Fast height growth is key to non-native conifers invasiveness in temperate forests

peer reviewedMany exotic conifer species have been introduced for wood production in temperate regions. Some of these species can display an invasive behavior and negatively impact native ecosystems. It is therefore crucial to identify potentially invasive species before they are widely planted. Seedling high relative growth rate (RGR) and specific leaf area (SLA) have been associated with enhanced invasiveness of trees in previous studies. However, it has been mainly demonstrated for light-demanding species in disturbed habitats, less for shade-tolerant species in closed forests. Here, we investigated the link between seedlings growth traits of 15 exotic conifer species and invasiveness considered at both global and local scale. Seedlings were grown outdoor, under a shade net, and harvested after 4 and 10 weeks. RGR, SLA, Shoot–Root ratio, shoot relative growth rate, relative height growth rate (RHGR) and relative needles production rate were measured. We developed a continuous approach to position each species along a gradient of invasiveness. Local invasiveness consists of a value based on regeneration densities and dispersal distances observed in forest arboreta in Southern Belgium, and is therefore related to the ability of species to invade closed forest ecosystems. Global invasiveness was calculated based on the GBIF Database and the Global Compendium of Weeds, and encompasses all potentially invaded habitats. It appeared that RHGR was positively related to both local and global invasiveness, while SLA was positively related to local invasiveness only. However, RGR was not significantly related with local nor global invasiveness. This study indicates that preferential investment in rapid vertical growth associated with fast resource acquisition is a strategy enhancing invasiveness of non-native conifers, also in closed, shaded temperate forests

Invasive Acer negundo outperforms native species in non-limiting resource environments due to its higher phenotypic plasticity

<p>Abstract</p> <p>Background</p> <p>To identify the determinants of invasiveness, comparisons of traits of invasive and native species are commonly performed. Invasiveness is generally linked to higher values of reproductive, physiological and growth-related traits of the invasives relative to the natives in the introduced range. Phenotypic plasticity of these traits has also been cited to increase the success of invasive species but has been little studied in invasive tree species. In a greenhouse experiment, we compared ecophysiological traits between an invasive species to Europe, <it>Acer negundo</it>, and early- and late-successional co-occurring native species, under different light, nutrient availability and disturbance regimes. We also compared species of the same species groups <it>in </it><it>situ</it>, in riparian forests.</p> <p>Results</p> <p>Under non-limiting resources, <it>A. negundo </it>seedlings showed higher growth rates than the native species. However, <it>A. negundo </it>displayed equivalent or lower photosynthetic capacities and nitrogen content per unit leaf area compared to the native species; these findings were observed both on the seedlings in the greenhouse experiment and on adult trees <it>in situ</it>. These physiological traits were mostly conservative along the different light, nutrient and disturbance environments. Overall, under non-limiting light and nutrient conditions, specific leaf area and total leaf area of <it>A. negundo </it>were substantially larger. The invasive species presented a higher plasticity in allocation to foliage and therefore in growth with increasing nutrient and light availability relative to the native species.</p> <p>Conclusions</p> <p>The higher level of plasticity of the invasive species in foliage allocation in response to light and nutrient availability induced a better growth in non-limiting resource environments. These results give us more elements on the invasiveness of <it>A. negundo </it>and suggest that such behaviour could explain the ability of <it>A. negundo </it>to outperform native tree species, contributes to its spread in European resource-rich riparian forests and impedes its establishment under closed-canopy hardwood forests.</p

Stakeholders' views on the global guidelines for the sustainable use of non‐native trees

