Liming and wood-ash addition have long been used to attenuate the effects of acidic deposition on forest soils with the goal of promoting tree growth. We performed quantitative meta-analyses of treatment studies from managed forest ecosystems to assess general tendencies of effects of treatment on seven selected measures of performance thought to reasonably reflect the effects of Ca-addition treatment. We retrieved over 350 independent trials from 110 peer-reviewed liming and wood-ash addition studies that were integrated to determine soil pH, base saturation (BS), tree foliar Ca concentration, tree growth, ectomychorrhizae root colonization, soil C-to-N ratio, and microbial indices. The results were quantified through three separate metaanalysis effect size metrics: unweighted relative values and two weighted metrics, Hedges' d and ln R. A surprising number of treatment trials (22%-85%) reported no significant effect, and soil pH and foliar Ca appeared more responsive to liming than to wood-ash addition, whereas BS and tree growth appeared more responsive to wood-ash addition. For six of the seven parameters, estimated mean effect sizes were similar in magnitude and positive in direction for all three meta-analysis metrics. Regression tree optimal models explained 38% of the variation in pH, 47% of the variation in BS, 51% of the variation in foliar Ca concentration, and 26% of the variation in tree growth. The largest predictors of effect size, within our selected group, were as follows: soil type for pH; soil type, trial duration in years, and species (hardwood or softwood) for BS; treatment dose and type for foliar Ca concentration; and trial duration, initial soil pH, and tree species for tree growth. This analysis shows that Ca additions are not universally beneficial and provides insight into when Ca additions to forest soils are likely to be most effective.Résumé : Le chaulage et l'ajout de cendre de bois sont utilisés depuis longtemps pour atténuer les effets des dépôts acides sur les sols forestiers dans le but de promouvoir la croissance des arbres. Nous avons réalisé des méta-analyses quantitatives des essais de traitement dans des écosystèmes forestiers aménagés dans le but d'évaluer les tendances générales des effets des traitements sur un choix de sept mesures de performance qui devraient raisonnablement refléter les effets d'un apport de Ca. Nous avons retrouvé plus de 350 essais indépendants provenant de 110 études portant sur le chaulage et l'ajout de cendre de bois révisées par les pairs. Ces essais ont été intégrés pour déterminer : le pH du sol, la saturation en bases (SB), la concentration du Ca foliaire des arbres, la croissance des arbres, la colonisation des racines par les ectomycorhizes, le rapport C à N du sol et des indices microbiens. Les résultats ont été quantifiés à l'aide de trois métriques distinctes des méta-analyses ayant trait à l'ampleur de l'effet : les valeurs relatives non pondérées et deux métriques pondérées, d de Hedges et lnR. Un nombre surprenant d'essais de traiteme...

Unraveling the cause(s) of declines in total phosphorus (TP) observed over the past three decades across many forested catchments in central Ontario remains a research priority. The objectives of this paper were firstly to test the assumption that weir water chemistry is representative of catchment changes at two adjacent headwater streams that have shown declines in TP and secondly use long-term measurements of weir water quality (1980–2008) to identify potential drivers of TP declines. Longitudinal measurements confirmed that weir water chemistry is generally representative of the entire stream channel, although channel-associated wetlands have a strong influence on TP. Additionally, processes operating in wetlands dictate seasonal patterns in TP, and differences in wetland cover explain the approximately twofold difference in average TP between the two catchments. Changes in wetland cover or processes, however, cannot explain declines in TP. Rather, declines in TP are most coherent with declines in stream potassium (K) and nitrate (NO3-N), which also occurred over the past 30 years. We suggest that coincident declines in TP, NO3-N, and K may be best explained by recovery from a disturbance event.

Declining concentrations of Ca and other base cations in soils and surface waters in eastern North America have led to concerns that forests may become nutrient limited, particularly in regions that are harvested. We constructed a nutrient budget for a selection harvest in central Ontario that is typical of eastern North America. Atmospheric deposition (5-year average) and mineral weathering (PROFILE) were considered as the sole inputs to the forest, while exports included nutrient losses in streams and removed in stems. Sugar maple ( Acer saccharum Marsh.) was the only tree species removed in the study (∼30% of basal area) and harvesting had no strong impact on stream chemistry. Mass balance calculations were performed on average values, but with estimates of uncertainty associated with each input parameter. A Monte Carlo simulation was run (10 000 runs) for Ca, Mg, K, Na, P, N, and S. In the absence of harvesting, average mass balance estimates are positive for all nutrients except S. When harvesting is considered, average mass balances remain positive for all nutrients except Ca, K, and S. Monte Carlo simulations demonstrate that mass balances for Na are always positive, while mass balances for Mg, K, N, P, and S range from slightly positive to slightly negative. In contrast, mass balance simulations for Ca are always negative and average net losses represent ∼1% of the current exchangeable soil Ca pool.

