Gradual conversion of black pine plantations in Karst region of Slovenia

1. Gradual conversion of black pine plantations in Karst region of Slovenia Jurij Diaci, Tomaž Adamič, Andrej Rozman, Dušan Roženbergar

2. Map of Slovenia and neighboring regions with position of the North Adriatic Karst (Kaligarič et al. 2006)

3. Karst in the 17th century: a barren, treeless rocky landscape and NE wind burja (bora) Black pine afforestation in 1895

5. 1. Introduction • 16,500 ha of black pine stands within the Karst region • increasing management risks (disease, fire), transformation is challenging (oaks?) • research within the region: Prebevšek (1981, 1998), Škulj (1988), Košiček (1992), Ferlin et al. (1998) • research of natural and planted black pine stands: Vallauri (2002), Anić (2003), Zlatanov et al. (2010), Prevosto et al. (2011), Tiscar in Linares (2011), Kerr et al. (2012), Herrero et al. (2013), Portoghesi et al. (2013) • research on scotc pine stands in succession: Mosandl in Kleinert (1998), Lust et al. (1998), Dobrowolska (2006) • few studies relied on detailed ground vegetation assessment and direct measurement of ecological factors as light climate and soil moisture

6. 1. Introduction Research objectives: - analyze the structure of regeneration and its dependence on abiotic (light, soil moisture, relief...) and biotic factors (competitive plants including herbs, seed trees ...) - propose guidelines for the transformation of black pine stands based on natural regeneration

7. 2. Methods • Geology: carbonate with some silicate (chert, flysch) • Soil: variable (rendzinas and brown soils) • Recent / Potential natural vegetation(Daskobler in Kutnar, 1998): • Seslerioautumnalis-Qercetumpetraeae • Ostryo-Qercetumpubescentis • Seslerio-Ostryetum • Climate: Godnje (12.00;1234 mm) • Senj – CRO (14.90; 1212 mm), Bulgaria – Balkan (10.00; 650 mm), • Abruzzi (10.10; 1130 mm), F Alps (10.20; 787 mm), Pyrenees (480 mm) • Stand structure: 87% black pine, 2% oaks, 1% noble broadleaves, 10% other b. / two story stands • growing stock: 200 (100) m3/ha; increment 5 (2.3) m3/ha/year

9. 2. Methods • 44 plots 25 x 25 m in size • 4 plot categories: closed stand - 14 pl., opened stand - 15 pl., gap edge - 15 pl., gap center - 7 pl. (1.2-4.4 ha) • 6 herb plots (center) and from 0-12 oak subplots (1.5 x 1.5 m) were placed on each plot Sketch of plot with subplots • plots: typical dendrometric data and some ecological features • 477 subplots: vegetation coverage according to the species, density of natural regeneration, typical ecological features, relative irradiance and soil water content N S

10. Gap 5

11. 3. Results Density of regeneration per hectare according to height classes and three species (28 trees, 31 shrubs, 120+ herbs) Legend: F_Ash – Flowering Ash, H_Hor – Hop Hornbeam, N_Brd – Noble Broadleaves

12. Share of tree species according to height classes Other N_Brd Elm Oak H_Hor F_Ash < 20 cm 20-130 cm > 130 cm Legend: F_Ash – Flowering Ash, H_Hor – Hop Hornbeam, N_Brd – Noble Broadleaves

13. Mean tree species density and SE per ha according to height class and stand type Oak < 20 cm Oak > 20 cm herb s. oak s. herb s. oak s. closed opened gap edge gap center Stand type closed opened gap edge gap center Stand type Hop Hornbeam > 20 cm Hop Hornbeam < 20 cm herb s. oak s. herb s. oak s. closed opened gap edge gap center Stand type closed opened gap edge gap center Stand type closed opened gap edge gap Flowering Ash < 20 cm Flowering Ash > 20 cm herb s. oak s. herb s. oak s. closed opened gap edge gap center Stand type closed opened gap edge gap center DIF 15% 28% 29% 52%

14. Share of (browsing) damage on regeneration according to species and height class < 20 cm 20-130 cm F_ash H_Hor Elm Oak N_Br Other Legend: F_Ash – Flowering Ash, H_Hor – Hop Hornbeam, N_Brd – Noble Broadleaves

15. Stand type effect plot Soil depth effect plot closed opened gap edge gap center Stand type Sessleria coverage effect plot Seed tree distance effect plot Effect display for terms in the negative binomial regression mixed model for the oak seedling < 20 cm density data. The gray color denotes 95-percent confidence envelopes aroundthe fitted effects. Only statistically significant factors are presented.

16. Organic soil horiz. depth effect plot Rock coverage effect plot clos. op. edge center Stand type Effect display for terms in the negative binomial regression mixed model for the oakseedling > 20 cm density data. The gray color denotes 95-percent confidence envelopes aroundthe fitted effects. Only statistically significant factors are presented.

17. Ordination-biplot of the principle coordinate analysis for vascular plant cover in the herb layer (Bray-Curtis distance measure). Green arrows represent Ellenberg indicator values, red arrows represent regeneration density and blue arrows represent measured ecological factors. Closed stand Opened stand Gap edge Gap center Legend: HR – Oak CGA – Hop Hornbeam MJES – Flowering Ash BREST – Elm Ellenberg indicator values: N – nitrogen F – soil moisture R – soil reaction H – humus

18. 4. Discussion • significant density of oak (2700 ha-1) and noble broadleaves • mast year of 2011 didn't yield any one-year-old seedlings • oak < 20 cm: closed stand (DIF 15%), deeper soils, thicker humus, seed trees • oak > 20 cm: open stands and gap edge (DIF 30%), humid and developed soils • similar results: e.g. Vallauri 2002, Anic 2003, Zlatanov 2010; Mosandl & Kleinert 1998, Dobrowolska 2006

19. 5. Conclusion Gradual conversion by means of natural regeneration is feasible: (1) regular thinnings for stability and advance regeneration (15-20% DIF) (2) creation of smaller gaps (0.05-0.10 ha, 30-40% DIFF) (3) protection of seedlings from harvesting and browsing damage, regulation of competitors