Species-specific, pan-European diameter increment models based on data of 2.3 million trees

ResearchBackground: Over the last decades, many forest simulators have been developed for the forests of individual European countries. The underlying growth models are usually based on national datasets of varying size, obtained from National Forest Inventories or from long-term research plots. Many of these models include country- and location-specific predictors, such as site quality indices that may aggregate climate, soil properties and topography effects. Consequently, it is not sensible to compare such models among countries, and it is often impossible to apply models outside the region or country they were developed for. However, there is a clear need for more generically applicable but still locally accurate and climate sensitive simulators at the European scale, which requires the development of models that are applicable across the European continent. The purpose of this study is to develop tree diameter increment models that are applicable at the European scale, but still locally accurate. We compiled and used a dataset of diameter increment observations of over 2.3 million trees from 10 National Forest Inventories in Europe and a set of 99 potential explanatory variables covering forest structure, weather, climate, soil and nutrient deposition. Results: Diameter increment models are presented for 20 species/species groups. Selection of explanatory variables was done using a combination of forward and backward selection methods. The explained variance ranged from 10% to 53% depending on the species. Variables related to forest structure (basal area of the stand and relative size of the tree) contributed most to the explained variance, but environmental variables were important to account for spatial patterns. The type of environmental variables included differed greatly among species. Conclusions: The presented diameter increment models are the first of their kind that are applicable at the European scale. This is an important step towards the development of a new generation of forest development simulators that can be applied at the European scale, but that are sensitive to variations in growing conditions and applicable to a wider range of management systems than before. This allows European scale but detailed analyses concerning topics like CO2 sequestration, wood mobilisation, long term impact of management, etcinfo:eu-repo/semantics/publishedVersio

The impact of atmospheric deposition and climate on forest growth in European monitoring plots: An individual tree growth model

In the climate change discussion, the possibility of carbon sequestration of forests plays an important role. Therefore, research on the effects of environmental changes on net primary productivity is interesting. In this study we investigated the influence of changing temperature, precipitation and deposition of sulphur and nitrogen compounds on forest growth. The database consisted of 654 plots of the European intensive monitoring program (Level II plots) with 5-year growth data for the period 1994–1999. Among these 654 plots only 382 plots in 18 European countries met the requirements necessary to be used in our analysis. Our analysis was done for common beech (Fagus sylvatica), oak (Quercus petraea and Q. robur), Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). We developed an individual tree growth model with measured basal area increment of each individual tree as responding growth factor and tree size (diameter at breast height), tree competition (basal area of larger trees and stand density index), site factors (soil C/N ratio, temperature), and environmental factors (temperature change compared to long-term average, nitrogen and sulphur deposition) as influencing parameters. Using a mixed model approach, all models for the tree species show a high goodness of fit with Pseudo-R2 between 0.33 and 0.44. Diameter at breast height and basal area of larger trees were highly influential variables in all models. Increasing temperature shows a positive effect on growth for all species except Norway spruce. Nitrogen deposition shows a positive impact on growth for all four species. This influence was significant with p <0.05 for all species except common beech. For beech the effect was nearly significant (p = 0.077). An increase of 1 kg N ha-1 yr-1 corresponds to an increase in basal area increment between 1.20% and 1.49% depending on species. Considering an average total carbon uptake for European forests near 1730 kg per hectare and year, this implies an estimated sequestration of approximately 21–26 kg carbon per kg nitrogen depositio

The impact of atmospheric deposition and climate on forest growth in European monitoring plots: An individual tree growth model

In the climate change discussion, the possibility of carbon sequestration of forests plays an important role. Therefore, research on the effects of environmental changes on net primary productivity is interesting. In this study we investigated the influence of changing temperature, precipitation and deposition of sulphur and nitrogen compounds on forest growth. The database consisted of 654 plots of the European intensive monitoring program (Level II plots) with 5-year growth data for the period 1994–1999. Among these 654 plots only 382 plots in 18 European countries met the requirements necessary to be used in our analysis. Our analysis was done for common beech (Fagus sylvatica), oak (Quercus petraea and Q. robur), Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). We developed an individual tree growth model with measured basal area increment of each individual tree as responding growth factor and tree size (diameter at breast height), tree competition (basal area of larger trees and stand density index), site factors (soil C/N ratio, temperature), and environmental factors (temperature change compared to long-term average, nitrogen and sulphur deposition) as influencing parameters. Using a mixed model approach, all models for the tree species show a high goodness of fit with Pseudo-R2 between 0.33 and 0.44. Diameter at breast height and basal area of larger trees were highly influential variables in all models. Increasing temperature shows a positive effect on growth for all species except Norway spruce. Nitrogen deposition shows a positive impact on growth for all four species. This influence was significant with p <0.05 for all species except common beech. For beech the effect was nearly significant (p = 0.077). An increase of 1 kg N ha-1 yr-1 corresponds to an increase in basal area increment between 1.20% and 1.49% depending on species. Considering an average total carbon uptake for European forests near 1730 kg per hectare and year, this implies an estimated sequestration of approximately 21–26 kg carbon per kg nitrogen depositio

