How do soil properties affect alpine treelines? General principles in a global perspective and novel findings from Rolwaling Himal, Nepal

Abstract

Little is known about how soil properties control tree growth at its upper limit. This paper reviews the state of knowledge and discusses the results specifically related to ecozones, to the scale-dependent importance of single factors, and to new findings from a near-natural treeline ecotone in Rolwaling Himal, Nepal. This paper identifies gaps in literature and shows where new research is needed, both conceptual and geographical. The review shows that at a global scale and throughout diverse ecozones, growing season soil temperature is considered a key factor for tree growth. Soil temperatures differ greatly at a local scale, and are mainly determined by local climatic, edaphic, and topographic conditions. Our result of 7.6 + 0.6 C for growing season mean soil temperature at treeline in Rolwaling is 1.2 K higher compared to the postulated 6.4 + 0.7 C for alpine treelines. We suggest a broadening of the +0.7C error term to cover the wide range at a local scale. The role of major soil nutrients and soil moisture for treeline shift has been underestimated by far. In Rolwaling, significantly decreasing nutrient availability (N, K, Mg) in soils and foliage with elevation might explain why treeline shift and global warming are decoupled. Further, soil moisture deficits early in the year impede seedling and sapling establishment, which could be an important mechanism that controls treeline position. These findings question previous results which argue that alpine treelines are unaffected by soil nutrient availability and

Land-use change under a warming climate facilitated upslope expansion of Himalayan silver fir (Abies spectabilis (D. Don) Spach)

“…The small increase in average atmospheric temperature has not yet impacted species distribution in this ecotone, although it has been noted in other regions (Matteodo et al 2013;Parmesan and Yohe 2003; Telwala et al 2013). However, reduced intensity of land use (Müller et al 2015) may also have synergistic effects with increased warming in the RLI area (Morueta-Holme et al 2015).…”

“…In the GCA, the practice of collecting dead tree branches and lopping signs were observed mainly in the dense forest at lower elevations. It is a near-natural or climatic treeline in this area (Müller et al 2015;Schickhoff et al 2014). …”

Limited prospects for future alpine treeline advance in the Canadian Rocky Mountains

“…Increasingly, the role of edaphic and geomorphic properties as primary drivers of treeline dynamics is being recognized (e.g., Brown & Vellend, , Macias‐Fauria & Johnson, , Müller et al, , Müller et al, , Sullivan, Ellison, Mcnown, Brownlee, & Sveinbjörnsson, ). Correspondingly, in our analysis of the relative importance of soil, predation and microsite availability on establishment potential, we found that the magnitude of the effect of soil properties was far greater than the constraints imposed by predation and microsites.…”

Quantifying the added value of convection-permitting climate simulations in complex terrain: a systematic evaluation of WRF over the Himalayas

“…Against this background, this study performs a systematic evaluation of a 1-year WRF simulation (October 2014-September 2015) over the highly complex terrain of Khumbu (Everest) and Rolwaling Himal in terms of reproducing the spatial distribution and annual and diurnal cycles of both temperature and precipitation and, for the latter, additionally the shift in timings of the peak precipitation hour. Further, the added value of two fine-scaled (at 5 and 1 km) convection-permitting simulations was assessed relative to coarser 25 km simulation with parameterized convection, based on a dense meteorological network, including the novel observations from our TREELINE project Schwab et al, 2016;Müller et al, 2016a).…”