The influence of climate and fructification on the inter-annual variability of stem growth and net primary productivity in an old-growth, mixed beech forest

Abstract

The periodic production of large seed crops by trees (masting) and its interaction with stem growth has long been the objective of tree physiology research. However, very little is known about the effects of masting on stem growth and total net primary productivity (NPP) at the stand scale. This study was conducted in an old-growth, mixed deciduous forest dominated by Fagus sylvatica (L.) and covers the period from 2003 to 2007, which comprised wet, dry and regular years as well as two masts of Fagus and one mast of the co-dominant tree species Fraxinus excelsior (L.) and Acer pseudoplatanus (L.). We combined analyses of weather conditions and stem growth at the tree level (inter- and intra-annual) with fruit, stem and leaf production, and estimates of total NPP at the stand level. Finally, we compared the annual demand of carbon for biomass production with net canopy assimilation (NCA), derived from eddy covariance flux measurements, chamber measurements and modelling. Annual stem growth of Fagus was most favoured by warm periods in spring and that of Fraxinus by high precipitation in June. For stem growth of Acer and for fruit production, no significant relationships with mean weather conditions were found. Intra-annual stem growth of all species was strongly reduced when the relative plant-available water in soil dropped below a threshold of about 60% between May and July. The inter-annual variations of NCA, total NPP and leaf NPP at the stand level were low (mean values 1313, 662 and 168 g C m(-2) year(-1), respectively), while wood and fruit production varied more and contrarily (wood: 169-241 g C m(-2) year(-1); fruits: 21-142 g C m(-2) year(-1)). In all years, an annual surplus of newly assimilated carbon was calculated (on average 100 g C m(-2) year(-1)). The results suggest that stem growth is generally not limited by insufficient carbon resources; only in mast years a short-term carbon shortage may occur in spring. In contrast to common assumption, stem growth alone is not a sufficient proxy for total biomass production or the control of carbon sequestration by weather extremes.

Sensitivity of European beech trees to unfavorable environmental factors on the edge and outside of their distribution range in northeastern Europe

“…The lack of humidity and heat during June-July was one of the key factors limiting the migration of beech trees northward. These findings agreed well with the known sensitivity of beech growth to drought in the period between budburst and the end of July (Dittmar et al 2003, Lebourgeois et al 2005, Mund et al 2010, Scharnweber et al 2011. A cold dormant period especially winter months is a likely accompanying factor limiting beech tree growth and distribution toward the northeast of Europe.…”

Extending a physiological forest growth model by an observation-based tree competition module improves spatial representation of diameter growth

“…However, no growth depression in that year became obvious from the average year ring width of both plots. Similar results had been reported from other beech stands in Germany and the Netherlands (Mund et al 2010;van der Werf et al 2007), which were attributed to favourable growth conditions in early spring or after drought. It should also be noted that 2002 was the wettest year in the simulation period so that soil water storages were well filled.…”

Climate sensitivity of radial growth in European beech (Fagus sylvatica L.) at different aspects in southwestern Germany

“…A negative correlation between fruit production and radial growth is often found for beech (e.g., Dittmar et al 2003;Drobyshev et al 2010), which does not necessarily reflect resource limitation or trade-off between reproductive and vegetative growth rather than different responses of fructification and stem growth to internal and external conditions (Mund et al 2010). As no information on fructification is available for our study site over the period 1934-1998, no years of remarkable growth depressions could be definitely related to masting.…”