Annual Basal Area Increment Research Articles

Enhanced interannual drought resilience in mixed stands: unveiling possible complementarity effects between tree species of the Spanish Northern Plateau

AbstractClimate change is expected to intensify drought in the Mediterranean region. Previous studies indicate that tree species mixing may reduce the water stress. Our study investigates the response to past drought events of four co-occurring Mediterranean species: Pinus pinea L. (stone pine), Pinus pinaster Ait. (maritime pine), Juniperus thurifera L. (Spanish juniper) and Quercus ilex L (holm oak). The study was performed at an interannual scale, both in monospecific and mixed stands. Annual tree ring widths data measured on increment cores and stem discs obtained from 281 trees were used to quantify the responses to drought events using complementary resilience indices. Additionally, we assessed tree intra- and inter-specific competition impact over the past 25 years. We fitted and compared generalised linear mixed models to determine the influence of species identity, stand composition as intra-specific and inter-specific competition on complementary resilience indices and annual basal area increment. The co-existence with other species enhanced the resistance to drought of the stone pine as the resilience capacity of the Spanish juniper. Conversely, maritime pine’s drought resistance declined considerably in mixed stands. Notably, only the anisohydric species Spanish juniper and holm oak were able to return to pre-disturbance growth rates after the drought. The influence of competition on tree growth was found to differ according to the hydrological conditions of each year and varied based on the specific source of competition. Our study showed that mixed stands in the Spanish Northern Plateau, especially with holm oak and Spanish juniper, are more resilient to prolonged droughts due to spatio-temporal complementarity and subsequent competition reduction. That is another reason for which such composed mixed stands should be promoted in the arid conditions of the Spanish Northern Plateau.

Elevation-dependent tree growth response to climate in a natural Scots pine/downy birch forest in northern Sweden.

Forests dominate the landscape at high latitudes in the boreal regions and contribute significantly to the global carbon stock. Large areas are protected and provide possibilities to analyze natural forest dynamics including resilience to climate change. In Fennoscandia, Scots pine (Pinus sylvestris L.) and downy birch (Betula pubescens Ehrh.) often coexist in natural forests close to the limits of their ecological ranges. Tree growth in these forests is generally thought to be limited by temperature, and changes in growth trends can therefore serve as early indicators of the impact of global warming on natural ecosystems. We sampled 592 Scots pine and downy birch trees along two elevational gradients spanning the transition from the forest zone to the coniferous treeline in Tjeggelvas nature reserve, northern Sweden. Based on the tree-ring data, we compared annual basal area increment (BAI) trends from 1902 to 2021, analyzed the ring-width indices (RWI) in relation to local climate data, and investigated trends in climate-growth relationships. We found that the mean annual growth of both species was higher in more recent years than at the beginning of the 20th century. The RWI were positively correlated with summer temperatures, however, we found a much stronger relationship for Scots pine than downy birch. We noticed a decrease in the importance of summer temperature for Scots pine growth, whereas the importance of late spring temperatures increased over the 120-year-long study period. Due to strongly positive BAI trends combined with a decrease in temperature sensitivity, the overall conclusion of our study is that the influence of increasing temperatures is still positive and outweighs the negative impacts of climate change on Scots pine growth in natural forests in northern Sweden, particularly at higher elevations. Natural forests are important natural experiments that contrast the managed forests and are key to understanding the latter.

