Growth of hartweg’s pine ( Pinus hartwegii ) parasitized by two dwarf mistletoe species ( Arceuthobium spp.)

Abstract

Coniferous forests occupy a large extent ( 7 %) of the Mexican territory. Within these forests, pines are a common and sometimes dominant component; however, several abiotic and biotic factors affect pines growth. Among the main biotic factors is the parasitic effect of dwarf mistletoes. In Zoquiapan (Iztaccíhuatl Popocatépetl National Park, Central Mexico) two dwarf mistletoe species coexist parasitizing Pinus hartwegii . The aim of this study was to know the effect of Arceuthobium globosum and A. vaginatum , either individually or as a pair, on P. hartwegii growth, allometric relations, and size susceptibility. We recorded diameter at breast height (dbh) and crown spread of P. hartwegii for 3 years on individuals infested by either one of the species, both, or none, as well as the infection severity. The relative growth rate (RGR) in diameter was strongly in uenced by the pines initial dbh; whereas the infecting species or severity did not show a differential effect. The allometric relation of dbh and height was affected by parasitism, where the trees infected by both species were shorter than the uninfected and infected by A. vaginatum at the same dbh. The parasitic effect does not differ among these mistletoe species. However, the host-size structure affects the presence and severity of infection; maintaining even-age stands provides a better scenario for a milder effect of parasitism, which should be considered for managing plans.