Reducing uncertainties in the response of tropical forests to global change requires understanding how intra- and interannual climatic variability selects for different species, community functional ...composition and ecosystem functioning, so that the response to climatic events of differing frequency and severity can be predicted.
Here we present an extensive dataset of hydraulic traits of dominant species in two tropical Amazon forests with contrasting precipitation regimes – low seasonality forest (LSF) and high seasonality forest (HSF) – and relate them to community and ecosystem response to the El Niño–Southern Oscillation (ENSO) of 2015.
Hydraulic traits indicated higher drought tolerance in the HSF than in the LSF. Despite more intense drought and lower plant water potentials in HSF during the 2015-ENSO, greater xylem embolism resistance maintained similar hydraulic safety margin as in LSF. This likely explains how ecosystem-scale whole-forest canopy conductance at HSF maintained a similar response to atmospheric drought as at LSF, despite their water transport systems operating at different water potentials.
Our results indicate that contrasting precipitation regimes (at seasonal and interannual time scales) select for assemblies of hydraulic traits and taxa at the community level, which may have a significant role in modulating forest drought response at ecosystem scales.
Understanding the relationship between photosynthesis, net primary productivity and growth in forest ecosystems is key to understanding how these ecosystems will respond to global anthropogenic ...change, yet the linkages among these components are rarely explored in detail. We provide the first comprehensive description of the productivity, respiration and carbon allocation of contrasting lowland Amazonian forests spanning gradients in seasonal water deficit and soil fertility. Using the largest data set assembled to date, ten sites in three countries all studied with a standardized methodology, we find that (i) gross primary productivity (GPP) has a simple relationship with seasonal water deficit, but that (ii) site‐to‐site variations in GPP have little power in explaining site‐to‐site spatial variations in net primary productivity (NPP) or growth because of concomitant changes in carbon use efficiency (CUE), and conversely, the woody growth rate of a tropical forest is a very poor proxy for its productivity. Moreover, (iii) spatial patterns of biomass are much more driven by patterns of residence times (i.e. tree mortality rates) than by spatial variation in productivity or tree growth. Current theory and models of tropical forest carbon cycling under projected scenarios of global atmospheric change can benefit from advancing beyond a focus on GPP. By improving our understanding of poorly understood processes such as CUE, NPP allocation and biomass turnover times, we can provide more complete and mechanistic approaches to linking climate and tropical forest carbon cycling.
Each year, tropical rivers export a dissolved organic carbon (DOC) flux to the global oceans that is equivalent to ~4% of the global land sink for atmospheric CO2. Among the most refractory fractions ...of terrigenous DOC is dissolved black carbon (DBC), which constitutes ~10% of the total DOC flux and derives from the charcoal and soot (aerosol) produced during biomass burning and fossil fuel combustion. Black carbon (BC) has disproportionate storage potential in oceanic pools and so its export has implications for the fate and residence time of terrigenous organic carbon (OC). In contrast to bulk DOC, there is limited knowledge of the environmental factors that control riverine fluxes of DBC. We thus completed a comprehensive assessment of the factors controlling DBC export in tropical rivers with catchments distributed across environmental gradients of hydrology, topography, climate, and soil properties. Generalized linear models explained 70 and 64% of the observed variance in DOC and DBC concentrations, respectively. DOC and DBC concentrations displayed coupled responses to the dominant factors controlling their riverine export (soil moisture, catchment slope, and catchment stocks of OC or BC, respectively) but varied divergently across gradients of temperature and soil properties. DBC concentrations also varied strongly with aerosol BC deposition rate, indicating further potential for deviation of DBC fluxes from those of DOC due to secondary inputs of DBC from this unmatched source. Overall, this study identifies the specific drivers of BC dynamics in river catchments and fundamentally enhances our understanding of refractory DOC export to the global oceans.
