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Application of the best available science to improve quantification of greenhouse gas (GHG) emissions at regional and national scales is key to climate action. Here, we present a two‐decade (2000–2019) GHG (CO2, CH4, and N2O) budget for Mexico derived from multiple products. Data from the National GHG Inventory, global observations, and the scientific literature were compared to identify knowledge gaps on GHG flux dynamics and discrepancies among estimates. Total mean annual GHG emissions were estimated at 695–910 TgCO2‐eq year−1 over these two decades, with 70% of the emissions attributable to CO2, 23% to CH4, and 5% to N2O (2% to other gases). When divided by sectors, we found agreement across emission estimates from various sources for fossil fuels, cattle, agriculture, and waste for all GHGs. However, considerable discrepancies were identified in the fluxes from terrestrial ecosystems. The disagreement was particularly large for the land CO2 sink, where net biome production estimations from the national inventory were double those from any other observational product. Extensive knowledge gaps exist, mainly related to aquatic systems (e.g., outgassing in rivers) and the lateral fluxes (e.g., wood trade). In addition, limited information is available on CH4 emissions from wetlands and soil CH4 consumption. We expect these results to guide future research to reduce estimation uncertainties and fill the information gaps across Mexico. Plain Language Summary: Mexico represents the 13th global emitter of greenhouse gases (GHGs) and the second among Latin American countries, releasing roughly 485 million tons of CO2, six million tons of CH4 (equivalent to 160 million tons of CO2), and 0.1 million tons of N2O (equivalent to 35 million tons of CO2). However, large uncertainties prevail in the estimation of several components of each flux; thus, the application of the best available science to account for and improve these estimations is essential for sound mitigation policies. Here, we used multiple available products (national inventories, satellites, flux towers, dynamic global vegetation models, inversion models, and other data sources) to advance our understanding of the GHG budget of Mexico over the last 20 years. We found that fluxes from fossil fuel combustion (including energy production, transportation, industry, etc.), agriculture, livestock, and waste management agree remarkably well across products. In contrast, we documented large differences among products for land‐based fluxes (e.g., CO2 capture) and scant available information on aquatic ecosystems (e.g., CH4 emission from wetlands) and on lateral fluxes (e.g., emissions from trade). We expect these results to help in guiding future measuring efforts and policies to mitigate GHG emissions from Mexico. Key Points: A greenhouse gas (GHG) budget for Mexico was calculated based on multiple products. We estimated fluxes for CO2, CH4, and N2O over the 2000–2019 periodTotal GHG emissions were 695 TgCO2‐eq year−1 in the national inventory and as much as a mean 910 TgCO2‐eq year−1 across productsGHG fluxes agreed well across products for emissions, but large discrepancies exist for the land CO2 and CH4 sinks [ABSTRACT FROM AUTHOR]

High-intensity hurricane disturbances have severe consequences on forest structure and functioning. Through wind force and heavy rainfall, they cause extensive canopy removal and an input of fine litter and woody debris well above normal levels. We examined litterfall N and P concentrations and fluxes before and after Hurricane Patricia (category 4) landfall in October 2015 in the seasonally dry tropical forest of the Chamela region, Jalisco, Mexico. Additionally, we compared the forest response to Patricia with those to Hurricane Jova (2011), from the Eastern North Pacific basin and to Hurricane Dean (2007) from the Atlantic basin. Nutrient concentrations in hurricane-induced litterfall in October 2015 were 2.2 times higher in leaf litter than in the woody fraction. Both litterfall N and P concentrations during the period November–February following the hurricane were generally higher than in similar periods in years previous to and after Patricia. Nutrient fluxes in October 2015 (75.9 kgN/ha and 3.6 kgP/ha) represented 55% (N) and 52% (P) of the total fluxes that year, which were much higher than those in any of the three years following the hurricane. These results suggest that forest biogeochemical resilience has changed in the short term. The annual litterfall N and P fluxes during the year of Hurricane Dean were lower than in 2011 and 2015, but similar to non-hurricane years. After Patricia, the annual N flux was higher, but the annual P flux lower than after Jova, and the former represents the largest annual N flux in our more than 25 years record. [ABSTRACT FROM AUTHOR]

