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Abstract: The association of N2-fixing species (NFS) could be an attractive option for achieving a sustainable increase of Eucalyptus plantations (EP) productivity through a positive balance between facilitative effects and competition between species. A randomised block design was replicated at four sites (Cenibra, USP, Suzano and IP) in Southern Brazil and at one site in Congo. The development of mono-specific stands of Acacia mangium (100A) and Eucalyptus grandis or urophylla × grandis (100E), was compared with N fertilisation treatment (100E+N) and with mixed-species plantations in a 1:1 ratio (50A:50E), and in an additive series with varying densities of acacia for the same density of eucalypt (25A:100E, 50A:100E, 100A:100E). The objectives were to assess the effect of mixtures on tree growth and stand production, and the behaviour of the two species in contrasting soil and climatic conditions. Tree growth was monitored over stand rotation and the biomass of aboveground tree components estimated at mid-rotation and at harvesting age. Eucalyptus height was 13% higher in Brazil than in Congo. Favourable ecological conditions in Congo and Cenibra led to 50% higher Acacia tree height than at the other sites. A depressive effect of Eucalyptus neighbour trees on Acacia height and circumference growth, lower in Congo than in Brazil, was observed in the mixtures from age 1–2years onwards. Depressive effects of acacia on eucalypt height and circumference growth were low in USP, Suzano and IP, high in Cenibra, and not observed in Congo, in 50A:50E and 25A:100E. A positive though insignificant response to N fertilisation was only found in USP and Congo. Complementarity for light and soil resource capture between Eucalyptus and Acacia trees resulted in mean annual increments in total stand stemwood biomass (MAI) that were 7–15%, 6–12%, and 40% higher in the additive series than for 100E in Cenibra, USP and Congo, respectively at mid-rotation. Whilst lasting complementarity and facilitation in Congo led to 17–34% higher MAI in mixtures than for 100E at harvesting age, MAIs were not significantly higher in mixtures than for 100E in Brazil. Mixed-species plantations of Eucalyptus and A. mangium might enhance aboveground stand production on poor nutrient soils in warm and humid tropical climates with low water limitations. [Copyright &y& Elsevier]

Abstract: Wood production varies substantially with resource availability, and the variation in wood production can result from several mechanisms: increased photosynthesis, and changes in partitioning of photosynthesis to wood production, belowground flux, foliage production or respiration. An understanding of the mechanistic basis for patterns in wood production within a stand and across landscapes requires a complete annual carbon budget. We measured annual carbon flows to wood production, foliage production and total belowground carbon flux (the sum of root production, root respiration, and mycorrhizal production and respiration) from ages three to five years in clonal Eucalyptus plantations at four sites in Brazil to test if fertility, water availability and stand structure changed wood production and by what mechanism. We also quantified the patterns in light interception and the efficiency of light use to provide additional mechanistic insights into growth responses and to determine if light-use efficiency was related to changes in flux and partitioning. The routine level of forest fertilization at these four sites was high enough that further increases in nutrient supply did not increase wood growth. Irrigation increased wood net primary productivity (age three to five) from 1.45 to 1.84kgm−2 year−1 of C (27%), because of increases in light interception (5%), photosynthetic efficiency (from 0.028 to 0.031molC/mol photons absorbed, 11%), gross primary productivity (from 3.62 to 4.28m−2 year−1 of C, 18%), and partitioning to wood (from 0.397 to 0.430 of photosynthesis, 8%). These changes increased light-use efficiency by 20%. Annual flux belowground varied among sites from 0.43 to 1.0m−2 year−1 of C but did not vary with water availability. Across the four sites for the irrigated and unirrigated treatments, light-use efficiency was positively correlated with gross primary productivity and partitioning to wood production. Increasing heterogeneity of stand structure (resulting from staggered timing of planting within plots) led to a 14% loss in wood biomass relative to uniform stand structure at age six. Light-use efficiency, gross primary productivity, and wood net primary productivity were lower, but not significantly so, in heterogeneous compared to uniform stands. [Copyright &y& Elsevier]

