Annual Tree Research Articles

Coupled forest zoning and agricultural intervention yields conflicting outcomes for tropical forest conservation in the Democratic Republic of the Congo (DRC)

Agricultural intensification and forest conservation are often seen as incompatible. Agricultural interventions can help boost food security for poor rural communities but in certain cases can exacerbate deforestation, known as the rebound effect. We tested whether coupling agricultural interventions with participatory forest zoning could improve food security and promote forest conservation in the Democratic Republic of the Congo. Simple agricultural interventions led to a >60% increase in cassava yields and a spill-over effect of improved cassava variety uptake in non-intervention zones. Household surveys conducted at the end of the 8 year project implementation period revealed that households that received agricultural interventions had more favorable attitudes toward forest zoning and conservation. The surveys also showed that farmers in the intervention domain practiced less land-intensive field and fallow management strategies compared to those practiced in the non-intervention domain. However, an 18 year time series analysis of Landsat satellite data revealed that agricultural expansion persisted in areas both with and without intervention assistance, and there is risk of a rebound effect. Approximately 70% of the tree cover loss that occurred outside of the agricultural areas was located within a 3 km buffer zone surrounding the outermost edges of the agricultural areas, which suggested that the majority of tree cover loss was caused by agricultural expansion. Within that 3 km buffer, average annual tree cover loss during the post-intervention period was higher in the intervention domain compared to the non-intervention domain (0.17% yr−1 compared to 0.11% yr−1 respectively, p < 0.001), suggesting risk of a rebound effect. The disconnection between household perceptions of zoning adherence and actual behavior indicates the importance of strengthening governance structures for community-based monitoring and enforcement.

Increasing Liana Abundance and Associated Reductions in Tree Growth in Secondary Seasonally Dry Tropical Forest

Lianas are thought to be increasing and altering tree growth and ecosystem productivity in tropical forests, but less research has focused on secondary or seasonally dry tropical forest. We report on an 11-year study of tree growth and liana presence from Guanacaste, Costa Rica, where we measured the diameter growth and liana presence on more than 1,700 trees in regenerating forest of different ages. We find that the proportion of trees without lianas is decreasing and the number of trees with lianas occupying more than 10% of tree’s crowns is increasing. We also find that lianas are affecting the diameter growth of trees. The 11-year average relative growth rates of trees with lianas in more than 10% of the tree’s crown are lower than the relative growth of trees with no lianas or lianas in less than 10% of their crown. Year-to-year, tree relative growth rate is related to annual precipitation and tree diameter. However, trees that were heavily infested with lianas (i.e., with lianas in more than 50% of their crowns) had lower relative growth and a weaker precipitation-growth relationship. This work underscores the value of long-term longitudinal data in secondary forest and adds critical data on dry forest liana abundance change.

The cost of fruit and the penalty of youth: Predicting mean annual seed production in single-species forest stands

Quantifying mean annual tree seed production is important for conservation and forestry applications, but its estimation remains a substantial challenge. Interspecies variation in seed production is often expressed as a trade-off between seed size and seed number, forming a key component of established models of mean annual seed production in forest stands. In this study we improved on these models by quantifying additional effects from accessory costs and reproductive maturity status, using data from temperate-zone Eucalyptus species to assess model performance.Firstly, by evaluating a range of reproductive traits, we found that seed rain density was more closely associated with ‘fruit cost per seed’ measures than seed size measures. For the most common measure of seed rain density (based on direct observations of free seed fall), woody capsule surface area per viable seed explained 70% of observed variation, while seed mass explained only 28% (n = 16 species).Secondly, an existing model based on seed mass, tree size and tree density was extended to include a stand maturity function, and to use alternative reproductive traits. For a smaller dataset with long-term observations and detailed stand measurements, the proportion of variance explained by the extended model ranged from 81 to 98% depending on trait selection (mean = 93%), with published models explaining less variance (75–83%, mean = 80%).By reframing interspecies variation in seed production as a trade-off between seed cost and seed number, we found evidence that investment in heavy fruit structures may represent a substantial constraint on seed output among forest stands from a common genus and region, although our results must be considered somewhat preliminary, given the small number of species examined. We have also developed an enhanced predictive model, which could be used with stand-level models for tree size and tree density to improve predictions of mean annual forest seed production in landscape simulations.

