The document discusses creating and managing blowouts in dune systems to restore habitat diversity. It provides examples from the PWN dunes of the Netherlands. Statistics show most natural blowouts form within 1000 meters of the beach and are 10-100 square meters in size. Both small and large blowouts can be reactivated. The size and goals of projects influence blowout size. Care must be taken when rejuvenating old blowouts that provide refuge. Erosion ridges are important habitat features that can be artificially created to manage blowouts. Overall the document explores considerations for intentionally creating blowouts through management and restoration efforts.

1. Dynamic Dunes 2015 – 7 October 2015
Workshop Creating blowouts: what to expect?
Examples and lessons from the PWN dunes
Tycho Hoogstrate & Dick Groenendijk

2. Dunes at Heemskerk; 1952 en 2008
Nitrogen deposition; declining grazing populations; grass and scrub encroachment.
Less open sand and mosaic with scrub and dune grassland is more homogeneous.

3. A few PWN-statistics…….
2003; North Holland Dune Reserve (5200 ha); counting visible blowouts on aerial photos.
Circa 80% of the blowouts within the
first 1000 meters from the beach.

4. Circa 60% of the blowouts 10-100 m2

6. Not only small scale blowouts
Reactivating rather large blowout at Heemskerk
(+25% compared with blowout from 1952 foto).

7. Size of blowout depends on the local situation (like distance from the
sea, geomorphological characters, presence/absence of other blowouts,
etcetera) as well as the goal of the project (reset of a grassland system
or small scale restauration of mosaic in grasslands).
Does size matter?

8. Last parts of dynamic blowouts at lime rich dunes at Castricum;
Valuable refugia of insects and plant species > be careful with
rejuvenation of these type of blowouts.

9. Small blowout near Castricum (5 km inland);
Still active partly due to recreation. More blow outs?
Rejuvenation? Better to handle scrub to prevent overgrowing
instead of managing the blowout itself.

10. Natural blowout near Bergen in lime poor dunes.
Erosion ridges

11. Erosion ridges found on many natural blowouts (near Egmond)

12. • Erosion ridges very important > home for many
insects
• Most erosion down the plant roots
• Plant material dying
• ‘Balcony structure’ > keeping dry sand > erosive

13. Artificial erosion ridges can be created easily.
Circa 20-30 cm high.
Southern slope of a large-sized blowout.
Creating erosion ridges

14. A few weeks after completion
• ‘Balcony structure’
• Note the absence of ridges in the background
• Sand can escape out of the project to provide dune
grasslands with a dusting of lime rich sand

15. No erosion ridges on
northern and western
slope; slope very gentle
Eastern slope with
steeper slope
Overview of the project after one year
Total area circa 1000 m2
Erosion ridges at southern slope
Large deposition zone

16. Art in the PWN-dunes………………

17. Sculpture garden
How to create small scale blowouts?
Just place art in the dunes!

18. Discussion topics
Is small scale eolean activity a cure for deteriorated Grey dunes?
Do we understand the process of small scale eolean activity
enough to make them?
When are blowouts successful?
Stabilization of blowouts: failure or success?
In which dune zones to create blowouts?
Which size and density of blowouts?
Which time scale for ‘planning’ blowouts?
How to create blowouts?
What are the clues to create successful blowouts?