Assessing forest growth across southwestern Oregon under a range of current and future global change scenarios using a process model, 3‐PG

With improvements in mapping regional distributions of vegetation using satellite‐derived information, there is an increasing interest in the assessment of current limitations on forest growth and in making projections of how productivity may be altered in response to changing climatic conditions and management policies. We utilised a simplified physiologically based process model (3‐PG) across a 54 000 km² mountainous region of southwestern Oregon, USA, to evaluate the degree to which maximum periodic mean annual increment (PAI) of forests could be predicted at a set of 448 forest inventory plots. The survey data were pooled into six broad forest types (coastal rain forest, interior coast range forest, mixed conifer, dry‐site Douglas‐fir, subalpine forest, and pine forest) and compared to the 3‐PG predictions at a spatial resolution of 1 km². We found good agreement (r² = 0.84) between mean PAI values of forest productivity for the six forest types with those obtained from field surveys. With confidence at this broader level of integration, we then ran model simulations to evaluate the constraints imposed by (i) soil fertility under current climatic conditions, (ii) the effect of doubling monthly precipitation across the region, and (iii) a widely used climatic change scenario that involves modifications in monthly mean temperatures and precipitation, as well as a doubling in atmospheric CO₂ concentrations. These analyses showed that optimum soil fertility would more than double growth, with the greatest response in the subalpine type and the least increase in the coastal rain forests. Doubling the precipitation increased productivity in the pine type (> 50%) with reduced responses elsewhere. The climate change scenario with doubled atmospheric CO₂ increased growth by 50% on average across all forest types, primarily as a result of a projected 33% increase in photosynthetic capacity. This modelling exercise indicates that, at a regional scale, a general relationship exists between simulated maximum leaf area index and maximum aboveground growth, supporting the contention that satellite‐derived estimates of leaf area index may be good measures of the potential productivity of temperate evergreen forests.     

Multiscale model intercomparisons of CO2 and H2O exchange rates in a maturing southeastern US pine forest

We compared four existing process‐based stand‐level models of varying complexity (physiological principles in predicting growth, photosynthesis and evapotranspiration, biogeochemical cycles, and stand to ecosystem carbon and evapotranspiration simulator) and a new nested model with 4 years of eddy‐covariance‐measured water vapor (LE) and CO₂ (Fc) fluxes at a maturing loblolly pine forest. The nested model resolves the ‘fast’ CO₂ and H₂O exchange processes using canopy turbulence theories and radiative transfer principles whereas slowly evolving processes were resolved using standard carbon allocation methods modified to improve leaf phenology. This model captured most of the intraannual variations in leaf area index (LAI), net ecosystem exchange (NEE), and LE for this stand in which maximum LAI was not at a steady state. The model comparisons suggest strong linkages between carbon production and LAI variability, especially at seasonal time scales. This linkage necessitates the use of multilayer models to reproduce the seasonal dynamics of LAI, NEE, and LE. However, our findings suggest that increasing model complexity, often justified for resolving faster processes, does not necessarily translate into improved predictive skills at all time scales. Additionally, none of the models tested here adequately captured drought effects on water and CO₂ fluxes. Furthermore, the good performance of some models in capturing flux variability on interannual time scales appears to stem from erroneous LAI dynamics and from sensitivity to droughts that injects unrealistic flux variability at longer time scales.     

A global assessment of forest surface albedo and its relationships with climate and atmospheric nitrogen deposition

We present a global assessment of the relationships between the short‐wave surface albedo of forests, derived from the MODIS satellite instrument product at 0.5° spatial resolution, with simulated atmospheric nitrogen deposition rates (N_dep), and climatic variables (mean annual temperature T_m and total annual precipitation P), compiled at the same spatial resolution. The analysis was performed on the following five forest plant functional types (PFTs): evergreen needle‐leaf forests (ENF); evergreen broad‐leaf forests (EBF); deciduous needle‐leaf forests (DNF); deciduous broad‐leaf forests (DBF); and mixed‐forests (MF). Generalized additive models (GAMs) were applied in the exploratory analysis to assess the functional nature of short‐wave surface albedo relations to environmental variables. The analysis showed evident correlations of albedo with environmental predictors when data were pooled across PFTs: T_m and N_dep displayed a positive relationship with forest albedo, while a negative relationship was detected with P. These correlations are primarily due to surface albedo differences between conifer and broad‐leaf species, and different species geographical distributions. However, the analysis performed within individual PFTs, strengthened by attempts to select ‘pure’ pixels in terms of species composition, showed significant correlations with annual precipitation and nitrogen deposition, pointing toward the potential effect of environmental variables on forest surface albedo at the ecosystem level. Overall, our global assessment emphasizes the importance of elucidating the ecological mechanisms that link environmental conditions and forest canopy properties for an improved parameterization of surface albedo in climate models.     