Crowding, climate, and the case for social distancing among trees.

In an emerging era of megadisturbance, bolstering forest resilience to wildfire, insects, and drought has become a central objective in many western forests. Climate has received considerable attention as a driver of these disturbances, but few studies have examined the complexities of climate-vegetation-disturbance interactions. Current strategies for creating resilient forests often rely on retrospective approaches, seeking to impart resilience by restoring historical conditions to contemporary landscapes, but historical conditions are becoming increasingly unattainable amidst modern bioclimatic conditions. What becomes an appropriate benchmark for resilience when we have novel forests, rapidly changing climate, and unprecedented disturbance regimes? We combined two longitudinal datasets-each representing some of the most comprehensive spatially explicit, annual tree mortality data in existence-in a post-hoc factorial design to examine the nonlinear relationships between fire, climate, forest spatial structure, and bark beetles. We found that while prefire drought elevated mortality risk, advantageous local neighborhoods could offset these effects. Surprisingly, mortality risk (Pm ) was higher in crowded local neighborhoods that burned in wet years (Pm =42%) compared with sparse neighborhoods that burned during drought (Pm =30%). Risk of beetle attack was also increased by drought, but lower conspecific crowding impeded the otherwise positive interaction between fire and beetle attack. Antecedent fire increased drought-related mortality over short timespans (<7 years) but reduced mortality over longer intervals. These results clarify interacting disturbance dynamics and provide a mechanistic underpinning for forest restoration strategies. Importantly, they demonstrate the potential for managed fire and silvicultural strategies to offset climate effects and bolster resilience to fire, beetles, and drought.

TRANSPIRATION RATE OF SCOTS PINE TREES ON VERY OLIGOTROPHIC SOILS OF NORMAL MOISTURE IN RELATION TO DIFFERENT METEOROLOGICAL CONDITION

Continuous monitoring of the tree ring formation and transpiration throughout the year is crucial for understanding the tree reaction to changes in meteorology, and evaluating its adaptiveness to recent environmental changes. Data were collected from four Pinus sylvestris L. trees which sapflow was measured by the heat wave propagation method using SFM1 sensors (ICT International, Australia) and annual tree stem increment by electronic dendrometer DRL26. Investigation was performed in middle age pine stand on very oligotrophic soil. Meteorological data revealed that 2019 was the year of drought. In this year pine transpiration rate and volume increment were the lowest. However, water was used most efficiently, which means that pines needed less water to produce 1 cm3 of wood. 2020 was characterized as a year of recovery of moisture regime, when during vegetation precipitation increased up to long term value and the mean air temperature was the lowest. Annaul volume increment of pine trees in this year was the biggest, transpiration rate the highest, but WUE was the smallest, indicating that pine used more water to produce 1 cm3 of wood. Obtained data on WUE during different growing season revealed that Scots pine trees are well adapted to recent meteorological condition. Increase in tree diameter reduced values of Scots pine WUE, what means that bigger pine trees used significantly less water to produce 1 cm3 of wood

A multi-scale dendroclimatological analysis of four common species in the southern Canadian boreal forest

A comprehensive assessment of the tree growth/climate relationship was undertaken to better understand the potential impacts of climate change on the growth dynamics of four widespread and common boreal tree species, namely jack pine (Pinus banksiana), black spruce (Picea mariana), eastern larch (Larix laricina), and trembling aspen (Populus tremuloides), located at the southern limits of the Canadian boreal forest. Over intra-annual time scales, results show that precipitation is likely the main driver of stem radius change (∆R), with jack pine radius exhibiting the most consistent positive relationship. Precipitation had a stronger relationship with stem radius variation in black spruce and eastern larch during periods when volumetric water content (VWC) in the root zone was below average, pointing to the likelihood that certain species rely more heavily on available moisture in the uppermost layers of the soil column to replenish stem water, especially during extended dry periods. Warm air temperatures had an immediate negative impact on stem water content due to transpiration. This was most marked during periods of reduced moisture availability in the root zone, when trees are more susceptible to net water volume loss. During periods when moisture was not limiting, a positive relationship between lagged air temperature and ∆R was detected. Warm air temperatures may therefore play an important role in stimulating radial growth when moisture requirements are met. At annual temporal resolution, the growth/climate relationship changed over the lifetime of our study species. Over the last several decades, the relationship between precipitation and annual radial tree growth has weakened, while positive relationships between spring and summer air temperature and annual radial tree growth have emerged, likely signaling a decrease in moisture limitations, and a positive response to spring warming. Our findings reveal that boreal forest tree species may benefit from spring and summer warming over the near term, providing there is sufficient moisture to support growth. Over the long term, rates of evapotranspiration are expected to overshadow gains in moisture related to an increase in precipitation. Under these circumstances, we are likely to see reduced growth rates and an increasingly negative response of boreal tree species growth to warm air temperatures.