Extreme weather events represent a large risk to food production systems. In this study, we evaluated the impacts of the 2011–2012 drought in Mexico, the worst in the last 70 years, on free-ranged livestock populations to link extreme weather events and production. We also considered the potential prevalence of recurring droughts under two contrasting future climate scenarios to examine what could happen over this century. Our results showed that cattle and goat stocks decreased about 3% in response to the drought countrywide. Regionally, the changes in cattle and goat populations generally mimicked the precipitation anomaly, with the strongest reductions across the driest areas in central and northern Mexico. Our work showed that the biophysical and management components of livestock production interact depending on the regions and the type of livestock, leading to a mosaic of spatial responses. It seems that the management of large herds limits the economic viability of drought crisis management options such as the importation of fodder and water, or by moving the animals to other pastures. Sheep herds were much less affected since more than 50% of the total sheep stock is raised in wetter states, which showed a relatively small (~ − 10%) precipitation anomaly during the drought. Under the severe climate change scenario, a greater frequency of extremely dry years (once every 3 years) would have negative impacts on livestock production regionally. Climate change together with already existing trends in overgrazing and soil erosion could further increase the sensitivity of livestock production across the country. Graphical abstract [ABSTRACT FROM AUTHOR]

Rainfall, runoff and sediment yield have been measured over three decades (1983–2015) in five contiguous small watersheds (12–28 ha) covered by mature tropical dry forest (TDF) at the Chamela Biological Field Station, UNAM, in the southern Pacific Coast of Jalisco, Mexico. Hydrological dynamics strongly drive the seasonal and inter-annual variability of TDF primary productivity, litter decomposition and nutrient cycling. Although the study region is constantly influenced by storms related to hurricane activity, they rarely make landfall. However, hurricanes have landed twice over a four-year period in the reserve: category 2 Hurricane Jova, in October 2011, and category 4 Hurricane Patricia, in October 2015. The long-term data has allowed to evaluate ecosystem’s response to these two major hydrometeorological events, in the context of the historic rainfall/runoff pattern. The results showed that antecedent precipitation and rainfall intensity were the major factors controlling rainfall-runoff and soil erosion processes. The analysis also showed the timing of the onset of the rainy season was very regular but the length of the rainy season was quite variable. The highly variable rainfall pattern and high probability of intense storms at the onset of the wet season were linked with the vulnerability of TDF to soil erosion. Also, two types of recurrent and intense drought periods have been identified: the high inter-annual droughts; and the frequent within-wet season droughts (“canículas”). There is a clear influence of the “El Niño”- Southern Oscillation phenomenon (ENSO) on the study area, with lower annual rainfall during its hot phase, and higher annual rainfall during its cold phase (“La Niña”). The relevance of these findings is discussed in terms of forest ecosystem management practices in the region and its implications concerning the current climate-change forecast for the study area. [ABSTRACT FROM AUTHOR]

Tropical dry forests (TDFs) on the Pacific Coast of Mexico experience seasonal droughts and very infrequent direct hurricane disturbance. Over a 4-year period, two hurricanes made landfall in the Chamela-Cuixmala Biosphere Reserve, Hurricane Jova (category 2) in October 2011 and Hurricane Patricia (category 4) in October 2015. Our permanent long-term watershed-scale research program in the reserve provided a unique opportunity to analyze the ecosystem response to these hydrometeorological extreme events. Since 1982, we have been collecting monthly litterfall samples in 120 litter traps across five small contiguous watersheds. A direct instantaneous effect of both hurricanes was a massive deposition of green and senescent leaves, and fine woody debris to the forest floor. Hurricane-month litterfall flux largely exceeded the amount produced in any month of the pre-disturbance period (1982–2010), suggesting low resistance to hurricanes. Post-Jova recovery was fast, a response likely explained by a combination of the unusually high dry-season precipitation and higher than average total annual precipitation, coupled to a large flux of P-enriched litter and the re-sprouting response of many TDF species. Annual litterfall the year following Patricia decreased to half of that during the hurricane year, concomitant with a decrease in annual rainfall 20% below average. Ecosystem resilience seems strongly linked to post-disturbance water availability. Therefore, drought after a hurricane may limit the capacity of tropical dry forests to rapidly recover. The implications of these climate-related disturbances for forest recovery and management are discussed. [ABSTRACT FROM AUTHOR]

