AbstractSecondary tropical forests are at the forefront of deforestation pressures. They store large amounts of carbon, which, if compensated for to avoid net emissions associated with conversion to non-forest uses, may help advance tropical forest conservation. We measured above- and below-ground carbon stocks down to 1 m soil depth across a secondary forest and in oil palm plantations in Malaysia. We calculated net carbon losses when converting secondary forests to oil palm plantations and estimated payments to avoid net emissions arising from land conversion to a 22-year oil palm rotation, based on land opportunity costs per hectare. We explored how estimates would vary between forests by also extracting carbon stock data for primary forest from the literature. When tree and soil carbon was accounted for, payments of US$18–51 tCO2–1 for secondary forests and US$14–40 tCO2–1 for primary forest would equal opportunity costs associated with oil palm plantations per hectare. If detailed assessments of soil carbon were not accounted for, payments to offset opportunity costs would need to be considerably higher for secondary forests (US$28–80 tCO2–1). These results show that assessment of carbon stocks down to 1 m soil depth in tropical forests can substantially influence the estimated value of avoided-emission payments.

We compared three methods of estimating gross primary production (GPP) of a boreal forest dominated by spruce and pine with the goals of 1) converging on the best estimate and 2) disaggregating the GPP among the two canopy species and the understory stratum. The three methods were: 1) eddy covariance (EC), 2) a soil-vegetation-atmosphere transfer model, APES, driven by meteorological data, and 3) an ecophysiological approach (Iso/SF) based on sap flux and phloem delta C-13, where sap flux is used to estimate stomatal conductance and delta C-13 is used to estimate intrinsic water-use efficiency (WUEi). The EC and APES methods agreed rather well, which was expected because APES was developed to predict eddy covariance data. The Iso/SF method, which is based on independent data, yielded lower estimates. This was partly because it excluded understory vegetation from the GPP estimate. We also found that the measured sap flux/transpiration estimates for spruce in Iso/SF were much lower than those from APES. In contrast, the absolute values for Scots pines were very similar between the two methods, especially in the summer. In both species, the seasonal dynamics match well among all methods. This multi-method approach allowed us to detect possible problems in the spruce sap-flux measurements, but successfully upscaled pine data from ecophysiological traits to stand and ecosystem functioning.

Demand for tropical timber is expected to rise due to an increased global need for sustainable renewable materials. However, sustainable tropical timber production remains a challenge for the global wood product supply chain, especially for high-value tropical hardwoods. Restoration of degraded lands through enrichment planting of native hardwood species could provide a solution, but the financial viability of using native tropical tree species remains largely unknown. We evaluated the financial viability of 22 hardwood tree species native to northern Borneo in enrichment plantings of a degraded forest in Sabah, Malaysia. We investigated how the species’ financial value, expressed as an internal rate of return (IRR) based on land expectation value, varied with their functional trait composition. We found that high financial value was positively correlated with trait values associated with a conservative growth strategy, i.e., financial value was negatively correlated with leaf calcium, magnesium, and nitrogen content, as well as with leaf pH and specific leaf area. Trees with these traits showed a high IRR, partly explained by relatively fast growth and high survival rates. For the most economically promising species, Shorea macrophylla , we estimated that enrichment planting for forest restoration could reach IRRs up to 7.8%. Our results showed that enrichment planting for high-value hardwood production in degraded forests can be financially viable, with variation among species, and that various traits associated with a more conservative growth strategy were linked to high financial value.

Background Fungal morphology such as the hydrophobicity of ectomycorrhizae may correspond to functional attributes including enzymatic capabilities, carbon (C) demand from host plants, temporal patterns of fruiting, C sequestration, and nitrogen (N) sequestration. Here, we assessed how ectomycorrhizal hydrophobicity influenced the timing of C dynamics and fungal processing of C and N, as integrated by fruiting patterns, δ 13 C, δ 15 N, and log e C/N of ectomycorrhizal sporocarps. Methods We linked δ 13 C, δ 15 N, log e C/N, and temporal fruiting patterns of ectomycorrhizal sporocarps and soils across seven N fertilization treatments in two Swedish Pinus sylvestris L. forests to ectomycorrhizal hydrophobicity and daily gross primary production. Results Gross primary production of seven and 6–9 days prior to collection correlated positively with sporocarp δ 13 C and log e C/N, respectively, reflecting transit times of peak delivery of plant-derived carbohydrates to sporocarp formation. Hydrophobic taxa fruited 10 days later than hydrophilic taxa, suggesting greater C demands for hydrophobic taxa. Taxa with hydrophobic ectomycorrhizae had lower δ 13 C, higher δ 15 N, and higher log e C/N (less protein) than taxa with hydrophilic ectomycorrhizae. Conclusions Long C accumulation times and high sequestration (hydrophobic taxa) versus low sequestration (hydrophilic taxa) of 13 C-enriched carbohydrates and 15 N-depleted chitin in mycelia could account for the late fruiting, 13 C depletion, and 15 N enrichment of hydrophobic sporocarps. We concluded that sporocarp production and hydrophobicity integrated functional information about the extent of belowground hyphal development and the C accumulation times of C transfers from host Pinus .

