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The eastward‐moving large‐scale convective system associated with the Madden‐Julian Oscillation (MJO) significantly impact global weather and climate. Recent decades have seen notable changes in the MJO's lifecycle due to non‐uniform tropical ocean warming, with the roles of natural climate variability and anthropogenic influence still requiring quantification. This study examines observed and projected long‐term changes in the MJO phase speed using four twentieth‐century reanalyses and CMIP6 simulations. We find a substantial increase in MJO phase speed in three reanalyses during the twentieth century (0.6–1.2 m s⁻1 century⁻1) and further increase in MJO phase speed during the twenty‐first century (0.3–1.5 m s⁻1 century⁻1), with notable multidecadal fluctuations. We attribute the overall acceleration of the MJO to the global warming‐driven increase in the meridional moisture gradient around the warm pool while attributing the multidecadal variability in the MJO phase speed to changes in the zonal moisture gradient associated with the Pacific Decadal Oscillation. Plain Language Summary: The Madden‐Julian Oscillation (MJO) is a crucial phenomenon in the tropics that impacts weather and climate globally. Although earlier research has discussed the observed changes in the MJO lifecycle due to tropical ocean warming, we still need to understand the role of natural climate variability associated with the MJO lifecycle. This study uses twentieth century reanalyses and future climate model projections to investigate how the speed of the MJO propagation has changed over time. We find that the speed of the MJO's eastward propagation has increased significantly in three of the reanalyses during the twentieth century and continues rising in the twenty‐first century. We believe that the overall increase in MJO speed is due to global warming, which enhances the meridional moisture difference around the warm pool area. We also noted significant multidecadal variation in the MJO propagation speed. The multidecadal changes in MJO speed are linked to variations in the zonal moisture difference influenced by the Pacific Decadal Oscillation. Key Points: Increasing MJO phase speed is identified in three twentieth‐century reanalysesWe attribute the MJO's eastward acceleration to the long‐term changes in the meridional moisture gradientPacific Decadal Oscillation influences multidecadal variation in the MJO phase speed [ABSTRACT FROM AUTHOR]

Surviving the seedling phase is crucial for the establishment of plant individuals and populations. In ecosystems with dynamic water availability such as temperate grasslands, seedlings should adjust their growth strategy not only to match the current conditions but also to secure resource acquisition in the future. Here, we explored evolutionary adaptations determining plant early growth strategies in herbaceous species of temperate grasslands differing in their requirements for soil water availability.We chose 15 plant genera, within which we selected species differing in their Ellenberg indicator values for moisture. We cultivated the seedlings under standard conditions with sufficient water supply for 4 weeks. Subsequently, we measured length‐based and mass‐based shoot:root ratio to investigate seedling growth strategy and its association with species ecological niche. Seed size and content of soil‐borne nutrients were considered as potential covariates affecting this association.Linear mixed‐effect models identified the length‐based shoot:root ratio of seedlings was positively associated with soil moisture requirements in a congeneric species comparison. Nitrogen and phosphorus seed concentrations had an additional negative effect on the shoot:root ratio. Neither of these trends was found for the mass‐based shoot:root ratio.We demonstrated for the first time that there might be a general adaptation modifying the seedling shoot:root ratio according to the species niche position on the soil moisture gradient in temperate grassland species across a broad range of angiosperm phylogeny. This adaptation seems to be affected by seed mineral nutrient reserves and may operate in parallel to the well‐known phenotypic plasticity. [ABSTRACT FROM AUTHOR]