Declining Growth Response of Siberian Spruce to Climate Variability on the Taiga–Tundra Border in the Putorana Mountains (Northwest Siberia)

Global warming is most pronounced at high latitudes where temperatures increase twice as fast as the global average. Boreal forest growth is generally limited by low temperatures, so elevated temperature is supposed to enhance biomass production and carbon sequestration. A large amount of evidence has recently shown inconsistent responses of tree growth derived from annual tree rings to increasing temperature. We studied Siberian spruce growth in the remote and isolated Putorana Mts, Western Siberia in populations at its natural distribution limit. Tree ring cores were sampled along vertical transect in 100, 200 and 350 m a.s.l. as the aim was to identify the tree growth rate at different altitudes. Detailed sampling site descriptions served to identify possible factors controlling the growth rate in extremely heterogeneous environments. Monthly climate data for the period 1900–2020 were extracted from the gridded CRU database. Tree ring chronologies confirmed long-lasting limited growth, and despite high year-to-year ring width variability, synchronous growth at vertical study sites dominantly controlled by climate. The positive tree ring growth response to summer temperature was significant for most of the 20th century but dramatically changed in recent decades, when unusually warm summers were reported. There was no, or even a negative growth rate correlation with precipitation, which indicates a sufficient water supply at the study sites. Elevated temperature in this region with a continental climate might turn the study localities to water-limited areas with many negative consequences on tree growth and related ecosystem services.

Early–latewood carbon isotope enhances the understanding of the relationship between tree biomass growth and forest-level carbon fluxes

Eddy covariance (EC) and biometric (based on tree diameter and tree ring measurements) methods are used extensively to estimate annual variability in forest productivity. Many previous studies obtained inconsistent findings between net ecosystem productivity (NEP) based on EC (NEPEC) and tree biomass growth based on biometric methods, partly because of delayed responses in trees due to temporary non-structural carbohydrate (NSC) storage. Direct measurement of the amount of NSCs stored in trees is challenging; however, using carbon (C) isotope ratios in different tree components is considered an indirect and effective alternative approach for assessing NSC dynamics. We measured stable C isotope ratios in earlywood (EW) and latewood (LW) of rings of 70 trees (categorized as 4–10, 10–20, and > 20 cm diameter at breast height [DBH]) to test relationships between trunk-growth NEPEC time series and annual tree biomass growth (based on tree ring width) in a young mixed forest in northern China over 13 years. Our results revealed a strong correlation (r = 0.691) between trunk-growth NEPEC (March–August in a calendar year) and tree biomass growth. The change in correlation between current-year EW δ13C and LW δ13C of the previous year observed in trees with 10–20 cm DBH, which accounted for 51.8% of the total tree biomass growth, was consistent with the synchronicity of trunk-growth NEPEC and tree biomass growth. Colder early growing seasons, which significantly increase the reliance of early-season structural growth on stored labile C accumulated in the previous year, may lead to postponed tree biomass growth responses related to NEPEC. In conclusion, this approach, investigating C isotope analysis in EW and LW, helps elucidate the relationships between tree biomass growth and stand-level C fluxes in forest sites.

