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There is a public debate on how boreal forests can deliver climate change mitigation benefits. While most debates regarding Fennoscandian forests have centered on the contrasting effects of actively managed and old-growth unmanaged forests on carbon uptake and storage, the impact of surface albedo has often been overlooked. According to the new EU forest strategy for 2030, with aim of improving quantity and quality of forests by promoting primary old-growth forests and avoiding clear-cutting, among others, we examined how albedo across a wide age range of boreal Pinus-dominated forests develops over time after wildfire (defined as unmanaged) and clear-cutting (defined as managed). We find that albedo decreases over time after disturbance, but mainly in managed forests. Annual mean albedo in young (<30 years) managed forests (0.36±0.04) is markedly larger than in young unmanaged forests (0.18±0.04). This difference is particularly prominent during winter, when snow-covered ground is present. The mean albedo over the entire unmanaged forest-age gradient (0.17±0.05) is significantly lower (p < 0.05) than that of the managed forest-age gradient (0.23±0.10). Considering the typically higher frequency of clear-cuts compared to wildfires in Fennoscandian forests, these albedo differences would be even larger over long time scales. Our findings reveal the importance of considering the climatic cooling potential of albedo when making decisions on how to optimize future forest management in northern boreal forests to mitigate climate change.

Aim: Allometric relationships, which describe plant growth patterns shaped by environmental conditions, reflect functional trade-offs and represent key functional traits that optimise adaptation, resource acquisition, stress tolerance and competition. Here, we assess how these allometric relationships and associated functional trade-offs drive ecosystem structure, functioning and competitive interactions between plant functional types (PFTs) in savanna ecosystems.

Location: Rainfall gradient, North Australian Tropical Transect (NATT), Australia.

Time Period: 1901–2022.

Taxon: Tree species of Northern Australia.

Methods: Using quantile regression, we established adaptive allometric relationships among diameter at breast height, tree height, crown radius and crown volume. These relationships were integrated into a dynamic vegetation model to simulate tree growth and competitive interactions in local patches across the broader savanna landscape. The model was validated using observed biomass, height, leaf area index and productivity data from six flux tower sites across the NATT. A neighbour removal experiment was conducted to analyse PFT performance under varying competitive pressure, expressed as a competitive index.

Results: The results demonstrate that incorporating adaptive allometric relationships improved the model's ability to represent vegetation dynamics and productivity. Tall Eucalyptus PFTs exhibited competitive dominance in high rainfall areas, while Acacia and other deciduous species thrived under drier conditions. The neighbour removal experiment revealed that competition strongly influenced PFT performance, with carbon mass production varying significantly between stand types. Tall Eucalyptus PFTs showed little response to neighbour removal, while other PFTs benefitted strongly from neighbour removal. The competitive index of PFTs increased significantly with rainfall, indicating stronger competition under wetter conditions.

Main Conclusions: Our findings suggest that savanna ecosystems are shaped by complex interactions between growth conditions, functional traits and adaptive strategies for coping with competition and stress. These interactions are reflected in allometric relationships and the associated trade-offs in plant growth strategies, which vary across different rainfall gradients.

Tropical montane cloud forests (TMCFs) are globally important ecosystems, acting as large carbon sinks and supporting exceptional biodiversity. However, climate-driven declines in rainfall threaten these forests, but their responses to long-term soil moisture deficit remain poorly understood. We implemented a 5-year throughfall exclusion (TFE) experiment in a Peruvian TMCF, reducing soil moisture by 69.1% across a 0.09 ha plot. We compared the full carbon cycle budget, and surveyed tree physiological traits linked to hydraulics, metabolism and nutrients in the TFE plot and an adjacent, unmodified control (CON) plot. Soil drought reduced gross primary productivity by 4.24 ± 1.97 Mg C ha−1 year−1 but did not change net primary productivity because of an equivalent 3.38 ± 1.42 Mg C ha−1 year−1 decline in autotrophic respiration. Net ecosystem exchange also remained unchanged over 5 years of soil drought. Trees did not change xylem conductivity, hydraulic safety margins or photosynthetic capacity in the TFE, but did have 0.027 ± 0.011 g cm−3 denser wood and 4.58% ± 1.03% higher trunk starch concentrations. These results suggest that trees in TMCF avoid hydraulic failure and carbon starvation under sustained soil moisture drought via metabolic downregulation, resource conservation and non-structural carbohydrate storage. However, reduced uptake of nutrients (nitrogen, phosphorus, calcium) and 90.6% ± 29.8% decline in fruit production may impact future growth and demography. Our findings demonstrate surprising resilience of TMCFs to sustained, severe soil drought but highlight potential impacts on nutrient cycling and reproduction under climate change. Understanding the impacts of soil drought in conjunction with other climatic changes (e.g., fog reduction, temperature increases) is needed to fully assess the resilience of TMCFs to climate change.