Remote sensing of protected areas to derive baseline vegetation functioning characteristics

Question: How can we derive baseline/reference situations to evaluate the impact of global change on terrestrial ecosystem functioning? Location: Main biomes (steppes to rain forests) of Argentina. Methods: We used AVHRR/NOAA satellite data to characterize vegetation functioning. We used the seasonal dynamics of the Normalized Difference Vegetation Index (NDVI), a linear estimator of the fraction of the photosynthetic active radiation intercepted by vegetation (f_PAR), and the surface temperature (Ts), for the period 1981–1993. We extracted the following indices: NDVI integral (NDVI‐I), NDVI relative range (R_rel), NDVI maximum value (V_max), date of maximum NDVI (D_max) and actual evapotranspiration. Results: f _PAR varied from 2 to 80%, in relation to changes in net primary production (NPP) from 83 to 1700 g.m‐².yr^‐1. NDVI‐I, Vmax and f_PAR had positive, curvilinear relationships to mean annual precipitation (MAP), NPP was linearly related to MAP. Tropical and subtropical biomes had a significantly lower seasonality (R_rel) than temperate ones. D_max was not correlated with the defined environmental gradients. Evapotranspiration ranged from 100 to 1100 mm.yr^‐1. Interannual variability of NDVI attributes varied across the temperature and precipitation gradients. Conclusions: Our results may be used to represent baseline conditions in evaluating the impact of land use changes across environmental gradients. The relationships between functional attributes and environmental variables provide a way to extrapolate ecological patterns from protected areas across modified habitats and to generate maps of ecosystem functioning.     

Semiempirical modeling of abiotic and biotic factors controlling ecosystem respiration across eddy covariance sites

In this study we examined ecosystem respiration (R_ECO) data from 104 sites belonging to FLUXNET, the global network of eddy covariance flux measurements. The goal was to identify the main factors involved in the variability of R_ECO: temporally and between sites as affected by climate, vegetation structure and plant functional type (PFT) (evergreen needleleaf, grasslands, etc.). We demonstrated that a model using only climate drivers as predictors of R_ECO failed to describe part of the temporal variability in the data and that the dependency on gross primary production (GPP) needed to be included as an additional driver of R_ECO. The maximum seasonal leaf area index (LAI_MAX) had an additional effect that explained the spatial variability of reference respiration (the respiration at reference temperature T_ref=15 °C, without stimulation introduced by photosynthetic activity and without water limitations), with a statistically significant linear relationship (r²=0.52, P<0.001, n=104) even within each PFT. Besides LAI_MAX, we found that reference respiration may be explained partially by total soil carbon content (SoilC). For undisturbed temperate and boreal forests a negative control of total nitrogen deposition (N_depo) on reference respiration was also identified. We developed a new semiempirical model incorporating abiotic factors (climate), recent productivity (daily GPP), general site productivity and canopy structure (LAI_MAX) which performed well in predicting the spatio‐temporal variability of R_ECO, explaining >70% of the variance for most vegetation types. Exceptions include tropical and Mediterranean broadleaf forests and deciduous broadleaf forests. Part of the variability in respiration that could not be described by our model may be attributed to a series of factors, including phenology in deciduous broadleaf forests and management practices in grasslands and croplands.     

