Seasonal variations of throughfall chemistry in pure and mixed stands of Oriental beech (Fagus orientalis Lipsky) in Hyrcanian forests (Iran)

International audienceAbstractKey messageThroughfall nutrient fluxes were generally higher in a mixed stand than in a pure stand of Oriental beech. Throughfall fluxes were higher than bulk precipitation fluxes except for nitrogen and indicate higher canopy uptake of this element in the pure stand compared to the mixed stand.ContextOriental beech is an economically relevant tree species for Iran and adjacent countries. Yet little is known about nutrient cycling in Oriental beech stands and the influence of the degree of mixture with other species.AimsWe assessed the effect of seasons on nutrient fluxes in precipitation and whether throughfall chemistry differed between pure and mixed stands.MethodsBulk precipitation in the open field and throughfall were sampled during one whole month within each season from August 2013 to May 2014 in a pure (81 % of beech trees on average) and a mixed stand (57 % of beech trees) of Oriental beech. Samples were analysed for pH, nitrate (NO3−), ammonium (NH4+), phosphorus (P), calcium (Ca2+), magnesium (Mg2+) and potassium (K+).ResultsNutrient concentrations were generally higher in the growing season than in the dormant season, both in bulk precipitation and in throughfall. Nutrient fluxes were higher in fall and these peaks coincided with higher amounts of precipitation. The concentrations and fluxes of NH4+, NO3−, P, Ca2+, Mg2+ and K+ were generally higher in the mixed stand than in the pure stand in all seasons. Compared to the open field, throughfall fluxes were usually higher, except for NO3− and NH4+, indicating direct canopy uptake of nitrogen.ConclusionCanopy composition in Oriental beech stands (owing to differences in foliage chemistry) and seasons (owing to differences in precipitation regime and phenological stages) have a significant effect on throughfall nutrient fluxes

Spatial heterogeneity and temporal stability of throughfall under individual Quercus brantii trees

Spatio‐temporal patterns of throughfall (TF) have often been studied under forest canopies. Few reports, however, have been made on small‐scale TF variability in deciduous forest stands. In the present research, the spatial heterogeneity and temporal stability of TF under five individual persian oak trees (Quercus brantii var. Persica) was quantified. The research site was in the Zagros forests in western Iran, where mean annual precipitation and temperature are equal to 587.2 mm and 16.9 °C, respectively. Data from 23 rainfall events were aggregated to assess the spatial correlation of TF. Variograms for TF beneath two of the five trees reached a stable sill at the range of 5–6 m. The redistribution of TF within the canopy was highly variable in time, attributable to seasonal variation in canopy foliation and meteorological factors. As the length of the sampling period increased, the spatial variability of TF decreased and the temporal stability of the TF pattern increased. Time stability plots of TF normalized with respect to mean and variance showed a moderate general persistence for all individual trees. We conclude that single trees modify the spatial distribution of TF reaching the forest floors

The potential impact of future climate on the distribution of European yew (Taxus baccata L.) in the Hyrcanian Forest region (Iran)

International audienceThe Hyrcanian Forest region is rich in relict species, and endemic and endangered species. Although there are concerns about climate change, its influence on tree species in the Hyrcanian forests in the north of Iran is still unidentified.Taxus baccatais among the few conifer species found in the region, and the present study aims to evaluate the potential impact of climate change on the distribution ofT. baccata. For this purpose, we used ensemble species distribution modeling with ten algorithms and based on two geographic extents (global and regional) and climate data for different climate change scenarios. For the regional extent, we calibrated the models in Hyrcanian forests including the three provinces in the north of Iran. For the global extent, we calibrated the models on the whole range distribution ofT. baccata. In both cases, we applied the models to predict the distribution ofT. baccatain northern Iran under current, 2050, and 2070 climates. In regional extent modeling, precipitation of coldest quarter and in global extent modeling temperature seasonality emerged as the most important variables. Present environmental suitability estimates indicated that the suitable area forT. baccatain Hyrcanian forests is 5.89 x 10(3) km(2)(regional modeling) to 9.74 x 10(3) km(2)(global modeling). The modeling suggests that climate change under representative concentration pathways (RCP) 8.5 is likely to lead to strong suitability reductions in the region, with just between 0.63 x 10(3) km(2)(regional modeling) and 0.57 x 10(3) km(2)(global modeling) suitable area in 2070. Hence,T. baccatarisks losing most currently suitable areas in the Hyrcanian forests under climate change. The results of the present study suggest there should be focus on conservation of areas predicted to remain suitable through near-future climate change and provide an estimate of the availability of suitable areas for the regeneration ofT. baccataand its use in reforestation