Southeastern pine savannas are subject to frequent disturbances, such as fire and hurricane. Hurricanes and other canopy disturbances open gaps essential for recruitment of competition-intolerant longleaf seedlings. Plots were previously established under three different canopy types: closed canopy, canopy open 10 years, and canopy open at least 30 years. Canopy photos were taken in the center of each plot in August to quantify light transmission. On September 1, 2008, Hurricane Gustav passed within 130 km of the study site in Tangipahoa Parish, Louisiana. The study site experienced tropical storm force winds, with wind speeds of 63-118 km/hr, resulting in fallen trees throughout the site. Canopy photos were retaken in October to quantify change in light transmission. It was expected that closed canopy plots would have lower light transmission than open plots, and that open plots would not differ from each other. It was also expected that more light would be transmitted after hurricane. An interaction between canopy and hurricane could indicate an edge effect, as trees near gap edges could be more susceptible to wind damage.
Results/Conclusions
Analysis indicated a significant effect of canopy (F2,43.4=25.26, p<0.0001), and hurricane (F1,43.1=9.16, p=0.0042), with no significant interaction (F2,43.1=0.70, p=0.5000). Orthogonal contrasts further indicated a significant difference between closed and open canopy (F1,43.3=49.32, p<0.0001), but no difference between canopy open 10 years and canopy open 30 years (F1,43.6=1.96, p=0.1689). The absence of an interaction between canopy condition and hurricane damage may be due to the open character of the longleaf pine savanna. Closed canopy plots had an average light transmittance of 41.29%; even under closed canopy, there may be enough space between trees that none are especially protected from high winds. Additionally, the change in light transmittance due to hurricane was small, with an average difference of about 2.25%, usually resulting from no more than one or two trees down per plot. Although the change was small, it may still have important implications for diversity; previous work at the site has shown a correlation between light transmittance and the number of species present in the understory.
