Terrestrial carbon stock mapping is important for the successful implementation of climate change mitigation policies. Its accuracy depends on the availability of reliable allometric models to infer ...oven‐dry aboveground biomass of trees from census data. The degree of uncertainty associated with previously published pantropical aboveground biomass allometries is large. We analyzed a global database of directly harvested trees at 58 sites, spanning a wide range of climatic conditions and vegetation types (4004 trees ≥ 5 cm trunk diameter). When trunk diameter, total tree height, and wood specific gravity were included in the aboveground biomass model as covariates, a single model was found to hold across tropical vegetation types, with no detectable effect of region or environmental factors. The mean percent bias and variance of this model was only slightly higher than that of locally fitted models. Wood specific gravity was an important predictor of aboveground biomass, especially when including a much broader range of vegetation types than previous studies. The generic tree diameter–height relationship depended linearly on a bioclimatic stress variable E, which compounds indices of temperature variability, precipitation variability, and drought intensity. For cases in which total tree height is unavailable for aboveground biomass estimation, a pantropical model incorporating wood density, trunk diameter, and the variable E outperformed previously published models without height. However, to minimize bias, the development of locally derived diameter–height relationships is advised whenever possible. Both new allometric models should contribute to improve the accuracy of biomass assessment protocols in tropical vegetation types, and to advancing our understanding of architectural and evolutionary constraints on woody plant development.
Extreme climatic and weather events are increasing in frequency and intensity across the world causing episodes of widespread tree mortality in many forested ecosystems. However, we have a limited ...understanding about which local factors influence tree mortality patterns, restricting our ability to predict tree mortality, especially within topographically complex tropical landscapes with a matrix of mature and secondary forests. We investigated the effects of two major local factors, topography and forest successional type, on climate‐induced tropical tree mortality patterns using an observational and modeling approach. The northernmost Neotropical dry forest endured an unprecedented episode of frost‐induced tree mortality after the historic February 2011 cold wave hit northwestern Mexico. In a moderately hilly landscape covering mature and secondary tropical dry forests, we surveyed 454 sites for the presence or absence of frost‐induced tree mortality. In addition, across forty‐eight 1 ha plots equally split into the two forest types, we examined 6,981 woody plants to estimate a frost‐disturbance severity metric using the density of frost‐killed trees. Elevation is the main factor modulating frost effects regardless of forest type. Higher occurrence probabilities of frost‐induced tree mortality at lowland forests can be explained by the strong influence of elevation on temperature distribution since heavier cold air masses move downhill during advective frosts. Holding elevation constant, the probability of frost‐induced tree mortality in mature forests was twice that of secondary forests but severity showed the opposite pattern, suggesting a cautious use of occurrence probabilities of tree mortality to infer severity of climate‐driven disturbances. Extreme frost events, in addition to altering forest successional pathways and ecosystem services, likely maintain and could ultimately shift latitudinal and altitudinal range margins of Neotropical dry forests.
Extreme climatic and weather events are increasing in frequency and intensity across the world causing episodes of widespread tree mortality. We investigated the effects of two major local factors, topography and forest successional type, on climate‐induced tropical tree mortality patterns in northwestern Mexico using an observational and modeling approach. Elevation is the main factor modulating frost effects. Holding elevation constant, the probability of frost‐induced tree mortality in mature forests was twice that of secondary forests but severity showed the opposite pattern, suggesting a cautious use of occurrence probabilities of tree mortality to infer climate‐driven disturbance severity.
•Two hurricanes produced immediate losses of, but then sustained increases of, greenness.•The duration of extended greenness may be due to the extra precipitation.•Loss of aboveground biomass was 11 ...and 23% for Hurricanes Jova and Patricia.•Biomass loss appears related to hurricane wind energy.
