Growth impacts of Psittacanthus angustifolius Kuijt on Pinus oocarpa Schiede in Honduras

The mistletoe Psittacanthus angustifolius Kuijt (Loranthaceae) severely parasitizes Pinus oocarpa Schiede in southern Mexico and Central America causing growth loss and increased mortality of severely infected trees. The objectives of this study were to use stem analysis to evaluate the impacts of P. angustifolius on P. oocarpa in terms of height and volume growth of individual trees in Honduras and to evaluate a five-class mistletoe rating system for predicting the effects of this mistletoe on the growth of P. oocarpa. Two study sites in Honduras were selected based on incidence and severity of mistletoe infection. Thirteen dominant or codominant trees from each of three true mistletoe rating (TMR) classes: 0, no infection; 2, moderate infection; and 4, severe infection were selected. Stem analysis was conducted on the 78 selected trees to determine their height increment, volume increment, and specific volume increment. To evaluate growth reductions, each infected tree was paired with a healthy tree from the same site by height at time of infection for periodic height increment, age for periodic specific volume increment, and by volume at time of infection for periodic volume increment. To evaluate the mistletoe rating system 95% confidence intervals were constructed to compare means for height and volume increments between mistletoe infection classes for the last year of growth. Growth losses of over 50% were observed in terms of periodic volume increment and periodic specific volume increment during the last 3-year period prior to sampling for trees in TMR class 4 from both sites. Analysis of the effectiveness of the mistletoe rating system for predicting growth losses produced inconsistent results between sites because duration of infection, which was not a component of the rating system, influenced growth losses.