Total phosphorus (TP) concentrations have declined in many lakes and streams across south-central Ontario, Canada, over the past three decades, and changes have been most pronounced in wetland-dominated catchments. In this study, longterm (1980-2007) patterns in TP concentrations in streams were assessed at four wetland-dominated catchments that drain into Dickie Lake (DE) in south-central Ontario. Two of the subcatchments (DE5 and DE6) have particularly large wetland components (31%-34% of catchment area), and these wetlands are characterized by numerous standing dead trees and many young live trees (18-27 years old). These two streams exhibited large peaks in TP and potassium (K) export in the early 1980s. In contrast, TP and K export from DE8 and DE10 (wetland cover 19%-20%) were relatively flat over the entire record , and field surveys indicated negligible standing dead biomass in these wetlands and a relatively healthy, mixed-age tree community. The coincidence of high TP and K concentrations in the DE5 and DE6 streams as well as evidence of a disturbance event in their wetlands during the early 1980s suggest that disturbance events (e.g., flooding) that lead to wetland tree mortality may contribute to patterns in surface water TP observed in this region.Résumé : Les concentrations de phosphore total (PT) sont en baisse dans de nombreux lacs et cours d'eau du centre-sud de l'Ontario (Canada) depuis les trois dernières décennies, les changements les plus marqués s'étant produits dans les bassins versants à prédominance de zones humides. La distribution à long terme des concentrations de PT dans les cours d'eau a été évaluée dans quatre bassins versants à prédominance de zones humides qui se déversent dans le lac Dickie (DE), dans le centre-sud de l'Ontario. Deux des sous-bassins (DE5 et DE6) ont des composantes de zones humides particulièrement importantes (de 31 % à 34 % du bassin), ces zones humides étant caractérisées par de nombreux chicots et de nombreux jeunes arbres vivants (âgés de 18 à 27 ans). Ces deux cours d'eau présentent de grandes pointes d'exportation de TP et de potassium (K) au début des années 1980. En revanche, l'exportation de TP et de K des sous-bassins DE8 et DE10 (couverture de zones humides représent-ant de 19 % à 20 % du bassin) était relativement constante durant toute la période , et les levés de terrain indiquent la présence d'une quantité négligeable de biomasse morte debout dans ces zones humides et d'une communauté d'arbres d'âges mixtes en relativement bonne santé. La coïncidence de fortes concentrations de PT et de K dans les cours d'eau DE5 et DE6, ainsi que des indices d'une perturbation de leurs zones humides au début des années 1980 donnent à penser que les évènements perturbateurs (p. ex. inondations) qui se traduisent par une mortalité des arbres des zones humides pourraient jouer un rôle dans la distribution du PT dans les eaux de surface observée dans cette région. [Traduit par la Rédaction]

Baker, S. R., Watmough, S. A. and Eimers, M. C. 2015. Phosphorus forms and response to changes in pH in acid-sensitive soils on the Precambrian Shield. Can. J. Soil Sci. 95: 95Á108. Soil acidification may explain declines in total phosphorus (TP) levels that have been observed in surface waters in central Ontario, Canada, but much of the research on phosphorus (P) mobility in pH manipulated soils has been performed at high P concentrations (i.e., !500 mM). This study investigated P fractionation in acidic (pH 54.6) soils in south-central Ontario and relationships between soil pH and P sorption at relatively low P concentrations to test whether long-term declines in soil pH could have increased soil P sorption. Soils from three forested catchments that vary naturally in soil pH and outlet stream [TP] (0.1Á0.4 mM in 2008) had very similar soil P concentrations and distributions (Hedley fractionation). Only hydrochloric-acid extractable P (i.e., apatite) differed amongst catchments and was greatest at the catchment with the highest stream [TP]. The fraction of P present as labile/ soluble P did not decline with pH as expected and experiments indicated that P sorption at P concentrations between 4.52 and 452.1 mM was insensitive to manipulated solution pH. Soils were, however, able to sorb!90% of P added in sorption experiments at [P] 5452.1 mM. These results suggest that acidification-induced P sorption in upland soils has not contributed to observed decreases in surface water TP concentrations.Key words: Phosphorus, acidification (soil), Hedley fractionation, sorption, Podzols, Ontario (central) Baker, S. R., Watmough, S. A. et Eimers, M. C. 2015. Types de phosphore et re´action de cet e´le´ment aux variations du pH dans les sols du bouclier pre´cambrien sensibles a`l'acidification. Can. J. Soil Sci. 95: 95Á108. L'acidification du sol pourrait expliquer la concentration de phosphore total (PT) plus faible observe´e dans les eaux superficielles du centre de l'Ontario, mais une bonne partie des recherches sur la mobilite´du phosphore (P) dans les sols dont le pH avait e´te´modifie´ont e´teé ffectue´es a`une concentration de P e´leve´e (a`savoir, supe´rieure a`500 mM). La pre´sente e´tude portait sur le fractionnement du P dans les sols acides (pH 54,6) du centre-sud de l'Ontario et sur les liens existant entre le pH du sol et la sorption du P aux concentrations de P relativement faibles. Elle devait e´tablir si l'acidification a`long terme du sol pouvait avoir accru la sorption du P dans le sol. Trois bassins hydrographiques forestiers dont le pH et la de´charge variaient naturellement [PT] (0,1Á0,4 mM en 2008) pre´sentaient une concentration et une distribution tre`s semblables du P dans leur sol (me´thode de fractionnement de Hedley). Seule la concentration de P extractible a`l'acide chlorhydrique (a`savoir, l'apatite) diffe´rait d'un bassin a`l'autre et atteignait un maximum dans le bassin a`la de´charge la plus importante [PT]. La fraction du P correspondant au P labile/soluble ne diminue pas avec le pH comme ...