A large number of non‐native trees (NNTs) have been introduced globally and widely planted, contributing significantly to the world's economy. Although some of these species present a limited risk of spreading beyond their planting sites, a growing number of NNTs are spreading and becoming invasive leading to diverse negative impacts on biodiversity, ecosystem functions and human well‐being. To help minimize the negative impacts and maximize the economic benefits of NNTs, Brundu et al. developed eight guidelines for the sustainable use of NNTs globally—the Global Guidelines for the Use of NNTs (GG‐NNTs). Here, we used an online survey to assess perceptions of key stakeholders towards NNTs, and explore their knowledge of and compliance with the GG‐NNTs. Our results show that stakeholders are generally aware that NNTs can provide benefits and cause negative impacts, often simultaneously and they consider that their organization complies with existing regulations and voluntary agreements concerning NNTs. However, they are not aware of or do not apply most of the eight recommendations included in the GG‐NNTs. We conclude that effectively managing invasions linked to NNTs requires both more communication efforts using an array of channels for improving stakeholder awareness and implementation of simple measures to reduce NNT impacts (e.g. via GG‐NNTs), and a deeper understanding of the barriers and reluctance of stakeholders to manage NNT invasions. Read the free Plain Language Summary for this article on the Journal blog

Using automated sanding to homogeneously break seed dormancy in black locust (Robinia pseudoacacia L., Fabaceae)

Physical dormancy of Robinia pseudoacacia seeds makes it a challenge for scientists and forest managers to obtain a homogeneous germination for larger seed samples. Water imbibition of the seeds can be achieved through manual piercing of the seed coat, but this method remains time consuming and heterogeneous. We tested several ecologically friendly methods to break seed dormancy, including manual pin puncture, water soaking, oven dry-heating (two temperatures) and sanding. Sanding was performed using an automatic grinder to control shaking duration (three durations) and get a homogeneous scraping of the coat. All methods, except dry-heating, resulted in successful dormancy breaking; water soaking was the least efficient method, attaining 57% germination. Sanding proved to be as efficient as puncturing (97%) but long duration sanding (10 or 15 min) could damage cotyledons, which would impede further development of the plant. Short-time sanding (5 min) proved to be the best method to reach high total germination and healthy (undamaged cotyledon) seedlings, and was successfully applied to 500 seeds. The reference puncture method and the automatic sanding were also tested on seeds of nine Fabaceae species and proved to be efficient for some species. Automated sanding can thus be used as a standard to break physical dormancy of black locust or other Fabaceae seeds to allow further comparative studies of plant populations or genotypes

Estimating the foliage area of Maritime pine (Pinus pinaster Aït.) branches and crowns with application to modelling the foliage area distribution in the crown

Destructive measurements of architecture and biomass were performed on 63 trees from three Pinus pinaster stands (5, 21 and 26 year-old) in order to determine the quantity and distribution of foliage area inside the crown. Allometric equations were developed per site and needle age, which allowed to correctly calculate ($R^2 = 0.71$ to 0.79) the foliage area of a branch, knowing its basal diameter and its relative insertion height in the crown. Using these equations, we estimated total crown foliage area. A non-linear function of tree diameter and tree age was fitted to these data ($R^2 = 0.82$ and 0.88). On the 5 and 26 year-old stands, we combined the branch level models and the architectural measurements to develop probability functions describing the vertical and horizontal foliage area distributions inside the crown. The parameters of the beta functions varied with needle and stand age, foliage being located mostly in the upper and outer part of the crown for the adult tree, whereas it was more abundant in the inner and lower parts of the crown in the 5 year-old trees. A simple representation of crown shape was added to the study, so that knowing tree age and diameter, it could be possible to fully describe the quantity of foliage area and its localisation inside a maritime pine crown.Estimation de la surface foliaire de branches et de houppiers de Pin maritime (Pinus pinaster Aït.) et son application pour modéliser la distribution de la surface foliaire dans le houppier. Afin de déterminer la quantité et la distribution de la surface foliaire dans un houppier de pin maritime, nous avons réalisé une analyse destructive de l'architecture et de la biomasse de 63 arbres issus de trois peuplements âgés de 5, 21 et 26 ans. Des équations allométriques par peuplement et année foliaire permettent de calculer correctement ($R^2 = 0,71$ à 0,79) la surface foliaire d'une branche connaissant son diamètre et sa hauteur relative d'insertion. L'utilisation de ces équations a permis d'estimer la surface foliaire totale du houppier. Un modèle arbre correspondant à une fonction puissance du diamètre de l'arbre et de l'inverse de son âge a été ajusté sur ces valeurs ($R^2 = 0,80$ et 0,88). D'autre part, la combinaison des modèles branches et des mesures architecturales a permis de paramétrer des fonctions de type bêta, sur les sites de 5 et 26 ans, décrivant les distributions verticales et horizontales de la surface foliaire dans le houppier. Leurs paramètres variaient avec l'âge du site et de la cohorte : le feuillage étant localisé dans la partie supérieure et extérieure du houppier chez les arbres adultes, et davantage vers le bas et l'intérieur de la couronne des arbres de 5 ans. Une représentation simplifiée de la forme du houppier a été ajoutée à l'établissement des profils de surface foliaire afin que la connaissance de l'âge et du diamètre à 1,30 m d'un pin maritime suffisent à établir une description quantitative et qualitative de son feuillage

