Academic literature on the topic 'Cambial phenology'

The objectives of this study were to (i) determine the extent of genetic variation and genetic control of cambial phenology in coastal Douglas-fir (Pseudotsugamenziesii var. menziesii (Mirb.) Franco), (ii) assess the degree to which cambial phenology is genetically related to bud-burst timing, (iii) examine genetic relationships between cambial phenology and growth traits, and (iv) evaluate the potential for indirectly altering cambial phenology in breeding programs when selection is for stem volume. Dates of diameter-growth initiation and cessation, and duration of diameter growth (i.e., cambial phenology traits), as well as diameter increment for a single growing season (1987, at the age of 15 years from seed), were estimated from cumulative diameter growth curves of individual trees of 60 open-pollinated families growing in one plantation. Data on stem height and diameter (DBH), and date of bud burst in 1987 were also collected. Dates of diameter-growth initiation and cessation differed significantly among families, but had lower estimated individual heritabilities (≤0.23) than date of bud burst (0.87). Weak genetic correlations between date of bud burst and dates of diameter-growth initiation and cessation (range −0.09 to 0.26) indicate that timing of diameter growth cannot be reliably predicted from observations on the more easily measured bud burst. Cambial phenology traits were weakly correlated with 1987 diameter increment and moderately correlated with 15-year DBH and volume. Selection of parents in this study for stem volume at age 15 and subsequent crosses among them, would be expected to lead to earlier initiation of diameter growth in the offspring, and possibly later cessation as well. The practical implications of these indirect responses in terms of increased risk of frost damage are unclear, since projected changes are small (i.e., a few days).

Bud and cambial zone phenologies of outdoor-grown, containerized seedlings of Pseudotsugamenziesii (Mirb.) Franco (Douglas-fir) were determined and compared. Morphological characteristics of the live primordial shoots were related to known stages of bud development, while cambial zone phenology was based on anatomical characteristics. Secondary growth in branches of P. menziesii seedlings was separated into six stages: (i) early wood formation; (ii) latewood formation; (iii) cessation of cambial cell division; (iv) dormancy; (v) cambial cell expansion; and (vi) resumption of cell division. Early wood formation by the cambial zone, and primary leaf initiation in the shoot tips occurred until July. During this time of maximal activity, differences in wall thickness and shape distinguished cambial cells from vascular cells in early differentiation stages. By late July, earlywood formation was changing to latewood formation and bud-scale initiation had begun. The transition to preformed leaf initiation in the buds occurred over a period of 1 month in August and September. Cambial cell division ceased in early September but tracheid differentiation continued until about the end of October. Preformed leaf initiation lasted until the buds became dormant in mid-November. The cambial zone was dormant from the end of November until the beginning of March, and in transverse section was characterized by a distinct boundary at the border of the xylem and regular, cigar-shaped cambial cells with thick radial walls. Resumption of cambial activity in the 1st week of April began with radial expansion, followed about 2 weeks later by cell division. Differentiation of earlywood tracheids and bud swelling began in early April. The majority of buds flushed in the 3rd week of April. Rays in the lateral shoots were composed of monoseriate files of radially elongated cells. Ray initials were not observed. Ultrastructural features indicated that the dictyosomes of the cambial cells were active during the winter period.

Abstract Climate change is expected to be heterogeneous across the world, with high impacts on the Himalayan ecosystems. There is a need to precisely document cambial phenology and wood formation in these regions to better understand climate-growth relationships and how trees face a warming climate. This study describes the dynamics of cambial phenology in pindrow fir (Abies pindrow) along its altitudinal gradient in the Himalaya. The stages of xylem phenology, and the duration and rate of wood formation were assessed from anatomical observations during the growing season from samples collected weekly from three sites at various altitudes (2392–2965 m a.s.l.) over two years. There were significant differences in the duration and rate of cell formation along the altitudinal gradient, which decreased at increasing altitudes. The growing season duration decreased by 5.2 and 3.7 days every 100 m of increase in altitude in 2014 and 2015, respectively, while the rate of cell formation decreased from 0.38 and 0.44 cells /day to 0.29 and 0.34 cells/day in 2014 and 2015, respectively. Cell production decreased from 63.3 and 67.0 cells to 38.3 and 45.2 cells with a decrease of 4.3 and 3.8 cells per 100 m increase in altitude in 2014 and 2015, respectively. The higher precipitation in 2015 increased the growth rate and resulted in a higher xylem production. Our findings give new insights into the dynamics of cambial phenology and help in better understanding of the potential impacts of climate change on tree growth and forest productivity of Himalayan forests.

The timings of the onset and ending of xylogenesis define the time window when environmental conditions are suitable for xylem formation. The relationship between the occurrence of xylem phenological events and the related climatic factors is critical to revealing how xylem formation responds to the changing climate. Given that temperature is the most important factor influencing growth in the boreal forest, we monitored air temperature and xylem phenology at five permanent plots of black spruce (Picea mariana (Mill.) BSP) along a latitudinal gradient of the boreal forest of Quebec, Canada. Microcores were collected weekly or biweekly from five to ten trees per site during the growing seasons from 2002 to 2019. We compared the relationships between air temperature and timings of the onset and termination of xylogenesis, testing the hypothesis that spring temperatures trigger the initiation of cambial activity. The onset of xylogenesis occurred from late May (DOY 149) to mid-June (DOY 163), and it terminated between late August (DOY 240) and late September (DOY 270). The spring phases of xylem phenology showed similar inter-annual variation among sites, while the variation in autumnal phases was less correlated among sites. The onset of xylogenesis was negatively correlated with the mean May temperature, and the correlations were consistent among sites, with r ranging from −0.61 to −0.77. The warmer May temperatures would advance cambial resumption, allowing the initial hypothesis that spring temperatures are a driving factor of xylogenesis to be accepted. With an increase of 1 °C in the mean May temperature, cambial resumption could be advanced by 2.7 days. Yet, no relationship between the termination of xylem phenology and monthly temperature was established, suggesting that other factors, possibly endogenous, could have affected the xylem phenology in autumn. Under warming conditions, we expect an advancement in the onset of xylogenesis, which may lengthen the growing season and potentially enhance cell production in black spruce.

