Fire Responses Shape Plant Communities in a Minimal Model for Fire Ecosystems across the World.

AbstractAcross plant communities worldwide, fire regimes reflect a combination of climatic factors and plant characteristics. To shed new light on the complex relationships between plant characteristics and fire regimes, we developed a new conceptual mechanistic model that includes plant competition, stochastic fires, and fire-vegetation feedback. Considering a single standing plant functional type, we observed that highly flammable and slowly colonizing plants can persist only when they have a strong fire response, while fast colonizing and less flammable plants can display a larger range of fire responses. At the community level, the fire response of the strongest competitor determines the existence of alternative ecological states (i.e., different plant communities) under the same environmental conditions. Specifically, when the strongest competitor had a very strong fire response, such as in Mediterranean forests, only one ecological state could be achieved. Conversely, when the strongest competitor was poorly fire adapted, alternative ecological states emerged-for example, between tropical humid savannas and forests or between different types of boreal forests. These findings underline the importance of including the plant fire response when modeling fire ecosystems, for example, to predict the vegetation response to invasive species or to climate change.

Facilitation and competition deconstructed: a mechanistic modelling approach to the stress gradient hypothesis applied to drylands.

Facilitative interactions among species are key in plant communities. While experimental tests support the Stress Gradient Hypothesis (SGH) as an association between facilitation and stress, whether the shape of net effects along stress gradients can be predicted is controversial, with no available mathematical modelling approaches. We proposed a novel test, using a modification of the R* model to study how negative and positive partial effects of plant interactions in drylands combine along two common stress gradients. We modelled different interactions: competition for water and light, amelioration of soil infiltration and/or grazing protection, obtaining that intensity and importance of facilitation did not generally increase along stress gradients, being dependent on the interaction type. While along the water stress gradient net interactions became more positive, reaching a maximum and then waning again, various outcomes were observed along the grazing gradient. Shape variety was mainly driven by the various shapes of the partial positive effects. Under resource stress, additive interaction effects can be expected, whereas when including grazing, the effects were non-additive. In the context of the SGH, deconstructing the effect of positive and negative interaction in a pairwise mechanistic models of drylands does not show a unique shape along stress gradients.

Woody clockworks: circadian regulation of night-time water use in Eucalyptus globulus.

The role of the circadian clock in controlling the metabolism of entire trees has seldom been considered. We tested whether the clock influences nocturnal whole-tree water use. Whole-tree chambers allowed the control of environmental variables (temperature, relative humidity). Night-time stomatal conductance (gs ) and sap flow (Q) were monitored in 6- to 8-m-tall Eucalyptus globulus trees during nights when environmental variables were kept constant, and also when conditions varied with time. Artificial neural networks were used to quantify the relative importance of circadian regulation of gs and Q. Under a constant environment, gs and Q declined from 0 to 6 h after dusk, but increased from 6 to 12 h after dusk. While the initial decline could be attributed to multiple processes, the subsequent increase is most consistent with circadian regulation of gs and Q. We conclude that endogenous regulation of gs is an important driver of night-time Q under natural environmental variability. The proportion of nocturnal Q variation associated with circadian regulation (23-56%) was comparable to that attributed to vapor pressure deficit variation (25-58%). This study contributes to our understanding of the linkages between molecular and cellular processes related to circadian regulation, and whole-tree processes related to ecosystem gas exchange in the field.

Impact assessment of temporary activities and events.

Temporary activities and events may have significant environmental impacts. However, they are often outside the scope of environmental assessment (EA) processes. Environmental requirements in authorization processes of activities are rare, except for some major events in sensitive areas. This article analyzes, first, the environmental impacts of outdoor temporary activities and events through a literature review; all the analyzed activities may have significant negative impacts. Then, the authorization of temporary activities, and their inclusion in EA systems, in a sample of jurisdictions worldwide was analyzed. Applying EA processes is more an exception than a rule for temporary activities. The article discusses the factors that influence activities' impacts, the conflict between precaution and operation, and the benefits and drawbacks of the application of different EA schemes to temporary activities, concluding with some proposals to improve the consideration of environmental aspects in activities' authorization. Before the authorization of activities and events, their environmental impacts should be analyzed and taken into account. This can be achieved through regulations in management plans submitted to strategic EA, through screening processes, or through environmental impact assessment when significant impacts are expected. Integr Environ Assess Manag 2023;19:1320-1332. © 2023 SETAC.

