Aboveground Biomass Increment Research Articles

No effect of invasive tree species on aboveground biomass increments of oaks and pines in temperate forests

Prunus serotina and Robinia pseudoacacia are the most widespread invasive trees in Central Europe. In addition, according to climate models, decreased growth of many economically and ecologically important native trees will likely be observed in the future. We aimed to assess the impact of these two neophytes, which differ in the biomass range and nitrogen-fixing abilities observed in Central European conditions, on the relative aboveground biomass increments of native oaks Quercus robur and Q. petraea and Scots pine Pinus sylvestris. We aimed to increase our understanding of the relationship between facilitation and competition between woody alien species and overstory native trees. We established 72 circular plots (0.05 ha) in two different forest habitat types and stands varying in age in western Poland. We chose plots with different abundances of the studied neophytes to determine how effects scaled along the quantitative invasion gradient. Furthermore, we collected growth cores of the studied native species, and we calculated aboveground biomass increments at the tree and stand levels. Then, we used generalized linear mixed-effects models to assess the impact of invasive species abundances on relative aboveground biomass increments of native tree species. We did not find a biologically or statistically significant impact of invasive R. pseudoacacia or P. serotina on the relative aboveground biomass increments of native oaks and pines along the quantitative gradient of invader biomass or on the proportion of total stand biomass accounted for by invaders. The neophytes did not act as native tree growth stimulators but also did not compete with them for resources, which would escalate the negative impact of climate change on pines and oaks. The neophytes should not significantly modify the carbon sequestration capacity of the native species. Our work combines elements of the per capita effect of invasion with research on mixed forest management.

Inter- and intra-year forest change detection and monitoring of aboveground biomass dynamics using Sentinel-2 and Landsat

National aboveground forest biomass products enable monitoring of biomass dynamics in a consistent and repeatable manner to inform carbon accounting and sustainable forest management activities. The availability of images of the Earth's surface from a combination of Landsat and Sentinel-2A and -2B provides an opportunity and capability to track intra-year biomass dynamics availing upon a twice weekly acquisition opportunity. We developed an algorithm that leverages these spatially and spectrally compatible data sources, called Tracking Intra- and Inter-year Change (TIIC), to monitor forest change across Canada's forested ecozones (>650Mha) in near-real time. Combining the stand-replacing change information from TIIC with spatially explicit maps of aboveground biomass (AGB), we demonstrate how intra-annual and inter-annual AGB dynamics, including losses due to stand-replacing disturbances and gains from vegetation growth, can be quantified temporally and spatially. Using independent validation data, our results for the focus year 2019 indicate that TIIC, by analysing images from May 30 to September 1, can accurately detect stand-replacing disturbances across Canada's forested ecozones with an overall accuracy of 99% and correctly attribute the type of change (i.e., wildfire or mechanical removal, the latter of which includes timber harvesting) with an overall accuracy of 99%. From an initial producer's accuracy of 23% for the changed class, accuracy increases incrementally as additional images are added throughout the growing season. attaining a producer's accuracy of 98% by the end of the analysis period. Intra-year change information complements information on long-term trends derived from annual time series monitoring over several decades. Our analysis of AGB dynamics indicated that in every ecozone, widespread small positive AGB increments yielded overall AGB gains that were greater than the sum of the large, punctual AGB losses resulting from stand-replacing disturbances. Overall in 2019, forest AGB increased across Canada's forested ecozones by 2.54%. Temporally, 80% of AGB losses stemming from mechanical removal occurred over the winter and are as such concentrated at the beginning of the growing season. In contrast, AGB losses linked to fires happen more stochastically throughout the growing season and occupy a greater area. By way of disturbance type, 36% of 2019 AGB loss was attributed to mechanical removal, and 64% was attributed to wildfire. Following the approach demonstrated herein, AGB changes can be tracked at a temporal frequency informative of forest management practices and ecological processes on the landscape, thereby refining our understanding of AGB dynamics.

