Censuses of tropical forest plots reveal large variation in biomass and plant composition. This paper evaluates whether such variation can emerge solely from realistic variation in a set of commonly ...measured soil chemical and physical properties. Controlled simulations were performed using a mechanistic model that includes forest dynamics, microbe-mediated biogeochemistry, and competition for nitrogen and phosphorus. Observations from 18 forest inventory plots in Guanacaste, Costa Rica were used to determine realistic variation in soil properties. In simulations of secondary succession, the across-plot range in plant biomass reached 30% of the mean and was attributable primarily to nutrient limitation and secondarily to soil texture differences that affected water availability. The contributions of different plant functional types to total biomass varied widely across plots and depended on soil nutrient status. In Central America, soil-induced variation in plant biomass increased with mean annual precipitation because of changes in nutrient limitation. In Central America, large variation in plant biomass and ecosystem composition arises mechanistically from realistic variation in soil properties. Finally, the degree of biomass and compositional variation is climate sensitive. In general, model predictions can be improved through better representation of soil nutrient processes, including their spatial variation.
Sensitivity of forest mortality to drought in carbon-dense tropical forests remains fraught with uncertainty, while extreme droughts are predicted to be more frequent and intense. Here, in this ...study, the potential of temporal autocorrelation of high-frequency variability in Landsat Enhanced Vegetation Index (EVI), an indicator of ecosystem resilience, to predict spatial and temporal variations of forest biomass mortality is evaluated against in situ census observations for 64 site-year combinations in Costa Rican tropical dry forests during the 2015 ENSO drought. Temporal autocorrelation, within the optimal moving window of 24 months, demonstrated robust predictive power for in situ mortality (leave-one- out cross-validation R2 = 0.54), which allows for estimates of annual biomass mortality patterns at 30 m resolution. Subsequent spatial analysis showed substantial fine-scale heterogeneity of forest mortality patterns, largely driven by drought intensity and ecosystem properties related to plant water use such as forest deciduousness and topography. Highly deciduous forest patches demonstrated much lower mortality sensitivity to drought stress than less deciduous forest patches after elevation was controlled. Our results highlight the potential of high-resolution remote sensing to “fingerprint” forest mortality and the significant role of ecosystem heterogeneity in forest biomass resistance to drought.
Ectomycorrhizal (ECM) symbioses support forest functioning globally, yet both the structure and function of ECM fungal communities in seasonally dry neotropical forests (SDTFs), known for extreme ...heterogeneity in vegetation and edaphic properties, remain under characterized.
Here, we evaluated the relative influences of seasonal versus spatial variation in ECM fungal community structure in soils from four environmentally divergent SDTFs. We also assessed the importance of biotic and abiotic drivers of SDTF ECM fungal community structure at regional scales, as well as ECM impacts on soil carbon (C) and nitrogen (N) cycling.
ECM fungal frequency, relative abundance and richness all increased in the wet season, but spatial rather than seasonal effects explained more variation in community composition. Across the four SDTFs investigated, differences in tree communities drove ECM fungal community turnover more than geographic distances, site abiotic conditions or soil chemistry. Although soil moisture and ECM tree basal area were stronger predictors of soil biogeochemistry, incorporating ECM fungal community composition and relative abundance added explanatory power to models of soil C and N cycling in the wet season.
Synthesis: Our results highlight the importance of seasonality and plant community composition in shaping different aspects of SDTF ECM fungal community structure and diversity as well as the potential for both the plant and fungal components of ECM symbioses to impact soil functioning across heterogenous SDTFs. Furthermore, our findings suggest that alterations in SDTF plant community composition due to climate or land‐use change will have important consequences for ECM fungal diversity and associated effects on soil biogeochemical cycling.
RESUMEN
Las ectomicorrizas mantienen el funcionamiento de los bosques a nivel global, sin embargo, pocos estudios han caracterizado la estructura y función de las comunidades de hongos ectomicorrícicos (ECM) en los Bosques Secos Neotropicales (BST), los cuales poseen una alta heterogeneidad en su composición florística y propiedades edáficas.
