Disease induced canopy gaps and the persistence niche

Background/Question/Methods

In forested ecosystems, perturbation due to tree death and subsequent canopy gap formation may have dramatic consequences for community dynamics. Historically, studies of gap dynamics have focused on patterns of recruitment and regeneration from seed to explain the mechanisms responsible for local species composition. However, in recent years the role of non-seed regeneration (resprouting) has garnered more attention. On the Atlantic and Gulf Coastal Plains, laurel wilt disease (LWD) has recently emerged as a widespread disturbance, primarily affecting Persea borbonia (redbay), a ubiquitous sub-canopy species. Early reports indicate that > 95% of redbay trees affected by LWD lose all above-ground biomass within 2 years of infection. However, redbay trees produce basal resprouts in response to LWD and may persist in a functionally altered state. The objective of this study was to quantify the resprouting response of redbay and its persistence in the community. We simulated the effects of LWD on healthy redbay trees in a maritime forest in coastal Mississippi. Six 20-m diameter plots were established along a 210-m transect. We recorded the diameter at breast height (DBH) of all trees within each plot (n=83): all trees were then girdled in March 2011. In January 2012, we recorded sprouting responses by measuring the DBH, basal diameter, and length of the longest sprout and counting the total number of sprouts produced on each girdled tree.

Results/Conclusions

Average basal area per tree was 33.0 ± 5.2 cm and the largest tree was 307.9 cm (19.8 DBH). All trees produced at least one sprout and the average number of sprouts per tree was 14 ± 1.1. Thirty-six trees had a sprout at or above breast height (average DBH = 0.4 ± 0.1 cm). Average basal diameter and length of the longest sprout were 0.8 ± 0.02 cm and 61.4 ± 2.4 cm, respectively. Tree basal area was most strongly correlated with the basal diameter of the longest sprout (R-square = 0.30, p < 0.001). Number of sprouts per tree (p < 0.001, R-square = 0.14) and length of the longest sprout (R-square = 0.15, p < 0.001) were more weakly related to tree basal area. Non-seed regeneration of redbay may be crucial to its survival. Furthermore, dense sprout production may alter light conditions and the dynamics of redbay-associated communities. Future work will focus on sprout survival and the effects of sprouts on the light environment and local plant community composition.