Large intercellular spaces were found in uniseriate as well as multiseriate cambial rays of Tectona grandis L., Azadirachta indica A. Juss., and Tamarindus indica L. During the period when the cambium is inactive, some of the ray cambial cells became oval to circular, resulting in the development of intercellular spaces. However, the cells were polygonal and compactly arranged during active growth of the cambium. Similarly, such spaces were also noticed in the rays of phloem and xylem. The occurrence of intercellular spaces in cambial rays is correlated with the phenology of trees and local climatic factors, and their possible significance is discussed.

Abstract Background and Aims Wood traits are increasingly being used to document tree performance. In the Congo Basin, however, weaker seasonality causes asynchrony of wood traits between trees. Here, we monitor growth and phenology data to date the formation of traits. Methods For two seasons, leaf and cambial phenology were monitored on four Terminalia superba trees (Mayombe) using cameras, cambial pinning and dendrometers. Subsequently, vessel lumen and parenchyma fractions as well as high-resolution isotopes (δ13C/δ18O) were quantified on the formed rings. All traits were dated and related to weather data. Key Results We observed between-tree differences in green-up of 45 d, with trees flushing before and after the rainy season. The lag between green-up and onset of xylem formation was 59 ± 21 d. The xylem growing season lasted 159 ± 17 d with between-tree differences of up to 53 d. Synchronized vessel, parenchyma and δ13C profiles were related to each other. Only parenchyma fraction and δ13C were correlated to weather variables, whereas the δ18O pattern showed no trend. Conclusions Asynchrony of leaf and cambial phenology complicates correct interpretation of environmental information recorded in wood. An integrated approach including high-resolution measurements of growth, stable isotopes and anatomical features allows exact dating of the formation of traits. This methodology offers a means to explore the asynchrony of growth in a rainforest and contribute to understanding this aspect of forest resilience.

Seasonal phenology is expressed in the annual rhythms of growth and quiescence, which may range from being sharply defined to weakly quantitative. These rhythms, both vegetative and reproductive, are a key aspect of a plant’s survival strategy. They enable the plant to both survive seasonal stresses and take advantage of favourable conditions, while making pollination efficient through synchronised flowering. Maturation in woody perennials causes some ontogenetic modulation of seasonal phenology. Shoot phenology is driven by various environmental cues, notably temperatures and daylength, with shoot extremities often being prime receptors. The phenology of shoot extremities is in turn seen as a strong driver of cambial activity, which itself is an aspect of shoot phenology and the basis of stem diameter growth. The aspects of cambial activity reflecting hoot–tip phenology primarily involve the timing of xylem formation and the anatomical and physical properties of xylem cells. The actual amount of diameter growth, however, is governed much more by other factors, notably the growth potential of the species, the space for the tree to grow in, and how favourable local conditions are for growth. Somehow, all tree species allocate resources to shoot extension and diameter growth to represent viable adaptive strategies, although there is no identified role of phenology per se in such allocation. Among species, Pinus radiata is extremely important commercially, largely through a high growth potential that reflects distinctive phenology. Much research on the species provides a basis for linking its phenology and shoot–tip architecture to seasonal timing of diameter growth and fine details of within-ring variation in xylem cell properties. This provides a baseline for comparison with many other tree species, conifers and hardwoods. Selected examples are considered to illustrate the range of adaptive strategies. Regulation of diameter growth and internal variation in wood properties reflects the response to competitive pressures. Modifying the regulation to optimise wood production and quality poses a great challenge for future domestication.

It is unclear how the anticipated climate change will affect the timing of phenology of different tree organs/tissues and thus the whole-tree functioning. We examined the timing of leaf phenology and secondary growth in three coexisting deciduous tree species (Quercus pubescens Willd., Fraxinus ornus L. and Ostrya carpinifolia Scop) from a sub-Mediterranean region in 2019. In addition, we investigated the relationship between leaf and cambial phenology and the onset of the potential functioning of initial conduits, as determined by the completed differentiation process (vessels) or final size (sieve tubes). For this purpose, leaf development was monitored and the microcores of cambium and the youngest phloem and xylem increments were repeatedly collected at 7–10-day intervals during the growing season. The results revealed differences in the timing of leaf development and seasonal radial growth patterns in spring among the studied tree species, depending on wood porosity. We found that cambial cell production started in all cases in the first half of March. However, in ring-porous Q. pubescens and F. ornus, radial growth in the stem occurred more than a month before buds were swollen, whereas in diffuse-porous O. carpinifolia, these two events were detected at almost the same time. The end of cambial cell production occurred earliest in F. ornus (mid-July) and two weeks later also in the other two species. The widest initial earlywood vessels and early phloem sieve tubes were found in Q. pubescens, the narrowest initial earlywood vessels in O. carpinifolia and the narrowest early phloem sieve tubes in F. ornus. This indicates differences in the efficiency of conducting systems among the studied species. This novel approach of studying phloem phenology and anatomy in relation to leaf and xylem development contributes to a better understanding of how different tree species adapt their structure of secondary vascular tissues in response to environmental change.