Behavioral thermoregulation is an efficient mechanism to buffer the physiological effects of climate change. Thermal ecology studies have traditionally tested how thermal constraints shape thermoregulatory behaviors without accounting for the potential major effects of landscape structure and water availability. Thus, we lack a general understanding of the multifactorial determinants of thermoregulatory behaviors in natural populations. In this study, we quantified the relative contribution of elevation, thermal gradient, moisture gradient, and landscape structure in explaining geographic variation in thermoregulation strategies of a terrestrial ectotherm species. We measured field‐active body temperature, thermal preferences, and operative environmental temperatures to calculate thermoregulation indices, including thermal quality of the habitat and thermoregulation efficiency for a very large sample of common lizards (Zootoca vivipara) from 21 populations over 3 yr across the Massif Central mountain range in France. We used an information‐theoretic approach to compare eight a priori thermo‐hydroregulation hypotheses predicting how behavioral thermoregulation should respond to environmental conditions. Environmental characteristics exerted little influence on thermal preference with the exception that females from habitats with permanent access to water had lower thermal preferences. Field body temperatures and accuracy of thermoregulation were best predicted by the interaction between air temperature and a moisture index. In mesic environments, field body temperature and thermoregulation accuracy increased with air temperature, but they decreased in drier habitats. Thermoregulation efficiency (difference between thermoregulation inaccuracy and the thermal quality of the habitat) was maximized in cooler and more humid environments and was mostly influenced by the thermal quality of the habitat. Our study highlights complex patterns of variation in thermoregulation strategies, which are mostly explained by the interaction between temperature and water availability, independent of the elevation gradient or thermal heterogeneity. Although changes in landscape structure were expected to be the main driver of extinction rate of temperate zone ectotherms with ongoing global change, we conclude that changes in water availability coupled with rising temperatures might have a drastic impact on the population dynamics of some ectotherm species. [ABSTRACT FROM AUTHOR]

Aim: Long‐term monitoring of forest understorey species was used to describe changes in native and invasive exotic plant abundances over time within different disturbed or undisturbed forest types. This information was then used to determine the predictive invasion model (passenger/opportunist, driver or back‐seat driver). Location: Cheat Ranger District of the Monongahela National Forest, West Virginia, USA. Methods: Understorey vegetation of mature and clear‐cut forests was sampled every 5–6 years for 16 years. Stands were stratified across three land types following a moisture gradient. Invasive plant richness, frequency and abundance were evaluated across land type and disturbance type with general linear mixed models. Change in richness, diversity and abundance of both native and invasive non‐native plants was evaluated as a measure of impact. Results: The mesic mature stands had the greatest invasive plant richness, frequency and abundance. The moderately mesic clear‐cut stands initially showed the greatest invasive plant richness, frequency and abundance, but over time these values became greater for the drier clear‐cuts. The mature forests showed no change in native species abundance in response to invasion. Clear‐cut‐drier stands showed a decrease, while the more mesic stands showed an increase in native plant richness, diversity and abundance in response to invasion. The drier clear‐cuts, with increasing invasions and negative native species impacts, were indicative of the back‐seat driver model. The hitchhiker model, a new term, described increasing plant invasions with no measurable impacts. Main Conclusions: The drier clear‐cut stands exhibit a lack of biotic resistance to invasion, unlike the mesic clear‐cut stands. Increasing invasion in the mature forests suggests that a threshold may be reached that results in impacts on the native vegetation, but with no increase in native plant abundance to help alleviate these effects. [ABSTRACT FROM AUTHOR]

During rain-free periods, the water table in peatlands falls and the moisture content ( MC) of top 10 cm, including the moss layer, depends upon the hydrophysical properties and the responses of the local composition of species to water deficit. Thus, the ecosystem becomes vulnerable to surface peat fires. The spread of such fires is often irregular; however, there is little understanding of how the fine-scale variation of peat MC can affect the spread of smouldering fire. We analyse the fine-scale distribution of surface MC from a degraded blanket bog (i.e., horizontal intervals of 10 cm), thus indirectly analysing the effect of fine-scale MC distribution on peat fire spread. We determine the relationship of vegetation and microtopography to the spatial distribution of near surface MC and the moisture gradient around patches of dry peat (less than 250% MC, moisture content in a dry mass basis). We found that the MC of the surface peat was distributed in clusters with dry patches (less than 250% MC) averaging 40 ± 15 cm in size. The MC gradient surrounding dry patches was 10 ± 7% MC∙cm−1. A mixed-effects model showed that dry patches were associated with lawns (of feather moss or Sphagnum) and hummocks of feather moss. Our model showed that wet patches were associated with both hummocks and hollows of Sphagnum. Therefore, the characterization of the surface MC in a fine-scale is critical if we are to understand the spread of fires in peatlands. [ABSTRACT FROM AUTHOR]

