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Data from: Influence of canopy openness, ungulate exclosure, and low-intensity fire for improved oak regeneration in temperate Europe

Citation

Petersson, Linda et al. (2021), Data from: Influence of canopy openness, ungulate exclosure, and low-intensity fire for improved oak regeneration in temperate Europe, Dryad, Dataset, https://doi.org/10.5061/dryad.cz8w9gj0h

Abstract

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 (Q. robur, Q. petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and low-intensity 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=0.034) and tended to increase survival (P=0.092). There was also a trend that protection from browsing positively affected RGRH (P=0.058) and survival (P=0.059). Burning reduced survival (P<0.001), 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=0.002). Burning altered 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<0.001) and their heights (P<0.001). Our results suggests 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 are needed.

Methods

The data was collected during a field experiment with five site in southern Sweden. The purpose was to record survival, growth and browsing damages on naturally regenerated oaks. We used a randomized block design with split-split plots and five blocks, i.e. sites. The main treatment was canopy manipulation to create different light levels (closed canopy = 0 or canopy gap = 1), with protection against browsing (no fence = 0 or fence = 1) nested within the canopy treatment, and a low-intensity surface fire (no burn = 0 or burn = 1) nested within the fence treatment. This created eight treatment combinations: closed canopy (0), closed canopy and fence (10), closed canopy, fence and burn (11), closed canopy and burn (1), canopy gap (100), canopy gap and fence (110), canopy gap, fence and burn (111) and canopy gap and burn (101).

Oak seedlings were permanently marked and followed during the experiment. Competing woody vegetation was recorded in four subplots (circular 2 squaremeter plots) in each treatment plot, specific individuals were not followed over time.

All variables are explained in the "variable.explanations" document.

Funding

The Foundation Oscar and Lili Lamms Memory

Erik and Ebba Larssons and Thure Rignells Foundation