Key Points
Common hydrological factors explain variability in riverine dissolved organic carbon and dissolved black carbon concentrations, however;
Variation in soil properties, temperature, antecedent rainfall, and aerosol deposition may drive divergence in their relative abundance
At an unprecedented geographic scale, we find that aerosol BC contributes significantly to riverine fluxes of DBC
Concerted political attention has focused on reducing deforestation, and this remains the cornerstone of most biodiversity conservation strategies. However, maintaining forest cover may not reduce ...anthropogenic forest disturbances, which are rarely considered in conservation programmes. These disturbances occur both within forests, including selective logging and wildfires, and at the landscape level, through edge, area and isolation effects. Until now, the combined effect of anthropogenic disturbance on the conservation value of remnant primary forests has remained unknown, making it impossible to assess the relative importance of forest disturbance and forest loss. Here we address these knowledge gaps using a large data set of plants, birds and dung beetles (1,538, 460 and 156 species, respectively) sampled in 36 catchments in the Brazilian state of Pará. Catchments retaining more than 69–80% forest cover lost more conservation value from disturbance than from forest loss. For example, a 20% loss of primary forest, the maximum level of deforestation allowed on Amazonian properties under Brazil’s Forest Code, resulted in a 39–54% loss of conservation value: 96–171% more than expected without considering disturbance effects. We extrapolated the disturbance-mediated loss of conservation value throughout Pará, which covers 25% of the Brazilian Amazon. Although disturbed forests retained considerable conservation value compared with deforested areas, the toll of disturbance outside Pará’s strictly protected areas is equivalent to the loss of 92,000–139,000 km2 of primary forest. Even this lowest estimate is greater than the area deforested across the entire Brazilian Amazon between 2006 and 2015 (ref. 10). Species distribution models showed that both landscape and within-forest disturbances contributed to biodiversity loss, with the greatest negative effects on species of high conservation and functional value. These results demonstrate an urgent need for policy interventions that go beyond the maintenance of forest cover to safeguard the hyper-diversity of tropical forest ecosystems.
The globally important carbon sink of intact, old-growth tropical humid forests is declining because of climate change, deforestation and degradation from fire and logging
. Recovering tropical ...secondary and degraded forests now cover about 10% of the tropical forest area
, but how much carbon they accumulate remains uncertain. Here we quantify the aboveground carbon (AGC) sink of recovering forests across three main continuous tropical humid regions: the Amazon, Borneo and Central Africa
. On the basis of satellite data products
, our analysis encompasses the heterogeneous spatial and temporal patterns of growth in degraded and secondary forests, influenced by key environmental and anthropogenic drivers. In the first 20 years of recovery, regrowth rates in Borneo were up to 45% and 58% higher than in Central Africa and the Amazon, respectively. This is due to variables such as temperature, water deficit and disturbance regimes. We find that regrowing degraded and secondary forests accumulated 107 Tg C year
(90-130 Tg C year
) between 1984 and 2018, counterbalancing 26% (21-34%) of carbon emissions from humid tropical forest loss during the same period. Protecting old-growth forests is therefore a priority. Furthermore, we estimate that conserving recovering degraded and secondary forests can have a feasible future carbon sink potential of 53 Tg C year
(44-62 Tg C year
) across the main tropical regions studied.
CONTEXT: Vegetation is projected to continue to undergo major structural changes in coming decades due to land conversion and climate change, including widespread forest die-offs. These vegetation ...changes are important not only for their local or regional climatic effects, but also because they can affect climate and subsequently vegetation in other regions or continents through “ecoclimate teleconnections”. OBJECTIVES: We propose that ecoclimate teleconnections are a fundamental link among regions within and across continents, and are central to advancing large-scale macrosystems ecology. METHODS AND RESULTS: We illustrate potential ecoclimate teleconnections in a bounding simulation that assumes complete tree cover loss in western North America due to tree die-off, and which predicts subsequent drying and reduced net primary productivity in other areas of North America, the Amazon and elsewhere. Central to accurately modeling such ecoclimate teleconnections is characterizing how vegetation change alters albedo and other components of the land-surface energy balance and then scales up to impact the climate system. We introduce a framework for rapid field-based characterization of vegetation structure and energy balance to help address this challenge. CONCLUSIONS: Ecoclimate teleconnections are likely a fundamental aspect of macrosystems ecology needed to account for alterations to large-scale atmospheric-ecological couplings in response to vegetation change, including deforestation, afforestation and die-off.