Forest resilience research using remote sensing and GIS – A systematic literature review

Forest resilience assessment is increasingly important given the current global environmental change. However, attributes and indicators to quantify forest resilience still need to be explored. Remote sensing (RS) and Geographical Information System (GIS) techniques are widely applied for forest resilience modeling. A bibliometric analysis was conducted to obtain insights concerning methods for quantifying forest resilience using RS/GIS. VosViewer and Bibliometrix R software were applied to analyze 117 articles from the Web of Science global database covering a period of 2011-2021. Using inclusion-exclusion criteria, 31 studies were examined, covering local, regional, and transnational ecosystem types. Satellite devices were used in 28 studies, whilst GIS dataset frameworks were used in the remaining studies. Multiple satellites and sensors were preferable to maximize results for modeling forest resilience. To estimate resilience, ecological attributes (above-ground biomass, tree-ring, and basal area increments) and remote-sensing derived indicators (vegetation indices, forest cover changes, deforestation rates, and forest productivity) were analyzed using conventional statistical tests or machine learning techniques. Studies combined experiments, observations, and process-based models demonstrated better results. Scale and resolution, indicator uncertainty, and data availability were among the constraints reported using RS/GIS. Therefore, a standardized framework for forest resilience assessment incorporating field observation with RS/GIS is needed.

Tree aboveground biomass increment and mortality in temperate mountain forests: Tracing dynamic changes along 25-year monitoring period

Tree aboveground biomass and its increment are sensitive forest and landscape dynamics indicators. Although various methods can measure forest biomass dynamics, only in situ, direct monitoring can substantially reduce the uncertainty related to unknown or uncontrolled factors. Within the present study, we aimed to isolate drivers of tree biomass increment, mortality, and recruitment in the Gorce National Park (GNP), Outer Western Carpathians, Poland. We used a unique database consisting of information collected between 1992 and 2017 (in 5-year intervals) within 389 permanent monitoring plots regularly distributed in the GNP area. This allowed us to calculate tree biomass and its increments and model them using a set of explanatory variables: proportion of particular tree species, mean temperature of the coldest quarter (bio11), mean precipitation of the warmest quarter (bio18), elevation, topographic wetness index (TWI), stand basal area (BA), diameter heterogeneity expressed by the coefficient of variation (DBH CV), and conservation regime. We applied generalized linear mixed-effects models (GLMMs), assuming the beta distribution of response variables, i.e. biomass proportions of increment, recruitment, and mortality of three main tree species: Norway spruce Picea abies (L.) Karst, European beech Fagus sylvatica L., and silver fir Abies alba Mill.In a large part of the GNP area, tree biomass increased. In the central and southern parts of the park, tree mortality was higher than in other parts, especially between 2002 and 2007, due to bark beetle outbreaks and intense wind damage. Stand dynamics of all species depended mainly on species proportion in stand biomass. The increment of Abies alba increased with TWI but decreased with BA and DBH CV. Recruitment decreased with BA and slope but increased with TWI and DBH CV, while mortality decreased with DBH CV and TWI. For Fagus sylvatica, increment increased with TWI but decreased with BA, elevation, and bio18, while recruitment decreased with BA and increased with TWI. Mortality decreased with DBH CV, bio11, and TWI but increased with BA. Picea abies increment increased with elevation but decreased with BA, slope, and DBH CV and weakly increased with bio11. Recruitment increased with TWI but decreased with BA and DBH CV, while mortality decreased with DBH CV, BA, and bio18. Water retention at the plot level, approximated by TWI, decreased mortality and increased recruitment of the studied species. Therefore, it can serve as an indicator of suitable microsites for their persistence. In addition, the increment was lower in strictly protected forests, while mortality was higher. Our study provided quantitative evidence of how climate, geomorphology, and forest stand characteristics modify stand dynamics.

Identification of photosynthetic parameters for superior yield of two super hybrid rice varieties: A cross-scale study from leaf to canopy.

