The uncoupling of secondary growth, cone and litter production by intradecadal climatic variability in a mediterranean scots pine forest

Abstract

The relationships between climate variability and canopy dynamics (monthly litter production), chemical composition of the litter, secondary growth and female-cone production were studied in an old growth Scots pine (Pinus sylvestris) forest over the 1993–2003 period. The forest was located at a Mediterranean mountain site (Valsaín, Segovia, central Spain). The temporally explicit relationships between the mentioned variables were explored by chronological cluster of their time series. Mean air temperature significantly influenced litter production and its seasonal and intradecadal patterns. Seasonal patterns of litter N and P content were negatively correlated with litter production, exhibiting minima of 5.3 g kg−1 (N) and 0.5 g kg−1 (P) by the end of the summer and maxima of 15 g kg−1 (N) and 1.2 g kg−1 (P) during winter; these results are interpreted as retranslocation before needle shedding in summer and loss of green needles in winter respectively. In general the driest and hottest years (1994 and 1995) were associated with significantly decreased secondary growth in the next year, an increased cone production, and an increased nutrient loss due to the combined effect of an increased litter production and an increased nutrient concentration of the litter. Climatic changes during the early stages of cone formation that take place during the spring led to alterations in masting and in the tri-annual process of cone production. Since each parameter studied was differentially affected by climatic variability, the overall effect of the short-term climatic changes experienced by the Scots pine forest studied was an uncoupling of litter production, secondary growth, and reproduction.