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Lebourgeois F.,Agro ParisTech | Lebourgeois F.,French National Institute for Agricultural Research | Eberle P.,Agro ParisTech | Eberle P.,French National Institute for Agricultural Research | And 3 more authors.
Forest Ecology and Management | Year: 2014

The aim of the study was to assess the effects of competition at both stand and tree levels on climate tree-growth relationships of 414 Abies alba and 243 Fagus sylvatica trees growing in 2 contrasting ecological conditions (north- and south-facing) under mountainous continental climate (mean altitude: 886m). Stand level competition was considered through three stand basal area (SBA) modalities (Low: 32m2/ha, Medium: 41 and High: 49) while tree level competition was assessed through three social statuses (SST, Dominant, Codominant and Suppressed trees). A strong specific response to climate was pointed out with different key periods; growth of Abies being mainly driven by previous and current late summer temperatures, while that of Fagus was controlled by April and June ones. No obvious difference between facing sides was evidenced. Competition at stand level prevailed on competition at tree level. In Low and Medium SBA, trees exhibited similar responses to climate whatever their social statuses. On the opposite, sensitivity to summer drought increased with dominancy in high SBA. Inter-specific differences and consequences for forest management are discussed. © 2014 Elsevier B.V.

Charru M.,French National Institute for Agricultural Research | Seynave I.,French National Institute for Agricultural Research | Herve J.-C.,Institute National Of Linformation Geographique Et Forestiere | Bontemps J.-D.,French National Institute for Agricultural Research
Trees - Structure and Function | Year: 2014

Key message: Productivity changes in Norway spruce show important regional and local spatial variations, highlighting their context dependence at different spatial scales. These variations suggest the enhancing role of climate warming, and interplay with local water and nutrient limitations. While forest growth changes have been observed in many places worldwide, their spatial variation and environmental origin remain poorly documented. Analysis of these historical changes in contrasted regional contexts, and their mapping over continuous environmental gradients, may help uncover their environmental causes. The approach was tested on Norway spruce (Picea abies) in three western European mountain contexts (Massif Central, Alps and Jura), using National Forest Inventory (NFI) data. We explored the environmental factors influencing stand basal area increment (BAI) in each context. We then estimated and compared mean regional changes in BAI and related these to the regional environmental limitations evidenced. Within each region, we further mapped local BAI trends using a geographically weighted regression (GWR) approach. In each region, local estimates of BAI changes were finally correlated to environmental indicators. We found an increase in BAI in the three regions over 1980-2005, greater in the Massif Central (+71 %) than in the Alps (+19 %) and the Jura Mountains (+21 %). Inter-regional differences in BAI changes suggested the release of a thermal constraint-found more important in the Massif Central-by the strong temperature increase over the period, and a limitation by water availability in the Jura and the Alps Mountains. Spatial patterns of BAI change revealed significant local variations in the Massif Central and the Alps. From the correlation analysis, these were again found consistent with the hypothesis of an enhancing effect of climate warming in these mountain ranges. They were also related to local soil nutritional status in the two regions, and negatively related to nitrogen deposition level in the Massif Central. As a main outcome, a strong context and spatial scale dependence of productivity changes is emphasized. In addition, the enhancing effect of climate warming on productivity is suggested, with local modulation by climatic and nutritional conditions. © 2013 Springer-Verlag Berlin Heidelberg.

Fadil A.,University of Otago | Denys P.,University of Otago | Tenzer R.,Wuhan University | Grenfell H.R.,Geomarine Research | And 2 more authors.
Journal of Geophysical Research: Oceans | Year: 2013

