Seedling Survival
Back to the Monitoring Hub
Achieve survival rates sufficient for restoration of native forests
Data collection in progress
Iron Curtain to Green Belt
Bulgaria
Problem: The forestry sector has in the past focused on planting non-native coniferous tree species, and this continues today. These plantations are disproportionately affected by pests, disease and fire as well as supporting low levels of native biodiversity. Planting native tree species can overcome many of these problems, but availability of seeds and seedlings of these species is currently limited.
Action: The project aims to help catalyse change in forestry culture and practice by supporting two nurseries to increase the availability of acorns and oak seedlings. The project will also plant native oak species in areas that were previously non-native conifer plantations and monitor their survival to assess if native species survival rates are comparable to non-natives, which is important criteria for change in the forestry sector.
Indicator: The percentage survival of native tree seedlings of three oak species planted in restoration areas will be measured to indicate the successful trialling of planting native, rather than non-native, species within forestry stands.
Methods
Surveys are conducted annually in October across 44 plots in 44 different forestry stands. The stands were planted in different years (or cohorts). This indicator’s methodology is based on national legislation for forestry for monitoring the survival rate of newly planted oak seedlings (Quercus cerris and Quercus frainetto). The number of seedlings and saplings that have survived and failed is measured by the Forest Service and depends on the size of the planted area:
- smaller than 0.2 ha – a full inventory over the whole territory of the seedlings is prescribed
- between 0.2 and 10 ha – the sample plots should cover at least 2% of the planted area
- more than 10 ha – the sample plots should cover at least 1.5% of the planted area
BSPB’s nursery growing native deciduous species, to eventually use in tree plantings to restore native deciduous tree stands within their project area. Photo: Svetoslav Spasov
Oak seedlings growing in the project’s nursery. Photo: Svetoslav Spasov.
Seedlings are surveyed in a rectangular sampling plot, covering at least five rows of the planted area. The sampling plots should represent the average condition of the planted area, and in the case of mixed trees should cover the complete mixing pattern. Foresters conduct a census of the vigorous and dead saplings (or empty spots where saplings used to be) over the entire plot, by tree species. From this, survival rate for that stand is calculated and then new seedlings are planted where previous ones failed to establish. Then in the following year when the next survey is conducted, a new survival rate is calculated, including surviving trees from both the original and follow-up planting years.
The final assessment of seedling survival is calculated three years after the original planting, or the third year survival rate per site. Overall survival per planting cohort is calculated as the weighted mean of each site’s third year survival, across all plots planted in the same year, corrected for the area of each plot surveyed (which varies).
Results
So far, the project has survival rates three years after the original planting for three cohorts of stands: stands planted in 2018 (n=4 stands, assessed for the last time in 2021) stands planted in 2019 (n=7 stands, assessed in 2022), and stands planted in 2020 (n=16, assessed in 2023). The figure below shows the survival rate of each stand per cohort, all planted with oak (Quercus) species.
Boxplots of the third year survival rate of sites in different planting cohorts. The horizontal line in each box represents the median value across the cohort, while the vertical placement of the black dots represent the third year survival rates of individual stands. The horizontal placement of the black dots simply distributes them across the width of the box, to avoid overlap with other dots.
The weighted mean survival rate per cohort is 79.01 for 2018 and 69.77 for 2019 and 59.27 for 2020.
This indicator will be used to assess whether the planting of native deciduous trees is successful enough to meet the criteria of 80% survival (see dotted line in graph above). For the forestry service, a survival rate of 80% is required for success. If survival rates fall below 80%, then the area must, by law, be replanted, which is costly for foresters and avoided whenever possible. This is therefore the target survival rate for native saplings, to demonstrate to the forestry sector that native trees can be used in future plantings as easily as non-native species.
We will update this page as survival rates become available for stands planted in subsequent years.
Partners
