Differential Trends of Qinghai Spruce Growth with Elevation in Northwestern China during the Recent Warming Hiatus

Abstract

Tree growth strongly responds to climate change, especially in semiarid mountainous areas. In recent decades, China has experienced dramatic climate warming; however, after 2000 the warming trend substantially slowed (indicative of a warming hiatus) in the semiarid areas of China. The responses of tree growth in respect to elevation during this warming hiatus are poorly understood. Here, we present the responses of Qinghai spruce (Picea crassifolia Kom.) growth to warming using a stand-total sampling strategy along an elevational gradient spanning seven plots in the Qilian Mountains. The results indicate that tree growth experienced a decreasing trend from 1980 to 2000 at all elevations, and the decreasing trend slowed with increasing elevation (i.e., a downward trend from −10.73 mm2 year−1 of the basal area increment (BAI) at 2800 m to −3.48 mm2 year−1 of BAI at 3300 m), with an overall standard deviation (STD) of 2.48 mm2 year−1. However, this trend reversed to an increasing trend after 2000, and the increasing trends at the low (2550–2900 m, 0.27–5.07 mm2 year−1 of BAI, p > 0.23) and middle (3000–3180 m, 2.08–2.46 mm2 year−1 of BAI, p > 0.2) elevations were much weaker than at high elevations (3300 m, 23.56 mm2 year−1 of BAI, p < 0.01). From 2000–2013, the difference in tree growth with elevation was much greater than in other sub-periods, with an overall STD of 7.69 mm2 year−1. The stronger drought conditions caused by dramatic climate warming dominated the decreased tree growth during 1980–2000, and the water deficit in the 2550–3180 m range was stronger than at 3300 m, which explained the serious negative trend in tree growth at low and middle elevations. After 2000, the warming hiatus was accompanied by increases in precipitation, which formed a wetting–warming climate. Although moisture availability was still a dominant limiting factor of tree growth, the relieved drought pressure might be the main reason for the recent recovery in the tree growth at middle and low elevations. Moreover, the increasing temperature significantly promoted tree growth at 3300 m, with a correlation coefficient between the temperature and BAI of 0.77 (p < 0.01). Our results implied that climate change drove different growth patterns at different elevations, which sheds light into forest management under the estimated future climate warming: those trees in low and middle elevations should be paid more attention with respect to maintaining tree growth, while high elevations could be a more suitable habitat for this species.

Divergent Seasonal Patterns of Qinghai Spruce Growth with Elevation in Northwestern China

“…Therefore, to assess the impacts of future climate change on forest growth, it is crucial to study the climatic forcing of tree growth at annual and seasonal time scales. However, a number of studies about growth-climate relationships were mostly based on tree-ring-based investigations [7][8][9][10]. Such studies do not fully explain the effects of climate conditions on tree growth and do Forests 2022, 13, 388 2 of 14 not capture seasonal growth changes and relevant growth-limiting factors.…”

“…tree growing in this region is a native evergreen conifer growing at an elevation of 2500-3300 m a.s.l. [7,9]. Earlier studies showed that daily and seasonal variation in stem growth of Qinghai spruce trees at the single scale and among tree classes, and that stem growth initiation was governed by air temperature and/or soil temperature [20,[23][24][25], and that growth cessation was affected by soil moisture under drought conditions [20].…”

Elevation Alone Alters Leaf N and Leaf C to N Ratio of Picea crassifolia Kom. in China’s Qilian Mountains

“…The species provides significant ecological functions, including the conservation of water resources and biodiversity, and the maintenance of ecological safety [17]. Recently, studies of P. crassifolia have focused on its growth response and adaption to global warming from a physiological perspective [18,19]. Yet knowledge remains limited regarding the response of P. crassifolia's leaf stoichiometry to environmental changes along elevational gradients.…”

The Variation in Water Consumption by Transpiration of Qinghai Spruce among Canopy Layers in the Qilian Mountains, Northwestern China

“…), located on a northwest-facing slope with a slope gradient of 27 • (Figure 1c). The forest in the plot consisted of Qinghai spruce ranging from 45 to 115 years in age [27]. The canopy density, i.e., the ratio of the total projected area of all trees to the total stand area, was 0.55.…”