Marks et al. (Ecol. Lett., 19, 2016, 743-751) show that tree diversity increases with tree height in North America and argue it reflects habitat 'suitability'. This finding conflicts with classical results, lacks controls for covariates of tree height, and can be explained alternatively using the modified Janzen-Connell effect and regional variance in habitats. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the hypothesis that maritime climatic factors associated with summer fog and low cloud stratus (summer marine layer) help explain the compositional diversity of chaparral in the coast range of central California. We randomly sampled chaparral species composition in 0.1‐hectare plots along a coast‐to‐interior gradient. For each plot, climatic variables were estimated and soil samples were analyzed. We used Cluster Analysis and Principle Components Analysis to objectively categorize plots into climate zone groups. Climate variables, vegetation composition and various diversity measures were compared across climate zone groups using ANOVA and nonmetric multidimensional scaling. Differences in climatic variables that relate to summer moisture availability and winter freeze events explained the majority of variance in measured conditions and coincided with three chaparral assemblages: maritime (lowland coast where the summer marine layer was strongest), transition (upland coast with mild summer marine layer influence and greater winter precipitation), and interior sites that generally lacked late summer water availability from either source. Species turnover (β‐diversity) was higher among maritime and transition sites than interior sites. Coastal chaparral differs from interior chaparral in having a higher obligate seeder to facultative seeder (resprouter) ratio and by being dominated by various Arctostaphylos species as opposed to the interior dominant, Adenostoma fasciculatum. The maritime climate influence along the California central coast is associated with patterns of woody plant composition and β‐diversity among sites. Summer fog in coastal lowlands and higher winter precipitation in coastal uplands combine to lower late dry season water deficit in coastal chaparral and contribute to longer fire return intervals that are associated with obligate seeders and more local endemism. Soil nutrients are comparatively less important in explaining plant community composition, but heterogeneous azonal soils contribute to local endemism and promote isolated chaparral patches within the dominant forest vegetation along the coast. [ABSTRACT FROM AUTHOR]

Understanding temporal effects of fire frequency on plant species diversity and vegetation structure is critical for managing tallgrass prairie (TGP), which occupies a mid‐continental longitudinal precipitation and productivity gradient. Eastern TGP has contributed little information toward understanding whether vegetation–fire interactions are uniform or change across this biome. We resampled 34 fire‐managed mid‐ and late‐successional ungrazed TGP remnants occurring across a dry to wet‐mesic moisture gradient in the Chicago region of Illinois, USA. We compared hypotheses that burning acts either as a stabilizing force or causes change in diversity and structure, depending upon fire frequency and successional stage. Based on western TGP, we expected a unimodal species richness distribution across a cover–productivity gradient, variable functional group responses to fire frequency, and a negative relationship between fire frequency and species richness. Species diversity was unimodal across the cover gradient and was more strongly humpbacked in stands with greater fire frequency. In support of a stabilizing hypothesis, temporal similarity of late‐successional vegetation had a logarithmic relationship with increasing fire frequency, while richness and evenness remained stable. Temporal similarity within mid‐successional stands was not correlated with fire frequency, while richness increased and evenness decreased over time. Functional group responses to fire frequency were variable. Summer forb richness increased under high fire frequency, while C4 grasses, spring forbs, and nitrogen‐fixing species decreased with fire exclusion. On mesic and wet‐mesic sites, vegetation structure measured by the ratio of woody to graminoid species was negatively correlated with abundance of forbs and with fire frequency. Our findings that species richness responds unimodally to an environmental‐productivity gradient, and that fire exclusion increases woody vegetation and leads to loss of C4 and N‐fixing species, suggest that these processes are uniform across the TGP biome and not affected by its rainfall–productivity gradient. However, increasing fire frequency in eastern TGP appears to increase richness of summer forbs and stabilize late‐successional vegetation in the absence of grazing, and these processes may differ across the longitudinal axis of TGP. Managing species diversity in ungrazed eastern TGP may be dependent upon high fire frequency that removes woody vegetation and prevents biomass accumulation. [ABSTRACT FROM AUTHOR]

