Key message
Neutral

The rate of defoliation and forest decline in Slovenia was relatively stable until 2020, with a slightly negative trend. After 2020, a deterioration of tree defoliation was observed.

Increased defoliation was detected in 2014 and 2015 due to ice storm and windthrows, followed by stable defoliation status for both conifers and broadleaves until 2020. After 2020, defoliation was observed to worsen in both conifers and broadleaves. This could be due to the effects of climate change, bark beetles, and, especially for deciduous trees, the effects of secondary damage following the 2014 ice storm and the 2022 summer drought. Average defoliation of conifers has been lower than average defoliation of deciduous trees since 2020.

In general, the average defoliation in Slovenian forests is 31.6% (2022) - still higher than the average of other European countries where defoliation has been accessed, where it was 23.5% in 2021. The trend of increasing defoliation can also be observed at the European level.

The most damaged tree species are black pine, sweet chestnut, oak (especially pedunculate oak), common beech and Norway spruce. According to recent findings, the annual variation in estimates is mainly a combination of unpredictable weather conditions between years and other biotic and abiotic causes.


Charts

Figure GZ01-1: Trend of average tree defoliation
Sources:

Slovenian Forestry Institute 2023

Show data
coniferous[%] deciduous[%] total[%]
1991 22.14 12.95 16.56
1993 22.46 15.68 19.59
1994 18.53 16.30 18.29
1995 26.86 18.07 21.42
1996 22.80 15.95 18.69
1997 24.69 20.49 22.21
1998 27.37 20.49 23.49
1999 28.65 21.87 25.62
2000 24.32 18.15 20.56
2001 25.90 21.46 24.62
2002 26.11 20.78 24.16
2003 25.13 20.75 23.56
2004 24.98 20.93 23.27
2005 24.99 22.21 23.47
2006 24.60 22.60 23.30
2007 24.56 25.87 25.37
2008 26.02 25.42 25.65
2009 26.36 25.86 26.05
2010 25.13 24.48 24.71
2011 25.95 23.81 25.45
2012 25.78 23.36 24.91
2013 26.14 24.46 25.87
2014 27.72 27.14 28.21
2015 29.69 26.30 28.08
2016 28.52 25.71 26.70
2017 28.60 26.86 27.46
2018 27.73 27.20 27.38
2019 28.68 27.61 27.97
2020 26.73 28.35 27.82
2021 29.41 31.31 30.69
2022 30.13 32.30 31.59
Figure GZ01-2: Trend in shares of damaged trees with defoliation above 25% (index of tree defoliation)
Sources:

Slovenian Forestry Institute 2023

Show data
coniferous[%] deciduous[%] total[%]
1991 26.40 9.35 15.57
1993 25.28 12.45 18.87
1994 16.35 13.00 15.69
1995 37.75 17.63 24.71
1996 27.52 12.62 18.94
1997 31.06 20.34 27.03
1998 38.87 21.72 28.81
1999 41.97 22.77 30.62
2000 30.32 16.86 22.28
2001 36.11 24.53 30.41
2002 41.49 24.36 30.85
2003 36.73 23.76 29.27
2004 40.51 23.67 29.27
2005 35.08 28.49 30.59
2006 32.20 27.80 29.40
2007 36.60 35.70 35.70
2008 40.74 34.56 36.90
2009 39.07 32.78 35.42
2010 42.79 23.23 31.72
2011 37.87 27.62 31.40
2012 37.03 23.01 29.04
2013 34.31 28.47 30.87
2014 39.95 34.90 38.29
2015 44.33 32.75 37.81
2016 41.89 31.31 33.81
2017 40.60 35.12 37.03
2018 40.33 33.86 36.08
2019 42.70 35.14 37.69
2020 41.11 36.61 38.07
2021 44.09 41.33 42.23
2022 48.55 43.96 45.45
Figure GZ01-3: Share of trees by individual defoliation class in 2022
Sources:

Slovenian Forestry Institute 2023

Show data
defoliation less than 10 %[% of trees] defoliation from 11 to 25 %[% of trees] defoliation more than 25 %[% of trees]
total 12.41 42.14 45.46
deciduous 8.99 47.05 43.96
coniferous 19.48 31.98 48.55

Methodology

Date of data source summarization