Exploring continental‐scale stand health – N : P ratio relationships for European forests

Abstract

SummaryUnderstanding the relationship between nitrogen (N) availability and stand health in forest ecosystems is crucial, because a large proportion of European forests is subjected to N-deposition levels beyond their retention capacity.We used data from a long-term forest monitoring programme (ICP Forests) to test the relationship between an index of N availability, foliar nitrogen : phosphorus (N : P) ratios, tree defoliation and discoloration. We hypothesized a segmented response of stand health to N : P ratios and an improved model-fit after correcting for climatic covariates.In accordance with the hypothesis, we found a segmented response with a breakpoint for conifer defoliation at N : P ratios as low as 7.3. Inclusion of climatic variables improved the fit of the models, but there was significant collinearity with N : P.Increases in N availability appear, at least for conifers, to have a negative effect on tree health even under N-limiting conditions. Regulation of N-deposition levels is consequently as timely as ever. We propose that increases in tree defoliation, other than resulting in serious plant fitness issues, may represent early diagnostic symptoms of N-addition related imbalances.

Monitoring ectomycorrhizal fungi at large scales for science, forest management, fungal conservation and environmental policy

“…European trees and ground floor vegetation are being monitored and are leading to significant findings (e.g. Dirnboeck et al 2014;Seidling et al 2008;Van Dobben and de Vries 2010;Veresoglou et al 2014), but fungi are not yet included in the current monitoring scheme. Science and conservation are areas that can be built into ICP Forests and/or may lead to useful spin-offs; research linked to these long-term plots has the potential to enhance the relevance of science and conservation.…”

Anthropogenic global shifts in biospheric N and P concentrations and ratios and their impacts on biodiversity, ecosystem productivity, food security, and human health

“…Declining health (high mortality and defoliation) has been recorded in forests with long‐term and persistently high atmospheric loads of N (Carnicer et al, ), imbalances in soil nutrients, and increasing P limitation (Schmitz et al, ; Veresoglou et al, ). The capacity of temperate forests to store P increases with age (Sardans & Penuelas, ), and proportional allocation among organs is linked to growth‐trait strategies.…”

“…The N:P ratios of plant organs may be involved in the phenomenon of masting, which intensifies at extreme low and high values of N:P (Fernández‐Martínez et al, ). Anthropogenic nutrient imbalances and the declining health of temperate forests in the Northern Hemisphere (Schmitz et al, ; Veresoglou et al, ) may thus affect the capacity of forest ecosystem services, such as C storage. Such impacts on ecosystem function and service delivery remain to be quantified.…”

“…The study of N and P concentrations and N:P ratios in rivers and basins allows the analysis of the effects of multiple human activities on nutrient budgets Zhang, Liu, et al, 2019) across a range of land uses (Romero et al, 2019;Sardans et al, 2012a;Zhang, Li, et al, 2019;Figure 5 Fenn et al, 1998;Franzaring, Holz, Zipperle, & Fangmeier, 2010;Prietzel & Stetter, 2010;Schmitz et al, 2019;Veresoglou et al, 2014;Wang, Sardans, et al, 2017), tend to be enriched more rapidly by N than P, thereby increasing the N:P ratios ( Figure 5). This trend has been exacerbated by the progressive replacement of P-rich with N-rich detergents (Sardans et al, 2012b and references therein).…”

Variables related to nitrogen deposition improve defoliation models for European forests

“…In particular, the foliar N/Ca and N/K ratios were the most influential in the case of beech; foliar N/Mg, N/Ca and N/P for spruce, and foliar N/P and N/Mg for pine, indicating that crown condition in all these tree species is related to imbalance in foliar nutrients (e.g. Veresoglou et al 2014). N-induced nutrient imbalances can be either caused by direct foliar N uptake (e.g.…”