Leaf life span as a simple predictor of evergreen forest zonation in China

Aim Our aim was to investigate how the average life span of canopy leaves might be used to predict the geographical distribution of natural forests at large geographical scales, and to explore the link between leaf characteristics and ecosystem functioning. We examine whether there is a general relationship between canopy mean leaf life span and climate (i.e. temperature and precipitation) that can be used to predict evergreen forest zonation in China. Location Forest areas in China. Methods During July and August of 2002–2004, we conducted a latitudinal forest transect spanning about 30° of latitude in eastern China. The canopy mean leaf life span was calculated to include all tree species (groups) in each forest plot through weighted averages scaled up from branch‐level measurements. Data from our previous work conducted in the Tibetan Alpine Vegetation Transects (TAVT) and from other investigators were compiled to supplement our results. Based on regression equations developed on the pooled data, and using gridded temperature and precipitation datasets, we simulated the distribution of canopy mean leaf life span for forests in China. The predicted leaf life span zonation was compared with a map of Chinese forest vegetation divisions published in 1980. Results Canopy mean leaf life span across 10 evergreen forest plots in eastern China showed a decreasing trend as mean annual temperature increased, following a common logistic pattern consistent with the data from the TAVT and other investigators. In pooled data for 40 evergreen forest plots across tropical and boreal regions, canopy mean leaf life span generally showed a negative relationship with mean annual temperature (r² = 0.72, P < 0.001), and a positive correlation with mean annual precipitation where mean annual temperature was > 8°C (r² = 0.45, P < 0.01). The climate‐based simulations of leaf life span zonation compared well with the previously published boundaries of forest vegetation divisions in eastern China. Main conclusions Our results reveal that mean leaf life span in evergreen forests follows a common logistic pattern associated with mean annual temperature and precipitation, which can in turn be used to predict evergreen forest zonation in eastern China.     

Variety of responses of plant phenolic concentration to CO2 enrichment

Leaf area index (LAI) of a stand of adult black alder trees(Alnus glutinosa L., Gaertn.) was determined by means of threeindependent methods. (1) The seasonal course of LAI was directlyobtained by counting leaves in situ and adding up their areas,estimated from harvested subsamples of leaves. (2) The seasonalvariation of LAI in the stand was estimated using the Li-CorLAI-2000 PCA in parallel and with this instrument a VegetationArea Index (VAI, projected area of all phyto-elements) was actuallymeasured. (3) Maximum LAI was calculated from leaf litter collectionstaking into account specific leaf area within different layersof the alder crown. Direct LAI estimates (1) and calculationsfrom leaf litter (3) revealed the same figure of maximum LAI(4.8). This LAI was reached in August. The LAI-2000 PCA capturedthe seasonal variation and underestimated, by 11% on average,the LAI obtained directly. Compared with results gained withother broad-leaved tree species the LAI-2000 PCA values foralder were reliable. It is suggested that this is due to thehorizontal homogeneous structure of the main leaf layer. Thisis in the periphery of the crown, where 90% of the light interceptionoccurs. Taking the het-erogeneity into account a satisfactorycompatibility of the three methods applied to the alder standwas achieved. Key words: Alnus glutinosa, leaf area index, in situ counting, LAI-2000 PCA, litter collections     

Traits and growth of liana regeneration in primary and secondary forests of Central Amazonia

Question: Do traits of liana regeneration differ among secondary forest types of varying land‐use history and primary forest? Location: Eighty kilometers north of Manaus, Brazil. Methods: We compared plant functional traits and growth rates of liana regeneration (<1.7‐m length) among two secondary forest types and primary forest. Secondary forest types were: Vismia (on land formerly clear‐cut, used for pasture and intensively burned) and Cecropia (no pasture usage or intensive fires after clear‐cut). Results: A principal components analysis indicated that most of the primary forest species exhibited a similar habit and were characterized by short shoots and small, round leaves with low specific leaf area, whereas secondary forest species had a broad range of trait values. At the plot level, primary and secondary forest communities were separated mainly by plant length and leaf size. Plant size varied more within secondary than within primary forest plots. The two secondary forest types could not be separated based on the traits of liana regeneration. Relative growth rate (RGR) did not correlate significantly with any measured plant trait, except for a negative relation to initial length. RGR increased with decreasing canopy cover and was highest in Vismia forest plots. Conclusion: Plant functional traits of liana regeneration were more similar in the primary forest and differed substantially from secondary forests, yet canopy cover only partly explained the observed differences.     

