Exotic species that become invasive can have a strong impact on the success of native species because of traits that enhance their competitive abilities. This study investigates three potential trait ...differences between common invasive and native shrubs that could enhance the competitive success of invasives: resistance to herbivory, length of autumn leaf retention, and timing of spring leaf emergence. We measured herbivory per plant by leaf-chewing insects, autumn leaf color change and retention, and spring leaf-out in five native and five invasive shrub species in Wildman Woods near Richmond, Indiana, during the fall of 2014 and the spring of 2015. Although we found variation among species, native plants as a group had significantly greater percent leaf herbivory per plant compared to invasive plants, while invasive plants kept chlorophyll significantly later in autumn and had longer leaf retention. Invasive plants also leaf out slightly earlier than native species. Our findings in 2014 were very similar to previous unpublished work in the same area on several of the same species in 2002, 2004, and 2007, suggesting that these patterns are consistent between years. Overall, we found evidence that lower herbivory rates, longer leaf retention in fall, and perhaps earlier leaf-out in spring could improve the competitive abilities of invasive shrub species through increased season-long photosynthesis.
Summary
The representation of stomatal regulation of transpiration and CO2 assimilation is key to forecasting terrestrial ecosystem responses to global change. Given its importance in determining the ...relationship between forest productivity and climate, accurate and mechanistic model representation of the relationship between stomatal conductance (gs) and assimilation is crucial.
We assess possible physiological and mechanistic controls on the estimation of the g1 (stomatal slope, inversely proportional to water use efficiency) and g0 (stomatal intercept) parameters, using diurnal gas exchange surveys and leaf‐level response curves of six tropical broadleaf evergreen tree species.
g1 estimated from ex situ response curves averaged 50% less than g1 estimated from survey data. While g0 and g1 varied between leaves of different phenological stages, the trend was not consistent among species. We identified a diurnal trend associated with g1 and g0 that significantly improved model projections of diurnal trends in transpiration.
The accuracy of modeled gs can be improved by accounting for variation in stomatal behavior across diurnal periods, and between measurement approaches, rather than focusing on phenological variation in stomatal behavior. Additional investigation into the primary mechanisms responsible for diurnal variation in g1 will be required to account for this phenomenon in land‐surface models.
•Vegetation gradients can differ in their phenologies, reflecting functional traits.•Rainfall was negatively related to leaf fall along a savanna–seasonal forest gradient.•Savanna species showed ...drought tolerance strategies.•Transition and SDTF vegetations had similar leaf strategies (drought avoidance).
Vegetation gradients, such as those between savanna and seasonally dry tropical forest (SDTF) vegetations, may experience nearly identical macroclimatic conditions but still differ because of local ecological filters selecting for distinct plant functional aspects related to water storage and use. We examined how leaf phenology, water potential, wood density, and wood saturated water content varied seasonally along a savanna, transition, and SDTF vegetation gradient at the eastern border of the Chapada Diamantina Highlands, Brazil. We monitored the leaf phenologies of 523 individuals of 48 woody species (20 savanna, 14 transition, and 14 SDTF species) for two years. We identified four phenological groups: brevideciduous, deciduous, evergreen (EG) plants having continuous growth, and evergreen plants having seasonal growth. Deciduous species were found throughout the gradient, while EG species accounted for more than 80% of relative density in savanna areas. Precipitation was negatively related to leaf fall for all phenological groups, and positively related for leaf flushing in deciduous species. More than 80% of all species exhibited wood densities between 0.50 and 0.91 g cm−3. The first principal component explained 77.64% of the observed variance, associated with wood saturated water content, water potential, and wood density. All of the savanna species were distributed along the positive axis of the principal component analysis as compared to SDTF species. We demonstrated that the effects of water limitations along the gradient were critical to the selection of functional traits associated with water-use strategies and expressive deciduousness in SDTF vegetation, interpreted as drought avoidance strategies.