Abstract: We examined the potential growth of clonal Eucalyptus plantations at eight locations across a 1000+ km gradient in Brazil by manipulating the supplies of nutrients and water, and altering the uniformity of tree sizes within plots. With no fertilization or irrigation, mean annual increments of stem wood were about 28% lower (16.2Mgha−1 yr−1, about 33m3 ha−1 yr−1) than yields achieved with current operational rates of fertilization (22.6Mgha−1 yr−1, about 46m3 ha−1 yr−1). Fertilization beyond current operational rates did not increase growth, whereas irrigation raised growth by about 30% (to 30.6Mgha−1 yr−1, about 62m3 ha−1 yr−1). The potential biological productivity (current annual increment) of the plantations was about one-third greater than these values, if based only on the period after achieving full canopies. The biological potential productivity was even greater if based only on the full-canopy period during the wet season, indicating that the maximum biological productivity across the sites (with irrigation, during the wet season) would be about 42Mgha−1 yr−1 (83m3 ha−1 yr−1). Stands with uniform structure (trees in plots planted in a single day) showed 13% greater growth than stands with higher heterogeneity of tree sizes (owing to a staggered planting time of up to 80 days). Higher water supply increased growth and also delayed by about 1 year the point where current annual increment and mean annual increment intersected, indicating opportunities for lengthening rotations for more productive treatments as well as the influence of year-to-year climate variations on optimal rotations periods. The growth response to treatments after canopy closure (mid-rotation) related well with full-rotation responses, offering an early opportunity for estimating whole-rotation yields. These results underscore the importance of resource supply, the efficiency of resource use, and stand uniformity in setting the bounds for productivity, and provide a baseline for evaluating the productivity achieved in operational plantations. The BEPP Project showed that water supply is the key resource determining levels of plantation productivity in Brazil. Future collaboration between scientists working on silviculture and genetics should lead to new insights on the mechanisms connecting water and growth, leading to improved matching of sites, clones, and silviculture. [Copyright &y& Elsevier]

[Display omitted] • Maximizing wood production in managed tropical dry forest depends on the regrowth of remaining stumps. • Knowing which species to selectively remove or manage for regrowth after disturbance is therefore crucial. • Capacity for coppicing may favor the eventual dominance of a few species in periodically disturbed tropical dry forests. The Caatinga is a tropical dry forest. Rational exploitation of Caatinga wood resources consists of sustainable forest management under coppice systems. Therefore, the recovery of the timber stock for the next cycle will depend on the regrowth and survival capacity of the exploited species, as well as on the future structure of the forest. The objective of this work was to characterize the survival, structure, and diversity of Caatinga submitted to coppicing under sustainable forest management comparing pre- and post-harvest conditions. Permanent plots were installed in a Caatinga in the municipality of Floresta-PE, Brazil, in 2013, and measured 2 years after clearcutting. Height and circumference at the base (CAB) of the stumps and shoots were obtained for two situations: pre-cut (grouping by live and dead stumps) and (ii) post-cut (shoots on only live stumps). In addition, all individual shrub-tree species (CAB ≥ 4 cm) not included in the post-cut situation were identified, measured (CAB and height total) and tagged as persisting (6 cm ≤ CAB) or growing (6 < CAB ≤ 4 cm) in 2015. The survival and mortality of the stumps were quantified, as well as changes in the horizontal structure and floristic diversity. There was a decrease in the number of species 2 years after cutting, mainly due to the loss of Croton rhamnifolius H. B. K. and Sapium glandulatum (Vell.) Pax and predominance of Cenostigma bracteosum (Tul.) E. Gagnon & G. P. Lewis, Aspidosperma pyrifolium Mart. , and Cnidoscolus quercifolius Pohl., resulting in a greater number of individuals of a few species. The outstanding regrowth capacity of these three species indicates that the forest remnant under study may eventually consist of populations with a predominance of species capable of coppicing. [ABSTRACT FROM AUTHOR]