Leaf area index determination in an alder forest: a comparison of three methods

Leaf area index (LAI) of a stand of adult black alder trees(Alnus glutinosa L., Gaertn.) was determined by means of threeindependent methods. (1) The seasonal course of LAI was directlyobtained by counting leaves in situ and adding up their areas,estimated from harvested subsamples of leaves. (2) The seasonalvariation of LAI in the stand was estimated using the Li-CorLAI-2000 PCA in parallel and with this instrument a VegetationArea Index (VAI, projected area of all phyto-elements) was actuallymeasured. (3) Maximum LAI was calculated from leaf litter collectionstaking into account specific leaf area within different layersof the alder crown. Direct LAI estimates (1) and calculationsfrom leaf litter (3) revealed the same figure of maximum LAI(4.8). This LAI was reached in August. The LAI-2000 PCA capturedthe seasonal variation and underestimated, by 11% on average,the LAI obtained directly. Compared with results gained withother broad-leaved tree species the LAI-2000 PCA values foralder were reliable. It is suggested that this is due to thehorizontal homogeneous structure of the main leaf layer. Thisis in the periphery of the crown, where 90% of the light interceptionoccurs. Taking the het-erogeneity into account a satisfactorycompatibility of the three methods applied to the alder standwas achieved. Key words: Alnus glutinosa, leaf area index, in situ counting, LAI-2000 PCA, litter collections     

3类典型温带山地森林的叶面积指数的季节动态: 多种监测方法比较

 叶面积指数(leaf area index, LAI)是定量描述冠层结构的最有效指标之一。鉴于森林冠层三维结构的高度复杂性和异质性, 迄今仍没有形成统一标准的LAI测量方法。该文利用LAI-2000冠层分析仪、CI-110冠层分析仪和半球摄影法(digital hemispherical photograph, DHP), 对北京东灵山地区以蒙古栎(Quercus mongolica)为主的落叶阔叶林、华北落叶松(Larix gmelinii var. principis-rupprechtii)林和油松(Pinus tabuliformis)林的有效叶面积指数(effective leaf area index, LAI_e)进行了动态监测, 探寻其季节变化规律。为准确地估算温带山地主要森林类型的LAI, 对光学仪器测量值进行了去除木质成分、聚集效应等校正, 与基于凋落物收集法的相应实测值进行了比较分析。结果表明: 3种典型森林在生长季期间叶片生长均呈现单峰型; 3种光学仪器测量方法的同期LAI_e数值大小顺序为: LAI-2000冠层分析仪>DHP>CI-110冠层分析仪。光学仪器的直接测量值LAI_e包含了木质成分的贡献, 钝化了季节动态的变化幅度, 这对有明显季节交替的落叶林尤为突出。经校正, LAI-2000冠层分析仪和DHP的测量值与实测值都表现出显著的相关性, 其中LAI-2000冠层分析仪最适于采用基于空隙大小的校正方法, 而基于空隙度和空隙大小的综合算法则是校正DHP的最佳选择。结合经济成本和野外实际操作等因素考虑, DHP具有更大的推广优势, 特别适用于温带山地落叶林。     

Biological spectrum and other structural functional attributes of the vegetation of Kumaun Himalaya

Spectra on life form, leaf size, leaf persistence, flowering season, and shade tolerance of trees in different vegetation types occurring within the north-western catchment of the river Gola in Kumaun Himalaya are presented. The flora of Quercus leucotrichophora, Quercus lanuginosa and Quercus floribunda forests is phanerophytic, that of Pinus roxburghii and mixed forests therophytic. The grassland vegetation is characterized by the largest percentage of hemicryptophytes. The flora of the whole area, is therophytic. The biological spectrum for the entire Kumaun Himalaya is characterized as therohemigeophytic. Among the various altitudinal zones, the tropical has a preponderance of phanerophytes, the temperate and the alpine of hemicryptophytes.The observations on leaf size indicate that with the exception of Pinus roxburghii forest, in all vegetation types, the species with microphylls are greater in number. In this region, the vegetation expression is evergreen, although the tree flora has a considerable content of deciduous elements. In all the forests, the flowering period in most of the trees is vernal.On the basis of relative density, the greatest proportions of adult trees in the Pinus roxburghii and Quercus lanuginosa forests are shade intolerant, while in the mixed and Quercus leucotrichophora forests maximum trees are intermediate in shade tolerance. With the exception of the Pinus roxburghii forest, all the forests exhibit the dominance of trees which are shade tolerant at the seedling stage. On the basis of relative density, all forest types, except for Pinus roxburghii forest, have 74.5 to 100% trees with the potentiality of vegetative reproduction.Financial support from the Indian Space Research Organisation, Banglore and University Grants Commission, New Delhi is gratefully acknowledged.     

