Long‐term change within a Neotropical forest: assessing differential functional and floristic responses to disturbance and drought

Disentangling the relative roles of biotic and abiotic forces influencing forest structure, function, and local community composition continues to be an important goal in ecology. Here, utilizing two forest surveys 20‐year apart from a Central American dry tropical forest, we assess the relative role of past disturbance and local climatic change in the form of increased drought in driving forest dynamics. We observe: (i) a net decrease in the number of trees; (ii) a decrease in total forest biomass by 7.7 Mg ha^?1 but when calculated on subquadrat basis the biomass per unit area did not change indicating scale sensitivity of forest biomass measures; (iii) that the decrease in the number of stems occurred mainly in the smallest sizes, and in more moist and evergreen habitats; (iv) that there has been an increase in the proportion of trees that are deciduous, compound leaved and are canopy species, and a concomitant reduction in trees that are evergreen, simple‐leaved, and understory species. These changes are opposite to predictions based on recovery from disturbance, and have resulted in (v) a uniform multivariate shift from a more mesic to a more xeric forest. Together, our results show that over relatively short time scales, community composition and the functional dominance may be more responsive to climate change than recovery to past disturbances. Our findings point to the importance of assessing proportional changes in forest composition and not just changes in absolute numbers. Our findings are also consistent with the hypothesis that tropical tree species exhibit differential sensitivity to changes in precipitation. Predicted future decreases in rainfall may result in quick differential shifts in forest function, physiognomy, and species composition. Quantifying proportional functional composition offers a basis for a predictive framework for how the structure, and diversity of tropical forests will respond to global change.     

Monoterpene ‘thermometer’ of tropical forest‐atmosphere response to climate warming

Tropical forests absorb large amounts of atmospheric CO₂ through photosynthesis but elevated temperatures suppress this absorption and promote monoterpene emissions. Using ¹³CO₂ labeling, here we show that monoterpene emissions from tropical leaves derive from recent photosynthesis and demonstrate distinct temperature optima for five groups (Groups 1–5), potentially corresponding to different enzymatic temperature‐dependent reaction mechanisms within β‐ocimene synthases. As diurnal and seasonal leaf temperatures increased during the Amazonian 2015 El Niño event, leaf and landscape monoterpene emissions showed strong linear enrichments of β‐ocimenes (+4.4% °C^?1) at the expense of other monoterpene isomers. The observed inverse temperature response of α‐pinene (?0.8% °C^?1), typically assumed to be the dominant monoterpene with moderate reactivity, was not accurately simulated by current global emission models. Given that β‐ocimenes are highly reactive with respect to both atmospheric and biological oxidants, the results suggest that highly reactive β‐ocimenes may play important roles in the thermotolerance of photosynthesis by functioning as effective antioxidants within plants and as efficient atmospheric precursors of secondary organic aerosols. Thus, monoterpene composition may represent a new sensitive ‘thermometer’ of leaf oxidative stress and atmospheric reactivity, and therefore a new tool in future studies of warming impacts on tropical biosphere‐atmosphere carbon‐cycle feedbacks.     

Long‐term variation in the distribution of the White‐bellied Sea‐Eagle (Haliaeetus leucogaster) across Australia

Abstract The White‐bellied Sea‐Eagle Haliaeetus leucogaster (Accipitridae) is widespread within Australia. However, in a number of states it is thought to be declining locally in response to human induced disturbance. Here we analyse the Australian Bird Atlas data to identify the extent and pattern of change in range and density of the species between three Atlas Periods (1901–1976, 1977–1981 and 1998–2001) using a new standardized frequency measure, the Occupancy Index (OI) for 1° blocks (approx. 100 km²) across the continent. At the continental scale, there was no significant difference in the spatial extent of occupancy between Atlas Periods. However, there were considerable changes in frequency and range extent between defined regions, and there were distinct differences in the pattern of change in OI between coastal and inland blocks over time. Coastal blocks showed much more change than inland blocks, with a clear increase in the use of coastal blocks, accompanied by a decrease in inland blocks, during the 1977–1981 Atlas Period, relative to both other Atlas Periods. While there were slight (and not statistically significant) trends for OI to increase in areas containing dams, and to decrease in urbanized coastal areas, the over‐riding factor associated with distributional shifts and frequency changes was apparently climatic fluctuation (the 1977–1981 period showing the influence of El Niño associated drought). Within this study, the impression of abundance was strongly dependent on both the temporal and spatial scale of analysis. This highlights the importance of large‐scale analysis in interpreting change in distribution and abundance of widespread species.     