• We evaluated turgor loss point and leaf water potential in Eucalyptus clones. • Correlation observed between πtlp calculated by PV curves and πo-osm using an osmometer. • πo-osm may be potentially useful for predicting πtlp in Eucalyptus. • πtlp was not correlated with drought tolerance of the genotypes we studied. Understanding the mechanisms governing drought tolerance in highly productive clonal Eucalyptus plantations in Brazil will become increasingly important with climate change driven increases in temperature and drought events. We quantified how leaf water potential, hydraulic safety margin (mid-day – pre-dawn leaf water potential, Ψδ) and the physiological parameters obtained from standard pressure–volume curves differed between four contrasting Eucalyptus genotypes across a temperature and water availability gradient in Brazil. We hypothesized that genotypes developed in dry areas were more drought tolerant and would exhibit lower mid-day leaf water potentials and turgor loss points than clones developed in wetter regions. Recognizing that standard pressure volume curves are time consuming and may not be a suitable screening tool for forest managers, we also tested if a key physiological parameter from the pressure–volume curve (turgor loss point, πtlp) could be accurately estimated from an osmometer as has been found in other species. We found no support for our first hypothesis; physiological parameters determined (including turgor loss point) from the pressure volume curves were not associated with the supposed drought tolerance of any of the clones. Similarly, mid-day leaf water potentials were not directly correlated with drought tolerance. The lack of support for our hypothesis may be because our measurements were taken during periods of minimum water stress. However, we did find that, overall, turgor loss point tended to be lower at the dry compared to wetter sites we studied suggesting that it may be a useful tool for assessing drought tolerance of Eucalyptus plantations in the future. We also found that estimates of osmotic potential at full turgor were similar between the pressure volume curve and osmometer techniques and that turgor loss point can be accurately estimated with an osmometer in highly productive Eucalyptus genotypes (R2 = 0.79). [ABSTRACT FROM AUTHOR]

• Higher planting densities resulted in more water use. • Both spacing and genotype directly affected water balance components. • Densities higher than about 1000 tree ha−1 are not recommended for very high potential productivity sites. • Lower planting densities can reduce water stress and balance wood production and water conservation. High stocking short rotation plantations provide high yields for bioenergy use and have been adopted worldwide, especially in tropical areas. This silvicultural approach might alter ecosystem water balances compared with lower stocking, longer rotation practices. The sensitivity of water balance to stocking might also differ among genotypes. We evaluated the primary components of ecosystem water balance (transpiration - E t , canopy interception - E i , soil evaporation – E s) for two hybrid clones that differ in drought tolerance and productivity (E. urophylla × E. grandis , Clone B2 and E.grandis × E.camaldulensis, Clone C3) planted in stockings ranging from 590 to 2,950 tree ha.-1 in a tropical region in Brazil. On a monthly time step, all water balance components of the two clones were largely related to the seasonality of rainfall, where the wet season represented 73% of the total rainfall, these processes corresponded on average to 76, 75, 67 and 70% of annual canopy interception, soil evaporation, transpiration and evapotranspiration (ET), respectively. For both clones, temperature (R2 = 0.32) and precipitation (R2 > 0.76) explained evapotranspiration responses while adding stocking as a second independent variable slightly improving the model for clone B2 but no improvement was detected for clone C3. When scaling up the monthly data to yearly analyses, all water balance components responded strongly to tree stocking for both clones during the two years of measurements (1.7 to 3.7 years-old). Annual transpiration rose linearly with stocking for the clone B2, rising from 550 mm yr−1 up to 1,039 mm yr−1, corresponding to 53–100% of precipitation (P). The clone C3 showed a much weaker influence of stocking on transpiration, rising only from 550 mm yr−1 at low stocking to 650 mm yr−1 at high stocking (53–63% of P). Canopy interception rose from about 230 mm yr−1 at low stocking to 300 mm yr−1 at high stocking, with little difference between the clones, ranging from 21 to 30% of P. Evaporation from the soil decreased with increased stocking for both clones and represented an average of 20–12% of P from lowest to highest stocking. Total evapotranspiration (ET – sum of E t , E i and E s) was about 1,000 to 1,050 mm yr−1 at low-to-moderate stockings of both clones, but the less-drought tolerant clone B2 showed substantially higher total evapotranspiration at high stocking (2,900 mm yr−1) compared to the clone C3 (2300 mm yr−1). The difference between precipitation and evapotranspiration (the overall ecosystem water balance) declined with increasing stocking, dropping below 0 at stockings higher than 1,030 tree ha−1 for both clones. High stocking in highly productive Eucalyptus plantations may be less sustainable across multiple rotations, since any deficit in the ecosystem water balance would need to come from longer-term soil water storage. Our results indicate that both genetics and tree stocking can be used as silviculture tools to manage the sustainably of short rotation forest plantations in the face of climate change. [ABSTRACT FROM AUTHOR]