The net primary productivity, carbon (C) stocks and turnover rates (i.e. C dynamics) of tropical forests are an important aspect of the global C cycle. These variables have been investigated in ...lowland tropical forests, but they have rarely been studied in tropical montane forests (TMFs). This study examines spatial patterns of above‐ and belowground C dynamics along a transect ranging from lowland Amazonia to the high Andes in SE Peru. Fine root biomass values increased from 1.50 Mg C ha⁻¹ at 194 m to 4.95 ± 0.62 Mg C ha⁻¹ at 3020 m, reaching a maximum of 6.83 ± 1.13 Mg C ha⁻¹ at the 2020 m elevation site. Aboveground biomass values decreased from 123.50 Mg C ha⁻¹ at 194 m to 47.03 Mg C ha⁻¹ at 3020 m. Mean annual belowground productivity was highest in the most fertile lowland plots (7.40 ± 1.00 Mg C ha⁻¹ yr⁻¹) and ranged between 3.43 ± 0.73 and 1.48 ± 0.40 Mg C ha⁻¹ yr⁻¹ in the premontane and montane plots. Mean annual aboveground productivity was estimated to vary between 9.50 ± 1.08 Mg C ha⁻¹ yr⁻¹ (210 m) and 2.59 ± 0.40 Mg C ha⁻¹ yr⁻¹ (2020 m), with consistently lower values observed in the cloud immersion zone of the montane forest. Fine root C residence time increased from 0.31 years in lowland Amazonia to 3.78 ± 0.81 years at 3020 m and stem C residence time remained constant along the elevational transect, with a mean of 54 ± 4 years. The ratio of fine root biomass to stem biomass increased significantly with increasing elevation, whereas the allocation of net primary productivity above‐ and belowground remained approximately constant at all elevations. Although net primary productivity declined in the TMF, the partitioning of productivity between the ecosystem subcomponents remained the same in lowland, premontane and montane forests.
Strategies to mitigate climate change by reducing deforestation and forest degradation (e.g. REDD+) require country‐ or region‐specific information on temporal changes in forest carbon (C) pools to ...develop accurate emission factors. The soil C pool is one of the most important C reservoirs, but is rarely included in national forest reference emission levels due to a lack of data. Here, we present the soil organic C (SOC) dynamics along 20 years of forest‐to‐pasture conversion in two subregions with different management practices during pasture establishment in the Colombian Amazon: high‐grazing intensity (HG) and low‐grazing intensity (LG) subregions. We determined the pattern of SOC change resulting from the conversion from forest (C3 plants) to pasture (C4 plants) by analysing total SOC stocks and the natural abundance of the stable isotopes 13C along two 20‐year chronosequences identified in each subregion. We also analysed soil N stocks and the natural abundance of 15N during pasture establishment. In general, total SOC stocks at 30 cm depth in the forest were similar for both subregions, with an average of 47.1 ± 1.8 Mg C ha−1 in HG and 48.7 ± 3.1 Mg C ha−1 in LG. However, 20 years after forest‐to‐pasture conversion SOC in HG decreased by 20%, whereas in LG SOC increased by 41%. This net SOC decrease in HG was due to a larger reduction in C3‐derived input and to a comparatively smaller increase in C4‐derived C input. In LG both C3‐ and C4‐derived C input increased along the chronosequence. N stocks were generally similar in both subregions and soil N stock changes during pasture establishment were correlated with SOC changes. These results emphasize the importance of management practices involving low‐grazing intensity in cattle activities to preserve SOC stocks and to reduce C emissions after land‐cover change from forest to pasture in the Colombian Amazon.
In less than 15 years, the Amazon region experienced three major droughts. Links between droughts and fires have been demonstrated for the 1997/1998, 2005, and 2010 droughts. In 2010, emissions of ...510 ± 120 Tg C were associated to fire alone in Amazonia. Existing approaches have, however, not yet disentangled the proportional contribution of multiple land cover sources to this total. We develop a novel integration of multisensor and multitemporal satellite‐derived data on land cover, active fires, and burned area and an empirical model of fire‐induced biomass loss to quantify the extent of burned areas and resulting biomass loss for multiple land covers in Mato Grosso (MT) state, southern Amazonia—the 2010 drought most impacted region. We show that 10.77% (96,855 km2) of MT burned. We estimated a gross carbon emission of 56.21 ± 22.5 Tg C from direct combustion of biomass, with an additional 29.4 ± 10 Tg C committed to be emitted in the following years due to dead wood decay. It is estimated that old‐growth forest fires in the whole Brazilian Legal Amazon (BLA) have contributed to 14.81 Tg of C (11.75 Tg C to 17.87 Tg C) emissions to the atmosphere during the 2010 fire season, with an affected area of 27,555 km2. Total C loss from the 2010 fires in MT state and old‐growth forest fires in the BLA represent, respectively, 77% (47% to 107%) and 86% (68.2% to 103%) of Brazil's National Plan on Climate Change annual target for Amazonia C emission reductions from deforestation.