Seasonal patterns in rainforest litterfall: Detecting endogenous and environmental influences from long‐term sampling

Tropical rainforests play an important role in the storage and cycling of global terrestrial carbon. In the carbon cycle, net primary productivity of forests is linked to soil respiration through the production and decomposition of forest litter. Climate seasonality appears to influence the production of litter although there is considerable variability within and across forests that makes accurate estimates challenging. We explored the effects of climate seasonality on litterfall dynamics in a lowland humid rainforest over a 7‐year period from 2007 to 2013, including an El Niño/La Niña cycle in 2010/2011. Litterfall was sampled fortnightly in 24 traps of 0.50 m diameter within a 1‐ha forest plot. Total mean litterfall was 10.48 ± 1.32 (±SD, dry weight) Mg ha^?1 year^?1 and seasonal in distribution. The different components of litterfall were divided into L_Leaf (63.5%), L_Wood (27.7%) and L_{FF[flowers & fruit]} (8.8%), which all demonstrated seasonal dynamics. Peak falls in L_Leaf and L_Wood were highly predictable, coinciding with maximum daily temperatures and 1 and 2 months prior to maximum monthly rainfall. The El Niño/La Niña cycle coincided with elevated local winter temperatures and peak falls of L_Leaf and L_Wood. Importantly, we establish how sampling length and generalized additive models eliminate the requirement for extensive within‐site sampling when the intention is to describe dynamics in litterfall patterns. Further, a greater understanding of seasonal cycles in litterfall allows us to distinguish between endogenous controls and environmental factors, such as El Niño events, which may have significant impacts on biochemical cycles.     

Climate‐growth analysis for a Mexican dry forest tree shows strong impact of sea surface temperatures and predicts future growth declines

Tropical forests will experience relatively large changes in temperature and rainfall towards the end of this century. Little is known about how tropical trees will respond to these changes. We used tree rings to establish climate‐growth relations of a pioneer tree, Mimosa acantholoba, occurring in tropical dry secondary forests in southern Mexico. The role of large‐scale climatic drivers in determining interannual growth variation was studied by correlating growth to sea surface temperature anomalies (SSTA) of the Atlantic and Pacific Oceans, including the El Niño‐Southern Oscillation (ENSO). Annual growth varied eightfold over 1970–2007, and was correlated with wet season rainfall (r=0.75). Temperature, cloud cover and solar variation did not affect growth, although these climate variables correlated with growth due to their relations with rainfall. Strong positive correlations between growth and SSTA occurred in the North tropical Atlantic during the first half of the year, and in the Pacific during the second half of the year. The Pacific influence corresponded closely to ENSO‐like influences with negative effects of high SSTA in the eastern Pacific Niño3.4 region on growth due to decreases in rainfall. During El Niño years growth was reduced by 37%. We estimated how growth would be affected by the predicted trend of decreasing rainfall in Central America towards the end of this century. Using rainfall predictions of two sets of climate models, we estimated that growth at the end of this century will be reduced by 12% under a medium (A1B) and 21% under a high (A2) emission scenario. These results suggest that climate change may have repercussions for the carbon sequestration capacity of tropical dry forests in the region.     