Hurricanes are meteorological events with intense effects on coastal ecosystems where the change in wind kinetic energy is first concentrated. The quantification of forest change and the understanding of forest recovery trajectories after hurricane impact require a series of observations from before and after the event. Our objective was to quantify the immediate and delayed impacts of two successive large hurricanes, Jova (October 2011) and Patricia (October 2015) on the canopy structure and some ecosystem functions of the Chamela tropical dry forest on the Pacific coast of Mexico. This forest is not typically affected by large disturbance events, but has a background of extreme rainfall seasonality and corresponding phenological responses. We used a series of detailed historic and recent measurements of canopy structure and Photosynthetic Photon Flux Density (PPFD) coupled with a continuous series of remote sensing indices (NDVI) to help assemble a comprehensive view of the effects from hurricanes Jova and Patricia, category 2 and 4 in the Saffir-Simpson Hurricane Wind Scale, respectively. From ground-based LiDAR observations of canopy structure we estimated aboveground forest biomass at various times before and after the hurricanes. The net aboveground biomass loss from the two hurricanes combined (26.4 Mg ha−1) was about 33.7% of the pre-hurricane value of 78.4 Mg ha−1. Biomass loss from the first hurricane was about 8.6 Mg ha−1 (11.0% of the original). Damage from the second storm alone might have been as much as 22.7%, depending on the course of recovery between hurricanes. We also found a temporary decline in the fraction of Absorbed Photosynthetically Active Radiation (fAPAR). NDVI, well correlated to fAPAR, also showed this pattern after both hurricanes. Canopy structure was considerably altered by both hurricanes, including leaf area and persistent vertical and horizontal woody components. The effects of wind and precipitation differed in several ways: whereas biomass loss appears related to hurricane wind energy, the duration of extended greenness may be due to the extra aseasonal precipitation. Our data suggest that different aspects of ecosystem structure and function will recover at different time scales. The recovery of greenness occurs rapidly, on the order of weeks to months but canopy cover and production will recover more slowly. The re-establishment of persistent canopy structure and total biomass will likely take decades in the absence of other major disturbances or active forest management.
Extreme climatic and anthropogenic disturbance events are driving forces of regional and global forest change. This special issue is dedicated towards evaluating tropical dry forest resilience to ...such events in Mexico at the landscape, ecosystem, community and population levels. Collectively, the articles herein suggest that tropical dry forests are highly resilient to these extreme disturbances, at least in the short-term, because different patterns and processes across ecological levels can recover relatively quickly to pre-disturbance conditions. However, because forest recovery is strongly controlled by water availability, extreme dry years after disturbance may limit its resilience capacity. Understanding the precipitation regime in these seasonally dry forests will be crucial for improving their management as the frequency of extreme events increases. A common theme of several articles in this special issue is that resilience of tropical dry forests to the interacting effects of climatic and anthropogenic disturbances seems so far idiosyncratic and unpredictable and merits further research in the long-term.
•A severe frost induced extensive tree mortality in the northmost Neotropical dry forest.•Elevation mediated frost impact across the lowland landscape.•NDVI spectral index was highly sensitive to ...frost-induced vegetation damage.•Negative NDVI anomalies predominated after the frost.•The relationship between NDVI anomalies and ground-based observations confirmed frost severity.•Higher frost-disturbance severity stimulated more new recruitment and less tree resprouting.
Extreme climatic and weather events are inducing widespread tree mortality in many forest ecosystems worldwide. A severe frost related to the historic cold wave that affected much of North America in early February 2011 triggered extensive tree mortality in the lowland tropical dry forest in northwestern Mexico. In this landscape, we assessed frost-induced vegetation damage using anomalies of the widely used NDVI spectral index calculated with a 12-year pre-disturbance reference period. In addition, NDVI anomalies were related to ground-based measures of frost-disturbance severity (density of frost-killed trees) and forest recovery (post-frost recruits and resprouting of surviving trees) obtained in 48 1-ha study plots distributed across the landscape. We found negative NDVI anomalies in 84% of our study area, indicating widespread frost-induced vegetation damage. The relationship between NDVI anomalies and density of frost-killed trees confirmed the level of frost damage across the lowland vegetation, suggesting that even small deviations from long-term mean NDVI values may hint to severe disturbance on forest structure and function. Higher frost-disturbance severity stimulated more new recruitment and less tree resprouting. Our results demonstrate the reliability of spectral indices for rapid assessment of climate-induced vegetation change, the high vulnerability of tropical dry forests to extreme frost and the predominant mechanism of vegetation recovery after severe frost disturbance.
•Long-term data useful to evaluate ecosystem’s relative response to hurricanes.•The onset of the rainy season is remarkably more predictable than its ending.•Length of the rainy season can be shorter ...than 3months or larger than 7months.•Highly erosive storms are frequent and occur any time, even during dry season.•There is frequent presence of droughts during the wet season (“canículas”).
Rainfall, runoff and sediment yield have been measured over three decades (1983–2015) in five contiguous small watersheds (12–28ha) 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.
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.