Trunk-associated invertebrates were sampled on marri trees ( Eucalyptus ( Corymbia) calophylla) along a transect from Karragullen, near Perth, through to Dryandra, 150 km to the south-east. This represents a drop in annual rainfall from 1078 to 504 mm, which is accompanied by a change from jarrah ( Eucalyptus marginata) forest to wandoo ( Eucalyptus wandoo) woodland. Invertebrates were sampled by intercept traps, which collect invertebrates that attempt to land on the trunks, and bark traps, which collect invertebrates that move, or live, on the trunk. Trends are reported here at the ordinal level. The variety and abundance of invertebrates sampled was generally greater in the intercept than the bark traps. Invertebrate abundance, activity and biomass on bark were strongly seasonal, with greater numbers being found during the moister periods. Invertebrate abundances tended to be greater at the drier, eastern end of the transect, particularly on the three sites within wandoo woodland. These trends were analysed in terms of rainfall, soil nutrients and plant community composition. The analysis failed to detect an underlying influence of any of these factors, suggesting that the observed trends on marri trunks may be the result of invertebrate responses to the dominant tree species at the western and eastern ends of the transect, namely jarrah and wandoo respectively. [ABSTRACT FROM AUTHOR]

Despite the enormous contribution of invertebrates to global biodiversity and ecosystem function, the patterns and causes of insect responses to tropical rainforest destruction and fragmentation remain poorly understood. We studied the responses of beetles to these factors in a fragmented upland rainforest landscape in north-east Queensland, Australia. Beetles were sampled using flight interception traps from six replicate sites in rainforest interior, rainforest edge, small rainforest remnants and pasture, interspersed across about 600 km2. Beetles from 10 family/subfamily groups were sorted to species. There were three major findings. First, converting rainforest into pasture has a very strong negative effect on beetle diversity and species composition. Very few beetle species were present in pasture and none of the most abundant species was more abundant in pasture than rainforest. Second, beetle assemblages appeared to respond to climate. Beetle species composition in drier rainforest habitats was different from that of moister rainforest and there were species unique to each rainforest type. Third, beetle species composition differed between small remnants and interior rainforest: drier-associated species were more abundant in small remnants, whereas wetter-associated species were more abundant in interiors. Edges tended to be intermediate. We argue that this pattern can be attributed to a fragmentation effect mediated by differences in microclimate rather than by floristic, structural, or area and isolation effects. [ABSTRACT FROM AUTHOR]

Trunk–associated invertebrates were sampled on two rough-barked tree species (jarrah, Eucalyptus marginata and marri, E. calophylla) at Karragullen, in the hills near Perth, Western Australia, and on these two species plus two smooth-barked species (wandoo, E. wandoo, and powderbark wandoo, E. accedens) at Dryandra, a drier site situated 150 km to the south-east. Invertebrates were sampled by intercept traps, which collect animals that attempt to land on the trunks, and photo-eclector bark traps, which collect invertebrates that move, or live, on the trunk. The range and abundance of invertebrates sampled was generally greater in the intercept than the bark traps. Invertebrate abundance and activity (but not biomass) on bark was strongly seasonal, with greater numbers being found during the moister periods. The two smooth-barked species supported, and were visited by, more invertebrates than the two rough-barked species. There was some evidence that jarrah supported more invertebrates than marri at both Karragullen and Dryandra, although the results were equivocal. Within the two smooth-barked species, wandoo tended to support more invertebrates than powderbark wandoo. These trends are discussed in terms of the characteristics of the bark of these trees and the environments in which they occur. [ABSTRACT FROM AUTHOR]