Spatiotemporal variation in the negative effect of neighbourhood crowding on stem growth

Abstract Neighbourhood interactions drive tree growth and forest ecosystem functioning. The strength of interactions depends on the climate. However, it remains unclear how plant–plant interactions are modified by environmental conditions operating both spatially and temporally, which is crucial for predicting forest dynamics under climate change and for effective forest management. In this study, we used annual growth data for 4139 stems from 2010 to 2021 across 50 permanent forest plots located at six sites in eastern China. We quantified the effect of neighbourhood crowding on the annual basal area increment. We explored how interactions among neighbouring trees vary with water availability and temperature gradients in the spatial (across sites) and temporal (across time within sites) dimensions. Our findings revealed a negative impact of neighbourhood crowding on stem basal area growth, which is size‐ and trait‐dependent at some sites. The negative effects of light competition tended to be more intense at warmer sites, supporting the stress‐gradient hypothesis (SGH) in a spatial dimension. However, the patterns of crowding effects along interannual climate anomalies are inconsistent across sites, making it difficult to predict crowding effects under the SGH framework in a temporal dimension. Synthesis: Our study demonstrated that tree interactions depend on the climate context. The climate dependence of interactions may be inconsistent between the spatial and temporal dimensions. Light competition across sites supported the SGH in the spatial dimension but not in the temporal dimension. These results further highlight the complexity of biotic interactions and the need for caution when extrapolating findings from the spatial to the temporal dimension.

Differences in Response of Tree Species at Different Succession Stages to Neighborhood Competition

Neighborhood competition influences tree growth, which can affect species composition and community succession. However, there is a lack of understanding regarding how dominant tree species at different successional stages of forest communities respond in terms of crown architecture and functional traits during their growth process to neighborhood competition. In this study, we analyzed the responses of average annual basal area increment (BAI), crown architecture, and leaf functional traits of early-successional species (Cunninghamia lanceolata and Pinus massoniana), transitional species (Alniphyllum fortunei and Choerospondias axillaris), and late-successional species (Elaeocarpus duclouxii and Castanopsis carlesii) to neighbor competition in a secondary evergreen broad-leaved forest. We found that the BAI of all species is negatively correlated with competition intensity. Notably, early-successional and transitional species exhibited a more rapid decline in growth rates compared to late-successional species in response to increased competition. Among these tree species, the response of crown structure to neighbor competition exhibited variation. Early-successional and transitional species displayed a negative correlation between the competition index and crown area (CA)/diameter, while a positive correlation emerged between the lowest branch height (LBH)/height. Conversely, late-successional species followed the opposite trend. In terms of leaf functional traits, specific leaf area (SLA) showed heightened sensitivity to neighborhood competition, with a positive correlation between SLA of all tree species and the competition index. Furthermore, water use efficiency (WUE) demonstrated negative correlations with the competition index in early-successional and transitional trees, while a positive correlation emerged with late-successional trees. These findings suggest that early-successional and transitional trees prioritize vertical canopy growth, whereas late-successional trees tend to favor horizontal canopy expansion in response to neighboring competition. Additionally, early-successional and transitional trees experience more significant suppression of radial growth rate. Our research contributes to a deeper understanding of the underlying mechanisms driving changes in species composition and community succession.

Constrained trait variation by water availability modulates radial growth in evergreen and deciduous Mediterranean oaks

Spatial and temporal variation in functional traits allows trees to adjust to shifting environmental conditions such as water stress. However, the change of traits, both mean and variances, along water availability gradients and across growing seasons, as well as their covariation with tree performance, have been rarely assessed. We examined intraspecific trait variation in coexisting evergreen (Quercus ilex ssp. ilex and Q. ilex ssp. ballota) and deciduous (Quercus faginea and Quercus humilis) Mediterranean oaks along a wide water availability gradient in northeastern Spain during six years. We measured leaf area (LA), shoot twig mass (Sm), leaf mass per area (LMA) and the ratio of shoot twig to leaf biomass (Sm:Lm). We characterized tree performance through basal area increment (BAI) and drought resilience indices. Higher variation was found within individuals than between individuals across populations and years. Within species, we found trait adjustments toward more conservative water-use (low LA and Sm and high LMA) with increasing drier conditions. Intraspecific trait variation was constrained by water availability, particularly on the deciduous species. In Q. ilex, trait variance of LMA positively covaried with annual BAI, whereas variance of LA, Sm and Sm:Lm was positively related to resistance and resilience against the severe 2012 drought in deciduous oaks. Our results support a tradeoff between the ability to tolerate drought and the capacity to cope with unpredictable changes in the environment through increased intraspecific trait variation, which may have implications on tree performance in the face of increased extreme events.