Enhancing photosynthetic capacity is widely accepted as critical to advancing crop yield. Therefore, identifying photosynthetic parameters positively related to biomass accumulation in elite cultivars is the major focus of current rice research. In this work, we assessed leaf photosynthetic performance, canopy photosynthesis, and yield attributes of super hybrid rice cultivars Y-liangyou 3218 (YLY3218) and Y-liangyou 5867 (YLY5867) at tillering stage and flowering stage, using inbred super rice cultivars Zhendao11(ZD11) and Nanjing 9108 (NJ9108) as control. A diurnal canopy photosynthesis model was applied to estimate the influence of key environmental factors, canopy attributes, and canopy nitrogen status on daily aboveground biomass increment (AMDAY). Results showed that primarily the light-saturated photosynthetic rate at tillering stage contributed to the advancing yield and biomass of super hybrid rice in comparison to inbred super rice, and the light-saturated photosynthetic rate between them was similar at flowering stage. At tillering stage, the higher CO2 diffusion capacity, together with higher biochemical capacity (i.e., maximum carboxylation rate of Rubisco, maximum electron transport rate (J max), and triose phosphate utilization rate) favored leaf photosynthesis of super hybrid rice. Similarly, AMDAY in super hybrid rice was higher than inbred super rice at tillering stage, and comparable at flowering stage partially due to increased canopy nitrogen concentration (SLNave) of inbred super rice. At tillering stage, model simulation revealed that replacement of J max and g m in inbred super rice by super hybrid rice always had a positive effect on AMDAY, and the averaged AMDAY increment was 5.7% and 3.4%, respectively. Simultaneously, the 20% enhancement of total canopy nitrogen concentration through the improvement of SLNave (TNC-SLNave) resulted in the highest AMDAY across cultivars, with an average increase of 11.2%. In conclusion, the advancing yield performance of YLY3218 and YLY5867 was due to the higher J max and g m at tillering stage, and TCN-SLNave is a promising target for future super rice breeding programs.

Allometric relationships between above-ground biomass increment and stand characteristics for crimean pine in Taşköprü, Turkey

Background: Biomass increment, one of the main components of net primary production (NPP) in forest ecosystems, plays an important role as well as total biomass in the global carbon cycle. In this study, the changes of increments of the above-ground total, stem and branch biomasses depending on stand characteristics (i.e., stand age, stand density, and site index) were investigated, and these relations were modeled for Crimean pine (Pinus nigra J.F.Arnold subsp. pallasiana (Lamb.) Holmboe) stands in Taşköprü region of Türkiye. Data were obtained from 109 sample trees within 74 sample plots representing the wide range of possible stand characteristics. Results: The equations developed for above-ground total, stem and branch biomass increments have quite high coefficients of determination (R 2 =0.784, 0.684 and 0.780, respectively), whereas low root mean square errors (RMSE=0.749, 0.692 and 0.116, respectively). The results indicated that the biomass increment estimates from the allometric equations developed were decreasing with stand age and increasing with stand density and site index and also stand density is the strongest stand characteristic on biomass increment. Conclusion: The estimates are also consistent with the growth patterns, so the equations can be used for biomass increment estimations and also for carbon storage and NPP projections for Crimean pine stands of the region.

Wall-to-Wall Mapping of Forest Biomass and Wood Volume Increment in Italy

Several political initiatives aim to achieve net-zero emissions by the middle of the twenty-first century. In this context, forests are crucial as a carbon sink to store unavoidable emissions. Assessing the carbon sequestration potential of forest ecosystems is pivotal to the availability of accurate forest variable estimates for supporting international reporting and appropriate forest management strategies. Spatially explicit estimates are even more important for Mediterranean countries such as Italy, where the capacity of forests to act as sinks is decreasing due to climate change. This study aimed to develop a spatial approach to obtain high-resolution maps of Italian forest above-ground biomass (ITA-BIO) and current annual volume increment (ITA-CAI), based on remotely sensed and meteorological data. The ITA-BIO estimates were compared with those obtained with two available biomass maps developed in the framework of two international projects (i.e., the Joint Research Center and the European Space Agency biomass maps, namely, JRC-BIO and ESA-BIO). The estimates from ITA-BIO, JRC-BIO, ESA-BIO, and ITA-CAI were compared with the 2nd Italian NFI (INFC) official estimates at regional level (NUT2). The estimates from ITA-BIO are in good agreement with the INFC estimates (R2 = 0.95, mean difference = 3.8 t ha−1), while for JRC-BIO and ESA-BIO, the estimates show R2 of 0.90 and 0.70, respectively, and mean differences of 13.5 and of 21.8 t ha−1 with respect to the INFC estimates. ITA-CAI estimates are also in good agreement with the INFC estimates (R2 = 0.93), even if they tend to be slightly biased. The produced maps are hosted on a web-based forest resources management Decision Support System developed under the project AGRIDIGIT (ForestView) and represent a key element in supporting the new Green Deal in Italy, the European Forest Strategy 2030 and the Italian Forest Strategy.

