Influence of canopy openness, ungulate exclosure, and low‐intensity fire for improved oak regeneration in temperate Europe
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Ecology and Evolution
Failed oak regeneration is widely reported in temperate forests and has been linked in part to changed disturbance regimes and land-use. We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks (Quercus robur, Quercus petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and lowintensity surface fire (burn/no burn). Survival, relative height growth (RGRH), browsing damage on naturally regenerated oaks (≤300 cm tall), and changes in competing woody vegetation were monitored over three years. Greater light availability in canopy gaps increased oak RGRH (p = .034) and tended to increase survival (p = .092). There was also a trend that protection from browsing positively affected RGRH (p = .058) and survival (p = .059). Burning reduced survival (p < .001), nonetheless, survival rates were relatively high across treatment combinations at the end of the experiment (54%– 92%). Most oaks receiving fire were top-killed and survived by producing new sprouts; therefore, RGRH in burned plots became strongly negative the first year. Thereafter, RGRH was greater in burned plots (p = .002). Burning altered the patterns of ungulate browsing frequency on oaks. Overall, browsing frequency was greater during winter; however, in recently burned plots summer browsing was prominent. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals (p < .001) and their heights (p < .001). Our results suggest that young, temperate European oaks may respond similarly to fire as their North American congeners. However, disturbance from a single low-intensity fire may not be sufficient to ensure a persistent competitive advantage—multiple fires and canopy thinning to increase light availability may be needed. Further research investigating long-term fire effects on oaks of various ages, species-specific response of competitors and implications for biodiversity conservation is needed.
Petersson, Linda K.; Dey, Daniel C.; Felton, Annika M.; Gardiner, Emile S.; Löf, Magnus. 2020. Influence of canopy openness, ungulate exclosure, and low‐intensity fire for improved oak regeneration in temperate Europe. Ecology and Evolution. 10(5): 2626-2637. https://doi.org/10.1002/ece3.6092.