Resprouting of saplings following a tropical rainforest fire in north‐east Queensland,Australia

Abstract In 2002, fire burnt areas of Mesophyll‐ and Notophyll Vine Forest in the Smithfield Conservation Park near Cairns, Australia. We assessed the ability of rainforest plant species to persist through fire via resprouting. Natural rates of mortality and resprouting in unburnt areas were assessed for all saplings (stems < 2 m) via 13, 2 × 50 m belt transects, and compared to estimates of mortality and resprouting in 26 transects in burnt areas. We also tested the resprouting ability per‐individual stem of each species against all other stems with which it co‐occurred. Totals of 1242 stems (138 species) were sampled in burnt transects and 503 stems (95 species) in unburnt transects (total number of unique species = 169). There was no difference in the number of stems existing prior to the fire in burnt and unburnt areas when expressed on a per‐sample area basis. Resprouting from basal shoots and root suckers was significantly greater in burnt than in unburnt areas, but rates of stem sprouting were not different. In burnt areas 72 species were tested for resprouting ability and most (65/72) resprouted at similar rates. All species analysed contained individuals that resprouted. The resprouting response of five species was significantly lower, and in two species was significantly higher. For these species especially, fire may act as a mechanism altering relative abundances. The fire coincided with an extreme El Niño event. Current predictions indicate El Niño conditions may become increasingly common, suggesting fire events within rainforest could become more frequent. Resprouting as a general phenomenon of rainforest species, and differential resprouting ability between species should therefore be an important consideration in assessing the potential path of vegetation change in rainforests after fire.     

Long‐term variation in Amazon forest dynamics

Questions: Have forest dynamics changed significantly in intact Amazon rainforests since the early 1980s? If so, what environmental drivers might potentially be responsible? Location: Central Amazonia, north of Manaus, Brazil. Methods: Within 20 1‐ha plots scattered over ～300 km², all trees (≥10 cm diameter at breast height) were marked, identified, and measured five times between 1981 and 2003. We estimated stand‐level dynamics (mortality, recruitment, and growth) for each census interval and evaluated weather parameters over the study period. Results: We observed a widespread, significant increase in tree mortality across our plots. Tree recruitment also rose significantly over time but lagged behind mortality. Tree growth generally accelerated but varied considerably among census intervals, and was lowest when mortality was highest. Tree basal area rose 4% overall, but stem number exhibited no clear trend. In terms of climate variation, annual maximum and minimum temperatures increased significantly during our study. Rainfall anomalies were strongly and positively associated with ENSO events. Conclusions: The increasing forest dynamics, growth, and basal area observed are broadly consistent with the CO₂ fertilization hypothesis. However, pronounced shorter‐term variability in stand dynamics might be associated with climatic vicissitudes. Tree mortality peaked, and tree recruitment and growth declined during atypically wet periods. Tree growth was fastest during dry periods, when reduced cloudiness might have increased available solar radiation. Inferences about causality are tenuous because tree data were collected only at multi‐year intervals. Mean temperatures and rainfall seasonality have both increased over time in central Amazonia, and these could potentially have long‐term effects on forest dynamics and carbon storage.     

Birth seasonality and offspring production in threatened neotropical primates related to climate

Given the threatened status of many primate species, the impacts of global warming on primate reproduction and, consequently, population growth should be of concern. We examined relations between climatic variability and birth seasonality, offspring production, and infant sex ratios in two ateline primates, northern muriquis, and woolly monkeys. In both species, the annual birth season was delayed by dry conditions and El Niño years, and delayed birth seasons were linked to lower birth rates. Additionally, increased mean annual temperatures were associated with lower birth rates for northern muriquis. Offspring sex ratios varied with climatic conditions in both species, but in different ways: directly in woolly monkeys and indirectly in northern muriquis. Woolly monkeys displayed an increase in the proportion of males among offspring in association with El Niño events, whereas in northern muriquis, increases in the proportion of males among offspring were associated with delayed onset of the birth season, which itself was related, although weakly, to warm, dry conditions. These results illustrate that global warming, increased drought frequency, and changes in the frequency of El Niño events could limit primate reproductive output, threatening the persistence and recovery of ateline primate populations.     

A boundary current drives synchronous growth of marine fishes across tropical and temperate latitudes

Entrainment of growth patterns of multiple species to single climatic drivers can lower ecosystem resilience and increase the risk of species extinction during stressful climatic events. However, predictions of the effects of climate change on the productivity and dynamics of marine fishes are hampered by a lack of historical data on growth patterns. We use otolith biochronologies to show that the strength of a boundary current, modulated by the El Niño‐Southern Oscillation, accounted for almost half of the shared variance in annual growth patterns of five of six species of tropical and temperate marine fishes across 23° of latitude (3000 km) in Western Australia. Stronger flow during La Niña years drove increased growth of five species, whereas weaker flow during El Niño years reduced growth. Our work is the first to link the growth patterns of multiple fishes with a single oceanographic/climate phenomenon at large spatial scales and across multiple climate zones, habitat types, trophic levels and depth ranges. Extreme La Niña and El Niño events are predicted to occur more frequently in the future and these are likely to have implications for these vulnerable ecosystems, such as a limited capacity of the marine taxa to recover from stressful climatic events.     