Investigations in long-term instrumental tidal records reveal that 20th century sea level along the coast of New Zealand is rising at 1.46 ± 0.10 mm/yr in agreement with the regional rates from southern Australia and Tasmania. We extend the advanced altimeter-gauge approach of combining satellite altimetry and tide gauge data with constraint equations from long-term adjacent tide gauge records to assess its performance in open seas and to explore the impact of vertical land motion on the observed relative sea level. This approach has again proven to be a robust method with an accuracy of 0.4 mm/yr. While no clear sea level rise pattern can be inferred once the tide gauge apparent sea level trends are corrected for vertical land motions from GPS, the advanced altimeter-gauge and geological vertical rates are completely consistent and reveal three temporal phases of sea level rise marked by an increase from 1.46 ± 0.10 mm/yr to 1.72 ± 0.10 mm/yr during the period (1900-1936), followed by a decrease to 1.48 ± 0.10 mm/yr during the period (1936-1956), and a substantial increase to 2.60 ± 0.10 mm/yr during the period (1956-1975). In contrast, the 20th century microfossil proxy records of absolute sea level rise display twice the tide gauge sea level rise rate of 3.17 ± 0.30 mm/yr and 3.28 ± 0.45 mm/yr, respectively, once salt-marsh records are corrected using GPS and geological vertical rates. Differential autocompaction and transfer functions are possible factors, which need further investigation. Key Points Vertical motion at tide gauge using GPS, altimeter-gauge, and geological data New Zealand 20th century sea level rise instrumental and proxy 20th century sea level rise difference ©2013. American Geophysical Union. All Rights Reserved.

Bontemps J.-D.,Agro ParisTech | Bontemps J.-D.,French National Institute for Agricultural Research | Gelhaye P.,Agro ParisTech | Gelhaye P.,French National Institute for Agricultural Research | And 3 more authors.
Annals of Forest Science | Year: 2013

• Context: While historical increases in forest growth have been largely documented, investigations on historical wood density changes remain anecdotic. They suggest possible density decreases in softwoods and ring-porous hardwoods, but are lacking for diffuse-porous hardwoods. • Aims: To evaluate the historical change in mean ring density of common beech, in a regional context where a ring-porous hardwood and a softwood have been studied, and assess the additional effect of past historical increases in radial growth (+50 % over 100 years), resulting from the existence of a positive ring size-density relationship in broadleaved species. • Methods: Seventy-four trees in 28 stands were sampled in Northeastern France to accurately separate developmental stage and historical signals in ring attributes. First, the historical change in mean ring density at 1.30 m (X-ray microdensitometry) was estimated statistically, at constant developmental stage and ring width. The effect of past growth increases was then added to assess the net historical change in wood density. • Results: A progressive centennial decrease in mean ring density of -55 kg m-3 (-7.5 %) was identified (-10 % following the most recent decline). The centennial growth increase induced a maximum +25 kg m-3 increase in mean ring density, whose net variation thus remained negative (-30 kg m-3). • Conclusions: This finding of a moderate but significant decrease in wood density that exceeds the effect of the positive growth change extends earlier reports obtained on other wood patterns in a same regional context and elsewhere. Despite their origin not being understood, such decreases hence form an issue for forest carbon accounting. © 2013 INRA and Springer-Verlag France.

Cadio C.,Yale University | Cadio C.,CNRS Paris Institute of Global Physics | Ballmer M.D.,University of Hawaii at Manoa | Panet I.,CNRS Paris Institute of Global Physics | And 3 more authors.
Earth and Planetary Science Letters | Year: 2012

Analyzing the formation mechanism of hotspot swells enhances our understanding of intraplate volcanism and the underlying geodynamical processes. The two main hypotheses for the origin of the archetypal Hawaiian swell are thermal lithospheric thinning, and dynamic support by an ascending plume. Any successful model would have to be able to simultaneously explain the swell topography and the corresponding geoid anomaly. In simple models of isostatic compensation, the geoid-to-topography ratio (GTR) is linearly related to the depth of the compensating mass; therefore it is often considered a fundamental parameter to assess swell support mechanisms. Previous estimates for the geoid-to-topography ratio (GTR) of the Hawaiian swell however are biased towards low values by incomplete removal of the effects of volcanic loading and lithospheric flexure. In order to resolve these issues, we here apply a continuous wavelet transform, which allows resolution of lateral variations of the GTR at various spatial scales. In a series of synthetic tests, the robustness of this approach and its power to identify the origin of hotspot swells are established. With 8. m/km on the youngest part of the chain, the recovered GTR agrees well with the predictions for dynamic support, therefore ruling out thermal rejuvenation as an important mechanism. We also find that the depth of the compensating mass decays by 20. km over a distance of 500. km from Hawaii to Kauai, and identify sublithospheric erosion by small-scale convection in the ponded plume material as a viable mechanism to support this decay. © 2012.

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