News Climate, Forestry

According to an experiment conducted in Luke denser snowpack or lack of snow cover due to warmer winters could have a major impact on forest ecosystems. Winter climate change might have a negative effect on forest growth and productivity that could partially counteract the positive growth effects predicted due to increasing summer time temperatures.

Winter warming is expected to affect snow cover in boreal forest by increasing ground ice encasement, snow compaction or even events of complete lack of snow cover. Of these predicted changes ice encasement appeared to be the most harmful winter conditions to Scots pine and Norway spruce seedlings. These effects could influence forest regeneration with important implications for boreal forest ecology and the associated economy such as forest regeneration costs.

So far, models forecasting growth and productivity of boreal forest under climate change scenarios only consider changing conditions during the growing season. Our results indicate that the possible consequences of winter climate change should be taken into consideration in these models.

Snow manipulation treatments in Finnish Lapland

To understand the effect of changing snow conditions on soil microclimate as well as on the survival and growth of Norway spruce and Scots pine seedlings, a research team in Luke subjected forest experimental plots in Rovaniemi to different snow manipulation treatments.

In addition to ambient conditions, three snow manipulation levels were applied, each representing different scenarios of how winter climate change may affect snow conditions and snowpack properties: snow compaction, ground ice encasement and complete snow removal.

After one year of snow manipulation, the research showed that:

  • Snow removal led to deeper soil frost during winter, but no clear effect of ice encasement or snow compaction done in early winter was observed on soil temperature (1).
  • Hypoxia and accumulation of CO2 developed also in ambient conditions, due to naturally occurring rain-on-snow events but both hypoxia and CO2 accumulation were highest under ice encasement conditions More importantly, CO2 concentrations were above the harmful level of 5% for 17 days after ice encasement in early winter whereas this level was not exceeded in ambient conditions (Fig. 1) (1).
  • Snow manipulation had a strong effect on survival and health of seedlings planted in the previous autumn: ice encasement was the most damaging winter condition for both species, decreasing the proportion of healthy seedlings by 47% for spruce and 76% for pine compared to ambient conditions (Fig. 2) (1).
  • Seedlings in all three treatments tended to grow less in the following summer than seedlings in ambient conditions, the strongest effect being on spruce growth after ice encasement.
  • Snow manipulation had no effect on acidic boreal forest soil microbial community structure or function. The microbial communities were dominated by highly resilient taxa that seem to be insensitive to one-year changes in snow conditions (2).

martz-fig-1
Fig 1. Effect of snow manipulation on CO2 and O2 concentrations 2-cm deep in humus layer. Mean daily air temperature at field site is depicted. Snow watering occasions are indicated by blue diamonds. For better clarity, one-sided error bars are depicted. Values are means ± SE (n = 10).

martz-fig-2
Fig 2. Effect of snow manipulation on spruce (a) and pine (b) seedling survival and health the following summer. Seedlings were inventoried on June 6 and July 11, 2014. Class 1: <50% brown needles, class 2: > 50% brown needles. An asterisk indicates a statistically significant difference with AMB plots at p < 0.05. Values are means (n = 10).

Biochemical analyses of carbon and nitrogen pools in seedlings collected after the second and third winters of snow-manipulation are under progress and should shed light on physiological and molecular mechanisms underlying winter damages.

At the present stage of the study, new questions are arising, such as: What is the most damaging winter stress? How does the development stage of seedling affect its response to changing snow conditions? In a larger scale, what is the effect of different snow conditions in forest ecosystem functioning?

References

  1. Martz F, Vuosku J, Ovaskainen A, Stark S, Rautio P. (2016) The Snow Must Go On: Ground Ice Encasement, Snow Compaction and Absence of Snow Differently Cause Soil Hypoxia, CO2 Accumulation and Tree Seedling Damage in Boreal Forest. PLoS ONE. 2016 06/02;11(6):e0156620.
  2. Vuosku J, Männistö M, Stark S, Ovaskainen A, Suokas M, Saravesi K, et al. (2016) The influence of snow conditions on the structure of bacterial and fungal communities in boreal coniferous forests. In: Plant and Microbe Adaptation to Cold, 22–25 May 2016; Seattle, USA.

Academy of Finland project funding: Winter in changing climate: effects of snow conditions on plants, soil and their interactions in the boreal forest (decision 267092), 2013-2017, project leader: Pasi Rautio, Luke Rovaniemi.

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