Cross-continental hydroclimate proxies: Tree-rings in Central Chile reconstruct historical streamflow in Southeastern South American rivers

Regional teleconnections permit cross-continental modeling of hydroclimate throughout the world. Tree-rings are a good hydroclimatic proxy used to reconstruct drought and streamflow in regions that respond to common global forcings. We used a multi-species dataset of 32 tree-ring width chronologies from Chile and Uruguay as a climate proxy to infer annual streamflow (Q) variability in the Negro River basin, a grassland-dominated watershed of lowland Southeastern South America. A positive linear correlation between tree-ring chronologies from Central Chile and annual Negro River instrumental streamflow from 1957 to 2012 indicated a cross-continental teleconnection between hydroclimate variability in Central Chile and Northeastern Uruguay. This relationship was mediated in part by the El Niño Southern Oscillation (ENSO), whereby the El Nino 3.4 Index was positively correlated with regional rainfall, annual tree growth, and Q anomalies. Despite the proximity of Uruguayan tree-ring chronologies to Negro River hydrometric stations, the Chilean tree-ring chronologies best predicted annual streamflow. Thus, using tree-ring data from four long-term moisture-sensitive chronologies of the species Cryptocarya alba in Central Chile (32–34°S), we present the first streamflow reconstruction (1890–2009) in the lower La Plata Basin. The reconstruction supports regional evidence for increasing frequency of extreme flood years over the past century in Uruguay. We demonstrate how climate teleconnections that mediate local hydroclimate variability permit the cross-continental reconstruction of streamflow, filling a major geographical gap in historical proxies for flooding and drought in grassland biomes of the southern hemisphere.

Distribution of mechanical properties in annual growth rings of deciduous trees measured using scanning naation

The paper presents the results of mechanical properties scanning by means of naation across the annual growth rings of deciduous trees wood, small-leaved lime (Tilia cordata) and common oak (Quercus robur) in particular. Significant variations in microhardness H and Young's modulus E radial dependencies have been found for any of the studied species. Results can be useful 1) to amend the understanding the nature of macromechanical properties of various wood species and to reveal the details of their formation depending upon microstructural characteristics, 2) to optimize the technologies of growing, reinforcement and subsequent usage of the wood, 3) to develop new independent methods in dendrochronology and dendroclimatology Keywords: nanocomposites, naation, nano-/microhardness and Young's modulus scanning, tree annual growth rings, dendrochronology

Global Ecopotential of Dendrochronology

Drought is a meteorological phenomenon that has influenced the life of human society for ages and still has a great impact on it. This phenomenon can be divided into a group of sub-phenomena, e.g. soil and air droughts, winter droughts, etc.… From a physiological point of view, drought may have different consequences in different periods of a growing season. It seems however difficult to describe quantitative characteristics of a physiologically important drought using any meteorological parameters because within an ecosystem the results of the interaction of ecological factors may change the way plants respond to a certain limited number of values of meteorological parameters. Photosynthesis and transpiration characteristics predetermine that the function modelling annual tree ring variability will always and under any conditions have a variable that will depend on drought. The objective of dendroclimatic studies can be either to separate a drought-associated climatic signal from the tree ring chronology or, on the contrary, to search a chronology with a “clear” and easily detected drought-associated signal. Having retrospective aspects, Dendroclimatic studies show considerable promise for the evaluation of droughts including those that have an impact on crop yields. Such studies can give further information for crop yield forecasts.

Conifer establishment after the eruption of the Paricutin volcano in central Mexico

Volcanic eruptions have large effects on forest ecosystems and create new substrates, triggering primary succession processes. The Paricutín volcano, born in central-western Mexico, erupted between 1943 and 1952. After the cessation of the eruptive activity, plant colonization began on the lava flows and tephra deposits, including the conifer species that dominate the surrounding mature forests. This study aims to reconstruct the history of the establishment of conifer trees on the substrates created by the Paricutín eruption. 16 sampling plots were established along three transects with northern, southern, and south-western aspects, located every 250 ​m from the preserved forest to the volcanic cone. Increment cores from 400 conifer trees were extracted and their age was determined by cross-dating annual tree rings. The order of the species colonization and the tree establishment, abundance, and dominance patterns were characterized. Also, the influence of the distance from the mature forests and the inter-annual climatic conditions on the temporal tree establishment pattern was evaluated. Eight pine and one fir species have been established since 1970, only 18 years after the end of the eruptive period. However, tree establishment increased by 12.9% annually after 1995, with the youngest tree in our sample getting established in 2015. We did not find a well-defined temporal and spatial pattern of species arrival, which suggests that colonization occurred randomly, although the four pine species that were established early became the most abundant and dominant. Tree establishment was not influenced by the distance from the mature forest, and wet inter-annual conditions did not enhance pulses of tree recruitment, exhibiting a continuous tree establishment pattern. Conifer species have shown a great capacity for colonizing volcanic substrates created by the Paricutín eruption, which suggests that tropical montane conifers can regenerate rapidly under high-magnitude disturbances. These findings support the use of these forest species for ecological restoration.

