DOI: 10.5061/dryad.cz8w9gj0h
title: Data from: Influence of canopy openness, ungulate exclosure, and low-intensity fire for improved oak regeneration in temperate Europe

description: 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&lt;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&lt;0.001) and their heights
 (P&lt;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.
description: 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.