En este trabajo se evaluó la influencia relativa de la variación estacional vs. espacial sobre la estructura de la comunidad de hongos ECM en suelos de cuatro BST que divergen en sus características ambientales. También se estimó la importancia de los factores bióticos y abióticos sobre la estructura de las comunidades de hongos ECM de estos bosques a escalas regionales, y su impacto en el ciclo del carbono (C) y nitrógeno (N) en los suelos.
La frecuencia, abundancia relativa, y riqueza de los hongos ECM incrementó durante la estación lluviosa. No obstante, la variación en la composición comunitaria de hongos EM fue mayormente explicada por factores espaciales. En comparación con las distancias geográficas, las condiciones abióticas y la química de los suelos, las diferencias en la composición de especies de árboles tuvieron un rol más determinante en el recambio comunitario de los hongos ECM entre los cuatro BST estudiados. Aunque la humedad del suelo y el área basal de los árboles con ECM fueron los predictores más fuertes de la biogeoquímica de los suelos, la incorporación de la composición de las comunidades de hongos ECM y su abundancia relativa, mejoró el poder explicativo de los modelos de ciclado de C y N en los suelos durante la época de lluvias.
Síntesis: Los resultados de este estudio resaltan la importancia de la estacionalidad de las lluvias y la composición de las comunidades vegetales como determinantes de diferentes aspectos de la estructura y diversidad de las comunidades de hongos ECM en los BST, además del potencial que tanto las plantas, como el componente simbiótico de las ectomicorrizas tienen para impactar el funcionamiento de los suelos en los BST heterogéneos. Mas aún, los resultados sugieren que las alteraciones en la composición de las comunidades de plantas en los BST generados por cambios climáticos o en el uso del suelo, tendrán importantes consecuencias sobre la diversidad de hongos ECM y efectos asociados en el ciclado biogeoquímico en los suelos.
These results highlight the importance of seasonality and plant community composition in shaping different aspects of SDTF ECM fungal community structure and diversity as well as the potential for both the plant and fungal components of ECM symbioses to impact soil functioning across heterogenous SDTFs. Furthermore, these findings suggest that alterations in SDTF plant community composition due to climate or land‐use change will have important consequences for ECM fungal diversity and associated effects on soil biogeochemical cycling.Editor's Choice
Summary
<list list-type='bullet'>
Leaf habit has been hypothesized to define a linkage between the slow‐fast plant economic spectrum and the drought resistance‐avoidance trade‐off in tropical forests ...(‘slow‐safe vs fast‐risky’). However, variation in hydraulic traits as a function of leaf habit has rarely been explored for a large number of species.
We sampled leaf and branch functional traits of 97 tropical dry forest tree species from four sites to investigate whether patterns of trait variation varied consistently in relation to leaf habit along the ‘slow‐safe vs fast‐risky’ trade‐off.
Leaf habit explained from 0% to 43.69% of individual trait variation. We found that evergreen and semi‐deciduous species differed in their location along the multivariate trait ordination when compared to deciduous species. While deciduous species showed consistent trait values, evergreen species trait values varied as a function of the site. Last, trait values varied in relation to the proportion of deciduous species in the plant community.
We found that leaf habit describes the strategies that define drought avoidance and plant economics in tropical trees. However, leaf habit alone does not explain patterns of trait variation, which suggests quantifying site‐specific or species‐specific uncertainty in trait variation as the way forward.
The availability of nitrogen (N) and phosphorus (P) controls the flow of carbon (C) among plants, soils, and the atmosphere, thereby shaping terrestrial ecosystem responses to global change. Soil C, ...N, and P cycles are linked by drivers operating at multiple spatial and temporal scales: landscape-level variation in macroclimate and soil geochemistry, stand-scale heterogeneity in forest composition, and microbial community dynamics at the soil pore scale. Yet in many biomes, we do not know at which scales most of the biogeochemical variation emerges, nor which processes drive cross-scale feedbacks. Here, we examined the drivers and spatial/temporal scales of variation in soil biogeochemistry across four tropical dry forests spanning steep environmental gradients. To do so, we quantified soil C, N, and P pools, extracellular enzyme activities, and microbial community structure across wet and dry seasons in 16 plots located in Colombia, Costa Rica, Mexico, and Puerto Rico. Soil biogeochemistry exhibited marked heterogeneity across the 16 plots, with total organic C, N, and P pools varying fourfold, and inorganic nutrient pools by an order of magnitude. Most soil characteristics changed more across space (i.e., among sites and plots) than over time (between dry and wet season samplings). We observed stoichiometric decoupling among C, N, and P cycles, which may reflect their divergent biogeochemical drivers. Organic C and N pool sizes were positively correlated with the relative abundance of ectomycorrhizal trees and legumes. By contrast, the distribution of soil P pools was driven by soil geochemistry, with larger inorganic P pools in soils with P-rich parent material. Most earth system models assume that soils within a texture class operate similarly, and ignore subgrid cell variation in soil properties. Here we reveal that soil nutrient pools and fluxes exhibit as much variation among four Neotropical dry forests as is observed across terrestrial ecosystems at the global scale. Soil biogeochemical patterns are driven not only by regional differences in soil parent material and climate, but also by local-scale variation in plant and microbial communities. Thus, the biogeochemical patterns we observed across the Neotropical dry forest biome challenge representation of soil processes in ecosystem models.