The tropical rainforest has various lists of crucial functions in forest productivity. However, unsustainable logging method has led to the decline of soil fertility in the forest. This study aimed to investigate the impacts of different logging methods on the soil’s physical and chemical properties at Gunung Rara Forest Reserve, Sabah, Malaysia. The logging treatments were supervised logging with climber cutting (SLCC) and conventional logging (CL), and a virgin forest (VF) was used as the control plot. The size for each plot was one hectare and each was replicated into four plots making the total plots 12. Soil sampling was done at four depths (0–10 cm, 10–20 cm, 20–50 cm, and 50–100 cm) for soil analysis and bulk density. The finding shows that the soil properties in the treatment plots were not significantly different from the untreated plot. The soil organic matter, total nitrogen, and total carbon decreased with soil depths. The soil in all study areas was found acidic, ranging from 4.12 to 4.46. The soil textures were clay, sandy clay loam, and sandy loam. The SLCC plot recorded a higher mean of soil organic matter (5.93–7.40%), total phosphorus (0.08–0.09 meq/100 g), and cation exchange capacity (5.69–7.05 meq/100 g) compared to other plots. This study highlights the importance of analysing the impact of different logging methods on the soil’s physicochemical properties.

A global push to increase reliance on sustainable renewable materials is expected to increase the demand for tropical timber. However, sustainable production of tropical timber, especially high-value tropical hardwoods, remains a challenge for the global wood product supply chain. Restoration of degraded lands through enrichment planting of native tree species could provide a solution, but its financial viability for the majority of native tropical tree species is unknown. We evaluated the financial viability of 22 tree hardwood species native to northern Borneo in enrichment plantings of a degraded forest in Sabah, Malaysia. In addition, we investigated how the species’ financial value varied with their plant functional trait composition. Our results suggest that enrichment planting for forest restoration could be financially viable, with internal rates of return of up to 13% for the most valuable species. Shorea macrophylla , Shorea leprosula , and Diospyros sp. showed particularly high financial potential. Different traits were associated with financial value in the Dipterocarpaceae family and non-dipterocarps. In dipterocarps, high financial value correlated with low wood density, leaf pH, magnesium content, relative crown depth, and stem slenderness, whereas in non-dipterocarps it correlated with high leaf potassium, magnesium, and pH levels, as well as wood density. These correlations did not follow the distributions predicted by the plant economic spectrum. Our results show that enrichment planting for high value hardwood production in degraded forests can be financially viable, at least for some species, and that the traits linked to high financial value differ between taxonomic groups.

This review presents how the boreal and the tropical forests affect the atmosphere, its chemical composition, its function, and further how that affects the climate and, in return, the ecosystems through feedback processes. Observations from key tower sites standing out due to their long-term comprehensive observations: The Amazon Tall Tower Observatory in Central Amazonia, the Zotino Tall Tower Observatory in Siberia, and the Station to Measure Ecosystem-Atmosphere Relations at Hyytiäla in Finland. The review is complemented by short-term observations from networks and large experiments. The review discusses atmospheric chemistry observations, aerosol formation and processing, physiochemical aerosol, and cloud condensation nuclei properties and finds surprising similarities and important differences in the two ecosystems. The aerosol concentrations and chemistry are similar, particularly concerning the main chemical components, both dominated by an organic fraction, while the boreal ecosystem has generally higher concentrations of inorganics, due to higher influence of long-range transported air pollution. The emissions of biogenic volatile organic compounds are dominated by isoprene and monoterpene in the tropical and boreal regions, respectively, being the main precursors of the organic aerosol fraction. Observations and modeling studies show that climate change and deforestation affect the ecosystems such that the carbon and hydrological cycles in Amazonia are changing to carbon neutrality and affect precipitation downwind. In Africa, the tropical forests are so far maintaining their carbon sink. It is urgent to better understand the interaction between these major ecosystems, the atmosphere, and climate, which calls for more observation sites, providing long-term data on water, carbon, and other biogeochemical cycles. This is essential in finding a sustainable balance between forest preservation and reforestation versus a potential increase in food production and biofuels, which are critical in maintaining ecosystem services and global climate stability. Reducing global warming and deforestation is vital for tropical forests.