A witness of a tree’s past conditions is the wood itself. The main research question of this dissertation is how to assess and reveal the driving forces of the patterns of wood traits on pith-to-bark cross-sections in tropical trees. Cambial and leaf phenology was monitored in the Luki Reserve (Mayombe forest, D.R. Congo). Furthermore, X-ray CT densitometry was explored to assess traits in a reliable way, for multiple species. Variability in phenology is observed for T. superba, which requires traits of individual trees to be fixed on a time axis. Furthermore, X-ray CT is a suitable method for assessing traits in a fast way. Cambial activity of understory trees has shown to be species-specific, whilst many trees show zero xylem growth. Finally, 66 years of tree growth was analysed, while trait analysis revealed a median ring count of only 32, thus implying many non-periodical rings. This work presents methodological improvements to measure traits as continuous variables from pith to bark, but also acknowledges that phenology still remains a key aspect in order to fix traits on a time axis.

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No cerrado, as estações são bem demarcadas pela sazonalidade pluvial, portanto, espera-se que haja uma sazonalidade na atividade do câmbio vascular. Kielmeyera grandiflora é considerada uma espécie modelo para estudos de atividade cambial em ramos, pois possui módulos de crescimento bem demarcados, formados por cicatrizes da gema terminal. Nosso objetivo foi de entender qual a relação entre a atividade cambial de Kielmeyera grandiflora (Wawra) Saddi (Calophyllaceae), os fatores ambientais e a fenologia e responder se a atividade cambial varia entre três módulos de crescimentos consecutivos. A área de estudo é um fragmento de cerrado em regeneração no município de Botucatu, estado de São Paulo, Brasil (S 22º53’11.0’’, W 48º29’17.3’’). Foram amostrados mensalmente os três últimos módulos de crescimento dos ramos de três indivíduos durante o período de fevereiro de 2012 a fevereiro de 2013. No mesmo período, a fenologia (brotação, folhas novas, folhas adultas, folhas senescentes e queda foliar) foram avaliadas. O material foi fixado em CRAF III para conservação do conteúdo celular. As amostras foram desidratadas em série alcoólica e incluídas em resina metacrilato para posterior corte em micrótomo rotativo. As análises foram feitas em fotomicroscópio de luz. Utilizamos Modelo Generalizado Linear Misto (GLMM) com erro Binomial para a variável resposta presença/ausência da atividade cambial e erro de Poisson para a variável resposta de contagem de paredes recém formadas. O início da atividade cambial, a brotação e o desenvolvimento de folhas novas ocorreram durante o mês de agosto no período seco. O período de atividade cambial sobrepôs-se à estação chuvosa, temperaturas elevadas e comprimento do dia entre 12 e 13,6 h. O câmbio vascular entrou em dormência em maio, mês que ainda chovia, contudo a temperatura e o comprimento do dia passavam por quedas acentuadas. A variação da atividade cambial entre os módulos de crescimento foi representativa somente no período de reativação cambial, mostrando que o módulo 1, mais próximo às fontes de auxina, apesar de ter iniciado atividade junto ao módulo 3, produziu em todo o período analisado, maior quantidade de células novas, possivelmente devido à ação de hormônios produzidos nos tecidos jovens e em desenvolvimento.
In the cerrado, the seasons are well marked by rain seasonality; therefore, there is a seasonality in the vascular cambium activity. Kielmeyera grandiflora is considered a model for branch cambial activity studies because it has well marked growth modules formed by terminal bud scars. Our goal was to understand what the relationship between cambial activity of Kielmeyera grandiflora (Wawra) Saddi (Calophyllaceae), environmental factors and the phenology and answear wheter cambial activity varies between three consecutive sections of internodal growth. The study area is a cerrado fragment in regeneration in the city of Botucatu, São Paulo State, Brazil (22° 53 ' S 11.0 '', W 48° 29 ' 17.3 ''). Were sampled on a monthly basis the last three modules of growth of branches of three individuals during the period between February 2012 to February 2013. The material was fixed in CRAF III for preservation of cell content. The samples were dehydrated in alcohol series and included in historesin for further cut in rotary microtome. Analyses were made on light microscope. We used Generalized Linear Mixed Model (GLMM) with Binomial error for the variable reply presence/absence of cambial activity and Poisson error for the variable count response of newly formed walls. The beginning of cambial activity, the sprouting and the development of new leaves occurred during the month of August in the dry period. The period of cambial activity overlapped the rainy season, high temperatures and day length between 12 and 13, 6 h. The vascular cambium dormancy was observed in May, a raining month; however, temperature and day length was decreasing. The variation of cambial activity between the internodal growth sections was representative just in reactivation period, showing that the younger internodal section, closest to the sources of auxin, has produced in the whole study period a larger number of new cells that the older, possibly due to the action of hormones produced in young and development tissues.

