Abstract
Resource allocation to different plant tissues is likely to be affected by high investment into fruit production during mast years. However, there is a large knowledge gap concerning species-specific differences in resource dynamics. We investigated the influence of mast years on stem growth, leaf production, and leaf carbon (C), nitrogen (N), and phosphorus (P) concentrations and contents in Fagus sylvatica, Quercus petraea, and Q. robur at continental and climate region scales using long-term data from the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) and similar datasets. We discussed the results in the light of opposing resource dynamics hypotheses: (i) resource accumulation before mast years and exhaustion after mast years (resource storage hypothesis), (ii) shifting resources from vegetative to generative compartments (resource switching hypothesis), and (iii) investing resources concurrently in both vegetative and generative compartments (resource matching hypothesis). Linear mixed-effects modelling (LMM) showed that both stem growth and leaf production were negatively influenced by weather conditions which simultaneously lead to high fruit production. Thus, the impact of generative on vegetative growth is intermixed with effects of environmental factors. Superposed epoch analyses and LMM showed that for mast behaviour in F. sylvatica, there are indicators supporting the resource storage and the resource switching hypotheses. Before mast years, resources were accumulated, while during mast years resources switched from vegetative to generative tissues with reduced stem and leaf growth. For the Quercus species, stem growth was reduced after mast years, which supports the resource storage hypothesis. LMM showed that leaf C concentrations did not change with increasing fruit production in neither species. Leaf N and P concentrations increased in F. sylvatica, but not in Quercus species. Leaf N and P contents decreased with increasing fruit production in all species, as did leaf C content in F. sylvatica. Overall, our findings suggest different resource dynamics strategies in F. sylvatica and Quercus species, which might lead to differences in their adaptive capacity to a changing climate.
Highlights
Synchronised occurrence of mass seed and fruit production in stands and forests is a reproductive phenomenon of many long-lived plant species (Nilsson and Wästljung, 1987; Kelly, 1994; Kelly and Sork, 2002; Nussbaumer et al, 2018; Vacchiano et al, 2018)
Resource depletion was present in the years after the mast year, but in the mast year itself, resource allocation to vegetative tissues was not different from other years
For leaf N, P, and C in all species we suggest that resource switching is present in years with high fruit production
Summary
Synchronised occurrence of mass seed and fruit production in stands and forests is a reproductive phenomenon of many long-lived plant species (Nilsson and Wästljung, 1987; Kelly, 1994; Kelly and Sork, 2002; Nussbaumer et al, 2018; Vacchiano et al, 2018). Mast years play an important role in ecosystems in many ways, e.g., they provide an additional food source for forest wildlife, for example for red deer (Picard et al, 1991), wild boar (Henry and Conley, 1972; Wohlgemuth et al, 2016) or bird species (Herrera et al, 1994). It can even impact the migration pattern of birds, for example bramblings which are known to winter further north after beech mast years in Middle Europe (Jenni, 1987). This potentially leads to higher infection rates of e.g., Lyme Borreliosis or diseases induced by Hanta viruses (Vapalahti et al, 2003; Ostfeld, 2013; Brugger et al, 2018)
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