Evaluation of growth responses of six gymnosperm species under long-term excessive irrigation and traits determining species resistance to waterlogging

In the era of extreme weather events, plant resistance to excessive water should be considered for plantations in frequently flooded areas to ensure their maximum survival and conservation of natural habitats. Therefore, we quantified the resistance to excessive irrigation (REI) in seedlings of six conifer species on the basis of their morphological, physiological, and biochemical traits. Two different irrigation regimes, natural precipitation as a control treatment and additional irrigation by sprinklers (30.89 ± 2.80% above natural precipitation) as excessive irrigation, were applied for three consecutive years. The changes in the morphological, physiological, and biochemical traits under long-term excessive irrigation were species-specific. There were three distinct responses in biomass accumulation: drought-susceptible Chamaecyparis obtusa and Abies holophylla significantly increased their aboveground and underground biomass and showed a strong REI; Pinus thunbergii and P. densiflora, both resistant to drought, significantly decreased their aboveground and underground biomass and showed a weak REI. Larix kaempferi and Pinus koraiensis showed a medium REI with only aboveground biomass increment in the former and no biomass change in the latter. Plant biomass responses corresponded well with the changes in morphological, physiological, and biochemical traits. Biomass augmentation resulted from an increase in leaf size, leaf mass per area (LMA), maximum photosynthesis rate, and leaf water potential. Flavonoids, LMA, and stomatal conductance are the most important traits to assess species REI. This study elucidates plant responses to excess water and traits that drive their tolerance. The findings will help in the selection of species for flood-tolerant afforestation programs and establishment of sustainable forests in regions with increased frequency and severity of excessive rainfall.

Aboveground biomass increments over 26\xa0years (1993\u20132019) in an old-growth cool-temperate forest in northern Japan

Assessing long-term changes in the biomass of old-growth forests with consideration of climate effects is essential for understanding forest ecosystem functions under a changing climate. Long-term biomass changes are the result of accumulated short-term changes, which can be affected by endogenous processes such as gap filling in small-scale canopy openings. Here, we used 26 years (1993–2019) of repeated tree census data in an old-growth, cool-temperate, mixed deciduous forest that contains three topographic units (riparian, denuded slope, and terrace) in northern Japan to document decadal changes in aboveground biomass (AGB) and their processes in relation to endogenous processes and climatic factors. AGB increased steadily over the 26 years in all topographic units, but different tree species contributed to the increase among the topographic units. AGB gain within each topographic unit exceeded AGB loss via tree mortality in most of the measurement periods despite substantial temporal variation in AGB loss. At the local scale, variations in AGB gain were partially explained by compensating growth of trees around canopy gaps. Climate affected the local-scale AGB gain: the gain was larger in the measurement periods with higher mean air temperature during the current summer but smaller in those with higher mean air temperature during the previous autumn, synchronously in all topographic units. The influences of decadal summer and autumn warming on AGB growth appeared to be counteracting, suggesting that the observed steady AGB increase in KRRF is not fully explained by the warming. Future studies should consider global and regional environmental factors such as elevated CO2 concentrations and nitrogen deposition, and include cool-temperate forests with a broader temperature range to improve our understanding on biomass accumulation in this type of forests under climate change.

