We compiled a global database for leaf, stem and root biomass representing c. 11 000 records for c. 1200 herbaceous and woody species grown under either controlled or field conditions. We used this ...data set to analyse allometric relationships and fractional biomass distribution to leaves, stems and roots.
We tested whether allometric scaling exponents are generally constant across plant sizes as predicted by metabolic scaling theory, or whether instead they change dynamically with plant size. We also quantified interspecific variation in biomass distribution among plant families and functional groups.
Across all species combined, leaf vs stem and leaf vs root scaling exponents decreased from c. 1.00 for small plants to c. 0.60 for the largest trees considered. Evergreens had substantially higher leaf mass fractions (LMFs) than deciduous species, whereas graminoids maintained higher root mass fractions (RMFs) than eudicotyledonous herbs.
These patterns do not support the hypothesis of fixed allometric exponents. Rather, continuous shifts in allometric exponents with plant size during ontogeny and evolution are the norm. Across seed plants, variation in biomass distribution among species is related more to function than phylogeny. We propose that the higher LMF of evergreens at least partly compensates for their relatively low leaf area: leaf mass ratio.
1. There is increasing evidence that species diversity enhances the temporal stability (TS) of community productivity in different ecosystems, although its effect at the population and tree levels ...seems to be negative or neutral. Asynchrony in species responses to environmental conditions was found to be one of the main drivers of this stabilizing process. However, the effect of species mixing on the stability of productivity, and the relative importance of the associated mechanisms, remain poorly understood in forest communities. 2. We investigated the way mixing species influenced the TS of productivity in Pinus sylvestris L. and Fagus sylvatica L. forests, and attempted to determine the main drivers among overyielding, asynchrony between species annual growth responses to environmental conditions, and temporal shifts in species interactions. We used a network of 93 experimental plots distributed across Europe to compare the TS of basal area growth over a 15-year period (1999-2013) in mixed and monospecific forest stands at different organizational levels, namely the community, population and individual tree levels. 3. Mixed stands showed a higher TS of basal area growth than monospecific stands at the community level, but not at the population or individual tree levels. The TS at the community level was related to asynchrony between species growth in mixtures, but not to overyielding nor to asynchrony between species growth in monospecific stands. Temporal shifts in species interactions were also related to asynchrony and to the mixing effect on the TS. 4. Synthesis. Our findings confirm that species mixing can stabilize productivity at the community level, whereas there is a neutral or negative effect on stability at the population and individual tree levels. The contrasting findings regarding the relationships between the temporal stability and asynchrony in species growth in mixed and monospecific stands suggest that the main driver in the stabilizing process may be the temporal niche complementarity between species rather than differences in species' intrinsic responses to environmental conditions.
Climate change is increasing the severity and frequency of droughts around the globe, leading to tree mortality that reduces production and provision of other ecosystem services. Recent studies show ...that growth of mixed stands may be more resilient to drought than pure stands. The two most economically important and widely distributed tree species in Europe are Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.), but little is known about their susceptibility to drought when coexist.
This paper analyses the resilience (resistance, recovery rate and recovery time) at individual‐tree level using a network of tree‐ring collections from 22 sites along a climatic gradient from central Europe to Scandinavia. We aimed to identify differences in growth following drought between the two species and between mixed and pure stands, and how environmental variables (climate, topography and site location) and tree characteristics influence them.
We found that both the timing and duration of drought drive the different responses between species and compositions. Norway spruce showed higher vulnerability to summer drought, with both lower resistance and a longer recovery time than Scots pine. Mixtures provided higher drought resistance for both species compared to pure stands, but the benefit decreases with the duration of the drought. Especially climate sensitive and old trees in climatically marginal sites were more affected by drought stress.
Synthesis. Promoting Scots pine and mixed forests is a promising strategy for adapting European forests to climate change. However, if future droughts become longer, the advantage of mixed stands could disappear which would be especially negative for Norway spruce.
Mixtures of Scots pine and Norway spruce provided higher drought resistance for both species compared to pure stands, but the benefit decreases with drought duration. Norway spruce showed higher vulnerability to summer drought, with both lower resistance and a longer recovery time. Promoting Scots pine and mixed forests is a promising strategy for adapting European forests to climate change.
The increasing disturbances in monocultures around the world are testimony to their instability under global change. Many studies have claimed that temporal stability of productivity increases with ...species richness, although the ecological fundamentals have mainly been investigated through diversity experiments. To adequately manage forest ecosystems, it is necessary to have a comprehensive understanding of the effect of mixing species on the temporal stability of productivity and the way in which it is influenced by climate conditions across large geographical areas.
Here, we used a unique dataset of 261 stands combining pure and two‐species mixtures of four relevant tree species over a wide range of climate conditions in Europe to examine the effect of species mixing on the level and temporal stability of productivity. Structural equation modelling was employed to further explore the direct and indirect influence of climate, overyielding, species asynchrony and additive effect (i.e. temporal stability expected from the species growth in monospecific stands) on temporal stability in mixed forests.