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Annual maps of the remote sensing green-up date derived from SPOT-VEGETATION data were compared to the phenological observations collected by the PlantWatch citizen science project across Canada ...between 1998 and 2012. Green-up dates were found to relate to the leaf-out dates for four woody species (Populus tremuloides, Acer rubrum, Syringa vulgaris, Larix laricina), with a RMSE from 13.6 to 15.6days. This was true for all landcover types except in pixels where agriculture or water bodies were dominant. This is less accurate than the results from previous studies for boreal Eurasia (RMSE=8.7days), with phenology data from an operational network. When data were aggregated at a regional level, the remote sensing green-up date matched well with the interannual variations in leafing and also in flowering of most of the recorded species. These included spring events for trees, shrubs and non-woody plants which were either native to Canada or introduced. For most plants, spring flowering and leafing times are functions of accumulated temperature. For this reason, plant species develop in a predictable sequence, and interannual variations in this cohort of species leafing and flowering are correlated. This explains the correlation with remote sensing green-up. Data from this volunteer PlantWatch network proved consistent with independent satellite data, suggesting that combining the two will strengthen the future capacity to monitor vegetation changes.
•Green-up is compared with citizen phenological observations across Canada.•Green-up correlates with the leaf-out dates of the four tested woody plant species.•Green-up correlates with the herbaceous, shrub and tree flowering dates.•Green-up matches plant community phenology interannual variations.
•Leaf phenology monitoring using digital cameras in tropical vegetation.•Digital images can track temporal changes in the vegetation structure.•Phenocams are potential tools for conservation ...biology.•Phenocams for tropical phenology monitoring are a promising research field in Brazil.
The application of digital cameras to monitor the environment is becoming global and changing the way of phenological data collection. The technique of repeated digital photographs to monitor plant phenology (phenocams) has increased due to its low-cost investment, reduced size, easy set up installation, and the possibility of handling high-resolution near-remote data. Considering the widespread use of phenocams worldwide, our main goals here are: (i) to provide a step-by-step guide for phenocam set up in the tropics, reinforce its appliance as an efficient tool for monitoring tropical phenology and foster networking, (ii) to discuss phenocam applications for biological conservation, management, and ecological restoration. We provide the concepts and properties for image analysis which allow representing the phenological status of the vegetation. The association of a long-term imagery data with local sensors (e.g., meteorological stations and surface-atmosphere flux towers) allows a wide range of studies, especially linking phenological patterns to climatic drivers; and the impact of climate changes on plant responses. We show phenocams applications for conservation as to document disturbances and changes on vegetation structure, such as deforestation, fire events, and flooding and the vegetation recovery. Networks of phenocams are growing globally and represent an important tool for conservation and restoration, as it provides hourly to daily information of monitored systems spread over several sites, ecosystems, and climatic zones. Moreover, websites enriched by vegetation dynamic imagery data can promote science knowledge by engaging citizen science participation.
Recent shifts in phenology are the best documented biological response to current anthropogenic climate change, yet remain poorly understood from a functional point of view. Prevailing analyses are ...phenomenological and approximate, only correlating temperature records to imprecise records of phenological events. To advance our understanding of phenological responses to climate change, we developed, calibrated, and validated process-based models of leaf unfolding for 22 North American tree species. Using daily meteorological data predicted by two scenarios (A2: +3.2 °C and B2: +1 °C) from the HadCM3 GCM, we predicted and compared range-wide shifts of leaf unfolding in the 20th and 21st centuries for each species. Model predictions suggest that climate change will affect leaf phenology in almost all species studied, with an average advancement during the 21st century of 5.0 days in the A2 scenario and 9.2 days in the B2 scenario. Our model also suggests that lack of sufficient chilling temperatures to break bud dormancy will decrease the rate of advancement in leaf unfolding date during the 21st century for many species. Some temperate species may even have years with abnormal budburst due to insufficient chilling. Species fell into two groups based on their sensitivity to climate change: (1) species that consistently had a greater advance in their leaf unfolding date with increasing latitude and (2) species in which the advance in leaf unfolding differed from the center to the northern vs. southern margins of their range. At the interspecific level, we predicted that early-leafing species tended to show a greater advance in leaf unfolding date than late-leafing species; and that species with larger ranges tend to show stronger phenological changes. These predicted changes in phenology have significant implications for the frost susceptibility of species, their interspecific relationships, and their distributional shifts.