Detection and attribution of vegetation greening trend in China over the last 30 years

The reliable detection and attribution of changes in vegetation growth is a prerequisite for the development of strategies for the sustainable management of ecosystems. This is an extraordinary challenge. To our knowledge, this study is the first to comprehensively detect and attribute a greening trend in China over the last three decades. We use three different satellite‐derived Leaf Area Index (LAI) datasets for detection as well as five different process‐based ecosystem models for attribution. Rising atmospheric CO₂ concentration and nitrogen deposition are identified as the most likely causes of the greening trend in China, explaining 85% and 41% of the average growing‐season LAI trend (LAI_GS) estimated by satellite datasets (average trend of 0.0070 yr^?1, ranging from 0.0035 yr^?1 to 0.0127 yr^?1), respectively. The contribution of nitrogen deposition is more clearly seen in southern China than in the north of the country. Models disagree about the contribution of climate change alone to the trend in LAI_GS at the country scale (one model shows a significant increasing trend, whereas two others show significant decreasing trends). However, the models generally agree on the negative impacts of climate change in north China and Inner Mongolia and the positive impact in the Qinghai–Xizang plateau. Provincial forest area change tends to be significantly correlated with the trend of LAI_GS (P < 0.05), and marginally significantly (P = 0.07) correlated with the residual of LAI_GS trend, calculated as the trend observed by satellite minus that estimated by models through considering the effects of climate change, rising CO₂ concentration and nitrogen deposition, across different provinces. This result highlights the important role of China's afforestation program in explaining the spatial patterns of trend in vegetation growth.     

Long-term dynamics of vegetation indices in dark coniferous forest after Siberian moth disturbance

This study considers long-term dynamics of the vegetation indices derived from Landsat imagery of the period from 1989 to 2014. The mass death and damage of forests by Siberian moth occurred in dark coniferous taiga in 1994–1996. The images have covered both altered (disturbed) and background forest conditions. The case study of the forest massive is located in the model area of the Angara Taiga Region of Eastern Siberia (Krasnoyarsk krai). The values of spectral brightness of satellite images are represented by produced index images of NDVI vegetation index and shortwave vegetation index SWVI. The study employed forest-surveying materials from 1992 and data on the degrees of forest damage during the first (in 1995) and second (in 1996) year of Siberian moth outbreak. The latter was obtained by forest-pathology research using production-scale spectrozonal aerophotography. The average background values of indices have gradually decreased with the forest age or remained constant, excluding the young growth stage and 200-year-old light coniferous forests. High seasonal variability of NDVI compared to SWVI is the key to use satellite data for the timeframe of a week in June for every year to analyze long-term dynamics. We have approved the conclusion of other researchers that both the mean and the coefficient of variation of SWVI are the most informative in the evaluation of the degree of Siberian moth damage of forests. We recommend recognizing three degrees of forest damage by Siberian moth—light, moderate, and severe (continuous). Long-term dynamics of vegetation indices in disturbed forests has been marked with demutation and inhomogeneity of stand cover. Taking into account the intensity and frequency of wildfires, it is highly probable that reforestation will not occur in dark coniferous forests. Therefore, the regular satellite monitoring of the sites of Silk moth occurrence would be useful.     

Effects of nutrient additions on ecosystem carbon cycle in a Puerto Rican tropical wet forest

Wet tropical forests play a critical role in global ecosystem carbon (C) cycle, but C allocation and the response of different C pools to nutrient addition in these forests remain poorly understood. We measured soil organic carbon (SOC), litterfall, root biomass, microbial biomass and soil physical and chemical properties in a wet tropical forest from May 1996 to July 1997 following a 7‐year continuous fertilization. We found that although there was no significant difference in total SOC in the top 0–10 cm of the soils between the fertilization plots (5.42±0.18 kg m^?2) and the control plots (5.27±0.22 kg m^?2), the proportion of the heavy‐fraction organic C in the total SOC was significantly higher in the fertilized plots (59%) than in the control plots (46%) (P<0.05). The annual decomposition rate of fertilized leaf litter was 13% higher than that of the control leaf litter. We also found that fertilization significantly increased microbial biomass (fungi+bacteria) with 952±48 mg kg^?1soil in the fertilized plots and 755±37 mg kg^?1soil in the control plots. Our results suggest that fertilization in tropical forests may enhance long‐term C sequestration in the soils of tropical wet forests.     

