•Tree architecture before and during canopy closure is analyzed.•Inter-tree competition strongly affects architectural development.•Diversity and identity of neighbors are not yet important ...determinants.•Regulating inter-tree competition might facilitate tree quality shaping.
It is acknowledged that trees behave remarkably plastic in response to environmental conditions. Even so, knowledge of how tree architecture in pure and mixed stands compare is largely underexplored. Such information is relevant from a fundamental ecological and an applied silvicultural perspective, given the increased attention for mixed species silviculture and the close linkages between tree architecture and high-quality timber production. The main objective of this work was to test the effects of competition, diversity and species identity of neighboring trees on the architecture of five important European tree species (Quercus robur, Betula pendula, Fagus sylvatica, Pinus sylvestris and Tilia cordata) in a temperate plantation before and during canopy closure.
Data were collected in FORBIO-Zedelgem, a five-year old tree diversity experiment in Belgium. For 396 trees we measured architectural properties including branchiness, tree height-to-diameter (HD) ratio, branch diameter and branch insertion angle, and we investigated how these properties were shaped in different competitive neighborhoods using mixed regression models.
Species showed contrasting architectural responses to neighborhood competition, in line with species life-history strategies. In more competitive environments, trees of Q. robur (slow growing and light-demanding) increased HD ratio and branch insertion angle to optimize light foraging in the upper canopy; trees of B. pendula (fast growing and light-demanding) increased HD ratio and decreased branching following the branch autonomy principle; trees of F. sylvatica (slow growing and shade tolerant) increased branching to improve light uptake under shading and finally, trees of P. sylvestris (fast growing and light-demanding) and T. cordata (slow growing and shade tolerant) were not shaped in response to competition. Diversity and identity of species in a trees’ neighborhood did not contribute to the architectural plasticity, although competitive differences between pure and mixed stands underpinned such effects for B. pendula, with lower branching in the highly competitive monocultures.
We conclude that competition between trees, but not diversity, influences the architecture of young plantation trees before and during canopy closure in mixtures. To guide tree architectural development towards high-quality timber, management may have to pay considerable attention to competitive processes already in the juvenile forest stages.
Tree decline is a global concern and the primary cause is often unknown. Complex interactions between fluctuations in nitrogen (N) and acidifying compounds have been proposed as factors causing ...nutrient imbalances and decreasing stress tolerance of oak trees. Microorganisms are crucial in regulating soil N available to plants, yet little is known about the relationships between soil N-cycling and tree health. Here, we combined high-throughput sequencing and qPCR analysis of key nitrification and denitrification genes with soil chemical analyses to characterise ammonia-oxidising bacteria (AOB), archaea (AOA) and denitrifying communities in soils associated with symptomatic (declining) and asymptomatic (apparently healthy) oak trees (Quercus robur and Q. petraea) in the United Kingdom. Asymptomatic trees were associated with a higher abundance of AOB that is driven positively by soil pH. No relationship was found between AOA abundance and tree health. However, AOA abundance was driven by lower concentrations of NH
, further supporting the idea of AOA favouring lower soil NH
concentrations. Denitrifier abundance was influenced primarily by soil C:N ratio, and correlations with AOB regardless of tree health. These findings indicate that amelioration of soil acidification by balancing C:N may affect AOB abundance driving N transformations, reducing stress on declining oak trees.
•Three thinning treatments of different intensity were applied to Quercus robur mixed plantation.•Tree growth and WUEi were affected by crown asymmetry and competition.•High presence of alder ...influenced tree growth due to resources competitions.•The very high selective thinning resulted to be the most appropriate management practice.•Thinning increased productivity and limited water loss.
Thinning intensity is an important factor affecting forest structure and density and influencing tree growth.