Leaching – the release of elements from organic matter through dissolution in water – plays an important role in biogeochemical cycling and ecosystem processes. However, our limited understanding of the patterns and underlying drivers of element solubility in leaves hinders accurate predictions of leaching over space and time in terrestrial ecosystems. In this study, we quantify the solubility of carbon (C), nitrogen (N) and phosphorus (P) from leaves of Betula pubescens – a widespread boreal tree species – across a post-fire retrogressive chronosequence. We then relate solubility to variation in leaf-level traits and ecosystem properties (e.g. soil chemistry, tree density and productivity) across the chronosequence to quantify micro- and macro-scale determinants of leaching. We find that P is much more soluble than C and N and is released in solution mainly in readily accessible mineral form. Solubility patterns are strongly related to foliar chemical and structural traits, particularly for green leaves. Metrics related to ecosystem properties exert a stronger influence over solubility from senesced leaf litter. Overall, our results indicate that leaching could constitute an important flux of nutrients to the soil, particularly for P. The rate and spatio-temporal pattern of this leaching flux may be predicted from foliar traits and ecosystem properties. Further application of the method should allow for rapid integration of leaching-related foliar traits into broader plant trait frameworks and models of ecosystem biogeochemical cycling.

Effective environmental policies for the tropics depend on accurate, representative scientific data. However, there is strong evidence from particular disciplines and regions that existing research is patchily distributed. Here, we show that poor representation of sampling and citation in some biomes and across key environmental gradients from all disciplines for the entire tropics may lead to flawed scientific paradigms and inappropriate policy prescriptions. We map sampling locations and citations from 2 738 published studies in natural terrestrial tropical environments across all disciplines to identify gaps in field sampling effort and research attention. Five ecoregions – all in moist broadleaf forests – generate 22% of the total citations but cover only 3% of the tropical land area. By contrast, drier biomes with low tree cover account collectively for 57% of the tropical area but generate only 20% of total citations. Locations that are drier, colder, with greater plant species richness, lower tree cover and facing greater climate change extremes are under-sampled and under-cited. Our results will help to correct these imbalances to improve the scientific basis for environmental policies across the tropics.

Climate, forest successional stage, and soil substrate age can alter herbivore communities and their effects on biogeochemical cycling, but the size and spatial variability of these effects are poorly quantified. To address this knowledge gap, we established a globally distributed network of 50 broadleaved old-growth forests across six continents, encompassing well-constrained local-scale gradients in mean annual temperature (MAT), mean annual precipitation (MAP), succession, and soil substrate age. We used this network to investigate how these variables impact insect foliar herbivory and the associated carbon, nitrogen, phosphorus, and silica fluxes in forest ecosystems. Over 1 to 2 years, we measured stand-level foliar biomass production, leaf-level herbivory, and foliar element concentrations. At the global scale, insect herbivores liberated higher amounts of elements from the canopies of warmer and drier sites than those of cooler and wetter sites with patterns for phosphorus being most pronounced. MAT exerted a stronger influence over insect-mediated element fluxes than MAP. Foliar biomass production and leaf-level herbivory responses to MAT and MAP were mainly responsible for the observed changes in insect-mediated element fluxes; we also observed minor effects of foliar phosphorus concentration on phosphorus fluxes. Local-scale trends were mixed and successional stage or soil substrate age did not appear to influence insect herbivore-mediated element fluxes. These results demonstrate that climate effects on plant-herbivore interactions are stronger at large than small scales, at which herbivory rates and nutrient fluxes appear to be more strongly affected by a diversity of non-climate factors.

Dry and unproductive Scots pine forests in the northern boreal forest zone provide conditions where ground-dwelling lichens can thrive. These lichens are a crucial winter forage for reindeer. Reindeer reduce lichen biomass both by consumption and trampling, leading to cascading effects on microclimate, litter inputs, and soil carbon dynamics. To investigate long-term impacts of reindeer exclusion, we assessed the plant biomass, soil nutrients, and soil organic carbon (SOC) quantity and quality in three dry pine forest sites in northern Finland, where reindeer have been excluded for over 50 years. Within exclosures, lichen biomass was 4.5 times higher and dwarf shrub biomass nearly doubled compared to grazed controls. These vegetation changes were associated with a 33% higher soil moisture and 0.8 °C lower summer soil temperatures at 8 cm depth beneath the thicker lichen mats. The organic layer SOC stock was 28% higher in exclosures. Spectroscopic analysis using ¹³C NMR spectroscopy revealed 9.5% higher O-alkyl carbon (carbohydrates) content and lower methoxy (–5.1%), alkyl (–6.9%), and carbonyl (–8.7%) content, reflecting a younger, more labile carbon pool. Despite these changes, soil nutrient concentrations and C∶N ratios remained unchanged between treatments, suggesting that altered SOC storage and composition result primarily from increased litter inputs and microclimatic changes.  We conclude that in lichen-rich boreal forests, long-term reindeer exclusion enhances SOC stocks and promote a shift toward more decomposable soil organic matter, with potential implications for carbon stability following disturbance. 