O estado do Acre possui uma vocação eminentemente florestal, devido a alta abundância natural de espécies madeireiras em um ecossistema caracterizado pela biodiversidade de espécies tropicais. Pesquisas em dendrocronologia nessa região tropical indicam que 35-50% das espécies arbóreas formam anéis de crescimento. Neste sentido, a dendrocronologia, método baseado na análise de anéis de crescimento anuais no lenho, torna-se importante ferramenta, fornecendo dados de longos períodos de crescimento e estimativas acuradas da idade das árvores, para o entendimento da dinâmica da floresta e desenvolvimento de sistemas de manejo florestal sustentados. Portanto, o objetivo dessa pesquisa foi o de estudar três espécies arbóreas de ocorrência natural no Acre, verificar a influência da quantidade total e distribuição sazonal de pluviosidade, temperatura e evapotranspiração, e os aspectos fenológicos apresentados por cada espécie, no seu crescimento em diâmetro e na qualidade do lenho produzido. O estudo foi realizado em três diferentes sítios, sendo que na Reserva Experimental Catuaba, havia três diferentes microsítios: floresta primária, borda de floresta e pastagem. Avaliou-se mensalmente o incremento em circunferência do tronco das árvores com dendrômetros e a fenologia com observações visuais das árvores das espécies selecionadas. Foram retiradas amostras de lenho no DAP do tronco para as avaliações dendrocronológicas, de densitometria de raios X e anatômicas do lenho. Verificou-se que a fenologia das árvores das espécies estudadas é regulada pela precipitação no mês corrente ou dos meses anteriores. Observou-se que a formação dos anéis de crescimento das árvores dessas espécies é regulada pela evapotranspiração, e pelas fenofases de queda e brotação de folhas nas diferentes estações sazonais do ano, indicando que possuem potencial para estudos paleoclimáticos. A análise da densitometria de raios X e anatômica do lenho mostrou ser possível separar seções de lenho juvenil e adulto no sentido radial do tronco das árvores. Houve diferença significativa no ritmo de crescimento do tronco das árvores entre as espécies, sítios e microsítios. Há grande potencial do uso da dendrocronologia aliada ao uso de parcelas de inventário permanente para a definição do ciclo de corte das árvores dessas espécies
The state of Acre has an eminently forest asset due the high natural timber species abundance in an ecosystem characterized by the biodiversity of tree tropical species. Researches in dendrochronology in this tropical region indicate that 35-50% of species form tree rings. Therefore, dendrochronology, a method based on tree ring analysis becomes important tool, providing data for long growth periods and accurate estimates of trees age, to understanding the forest dynamics and the development of sustainable forestry management. Thus, the objective of this research was to study some tree species of natural occurrence in Acre, verify influence of total amount and seasonal distribution of rainfall, temperature and evapotranspiration, and phenological aspects presented by each species in their growth in diameter and quality of timber produced. The study was conducted at three different sites, and in the Catuaba Experimental Reserve in three different microsites: primary forest, pasture and forest edge.The increase in the circumference the trunk was assessed monthly with a dendrometer and phenology was evaluated with visual observations in selected tree species. Samples were collected from wood in the DBH of the trunk for dendrochronological, X-ray densitometry and wood anatomy assessments. It was found that the phenology of the trees species is regulated by rainfall in the current month or previous months. It was observed that the formation of growth rings of trees of these species is regulated by evapotranspiration, and by phenophases of fall and sprouting new leaf during the year, indicating that these species have potential for paleoclimate studies. The analysis of Xray densitometry and anatomical of the wood allowed to separate portions of the juvenile and adult wood in radial section of the trunk. There were significant differences in the growth of the trunk of tress between species, sites and microsites. There is great potential for the use of dendrochronology combined with the use of permanent inventory plots to define cutting cycles for these species.

Una de les principals preocupacions en l’agricultura és la incertesa deguda als efectes del canvi climàtic. En aquest aspecte, l’estudi i adopció de noves tècniques de maneig dels cultius i la gestió de l’aigua són elements essencials per tal de garantir la productivitat dels cultius. En la regió mediterrània, la vinya (Vitis vinifera L.) representa un dels cultius més importants, el qual es podria veure afectat especialment en aquelles zones on no hi ha disponibilitat d’aigua. A més, en els últims anys s’ha observat un avançament en la fenologia de la vinya, provocant que, entre d’altres, la fase de la post-verema esdevingui una fase crítica degut a la seva major durada i sota unes condicions més càlides i amb menor precipitació. Degut a que en els propers anys es preveu un increment en la freqüència i intensitat dels esdeveniments de sequera, a més d’un augment significatiu de les temperatures, els elements crítics per combatre els efectes del canvi climàtic són: la disponibilitat de models fenològics per predir els patrons estacionals de les fases fenològiques; i la selecció del moment més idoni per l’adopció d’estratègies de reg deficitari, per tal d’estalviar aigua i poder garantir uns bons rendiments productius de la verema amb la composició dels raïms adequada per a l’elaboració de vins i caves.
Una de las principales preocupaciones en la agricultura es la incertidumbre de los efectos del cambio climático. Por este motivo, el estudio y la adopción de nuevas técnicas de manejo de los cultivos y de la gestión del agua son elementos esenciales para garantizar la productividad de los cultivos. En la zona del mediterráneo, el viñedo (Vitis vinifera L.) representa uno de los cultivos más importantes, el cual se podría ver afectado especialmente en las zonas donde no hay disponibilidad de agua. Además, en los últimos años se ha observado un adelanto en la fenología de la viña, provocando que, entre otros, la fase de la post-vendimia esdevenga una fase crítica debido a su mayor duración y bajo unas condiciones más cálidas y con una menor pluviometría. Debido a que en los próximos años se prevé un incremento en la frecuencia e intensidad de los eventos de sequía, además de un aumento significativo de las temperaturas, los elementos críticos para combatir los efectos del cambio climático son: la disponibilidad de modelos fenológicos para predecir los patrones estacionales de las fases fenológicas; y la selección del momento más idóneo para la adopción de estrategias de riego deficitario, para el ahorro de agua y garantizar unos buenos rendimientos productivos de la vendimia con una composición de las bayas adecuada para la elaboración de vinos y cavas.
One of the main concerns in agriculture is the effect of climate change. As a result, studying the adoption of new management techniques and managing water use are essential for guaranteeing crop productivity. In the Mediterranean region, the grapevine (Vitis vinifera L.) is one of the most important crops affected by water availability, especially in areas without irrigation. Moreover, over the last years has been observed advancements in grapevine phenology, where the post-harvest period is becoming a critical stage due to their longer duration under warmer and dryer conditions. Due to the expected increases in the frequency and intensity of drought events and rising temperatures, the critical elements for combating the effects of climate change are: the availability of phenological models to predict seasonal patterns in the key phenological stages; and the selection of the most suitable moment at which to apply regulated deficit irrigation strategies. Their study is required to water savings and to guarantee good yields with the desired berry composition for wine and sparkling wine production.