Variability in growth-determining hydraulic wood and leaf traits in Melia dubia across a steep water availability gradient in southern India

In India, short-rotation plantations have increasingly been promoted over the last decades in response to altered forest management policy and increased wood demand. Understanding how short-rotation forest species coordinate fast growth with water demand and carbon investment will help improving management decisions.We investigated the intra-specific variability in growth performance, leaf traits, and wood anatomical and derived hydraulic properties in 31 Melia dubia (Meliaceae) plantations along a steep rainfall gradient from 450 to 1,700 mm yr−1, and addressed the role of different irrigation practices and soil nutrient availability.We found water supply and soil nutrient status to have a dominant influence on the aboveground biomass increment (AGBI) of M.dubia. AGBI was higher at irrigated sites with a less negative climatological water balance (i.e. with lower rainfall) and at sites with higher soil phosphorus availability. Stem wood anatomical traits associated with the water transport capacity mirrored the patterns in AGBI. At sites with higher water and soil phosphorus availability, the xylem was composed of larger vessel diameters and lower vessel densities. However, both branch wood anatomical traits and leaf traits including the leaf-to-sapwood area ratio were largely independent of water availability and soil conditions.We conclude that a high stem hydraulic efficiency determined by large xylem vessels is a prerequisite for high aboveground productivity, and that the growth of M. dubia may often be phosphorus-limited. Short-rotation plantations with M.dubia will therefore clearly benefits from continuous irrigation in regions that receive annual precipitations substantially below 1,000 mm yr−1. This highlights the potential to increase yields in this important short-rotation forest species by improving irrigation and fertilization protocols.

Water Availability Controls the Biomass Increment of Melia dubia in South India

Farmland tree cultivation is considered an important option for enhancing wood production. In South India, the native leaf-deciduous tree species Melia dubia is popular for short-rotation plantations. Across a rainfall gradient from 420 to 2170 mm year–1, we studied 186 farmland woodlots between one and nine years in age. The objectives were to identify the main factors controlling aboveground biomass (AGB) and growth rates. A power-law growth model predicts an average stand-level AGB of 93.8 Mg ha–1 for nine-year-old woodlots. The resulting average annual AGB increment over the length of the rotation cycle is 10.4 Mg ha–1 year–1, which falls within the range reported for other tropical tree plantations. When expressing the parameters of the growth model as functions of management, climate and soil variables, it explains 65% of the variance in AGB. The results indicate that water availability is the main driver of the growth of M. dubia. Compared to the effects of water availability, the effects of soil nutrients are 26% to 60% smaller. We conclude that because of its high biomass accumulation rates in farm forestry, M. dubia is a promising candidate for short-rotation plantations in South India and beyond.

Fine root biomass, production, and turnover rate in a temperate deciduous broadleaved forest in the Maoer Mountain, China

Fine roots play an important role in energy flow and substance cycling in forests. How-ever, the estimates of biomass, production and turnover of fine roots remain large uncertainties, and the mechanism underlying local-scale spatial variation in fine roots is still unclear. In a temperate secondary forest in the Maoer Mountain in Northeast China, we investigated the vertical distribution of fine root biomass and necromass at the 0-100 cm profile and the dynamics, production and turnover rate of fine root in 0-20 cm soil layer. The sequential coring (including the Decision Matrix and the Maximum-Minimum formula) and the ingrowth core (3 cm diameter and 5 cm diameter) were compared in estimating production and turnover rate of fine roots. Forest stand variables that might affect fine roots were also explored. The results showed that 76.8% of fine root biomass and 62.9% of necromass concentrated in the 0-20 cm soil layer, and that both decreased exponentially with increa-sing soil depth. The seasonal variation in both fine root biomass and necromass was not significant in 0-20 cm soil layer, which might be related to the negligible snowfall in winter and the extremely high precipitation in summer. There was no significant difference in the results of the estimated fine root production between two diameter ingrowth cores. After log-transformed, fine root production and turnover rate estimated by the Decision Matrix, the Maximum-Minimum formula and ingrowth cores were significantly different among methods. With the increases of soil nutrient concentrations, fine root biomass/fine root necromass ratio significantly increased, fine root necromass significantly decreased, whereas fine root biomass, productivity, and turnover rate were not related to soil nutrient. There was a significant positive correlation between fine root production and aboveground woody biomass increment in the previous-year but not current-year.

