Vapor–pressure deficit and extreme climatic variables limit tree growth

Self Cite

197

110

Extreme climate events (ECEs) such as severe droughts, heat waves, and late spring frosts are rare but exert a paramount role in shaping tree species distributions. The frequency of such ECEs is expected to increase with climate warming, threatening the sustainability of temperate forests. Here, we analyzed 2,844 tree‐ring width series of five dominant European tree species from 104 Swiss sites ranging from 400 to 2,200 m a.s.l. for the period 1930–2016. We found that (a) the broadleaved oak and beech are sensitive to late frosts that strongly reduce current year growth; however, tree growth is highly resilient and fully recovers within 2 years; (b) radial growth of the conifers larch and spruce is strongly and enduringly reduced by spring droughts—these species are the least resistant and resilient to droughts; (c) oak, silver fir, and to a lower extent beech, show higher resistance and resilience to spring droughts and seem therefore better adapted to the future climate. Our results allow a robust comparison of the tree growth responses to drought and spring frost across large climatic gradients and provide striking evidence that the growth of some of the most abundant and economically important European tree species will be increasingly limited by climate warming. These results could serve for supporting species selection to maintain the sustainability of forest ecosystem services under the expected increase in ECEs.

Section: Discussionsupporting

confidence: 93%

Contrasting resistance and resilience to extreme drought and late spring frost in five major European tree species

Vitasse

Bottero

Cailleret

et al. 2019

Self Cite

197

110

“…Additionally, there may well be differences in the ecophysiological responses of Bornean tree species to VPD compared to those of the Neotropical montane species studied in Motzer et al (), although we note that both systems are characterized by relatively aseasonal climates and that in selecting a VPD threshold of 12 hPa we adopted the upper limit identified in the above‐mentioned study. Nonetheless, to assess how sensitive our estimates are to the choice of VPD threshold, we repeated the analysis assuming a VPD max of 15 hPa as a limit to transpiration, which is in line with recent estimates for temperate tree species in Europe (Sanginés de Cárcer et al, ).…”

Section: Methodsmentioning

confidence: 95%

“…VPD is the difference between the saturation water vapour pressure ( e s ) and the actual water vapour pressure ( e )—in other words the difference between how much moisture the air can hold before becoming saturated and the amount of moisture actually present in the air. As such, VPD is intimately linked to water transport and transpiration in plants (Anderson, ; Motzer, Munz, Kuppers, Schmitt, & Anhuf, ; Will, Wilson, Zou, & Hennessey, ), with high VPD driving reduced growth and survival in both temperate and tropical trees (McDowell et al, ; Sanginés de Cárcer et al, ). Given that

RH = (e false/ e_{s}) \times 100

, VPD can be expressed as

[()(100 - RH) false/ 100] \times e_{s}

, where e s is derived from T using Bolton's () equation:

e_{s} = 6.112 {\times e}^{\frac{17.67 \times T}{T + 243.5}}

.…”

Section: Methodsmentioning

confidence: 99%

Canopy structure and topography jointly constrain the microclimate of human‐modified tropical landscapes

Jucker

Hardwick

Both

et al. 2018

192

203

Local‐scale microclimatic conditions in forest understoreys play a key role in shaping the composition, diversity and function of these ecosystems. Consequently, understanding what drives variation in forest microclimate is critical to forecasting ecosystem responses to global change, particularly in the tropics where many species already operate close to their thermal limits and rapid land‐use transformation is profoundly altering local environments. Yet our ability to characterize forest microclimate at ecologically meaningful scales remains limited, as understorey conditions cannot be directly measured from outside the canopy. To address this challenge, we established a network of microclimate sensors across a land‐use intensity gradient spanning from old‐growth forests to oil‐palm plantations in Borneo. We then combined these observations with high‐resolution airborne laser scanning data to characterize how topography and canopy structure shape variation in microclimate both locally and across the landscape. In the processes, we generated high‐resolution microclimate surfaces spanning over 350 km2, which we used to explore the potential impacts of habitat degradation on forest regeneration under both current and future climate scenarios. We found that topography and vegetation structure were strong predictors of local microclimate, with elevation and terrain curvature primarily constraining daily mean temperatures and vapour pressure deficit (VPD), whereas canopy height had a clear dampening effect on microclimate extremes. This buffering effect was particularly pronounced on wind‐exposed slopes but tended to saturate once canopy height exceeded 20 m—suggesting that despite intensive logging, secondary forests remain largely thermally buffered. Nonetheless, at a landscape‐scale microclimate was highly heterogeneous, with maximum daily temperatures ranging between 24.2 and 37.2°C and VPD spanning two orders of magnitude. Based on this, we estimate that by the end of the century forest regeneration could be hampered in degraded secondary forests that characterize much of Borneo's lowlands if temperatures continue to rise following projected trends.

“…These differences may depend on different rooting systems or hydraulic responses to drought (e.g. differences in stomatal responses to high water deficits; Forner, Aranda, Granier, & Valladares, ; Sanginés de Cárcer et al, ).…”

Section: Discussionmentioning

confidence: 99%

The impact of drought spells on forests depends on site conditions: The case of 2017 summer heat wave in southern Europe

Rita

Camarero

Nolè

et al. 2019

A major component of climate change is an increase in temperature and precipitation variability. Over the last few decades, an increase in the frequency of extremely warm temperatures and drought severity has been observed across Europe. These warmer and drier conditions may reduce productivity and trigger compositional shifts in forest communities. However, we still lack a robust, biogeographical characterization of the negative impacts of climate extremes, such as droughts on forests. In this context, we investigated the impact of the 2017 summer drought on European forests. The normalized difference vegetation index (NDVI) was used as a proxy of forest productivity and was related to the standardized precipitation evapotranspiration index, which accounts for the temperature effects of the climate water balance. The spatial pattern of NDVI reduction in 2017 was largely driven by the extremely warm summer for parts of the central and eastern Mediterranean Basin (Italian and Balkan Peninsulas). The vulnerability to the 2017 summer drought was heterogeneously distributed over Europe, and topographic factors buffered some of the negative impacts. Mediterranean forests dominated by oak species were the most negatively impacted, whereas Pinus pinaster was the most resilient species. The impact of drought on the NDVI decreased at high elevations and mainly on east and north‐east facing slopes. We illustrate how an adequate characterization of the coupling between climate conditions and forest productivity (NDVI) allows the determination of the most vulnerable areas to drought. This approach could be widely used for other extreme climate events and when considering other spatially resolved proxies of forest growth and health.