• Leaf area index (LAI) varied among clones but increased with planting density. • Average stand transpiration at low tree density was 40% lower (622 mm) than that exhibited by high density (879 mm). • Selection of clonal material and silvicultural treatments could maximize productivity while minimizing water use. • WUE were significant different among three clones, but it was not sensitive to planting density variation. We examined the influence of stand density and genotype on transpiration and water use efficiency in high productivity plantations. Three widely planted Eucalyptus clones that differ in drought tolerance and productivity (E. urophylla , E. urophylla × E. grandis and E. grandis × E. camaldulensis, clones IP, B2 and C3, respectively) were measured at four densities (590, 1030, 1420, and 2950 trees ha−1). Over the 1-year study period (1.5–2.5 years after planting), individual biomass increment decreased with increasing density, from 21 kg tree−1 at 590 trees ha−1 to 6 kg tree−1 at 2950 trees ha−1. Stand increment typically follows the reverse pattern, increasing as density increases. This was the case for two clones (IP and B2), but stand increment was consistent across tree spacings for C3. Transpiration increased with density, from a low of 622 mm yr−1 to a high of 879 mm y−1. Some of the increased water use resulted from higher leaf area index at higher densities. The B2 clone transpired the most water on average, produced the greatest increment (23 Mg ha−1 yr−1 for 1030 trees ha−1), and produced the most wood L−1 transpiration (water use efficiency, 2.3 g biomass L−1). The clone C3 had the lowest increment (only 12 Mg ha−1 yr−1) because of the combination of low transpiration and low water use efficiency (only 1.5 g biomass L−1). Optimizing clone selection and silviculture for the combination of high yield and high water use efficiency may help reduce risks from drought as well as water conservation. [ABSTRACT FROM AUTHOR]

• We developed a set of parameters for the highest phenotypic plasticity Eucalyptus clone in Brazil. • Model calibration was performed in four experimental sites related to Brazilian climate diversity. • Model validation were obtained in 10 other sites of the same experimental network. • The model was able to capture the soil and climate differences to predict the clone productivity. • 3-PG model estimated productivity for extensive areas not yet exploited for Eucalyptus plantations. Different ecophysiological models are used to predict the productivity of forest plantations worldwide. The Physiological Principles in Prediction Growth (3-PG) model has been successfully used for this purpose since 1997. In this study, the 3-PG model was parameterized and validated to predict the productivity of the most planted clonal eucalypts in Brazil (Eucalyptus urophylla) in different regions of the country and assess the attainable productivity of this same clone for a region little exploited for this plantations in the country. Through data collection carried out between 2012 and 2018, conducted in 36 sites distributed across an environmental gradient that spans over 3500 km in Brazil, it was possible to parameterize the 3-PG model using data that represent a portion of the soil and climate diversity of forest plantations in Brazil. We determined the initial biomass of the compartments (stem, leaf, and root), relationship between net and gross productivity, average wood density, maximum stem biomass for 1000 trees ha−1, maximum stomatal conductance, bark and branch fractions for the initial and mature age, specific leaf area for the initial and mature age, and allometric parameters at different ages. Considering the model initialization period, the initial age was defined at 12 months after planting and the final age was considered at 80 months. Model calibration was performed in four experimental sites (special sites for the calibration set), which correspond to the environmental diversities of the project, and model validation was performed by applying the setup of the model obtained in 10 other sites (regular sites for validation set) of the same experimental network. In all sites tested, estimates of basal area, diameter at breast height, leaf area index, and stem biomass agreed with the measured values. On average, the estimates of diameter and breast height were 4.91% higher than the observed measures, whereas the stem biomass estimates were 16.44% lower and the leaf area index was 26.22% lower; moreover, the estimates were overestimated for the first three years and underestimated in recent years. Overall, the model was able to capture the soil and climate differences for predicting E. urophylla clone productivity. Its application in a region not yet exploited for eucalypts plantations may help investors in the region select areas for acquisition, planting extensions, and extend production technologies. [ABSTRACT FROM AUTHOR]

