Growing season

Growing season is expected to increase across Canada, with implications for forest productivity and composition.

The length of the growing season is an important determinant of plant growth and distribution. Longer growing seasons may increase plant productivity and allow for new planting opportunities in agricultural and forestry settings. However, related changes in pest species, fire regimes, droughts, and other climate extremes may limit the extent to which these gains are realized.

There has been a significant increase in growing season length (approximately 2 days/decade) across the country over the 1950–2010 period. If CO2 emissions continue to increase, it is projected that growing seasons at the end of the 21st century will be 20–40 days longer than those currently experienced across much of Canada.

Read how growing season and its indicators are defined

Why growing season is important

Growing season length has implications for both agricultural and forest productivity.

The length of the growing season indicates the amount of time that plants have to grow during a given year. It is an important determinant of plant growth and distribution. In principle, longer growing seasons could indicate increased productivity and new planting opportunities in agricultural and forest settings. However, climate change–related increases in risks associated with pests, droughts, fires and other climate extremes may limit the extent to which these gains are realized.

What has changed

Growing season length has increased across Canada over the period 1950–2010.

Figure 1 – Graph displaying growing season length (days) in Canada between 1950 and 2010.

Figure 1 – Past trends in growing season length for Canada (1950–2010)

Graph data - Figure 1
Table listing growing season length (in days) for Canada every year between 1950 and 2010.
Year Growing season length (days)
1950 62.82
1951 72.69
1952 77.06
1953 80.5
1954 81.81
1955 77.98
1956 69.38
1957 71.87
1958 78.99
1959 66.42
1960 83.37
1961 75.25
1962 76.57
1963 77.85
1964 66.3
1965 67.85
1966 80.81
1967 69.31
1968 73.71
1969 65.18
1970 76.18
1971 81.36
1972 66.39
1973 80.01
1974 73.14
1975 81.92
1976 74.5
1977 81.4
1978 68.62
1979 75.75
1980 75.34
1981 79.33
1982 68.31
1983 76.73
1984 74.23
1985 71.11
1986 64.21
1987 77.28
1988 86.05
1989 79.19
1990 76.31
1991 78.37
1992 64.49
1993 79.27
1994 83.31
1995 79.9
1996 78.92
1997 81.28
1998 96.37
1999 80.54
2000 77.28
2001 85.67
2002 72.56
2003 82.17
2004 74.1
2005 86.56
2006 89.24
2007 83.64
2008 82.88
2009 83.59
2010 88.38

Despite considerable annual variation, there was a significant increase in growing season length (1.7 days/decade) across the country over the 1950–2010 period (Figure 1). The pattern of change is relatively consistent across the country (Figure 2). Further analyses (not shown here) indicate that this change has been driven by both earlier start dates in the spring and later end dates in the fall.

Two maps showing growing season length (days) in Canada, one  between 1951 and 1980, and the other between 1981 and 2010

Figure 2 – Growing season length for Canada for two time periods: 1951–1980 (left) and 1981–2010 (right)

Larger image [455 Kb]

Set of five maps of Canada showing the length of  growing season for the reference period (1981–2010) compared to the projected length of growing season for the short term (2011–2040), medium term (2041–2070), and long term (2071–2100) using climate scenario RCP 2.6 and again, for the long term, using climate scenario RCP 8.5.

Figure 3 – Reference period (1981–2010) and projected length of growing season for the short- (2011–2040), medium- (2041–2070), and long-term (2071–2100) under the Representative Concentration Pathway (RCP)Footnote * 2.6 (rapid emissions reductions) and, for the long-term (2071–2100), under RCP 8.5 (continued emissions increases) for Canada

Larger image [301 Kb]

 

The outlook

Growing season length is projected to increase as the century progresses.

Substantial increases in growing season length are projected by the end of the current century, with growing seasons 20–40 days longer than those currently experienced across much of the country (Figure 3).

How growing season and its indicators are defined

The growing season is the period during which the weather conditions are conducive to plant growth. The length of the growing season is limited by different factors, such as air temperature, frost days, rainfall, or daylight hours.

For this project, growing season length is calculated as the number of days between the last occurrence of 0°C in spring and the first occurrence of 0°C in fall. While each plant species has unique environmental cues to start and end its annual growth cycle, this growing season metric is a widely used general indicator of the timing of plant photosynthetic activity. Previously developed grids of daily minimum temperature for each day were used to get estimates over the 1950–2010 period across Canada (see research details). Future growing season length was estimated from a suite of 57 readily available predictor variables (e.g., monthly and annual temperature and precipitation variables) using a modern statistical technique called boosted regression trees (BRT) (see research details).

Sources and references for growing season and its indicators

Canadian Forest Service key contacts

John H. Pedlar, Forest Landscape Biologist, Great Lakes Forestry Centre
Daniel W. McKenney, Chief, Landscape Analysis and Applications, Great Lakes Forestry Centre
David Price, Research Scientist, Integrative Climate Change Impacts Modelling, Northern Forestry Centre

Adaptation tools and resources

Forest Change Toolkit – a list of tools and resources for climate change adaptation

Find out more
Related Canadian Forest Service research