The soil carbon pool holds an enormous amount of carbon, making it the largest reservoir in the terrestrial ecosystem. However, there is growing concern that unsustainable logging methods damage the soil ecosystem, thus triggering the release of soil carbon into the atmosphere hence contributing to ongoing climate change. This study uses a replicated (n = 4) logging experiment to examine the impact of supervised logging with climber cutting (SLCC) and conventional logging (CL) on basic soil characteristics, litter input to soils, soil carbon pools, and soil respiration in a mixed dipterocarp forest 26 years after logging. This study found that there was no significant difference observed in the soil physicochemical properties and total carbon pools between the logging treatments and the virgin forest. Soil carbon pools dominated the total carbon pools, and the highest mean value was recorded in SLCC (87.95 ± 13.67 Mg C ha−1). Conventional logging had a lower mean value (71.17 ± 12.09 Mg C ha−1) than virgin forest (83.20 ± 11.97 Mg C ha−1). SLCC also shows a higher value of soil respiration rate (161.75 ± 21.67 mg C m−2 h−1) than CL (140.54 ± 12.54 mg C m−2 h−1). These findings highlight the importance of accurate quantification of the effect of different logging methods on the forest’s carbon pools.

Trees in northern latitude ecosystems are projected to experience increasing drought stress as a result of rising air temperatures and changes in precipitation patterns in northern latitude ecosystems. However, most drought‐related studies on high‐latitude boreal forests (>50°N) have been conducted in North America, with few studies quantifying the response in European and Eurasian boreal forests. Here, we tested how daily whole‐tree transpiration ( Q , Liters day −1 ) and Q normalized for mean daytime vapor pressure deficit ( Q DZ , Liters day −1 kPa −1 ) were affected by the historic 2018 drought in Europe. More specifically, we examined how tree species, size, and topographic position affected drought response in high‐latitude mature boreal forest trees. We monitored 30 Pinus sylvestris (pine) and 30 Picea abies (spruce) trees distributed across a topographic gradient in northern Sweden. In general, pine showed a greater Q DZ control compared to spruce during periods of severe drought (standardized precipitation–evapotranspiration index: SPEI < −1.5), suggesting that the latter are more sensitive to drought. Overall, Q DZ reductions (using non‐drought Q DZ as reference) were less pronounced in larger trees during severe drought, but there was a species‐specific pattern: Q DZ reductions were greater in pine trees at high elevations and greater in spruce trees at lower elevations. Despite lower Q DZ during severe drought, drought spells were interspersed with small precipitation events and overcast conditions, and Q DZ returned to pre‐drought conditions relatively quickly. This study highlights unique species‐specific responses to drought, which are additionally driven by a codependent interaction among tree size, relative topographic position, and unique regional climate conditions.

Deforestation has created heterogeneous patches of old-growth and secondary forests throughout Southeast Asia, posing challenges for understanding the hydrological and carbon cycles. In addition to changes in species composition, environmental conditions differ across successional stages which in turn can influence forest water use and productivity. Here, we investigated leaf-level area-based photosynthesis (Aarea) and stomatal conductance (gs) of 11 tree species dominating an old-growth (OF; >200 years), an intermediate (IF; -44 years), and a young forest (YF; -4 years) in Thailand during both the wet and dry season. Specifically, we compared Aarea and gs and assessed the sensitivity of gs to vapor pressure deficit (VPD). We also examined relationships between gas exchange parameters and key functional leaf traits, including leaf mass per area (LMA), nitrogen (N), phosphorus (P), and chlorophyll concentration. All three forests showed comparable Aarea and gs in the wet season, whereas significantly lower values were observed in IF during the dry season. All forest stages displayed similar sensitivity of gs to VPD. Among the leaf functional traits considered, LMA, N and P were significantly higher in YF compared to the other two successional stages. Our results suggested that forest succession may not influence gas exchange, rather, canopy development associated with forest stage produced the main effect. Furthermore, the young forest was the most active in resource acquisition with its high LMA and leaf nutrient concentrations, which could result in high photosynthetic rates. However, low soil water availability in YF possibly limit the gas exchange rates thereby making them similar to those in the old-growth forest. These findings highlight the potential effects of canopy characteristics inherent in successional forests on water and carbon exchanges between trees and the atmosphere and their sensitivity to atmospheric drought. These results call for the need for further studies to identify the main factors influencing forest productivity during secondary succession in the tropics, particularly in the Southeast Asian region where such information is lacking.

Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land–atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The “sapfluxnetr” R package – designed to access, visualize, and process SAPFLUXNET data – is available from CRAN.

Improving our ability to detect changes in terrestrial and aquatic systems is a grand challenge in the environmental sciences. In a world experiencing increasingly rapid rates of climate change and ecosystem transformation, our ability to understand and predict how, when, where, and why changes occur is essential for adapting and mitigating human behaviours. In this context, long-term field research infrastructures have a fundamentally important role to play. For northern boreal landscapes, the Krycklan Catchment Study (KCS) has supported monitoring and research aimed at revealing these changes since it was initiated in 1980. Early studies focused on forest regeneration and microclimatic conditions, nutrient balances and forest hydrology, which included monitoring climate variables, water balance components, and stream water chemistry. The research infrastructure has expanded over the years to encompass a 6790 ha catchment, which currently includes 11 gauged streams, ca. 1000 soil lysimeters, 150 groundwater wells, >500 permanent forest inventory plots, and a 150 m tall tower (a combined ecosystem-atmosphere station of the ICOS, Integrated Carbon Observation System) for measurements of atmospheric gas concentrations and biosphere-atmosphere exchanges of carbon, water, and energy. In addition, the KCS has also been the focus of numerous high resolution multi-spectral LiDAR measurements and large scale experiments. This large collection of equipment and data generation supports a range of disciplinary studies, but more importantly fosters multi-, trans-, and interdisciplinary research opportunities. The KCS attracts a broad collection of scientists, including biogeochemists, ecologists, foresters, geologists, hydrologists, limnologists, soil scientists, and social scientists, all of whom bring their knowledge and experience to the site. The combination of long-term monitoring, shorter-term research projects, and large-scale experiments, including manipulations of climate and various forest management practices, has contributed much to our understanding of boreal landscape functioning, while also supporting the development of models and guidelines for research, policy, and management.

As a result of canopy interception and transpiration, trees are often assumed to have negative effects on the local hydrological budget resulting in reduced soil and groundwater resources. However, it has also been shown that trees can have positive effects through reducing surface run-off and improving soil infiltrability and groundwater recharge, especially in many tropical ecosystems characterized by high rain intensity and degradation-prone soils. In this study, we used isotopic measurements of soil water to better understand the main processes by which trees influence local soil water dynamics within a tropical pasture with scattered tree cover in the Copan River catchment, Honduras. We also determined the stable isotope signature of xylem water in grasses and trees to assess potential competition for water sources during the wet and dry seasons. During the wet season, when soil water availability was not limiting, both grasses and trees primarily utilized soil water near the soil surface (i.e., 0–10 cm). In contrast, during the dry season, we observed niche partitioning for water resources where grasses primarily utilized soil moisture at deeper soil depth (i.e., 90–100 cm) while trees relied heavily on groundwater. Moreover, isotopic data of soil water suggest that trees reduce evaporative water losses from the soil surface, as indicated by the lack of correlation between soil water content and lc-excess (line condition excess) values of surface soil water under trees, and enhance preferential flow as suggested by less negative lc-excess values under trees compared to open areas during the dry season. Taken together, our findings provide further support that trees can have positive effects on the local water balance with implication for landscape management, promoting the inclusion of scattered trees to provide water ecosystem services in silvopastoral systems, adding to other ecosystem services like biodiversity or carbon sequestration.

Forests pass water and carbon through while converting portions to streamflow, soil organic matter, wood production, and other ecosystem services. The efficiencies of these transfers are but poorly quantified. New theory and new instruments have made it possible to use stable isotope composition to provide this quantification of efficiencies wherever there is a measurable difference between the branches of a branchpoint. We present a linked conceptual model that relies on isotopes of hydrogen, carbon, and oxygen to describe these branchpoints along the pathway from precipitation to soil and biomass carbon sequestration and illustrate how it can be tested and generalized.

Forests have long been locations of contestation between people and state bureaucracies, and among the knowledge frameworks of local users, foresters, ecologists, and conservationists. An essential framing of the debate has been between the categories of primary and secondary forest. In this introduction to a collection of papers that address the questions of what basis, in what sense, and for whom primary forest is 'primary' and secondary forest is 'secondary,' and whether these are useful distinctions, we outline this debate and propose a new conceptual model that departs from the simple binary of primary and secondary forests. Rather, we propose that attention should be given to the nature of the disturbance that may alter forest ecology, the forms of regeneration that follow, and the governance context within which this takes place.

