Anomalous diameter growth and population age structure in mature Canary Islands pine stands
Barbour, Michael G.; Del Arco, Marcelino J.; Raven, Natalie; Garcia-Baquero, Gonzalo
Canary Islands pine (Pinus canariensis Chr. Sm. ex DC) is often described as serotinous, even though most serotinous attributes are absent or weakly developed and the trees do not seem to experience a natural fire regime that would favor and sustain serotiny. We studied the age structure of 22 old-growth stands on the slopes of Mt. Teide on Tenerife, Canary Islands. Statistically robust relationships between trunk diameter at breast height and tree age allowed us to use diameter-age regressions to summarize population age structures and to reconstruct disturbance history. The age structure of only one stand statistically fit the null hypothesis's expectation of a smoothly declining L-shaped negative exponential, non-disturbance population model. Departures from the model commonly featured high densities of seedlings and saplings in the absence of recent fires (indicating that regeneration is independent of fire) and age structures that exhibited one or more peaks of establishment, the average number of years between peaks being 78 yr. Onset of sexual reproduction averaged 46 yr, and the age of mature overstory individuals often exceeded 200 yr. Anomalously, variation in most vegetation attributes, including stem diameter growth, failed to significantly correlate with major abiotic gradients-elevation, temperature, precipitation, exposure to trade wind clouds, slope aspect and steepness, and geological substrate in habitats where P. canariensis dominated.