Dendrochronological analysis of single-tree interactions in mixed pine-oak stands of central Arizona, USA

Radial growth of ponderosa pine after stand establishment was dendrochronologically analyzed in relation to varying amounts of Gambel oak presence on the Beaver Creek Experimental Watershed, Arizona. Climate, topography, soil parent material, vegetation structure and soil type were uniform across selected sites. Intra- and inter-specific competition affecting individual pines was quantified using an age-independent index, also modified for asymmetric competition. Pine mean ring width and mean ring area were regressed against competition indices, pine age, and height index after accounting for sites and plots in sites. Dendrochronological techniques provided accurate high resolution data, which were used to reconstruct the growth history of individual pines and stands. Site interactions were never significant, and fitted models explained from 50 to 66% of the total variance. Regression statistics were best when competition indices assumed symmetric interactions. Mean radial growth of pine over 5 and 10 years was negatively related to intra-specific competition, but was not significantly related to inter-specific competition between pine and oak. This could be attributed to the positive influence of oak on soil nutrient status and/or to increased pine spacing caused by the presence of oak.