Temporal changes in size inequality and stand growth partitioning between tree sizes under various thinning intensities in subtropical Cunninghamia lanceolata plantations

Stand structural complexity and growth partitioning between different tree sizes influence trees competition and resource use efficiency, and thus are closely linked to stand productivity. The main aim of this study was to examine how the stand structure complexity (Gini coefficient Gini) and size-related partitioning of stand growth (growth dominance coefficient GDC and size-growth relationship SGR) temporally changed after different thinning intensities in Chinese fir (Cunninghamia lanceolata) forests, Southeastern China. We analyzed the data of 6 repeated measurements over a nearly 10-year period from a forest thinning experiment with progressively increasing intensity (0, 20%, 25%, 33% and 50% reduction of stand density by selection logging of releasing target trees) and assessed the effects of different thinning intensities using generalized mixed effect model. The thinning intensity of 0 was taken as a control group to identify the stand changes in unthinned stands over time. Size heterogeneity and the relative contribution of larger trees to total stand growth tended to increase as forest grew without thinning management. While the increases in Gini and SGR (excluding between 0 and 0.5) overall negatively influenced the average annual basal area increment of the remaining trees (BAI). Gini in thinned stands decreased during the short term (two years or more) after thinning and the heavy thinning had lower Gini than other treatments several years (eight years or less) after thinning. GDC reduced greater with increasing thinning intensity, and thinning had a significant negative effect on Gini and SGR and a positive effect on BAI. The thinning impacts on BAI increased with the thinning intensity, while the effect magnitudes of different thinning intensities on Gini and SGR were: T50 < T20 < T25 < T33. Overall, thinning increased the stand growth partitioning of small trees, contributing to a uniform stand structure. However, the changes in stand structural complexity and the partitioning of stand growth were related to both thinning intensity and post-thinning time, particularly to thinning intensity. The results provided some implications for designing the intensity and timing of thinning, as well as for determining the size classes of removed trees for different management goals.

Continuous cover forestry: Which sampling method should be used to ensure sustainable management?

The transformation of even-aged forests into continuous cover forests to improve resilience and to promote biodiversity in Central Europe necessitates a re-evaluation of forest sampling designs. This study examines the precision and accuracy of two widely used terrestrial sampling methods, namely Angle Count Sampling and Fixed Area Plot Sampling. By simulating multiple samples in typical well-established Plenter forests in Switzerland, we analyse the error components and variabilities of the different methods for three key stand parameters: stem number per hectare, basal area per hectare and annual basal area increment per hectare. Our results suggest that, depending on the parameter of interest, the standard deviation, and the acceptable margin of error, the number of needed sample plots exhibits a large variation. Since the key stand parameters for ensuring sustainability in Plenter forests are the stem number by diameter at breast height class and the basal area increment, our results suggest that a Fixed Area Plot with 300 m² circles is the best compromise between cost efficiency and precision for the sampled Plenter forest data. Alternatively, a Fixed Area Plot of 500 m² or a combined Angle Count Sampling method with a basal area factor of 4 m²/ha and a 200 m² Fixed Area Plot may be considered.

Size of sampling units aproppriate for management level forest inventory in Eastern Amazon, Brazil

This study aimed to indicate the ideal sample size for continuous forest inventories in the tropical forest in Amapá. Data were obtained from a monitoring inventory started in 2010 and completed in 2016, in five permanent sampling units of 100m x 100m with an inclusion level of DBH ≥ 10cm. Randomly allocated sample subunits with five different dimensions ranging from 400 m2 to 1600 m2 were simulated within these units. The measurement times of each sampling unit, from the first to the last three, were timed. Dimensions were analyzed for their accuracy and relative efficiency. Given the above and depending on the purpose of the inventory, the standard sampling unit of 1 ha (100 m x 100 m) is recommended for the inventory variables. The 20 m x 20 m (400 m2) square sampling unit was the most suitable for monitoring growth variables (annual increment in diameter, basal area, and volume), indicating that these sampling units for continuous inventories can become an essential alternative for use in monitoring inventory in the region.