La fenologia és la clau per a controlar els processos fisicoquímics i biològics, especialment l’albedo, la rugositat superficial, conductància de les fulles, fluxos de carboni, aigua i energia. Per tant, l’estimació de la fenologia és cada vegada més important per a comprendre els efectes del canvi climàtic en els ecosistemes i les interaccions biosfera-atmosfera. La teledetecció és una eina útil per a caracteritzar la fenologia, encara que no existeix un consens sobre el tipus de sensor satel·litari i metodologia òptims per a extreure mètriques fenològiques. Els objectius principals de la meva investigació van ser (i) millorar l’estimació de la fenologia vegetal a partir de dades satel·litàries, (ii) validar les estimacions fenològiques amb observacions terrestres i teledetecció propera a la superfície, i (iii) comprendre les relacions entre les variables climàtiques i la fenologia en un context de canvi climàtic, així com avaluar les respostes de la vegetació en esdeveniments extrems. Aquests objectius s’exploren en els següents tres capítols de la tesi. En el capítol 2, vaig investigar la sensibilitat de la fenologia a (I) la variable de vegetació: índex de vegetació NDVI, índex d’àrea foliar (LAI), fracció de radiació fotosintèticament activa absorbida (FAPAR) i fracció de coberta vegetal (FCOVER); (II) el mètode suavitzat per a derivar trajectòries estacionals; i (III) el mètode d’estimació fenològica: llindars, funció logística, mitjana mòbil i primera derivada. El mètode basat en llindars aplicat a la sèrie temporal Copernicus Global Land LAI V2 suavitzada va donar resultats òptims al validar-los amb observacions terrestres, amb errors quadràtics mitjans de ~10 d i ~25 d per a l’inici d’estació fenològica i la senescència respectivament. En el tercer capítol vaig utilitzar mesures fenològiques continues de PhenoCam i FLUXNET a alta resolució temporal (30 minuts). Això permet una comparació més robusta i precisa amb la fenologia estimada a partir de satèl·lit, evitant problemes relacionats amb les diferències en la definició de mètriques fenològiques. Vaig validar la fenologia estimada a partir de sèries de temps de LAI amb PhenoCam i FluxNet en 80 boscos caducifolis. Els resultats van mostrar una forta correlació (R2 > 0,7) entre la fenologia obtinguda mitjançant teledetecció i les observacions terrestres per a l’inici d’estació i R2 > 0,5 per al final d’estació. El mètode basat en llindars va funcionar millor amb un error quadràtic mitjà de ~9 d amb PhenoCam i ~7 d amb FLUXNET per a l’inici de l’estació, i ~12 d i ~10 d, respectivament, per a la senescència. En el quart capítol vaig investigar els patrons espai – temporals de la resposta fenològica a les anomalies climàtiques en l’hemisferi nord utilitzant la fenologia estimada en el Capítol 2 i validat en el Capítol 2 i Capítol 3, i conjunts de dades climàtiques de múltiples fonts per a 2000-2018 a resolucions de 0,1º. També vaig avaluar l’impacte de les onades de calor extremes i les sequeres en la fenologia. Les anàlisi de correlació parcial de les mètriques fenològiques estimades amb satèl·lit i les variables climàtiques van indicar que els canvis en la temperatura pre estacional van tenir major influència sobre les anomalies fenològiques que la precipitació: com més alta és la temperatura, més aviat es l’inici estacional en la majoria de boscos caducifolis (coeficient de correlació mitjà de -0,31). Tant la temperatura com la precipitació van contribuir a l’avanç i retard del final d’estació. Un retard en la senescència es va correlacionar significativament amb un índex de precipitació – evapotranspiració estandarditzat (SPEI) positiu (~ 30% dels boscos). El final i inici d’estació va canviar > 20 d en resposta de l’onada de calor en la major part d’Europa en 2003 i als Estats Units d’Amèrica l’any 2012.
La fenología es clave para controlar los procesos fisicoquímicos y biológicos, especialmente el albedo, la rugosidad superficial, conductancia de las hojas, flujos de carbono, agua y energía. Por lo tanto, la estimación de la fenología es cada vez más importante para comprender los efectos del cambio climático en los ecosistemas y las interacciones biosfera-atmósfera. La teledetección es una herramienta útil para caracterizar la fenología, aunque no existe consenso sobre el tipo de sensor satelital y metodología óptimos para extraer métricas fenológicas. Los objetivos principales de mi investigación fueron (i) mejorar la estimación de la fenología vegetal a partir de datos satelitales, (ii) validar las estimaciones fenológicas con observaciones terrestres y teledetección cercana a la superficie, y (iii) comprender las relaciones entre las variables climáticas y la fenología en un contexto de cambio climático, así como evaluar las respuestas de la vegetación a eventos extremos. Estos objetivos se exploran en los siguientes tres capítulos de la tesis. En el capítulo 2, investigué la sensibilidad de la fenología a (I) la variable de vegetación: índice de vegetación NDVI, índice de área foliar (LAI), fracción de radiación fotosintéticamente activa absorbida (FAPAR) y fracción de cubierta vegetal (FCOVER); (II) el método de suavizado para derivar trayectorias estacionales; y (III) el método de estimación fenológica: umbrales, función logística, media móvil y primera derivada. El método basado en umbrales aplicado a la serie temporal Copernicus Global Land LAI V2 suavizada dio resultados óptimos al validarlos con observaciones terrestres, con errores cuadráticos medios de ~10 d y ~25 d para el inicio de estación fenológica y la senescencia respectivamente. En el tercer capítulo, utilicé medidas fenológicas continuas de PhenoCam y FLUXNET a alta resolución temporal (30 minutos). Esto permite una comparación más robusta y precisa con la fenología estimada a partir de satélite, evitando problemas relacionados con las diferencias en la definición de métricas fenológicas. Validé la fenología estimada a partir de series de tiempo de LAI con PhenoCam y FluxNet en 80 bosques caducifolios. Los resultados mostraron una fuerte correlación (R2 > 0,7) entre la fenología obtenida mediante teledetección y las observaciones terrestres para el inicio de estación y R2 > 0,5 para el final de estación. El método basado en umbrales funcionó mejor con un error cuadrático medio de ~9 d con PhenoCam y ~7 d con FLUXNET para el inicio de estación, y ~12 d y ~10 d, respectivamente, para la senescencia. En el cuarto capítulo, investigué los patrones espacio-temporales de la respuesta fenológica a las anomalías climáticas en el hemisferio norte utilizando la fenología estimada en el Capítulo 2 y validado en el Capítulo 2 y Capítulo 3, y conjuntos de datos climáticos de múltiples fuentes para 2000-2018 a resoluciones de 0.1°. También evalué el impacto de las olas de calor extremas y las sequías en la fenología. Los análisis de correlación parcial de las métricas fenológicas estimadas con satélite y las variables climáticas, indicaron que los cambios en la temperatura pre estacional tuvieron mayor influencia sobre las anomalías fenológicas que la precipitación: cuanto mayor es la temperatura, más temprano es el comienzo estacional en la mayoría de los bosques caducifolios (coeficiente de correlación medio de -0,31). Tanto la temperatura como la precipitación contribuyeron al avance y retraso del final de estación. Un atraso en la senescencia se correlacionó significativamente con un índice de precipitación-evapotranspiración estandarizado (SPEI) positivo (~ 30% de los bosques). El final e inicio de estación cambió >20 d en respuesta a la ola de calor en la mayor parte de Europa en 2003 y en los Estados Unidos de América en 2012.
Phenology is key to control physicochemical and biological processes, especially albedo, surface roughness, canopy conductance and fluxes of carbon, water and energy. High-quality retrieval of land surface phenology (LSP) is thus increasingly important for understanding the effects of climate change on ecosystem function and biosphere–atmosphere interactions. Remote sensing is a useful tool for characterizing LSP although no consensus exists on the optimal satellite dataset and the method to extract phenology metrics. I aimed to (i) improve the retrieval of Land Surface Phenology from satellite data, (ii) validate LSP with ground observations and near surface remote sensing, and (iii) understand the relationships between climate variables and phenology in a climate change context, as well as to assess the responses of vegetation to extreme events. These three main research objectives are explored in the three chapters of the thesis. In chapter 2, I investigated the sensitivity of phenology to (I) the input vegetation variable: normalized difference vegetation index (NDVI), leaf area index (LAI), fraction of absorbed photosynthetically active radiation (FAPAR), and fraction of vegetation cover (FCOVER); (II) the smoothing and gap filling method for deriving seasonal trajectories; and (III) the phenological extraction method: threshold, logistic-function, moving-average and first derivative based approaches. The threshold-based method applied to the smoothed and gap-filled Copernicus Global Land LAI V2 time series agreed the best with the ground phenology, with root mean square errors of ~10 d and ~25 d for the timing of the start of the season (SoS) and the end of the season (EoS), respectively. In the third chapter, I took advantage of PhenoCam and FLUXNET capability of continuous monitoring of vegetation seasonal growth at very high temporal resolution (every 30 minutes). This allows a more robust and accurate comparison with LSP derived from satellite time series avoiding problems related to the differences in the definition of phenology metrics. I validated LSP estimated from LAI time series with near-surface PhenoCam and eddy covariance FLUXNET data over 80 sites of deciduous broadleaf forest. Results showed a strong correlation (R2 > 0.7) between the satellite LSP and ground-based observations from both PhenoCam and FLUXNET for the timing of the start (SoS) and R2 > 0.5 for the end of season (EoS). The threshold-based method performed the best with a root mean square error of ~9 d with PhenoCam and ~7 d with FLUXNET for the timing of SoS, and ~12 d and ~10 d, respectively, for the timing of EoS. In the fourth chapter, I investigated the spatio-temporal patterns of the response of deciduous forests to climatic anomalies in the Northern Hemisphere using LSP derived in Chapter 1 and validated in Chapter 1 and Chapter 2, and multi-source climatic data sets for 2000–2018 at resolutions of 0.1°. I also assessed the impact of extreme heatwaves and droughts on deciduous forest phenology. Analyses of partial correlations of phenological metrics with the timing of the start of the season (SoS), end of the season (EoS), and climatic variables indicated that changes in preseason temperature played a stronger role than precipitation in the interannual variability of SoS anomalies: the higher the temperature, the earlier the SoS in most deciduous forests in the Northern Hemisphere (mean correlation coefficient of -0.31). Both temperature and precipitation contributed to the advance and delay of EoS. A later EoS was significantly correlated with a positive standardized precipitation-evapotranspiration index (SPEI) at the regional scale (~30% of deciduous forests). The timings of EoS and SoS shifted by >20 d in response to heat waves throughout most of Europe in 2003 and in the United States of America in 2012.
Universitat Autònoma de Barcelona. Programa de Doctorat en Ecologia Terrestre