We showed that by adding only one tree species to monocultures, the level (overyielding: +6%) and stability (temporal stability: +12%) of stand growth increased significantly. We identified the key effect of temperature on destabilizing stand growth, which may be mitigated by mixing species. We further confirmed asynchrony as the main driver of temporal stability in mixed stands, through both the additive effect and species interactions, which modify between‐species asynchrony in mixtures in comparison to monocultures.
Synthesis and applications. This study highlights the emergent properties associated with mixing two species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature‐based climate solution, which could contribute towards meeting EU climate target policies.
Resumen
Las cada vez más frecuentes perturbaciones en masas forestales monoespecíficas en todo el mundo, son una muestra de su inestabilidad bajo el cambio climático. Numerosos estudios indican que la estabilidad temporal de la productividad aumenta con la riqueza de especies, aunque los fundamentos ecológicos de esta relación se han estudiado principalmente en experimentos de diversidad de especies. Para una gestión adecuada de los ecosistemas forestales, es necesaria una mejor comprensión del efecto de la mezcla de especies en la estabilidad temporal de la productividad y de cómo esta se ve modificada por las condiciones climáticas.
En este trabajo usamos una base de datos única de 261 masas monoespecíficas y mixtas de dos especies a largo de un amplio rango de condiciones climáticas para examinar el efecto de la mezcla de especies en el nivel y estabilidad temporal de la productividad. Las mezclas estudiadas son combinaciones de dos especies entre cuatro de las especies forestales más relevantes en Europa. Se utilizan modelos de ecuaciones estructurales para explorar la influencia directa e indirecta del clima, el mayor crecimiento en mixtas que en puras (overyielding), la asincronía entre especies y el efecto aditivo (estabilidad temporal esperada según el crecimiento de las dos especies en las masas puras) en la estabilidad temporal en masas mixtas.
Los resultados muestran que añadiendo solo una especie a las masas monoespecíficas el nivel (overyielding: +6%) y la estabilidad temporal (+12%) del crecimiento aumentan significativamente. Se ha identificado que la temperatura tiene un efecto clave en la desestabilización del crecimiento, que puede ser mitigado en parte por la mezcla de especies. Se confirma que la asincronía, a través del efecto aditivo y de la interacción de especies (que modifica la asincronía entre especies en masas mixtas con respecto a la de las masas monoespecíficas), es el principal factor que explica la mayor estabilidad temporal en masas mixtas.
Síntesis y aplicaciones. Este estudio revela las propiedades emergentes asociadas a la mezcla de dos especies, que resultan en sistemas de producción eficientes y estables. Se identifica el impacto negativo de las temperaturas en la estabilidad temporal de la productividad y cómo el efecto estabilizador de la mezcla de dos especies puede contrarrestar este impacto. El nivel y la estabilidad temporal del crecimiento estudiados en este trabajo son fundamentales en los servicios ecosistémicos ligados al nivel y el ritmo del crecimiento forestal. Los resultados subrayan que la mezcla de dos especies puede ser una realista y efectiva solución climática basada en la naturaleza, que contribuya a cumplir los objetivos climáticos de la EU.
This study highlights the emergent properties associated with mixing two‐species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature‐based climate solution, which could contribute towards meeting EU climate target policies.
The island of El Hierro is the smallest and youngest island in the Canary archipelago. It has been recognized as a UNESCO Biosphere Reserve since 2000, and it has a population of approximately 10,000 ...inhabitants. The aim of this study was to determine the amount of CO2 emissions absorbed by the forest stands of the island of El Hierro and compare it to the emissions generated by the population. It is noteworthy that there is a hydro‐wind energy production project on the island that has significantly minimized the emissions linked to energy production. In short, El Hierro's forest stands are capable of capturing 46,785 tons of CO2 annually, while emissions associated with electricity production and emissions linked to road mobility are below the island's carbon sequestration capacity since the Gorona del Viento renewable energy project was built. By working on investment in renewable energies to produce energy and changing mobility with the use of electric vehicles, a small island like El Hierro can adapt to ecological transition by the year 2040. This is a goal set by the government to drastically reduce emissions in the Canary Islands.
•A database containing nearly 1000 European biomass equations was developed.•Biomass and leaf area allometry were influenced by stand structure.•Species traits were correlated with interspecific ...differences in responses to stand structure.
Biomass and leaf area equations are often required to assess or model forest productivity, carbon stocks and other ecosystem services. These factors are influenced by climate, age and stand structural attributes including stand density and tree species diversity or species composition. However, such covariates are rarely included in biomass and leaf area equations. We reviewed the literature and built a database of biomass and leaf area equations for 24 European tree species and 3 introduced species. The final dataset contained 973 equations. Most of the equations were site-specific and therefore restricted to the edaphic, climatic and stand structural conditions of the given site. To overcome this limitation, the database was used to develop regional species-specific equations that can be used in a wide range of stands and to quantify the effects of climate, age and stand structure on biomass or leaf area. The analysis showed considerable inter- and intra-specific variability in biomass relationships. The intra-specific variability was related to climate, age or stand characteristics, while the inter-specific variability was correlated with traits such as wood density, specific leaf area and shade tolerance. The analysis also showed that foliage mass is more variable than stem or total aboveground biomass, both within and between species, and these biomass components have contrasting responses to age and changes in stand structure. Despite the large number of published equations, many species are still not well represented. Therefore, generic equations were developed that include species-specific wood density instead of species identity. Further improvements may be possible if future studies quantify the stand structure of individual tree neighbourhoods instead of using the stand means for all trees sampled with the given stand.