Climate change-related growth improvements in a wide niche-breadth tree species across contrasting environments.

The vulnerability and responsiveness of forests to drought are immensely variable across biomes. Intraspecific tree responses to drought in species with wide niche breadths that grow across contrasting climatically environments might provide key information regarding forest resistance and changes in species distribution under climate change. Using a species with an exceptionally wide niche breath, we tested the hypothesis that tree populations thriving in dry environments are more resistant to drought than those growing in moist locations. We determined temporal trends in tree radial growth of 12 tree populations of Nothofagus antarctica (Nothofagaceae) located across a sharp precipitation gradient (annual precipitation of 500-2000 mm) in Chile and Argentina. Using dendrochronological methods, we fitted generalized additive mixed-effect models to predict the annual basal area increment as a function of year and dryness (De Martonne aridity index). We also measured carbon and oxygen isotope signals (and estimated intrinsic water-use efficiency) to provide potential physiological causes for tree growth responses to drought. We found unexpected improvements in growth during 1980-1998 in moist sites, while growth responses in dry sites were mixed. All populations, independent of site moisture, showed an increase in their intrinsic water-use efficiency in recent decades, a tendency that seemed to be explained by an increase in the photosynthetic rate instead of drought-induced stomatal closure, given that δ18O did not change with time. The absence of drought-induced negative effects on tree growth in a tree species with a wide niche breadth is promising because it might relate to the causal mechanisms tree species possess to face ongoing drought events. We suggest that the drought resistance of N. antarctica might be attributable to its low stature and relatively low growth rate.

Fire-caused mortality within tree neighborhoods increases growth of Pinus lambertiana more than growth of Abies concolor

Global increases in large-tree mortality and multiple disturbances such as fire, drought, and pestilence increase the importance of understanding how large-tree growth responds to changes in competitive neighborhoods. We used 34,175 spatially mapped trees within 25.6 ha that burned at low to moderate severity in 2013 to investigate how changes to tree neighborhoods affected growth of 3,652 surviving trees of two species, Abies concolor (white fir) and Pinus lambertiana (sugar pine). Using diameter measurements taken in 2014 and 2019, we estimated post-fire radial growth of each surviving tree. We modeled annual basal area increment as a function of diameter and extracted residuals to yield relative growth rate (RGR). We used a multi-model approach and AIC to compare the species-specific effects on RGR of all post-fire tree mortality within a neighborhood radius versus mortality broken down by cause. To represent density reduction around each surviving tree, we computed crowding metrics for neighborhood radii up to 20 m for all tree mortality combined and for each mortality cause. The best-fit model included terms for density reduction within 10 m of the surviving tree due to 1) fire or mechanical damage and 2) bark beetle mortality, as well as their interactions with species and diameter. Density reduction due to fire or mechanical damage had a positive effect on RGR that was nearly twice as strong for P. lambertiana as A. concolor. Tree diameter interacted with density reduction for just P. lambertiana. Small-diameter (10-cm) P. lambertiana had a fourfold larger increase in basal area increment than large-diameter (60-cm) P. lambertiana as density reduction due to fire or mechanical damage ranged from 0 to 100 %. The strong growth response of medium-diameter P. lambertiana to density reductions could eventually increase the abundance of large-diameter (≥60 cm) P. lambertiana. In conjunction with mortality rates, which were lower for large-diameter P. lambertiana (0.97 %) than A. concolor (3.31 %), this could increase the relative abundance of large-diameter P. lambertiana from 51.2 % in 2020 to 62.6 % by 2050. Changes to competitive neighborhoods can have species-specific effects on large-tree growth, an important consideration for long-term management of fire-prone forests.

