to variations in atmosphere moisture), rather than completely submerged during growth 67 .…”

Rangeland rehabilitation using micro-catchments and native species in Turkana County, Kenya

“…However, water use efficiency can reduce if infiltration and water holding capacity is not addressed (Hatfield and Dold, 2019;Stroosnijder et al, 2012). A combination of these native species and the use of water harvesting technologies in Turkana County as a strategy for rehabilitation can significantly provide a platform for promoting regeneration of native plant species to improve forest and ground cover as well as improving communities' livelihoods (Castruita-Esparza et al, 2019;Jama and Zeila, 2005). Micro-catchments are rainwater harvesting structures that collect rainfall run-off and direct it to the planting hole, thus improving soil moisture and plant vigour (Haruna, 2014;Rahman et al, 2020).…”