•Foliar decay rates were species-specific in unmanaged plots of Mediterranean mixed-oak pine.•Thinning reduces the decay rate of oak leaves.•C concentration was not affected by thinning, whereas ...heavy thinning reduced N and P concentration.•Heavy thinning of Mediterranean sites might have an aridification effect negatively affecting the decomposition process.
Leaf litter decomposition is a major pathway for nutrient recycling and a chief factor controlling ecosystem primary productivity. The aim of this study was to analyze the effect of forest thinning on the early-stage foliar decomposition rate and nutrient immobilization-release pattern in a mixed Quercus pyrenaica-Pinus pinaster forest growing in the western Mediterranean basin. Two thinning treatments, differing in the intensity of canopy reduction, were compared with a control (unthinned) situation. Oak leaves showed faster decomposition rates than pine needles in unthinned plots. Intense canopy reduction (40% of basal area removed) reduced decomposition rates in both species whereas intermediate reduction (25% of basal area removed) increased decomposition of needles to a rate similar to that of oak leaves. C and N transfer from N-rich to N-poor foliar litter was not detected, indicating a marginal role of canopy reduction in this process. A decoupling of the decomposition rate from immobilization-release pattern was found for mobile elements (K and Mg) at intermediate levels of canopy cover whereas Ca dynamics indicated that pine needles had not started the lignin-mediated degradation phase two years after incubation. We finally hypothesized that strong reductions of canopy cover in dry Mediterranean sites might have an aridification effect on litter decomposition.
•The two species showed intra-annual stem radial variation synchrony.•Spring and autumn radial increment onset was earlier for maritime pine.•Maritime pine showed a higher sensitivity to summer ...drought.•Species differences in weather response may reduce competition for resources.
Species complementarity by morphological and physiological trait differences could cause distinct temporal and spatial use of resources. Accordingly, mixed stands may enhance production, biodiversity and/or provide a better adaptation to future climate conditions. We aim to identify species differences in intra-annual stem radial variation patterns, and to recognize species-specific responses to contrasting weather conditions at key intra-annual growth phases. Stem radial variation was recorded from high temporal resolution point dendrometers (2012–2014) installed on twelve dominant maritime pine and Pyrenean oak trees in two mixed stands in central Spain. Species differences in stem radial variation were analyzed by synchrony statistics, intra-annual pattern modelling, and evaluating the dependence of main intra-annual growth phases on climate conditions. Both species showed important differences on intra-annual radial increment pattern despite general stem radial variation synchrony. Radial increment onset was earlier for maritime pine during the spring and rainy autumns. Species-specific responses to weather indicate that stem radial variation increased with autumn temperature in maritime pine, but decreased in Pyrenean oak trees. However, summer vapor pressure deficit may reduce stem radial variation for maritime pine. Therefore, maritime pine would adapt more efficiently to warmer temperatures associated with climate change, although summer water stress may reduce this competitive bonus.
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•A Pinus pinaster plantation in Central Spain was cut using group selection system.•Maritime pine seedling survival was analyzed.•Gaps and mid-shade positions within the gap had a ...positive effect on survival.•Summer conditions are more stressful, resulting in higher seedling mortality levels.•Group selection system would be a suitable method for maritime pine regeneration.
Diversification of forests, both in terms of structure and species, has been identified as one of the main strategies for adapting forests to climate change. Among the different options available for managers to promote diversification, regeneration cuttings are a suitable option to meet these objectives in adult stands close to rotation ages. The regeneration of maritime pine (Pinus pinaster Ait.) stands is a major issue throughout its distribution area, with summer survival being the main bottleneck for seedling establishment and development. Group selection cutting system may be the best option to promote uneven-aged and mixed structures in shade intolerant species, such as maritime pine. Gaps generate different regeneration niches for species of contrasting shade tolerance while creating uneven-aged stands, which are potentially more resilient to the impacts of climate change.
In our experiment, gaps of two different sizes (1.5 and 2.5 times the dominant height of the stand, both sizes being smaller than those proposed in literature) were opened up to test the effects on natural regeneration success in a planted 53-year-old maritime pine stand in Central Spain. There were nine gaps of each size, along with nine control plots, containing 1-m radius subplots distributed within them to record natural regeneration of maritime pine and other species, in addition to several ecological factors and seedling characteristics. A survival model was fitted to highlight the main factors driving seedling survival. Gaps were found to have a significant positive effect on seedling survival, as well as mid-shade positions within the gaps and the age of the seedlings. Summer was found to have a negative effect on seedling survival. No effect of inter-species competition (scrub or herbs), litter coverage or geomorphological characteristics (slope, aspect or altitude) was found. Our results indicate, therefore, that group selection system cuttings, even with small gap sizes (1.5 and 2.5 times the dominant height), would provide a suitable method for the regeneration of Mediterranean maritime pine plantations.
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