The impact of the Asian chestnut gall wasp (Dryocosmus kuriphilus) on chestnut tree growth may be mediated by site resources

IntroductionThe Asian chestnut gall wasp (Dryocosmus kuriphilus) is a major pest of chestnut trees worldwide, seriously affecting chestnut cultivation. Information concerning the effects of gall wasp attack on diameter growth of chestnut trees is currently scarce and limited to coppice stands and to use of the growth of a non-target control species (unaffected by the pest) for reference purposes. The effects of the pest on widely-spaced plantations (grown at a much lower density than chestnut coppices) and the use of explicitly-observed annual infestation rate data remain to be explored.MethodsIn the present study, we analyzed the impact of the chestnut gall wasp on the diameter growth of chestnut trees, using data from 16 experimental plots established in widely-spaced plantations located in good quality sites. Two of the plots are in plantations where a susceptible hybrid chestnut clone and a chestnut clone resistant to the gall wasp coexist, whereas the remaining 14 plots are in Castanea sativa plantations where the level of gall wasp infestation varies across trees and years. The plots were surveyed to determine the diameter growth of the trees and the level of infestation during 5 years (2017–2021).ResultsThe infestation level corresponding to the theoretical damage threshold was surpassed inmost plots during the study period. Nevertheless, there were no differences in the growth of attacked and unaffected plants in the two plots planted with hybrid clones with contrasting susceptibility to the gall wasp. The attack had a modest effect in C. sativa plots, with a mean reduction in annual basal area increment of 9.9%.DiscussionThese findings apparently contradict previous reports of a marked reduction in radial growth of chestnut coppice trees due to gall wasp attack. The difference in findings may be related to increased compensation for herbivory with increasing levels of resources (especially light) in the plantations under study, which were less dense than previously studied stands. The study outcomes add to existing knowledge on the impact of chestnut gall wasp on wood formation and may have implications regarding planting site recommendations and subsequent stand management.

Urban CO2 imprints on carbon isotope and growth of Chinese pine in the Beijing metropolitan region

Rapid urbanization has occurred globally and resulted in increasing CO2 emissions from urban areas. Compared to natural forests, urban forests are subject to higher atmospheric CO2 concentrations in view of strong urban-periurban-rural gradients of CO2 emissions. However, relevant insights in the CO2-associated urban imprints on the physiology and growth of regional forests remain lacking. By sampling foliage and tree rings of Chinese pine (Pinus tabuliformis) in the Beijing metropolitan region, China, we explored whether and how urban CO2 emissions affect stable carbon isotope ratios (δ13C) and tree growth spatially and/or temporally. The results indicate a significant decrease in foliar δ13C values towards the urban center and this pattern was mainly explained by the urban-periurban-rural gradients of CO2 emissions as surrogated by trunk road density. Tree-ring δ13C values showed a significant decrease over last four decades and this trend was mainly explained by rising levels of CO2 and secondarily mediated by the variations of aridity index during growing season. Moreover, annual basal area increment of Chinese pine was significantly accelerated during last two decades, being mainly driven by increasing CO2 emissions and secondarily mediated by climate variations. These findings reveal significant CO2-associated imprints of urbanization on plant growth and provide empirical evidences of significant CO2-induced alteration of carbon cycles in urban forests.

Land-use change and windstorms legacies drove the recolonization dynamics of laurel forests in Tenerife, Canary islands