Core leaf traits, such as leaf mass per area (LMA) and leaf nitrogen (N) and phosphorus (P) concentrations in green and senesced leaves, are currently used to discern patterns of variation, constraints, and relations to nutrient availability and climate among plant species up to the biomes and global scale. These traits and nutrient resorption were measured in 21 woody species in three phenological groups of the Chamela tropical dry forest (TDF) during a 3-year study period under conditions of contrasting rainfall. The LMA was similar among years and showed negative relationships with green-leaf N and P concentrations, in agreement with the global assessments. Community-level mean N concentrations in green and senesced leaves did not change among years, but P concentrations decreased with lower water availability in dry years. Both mean and minimum foliar N:P mass ratios increased with diminishing rainfall, suggesting that leaf stoichiometry reflects a water control on soil P limitation in this forest. In the wet year, green-leaf N and P concentrations were not correlated, and there were high coefficients of variation among species in leaf P and N:P ratios, indicating that species variability and physiological constraints are expressed in leaf stoichiometry upon the removal of water limitation. The resorption efficiency and proficiency of P, but not N, increased in years with low rainfall, suggesting that the costs of nutrient resorption relative to acquisition from soil differ between N and P and that P conservation increases when rainfall decreases in the Chamela TDF. Our results support the proposal that water availability controls P dynamics in this ecosystem. [ABSTRACT FROM AUTHOR]

Abstract: We compared the structure and diversity of secondary tropical dry forests, growing in sites cleared by bulldozer 30 years ago and subjected to different land uses prior to abandonment: (a) housing development (HD), (b) pasture (P), and (c) no use (NU). We sampled two forest sites representing each of the three former land-use types (i.e., a total of six sites) and measured the diameter at breast height (dbh) of all stems with dbh ≥1cm and at least 2m in height. All individuals were identified to species and classified into each of four dbh sizes-classes: 1–3, 3–5, 5–10, and >10cm. No major differences in structure or diversity were evident among land-use types. Total tree densities varied from 2575±55 to 4745±985individuals/ha and total basal areas ranged from 12.5±2.6 to 14.6±0.3m2/ha (mean and S.E.). Neither one differed significantly (p <0.05) among land-use types. Overall, the most abundant tree size-class was the 1–3cm dbh (47% of the total number of trees), whereas trees greater than 10cm dbh were the least abundant (4%). We found significantly higher density and basal area (p =0.01) in NU than in HD and P only in the smallest trees (1–3cmdbh). We identified a total of 87 species in 28 families. The Leguminosae plant family had the greatest species richness and number of individuals in all land-use types. The HD land-use type showed lower total species richness than P and NU only with two of the four nonparametric estimators. Observed species richness decreased as dbh increased in all land-use types. At least 5 legumes were among the 10 most dominant species in all land-use types, of which the non-native Mimosa arenosa was the most dominant one. It represented between 42% and 52% of the total basal area in each land-use type. The secondary forests have reached, on average, 74% and 22% of the total density and basal area, respectively, of an average primary tropical dry forest of Mexico. The high number of individuals 1–3cmdbh (48% of the total and 83% of the species) suggest that regeneration is occurring in all land-use types, although to different degrees. The absence of small individuals of M. arenosa and a high abundance of primary forest species at NU, suggest that M. arenosa is being replaced at these sites. [Copyright &y& Elsevier]

Seasonal variation of dissolved organic C (DOC) and its effects on microbial activity and N dynamics were studied during two consecutive years in soils with different organic C concentrations (hilltop and hillslope) in a tropical deciduous forest of Mexico. We found that DOC concentrations were higher at the hilltop than at the hillslope soils, and in both soils generally decreased from the dry to the rainy season during the two study years. Microbial biomass and potential C mineralization rates, as well as dissolved organic N (DON) and NH concentrations and net N immobilization were higher in soils with higher DOC than in soils with lower DOC. In contrast, net N immobilization and NH concentration were depleted in the soil with lowest DOC, whereas NO concentrations and net nitrification increased. Negative correlations between net nitrification and DOC concentration suggested that NH was transformed to NO by nitrifiers when the C availability was depleted. Taken together, our results suggest that available C appears to control soil microbial activity and N dynamics, and that microbial N immobilization is facilitated by active heterotrophic microorganisms stimulated by high C availability. Soil autotrophic nitrification is magnified by decreases in C availability for heterotrophic microbial activity. This study provides an experimental data set that supports the conceptual model to show and highlight that microbial dynamics and N transformations could be functionally coupled with DOC availability in the tropical deciduous forest soils. [ABSTRACT FROM AUTHOR]