Climate change induced declines in fuel moisture may turn currently fire-free Pyrenean mountain forests into fire-prone ecosystems.

Fuel moisture limits the availability of fuel to wildfires in many forest areas worldwide, but the effects of climate change on moisture constraints remain largely unknown. Here we addressed how climate affects fuel moisture in pine stands from Catalonia, NE Spain, and the potential effects of increasing climate aridity on burned area in the Pyrenees, a mesic mountainous area where fire is currently rare. We first quantified variation in fuel moisture in six sites distributed across an altitudinal gradient where the long-term mean annual temperature and precipitation vary by 6-15 °C and 395-933 mm, respectively. We observed significant spatial variation in live (78-162%) and dead (10-15%) fuel moisture across sites. The pattern of variation was negatively linked (r = |0.6|-|0.9|) to increases in vapor pressure deficit (VPD) and in the Aridity Index. Using seasonal fire records over 2006-2020, we observed that summer burned area in the Mediterranean forests of Northeast Spain and Southern France was strongly dependent on VPD (r = 0.93), the major driver (and predictor) of dead fuel moisture content (DFMC) at our sites. Based on the difference between VPD thresholds associated with large wildfire seasons in the Mediterranean (3.6 kPa) and the maximum VPD observed in surrounding Pyrenean mountains (3.1 kPa), we quantified the "safety margin" for Pyrenean forests (difference between actual VPD and that associated with large wildfires) at 0.5 kPa. The effects of live fuel moisture content (LFMC) on burned area were not significant under current conditions, a situation that may change with projected increases in climate aridity. Overall, our results indicate that DFMC in currently fire-free areas in Europe, like the Pyrenees, with vast amounts of fuel in many forest stands, may reach critical dryness thresholds beyond the safety margin and experience large wildfires after only mild increases in VPD, although LFMC can modulate the response.

Potential of land use activities to offset road traffic greenhouse gas emissions in Central Spain.

The transport sector is one of the main sources of greenhouse gases, adding in Spain near a quarter of the total national emissions, the majority in road transport. Therefore, road contribution to climate change should be mitigated to achieve the proposed goals in the fight against climate change. Policies and strategies suggest several preventive mitigation options, but have paid little attention to compensatory mitigation. We have conducted a theoretical case study in a Spanish province, Segovia, estimating the carbon dioxide emissions in the road network between 2015 and 2050, and analysing different compensation possibilities through conservation agriculture, agroforestry, afforestation and hedgerow plantation. We have calculated carbon sequestration in the reference period and costs per tonne for each option, estimating the budget range of offsetting road carbon emission, and funding possibilities, especially through fuel taxes. The paper demonstrates that offsetting carbon emissions produced by roads in this area is technically possible and highly desirable, unifying carbon sequestration, biodiversity improvement and rural development. The main challenge is funding, which depends largely on the political will and the awareness of the citizens.

Tuberculosis endobronquial: experiencia en el Hospital Santa Clara de Bogotá 1980-1990

Se estudiaron los pacientes con lesiones endobronquiales por broncofibroscopia en el período de 1980-1990 en el servicio de Broncoscopia en el Hospiatl Santa Clara de Bogotá, a quienes se les practicó estudio directo con ZN y cultivo en medio de Ogawa-Kudoh de lavado y cepillado bronquial. Además se tomaron biopsias de las lesiones visualizadas durante el procedimiento, enviándose a cultivo para BK e histopatología. Presentamos 84 pacientes con diagnóstico de tuberculosis endobronquial, en quienes las baciloscopias fueron siempre negativas. Se les practicó broncofibroscopia con diagnósticos provisionales de tuberculosis, cáncer broncogénico, neumonía de resolución lenta, sarcoidosis, EPID y bronquiectasias. Durante el procedimiento se observaron cambios que en nuestra experiencia son eventualmente característicos y elporcentaje de acierto fue de 100 por ciento.