Responses of an Australian freshwater turtle to drought‐flood cycles along a natural to urban gradient

Urban areas provide habitat for numerous native species, but life in towns and cities presents many challenges. The effect of climate on the ecology and the behaviour of non‐volant vertebrates inhabiting urban habitats have received little attention. In this study, we investigated demography, growth rates, movements and reproduction of a semi‐aquatic freshwater turtle, Chelodina longicollis, along a natural to urban gradient during a period of relatively high rainfall (2011–2014) and compared this to a previous study in the same system during drought (2006–2007). In addition to changes in rainfall, urbanization increased considerably over the same time period and a pest‐exclusion fence was constructed to mitigate against urban hazards encroaching on the adjacent reserve. Turtles grew at similar rates, had similar abundances and sex ratios and had similar reproductive output across the gradient from urban to non‐urban sites during the wet period. Despite increasing urbanization, recruitment occurred at all sites and survivorship estimates were similar among sites. Turtles moved among wetlands at high rates and over long distances (6 km), underscoring the importance of movements in urban landscapes. Our results contrast with those for the same system during drought, when turtles were less abundant and grew slower in the nature reserve compared with the urban environment. Our results underscore the strong influence climate can have on population dynamics and resilience of species to changes brought about by urbanization. Further monitoring is required to understand the long‐term population responses of long‐lived species to drought cycles.     

Response of wheat growth,grain yield and water use to elevated CO2 under a Free‐Air CO2 Enrichment (FACE) experiment and modelling in a semi‐arid environment

The response of wheat crops to elevated CO₂ (eCO₂) was measured and modelled with the Australian Grains Free‐Air CO₂ Enrichment experiment, located at Horsham, Australia. Treatments included CO₂ by water, N and temperature. The location represents a semi‐arid environment with a seasonal VPD of around 0.5 kPa. Over 3 years, the observed mean biomass at anthesis and grain yield ranged from 4200 to 10 200 kg ha^?1 and 1600 to 3900 kg ha^?1, respectively, over various sowing times and irrigation regimes. The mean observed response to daytime eCO₂ (from 365 to 550 μmol mol^?1 CO₂) was relatively consistent for biomass at stem elongation and at anthesis and LAI at anthesis and grain yield with 21%, 23%, 21% and 26%, respectively. Seasonal water use was decreased from 320 to 301 mm (P = 0.10) by eCO₂, increasing water use efficiency for biomass and yield, 36% and 31%, respectively. The performance of six models (APSIM‐Wheat, APSIM‐Nwheat, CAT‐Wheat, CROPSYST, OLEARY‐CONNOR and SALUS) in simulating crop responses to eCO₂ was similar and within or close to the experimental error for accumulated biomass, yield and water use response, despite some variations in early growth and LAI. The primary mechanism of biomass accumulation via radiation use efficiency (RUE) or transpiration efficiency (TE) was not critical to define the overall response to eCO₂. However, under irrigation, the effect of late sowing on response to eCO₂ to biomass accumulation at DC65 was substantial in the observed data (~40%), but the simulated response was smaller, ranging from 17% to 28%. Simulated response from all six models under no water or nitrogen stress showed similar response to eCO₂ under irrigation, but the differences compared to the dryland treatment were small. Further experimental work on the interactive effects of eCO₂, water and temperature is required to resolve these model discrepancies.     

