Structural and functional traits predict short term response of tropical dry forests to a high intensity hurricane

Abstract

Tropical dry forest (TDF) is the most threatened of all tropical forest ecosystems worldwide. In the tropical dry forest of the Pacific Coast of Mexico, in addition to human disturbance, the vegetation has been subjected to natural disturbances such as droughts and hurricanes. The average cyclone intensity and the number of very intense category 4 and 5 storms are predicted to increase in this area and such extreme meteorological events generate further stress to the vegetation. Given that in October 2015 the category 4 hurricane “Patricia” landed on the Chamela-Cuixmala TDF, in this study we: (1) evaluated the effect of a high intensity hurricane on TDF vegetation at two habitat types (secondary forest and old-growth forest); and (2) determined how the vegetation attributes at the species and stand level could be defining the vegetation type of damage, and its recovery capacity. For this purpose, we evaluated species composition, vegetation structure and individuals biomechanical traits in eight vegetation plots, four corresponding to old-growth forests (OGF) and four corresponding to secondary forests (SF), before and after the hurricane. Additionally, after the hurricane we also evaluated the damage, leaf functional traits and resprouting ability at the individual level. In total, we evaluated 3732 individuals of 279 species. Data were analyzed by contrasting the vegetation damage and resprouting ability between SF and OGF. Then, we evaluated for the potential relationship between vegetation composition and structure (stand-level attributes) and vegetation damage and recovery capacity. Finally, we evaluated the association between biomechanical and leaf functional traits and the vegetation damage and recovery at the species level. In general, the most severe types of damage were biased toward taller trees as they could be more vulnerable to mechanical instability. We found that OGF received a greater proportion of severe types of damage than SF, although tall trees in SF could face a higher mortality. Harsh environmental conditions preceding the hurricane could also increase the mortality and limit the resprouting ability in SF. Besides, stems with low height and low wood density were related to a greater resprouting ability. This ability was also associated to leaf functional traits such as the relative chlorophyll content, specific leaf area, leaf fresh mass and leaf density, indicating a greater biomass acquisition in species with higher photosynthetic capacity and resistant tissues. These results suggest that in scenarios of increasing frequency and/or intensity of hurricanes, the TDF of the Pacific Coast of Mexico could change their physiognomy toward a canopy of lower height. The proportion of species combining the capacity to resist damage and harsh environmental conditions with a high resprouting ability (i.e. smaller sizes, productive and resistant tissues, such as the TDF pioneer species), could increase as well.