Hurricane disturbance and local temperature are associated with growth and disease patterns in the endangered Florida...

Climate refugia endemics have persisted through past environmental shifts, but their responses to modern severe weather remain poorly understood. Torreya taxifolia (Taxaceae), a critically endangered conifer endemic to steephead ravines of Florida and Georgia, has declined for decades due to fungal canker diseases. Hurricane Michael, a Category 5 storm in 2018, caused extensive forest damage in its refugial habitat. We investigated how natural variation in disturbance was linked to tree health and microclimatic conditions relevant to disease.

We monitored the health and habitat of 40 wild T. taxifolia individuals for 4 years after the hurricane by measuring branch growth and mortality and temperature and light around each T. taxifolia. We assessed the abundance and area of fungal cankers. Hurricane disturbance was characterized using complementary metrics of forest structural change (basal area) and the size-weighted abundance of fallen and standing trees.

Tree fall was associated with increased branch growth when quantified with summed diameter at breast height (DBH) metrics, but not with basal area metrics. Neither metric of tree fall was significantly associated with branch mortality. Local temperatures were positively associated with canker abundance, though not with total canker area, and were not directly linked to measures of forest change.

Hurricane disturbance was associated with short-term after-storm growth responses among surviving T. taxifolia individuals, while warmer local conditions were linked to increased canker disease symptoms. Together, these results suggest that torreya growth was more closely associated with neighborhood-scale disturbance intensity than with broad reductions in stand-level biomass.