Laurel forests are quite relevant for biodiversity conservation and are among the island ecosystems most severely damaged by human activities. In the past, Canary laurel forests have been greatly altered by logging, livestock and agriculture. The remains of laurel forests are currently protected in the Canary Islands (Spain). However, we miss basic information needed for their restoration and adaptive management, such as tree longevity, growth potential and responsiveness to natural and anthropogenic disturbances. Using dendrochronological methods, we studied how forest dynamic is related to land-use change and windstorms in two well-preserved laurel forests on Tenerife Island. Wood cores were collected from over 80 trees per stand at three stands per forest. We used ring-width series to estimate tree ages and calculate annual basal area increments (BAI), cumulative diameter increases, and changes indicative of released and suppressed growth. Twelve tree species were found in all stands, with Laurus novocanariensis, Ilex canariensis and Morella faya being the most common species. Although some individuals were over 100 years old, 61.8%–88.9% of the trees per stand established between 1940 and 1970, coinciding with a post-war period of land abandonment, rural exodus and the onset of a tourism economy. Some trees have shown growth rates larger than 1 ​cm diameter per year and most species have had increasing BAI trends over the past decades. Strong growth releases occurred after windstorms at both sites, but the effects of windstorms were site-dependent, with the 1958 storm affecting mainly the eastern tip of the island (Anaga massif) and the 1991 storm the western tip (Teno massif). Given the great ability of laurel forest trees to establish after land use cessation and to increase growth after local disturbances such as windstorms, passive restoration may be sufficient to regenerate this habitat in currently degraded areas.

Tree diversity effects on productivity depend on mycorrhizae and life strategies in a temperate forest experiment.

Tree species are known to predominantly interact either with arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. However, there is a knowledge gap regarding whether these mycorrhizae differently influence biodiversity-ecosystem functioning (BEF) relationships and whether a combination of both can increase community productivity. In 2015, we established a tree-diversity experiment by growing tree communities with varying species richness levels (one, two, or four species) and either with AM or EM tree species or a combination of both. We investigated basal area and annual basal area increment from 2015 to 2020 as proxies for community productivity. We found significant positive relationships between tree species richness and community productivity, which strengthened over time. Further, AM and EM tree species differently influenced productivity; however, there was no overyielding when AM and EM trees grew together. EM tree communities were characterized by low productivity in the beginning but an increase of increment over time and showed overall strong biodiversity effects. For AM tree communities the opposite was true. Although young trees did not benefit from the presence of the other mycorrhizal type, dissimilar mechanisms underlying BEF relationships in AM and EM trees indicate that maximizing tree and mycorrhizal diversity may increase ecosystem functioning in the long run.

Does natural root grafting make trees better competitors?

Natural root grafts (anastomoses) are morphological unions formed between roots of different trees. Common root systems allow translocation of water, nutrients and photosynthesis products between grafted trees, affecting their growth and their physiology. As carbohydrates are redistributed among grafted trees, the formation of a common root system could reduce the negative effect of intraspecific competition for light or soil resources within stands. The aim of this study was to investigate the role of root grafting on intraspecific competition and growth of balsam fir Abies balsamea. We studied inter‐tree relationships in three natural balsam fir stands of the boreal forest of Quebec (Canada) that contained an average 36% of grafted trees. At each stand, ring width and basal area of trees were measured using dendrochronology techniques. We used mixed linear models to test the effect of root grafting and intraspecific competition on annual basal area increment of trees. Trees before grafting had higher growth rates than trees once grafted. Thus, root grafting did not improve tree growth. Growth of grafted trees was more negatively affected by intraspecific competition than growth of non‐grafted trees. Thus, grafted trees cannot be considered as better competitors than non‐grafted trees. Under high intraspecific competition, growth of larger grafted trees was less affected than that of smaller trees suggesting that they were able to divert resources at their advantage within a union. Our study demonstrated that grafted trees acted on each other's growth and provides support for the idea that grafted trees respond to competition for resources more as a community rather than as individual trees.