Exploring wood anatomy, density and chemistry profiles to understand the tree-ring formation in Amazonian tree species

Long-term analysis of tree growth using annual tree rings is increasingly in demand for tropical tree species. The basis of these studies has traditionally been the anatomical identification of the annual ring boundary. However, the structure of these annual rings has been sparsely explored for complementary physical and chemical wood traits. Here, we explore the relationships among wood density features and chemical elements (S, K, Ca, Mn) involved in the annual tree ring formation of 12 tropical tree species from non-flooded forest in the southern Amazon basin. Transverse wood sections were used for each species to determine: 1) macroscopic distinction (radial growth and wood density), 2) microscopic analyse of vessels, axial and ray parenchyma (anatomy) and 3) X-ray densitometry (physical) and X-ray fluorescence (chemical). For some species, the profiles of wood density, and Ca and Mn content showed intra- and inter-annual patterns that allowed to define and characterize the growth boundary of tree rings. Ca, K and S were mainly distributed in axial parenchyma cells, and around vessels, whereas, Mn was mainly distributed in fibres. Our results showed significant species-specific correlations between tree-ring width, density and concentrations of Ca, K and Mn. The anatomical characterization and the complementary information provided by the density and chemical profiles in some Amazonian species can represent a valuable proxy to improve the definition of annual ring-boundaries and improve the understanding of long-term growth and physiological patterns.

Directional Variability in Response of Pinus koraiensis Radial Growth to Climate Change

Climate change affects forest ecosystems at a variety of scales, from the composition of landscapes to the growth of individual trees. Research across regions and tree species has produced contradictory findings on the effects of climate variables on radial growth. Here, we examine tree ring samples taken from four directions of a tree to determine whether there is directional variability in tree growth in relation to climate trends. The results showed directional differences in the temporal growth processes of Pinus koraiensis, with more commonalities between the west and north directions and between the east and south directions. The contemporaneous June maximum temperature was the main climate factor associated with the difference between the growth of tree rings toward the east or west. Annual tree ring growth toward the east was more affected by the year’s temperature while growth toward the south was more sensitive to the year’s precipitation. Our research demonstrates that diverse response of tree growth to climate may exist at intra-individual scale. This contributes to understanding the sensitivity of tree growth to climate change at differ scales.

Natural capital evaluation in the FutureCity of Shimokawa, Northern Japan, based on forest economics.

We have pragmatically but accurately evaluated the natural capital of a small northern town, Shimokawa, Hokkaido, Japan. The key industries are forestry, wood manufacturing, and agriculture. From an environmental perspective, Shimokawa was nominated as a Japanese FutureCity. Consequently, the total natural capital value (NCV) of the forest and agricultural lands was calculated to be 1.326 billion USD/year (or 24,161 USD/ha/year) and 44 million USD/year (or 19,692 USD/ha/year), respectively, in 2012. The sum of these NCVs was more than 7 times greater than the yearly gross production of the town, although the forest had a higher NCV because of the larger area (54,862ha for forest area), compared with 2953ha for agricultural area. This substantial NCV is mainly generated by sustainable forest management. The timber account showed that the annual tree growth was greater than the annual harvest of trees. The CO2 account derived from a one-year calculation showed that the town served as a CO2 sink at 107,249 t-CO2/year due to the large amount of annual tree growth and CO2 storage in the harvested wood products even if CO2 was emitted from industries and households. The forestry and wood manufacturing industries, as well as agriculture, created socioeconomic effects for the townspeople, ranging from job creation, study tours, and social welfare. This NCV accounting for Shimokawa town ensures the sustainable use of valuable environmental assets and will help other communities recognize their own NCV accounts.

