On the hidden significance of differing micro-sites on tree-ring based climate reconstructions

Abstract

2015). On the hidden significance of differing micro-sites on tree-ring based climate reconstructions. Silva Fennica vol. 49 no. 1 article id 1220. 12 p. Highlights• Pines and spruces show growth level differences in wet and dry micro-sites with higher growth rates in the dry sites.• Spruces show a robust climate-growth relationship with June-July temperatures.• Application of collective detrending methods can bias long-term trends in climate reconstructions, if relict and recent samples originate from different micro-sites. AbstractTree-ring chronologies are commonly extended back in time by combining samples from living trees with relict material preserved in man-made structures or natural archives (e.g. lakes). Although spatially close, these natural archives and living-tree-sites often comprise different micro-climates. Inhomogeneous growth conditions among these habitats, which may yield offsets in growth-rates, require caution in data processing. Here we assess species-specific growth dynamics in two micro-habitats and their potential effects on long chronologies by combining tree-ring data from different living-tree-sites with an "artificial" subfossil dataset. Well replicated (n > 80) Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) chronologies from northern Fennoscandia, sampled directly at the lakeshore (wet) and several meters beyond the lakeshore (dry) reveal high coherence of the variance between micro-sites (r spruce = 0.59, r pine = 0.68). Significant differences of the Regional Curves (RC) indicate faster growth of both species at the drier site though. Growth differences are more pronounced between the spruce micro-sites. The combination of recent dry and wet spruce data with artificial relict data results in two long chronologies covering the last 800 years with substantially different trends, although they consist of the same relict material and the micro-site chronologies correlate significantly over the past two centuries. The combination of spruce samples from dry inland micro-sites with subfossil samples originating from the wet lake shore can result in an underestimation of past temperatures prior to the 19th century. Such effects, hidden in the composition of long chronologies (living trees + subfossil samples) can bias long-term trends in climate reconstructions.

Arctic moistening provides negative feedbacks to riparian plants

“…In addition to the well‐established link between the summer (especially July) temperature and P. sylvestris growth in Lapland (Düthorn et al., ; Helama, ; Helama, Lindholm, Meriläinen, Timonen, & Eronen, ; Hilasvuori et al., ; McCarroll et al., ), recorded also in our setting (Figure a), the radial growth was additionally influenced by irradiance (Figure c). Observed over the three summer months, this signal was distinctly different in comparison to that of more specific influence of July temperature, thus indicating that the two climate signals represent separate temperature/irradiance responses.…”

“…Concentrating on P. sylvestris data, the radial growth was found markedly reduced on wet soils, in comparison to dry substrates, in central Scandinavian mountains (Linderholm, ) and in northern Scotland (Moir et al., ). Similarly, the riparian trees exhibited reduced radial growth in comparison to dry soil microsite in northern Finland (Düthorn et al., , ), whereas in northern Sweden especially the growth of young riparian pines exceeded that of their dry soil counterparts (Düthorn et al., ). In central and south boreal settings, the growth of riparian pines have been found either increased (Düthorn et al., ) or decreased (Helama et al., ) compared to upland pines.…”

“…radial growth) records for analysing the effects of changing lake water level and highly variable subarctic climate on Scots pine (Pinus sylvestris L.), the main tree species of the forested ecosystem in high-latitude Europe, Finnish Lapland, that has generally low tolerance to flooding and waterlogging (Glenz, Schlaepfer, Iorgulescu, & Kienast, 2006). First, although tree-ring chronologies of P. sylvestris have previously been developed for studying the tree growth variability in boreal lakeshore and control stands (D€ uthorn, Holzk€ amper, Timonen, & Esper, 2013;D€ uthorn, Schneider, G€ unther, Gl€ aser, & Esper, 2016;D€ uthorn et al, 2015;Helama et al, 2013;Linderholm et al, 2014), there is a critical lack of d 13 C data to delve into the ecophysiological processes and their external drivers. Here we emphasize the value of using such data to derive indications of anomalies in stomatal conductance and assimilation that may be generally affected from changing water level (Kozlowski, 1984;Parent et al, 2008;Sojka, 1992;Wang et al, 2017) as having been previously reported also for P. sylvestris seedlings (Lotocki, 1977;Repo, Heiskanen, Sutinen, Sutinen, & Lehto, 2017;Repo et al, 2016).…”

Ranking of tree-ring based temperature reconstructions of the past millennium

“…If not, older sections of a millennial-length chronology can have different growth rates and climate signals than those sections dominated by samples from living trees (Boswijk et al, 2014;Linderholm et al, 2014;Tegel et al, 2010). For example, remnant samples from a sub-alpine site in the Alps are ideally combined with samples from living trees growing on the same slope, at the same elevation and aspect (Neuwirth et al, 2004); sub-fossil trees from a shallow lake in Fennoscandia are ideally combined with trees growing around the lake, as opposed to drier inland locations (Düthorn et al, 2013(Düthorn et al, , 2015.…”

Influence of sampling and disturbance history on climatic sensitivity of temperature-limited conifers

“…Mérian et al, 2013;Osborn et al, 1997;Wigley et al, 1984), sampling design and microsite conditions (e.g. Cherubini et al, 1998;Düthorn et al, 2013Düthorn et al, , 2015Nehrbass-Ahles et al, 2014), and tree age (e.g. Carrer and Urbinati, 2004;Esper et al, 2008;Fish et al, 2010).…”