Effects of fire on native columnar and globular cacti of Puerto Rico: a case study of El Faro, Cabo Rojo

Abstract

Background: Many Puerto Rican ecosystems evolved without a regular fire regime. As such, many native plants lack adaptations necessary to survive even low-intensity fires. Human-caused fires are increasing in frequency, in part promoted by the presence of invasive grasses. During the afternoon of 19 February 2014, a wildfire burned a large portion of the dry forest in El Faro Natural Reserve, Cabo Rojo, Puerto Rico. Using a previously monitored population, we documented the mortality and morphological damage on three columnar and semi-epiphytic cactus species (Pilosocereus royenii [L.] Byles & Rowley, Harrisia portoricensis Britton, and Leptocereus quadricostatus Britton) and one globular species (Melocactus intortus [Mill.] Urb.) in relation to canopy cover and cactus growth strategy. Results: Our results suggest that M. intortus and H. portoricensis were more susceptible to fire damage. Cacti growing in areas dominated by grasses and shrubs were significantly more likely to burn than those growing under a closed tree canopy. Apart from L. quadricostatus, cacti that survived at least one year after the fire had lost spines, developed scarring tissue in some or all ribs, and few were able to regrow. Conclusions: Because extensive tissue damage and environmental alterations were observed during the postfire survey, which occurred between 14 to 19 months after the fire, we argue there will be significant delayed mortality and that the mortality estimates presented here are conservative.

Global change impacts on cacti (Cactaceae): current threats, challenges and conservation solutions

“…As restoration ecologists and practitioners know, the widespread removal of destructive invasive species can be a daunting task that is rarely successful without broad support across agencies, communities and institutions. As mentioned earlier, non-native, fire-adapted grasses have dramatically altered the fire cycle of many dryland areas, resulting in massive mortality mosaics of succulent plants and less suitable habitat for regermination ( Shyrock et al , 2014 ; Bracamonte et al , 2017 ; Carrera-Martinez et al , 2020 ; Wilder et al , 2021 ). In southern and central Arizona, USA, initiatives to map and remove the non-native C 4 fire-adapted grass Cenchrus ciliaris across large parcels of private and public lands have been spearheaded by stakeholders working with institutions such as the Sonoran Desert Museum near Tucson ( https://www.desertmuseum.org/buffelgrass/ ) and the Central Arizona Conservation Alliance, which supports regional parks in the Phoenix area ( https://cazca.org ).…”

“…The presence of non-native grasses in tropical dry forests, which host some of the highest cactus diversity in the world, is altering fire frequencies and intensity. For example, cacti growing in a tropical dry forest ecosystem in Puerto Rico were more likely to burn in areas dominated by invasive grasses and native shrubs than those growing under a closed tree canopy in the absence of grasses ( Carrera-Martinez et al , 2020 ). However, the emerging threat of wildfires to native cacti in tropical dry forests is not driven exclusively by grass invasion and climate change.…”