IMPACT OF GOLD MINING ON FLORA: THE CASE OF THE SISSENGUE GOLD MINE (NORTHERN COTE DIVOIRE)

This study was initiated to contribute to the sustainable management of biodiversity in mining sites in Cote dIvoire. Its objective is to determine the impacts of gold mining activities on the flora of the Sissengue gold mine located in the department of Tengrela in northern Cote dIvoire. The flora inventory was conducted along a 500 m transect combined with the surface survey and roving inventory methods. The surface survey method consisted of delimiting a 25 m x 25 m (400 m2) plot at the end of each transect. In total, nine (09) types of land use were identified in the site, namely annual crops, perennial crops, open forests, forest galleries, tree savannahs, shrub savannahs, burned areas, lakes or water reservoirs, and locality. The floristic inventories carried out in seven (07) types of land occupations allowed the identification of 207 plant species distributed among 155 genera and 61 families. In addition, thirteen (13) species with special ecological status and seven (07) species included in the IUCN red list, four of which are vulnerable. However, the floristic diversity is low in all plant formations with an average of 1.91. The shrubby savannahs record the highest densities with 1705 stems/ha while the forest galleries and open forests record the highest values of basal area, with respectively 37.2 m2/ha and 28.1 m2/ha. These vegetation formations are disturbed by the mines gold mining activities. Efforts to conserve areas dedicated to biodiversity conservation must be a priority for mining sites in Cote dIvoire.

Joint effects of climate, tree size, and year on annual tree growth derived from tree-ring records of ten globally distributed forests.

Tree rings provide an invaluable long‐term record for understanding how climate and other drivers shape tree growth and forest productivity. However, conventional tree‐ring analysis methods were not designed to simultaneously test effects of climate, tree size, and other drivers on individual growth. This has limited the potential to test ecologically relevant hypotheses on tree growth sensitivity to environmental drivers and their interactions with tree size. Here, we develop and apply a new method to simultaneously model nonlinear effects of primary climate drivers, reconstructed tree diameter at breast height (DBH), and calendar year in generalized least squares models that account for the temporal autocorrelation inherent to each individual tree's growth. We analyze data from 3811 trees representing 40 species at 10 globally distributed sites, showing that precipitation, temperature, DBH, and calendar year have additively, and often interactively, influenced annual growth over the past 120 years. Growth responses were predominantly positive to precipitation (usually over ≥3‐month seasonal windows) and negative to temperature (usually maximum temperature, over ≤3‐month seasonal windows), with concave‐down responses in 63% of relationships. Climate sensitivity commonly varied with DBH (45% of cases tested), with larger trees usually more sensitive. Trends in ring width at small DBH were linked to the light environment under which trees established, but basal area or biomass increments consistently reached maxima at intermediate DBH. Accounting for climate and DBH, growth rate declined over time for 92% of species in secondary or disturbed stands, whereas growth trends were mixed in older forests. These trends were largely attributable to stand dynamics as cohorts and stands age, which remain challenging to disentangle from global change drivers. By providing a parsimonious approach for characterizing multiple interacting drivers of tree growth, our method reveals a more complete picture of the factors influencing growth than has previously been possible.

Tree-Ring Based Reconstruction of Historical Fire in an Endangered Ecosystem in the Florida Keys

Big Pine Key, Florida, is home to one of Earth’s largest swaths of the critically-endangered dry forests. Known as pine rocklands, this fire-adapted ecosystem must experience regular fire to persist and remain healthy. Pine rocklands are composed of a sole canopy species: the South Florida slash pine (Pinus elliottii var. densa), along with a dense understory of various woody and herbaceous species, and minimal surface moisture and soil development. Slash pine record wildfire activity of the surrounding area via fire scars preserved within the annual tree rings formed by the species. Our study used dendrochronology to investigate the fire history of the pine rocklands on Big Pine Key, specifically within and around the National Key Deer Refuge (NKDR) because it is the largest segment of unfragmented pine rockland on the island. We combined the results found within the NKDR with those of a previous study completed in 2011, and incorporated historical documents and reports of prescribed and natural fires through November 2019 into our evaluation of fire history on Big Pine Key. We conclude that prescribed burning practices are vital to truly restore natural fire behavior, and repeated burning on these islands in the future must be prioritized.