Removal of invasive shrubs alters light but not leaf litter inputs in a deciduous forest understory

The establishment and spread of non‐native, invasive shrubs in forests poses an important obstacle to natural resource conservation and management. This study assesses the impacts of the physical removal of a complex of woody invasive shrub species on deciduous forest understory resources. We compared leaf litter quantity and quality and understory light transmittance in five pairs of invaded and removal plots in an oak‐dominated suburban mature forest. Removal plots were cleared of all non‐native invasive shrubs. The invasive shrubs were abundant (143,456 stems/ha) and diverse, dominated by species in the genera Ligustrum, Viburnum, Lonicera, and Euonymus. Annual leaf litter biomass and carbon inputs of invaded plots were not different from removal plots due to low leaf litter biomass of invasive shrubs. Invasive shrub litter had higher nitrogen (N) concentrations than native species; however, low biomass of invasive litter led to low N inputs by litter of invasive species compared to native. Light transmittance at the forest floor and at 2 m was lower in invaded plots than in removal plots. We conclude that the removal of the abundant invasive shrubs from a native deciduous forest understory did not alter litter quantity or N inputs, one measure of litter quality, and increased forest understory light availability. More light in the forest understory could facilitate the restoration of forest understory dynamics.     

Accuracy of the AVHRR vegetation index as a predictor of biomass,primary productivity and net CO2 flux

The Normalized Difference Vegetation Index (NDVI) or greenness index, based on the Advanced Very High Resolution Radiometer (AVHRR) aboard the NOAA-7 satellite, has been widely interpreted as a measure of regional to global vegetation patterns. This study provides the first rigorous, quantitative evaluation of global relationships between the NDVI and geographically representative vegetation data-bases, including field metabolic measurements and carbon-balance results from global simulation models. Geographic reliability of the NDVI is judged by comparing NDVI values for different surface types with a general global trend and by statistical analysis of relationships to biomass amounts, net and gross primary productivity, and actual evapotranspiration. NDVI data appear to be relatively reliable predictors of primary productivity except in areas of complex terrain, for seasonal values at high latitudes, and in extreme deserts. The strength of the NDVI-productivity relationship seems comparable to that of earlier climate-based productivity models. Little consistent relationship was found, across different vegetation types, between NDVI and biomass amounts or net biospheric CO₂ flux.Abbreviations AET= Actual Evapotranspiration - AVHRR= Advanced Very High Resolution Radiometer - GPP= Gross Primary Production - GVI= Global Vegetation Index - NDVI= Normalized Difference Vegetation Index - NPP= Net Primary Production     

Functional community structure of African monodominant Gilbertiodendron dewevrei forest influenced by local environmental filtering

Monodominant patches of forest dominated by Gilbertiodendron dewevrei are commonly found in central African tropical forests, alongside forests with high species diversity. Although these forests are generally found sparsely distributed along rivers, their occurrence is not thought to be (clearly) driven by edaphic conditions but rather by trait combinations of G. dewevrei that aid in achieving monodominance. Functional community structure between these monodominant and mixed forests has, however, not yet been compared. Additionally, little is known about nondominant species in the monodominant forest community. These two topics are addressed in this study. We investigate the functional community structure of 10 one‐hectare plots of monodominant and mixed forests in a central region of the Congo basin, in DR Congo. Thirteen leaf and wood traits are measured, covering 95% (basal area weighted) of all species present in the plots, including leaf nutrient contents, leaf isotopic compositions, specific leaf area, wood density, and vessel anatomy. The trait‐based assessment of G. dewevrei shows an ensemble of traits related to water use and transport that could be favorable for its location near forest rivers. Moreover, indications have been found for N and P limitations in the monodominant forest, possibly related to ectomycorrhizal associations formed with G. dewevrei. Reduced leaf N and P contents are found at the community level for the monodominant forest and for different nondominant groups, as compared to those in the mixed forest. In summary, this work shows that environmental filtering does prevail in the monodominant G. dewevrei forest, leading to lower functional diversity in this forest type, with the dominant species showing beneficial traits related to its common riverine locations and with reduced soil N and P availability found in this environment, both coregulating the tree community assembly.     