Implications of CO2 fertilization for future climate change in a coupled climate–carbon model

The terrestrial carbon cycle plays a critical role in determining levels of atmospheric CO₂ that result from anthropogenic carbon emissions. Elevated atmospheric CO₂ is thought to stimulate terrestrial carbon uptake, through the process of CO₂ fertilization of vegetation productivity. This negative carbon cycle feedback results in reduced atmospheric CO₂ growth, and has likely accounted for a substantial portion of the historical terrestrial carbon sink. However, the future strength of CO₂ fertilization in response to continued carbon emissions and atmospheric CO₂ rise is highly uncertain. In this paper, the ramifications of CO₂ fertilization in simulations of future climate change are explored, using an intermediate complexity coupled climate–carbon model. It is shown that the absence of future CO₂ fertilization results in substantially higher future CO₂ levels in the atmosphere, as this removes the dominant contributor to future terrestrial carbon uptake in the model. As a result, climate changes are larger, though the radiative effect of higher CO₂ on surface temperatures in the model is offset by about 30% due to reduced positive dynamic vegetation feedbacks; that is, the removal of CO₂ fertilization results in less vegetation expansion in the model, which would otherwise constitute an important positive surface albedo‐temperature feedback. However, the effect of larger climate changes has other important implications for the carbon cycle – notably to further weaken remaining carbon sinks in the model. As a result, positive climate–carbon cycle feedbacks are larger when CO₂ fertilization is absent. This creates an interesting synergism of terrestrial carbon cycle feedbacks, whereby positive (climate–carbon cycle) feedbacks are amplified when a negative (CO₂ fertilization) feedback is removed.     

CO2 stabilization,climate change and the terrestrial carbon sink

A nonequilibrium, dynamic, global vegetation model, Hybrid v4.1, with a subdaily timestep, was driven by increasing CO₂ and transient climate output from the UK Hadley Centre GCM (HadCM2) with simulated daily and interannual variability. Three IPCC emission scenarios were used: (i) IS92a, giving 790 ppm CO₂ by 2100, (ii) CO₂ stabilization at 750 ppm by 2225, and (iii) CO₂ stabilization at 550 ppm by 2150. Land use and future N deposition were not included. In the IS92a scenario, boreal and tropical lands warmed 4.5 °C by 2100 with rainfall decreased in parts of the tropics, where temperatures increased over 6 °C in some years and vapour pressure deficits (VPD) doubled. Stabilization at 750 ppm CO₂ delayed these changes by about 100 years while stabilization at 550 ppm limited the rise in global land surface temperature to 2.5 °C and lessened the appearance of relatively hot, dry areas in the tropics. Present‐day global predictions were 645 PgC in vegetation, 1190 PgC in soils, a mean carbon residence time of 40 years, NPP 47 PgC y^?1 and NEP (the terrestrial sink) about 1 PgC y^?1, distributed at both high and tropical latitudes. With IS92a emissions, the high latitude sink increased to the year 2100, as forest NPP accelerated and forest vegetation carbon stocks increased. The tropics became a source of CO₂ as forest dieback occurred in relatively hot, dry areas in 2060–2080. High VPDs and temperatures reduced NPP in tropical forests, primarily by reducing stomatal conductance and increasing maintenance respiration. Global NEP peaked at 3–4 PgC y^?1 in 2020–2050 and then decreased abruptly to near zero by 2100 as the tropical source offset the high‐latitude sink. The pattern of change in NEP was similar with CO₂ stabilization at 750 ppm, but was delayed by about 100 years and with a less abrupt collapse in global NEP. CO₂ stabilization at 550 ppm prevented sustained tropical forest dieback and enabled recovery to occur in favourable years, while maintaining a similar time course of global NEP as occurred with 750 ppm stabilization. By lessening dieback, stabilization increased the fraction of carbon emissions taken up by the land. Comparable studies and other evidence are discussed: climate‐induced tropical forest dieback is considered a plausible risk of following an unmitigated emissions scenario.     