The main objective of the study is to evaluate how the different intensity of thinning can influence, in the short and long term, the productivity and intrinsic water use efficiency (WUEi) of Quercus robur L., a widespread European species. Three thinning types of different intensity were applied in 14-year mixed plantation of Quercus robur L. growing with Alnus glutinosa (L) Gaertn., a N-fixing species, with an initial density of 625 trees/ha. A multidisciplinary approach was applied, coupling the tree-ring analyses with the measurements of stable isotopes of carbon and oxygen.
Findings highlighted how the different conditions of light and competition, determined by the type and intensity of thinning, triggered different responses of Q. robur species in terms of growth and WUEi.
Data suggested that the moderate selective thinning (31% reduction of total biomass) was not able to reduce the high competition for resources among individuals: this condition negatively influenced the trees growth. The presence of the N-fixing species, left after the thinning, was not able to counteract the negative effect of competition.
A negative effect on productivity was recorded with the geometric thinning (62% reduction of total biomass). Indeed, this treatment resulted in an increase of asymmetry of the canopy (0.90 vs 0.83, respectively in pre- and post-thinning period), due to the partial crown competition from one side and with a consequent limitation of the photosynthetic activity of the trees. Finally, the very high selective thinning (75% reduction of total biomass) resulted to be the most appropriate management practice, as it guarantees positive effects both in terms of growth and intrinsic water use efficiency. The post thinning conditions determined high photosynthesis rates, an increase of productivity and a limited water loss.
•Insect herbivory in oak leaves varied with stand isolation, tree diversity and forest stratum.•Insect herbivory increased with stand isolation at the landscape level.•Tree diversity effects ...concerned only the upper stratum.•The effects of tree diversity and forest stratum on herbivory were only partially mediated by leaf traits.
Tree diversity has long been recognized as a major driver of insect herbivory in forest ecosystems. However, predicting the strength and direction of tree diversity effects in real-world situations has proven elusive. One likely reason is that most studies have focused on within-stand dynamics and insufficiently captured other ecological drivers of insect herbivory that can act at broader (i.e., landscape) and finer (i.e., individual trees) scales. We measured herbivory as leaf area consumed by insect herbivores in pedunculate oaks (Quercus robur) growing in mixed and pure forest stands in southwestern France. We assessed the effects of oak spatial isolation within the landscape, tree stand diversity, forest canopy stratification as well as the influence of leaf traits on insect herbivory. Insect herbivory increased with stand isolation regardless of tree diversity. Diversity effects were contingent upon the canopy stratum as insect herbivory in mixed stands exceeded that of pure stands only in the upper stratum. Leaf traits varied between pure and mixed stands and among canopy strata. Insect herbivory was negatively correlated with LDMC and positively with SLA. However, the observed effects of tree diversity, canopy stratum and stand isolation on insect herbivory were only partially driven by variability in oak leaf traits. Our findings illustrate that, in real-world contexts, insect herbivory can be driven by a complex interplay of multiple, scale-dependent drivers. They help step forward towards a more profound understanding of the complex forces drive insect herbivory in managed forest ecosystems.
•We analyzed the genetic diversity and genetic differentiation among 20 populations.•The current gene pool of Q. robur populations in the Southern Urals remains stable.•The historically short period ...of these processes might be reason for this phenomenon.
Development of agriculture in the forest and forest-steppe zones of the vast East European plain over the past millennium has resulted to a significant decrease of broad-leaved forests habitat. It is expected that the disintegration of the forest tree species distribution ranges will lead to the erosion of the population genetic diversity of due to limited gene flow, impacts on gene pools of genetic drift and inbreeding. To investigate this threat, we analyzed the genetic diversity and differentiation among 20 populations of pedunculate oak (Quercus robur L.) from the Ural Mountains (Russia) and neighboring lowlands and foothills. A set of 412 nuclear SNPs loci was used for our study. A positive correlation (r = 0.168, p < 0.05) was observed between genetic and geographical distances. The most genetic variation was distributed within populations (fixation index FST = 0.054). It was found that the values of genetic diversity are similar in large continuous mountain stands (effective number of alleles ne = 1.340, observed heterozygosity HO = 0.213, expected heterozygosity HE = 0.200), in spatially highly fragmented forests of the Cis-Urals (ne = 1.340, HO = 0.210, HE = 0.200) and geographically isolated marginal habitats with populations of hundreds individuals (ne = 1.338, HO = 0.206, HE = 0.198). Only in populations with few dozen individuals, we revealed a statistically significant decrease in the genetic diversity (ne = 1.312, HO = 0.211, HE = 0.184) and increase of numbers of full sibs and level of kinship (the kinship-coefficient Kin = 0.078–0.128 vs Kin = -0.002–0.035 in other populations). Overall, our study demonstrates that the current gene pool of Q. robur populations in the study area remains stable under conditions of significant forest decline and habitat fragmentation. The historically short period of these processes in the region and the genetically successful gene flow between populations over long distances might be reasons for this phenomenon.