The Driving Factors of Subtropical Mature Forest Productivity: Stand Structure Matters

Forest productivity (increment of above-ground biomass) is determined by biodiversity but also by stand structure attributes. However, the relative strengths of these drivers in determining productivity remain controversial in subtropical forests. In this study, we analyzed a tree growth data from 500 plots with in a 20 ha mature subtropical forest in eastern China. We used spatial simultaneous autoregressive error models to examine the effects of diversity variables (species richness, evenness, and composition), stand structural attributes (stand density, tree size range and diversity), environmental factors (topography and soil), and initial above-ground biomass (AGB) on productivity. We also applied structural equation models to quantify the relative importance of diversity, stand structure, environmental factors, and initial AGB in determining forest productivity. Our results showed that stand structure together with diversity and initial AGB governed forest productivity. Tree size diversity (DBH Shannon’s diversity index) had the largest positive effect on forest productivity. These results provide new evidence that structural explanatory variables have greater contributions to productivity for mature subtropical forests, strongly supporting the niche complementarity hypothesis. Our work highlights the importance of tree size diversity in promoting high forest productivity, and suggests that regulating and conserving complexity of forest stand structure should be among the most important goals in subtropical forest management.

Estimation of Net Primary Productivity and Net Annual Assimilation in the Forests of Kumaun Himalaya

Estimation of carbon uptake by the forests is required to measure the carbon flux of a region. In present study, net primary productivity (NPP) and net annual assimilation (NAA) of carbon was estimated in forests of Kumaun Himalaya by integration of field based measurements and information generated using satellite data. Aboveground NPP was estimated by quantification of aboveground biomass increment, root mortality and litterfall. Root mortality value was added to the biomass accumulation of root component to compute the total belowground productivity. Net Annual Assimilation (NAA) was computed as a difference between carbon uptake in NPP and litterfall plus root mortality. NPP values ranged from 5.20 t/ha/yr (degraded sal forest) to 21.38 t/ha/yr (temperate conifer forest). Total estimated values of net annual uptake of carbon and net annual assimilation of carbon in the study area were 748.93 × 10 4 t/yr and 457.27 × 10 4 t/yr, respectively. Estimation of NPP and NAA are useful for further computation of carbon flux to know the status of forest as sink or source of carbon to the atmosphere.

Thinning decreases above-ground biomass increment in central European beech forests but does not change individual tree resistance to climate events

European beech plays a prominent role in the adaptation of European forests to and mitigation of climate change. Forest management may increase the mitigation potential of beech forests by accelerating carbon accumulation in tree biomass, but little is known about the interaction between the rate of biomass expansion in beech and its sensitivity to climate variation or its resistance to extreme drought episodes. A 60-year thinning experiment in beech forests in Central Europe was used to generate tree-ring width series describing past radial growth of dominant, co-dominant and sub-dominant beech trees. Randomisation applied to daily climate data was used to find the period of the year during which climate best explains beech growth. Results show that carbon uptake by above-ground biomass is higher in unmanaged stands and that thinning does not affect beech growth sensitivity to climate. Further, this study shows that average daily temperature amplitude and precipitation in March-July are the best predictors of radial growth in beech at lower-elevation sites. In a key finding, this research shows that site quality and thinning intensity increase tree size, which in turn lowers their resistance to drought. Using forest management to increase the productivity of European beech may thus increase its vulnerability to climate change.

