Detecting potential regional effects of increased atmospheric CO₂ on growth rates of western juniper

Abstract

Evidence of an atmospheric CO2 fertilization effect on radial growth rates was uncovered by examining climate–growth relationships for seven western juniper tree‐ring chronologies in central Oregon using multiple regression models. Consistent upward trends of the residuals from dendroclimatic models indicated a decreased ability for climate parameters to predict growth with time. Additionally, an assessment was made of whether enhanced growth was detectable under drought conditions, because a major benefit of elevated atmospheric CO2 is the reduction of water stress. Mean ring indices were compared between ecologically comparable drought years, when atmospheric CO2 was lower (1896–1949), and more recent drought years that occurred under higher atmospheric CO2 concentrations (1950–96/98). The results presented herein show that: (i) residuals from climate/growth models had a significant positive trend at six of seven sites, suggesting the presence of a nonclimatic factor causing increased growth during recent decades; (ii) overall growth was 23% greater in the latter half of the 20th century; (iii) growth indices during matched drought and matched wet years were 63% and 30% greater, respectively, in the later 20th century than the earlier 20th century; and (iv) harsher sites had greater responses during drought periods between early and late periods. While it is not possible to rule out other factors, these results are consistent with expectations for CO2 fertilization effects.

Black pine (Pinus nigra Arn.) growth divergence along a latitudinal gradient in Western Mediterranean mountains

“…Jacoby and D'Arrigo, 1997;Kienast and Luxmoore, 1988;Körner et al, 2005). Furthermore, an improvement of WUE caused by increasing CO 2 concentration has already been suggested in black pine in the Austrian Alps (Leal et al, 2008) and for other species in the Mediterranean (Martínez-Vilalta et al, 2008;Rathgeber et al, 2000) and North America (Knapp et al, 2001). Rathgeber et al (2000) suggested that a combination of warming winters and double CO 2 concentrations enhanced net primary productivity of P. halepensis stands, in accordance with our results of positive trenders.…”

“…The fact that the ratio of positive trenders were inversely correlated with site productivity and latitude (Fig. 5) agrees with previous studies suggesting that the effect of rising CO 2 concentration would be higher in arid sites (Idso and Idso, 1994;Knapp et al, 2001;Soulé and Knapp, 2006) because the increase in WUE would reduce the drought stress of plants (Morison, 1993), although studies in trees are not conclusive (e.g. Jacoby and D'Arrigo, 1997;Kienast and Luxmoore, 1988;Körner et al, 2005).…”

“…In Mediterranean forests, global warming further increases the already high water stress which would reduce tree growth (Macias et al, 2006;Piovesan et al, 2008;Sarris et al, 2007). However, some studies have suggested the rising CO 2 concentration as an explanation of a possible growth increase of trees in dry temperate climates (Knapp et al, 2001;Martínez-Vilalta et al, 2008). CO 2 -induced increase of water-use efficiency (WUE) would be more evident at sites with greater stress and more severely limiting resources (e.g.…”

Climate-growth variability in Quercus ilex L. west Iberian open woodlands of different stand density

“…The effect of increasing temperature upon plants, in the absence of an increase in precipitation, increases ETP rates and water stress, which together with increasing CO 2 concentrations (Raupach et al, 2007) are likely to affect tree sensitivity and growth. Different authors report different responses to increasing CO 2 concentrations, although in general relative radial growth increases in dry environments due to higher water-use efficiency (WUE) are expected (Hattenschwiler et al, 1997;Knapp et al, 2001;Soulé and Knapp, 2006;Tognetti et al, 2000). However, if ETP increases in Mediterranean ecosystems, water stress could dominate over the CO 2 -induced WUE increase (if any), resulting in important changes in latitudinal and altitudinal shift of species distribution (Benito Garzón et al, 2008).…”

Surface Temperature Reconstructions for the Last 2,000 Years

“…In old age these trees can assume a "strip-bark" form, characterized by a band of trunk that remains alive and continues to grow after the rest of the stem has died. Such trees are sensitive to higher atmospheric CO 2 concentrations (Graybill and Idso 1993), possibly because of greater water-use efficiency (Knapp et al 2001, Bunn et al 2003 or different carbon partitioning among tree parts (Tang et al 1999). Support for a direct CO 2 influence on tree ring records extracted from "full-bark" trees is less conclusive.…”