The understory vegetation of boreal forests plays a crucial role in maintaining biodiversity by creating habitats, supplying food resources, and regulating microclimate and soil conditions. This essential layer is frequently affected by disturbances such as forest fires and clear-cutting, which significantly alter understory communities and the ecosystem resource availability and heterogeneity. This study aimed to understand how these disturbances influence the spatial and temporal dynamics of key ecosystem resources, and subsequently the patterns of understory diversity. We analyzed and compared understory vegetation diversity in a rotational management chronosequence and an unmanaged fire chronosequence of Scots pine Pinus sylvestris forests across northern Sweden. We assessed the relationship of above- and belowground resource availability and heterogeneity with alpha and beta diversity using generalized additive models and multivariate analyses. We found that belowground resource availability (especially inorganic nitrogen) and aboveground resource heterogeneity (especially variation in forest structural complexity) were most strongly positively correlated with alpha and beta diversity, varying across successional stages. In early stages (0–60 years), high availability of belowground resources and aboveground heterogeneity was associated with high alpha and beta diversity. In mid-stages (100–200 years), reduced belowground resource availability and aboveground heterogeneity was linked to lower diversity. In late stages (> 250 years, which only exists in the unmanaged fire chronosequence), increased aboveground heterogeneity associated with tree mortality was linked to a resurgence in alpha and beta diversity. These results highlight the necessity of maintaining a mosaic of stands with different disturbance regimes and successional stages, particularly early post-fire stands and late successional stands, which are currently much rarer on the landscape, to support biodiversity at the landscape level.

Environmental gradients affect vegetation structure and ecosystem productivity. Along the northern Australia tropical transect (NATT), which transitions from tropical moist conditions in the north to arid conditions in the south, vegetation composition and structure are closely tied to rainfall patterns. We hypothesise that biotic competition and abiotic stress exhibit opposing patterns along the NATT rainfall gradient and aim to disentangle these effects on vegetation structure and productivity. Using a trait-based dynamic vegetation model, we simulated vegetation responses to varying competition and stress along the NATT. The model successfully simulated spatial variations and temporal patterns in carbon and water fluxes, where evapotranspiration and gross primary productivity decrease with rainfall along the gradient. Simulation results showed that taller and medium-sized Eucalyptus had higher carbon mass, leaf area index, and foliar projective cover at the wet end of the gradient. In contrast, Acacia and grasses were dominant at the dry end. Crown coverage shows spatial and temporal variability with rainfall, with higher variability in tree plant functional types (PFTs) crown cover in the north and more uniform in the south, while grasses have maximum coverage during the wet season in the dry end of the gradient. These patterns suggest a shift in the importance of biotic versus abiotic factors, with competition playing a more significant role in the wet region and stress becoming more influential as aridity increases in the south. Overall, our study underscores water availability as a primary driver of vegetation structure and highlights the role of competition and stress in modulating ecosystem structure, composition, and productivity along the rainfall gradient.

Fog makes a significant contribution to the hydrology of a wide range of important terrestrial ecosystems. The amount and frequency of fog immersion are affected by rapid ongoing anthropogenic changes but the impacts of these changes remain relatively poorly understood compared with changes in rainfall.

Here, we present the design and performance of a novel experiment to actively manipulate low lying fog abundance in an old-growth tropical montane cloud forest (TMCF) in Peru—the Wayqecha Amazon Cloud Curtain Ecosystem Experiment (WACCEE). The treatment consists of a 30 m high, 40 m wide mesh curtain suspended between two towers and extending down to the ground, and two supplementary curtains orientated diagonally inwards from the top of each tower and secured to the ground upslope. The curtains divert and intercept airborne water droplets in fog moving upslope, thereby depriving a ~420 m2 patch of forest immediately behind the curtains of this water source. We monitored inside the treatment and a nearby unmodified control plot various metrics of water availability (air humidity, vapour pressure deficit, leaf wetness and soil moisture) and other potentially confounding variables (radiation, air and soil temperature) above and below the forest canopy. The treatment caused a strong reduction in both air humidity and leaf wetness, and an increase in vapour pressure deficit, above the canopy compared to the control plot. This effect was most pronounced during the nighttime (20:00–05:00). Below-canopy shifts within the treatment were more subtle: relative humidity at 2 m height above the ground was significantly suppressed during the daytime, while soil moisture was apparently elevated. The treatment caused a small but significant increase in air temperature above the canopy but a decrease in temperature in and near the soil, while mixed effects were observed at 2 m height above the ground. Above-canopy radiation was slightly elevated on the treatment relative to the control, particularly during the dry season. Further application of the method in other systems where fog plays a major role in ecosystem processes could improve our understanding of the ecological impacts of this important but understudied climate driver.