En los bosques de pino con un régimen histórico de incendios superficiales frecuentes de baja severidad, bajo condiciones extremas del estado del tiempo o a consecuencia de la supresión del fuego, la ...severidad de los incendios puede incrementar. La respuesta de la vegetación a eventos de incendios severos se estudió en una cronosecuencia postincendio de 8 años, 28 años y 60 años en un bosque dominado por Pinus douglasiana en México. La densidad de árboles con diámetro > 2.5 cm y su área basal alcanzaron valores de 1095 árboles ha-1 ± 609 árboles ha-1 y 10.0 m2 ha-1 ± 2.2 m2 ha-1 a los 8 años; a los 28 años el área basal (44.6 m2 ha-1 ± 3.0 m2 ha-1) fue cercana a la de los rodales de 60 años (49.0 m2 ha-1 ± 6.4 m2 ha-1). Los pinos mantuvieron el mayor valor de importancia con el tiempo postincendio, se observó la formación de un subdosel de latifoliadas tolerantes a la sombra y un aumento en la riqueza y diversidad de especies; también se documentó que periodos largos sin incendios incrementan la carga de combustibles superficiales ligeros (66.0 Mg ha-1 ± 5.5 Mg ha-1 en los sitios de 28 años y 61.5 Mg ha-1 ± 4.6 Mg ha-1 en los sitios de 60 años) y modifican el comportamiento del fuego (velocidad de propagación de 1.3 m s-1 a 4.1 m s-1 y la longitud de la llama de 0.7 m a 1.7 m entre los rodales de 8 años y los de 28 años y 60 años combinados). El manejo de los bosques de pino debe considerar el balance entre objetivos de conservación biológica y mitigación del peligro de incendios de alta severidad.
Seed arrival is a limiting factor for the regeneration of diverse tropical forests and may be an important mechanism that drives patterns of tree species' distribution. Here we quantify spatial and ...seasonal variation in seed rain of secondary forests in southern Bahia, Brazil. We also examine whether secondary forest age enhances seed dispersal and whether seed rain density and diversity in secondary forests decay with distance from mature forest. Across a chronosequence of 15 pairs of mature and secondary forests, 105 seed traps were installed and monitored for one year. We tested the effects of secondary forest age, distance from mature forest, and seasonality on monthly seed rain density, diversity, seed dispersal mode, and diaspore size. We found that secondary forest age had strong, positive effects on the diversity of seed rain, which was generally higher during the wet season. Moreover, contrasting patterns among diversity indices revealed that seeds of rare species occurred more often in 40 yr old secondary forests and mature forests. While the proportion of biotically and abiotically dispersed seeds did not change significantly with distance from mature forest across all forest age classes, we found that biotically dispersed seeds contributed disproportionately more to seed rain diversity. Our results emphasize the importance of biotic dispersal to enhance diversity during secondary succession and suggest that changes in secondary forest structure have the potential to enhance the diversity of tropical secondary forests, principally by increasing dispersal of rare species.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Management and climate change can disturb tropical dry forest ecosystems.•Population dynamics helps to understand driving factors and disturbance effects.•We modeled dynamics for small mammals in a ...protected forest in Mexico.•Rainfall predicted changes; extreme rainfall caused local extinction of one species.•Protected refugia can serve as source for repopulation after such extinctions.
Understanding the consequences of biotic and abiotic variability on population dynamics is fundamental to assessing anthropogenic impacts, such as global climate disruption, on populations and species. Our understanding from studies to date is poor, although some long-term studies of small mammals in temperate ecosystems have elucidated the roles of climate and of interspecific interactions in their population dynamics. However, the lack of long-term studies in the tropics is a major impediment to understanding species and ecosystems in these regions. We analyzed the long-term population dynamics of seven species of small mammals from two adjacent tropical dry forests with contrasting phenology in a protected area of western Mexico. We modeled these dynamics using data from an 18-year live-trapping database, and we evaluated the effects of intra- and interspecific interactions, primary productivity, temperature, precipitation, and unusual climate events. Intraspecific interactions were the most common factors in every population, while interspecific interactions had only a mild positive interaction between few species. While we found that the effect of temperature was not relevant to population dynamics, precipitation caused positive effects on all species, either by directly enhancing the reproductive rate or, indirectly, by triggering changes in primary productivity. Extreme climate events created intense signals. Oryzomys melanotis, an invasive and opportunistic species, benefited from these events, and two populations were harmed by them: Peromyscus perfulvus and Liomys pictus, the small mammal with the most abundant population of the upland forest, which was extirpated for over 16 months. Our results suggest that sharp reductions in precipitation and more frequent extreme climate events—both predicted by global climate disruption regional models—would have dramatic effects, adding to the other anthropogenic pressures these forests are already suffering (habitat loss, excessive management). These results emphasize the importance of protected and unmanaged refugia, such as our study site, to provide sources for refaunation following local extinctions.
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