Short-rotation plantations are extending worldwide due to the increased demand for pulp and wood. Reliable estimations of recent expansion of short-rotation plantation areas and associated land use changes are a prerequisite to assess their environmental impact on regional carbon and water cycles, and on climate. A binary classification methodology using MODerate resolution Imaging Spectroradiometer (MODIS) 16-day 250 m NDVI time series was developed and applied to classify Eucalyptus plantations across Brazil. The identification of Eucalyptus plantations specific patterns in the time series was based on the calculation of matching functions between the NDVI time series and a ~ 2 years long reference time series. Among the seven tested matching functions, the bounding envelope was the most successful. This method was robust to residual noise on the NDVI time series, and a threshold coefficient for the binary classification was adjusted using an omission-commission criteria. With this method, it was possible to detect any presence of Eucalyptus between 2003 and 2009 at monthly time-steps, including the periods of bare soils between two rotations that are typically 6–7 years long. The dates of first afforestation, of clear-cut at the end of a rotation, and of re-planting at the beginning of a new rotation were retrieved from the NDVI time series with a precision of ~ 66 days. The final almost continuous tri-dimensional map (space and time) was validated with three different datasets, from local to regional data. All three datasets gave similarly high global accuracy statistics, but a global underestimation of Eucalyptus areas compared to large scales census was observed. Discrepancies and way to improve the Eucalyptus area estimates were discussed in this study. The developed methodology could be applied to other short-rotation tree plantations. [ABSTRACT FROM AUTHOR]

Abstract: The use of remote sensing is necessary for monitoring forest carbon stocks at large scales. Optical remote sensing, although not the most suitable technique for the direct estimation of stand biomass, offers the advantage of providing large temporal and spatial datasets. In particular, information on canopy structure is encompassed in stand reflectance time series. This study focused on the example of Eucalyptus forest plantations, which have recently attracted much attention as a result of their high expansion rate in many tropical countries. Stand scale time-series of Normalized Difference Vegetation Index (NDVI) were obtained from MODIS satellite data after a procedure involving un-mixing and interpolation, on about 15,000ha of plantations in southern Brazil. The comparison of the planting date of the current rotation (and therefore the age of the stands) estimated from these time series with real values provided by the company showed that the root mean square error was 35.5days. Age alone explained more than 82% of stand wood volume variability and 87% of stand dominant height variability. Age variables were combined with other variables derived from the NDVI time series and simple bioclimatic data by means of linear (Stepwise) or nonlinear (Random Forest) regressions. The nonlinear regressions gave r-square values of 0.90 for volume and 0.92 for dominant height, and an accuracy of about 25m3/ha for volume (15% of the volume average value) and about 1.6m for dominant height (8% of the height average value). The improvement including NDVI and bioclimatic data comes from the fact that the cumulative NDVI since planting date integrates the interannual variability of leaf area index (LAI), light interception by the foliage and growth due for example to variations of seasonal water stress. The accuracy of biomass and height predictions was strongly improved by using the NDVI integrated over the two first years after planting, which are critical for stand establishment. These results open perspectives for cost-effective monitoring of biomass at large scales in intensively-managed plantation forests. [Copyright &y& Elsevier]