Key Points
The 10.77% (96,855 km2) of MT burned during the 2010 dry season
Mato Grosso gross c emission in 2010 was 56.21 ± 22.5 Tg C
Old‐growth forest fire emission in 2010 in the Brazilian Amazon was 14.81 Tg C
Canopy gaps are openings in the forest canopy resulting from branch fall and tree mortality events. The geographical distribution of large canopy gaps may reflect underlying variation in mortality ...and growth processes. However, a lack of data at the appropriate scale has limited our ability to study this relationship until now.
We detected canopy gaps using a unique LiDAR dataset consisting of 650 transects randomly distributed across 2500 km2 of the Brazilian Amazon. We characterized the size distribution of canopy gaps using a power law and we explore the variation in the exponent, α. We evaluated how the α varies across the Amazon, in response to disturbance by humans and natural environmental processes that influence tree mortality rates.
We observed that South‐eastern forests contained a higher proportion of large gaps than North‐western, which is consistent with recent work showing greater tree mortality rates in the Southeast than the Northwest. Regions characterized by strong wind gust speeds, frequent lightning and greater water shortage also had a high proportion of large gaps, indicating that geographical variation in α is a reflection of underlying disturbance processes. Forests on fertile soils were also found to contain a high proportion of large gaps, in part because trees grow tall on these sites and create large gaps when they fall; thus, canopy gap analysis picked up differences in growth as well as mortality processes. Finally, we found that human‐modified forests had a higher proportion of large gaps than intact forests, as we would expect given that these forests have been disturbed.
Synthesis. The proportion of large gaps in the forest canopy varied substantially over the Brazilian Amazon. We have shown that the trends can be explained by geographical variation in disturbance and growth. The frequency of extreme weather events is predicted to increase under climate change, and changes could lead to greater forest disturbance, which should be detectable as an increased proportion of large gaps in intact forests.
Resumo
Clareiras são aberturas no dossel da floresta decorrentes da queda de galhos e de processos de mortalidade das árvores. A distribuição geográfica de grandes clareiras pode refletir uma variação desses processos de crescimento e mortalidade. Contudo, a falta de informação em escala apropriada, até o momento, tem limitado a capacidade de estudar essa relação.
Nós detectamos essas clareiras utilizando um conjunto de dados LiDAR contento 650 transectos aleatoriamente distribuídos em aproximadamente 2500 km2 de floresta na Amazônia Brasileira. Com isso, caracterizamos o tamanho e a distribuição das clareiras a partir da função power‐law e exploramos a variação no coeficiente α dessa função. Avaliamos como o α varia ao longo da Amazônia em resposta da perturbação antrópica e dos processos ambientais que ocorrem naturalmente e que influenciam a taxa de mortalidade das árvores.
Foi possível observar que florestas localizadas na região Sudeste continham uma maior proporção de grandes clareiras que a região Noroeste da Amazônia, o que é consistente com um estudo recente que mostrou uma maior taxa de mortalidade seguindo o mesmo padrão. Locais caracterizados por ventos fortes, alta frequência de queda de raios e acentuado déficit hídrico apresentaram uma maior proporção de clareiras grandes, indicando que a variação geográfica em α pode ser um reflexo dos processos de perturbação subjacentes. Florestas sobre solos férteis também tendem a apresentar uma maior proporção de clareiras maiores, em parte porque as árvores crescem mais em altura nesses locais e criam clareiras maiores quando caem. Portanto, a análise de clareias capturou diferenças em crescimento e, também, em processos de mortalidade. Por fim, este estudo mostrou que florestas modificadas pelo homem tem maior proporção de clareiras maiores que as florestas intactas, como esperado para florestas onde há algum nível de perturbação antrópica.
Síntese. A proporção de grandes clareiras no dossel florestal variou substancialmente ao longo da Amazônia Brasileira. Neste trabalho, mostramos que a tendência na distribuição do tamanho e frequência das clareiras pode ser explicada pela variação geográfica dos processos de perturbação e crescimento da floresta. Eventos climáticos extremos serão mais frequentes por consequência das mudanças climáticas e, tais alterações, irão acelerar processos de perturbação florestal onde será possível detectar o aumento da proporção de grandes clareiras mesmo em florestas intactas.
The proportion of large gaps in the forest canopy varied substantially over the Brazilian Amazon. We have shown that the trends can be explained by geographical variation in disturbance and growth. The frequency of extreme weather events is predicted to increase under climate change, and changes could lead to greater forest disturbance, which should be detectable as an increased proportion of large gaps in intact forests.
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