Early season short-day treatment did not affect the field performance of Pinus sylvestris container seedlings in summer planting

Abstract

When Scots pine (Pinus sylvestris L.) seedlings are short-day (SD) treated in May or early June, height growth ceases but seedlings reflush within a few weeks and grow secondary needles (later referred to as early SD treatment). These “2-year-old-like” seedlings have been thought to be more stress tolerant than traditional 1-year-old pine seedlings, and thus suitable for summer and autumn plantings. To test this, seedlings sown in April were early SD treated over a 3-week period from the beginning of June and the seedlings were planted at 10-day intervals from the beginning of July until the end of September, and also during the following spring. Neither survival nor height growth of early SD-treated seedlings differed from untreated (1-year-old) seedlings. Moreover, for both early SD-treated seedlings and 1-year-old seedlings, those planted in summer grew and survived better after planting but had more multiple leaders than seedlings planted in autumn or spring.

Keywords:

• Pinus sylvestris
• photoperiod
• planting date
• short-day treatment

Acknowledgements

The experiment was conducted in cooperation with UPM-Kymmene Metsä. We are grateful to the corporation and also to Kyösti Konttinen, Ritva Pitkänen, Pekka Savola, and Pekka Voipio for their technical assistance in establishing the experiment and collecting the data. We also thank Dr Juha Lappi for his statistical advice, Dr Johanna Riikonen for her valuable comments on the manuscript and Ms Sheryl Hinkkanen for checking the language.