The response of forest ecosystems to increased atmospheric CO₂is constrained by nutrient availability. It is thus crucial to account for nutrient limitation when studying the forest response to ...climate change. The objectives of this study were to describe the nutritional status of the main European tree species, to identify growth‐limiting nutrients and to assess changes in tree nutrition during the past two decades. We analysed the foliar nutrition data collected during 1992–2009 on the intensive forest monitoring plots of the ICP Forests programme. Of the 22 significant temporal trends that were observed in foliar nutrient concentrations, 20 were decreasing and two were increasing. Some of these trends were alarming, among which the foliar P concentration in F. sylvatica, Q. Petraea and P. sylvestris that significantly deteriorated during 1992–2009. In Q. Petraea and P. sylvestris, the decrease in foliar P concentration was more pronounced on plots with low foliar P status, meaning that trees with latent P deficiency could become deficient in the near future. Increased tree productivity, possibly resulting from high N deposition and from the global increase in atmospheric CO₂, has led to higher nutrient demand by trees. As the soil nutrient supply was not always sufficient to meet the demands of faster growing trees, this could partly explain the deterioration of tree mineral nutrition. The results suggest that when evaluating forest carbon storage capacity and when planning to reduce CO₂emissions by increasing use of wood biomass for bioenergy, it is crucial that nutrient limitations for forest growth are considered.
•Phenology of wood shows high variability across locations, species and years.•The coupling between leaf- and wood growth phenology has few generic trends.•Temperature and climate are key drivers of ...wood growth phenology variability.•Summer droughts shortens the wood-growing season.
Wood growth phenology of temperate deciduous trees is less studied than leaf phenology, hindering the understanding of their interaction. In order to describe the variability of wood growth and leaf phenology across locations, species and years, we performed phenological observations of both xylem formation and leaf development in three typical temperate forest areas in Western Europe (Northern Spain, Belgium and Southern Norway) for four common deciduous tree species (Fagus sylvatica L., Betula pendula Roth., Populus tremula L. and Quercus robur L.) in 2018, 2019 and 2020, with only beech and birch being studied in the final year.
The earliest cambial reactivation in spring occurred at the Belgian stands while the end of cambial activity and wood growth cessation generally occurred first in Norway. Results did not show much consistency across species, sites or years and lacked general patterns, except for the end of cambial activity, which occurred generally first in birch. For all species, the site variation in phenophases (up to three months) was substantially larger than the inter-annual variability (up to six weeks). The timeline of bud-burst and cambium reactivation, as well as of foliar senescence and cessation of wood growth, were variable across species even with the same type of wood porosity. Our results suggest that wood growth and leaf phenology are less well connected than previously thought. Linear models showed that temperature is the dominant driver of wood growth phenology, but with climate zone also having an effect, especially at the start of the growing season. Drought conditions, on the other hand, have a larger effect on the timing of wood growth cessation. Our comprehensive analysis represents the first large regional assessment of wood growth phenology in common European deciduous tree species, providing not only new fundamental insights but also a unique dataset for future modelling applications.