Warming temperatures are increasing rainfall extremes, yet arthropod responses to climatic fluctuations remain poorly understood. Here, we used spatiotemporal variation in tropical montane climate as ...a natural experiment to compare the importance of biotic versus abiotic drivers in regulating arthropod biomass. We combined intensive field data on arthropods, leaf phenology and in situ weather across a 1700–3100 m elevation and rainfall gradient, along with desiccation‐resistance experiments and multi‐decadal modelling. We found limited support for biotic drivers with weak increases in some herbivorous taxa on shrubs with new leaves, but no landscape‐scale effects of leaf phenology, which tracked light and cloud cover. Instead, rainfall explained extensive interannual variability with maximum biomass at intermediate rainfall (130 mm month−1) as both 3 months of high and low rainfall reduced arthropods by half. Based on 50 years of regional rainfall, our dynamic arthropod model predicted shifts in the timing of biomass maxima within cloud forests before plant communities transition to seasonally deciduous dry forests (mean annual rainfall 1000–2500 mm vs. <800 mm). Rainfall magnitude was the primary driver, but during high solar insolation, the ‘drying power of air’ (VPDmax) reduced biomass within days contributing to drought related to the El Niño‐Southern Oscillation (ENSO). Highlighting risks from drought, experiments demonstrated community‐wide susceptibility to desiccation except for some caterpillars in which melanin‐based coloration appeared to reduce the effects of evaporative drying. Overall, we provide multiple lines of evidence that several months of heavy rain or drought reduce arthropod biomass independently of deep‐rooted plants with the potential to destabilize insectivore food webs.
Resumen
El aumento de las temperaturas está incrementando los extremos de precipitación, pero las respuestas de los artrópodos a las fluctuaciones climáticas siguen siendo poco conocidas. Aquí, utilizamos la variación espaciotemporal en el clima montano tropical como un experimento natural para comparar la importancia de los factores bióticos versus abióticos en la regulación de la biomasa de artrópodos. Combinamos datos de campo intensivos de artrópodos, fenología de las hojas y clima in situ a lo largo de un gradiente altitudinal de 1700 a 3100 m y un gradiente de precipitación, junto con experimentos de resistencia a la desecación y modelos multi‐decenales. Encontramos evidencia limitada para los factores bióticos con aumentos débiles en algunos taxones de herbívoros en arbustos con hojas nuevas, pero no hubo efectos a escala de paisaje en la fenología de la hoja, que rastreaba la luz y la cubierta de nubes. En cambio, las precipitaciones explicaron la amplia variabilidad interanual con una biomasa máxima en precipitaciones intermedias (130 mm mes−1), ya que los tres meses de precipitaciones altas y bajas redujeron los artrópodos a la mitad. Basándose en 50 años de precipitación regional, nuestro modelo dinámico de artrópodos predijo cambios en el momento de los máximos de biomasa dentro del bosque nuboso antes de que las comunidades de plantas hicieran la transición al bosque seco estacional caducifolio (precipitación media anual 1000–2500 mm vs. <800 mm). La magnitud de las lluvias fue el principal factor, pero durante la alta insolación solar, el “poder de secado del aire” (VPDmax) redujo la biomasa en cuestión de días, lo que contribuyó a la sequía relacionada con El Niño‐Southern Oscillation (ENSO). Destacando los riesgos de la sequía, los experimentos demostraron la susceptibilidad de toda la comunidad a la desecación, excepto en el caso de algunas orugas en las que la coloración a base de melanina parece reducir los efectos de la desecación por evaporación. En resumen, proporcionamos múltiples líneas de evidencia de que varios meses de fuertes lluvias o sequías reducen la biomasa de artrópodos independientemente de las plantas de raíces profundas con el potencial de desestabilizar las redes alimentarias de los insectívoros.