Estimation de la biomasse aérienne du sous-bois de peuplements de pin maritime à l’aide de mesures de recouvrement

• Understorey plays a major role in forest fluxes and stocks balances, however this compartment is generally poorly quantified. Our objectives were to establish models to estimate understorey biomass using vegetation cover measurements and to investigate upscaling methodologies from stand to regional level. • Understorey aboveground biomass measurements were undertaken in Maritime pine stands of mesohygric, mesic and dry moorlands in South West France. • Average biomass stock in this compartment was estimated to 3.50 t DM ha−1. The more abundant species groups varied with moorland types, with a higher relative contribution of herbaceous species (23.3%), bracken (59.2%) and mosses (31.6%) for mesohygric, mesic and dry moorlands, respectively. For each species group, we established significant relationships to estimate biomass using a volumetric index, based on cover and height measurements. No relationship between stand characteristics and understorey biomass was founded. We investigated the upscaling of these estimations to a several thousands hectare area using understorey cover measurements done along a regular spatial grid. The only significant correlation linked one satellite vegetation index to understorey biomass. • We successfully developed empirical relationships to estimate the understorey biomass at the stand level. Further investigations could focus on the analysis of understorey variability over a finer space grid and the potential use of satellite vegetation [email protected]@pierroton.inra.fr• Le sous-bois est un compartiment non négligeable dans les études de stocks et de flux des forêts; cependant il est encore mal quantifié. Les objectifs de notre étude étaient d’établir des relations permettant d’estimer la biomasse du sous-bois de peuplements et d’analyser les possibilités d’extrapolation à l’échelle du massif. • Des mesures de biomasse aérienne de sous-bois ont été réalisées sur une série de peuplements de pin maritime en Landes mésohygrophile, mésophile et sèche dans le Sud-Ouest de la France. • Nous avons estimé le stock moyen de biomasse dans ce compartiment à 3.50 t MS ha−1. Le groupe d’espèces le plus abondant diffère selon le type de landes : herbacées (23.3 %), fougères (59.2 %)et mousses (31.6 %) en landes mésohygrophile, mésophile et sèche, respectivement. Pour chaque groupe d’espèces, des relations significatives ont été mises en évidence entre un indice volumique et la biomasse de sous-bois. Aucune relation n’a été mise en évidence entre les caractéristiques du peuplement et la biomasse du sous-bois. Nous avons envisagé le calcul à l’échelle d’une zone atelier de plusieurs milliers d’hectares en utilisant une grille spatialisée de relevés de recouvrements. Seul un indice satellite de végétation a présenté une corrélation positive avec la biomasse du sous-bois. • Les relations que nous avons développées permettent d’estimer la biomasse du sous-bois à l’échelle du peuplement. L’analyse spatiale à une échelle plus fine et l’utilisation d’un indice de végétation pourraient être des pistes à explorer