Sensitivity of forest mortality to drought in carbon‐dense tropical forests remains fraught with uncertainty, while extreme droughts are predicted to be more frequent and intense. Here, the potential ...of temporal autocorrelation of high‐frequency variability in Landsat Enhanced Vegetation Index (EVI), an indicator of ecosystem resilience, to predict spatial and temporal variations of forest biomass mortality is evaluated against in situ census observations for 64 site‐year combinations in Costa Rican tropical dry forests during the 2015 ENSO drought. Temporal autocorrelation, within the optimal moving window of 24 months, demonstrated robust predictive power for in situ mortality (leave‐one‐out cross‐validation R2 = 0.54), which allows for estimates of annual biomass mortality patterns at 30 m resolution. Subsequent spatial analysis showed substantial fine‐scale heterogeneity of forest mortality patterns, largely driven by drought intensity and ecosystem properties related to plant water use such as forest deciduousness and topography. Highly deciduous forest patches demonstrated much lower mortality sensitivity to drought stress than less deciduous forest patches after elevation was controlled. Our results highlight the potential of high‐resolution remote sensing to “fingerprint” forest mortality and the significant role of ecosystem heterogeneity in forest biomass resistance to drought.
Temporal autocorrelation of Landsat EVI residuals, an indicator of ecosystem resilience, demonstrated robust predictive power for in situ mortality over tropical dry forests in Costa Rica. Results highlight the potential of high‐resolution remote sensing to “fingerprint” the spatial heterogeneity of forest mortality.
Many modeling studies have indicated that deforestation will increase the average annual temperature in the Amazon. However, few studies have investigated the potential for deforestation to change ...the frequency and intensity of extreme events. This problem is addressed here using a variable-resolution GCM. The characteristic length scale (CLS) of the model’s grid mesh over South America is 25 km, comparable to that used by limited-area models. For computational efficiency, the CLS increases to 200 km over the rest of the world. It is found that deforestation induces large changes in the frequency of wintertime extreme cold events. Large increases in cold event frequency and intensity occur in the western Amazon and, surprisingly, in parts of southern South America, far from the actual deforested area. One possible mechanism for these remote effects involves changes in the position of the subtropical jet, caused by temperature changes in the Amazon. Increased understanding of these potential changes in extreme events will be important for local agriculture, natural ecosystems, and the human population.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Lateral carbon transport (LCT), the flux of terrestrial C transported to aquatic ecosystems, displaces carbon (C) across the terrestrial‐aquatic continuum and is on the same order of magnitude as ...terrestrial net ecosystem production. However, few continental scale C models include LCT or the C‐hydrology linkages necessary for modeling LCT. Those that do exist, borrow processes and conceptual understanding from watershed scale models, assuming that large‐scale and small‐scale drivers of LCT are the same. We develop a conceptual framework of LCT, which focuses on lateral dissolved organic carbon (DOC) transport (LCT‐DOC), and operationalize it with a coupled terrestrial‐aquatic C and hydrology model. After comparing our model LCT‐DOC to previous estimates derived from a summation of landscape scale fluxes for the Contiguous U.S., we use model experiments to partition the importance of LCT‐DOC drivers including total annual precipitation, air temperature, and plant traits, which interact across regional and local scales. We find that climate is the strongest driver of LCT‐DOC, where LCT‐DOC is positively related to precipitation but inversely related to temperature at continental scales. However, the net effect of climate on LCT‐DOC is the product of cross‐scale interactions between climate and vegetation. Plant traits also interact strongly with climate and have a measurable influence on LCT‐DOC, with water use efficiency as the most influential plant trait because it couples terrestrial water and C cycling. We demonstrate that our conceptual framework and relatively simple linked C‐hydrology process model of LCT‐DOC can inform hypotheses and predict LCT‐DOC.