Although two‐thirds of terrestrial vertebrates consume insects and spiders, how changing rainfall regimes will affect arthropods remains poorly understood. Using spatiotemporal variation in tropical montane climate as a natural experiment, we show arthropod biomass maxima at intermediate rainfall as 3 months of both wet and dry extremes reduced arthropods by half. Integrating field estimates with local and regional rainfall to model biomass over 50 years, our intermediate rainfall model predicted locally asynchronous arthropod phenology across low‐latitude mountains. Rapid response of arthropods to increasing rainfall extremes could have cascading effects on terrestrial food webs and a range of ecosystem functions.
Introduction: Defined seasonality in savanna species can stimulate physiological responses that maximize photosynthetic metabolism and productivity. However, those physiological responses are also ...linked to the phenological status of the whole plant, including leaf phenophases. Objective: To study how physiological traits influence phenophase timing among congeneric and co-occurring savanna species. Methods: We evaluated the leaf phenology and physiological traits of populations of Byrsonima intermedia, B. coccolobifolia, and B. verbascifolia. Physiological measurements were performed at the onset of the dry and rainy seasons and again late in the season. Results: B. intermedia and B. coccolobifolia were classified as brevideciduous and B. verbascifolia as evergreen. The maximum quantum yield for B. intermedia and B. coccolobifolia were lowest during the dry season. At the onset of the dry period, the highest chloroplastidic pigment levels were observed, which decreased as the season advanced, total chlorophyll/carotenoid ratios were lowest, and carotenoid contents were highest. We detected low starch content values at the start of the rainy season, coinciding with the resumption of plant growth. Two months into this season, the leaves were at their peak structural and functional maturity, with high water-soluble polysaccharide values and photosynthetic rates, and were storing large amounts of starch. Conclusions: Physiological and leaf phenological strategies of the Byrsonima species were related to drought resistance and acclimatization to the seasonality of savanna water resources. The oscillations of the parameters quantified during the year indicated a strong relationship with water seasonality and with the phenological status of the leaves.
Objective: We studied how physiological traits, and not only seasonality, influence phenophase timing among congeneric and co-occurring savanna species.
Methods: We followed the leaf phenologies and physiological traits of populations of Byrsonima intermedia, B. coccolobifolia, and B. verbascifolia native to the Brazilian savanna. Analyses of specific leaf mass, relative water content, leaf phenology, leaf carbohydrate content, chloroplastidic pigments, and photosynthetic efficiency were performed at different times during both the dry and rainy seasons. Physiological measurements were performed at the onset of the dry season and again late in that season, as well as at the onset of the rainy season and again late in the rainy season.
Results: Byrsonima intermedia and B. coccolobifolia were classified here as brevideciduous and B. verbascifolia as evergreen. Few variations in chlorophyll a fluorescence values were detected over the full year, with the lowest maximum quantum yield values (Fv/Fm) for B. intermedia and B. coccolobifolia occurring during the dry season. The deciduous species (B. verbascifolia) evidenced higher photosynthetic yields during periods of abundant water availability, mainly after its complete recovery after the start of the prolonged rainy period. The highest chloroplastidic pigment levels were observed at the onset of the dry period, although chlorophyll levels decreased as the dry season advanced. The lowest total chlorophyll/carotenoid ratios and the highest carotenoid contents observed at the onset of the dry season indicated that Byrsonima plants were still investing in mechanisms of photoprotection and the dissipation of excess energy from their photosynthetic systems even under water deficit conditions. We detected low starch content values at the onset of the rainy season, which coincides with the resumption of plant growth. At two months into the rainy season, the leaves were at their peak structural and functional maturity, exhibiting high water-soluble polysaccharide values and high photosynthetic rates, and were storing large amounts of starch.
Conclusions: Our data evidenced that the physiological and foliar phenological strategies of the Byrsonima species studied here were related to drought resistance and to acclimatization to the seasonality of savanna water resources. The oscillations of the parameters quantified during the year in the three studied species indicated not only a strong relationship with water seasonality, but also with the phenological statuses of the leaves.