Do dynamic global vegetation models capture the seasonality of carbon fluxes in the Amazon basin? A data‐model intercomparison

To predict forest response to long‐term climate change with high confidence requires that dynamic global vegetation models (DGVMs) be successfully tested against ecosystem response to short‐term variations in environmental drivers, including regular seasonal patterns. Here, we used an integrated dataset from four forests in the Brasil flux network, spanning a range of dry‐season intensities and lengths, to determine how well four state‐of‐the‐art models (IBIS, ED2, JULES, and CLM3.5) simulated the seasonality of carbon exchanges in Amazonian tropical forests. We found that most DGVMs poorly represented the annual cycle of gross primary productivity (GPP), of photosynthetic capacity (Pc), and of other fluxes and pools. Models simulated consistent dry‐season declines in GPP in the equatorial Amazon (Manaus K34, Santarem K67, and Caxiuanã CAX); a contrast to observed GPP increases. Model simulated dry‐season GPP reductions were driven by an external environmental factor, ‘soil water stress’ and consequently by a constant or decreasing photosynthetic infrastructure (Pc), while observed dry‐season GPP resulted from a combination of internal biological (leaf‐flush and abscission and increased Pc) and environmental (incoming radiation) causes. Moreover, we found models generally overestimated observed seasonal net ecosystem exchange (NEE) and respiration (R_e) at equatorial locations. In contrast, a southern Amazon forest (Jarú RJA) exhibited dry‐season declines in GPP and R_e consistent with most DGVMs simulations. While water limitation was represented in models and the primary driver of seasonal photosynthesis in southern Amazonia, changes in internal biophysical processes, light‐harvesting adaptations (e.g., variations in leaf area index (LAI) and increasing leaf‐level assimilation rate related to leaf demography), and allocation lags between leaf and wood, dominated equatorial Amazon carbon flux dynamics and were deficient or absent from current model formulations. Correctly simulating flux seasonality at tropical forests requires a greater understanding and the incorporation of internal biophysical mechanisms in future model developments.     

Determinants of woody species richness in Scot pine and beech forests: climate, forest patch size and forest structure

We analysed patterns of woody species richness in Pinus sylvestris and Fagus sylvatica forests in Catalonia (NE Spain) from forestry inventory databank in relation to climate and landscape structure. Both types of forests are found within the same climatic range, although they have been managed following somewhat different goals. Overall, woody species richness significantly increased when conditions get closer to the Mediterranean ones, with milder temperatures. Differences between the two types of forests arose when comparing the relationship between richness and forest patch size. Woody species richness increased in pine forests with patch size, while the opposite trend was observed in beech forests. This pattern is explained by the different behaviour of structural canopy properties, since leaf area index and canopy cover showed a steeper increase with increasing forest patch size in Fagus forests than in Pinus ones. Accordingly, richness decreased with canopy cover in Fagus plots, but not in Pinus ones. We suggest that these differences would be related to management history, which may have enhanced the preservation of beech stands in larger forest landscape units.     

Structural and functional changes in Nothofagus pumilio forests along an altitudinal gradient in Tierra del Fuego,Argentina

Abstract. Structural (density, height, basal area, above‐ground tree biomass, leaf area index) and functional (leaf phenology, growth rate, fine litter fall, leaf decomposition) traits were quantified in four mature forests of Nothofagus pumilio (lenga) along an altitudinal sequence in Tierra del Fuego, Argentina. Three erect forest stands at 220, 440 and 540m and a krummholz stand at 640 m a.s.l. were selected. Along the altitudinal sequence, stem density increased while DBH, height, biomass, leaf‐size and growth period, mean growth rate and decay rate decreased. Dead stems increased and basal area and fine‐litter fall decreased with an increase in elevation among erect forests, but these trends inverted at krummholz. We suggest that krummholz is not only a morphological response to the adverse climate but is also a life form with functional advantages.