N cycling in tropical dry forests is driven by rainfall seasonality but the mechanisms involved are not well understood. We studied the seasonal variation in N dynamics and microbial biomass in the surface litter of a tropical dry forest ecosystem in Mexico over a 2-year period. Litter was collected at 4 different times of the year to determine changes in total, soluble, and microbial C and N concentrations. Additionally, litter from each sampling date was incubated under laboratory conditions to determine potential C mineralization rate, net N mineralization, net C and N microbial immobilization, and net nitrification. Litter C concentrations were highest in the early-dry season and lowest in the rainy season, while the seasonal changes in N concentrations varied between years. Litter P was higher in the rainy than in the early-dry season. Water-soluble organic C (WSOC) and water-soluble N concentrations were highest during the early- and late-dry seasons and represented up to 4.1 and 5.9% of the total C and N, respectively. NH and NO showed different seasonal and annual variations. They represented an average 23% of soluble N. Microbial C was generally higher in the dry than in the wet seasons, while microbial N was lowest in the late-dry and highest in the early-rainy seasons. Incubations showed that lowest potential C mineralization rates and C and N microbial immobilization occurred in rainy season litter, and were positively correlated to WSOC. Net nitrification was highest in rainy season litter. Our results showed that the seasonal pattern in N dynamics was influenced by rainfall seasonality and labile C availability, and not by microbial biomass. We propose a conceptual model to hypothesize how N dynamics in the litter layer of the Chamela tropical dry forest respond to the seasonal variation in rainfall. [ABSTRACT FROM AUTHOR]

The article discusses a study on the effects of land use and deforestation in ecosystems in Los Tuxtlas Region of Mexico. Topics include analysis of variables like total aboveground biomass, and nutrients in vegetation and soils; land use gradient in primary forests, pastures, and cornfields; and findings inferring loss of nitrogen and sulpher in young volcanic soils.

• Local power allometric models were developed to estimate secondary tropical dry forest biomass. • DBH was a highly significant (R2 ≥ 0.93) single predictor of biomass for the 27 studied tree species. • Accuracy (bias) and precision of allometric models were validated using numerical methods. • Using local or global wood density data did not affect the accuracy of our multispecies models. • Allometric models for species grouped by wood density were the most accurate among all models. Biomass estimates in tropical forests are mainly available for old-growth forests, but the expansion of tropical secondary forests urges the development of tools for more accurate estimations of biomass and carbon pools. In this study, we developed local allometric models to estimate aboveground biomass in secondary tropical dry forests of the Chamela region in western Mexico and compared their accuracy to that of non-local ("foreign") allometric models. We harvested 303 trees from 27 woody species contributing ≥75% of total basal area in secondary forest plots (5–45 y-old) distributed across the landscape. Nine to 14 individuals per species, covering the full natural range in stem diameter (DBH) found in an inventory, were measured for DBH and height (H) before harvesting. Subsamples from each stem and branches were used for dry mass and wood specific density (WSD) determinations. Power model functions were fitted to relate tree AGB to one or a multiplicative combination of three predictors (DBH, H, and WSD). Species-specific models with DBH alone explained a high percentage of the variance in tree AGB (R2 = 0.927 to 0.999). Among our multispecies models, fit and prediction of biomass improved when pooling the species into low and high WSD functional groups. Using local or global WSD data did not affect the accuracy of our multispecies models. In contrast, bias increased in foreign models with the use of global WSD values. We discuss the applicability of our allometric models and foreign models to improve the accuracy of biomass predictions in secondary tropical dry forests. [ABSTRACT FROM AUTHOR]

N cycling in tropical dry forests is driven by rainfall seasonality but the mechanisms involved are not well understood. We studied the seasonal variation in N dynamics and microbial biomass in the surface litter of a tropical dry forest ecosystem in Mexico over a 2-year period. Litter was collected at 4 different times of the year to determine changes in total, soluble, and microbial C and N concentrations. Additionally, litter from each sampling date was incubated under laboratory conditions to determine potential C mineralization rate, net N mineralization, net C and N microbial immobilization, and net nitrification. Litter C concentrations were highest in the early-dry season and lowest in the rainy season, while the seasonal changes in N concentrations varied between years. Litter P was higher in the rainy than in the early-dry season. Water-soluble organic C (WSOC) and water-soluble N concentrations were highest during the early- and late-dry seasons and represented up to 4.1 and 5.9% of the total C and N, respectively. NH (4) (+) and NO (3) (-) showed different seasonal and annual variations. They represented an average 23% of soluble N. Microbial C was generally higher in the dry than in the wet seasons, while microbial N was lowest in the late-dry and highest in the early-rainy seasons. Incubations showed that lowest potential C mineralization rates and C and N microbial immobilization occurred in rainy season litter, and were positively correlated to WSOC. Net nitrification was highest in rainy season litter. Our results showed that the seasonal pattern in N dynamics was influenced by rainfall seasonality and labile C availability, and not by microbial biomass. We propose a conceptual model to hypothesize how N dynamics in the litter layer of the Chamela tropical dry forest respond to the seasonal variation in rainfall.