Temperature and sheltering determine patterns of seedling establishment in an advancing subtropical treeline

Abstract

Questions: An advance of high-altitude treelines has been reported in response to warming climate throughout the globe. Understanding local controls on the establishment of seedlings above the treeline is essential for predicting wider patterns of treeline response from a process-based perspective. Here we investigate patterns of seedling establishment in relation to microsite conditions in an advancing treeline ecotone in the subtropics, using climate data recorded at the plant-relevant scale. We sought to determine which temperature factors were of importance, if sheltering plays an important role in seedling establishment and if the response varied with seedling age. Location:The Abies kawakamii treelines of the Central Mountain Range, Taiwan, 2800 to 3275 m a.s.l.Methods: Seedlings were monitored in plots covering a range of treeline structural forms over a period of 2 yrs. Temperatures were recorded at plant-relevant height (5 cm) above ground and depth below ground with data loggers. Microtopographic sheltering (at a 10-m scale) and surrounding vegetation were measured. The influence of the above variables on seedling number and growth was investigated using generalized linear models and linear mixed effect models, respectively.Results: Soil temperatures had more influence on seedling number than air temperature, whilst air temperature was positively associated with subsequent seedling growth. Establishment patterns were found to have a strong relationship with microtopographic sheltering, with more sheltered areas having elevated seedling numbers. Early growth may have significant implications for subsequent plant performance since smaller seedlings were more sensitive to both temperature and microtopography than larger seedlings.Conclusions: Air and soil temperatures and microtopography determine spatial patterns of seedling establishment. Our results suggest that establishment above the treeline is likely to continue as the climate warms, although advance will not be spatially uniform due to the modifying influence of topography. This variability has important implications for the persistence and extinction of alpine plant communities occurring above treeline in topographically complex systems.

Very high‐resolution digital elevation models: are multi‐scale derived variables ecologically relevant?

“…; Greenwood et al . ). However, the gradual emergence of very high‐resolution (VHR, ≤1 m) elevation data offered unprecedented level of details for exploring the morphological characteristics of landscape and promoted new applications (see Lassueur, Joost & Randin ; Kalbermatten et al .…”

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

“…Most data arrives from measurements in 10 cm soil depth, however some authors report from data measured in 5 cm or deeper (15, 20, 30, 50 cm) or in differing time periods (e.g. Bendix and Rafiqpoor, 2001;Cierjacks et al, 2008;Greenwood et al, 2015;Hät-tenschwiler et al, 2002;Hertel and Wesche, 2008;Karlsson and Weih, 2001;Liu and Luo, 2011;Rossi et al, 2007;Sveinbjörnsson et al, 2010;Walter and Medina, 1969;Wininger, 1981), which are not included in Table 2.…”

Community change and species richness reductions in rapidly advancing tree lines

“…The A. kawakamii forest is advancing upward in altitude on Hehuanshan in a complex and topographically mediated way, with considerable spatial variation (Greenwood et al ., , ). Following Harsch & Bader () and Greenwood et al .…”