Plain Language Summary
Runoff from land transports carbon (C) to nearby streams, rivers, and lakes, where it can be decomposed, stored, or transported further downstream. This lateral carbon transport (LCT) can be as large as annual storage of carbon in soil and moves C across the landscape. Much of our understanding of what controls LCT comes from small, location‐focused studies and many mathematical models used to understand this important process are also location‐specific. To understand LCT at large, continental scales, we must consider drivers that vary at those larger scales, such as vegetation type and climate, and incorporate those drivers into mathematical models. In this study, we develop a conceptual framework for LCT production and a mathematical model that integrate impacts of climate, plant characteristics, and interactions between them. We find that interactions among precipitation, temperature, and plants regulate LCT production at a continental scale.
Key Points
Created a new conceptual framework for understanding lateral DOC transport (LCT‐DOC) from terrestrial ecosystems at continental scales
Operationalized our conceptual framework with a simple coupled terrestrial‐aquatic hydrology and carbon process model
Identified cross‐scale interactions among climate (i.e., precipitation) and plant trait drivers of LCT‐DOC
Fire frequencies are changing in Neotropical savannas and
forests as a result of forest fragmentation and increasing drought. Such
changes in fire regime and climate are hypothesized to destabilize ...tropical
carbon storage, but there has been little consideration of the widespread
variability in tree fire tolerance strategies. To test how aboveground
carbon stocks change with fire frequency and composition of plants with
different fire tolerance strategies, we update the Ecosystem Demography
model 2 (ED2) with (i) a fire survivorship module based on tree bark
thickness (a key fire-tolerance trait across woody plants in savannas and
forests), and (ii) plant functional types representative of trees in the
region. With these updates, the model is better able to predict how fire
frequency affects population demography and aboveground woody carbon.
Simulations illustrate that the high survival rate of thick-barked, large
trees reduces carbon losses with increasing fire frequency, with high
investment in bark being particularly important in reducing losses in the
wettest sites. Additionally, in landscapes that frequently burn, bark
investment can broaden the range of climate and fire conditions under which
savannas occur by reducing the range of conditions leading to either
complete tree loss or complete grass loss. These results highlight that
tropical vegetation dynamics depend not only on rainfall and changing fire
frequencies but also on tree fire survival strategy. Further, our results
indicate that fire survival strategy is fundamentally important in
regulating tree size demography in ecosystems exposed to fire, which
increases the preservation of aboveground carbon stocks and the coexistence
of different plant functional groups.
The world's ocean and land ecosystems act as sinks for anthropogenic CO2, and over the last half century their combined sink strength grew steadily with increasing CO2 emissions. Recent analyses of ...the global carbon budget, however, have uncovered an abrupt, substantial ( ∼ 1 PgC yr−1) and sustained increase in the land sink in the late 1980s whose origin remains unclear. In the absence of this prominent shift in the land sink, increases in atmospheric CO2 concentrations since the late 1980s would have been ∼ 30 % larger than observed (or ∼ 12 ppm above current levels). Global data analyses are limited in regards to attributing causes to changes in the land sink because different regions are likely responding to different drivers. Here, we address this challenge by using terrestrial biosphere models constrained by observations to determine if there is independent evidence for the abrupt strengthening of the land sink. We find that net primary production significantly increased in the late 1980s (more so than heterotrophic respiration), consistent with the inferred increase in the global land sink, and that large-scale climate anomalies are responsible for this shift. We identify two key regions in which climatic constraints on plant growth have eased: northern Eurasia experienced warming, and northern Africa received increased precipitation. Whether these changes in continental climates are connected is uncertain, but North Atlantic climate variability is important. Our findings suggest that improved understanding of climate variability in the North Atlantic may be essential for more credible projections of the land sink under climate change.
PDF