Failed oak regeneration is widely reported in temperate forests and has been linked in part to changed disturbance regimes and land‐use. We investigated if the North American fire–oak hypothesis ...could be applicable to temperate European oaks (Quercus robur, Quercus petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and low‐intensity surface fire (burn/no burn). Survival, relative height growth (RGRH), browsing damage on naturally regenerated oaks (≤300 cm tall), and changes in competing woody vegetation were monitored over three years. Greater light availability in canopy gaps increased oak RGRH (p = .034) and tended to increase survival (p = .092). There was also a trend that protection from browsing positively affected RGRH (p = .058) and survival (p = .059). Burning reduced survival (p < .001), nonetheless, survival rates were relatively high across treatment combinations at the end of the experiment (54%–92%). Most oaks receiving fire were top‐killed and survived by producing new sprouts; therefore, RGRH in burned plots became strongly negative the first year. Thereafter, RGRH was greater in burned plots (p = .002). Burning altered the patterns of ungulate browsing frequency on oaks. Overall, browsing frequency was greater during winter; however, in recently burned plots summer browsing was prominent. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals (p < .001) and their heights (p < .001). Our results suggest that young, temperate European oaks may respond similarly to fire as their North American congeners. However, disturbance from a single low‐intensity fire may not be sufficient to ensure a persistent competitive advantage—multiple fires and canopy thinning to increase light availability may be needed. Further research investigating long‐term fire effects on oaks of various ages, species‐specific response of competitors and implications for biodiversity conservation is needed.
We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks. Although a low‐intensity fire reduced oak seedling survival, survival rates were relatively high across treatment combinations (54%–92%) and relative height growth was greater in burned plots after 2 years. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals and their heights, especially for conifers.
Acute Oak Decline (AOD) is a relatively new decline-disease affecting both native oak species (Quercus robur and Q. petraea) in Britain. The key aim of this study was to describe the symptoms, and ...signs of AOD, to set a baseline. The second aim was to compare and review the European literature on what appear to be similar disorders on oak. AOD is characterized by four key features: weeping patches more-or-less vertically aligned on oak tree trunks; cracks between bark plates from which dark fluid seeps; inner bark necrosis and the presence (in >90 per cent of cases) of larval galleries of the oak buprestid, Agrilus biguttatus, on the phloem–sapwood interface. In this study, it was noted that although larval galleries were present in the inner bark in 19 of 21 trees, the ‘D-shaped’ exit holes of the adult beetles were seen less frequently on bark plates of affected trees (33 per cent of cases). Similar disorders reported in Europe are compared with AOD in Britain and potential causes of the condition discussed. Based on the unmistakable symptoms, it is hypothesized that AOD is a distinctive, identifiable condition within the broader oak decline syndrome.
The oaks
Quercus robur
L. and
Quercus rubra
L. are grown worldwide. The oak fruits (acorns) fallen on the ground during the autumn are usually considered as unusable, although some possible ...applications have been reported. In the present study, the possible recovery of tocopherols from acorns of two oak species
Q. rubra
(
n
= 14) and
Q. robur
(
n
= 15) was evaluated. Four tocopherols (Ts) (α-T, β-T, γ-T, and δ-T) in the oak fruits of
Q. rubra
and
Q. robur
were identified. The
Q. robur
acorns had abundant γ-T (28.18 ± 6.7 mg/100 g dw), while in
Q. rubra
β-T was predominant (17.28 ± 2.91 mg/100 g dw), nearly 95 and 90% of total detected tocopherols, respectively. The variability of tocopherol levels within the same species was lower for
Q. rubra
(16.5%) and higher for
Q. robur
(23.4%). The principal component analysis, applied to four tocopherol homologues, confirmed their feasibility to distinguish two strictly separated groups: one for species
Q. rubra
and the other for
Q. robur
. The predominance of β-T in
Q. rubra
acorns is a unique finding in the plant world; therefore, acorns of this oak species can be used as an unconventional natural source of this rare tocopherol homologue.
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