Effects of Wood Hydraulic Properties on Water Use and Productivity of Tropical Rainforest Trees

The efficiency of the water transport system in trees sets physical limits to their productivity and water use. Although the coordination of carbon assimilation and hydraulic functions has long been documented, the mutual inter-relationships between wood anatomy, water use and productivity have not yet been jointly addressed in comprehensive field studies. Based on observational data from 99 Indonesian rainforest tree species from 37 families across 22 plots, we analyzed how wood anatomy and sap flux density relate to tree size and wood density, and tested their combined influence on aboveground biomass increment (ABI) and daily water use (DWU). Results from pairwise correlations were compared to the outcome of a structural equation model (SEM). Across species, we found a strong positive correlation between ABI and DWU. Wood hydraulic anatomy was more closely related to these indicators of plant performance than wood density. According to the SEM, the common effect of average tree size and sap flux density on the average stem increment and water use of a species was sufficient to fully explain the observed correlation between these variables. Notably, after controlling for average size, only a relatively small indirect effect of wood properties on stem increment and water use remained that was mediated by sap flux density, which was significantly higher for species with lighter and hydraulically more efficient wood. We conclude that wood hydraulic traits are mechanistically linked to water use and productivity via their influence on sap flow, but large parts of these commonly observed positive relationships can be attributed to confounding size effects.

Weather as main driver for masting and stem growth variation in stone pine supports compatible timber and nut co-production

Trade-offs between life-history traits are common in plants, and those involving growth and reproduction may be evident during mast years. The nutlike seeds of the stone pine (Pinus pinea L.) stand out among the most appreciated Mediterranean forest products, but its lengthy reproductive cycle makes the identification of masting mechanisms challenging. In the Spanish Northern Plateau, stone pine woodlands are managed as multifunctional forests. Here, we investigated whether timber and nut production are compatible goals in the region. Temporal ring-width and cone yield patterns were characterised in five monospecific stands since 1960. At tree level, we found an equivalent allocation of resources to reproductive and non-reproductive (aboveground) biomass for an average year, but harvest index exceeded 80% during mast years. These large yields, however, did not impose a penalty on aboveground biomass increment. Regionally, we reported a slightly larger magnitude of high-frequency synchronous growth (â = 0.50) compared with that of reproduction (â = 0.42), which is important to contextualise the ecological and economical relevance of masting for the species. By investigating growth-yield interannual dynamics, we found that both traits were strongly and positively correlated, although with a 3-year lag. Therefore, years favouring a high growth coincided with large conelet emergences leading to abundant seed rains to occur three years later, which pointed to key environmental drivers common to both traits. Actually, radial growth and reproduction partly responded to the same climate factors, with climate three years before seed rain being related to masting in a similar way as it was related to ring-width of this same year. Our results provide evidence for the proposed link between masting and growth, and suggest that resources are not diverted from growth during cone filling in stone pine. We conclude that timber production and nut production are perfectly compatible in this species.

Spatial and temporal variation of forest net primary productivity components on contrasting soils in northwestern Amazon

AbstractClimate is a strong determinant of tropical forest productivity; therefore, it is often assumed that Amazonian forest growing on the same local rainfall regime responds similarly to fluctuations in rainfall, independently of soil differences among them. We evaluated intra‐ and inter‐annual variation of net primary productivity (NPP) components, and forest dynamics during 2004–2012 yr in five forests on clay, clay‐loam, sandy‐clay‐loam, sandy‐loam and loamy‐sand soils, and the same local rainfall regime in northwestern Amazonia (Colombia). The questions were as follows: (1) Do NPP components and forest dynamics respond synchronously to temporal rainfall fluctuations? (2) Are the responses between above and belowground components and forest dynamics similar for different forest stands? A slight and complex synchronicity among different NPP components in their response to temporal rainfall fluctuations were found; few plots showed that aboveground biomass (AGB) and stem growth were susceptible to rainfall fluctuations, while belowground components (fine roots) showed correlation with one‐month lagged rainfall. Furthermore, despite that northwestern Amazonia is considered relatively aseasonal, litterfall showed high seasonality in the loam‐soil forest group, as well as the fine‐root mass, particularly during the 2005 drought. Litterfall correlation with rainfall of sandy‐loam terra‐firme forest was time lagged as well as fine‐root mass of the loamy‐sand forest. The correlation between mortality and rainfall was weak, except for the loamy‐sand forest (white‐sand forest, 77%). High mortality rates occurred in the non‐flooded forests for the censuses that included the dry years (2004–2005, 2005–2006). Interestingly, litterfall, AGB increment, and recruitment showed high correlation among forests, particularly within the loam‐soil forest group. Nonetheless, leaf area index (LAI) measured in the most contrasting forests (clay and loamy‐sand soil) was poorly correlated with rainfall, but highly correlated among them, which could be indicating a phenotypic response to the incident radiation in these sites; also, LAI did not reflect the differences in NPP components and their response to rainfall. Overall, the different temporal behavior of NPP components among forests in relation to rainfall fluctuations suggests the important role that soil exerts on the responses of plant species in each site, besides their effect on forest dynamics and community composition.

