Arne Verstraeten

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights Soil solution DOC concentrations in Flanders forests increased (2002e2012). Soil solution DOC fluxes showed less systematic trends. Deposition could not explain the increase of soil solution DOC concentrations. Stand deposition had a rather limited impact on soil solution DOC. a b s t r a c t Dissolved organic carbon (DOC) in the soil solution of forests originates from a number of biologically and/or biochemically mediated processes, including litter decomposition and leaching, soil organic matter mineralization, root exudation, mucilage and microbial activity. A variable amount of DOC reaches the forest floor through deposition, but limited information is available about its impact on soil solution DOC. In this study, trends and patterns of soil solution DOC were evaluated in relation to deposition of DOC over an 11-year period (2002e2012) at five ICP Forests intensive monitoring plots in Flanders, northern Belgium. Trend analysis over this period showed an increase of soil solution DOC concentrations for all observed depth intervals. Fluxes of DOC increased in the organic layer, but were nearly stable in the mineral soil. Annual leaching losses of DOC were higher in coniferous (55e61 kg C ha À1) compared to deciduous plots (19e30 kg C ha À1) but embody less than 0.05% of total 1-m soil organic C stocks. Temporal deposition patterns could not explain the increasing trends of soil solution DOC concentrations. Deposition fluxes of DOC were strongly correlated with soil solution fluxes of DOC, but their seasonal peaks were not simultaneous, which confirmed that airborne or canopy-derived DOC has a limited impact on soil solution DOC.

ABSTRACT Atmospheric deposition to forests has been monitored within the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) with sampling and analyses of bulk precipitation and throughfall at several hundred forested plots for more than 15 years. The current deposition of inorganic nitrogen (nitrate and ammonium) and sulphate is highest in central Europe as well as in some southern regions. We compared linear regression and Mann-Kendall trend analysis techniques often used to detect temporal trends in atmospheric deposition. The choice of method influenced the number of significant trends. Detection of trends was more powerful using monthly data compared to annual data. The slope of a trend needed to exceed a certain minimum in order to be detected despite the short-term variability of deposition. This variability could to a large extent be explained by meteorological processes, and the minimum slope of detectable trends was thus similar across sites and many ions. The overall decreasing trends for inorganic nitrogen and sulphate in the decade to 2010 were about 2% and 6%, respectively. Time series of about 10 and 6 years were required to detect significant trends in inorganic nitrogen and sulphate on a single plot. The strongest decreasing trends were observed in western central Europe in regions with relatively high deposition fluxes, whereas stable or slightly increasing deposition during the last 5 years was found east of the Alpine region as well as in northern Europe. Past reductions in anthropogenic emissions of both acidifying and eutrophying compounds can be confirmed due to the availability of long-term data series but further reductions are required to reduce deposition to European forests to levels below which significant harmful effects do not occur according to present knowledge.

Question: Does clear-felling influence forest herb colonization into post-agricultural forest?Location: A stand of poplar cultivars with a dense understorey of Acer pseudoplatanus in Muizen forest (northern Belgium), planted in 1952 on farmland adjacent to ancient forest and clear-felled in 1997.Methods: Shade-tolerant forest herbs were surveyed in 112 grid-based sample plots: just before clear-felling, and 5 and 10 yr afterwards. Shade-tolerant herbs were subdivided into ancient forest species (AFS) and other shade-tolerant species (OSS). Effects of clear-felling on species number per plot, total cover per plot and colonization rate of species groups were compared using non-parametrical tests. Species number per plot was modelled by means of generalized linear mixed models (GLMMs), with inventory time, distance to the nearest parcel edge, and cover of light-loving species (LS) as explanatory variables. The C-S-R signature (competitive, stress-tolerant and ruderal strategies, respectively) shift of sample plots was calculated on the selected shade-tolerant species.Results: Frequency of most species increased during the 10-yr period. Number of OSS increased more and faster than that of AFS. OSS increased to the level of the adjacent forest, but was lower where LS cover remained high. There was a positive correlation between the change of the colonization rate and the competitive plant strategy.Conclusions: We assume that clear-felling stimulated generative reproduction of shade-tolerant herbs, whereas quickly emerging woody species controlled competitive exclusion by LS. Succession of dark and light phases, such as provided by an understorey managed as a coppice, could promote colonization of shade-tolerant herbs into post-agricultural forest.

Question: Does clear-felling influence forest herb colonization into post-agricultural forest?Location: A stand of poplar cultivars with a dense understorey of Acer pseudoplatanus in Muizen forest (northern Belgium), planted in 1952 on farmland adjacent to ancient forest and clear-felled in 1997.Methods: Shade-tolerant forest herbs were surveyed in 112 grid-based sample plots: just before clear-felling, and 5 and 10 yr afterwards. Shade-tolerant herbs were subdivided into ancient forest species (AFS) and other shade-tolerant species (OSS). Effects of clear-felling on species number per plot, total cover per plot and colonization rate of species groups were compared using non-parametrical tests. Species number per plot was modelled by means of generalized linear mixed models (GLMMs), with inventory time, distance to the nearest parcel edge, and cover of light-loving species (LS) as explanatory variables. The C-S-R signature (competitive, stress-tolerant and ruderal strategies, respectively) shift of sample plots was calculated on the selected shade-tolerant species.Results: Frequency of most species increased during the 10-yr period. Number of OSS increased more and faster than that of AFS. OSS increased to the level of the adjacent forest, but was lower where LS cover remained high. There was a positive correlation between the change of the colonization rate and the competitive plant strategy.Conclusions: We assume that clear-felling stimulated generative reproduction of shade-tolerant herbs, whereas quickly emerging woody species controlled competitive exclusion by LS. Succession of dark and light phases, such as provided by an understorey managed as a coppice, could promote colonization of shade-tolerant herbs into post-agricultural forest.