ABSTRACT Aim Climate-driven changes affecting ecosystem primary production have been well documented for many vegetation types, while the effects of climate on plant populations remains unclear. Herein, we address the relationships between climatic variables and shoot density, reproductive allocation and shoot biomass in Leymus chinensis on a large-scale climatic gradient in 2000. Location Nine sites experiencing similar light regimes, but differing in longitude, precipitation and altitude were selected on the North-east China Transect (NECT) from 115° to 124°E, around a latitude of 43.5°N. Methods Densities of total, vegetative and reproductive shoots and of shoot biomass were measured twice over the growing season in each site. Climatic data were taken from the climate database of the Laboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese Academy of Sciences and from the local weather stations throughout the NECT. Results Densities of total, vegetative and reproductive shoots increased significantly from the west to the east and from dry to moist along the NECT, and were strongly correlated with annual precipitation (r 2 = 0.934, 0.943 and 0.863, respectively) and an aridity index (r 2 = 0.809, 0.816 and 0.744, respectively). The average total shoot density at the east end (470/m2 ) was about three times that at the west (160/m2 ). Reproductive allocation and shoot biomass for both vegetative and reproductive shoots increased with precipitation and declined with the aridity index along the NECT. There were positive correlations between shoot biomass and annual precipitation for vegetative shoots (P < 0.05, R 2 = 0.604) and March precipitation for reproductive shoots (P < 0.05, R 2 = 0.533), respectively. Main conclusions These findings suggest that L. chinensis adjusts to decreasing precipitation/increasing aridity by alterations in shoot density, reproductive... [ABSTRACT FROM AUTHOR]

Ski slope vegetation at Snoqualmie Pass in Washington State, USA, was surveyed in order to identify community types and to compare it with vegetation development patterns in Japan. Ski slopes in Japan, most of which were constructed after 1960, underwent heavy land recontouring, while those at Snoqualmie Pass were constructed before 1950 with less modification. Three points apply to Japanese ski slope vegetation and differentiate these slopes from those at Snoqualmie Pass: (i) grasslands of introduced species are widespread and persistent; (ii) unvegetated patches are uncommon; and (iii) wetland vegetation has developed. These differences are mainly derived from the intensity of human impact, history of the slope and its scale: namely, ski slopes in Washington are older and larger than those in Japan. Ski slope vegetation in Washington was primarily differentiated by a soil moisture gradient. The large size of Washington ski slopes permitted the inclusion and development of wetland habitats, whereas most ski slopes in Japan are constructed on ridges and do not contain wetlands. Most introduced species in Japan are eliminated soon after seeding. In contrast, the long-term management of ski slopes decreased soil erosion and/or unvegetated patches in Washington and created relatively permanent grasslands composed of introduced species. Tsuga heterophylla and Abies amabilis were found established on the ski slopes in Washington, whereas in Japan the pioneer tree species are shade-intolerant broadleaved species. These differences may be a result of the different disturbance histories of ski slopes in the two countries. In addition, along with the conifers, early successional forbs such as Anaphalis margaritacea and Epilobium angustifolium are well established on Washington ski slopes. Results show that disturbances created by ski slope development greatly affect the vegetation, even on older, less heavily impacted ski slopes. [ABSTRACT FROM AUTHOR]

Seed germinability at high temperature (25 °C) was found to differ among golf course populations of Poa annua L. located along a gradient of different intensities of turf irrigation and mowing practices. A seed germination index was calculated to express the effect of temperature on seed germination. The seed germination indices of the less managed populations from the golf roughs were uniformly low and less than 30%, with a mean index of 5%. Conversely, the germination indices of the golf green populations were high. Most seed families of the golf green populations had a germination index higher than 60%. A wide range of seed germination indices was found in seed families of the fairway populations, ranging from 10 to 90% with a mean index of 49%, and with a bimodal distribution. The results of this study indicate that rapid genetic differentiation in temperature-enforced seed dormancy among populations of Poa annua had taken place at the micro-ecological level. [ABSTRACT FROM AUTHOR]

Marks et al. (Ecology Letters, 19, 2016, 743) showed tree species richness correlates with maximum tree height, and interpret this as evidence that the environmental stressors that limit tree height also act as ecological filters on species richness. Here, we strengthen these arguments by further addressing the roles of environmental covariates and beta diversity. [ABSTRACT FROM AUTHOR]