•Infected and non-infected branches showed distinct stomata responses depending on host phenology.•Differences in regulation of water loss between branches were more apparent in the wet ...season.•Pre-dawn leaf water potentials were consistently more negative for infected branches.•Leaf mobile nutrient concentrations were lower in infected branches.•Host species adjust at the individual level to mistletoe physiological stress throughout the year.
Plants should have the ability to perceive physiological changes within their branches when infected by mistletoes, adjusting the use of resources between infected and uninfected branches which can be crucial for their survival in the long-term. Here we investigated how branches infected by the mistletoe Passovia ovata (Pohl ex DC.) Tiegh. and uninfected branches within the same individual tree respond to seasonal environmental changes across two hosts of contrasting leaf phenology (the evergreen Miconia albicans (SW.) Triana and the deciduous Byrsonima verbascifolia (L.) DC.). We measured key leaf traits (instantaneous gas exchange rates, diurnal courses of stomatal conductance, leaf water potential, specific leaf area and leaf macronutrient concentrations) during the peak of the wet and dry season in a seasonal savanna of central Brazil. Pre-dawn leaf water potentials were consistently more negative for infected branches of both hosts, suggesting that overnight water refilling of infected branches was more limited. However, infected and uninfected branches exhibited similar leaf water potentials at midday, suggesting that they undergo similar imbalances in water supply and demand during periods of high atmospheric evaporative demand. Infected and non-infected branches of the evergreen mistletoe showed tighter regulation of water loss, whereas infected branches of the deciduous host were less constrained in regulating leaf transpiration. We also found differences for nutrient concentrations: N, P and K were lower, while Ca was higher in leaves of infected branches. Physiological changes induced by mistletoe infection affected host performance, and were reflected in water and nutrient use differences between infected and uninfected branches. Our findings show that infection responses by mistletoes can be detected between branches within individual trees, and that host species with distinct patterns of leaf phenology are capable to adjust, at the individual level, to cope with mistletoe's imposed physiological stress throughout the year.
•Severe drought was observed during the 2015/2016 El Niño in dry dipterocarp forest.•Leaf phenology of dominant species except Sindora siamensis was shifted by El Niño.•Extra carbon loss occurred ...during the 2015/2016 El Niño dry season.•Rapid recovery of CO2 uptake in the wet season after El Niño was observed.
This study evaluates the impacts of the 2015/2016 El Niño event on the phenology and carbon dioxide (CO2) exchange in a secondary dry dipterocarp forest (DDF). In western Thailand, El Niño events significantly reduced rainfall and increased air temperature, leading to prolonged dry season with low soil water content and high vapor pressure deficit (VPD). During 2014–2017, leaf phenology was monitored and CO2 exchanges in this forest were measured by an eddy covariance method. During El Niño year, dry dipterocarp species were shed their leaves earlier when compared to neutral years (i.e. with no El Niño event). The species Shorea siamensis Miq. and Sindora siamensis Teijsm.&Miq. showed complete deciduousness during the dry season 2015/2016 as typically observed for these species, but the leafless period was longer than during non-El Niño years. Shorea roxburghii G.Don and Shorea obtusa Wall. showed untypically complete deciduousness during the El Niño year. For the species Sindora siamensis, however, the timing of first leaf expansion was not affected by the strong El Niño. In addition, El Niño resulted in a decline of the annual gross primary productivity (GPP) and evapotranspiration (ET) by 9.6 and 14.1%, respectively. The net ecosystem productivity (NEP) was only affected by El Niño during the dry months, but not during the following wet season therefore the total annual NEP was not significantly affected. Our result demonstrates that El Niño events have a strong impact on canopy duration of DDF ecosystem. However, our study suggests that the carbon loss during this prolonged dry season of 2015/2016 can be compensated in this young secondary DDF during the following wet season, leading to increased NEP on a yearly basis.
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