Stand-scale estimates of gross primary production (GPP) commonly depend on eddy-covariance or eddy-covariance derived models. Chamber-based methods provide an alternative, but they are tricky to scale up to the stand. We estimate GPP by combining isotopic δ13C of phloem sugars with sap-flow measurements. The method consists of calculating intrinsic water-use efficiency and transpiration to determine GPP. We have improved this approach by considering mesophyll conductance and seasonal variation in photosynthetic capacity and then compared our results to a semi-empirical eddy-covariance based model, PRELES. We compared a fertilised plot and an unfertilised plot in a monospecific Scots pine forest in northern Sweden. The method captured both the stand response to fertilisation and seasonal patterns, as PRELES did. Our results demonstrate the importance of considering a finite mesophyll conductance value to avoid an unreasonable overestimate of GPP. We have now applied the method in a mixed boreal forest where we will partition total stand GPP among the three dominant tree species (pine, spruce, and birch). This approach provides an independent test of GPP estimates and provides a means of estimating GPP where eddy-covariance assumptions are not met.

Although it is well known that evapotranspiration (ET) represents an important water flux at local to global scales, few studies have quantified the magnitude and relative importance of ET and its individual flux components in high-latitude forests. In this study, we combined empirical sapflux, throughfall, and eddy-covariance measurements with estimates from a process-based model to partition the water balance in a northern boreal forested catchment. This study was conducted within the Krycklan catchment, which has a rich history of hydrological measurements, thereby providing us with the unique opportunity to compare the absolute and relative magnitudes of ET and its flux components to other water balance components. During the growing season, ET represented ca. 85 % of the incoming precipitation. Both empirical results and model estimates suggested that tree transpiration (T) and evaporation of intercepted water from the tree canopy (I-C) represented 43 % and 31 % of ET, respectively, and together were equal to ca. 70 % of incoming precipitation during the growing season. Understory evapotranspiration (ETu) was less important than T and I-C during most of the study period, except for late autumn, when ETu was the largest ET flux component. Overall, our study high-lights the importance of trees in regulating the water cycle of boreal catchments, implying that forest management impacts on stand structure as well as climate change effects on tree growth are likely to have large cascading effects on the way water moves through these forested landscapes.

Methane (CH4) oxidation is an important process for regulating CH4 emissions from peatlands as it oxidizes CH4 to carbon dioxide (CO2). Our current knowledge about its temporal dynamics and contribution to ecosystem CO2 fluxes is, however, limited due to methodological constraints. Here, we present the first results from a novel method for quantifying in-situ CH4 oxidation at high temporal resolution. Using an automated chamber system, we measured the isotopic signature of heterotrophic respiration (CO2 emissions from vegetation-free plots) at a boreal mire in northern Sweden. Based on these data we calculated CH4 oxidation rates using a two-source isotope mixing model. During the measurement campaign, 74 % of potential CH4 fluxes from vegetation-free plots were oxidized to CO2, and CH4 oxidation contributed 20 ± 2.5 % to heterotrophic respiration corresponding to 10 ± 0.5 % of ecosystem respiration. Furthermore, the contribution of CH4 oxidation to heterotrophic respiration showed a distinct diurnal cycle being negligible during nighttime while contributing up to 35 ± 3.0 % during the daytime. Our results show that CH4 oxidation may represent an important component of the peatland ecosystem respiration and highlight the value of our method for measuring in-situ CH4 oxidation to better understand carbon dynamics in peatlands.

AimsThe growing demand from forest managers is to identify silvicultural practices to overcome projected water scarcity during the next decades. One solution is to mix tree species in the same stand, thereby increasing resource partitioning and minimizing competition for limited soil water. This study investigates the mixture approach for Quercus petraea (Matt.) Liebl. and Pinus sylvestris L. during an extreme summer drought event.MethodsDuring the summer drought event in 2016, we analyzed the isotopic signatures of large- and small-tree xylem and soil water throughout the soil profile to assess the depth of water uptake for both tree species. We also measured predawn leaf water potentials (PLWP) to assess water availability for individual tree species.ResultsWhen grown in pure stands, both species primarily utilized soil water near the surface. In contrast, partial niche complementarity for limited water resources between the two species in mixed stands resulted in less water constraint (i.e., less negative PLWP) for oak trees compared to pure stands, especially for small trees.ConclusionsResults from this study show that contrasting water use strategies can change water availability for trees and could help some species, though not all, to cope with the water scarcity predicted in a changing climate.