Mortality of urban pines in Helsinki explored using tree rings and climate records

Abstract

The mortality of Scots pine trees in and around Helsinki has been reported in recent years, but the causalities of these deaths have not so far been rigorously examined. Tree-ring analyses have previously shown to effectively reveal historical growth variability and thus hint at the stress factors behind tree mortality. Here, we analyzed the tree rings of pines in two tree classes (living and dead) from an urban park in Helsinki to reveal their growth variations and to examine the obtained chronologies along with climatic data. Guided by tree-ring information, the pine growth over the past century could be divided into four episodes: average growth conditions during the first half of the twentieth century, a suppressed growth period during the 1950s and 1960s, a growth release since the mid-1970s, and a period of recent mortality. The two tree classes became particularly differentiated during the release period in that the growth of surviving pines underwent a more positive and abrupt growth anomaly in comparison to dead pines. The survival of pines could also be linked to their sensitivity to droughts in a long-term context: The growth of still-living pines showed a statistically significant moisture sensitivity over the second half of the century only. The period 2002-2003 (coinciding with drought) was observed as a dendrochronologically dated episode with a 40% mortality. Overall, the results point to the importance of tree competitive strength and climate as predisposing and inciting/contributing factors behind the tree mortality.

Regional climatic signals in Scots pine growth with insights into snow and soil associations

“…Actually, the link between the April air temperatures and Scots pine growth is among the most controversial tree-ring correlations discussed in Finland and adjacent areas. This dendroclimatic association (Laitakari 1920;Holopainen et al 2006;Helama et al 2012;Hordo et al 2011) has not been significant in all studies (e.g., Henttonen 1984). Here, we showed that the April climate could influence the tree-ring growth primarily via soil temperatures.…”

Oak decline in a southern Finnish forest as affected by a drought sequence

“…Only one tree had a too large diameter for catching the pith and one tree was rotten inside. The relative growth rate (RGR) (Briffa and Melvin, 2011;Helama et al, 2012) for each tree was calculated as…”

Health condition of Tilia cordata Mill. trees growing in the urban environment

“…Urban trees are influenced by a wide range of various environmental factors and are in danger of being injured and damaged due to the impact of air pollution (Baldasano et al, 2003;Gregg et al, 2003), other forms of anthropogenic load (Pauleit et al, 2002;De Ridder et al, 2004), as well as by unfavourable meteorological factors (Holopainen et al, 2006;Helama et al, 2011). Deciduous trees are more resistant to pollution than conifers; therefore, they are more suitable for planting along the streets and are more common in urban areas than conifers (Helama et al, 2011).…”

“…Deciduous trees are more resistant to pollution than conifers; therefore, they are more suitable for planting along the streets and are more common in urban areas than conifers (Helama et al, 2011).…”