Le genre Larix intéresse les reboiseurs en raison de sa croissance rapide et de son bois apprécié. En particulier, le mélèze est une alternative intéressante au douglas pour les reboisements à basse et moyenne altitude. L'adaptation à l'environnement est une question clé pour les améliorateurs d'arbres forestiers. Cette question est particulièrement importante dans le cadre du changement climatique, où une diminution de la disponibilité en eau durant la saison de végétation est prédite. Trois espèces principales de mélèzes sont utilisées en reboisement en France : le mélèze d'Europe, le mélèze du Japon et leur hybride. Les bonnes performances du mélèze hybride en plantation témoignent de son grand potentiel. La structure cellulaire des cernes annuels reflète la réponse du cambium (division cellulaire, allongement et épaississement des parois) aux facteurs environnementaux (climat, fertilité, compétition...), ainsi que des stades physiologiques et l'effet de la génétique. La densité du bois peut être interprétée comme le produit de l'activité cambiale, et sa variation comme la réponse de l'arbre à son environnement. Toutefois, afin de bien avons combiné de façon originale microdensitométrie et blessures du cambium comprendre cette réponse et les variations du processus de xylogenèse lui-même, il est important de repérer les évènements qui se succèdent lors de la production des cellules de bois. Plusieurs approches permettent de dater la formation du bois. Nous (pinning method) afin d'étudier la dynamique de la fabrication du bois. Nous avons analysé les données obtenues du point de vue de l'améliorateur d'arbres forestiers. Cette nouvelle approche nous a permis d'aller au-delà le caractère statique du profil microdensitométrique (où la densité varie en fonction de la distance) afin de le convertir en profil dynamique (où la densité varie en fonction du temps). La variation de la phénologie de l'activité cambiale peut être vue comme un mécanisme ajustant bois peuvent être interprétées comme des caractères d'adaptation. L'intérêt pour les les le fonctionnement des arbres à leur environnement. Si cet ajustement améliore leur valeur adaptative (fitness), alors les variations correspondantes de l'anatomie du entre phénologie cambiale, formation du bois et stress pédoclimatiques afin de améliorateurs est double : d'un côté, il est urgent de mieux comprendre les liens concevoir des génotypes mieux adaptés à leur environnement. [...] Suite et fin du résumé dans la thèse.