The variation and trends of nitrogen cycling and nitrogen isotope composition in tree rings: the potential for fingerprinting climate extremes and bushfires

PurposeClimate extremes, such as droughts and floods, have become intensified and more frequent due to intensifying climate change. Increased atmospheric carbon dioxide (CO2) and warming-induced water limitation, as well as climate extremes, may alter carbon (C) and nitrogen (N) cycling in forest ecosystems. This provides a brief review of stable nitrogen isotopic composition (δ15N) in tree ring in relation to climate extremes and bushfires in context of N availability and losses in forest ecosystems.Material and methodsTree rings were extracted from four Pinus sylvestris and four Larix gmelinii sample trees, located in a boreal plantation forest of Mohe City, Heilongjiang Province, China. Tree rings were measured to obtain mean annual basal area increment (BAI), while tree ring δ15N and total N concentrations were measured on mass spectrometer at 3-year intervals. The tree ring δ15N data were related to possible climate extremes and bushfires. A brief review of the relevant literature was also undertaken to support our preliminary research findings.Results and discussionGlobally, increasing atmospheric CO2 concentration and water limitations have led to a warmer-drier climate. This has also been associated with increases of climate extremes such as drought and floods as well as bushfires. These extremes have been recorded with detrimental effects on plant and soil structures within forest ecosystems and play an important role in regulating N availability and losses in forest ecosystems. Studies of N deposition within forest ecosystems using soil and plant δ15N also showed that N losses under various climate extremes can occur through direct changes in N cycling, such as increasing soil nitrification and denitrification or leaching. It is highlighted that tree rings δ15N has the potential to fingerprint the intensity and frequency of climate extremes and bushfires in the forest ecosystems, but more such tree ring δ15N research needs to be done in diversified forest ecosystems to confirm the potential of using tree ring δ15N for quantifying the frequency and intensity of climate extremes and bushfires at both regional and global scale.ConclusionThe variation and trend of δ15N in the soil–plant-climate systems are closely linked to the N cycling in forest ecosystems, and tree ring δ15N has the great potential to fingerprint both intensity and frequency of climate extremes such as drought and floods as well as bushfires.

Half-a-century effects of a slow-release nitrogen fertilizer, ureaformaldehyde, on stand growth and soil processes in a Scots pine stand

Slow-release nitrogen fertilizers have received little attention as alternatives to conventional fast-release fertilizers in N-limited boreal forests. Slow-release fertilizers better match the rate at which trees can uptake nutrients from the soil solution and are less likely to be vulnerable to losses to the environment. Ureaformaldehyde is a polymer that is synthesized from formaldehyde and urea and mainly used as a nitrogen fertilizer in lawns and greenhouse cultivations. Our goal was to assess ureaformaldehyde (UF) as a forest fertilizer. We aimed to determine its long-term effects on tree ring widths and stand basal area growth and how the effects differ from those of a conventional fast-release N fertilizer, ammonium nitrate (AN). We also attempted to determine whether the fertilizer additions changed soil organic matter properties in the long term. The study site was an unfertile Scots pine (Pinus sylvestris L.) stand with study plots with both fertilizer treatments that were performed 47 years ago and unfertilized control plots. As expected, AN addition resulted in a sharp increase in tree ring widths and the annual basal area increment that lasted for approximately seven years. UF addition caused a slower increase that lasted much longer, approximately 17 years. In addition, the UF addition showed indications that it slightly enhanced the growth even during the last decade. Our results also suggested that different fertilization treatments resulted in differences in tree size distribution. After almost a half century, some signs of UF-induced effects were still visible in soil organic matter; for instance, the humus layer in the UF treatment had a lower C-to-N ratio by 7 units than that in the humus layer of the AN treatment. In conclusion, slow-release ureaformaldehyde has a considerably longer effect on tree growth than conventional ammonium-nitrate fertilizer and, after almost a half century, there were signs that it still increased nitrogen availability for trees.

