Characteristics and development of improved Pinus sylvestris in northern Sweden

Abstract

Genetic differences are described between improved and unimproved Scots pine (Pinus sylvestris L.) in 36 northern Swedish field tests, covering wide geographical and climatic gradients (latitude 62.3°–67.8°N). Improved trees were represented by progenies from controlled crosses of first-generation, phenotypically selected plus trees, whereas unimproved trees originated from unselected natural stands. Improved trees were superior in terms of height (9.2%), stem diameter (5.4%), and stem volume (18.9%) at the age of 27.4 years. The height growth of improved trees from ages of 10.5 years to 27.4 years was similar to that of unimproved trees at a site with a higher site index. Improved trees had a 5.5% greater height/diameter ratio (i.e., were more slender) than unimproved trees, whereas differences between the tree categories in terms of survival and frequencies of ramicorns and stem breaks were minor and mostly insignificant. Little or no interaction between tree categories and site conditions for growth characters was found, implying that the results are generally applicable. No difference in response to competition between the improved and unimproved trees was detected. However, differences in their reactions to transfer were found: survival rates increased more and height growth decreased less in improved trees than in unimproved trees when grown at a site south of their geographical origin. The use of competition and height indices based on neighbouring trees to adjust for bias and site variability in single-tree plots significantly improved the estimates.

Scots pine transfer effect models for growth and survival in Sweden and Finland

“…The models developed in this study share the same general features as previous models of transfer effects for Scots pine in Sweden (Persson and Ståhl 1993;Persson 1994;Andersson et al 2007). All models show an increase in height growth with transfer to the north but the models differ slightly in optimum transfer distance and the size of the increased height growth.…”

“…The half-sibs' origins were considered to be the stand location of the plus-trees and the full-sib origins were calculated as the mid-parent values (cf. Andersson et al 2007;O'Neill et al 2014;Farjat et al 2015). As progeny trials in both Finland and Sweden are designed to test well-adapted candidate trees within a restricted target area they are not well suited for developing transfer functions.…”

“…In our model, the optimum southward transfer was approximately 2° at milder sites and 3° at harsher sites. In the model developed by Andersson et al (2007), there is no optimum within the 4° transfer, but survival keeps increasing as the material is transferred further south. The model by Persson (1994) behaves in a similar way to that of Andersson et al (2007), except for the mildest sites (temperature sum 1250 DD) where the optimum transfer to the south is similar to our model, around 2°.…”

“…In the model developed by Andersson et al (2007), there is no optimum within the 4° transfer, but survival keeps increasing as the material is transferred further south. The model by Persson (1994) behaves in a similar way to that of Andersson et al (2007), except for the mildest sites (temperature sum 1250 DD) where the optimum transfer to the south is similar to our model, around 2°. These differences in optima are probably due to the different datasets used in the respective studies, but compared to those with the most overlapping and comprehensive data the differences are small.…”

“…For Scots pine in Sweden and Finland, temperature sum is well correlated with forest yield (Beuker 1994;Morén and Perttu 1994;Persson and Beuker 1997) and has been used as a key site descriptor in previous transfer-effect models (Persson and Ståhl 1993;Persson 1994;Andersson et al 2007). Due to the large heterogeneity in both time and space of the field data used, age of assessment (cf.…”