Le genre Larix intéresse les reboiseurs en raison de sa croissance rapide et de son bois apprécié. En particulier, le mélèze est une alternative intéressante au douglas pour les reboisements à basse et moyenne altitude. L'adaptation à l'environnement est une question clé pour les améliorateurs d'arbres forestiers. Cette question est particulièrement importante dans le cadre du changement climatique, où une diminution de la disponibilité en eau durant la saison de végétation est prédite. Trois espèces principales de mélèzes sont utilisées en reboisement en France : le mélèze d'Europe, le mélèze du Japon et leur hybride. Les bonnes performances du mélèze hybride en plantation témoignent de son grand potentiel. La structure cellulaire des cernes annuels reflète la réponse du cambium (division cellulaire, allongement et épaississement des parois) aux facteurs environnementaux (climat, fertilité, compétition…), ainsi que des stades physiologiques et l'effet de la génétique. La densité du bois peut être interprétée comme le produit de l'activité cambiale, et sa variation comme la réponse de l'arbre à son environnement. Toutefois, afin de bien avons combiné de façon originale microdensitométrie et blessures du cambium comprendre cette réponse et les variations du processus de xylogenèse lui-même, il est important de repérer les évènements qui se succèdent lors de la production des cellules de bois. Plusieurs approches permettent de dater la formation du bois. Nous (pinning method) afin d'étudier la dynamique de la fabrication du bois. Nous avons analysé les données obtenues du point de vue de l'améliorateur d'arbres forestiers. Cette nouvelle approche nous a permis d‘aller au-delà le caractère statique du profil microdensitométrique (où la densité varie en fonction de la distance) afin de le convertir en profil dynamique (où la densité varie en fonction du temps). La variation de la phénologie de l'activité cambiale peut être vue comme un mécanisme ajustant bois peuvent être interprétées comme des caractères d'adaptation. L'intérêt pour les les le fonctionnement des arbres à leur environnement. Si cet ajustement améliore leur valeur adaptative (fitness), alors les variations correspondantes de l'anatomie du entre phénologie cambiale, formation du bois et stress pédoclimatiques afin de améliorateurs est double : d'un côté, il est urgent de mieux comprendre les liens concevoir des génotypes mieux adaptés à leur environnement. […] Suite et fin du résumé dans la thèse
Larix is a genus of high interest for plantation due to its fast growth rate and appreciated wood quality. Larch has a great potential to be introduced in middle and lowland afforestations as an alternative to Douglas-fir. One important question for breeders is adaptation to environment. It is particularly relevant in the context of climatic changes where a strong decrease of soil water availability during the growth period is predicted. Three larch species are used by foresters in France for plantation establishment, for which breeders must supply more adapted material: European and Japanese larch and their interspecific hybrid. The higher performance of hybrid larch in afforestations demonstrates its great potential. The tissue structure of annual rings reflects the response of cambium (cell division, elongation and thickening of cell walls) to environmental factors (climate, soil fertility, competition, etc), as well as physiological states and genetics. Then, wood density can be interpreted as the result of cambial activity and its variation as the response of the tree to environment. However, to gain a better understanding of this response and of the variation of the xylogenesis process itself, it is important to spot the timing of wood cell production. There are different approaches to study the timing of wood formation. We used a combination of wood microdensitometry and of pinning method as a new approach to study the dynamic of wood formation from a tree improvement point of view. This new approach allowed us to go beyond the static character of the microdensity profile (where density variation is related to distance) and to transform it into a dynamic profile (where density variation is related to time). Variation in phenology of cambial activity can be seen as a mechanism better adjusting trees to their environment. If this adjustment improves fitness, then the corresponding tree anatomical response to environment variation may be seen as an adaptive response. As breeders, our interest is twice: on one side, a better understanding of cambial phenology and of wood formation in relation to pedo-climatic factors and climatic stress is urgent for profiling genotypes better fitted to their environment. On the other side, exploitation design trees with better wood properties. In larch, phenotypic variation of variables through breeding of knowledge about phenology of wood formation will help to related to the dates of initiation and completion of the formation of different tissues and to the total duration of ring formation is low. Last and final summary in the thesis

