Articles by Curt Almqvist

Reproduction in masting species is characterised by long intervals between good cone and seed production years, and only sparse reproduction between mast years. The physiological mechanisms behind masting, and how these are linked to internal resource status and external weather factors, is still a subject of scientific exploration and debate, as is the effect of climate change on masting. This study investigates cone production in one operational seed orchard in Sweden which was established with two different spacings and has since been subject to three tree thinning experiments. The spacings before thinning varied between 800 and 400 stems ha^–1, and then thinning reduced the stand density in all trials to half, i.e. between 400 and 200 stems ha^–1. In all three experiments cone production per tree was equal in un-thinned and thinned treatments, both in mast years and in non-mast years. Thus, the cone production per unit area was twice as high in the un-thinned areas. The conclusion from these experiments is that the establishment of Picea abies (L.) H. Karst. seed orchards with wide tree spacing is both a misuse of good orchard locations and bad economics.

• Almqvist, Skogforsk, Uppsala Science Park, SE-75183 Uppsala, Sweden https://orcid.org/0000-0001-5739-4854 E-mail: curt.almqvist@skogforsk.se

Light is an important environmental factor for all green plants. Its intensity, spectral composition and photoperiod can affect the regulatory pathways in plants that lead to floral initiation. In this report, results are presented from three experiments in which supplemental light with metal halide lamps (250 µmol m^–2 s^–1, 20 hours day^–1, approx. 6 weeks) was tested as a complement to other flowering stimulation treatments (elevated temperature, treatment with gibberellin A₄ and A ₇ (GA_4/7), restricted water supply) applied to potted Picea abies (L.) Karst. in the greenhouse. Flower stimulation in a greenhouse resulted in more floral initiation compared to flower stimulation outdoors. Supplemental light treatment increased floral initiation further, and to a larger extent in female than in male flowers. It also increased the proportion of trees and genotypes that induced reproductive buds. In a practical application of the supplemental light treatment to potted Picea abies breeding material, 90.6% of the clones produced either female or male flowers, or both. A subset of the same material kept outdoors, and thus subjected to natural light and temperatures, produced no flowers despite being treated with GA_4/7 and receiving a restricted water supply. In conclusion, supplemental light treatment facilitates breeding programmes, and seed production of highly improved base material from new selections for vegetative production programmes, to be more efficient.

• Almqvist, Skogforsk (The Forestry Research Institute of Sweden), Uppsala Science Park, 751 83 Uppsala, Sweden http://orcid.org/0000-0001-5739-4854 E-mail: curt.almqvist@skogforsk.se

Seed orchards are the link between tree breeding and reforestation. This paper presents data on cone, seed and pollen production and seed quality gathered over 21 years in a Pinus sylvestris (L.) experimental seed orchard containing plots with 14 different combinations of stand density and targeted pruning height. The treatments’ stand densities ranged from 267 to 4000 stems ha^-1, and the target graft heights ranged from 2 to 6 meters. Pollen production began at the same orchard age for all studied combinations of stand density and target height but the level of pollen production per hectare increased more rapidly in treatments with higher stand densities. In treatments with dense spacing, cone and seed production initially increased more rapidly than in treatments with wider spacing, thereby providing an earlier return on investment and a shorter seed production lag time. However, the levels of cone and seed production in such treatments over the entire study period were not appreciably different to those achieved in treatments with wider spacing and higher target height. The treatments did not differ substantially with respect to seed quality. These results show that comparable levels of seed production can be obtained with different combinations of stand density and target height, giving seed orchard owners and managers a wide range of viable management options.

• Almqvist, Skogforsk (The Forestry Research Institute of Sweden), Uppsala Science Park, SE-751 83 Uppsala, Sweden E-mail: curt.almqvist@skogforsk.se
• Jansson, Skogforsk (The Forestry Research Institute of Sweden), Uppsala Science Park, SE-751 83 Uppsala, Sweden E-mail: gunnar.jansson@skogforsk.se

• Sikström, Skogforsk (The Forestry Research Institute of Sweden), Uppsala Science Park, SE-751 83 Uppsala, Sweden E-mail: ulf.sikstrom@skogforsk.se
• Almqvist, Skogforsk (The Forestry Research Institute of Sweden), Uppsala Science Park, SE-751 83 Uppsala, Sweden E-mail: ca@nn.se
• Jansson, Skogforsk (The Forestry Research Institute of Sweden), Uppsala Science Park, SE-751 83 Uppsala, Sweden E-mail: gj@nn.se

• Hannerz, The Forestry Research Institute of Sweden (SkogForsk) Uppsala Science Park, SE-751 83 Uppsala, Sweden E-mail: mats.hannerz@skogforsk.se
• Almqvist, The Forestry Research Institute of Sweden (SkogForsk) Uppsala Science Park, SE-751 83 Uppsala, Sweden E-mail: ca@nn.se
• Hörnfeldt, Swedish University of Agricultural Sciences, Dept. of Forest Products and Markets, P.O. Box 7060, SE-750 07 Uppsala, Sweden E-mail: rh@nn.se