Altitude and community traits explain rain forest stand dynamics over a 2370‐m altitudinal gradient in Costa Rica

AbstractStand dynamic rates in Earth's vitally important tropical mountain rain forests are a central component of the response of these forests to global change, but their relationships to environmental gradients are poorly understood. We worked in mature forests on a 440–2810 m asl altitudinal gradient on Costa Rica's Talamanca Cordillera, making five censuses of 29 0.25‐ha permanent sample plots during 2012–2019. We determined mortality and recruitment rates, as well as basal area (G) increments, for individuals ≥10 cm diameter at breast height. Our main hypothesis was that stand dynamic rates decrease with altitude (therefore temperature); we also tested the hypotheses that rates increase with plot community‐weighted mean specific leaf area (CWM SLA) and decrease with CWM wood specific gravity (WSG). We developed regressions using generalized additive models to test our hypotheses. Mortality and recruitment rates decreased with altitude in line with our main hypothesis, though the strongly non‐linear mortality trend may be driven by extreme weather and temperature. Also, the best model for recruitment rates included plot CWM SLA with a negative relationship. Gross basal area increment ∆Ggross, the annual basal area increment of trees that survived the study period, had a hump‐shaped relationship to altitude, possibly related to the low CWM WSG of mid‐altitude forests. ∆Ggross was indeed negatively related to CWM WSG. However, net basal area growth (∆Gnet, the annualized difference between initial and final plot basal areas) was positively related to altitude due to low mortality in montane forests, in a model with CWM WSG with a negative relationship. ∆Gnet was negative in nine of the 29 plots at &lt;1500 m asl. Patterns of rain forest stand dynamics on this long altitudinal gradient go beyond a direct response to temperature, and further work is required to improve scenarios of forest response to climate change. CWM traits should be measured to improve understanding. The effects of storms and lightning on low‐ and middle‐altitude forest and the potentially high resilience of montane Fagaceae‐dominated forests require attention. Diversity, not generality, should be expected on comparing tropical forest altitudinal transects.

Influence of Neighborhood Competition on Douglas-Fir Growth Is Not Altered by Local Environmental Conditions and Climate

Abstract To evaluate impacts of competitive conditions in tree neighborhoods on growth responses as influenced by moisture availability and local environmental conditions, we sampled 102 codominant 40- to 70-year-old coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) in regions with relatively high and low moisture availability. We quantified local environmental conditions (topographic position index, heat load, and soil depth), and the annual basal area increment and climate moisture deficits during two growth periods: a five-year period prior to commercial thinning and years six to 10 after thinning. In both regions and growth periods, tree growth was higher for trees growing in local neighborhoods with lower competition. The density/growth relationships differed by region and by growth period in the moist regions, but they were not influenced by climate moisture deficit. Furthermore, including topographic position index, heat load, or soil depth did not improve model support. Our results highlight the importance of managing local competition and indicate that environmental factors such as soil depth, heat load, and topography may be less likely to warrant consideration when developing thinning prescriptions. This could allow foresters to accommodate other ecosystem services when designing density management treatments, at least within typical growing conditions.

Using crown characterisation variables as indicators of the vigour, competition and growth of Brazilian pine

Crown variables are used in growth and production models to increase the accuracy of estimates. These variables are costly and difficult to measure, mainly in dense native forests such as mixed ombrophilous forests (MOF), where Araucaria angustifolia is the predominant species. Thus, this study aimed to evaluate the effect of qualitative and quantitative variables to describe the vigour of the crown, competition and growth of A. angustifolia in Southern Brazil MOF. We selected trees in the MOF area and measured circumference at breast height (CBH) and total height (h). For the crowns, a ranking of values was established in the variables: Crown Shape (CS), Vertical crown Shape (VS), Distance between Branches (DB), Sociological Position (SP), percentage of Green Leaves (GL) and Crown Size (CZ). Periodic Annual Increment in basal area (PAIg) and a Competition Index (CI) were calculated. We used principal component analysis (PCA) and Hierarchical Cluster Analysis (HCA) to describe and classify the sampled trees. Two groups were generated: i) dominant and codominant trees, with higher growth, better vigour and better crown quality; and ii) suppressed trees with low vigour, consequently low increment and worse crown quality. The CI, when based only on diameter information, was inadequate to describe the competitive status of the trees, so information about crowns was necessary. Qualitative crowns variables are important to classify the vigour, current level of competition and to understand the different trends in A. angustifolia growth.