AbstractIn this chapter, we discuss post-photosynthetic processes that affect intra-annual variation in the stable isotopes of tree rings, such as timing of cell formations and turnover of stored carbohydrates, by combining research findings gained by using either natural-abundance or artificially-enriched carbon, oxygenand hydrogen isotopes. We focus on within-ring variation in stable isotope ratios, with an emphasis on aligning observed ratios in whole wood or extracted cellulose to seasonal dynamics in climate and phenology. We also present a discussion of isotopic fractionation that operates within the scope of observed variations across individual rings. We then introduce a model that traces the seasonal partitioning of photosynthate into tree rings via storage pool, which is based on experimental data gained from labeling studies using artificially enriched 13CO2 gas. Finally, we will describe our current understanding of post-photosynthetic signal transfer processes of oxygenand hydrogen isotopes from leaves to tree rings, such as exchange of oxygen and hydrogen between storage carbohydrates and local cambial water, and possible causes of difference in oxygen and hydrogen isotope fractionations. Finally, we discuss mechanisms behind how oxygen and hydrogen from foliar-absorbed liquid water is then incorporated into wood biomass, by introducing results gained from recent H218O and HDO pulse-labeling experiments.

AbstractIn this chapter, we discuss post-photosynthetic processes that affect intra-annual variation in the stable isotopes of tree rings, such as timing of cell formations and turnover of stored carbohydrates, by combining research findings gained by using either natural-abundance or artificially-enriched carbon, oxygenand hydrogen isotopes. We focus on within-ring variation in stable isotope ratios, with an emphasis on aligning observed ratios in whole wood or extracted cellulose to seasonal dynamics in climate and phenology. We also present a discussion of isotopic fractionation that operates within the scope of observed variations across individual rings. We then introduce a model that traces the seasonal partitioning of photosynthate into tree rings via storage pool, which is based on experimental data gained from labeling studies using artificially enriched 13CO2 gas. Finally, we will describe our current understanding of post-photosynthetic signal transfer processes of oxygenand hydrogen isotopes from leaves to tree rings, such as exchange of oxygen and hydrogen between storage carbohydrates and local cambial water, and possible causes of difference in oxygen and hydrogen isotope fractionations. Finally, we discuss mechanisms behind how oxygen and hydrogen from foliar-absorbed liquid water is then incorporated into wood biomass, by introducing results gained from recent H218O and HDO pulse-labeling experiments.

AbstractSpecies continuity under the harsh climatic conditions of the boreal forest requires trees to ensure the functioning of two main life processes, namely growth and reproduction. However, species survival becomes a challenge when environmental conditions become unstable and reach the taxa’s ecological tolerance limit. Survival in an unstable environment is possible through the concurring processes of phenotypic plasticity and local adaptation; each process has its advantages and shortcomings. Local adaptation allows attaining the best possible fitness under conditions of limited gene flow and strong directional selection, leading to specific adaptations to the local environment; however, there is a risk of maladaptation when conditions suddenly change. In turn, phenotypic plasticity provides trees an advantage when weather events change rapidly and enables a response expressed by the production of different phenotypes by the same genotype. However, this process is expensive in terms of costs in maintenance and causes developmental instability within the individual. Boreal trees utilize both processes as reflected in variations in their functional traits within the same species. In this chapter, we address the main life processes, presenting the variability of functional traits of flowering and seed production, xylem conductivity, bud and cambium phenology, as well as transpiration and photosynthesis, as a consequence of the interaction of genotype and environment. We describe the practical consequences of a variation in functional traits, as expressed in chemical and mechanical wood properties. Finally, we outline applications and perspectives for managing boreal forests in a context of heterogeneous and changing environmental conditions.