Effect of mulching dates modified for nature conservation on the yield and nitrogen fixation of green manure lucerne crops

Organically managed fields are highly attractive for wild animals of open agricultural landscapes because of a high percentage of green covered fields; for example, by green manures, catch crops and underseeds. Forage legumes are the main source of nitrogen in organic farming. Forage legumes are also important habitats for wild animals. The main ecological disadvantage is frequent mowing of forage crops. Increasing the time without disturbance in favour of wild animals may also decrease crop productivity and increase weed pressure. Here, we studied the effect of modified mulching dates on yield, nitrogen fixation and weed colonisation of lucerne green manure under pannonian site conditions during two vegetation periods in Eastern Austria. We compared a natural treatment, where the first mulching took place two weeks earlier and the second mulching two weeks later than in a conventional treatment with the latter. While in the first year the shoot dry-matter yield (–1.5 t ha$^{-1})$, nitrogen yield and the amount of fixed nitrogen (–44 kg N ha$^{-1})$ in lucerne were significantly lower in the natural than in the conventional treatment at the first cut, no differences could be detected in the second year. The seasonal amount of nitrogen fixation as well as the percentage of N derived from the atmosphere (N$_{\rm dfa})$ at both cuts did not differ between the treatments. The natural treatment also had no disadvantageous effects on weed coverage. Our results show that prolonging the period without disturbance in lucerne crops had no adverse agronomic effects with only one exception: the 14-day shorter development period in the natural treatment at the first cut decreased shoot yield and nitrogen fixation compared with the conventional treatment in the first year, when weather conditions were humid before the first cut and dry afterwards. We therefore recommend shifting mulching dates and prolonging cutting intervals in lucerne on organic farms under pannonian site conditions in favour of wild animals

The impact of nitrogen deposition on carbon sequestration by European forests and heathlands

In this study, we present estimated ranges in carbon (C) sequestration per kg nitrogen (N) addition in above-ground biomass and in soil organic matter for forests and heathlands, based on: (i) empirical relations between spatial patterns of carbon uptake and influencing environmental factors including nitrogen deposition (forests only), (ii) 15N field experiments, (iii) long-term low-dose N fertilizer experiments and (iv) results from ecosystem models. The results of the various studies are in close agreement and show that above-ground accumulation of carbon in forests is generally within the range 15–40 kg C/kg N. For heathlands, a range of 5–15 kg C/kg N has been observed based on low-dose N fertilizer experiments. The uncertainty in C sequestration per kg N addition in soils is larger than for above-ground biomass and varies on average between 5 and 35 kg C/kg N for both forests and heathlands. All together these data indicate a total carbon sequestration range of 5–75 kg C/kg N deposition for forest and heathlands, with a most common range of 20–40 kg C/kg N. Results cannot be extrapolated to systems with very high N inputs, nor to other ecosystems, such as peatlands, where the impact of N is much more variable, and may range from C sequestration to C losses

Assessment of the relative importance of nitrogen deposition, climate change and forest management on the sequestration of carbon by forest in Europe

This report summarizes results of studies assessing and predicting changes in forest growth and carbon sequestration in forests and forest soils in response to various scenarios with respect to changes in CO2 concentration, climate (precipitation and temperature), atmospheric deposition (N and S deposition) and forest management (forest management scenarios), using empirical and process oriented models, respectivel

Impacts of Nitrogen Deposition on Forest Ecosystem Services and Biodiversity

Nitrogen deposition has a beneficial or adverse effect on the provision of several forest ecosystem services, depending on the level of nitrogen deposition and the service considered. Biodiversity and water quality regulation are much more sensitive to increasing nitrogen deposition levels than wood production and carbon sequestration. Beyond a certain threshold, however, effects of nitrogen deposition on forest ecosystem services are always negative. This threshold is currently exceeded in much of Central Europe, eastern US and China. Estimates of the contribution of nitrogen to global forest carbon sequestration indicate that elevated nitrogen deposition is responsible for approximately 10–20% of the global terrestrial carbon sink. In areas with persisting high levels of nitrogen deposition forests can become saturated with nitrogen, which represents a risk to the permanence of this service in those areas