Assessing biotic and abiotic effects on forest productivity in three temperate forests.

It is well understood that biotic and abiotic variables influence forest productivity. However, in regard to temperate forests, the relative contributions of the aforementioned drivers to biomass demographic processes (i.e., the growth rates of the survivors and recruits) have not received a great deal of attention. Thus, this study focused on the identification of the relative influencing effects of biotic and abiotic variables in the demographic biomass processes of temperate forests.This study was conducted in the Changbai Mountain Nature Reserve, in northeastern China. Based on the observational data collected from three 5.2‐hectare forest plots, the annual above‐ground biomass (AGB) increment (productivity) of the surviving trees, recruits, and the total tree community (survivors + recruits) were estimated. Then, the changes in the forest productivity in response to biotic variables (including species diversity, structural diversity, and density variables) along with abiotic variables (including topographic and soil variables) were evaluated using linear mixed‐effect models.This study determined that the biotic variables regulated the variabilities in productivity. Density variables were the most critical drivers of the annual AGB increments of the surviving trees and total tree community. Structural diversity enhanced the annual AGB increments of the recruits, but diminished the annual AGB increments of the surviving trees and the total tree community. Species diversity and abiotic variables did not have impacts on the productivity in the examined forest plots.The results highlighted the important roles of forest density and structural diversity in the biomass demographic processes of temperate forests. The surviving and recruit trees were found to respond differently to the biotic variables, which suggested that the asymmetric competition had shaped the productivity dynamics in forests. Therefore, the findings emphasized the need to consider the demographic processes of forest productivity to better understand the functions of forests.

Effects of decadal experimental drought and climate extremes on vegetation growth in Mediterranean forests and shrublands

AbstractIncreased drought combined with extreme episodes of heatwaves is triggering severe impacts on vegetation growth, particularly for plant communities in arid and semiarid ecosystems. Although there is an abundance of short‐term field drought experiments in natural ecosystems, remaining knowledge gaps limit the understanding and prediction of vegetation growth to ongoing and future climate scenarios. Here, we assessed the impacts of long‐term (1999–2016) experimental drought (ca. −30% rainfall) on the vegetation growth of a Mediterranean high (H) and low (L)‐canopy forests and an early‐successional shrubland, as indicated by above‐ground biomass increment (ABI) and standing density, respectively. We found habitat context (impact of historical climate change, soil depth and successional status) of the study sites significantly affected the magnitude of climate impacts; there were synergistic effects of experimental drought and meteorological drought (Standardised Precipitation–Evapotranspiration Index, SPEI) as well as extreme dry years on vegetation growth. Long‐term experimental drought decreased the ABI for the two forest canopy types and the standing density for the shrubland. Water availabilities in winter–spring (SPEIs) were positively correlated with the ABI and standing density. Moreover, experimental drought decreased the vegetation growth in extreme dry years for the shrubland. We propose that future work not only study the vegetation dynamics with physiological, phenological and demographical changes in long‐term processes and across climate gradients, but also should explore the changes of multiple functions simultaneously (e.g. multifunctionality) under long‐term processes and extremes. This type of analysis of long‐term data is essential to understand and predict biodiversity loss, composition shifts, declines in ecosystem function and carbon budgets at temporal and spatial scales, to enable policy makers to design and implement strategies for the maintenance of sustainable ecosystem function under future climate change scenarios.