Given its wide climatic and geographical amplitude, lodgepole pine (Pinus contorta Dougl. ex Loud.) has been introduced outside its range as an important forestry plantation species, including in the boreal region of northern Sweden, where Scots pine (Pinus sylvestris L.) is the dominant native pine species. When a species is introduced into new regions, there is great uncertainty whether the trait differences of the introduced species or regional factors, such as climate or edaphic properties, will serve as the dominant control of ecosystem properties or processes. In this study, we examined whether the introduction of Pinus contorta (Pc) into Sweden has altered forest floor properties and processes, or whether these properties are more strongly controlled by regional factors. We compared forest floor pH, potential nitrogen (N) mineralization rates, bulk density, litter and forest floor depths, Carbon (C) and N concentrations and pool sizes, C:N ratios, and soil microbial communities using substrate-induced respiration and phospholipid-fatty-acid analysis, among stands of introduced P. contorta (SwPc), native Swedish Pinus sylvestris (Ps), and native Canadian P. contorta (CaPc).
Results/Conclusions
For most forest floor properties (pH, net NH4+ mineralization, bulk density, N mass, and the microbial phospholipid fatty acid community structure) SwPc sites were more similar to SwPs than to CaPc, whereas litter and forest floor depth were significantly higher in SwPc than the two other forest types. Our findings demonstrated that regional factors exerted a stronger control on most forest floor properties and processes than did species differences between the two Pinus species for the regions we studied. Our study suggests that the impact of species introductions on ecosystem processes are likely to be functions of both regional influences and ecological differences between the introduced and comparable native species.