Vascular plant richness along an elevation gradient at Monte Velino (Central Apennines, Italy)

Abstract

Biogeographia vol. XX VIII - 2007 (Pubb/icato il 30 dicembre 2007) Biogeografia del/’Appennino centrale e settenirionale: z‘rent'anni dopo Vascular plant richness along an elevation gradient at Monte Velino (Central Apennines, Italy) JEAN-PAUL THEURILLAT, MARCO IOCCI-II, MAURIZIO CUTINI, GIOVANNI DE MARCO Dz'pmqtz'me72to dzq Biologizz, Uni:/ersitiz degli Studi “Roma Tre”, z/idle G. Mczrc0m' 446, 00146 Roma (Italy); e—mzzz'[: t/Jeuril/@m2z'r0mzl3.it Key words: area, air temperature, chorotypes, isolation, life forms SUMMARY Species richness was studied during two years in 100 m elevation bands along an altitudinal transect from 1100 tn up to 2487 m asl on the south-western slope ofMonte Vclino. The 1300 to the 2200 ni elevation bands have a similar area in the range oFO.36 to 0.40 ltml. A total of636 taxa (species and subspecies) was recorded. Each species was attributed a life form, an elevation category and a chorotype. The richness per elevation band decreases monotonously along the transect with a plateau between 1300 and 1600 m asl. Because ofthe similarity of the area ofthe elevation bands between the 1300m and the 2200 m elevation band, the richness pattern along the transect is not merely a Function ofthe area. The rejection of the area hypothesis, at least between 1300 and 2300 m asl, is also demonstrated by the species traits. Most of them show a monotonous pattern with elevation, either decreasing or increasing. The cumulative increase of species richness along the transect follows the Arrheniusq power function 5 = C X A‘ with a 2 value ofO.291. Endemics peak at an intermediate elevation in the 2000 m elevation band and follow the isolation—area hypothesis. In that the species-density matches the adiabatic decrease of air temperature, we consider the latter as the driving Factor for the pattern of the species richness in relation to elevation. Colder temperatures (a) reduce the species pool in relation to elevation due to an increasingly colder and shorter vegetation period; (b) drive geomorphological processes that both reduce habitats number and spatial heterogeneity, and enhance their convergence and homogenization (temperature—physiography hypothesis). Therefore, area, temperature and isolation are the three main parameters to explain plant richness with elevation for Monte Velino. INTRODUCTION Patterns of plant diversity along elevational gradients have always been a topic of interest in biogeography. Different hypotheses have been put forward to explain elevational patterns including space limitation (area), range width of species, ecological and historical factors (Lomolino, 2001; MacArthur, 1972; Rahbek, 1995; Stevens, 1992). Usually a decrease in plant species richness is observed with increasing altitude (e.g. for high European mountains Ozenda, 1985, 1997; Grabherr et al., 1995; Korner, 2000; Theurillat et al., 2003) but sometimes species richness peaks at mid—altitudes (Rahbek, 1995; Grytnes,