The spatio-temporal pattern of release signals and tree growth in Fagus-Abies-Picea old-growth forests reveals unsteady gap-phase dynamics

Disturbances have been recognized as a key factor shaping the species composition, structure and dynamics of natural forest ecosystems. In Europe, where forests driven by spontaneous processes have survived in relic form, knowledge about natural disturbance regimes is still fragmentary. To expand this knowledge, we reconstructed stand-level growth and analyzed the spatio-temporal pattern of release signals in the increment chronologies of individual trees as indicators of disturbance events in the Western Carpathians (Central Europe). The study was carried out in five old-growth forests formed by Fagus sylvatica L., Abies alba Mill. and Picea abies (L.) H. Karst. Depending on the stand, the analyses included tree-ring series of 84–193 trees sampled over areas of 5.9–13.6 ha and aimed at determining (1) the spatio-temporal pattern of disturbance severity over the last two centuries, (2) whether disturbances have been synchronized in time across the study sites and (3) whether disturbances have induced pulsed dynamics of stand development manifested as fluctuations in radial tree increment at the level of entire stands. In the period 1850–2010, the percentage of decades with the proportion of released trees < 10, 10–20, 20–30 or more than 30% was 38, 41, 14 and 7%, respectively, and no instances of severe disturbances simultaneously impacting an extensive area and releasing the vast majority of trees were found. The release events were only weakly synchronized at the between-stand level. The spatial distribution of released trees varied over the decades, with a shift toward spatial independence for the most severe disturbances. At the stand level, the interchanging periods of increasing/decreasing tree growth lasted between 24 and 36 years, with the exception of one stand in which this period lasted 54 years. The revealed fluctuations in tree growth attributable to changes in stand density were relatively small and accounted on average for 7% of the total variation in annual tree increments. This suggests that local level disturbances introduce structural heterogeneity and strongly modify tree growth, but at the stand level, their effect is dispersed and causes only minor fluctuations. An over-dispersion of decadal release frequencies compared to the random model and spatial correlation of disturbing events on the one hand, and the lack of extensive disturbances, frequent occurrence of multiple releases in tree life histories, and small fluctuations in the reconstructed growth at the stand level on the other hand, suggest a disturbance regime which goes beyond random processes in a strict sense and is thus not entirely compatible with the classical model of gap-phase stand dynamics.

Are periodic (intra-annual) tangential bands of vessels in diffuse-porous tree species the equivalent of flood rings in ring-porous species? Reproducibility and cause

Tree rings from ring-porous species have often been used as flood proxy. Many ring-porous species produce characteristic flood rings in response to stem submersion during vessel formation. Flood rings have earlywood vessels that are more numerous and/or of smaller cross-sectional area than “normal” rings. This study aimed at determining if diffuse-porous balsam poplar and trembling aspen, like ring-porous black ash, produce anatomically distinct annual tree rings in response to flooding. More specifically, we asked (i) if periodic tangential bands of vessels (hereafter PTBV) could be as easily identified/quantified as flood rings and (ii) if PTBV could be associated with spring flooding. Sampling of black ash, balsam poplar and trembling aspen trees took place along a flood exposure gradient in the floodplain of Lake Duparquet in northwestern Québec. Two observers recorded flood rings and PTBV. Consistency between observers was greatest when identifying flood rings. In both diffuse-porous species, PTBV occurred less abundantly than flood rings in black ash. They also occurred less often in balsam poplar than in trembling aspen. Years in which PTBV were initiated early in the growing season were associated with years in which flood rings occurred. Like flood rings, early occurring PTBV were more abundant in springs characterized by high mean river discharge, extensive snow cover, cold temperatures and heavy precipitation. Early-occurring PTBV dominated in flooded sites and late-occurring ones dominated in the control site. However, PTBV of the late-types were also observed in both flood exposures indicating that spring flood may not be the only factor modulating their formation. While flood rings seem to be associated with a change in the transport of growth regulators resulting from stem submergence and excess water, PTBV may be reflective of rhythmic alterations in the transport of growth regulators resulting from either water excess or deficit. Despite promising findings, many questions remain before PTBV in riparian diffuse-porous species can be widely used as a flood proxy. Why do species and individual trees differ in their ability to record them? What is the full range of environmental conditions triggering PTBV’s formation especially in unflooded sites and in the late growing season?