Geographic variation in growth response of Douglas‐fir to interannual climate variability and projected climate change

We used 179 tree ring chronologies of Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] from the International Tree‐Ring Data Bank to study radial growth response to historical climate variability. For the coastal variety of Douglas‐fir, we found positive correlations of ring width with summer precipitation and temperature of the preceding winter, indicating that growth of coastal populations was limited by summer dryness and that photosynthesis in winter contributed to growth. For the interior variety, low precipitation and high growing season temperatures limited growth. Based on these relationships, we chose a simple heat moisture index (growing season temperature divided by precipitation of the preceding winter and current growing season) to predict growth response for the interior variety. For 105 tree ring chronologies or 81% of the interior samples, we found significant linear correlations with this heat moisture index, and moving correlation functions showed that the response was stable over time (1901–1980). We proceeded to use those relationships to predict regional growth response under 18 climate change scenarios for the 2020s, 2050s, and 2080s with unexpected results: for comparable changes in heat moisture index, the most southern and outlying populations of Douglas‐fir in Mexico showed the least reduction in productivity. Moderate growth reductions were found in the southern United States, and strongly negative response in the central Rocky Mountains. Growth reductions were further more pronounced for high than for low elevation populations. Based on regional differences in the slope of the growth–climate relationship, we propose that southern populations are better adapted to drought conditions and could therefore contain valuable genotypes for reforestation under climate change. The results support the view that climate change may impact species not just at the trailing edges but throughout their range due to genetic adaptation of populations to local environments.     

Long‐term exposure to elevated CO2 and O3 alters aspen foliar chemistry across developmental stages

Anthropogenic activities are altering levels of greenhouse gases to the extent that multiple and diverse ecosystem processes are being affected. Two gases that substantially influence forest health are atmospheric carbon dioxide (CO₂) and tropospheric ozone (O₃). Plant chemistry will play an important role in regulating ecosystem processes in future environments, but little information exists about the longitudinal effects of elevated CO₂ and O₃ on phytochemistry, especially for long‐lived species such as trees. To address this need, we analysed foliar chemical data from two genotypes of trembling aspen, Populus tremuloides, collected over 10 years of exposure to levels of CO₂ and O₃ predicted for the year 2050. Elevated CO₂ and O₃ altered both primary and secondary chemistry, and the magnitude and direction of the responses varied across developmental stages and between aspen genotypes. Our findings suggest that the effects of CO₂ and O₃ on phytochemical traits that influence forest processes will vary over tree developmental stages, highlighting the need to continue long‐term, experimental atmospheric change research.     

Regional and local determinants of drought resilience in tropical forests

The increase in severity of droughts associated with greater mortality and reduced vegetation growth is one of the main threats to tropical forests. Drought resilience of tropical forests is affected by multiple biotic and abiotic factors varying at different scales. Identifying those factors can help understanding the resilience to ongoing and future climate change. Altitude leads to high climate variation and to different forest formations, principally moist or dry tropical forests with contrasted vegetation structure. Each tropical forest can show distinct responses to droughts. Locally, topography is also a key factor controlling biotic and abiotic factors related to drought resilience in each forest type. Here, we show that topography has key roles controlling biotic and abiotic factors in each forest type. The most important abiotic factors are soil nutrients, water availability, and microclimate. The most important biotic factors are leaf economic and hydraulic plant traits, and vegetation structure. Both dry tropical forests and ridges (steeper and drier habitats) are more sensitive to droughts than moist tropical forest and valleys (flatter and wetter habitats). The higher mortality in ridges suggests that conservative traits are not sufficient to protect plants from drought in drier steeper habitats. Our synthesis highlights that altitude and topography gradients are essential to understand mechanisms of tropical forest''s resilience to future drought events. We described important factors related to drought resilience, however, many important knowledge gaps remain. Filling those gaps will help improve future practices and studies about mitigation capacity, conservation, and restoration of tropical ecosystems.     

El Niño events,the lean versus fat scenario,and long‐term guild dynamics of vertebrate predators in a South American semiarid ecosystem

Abstract Predator assemblages are complex systems in which asynchrony in the dynamics of resources and consumers, and the idiosyncratic perception of environmental conditions by the predators may obscure the detection of expected patterns. We disentangle the specific effects of these variables on the guild structure of a vertebrate predatory assemblage in a semiarid ecosystem of western South America. Over 16 years, this system faced dramatic fluctuations in prey availability associated with four El Niño events. After controlling for other sources of variation, we tested if increased resource availability is associated with higher niche overlaps, as expected from the lean/fat scenario. We determined the existence of two trophic guilds of predators (specialized mammal‐eaters and omnivorous species with emphasis on arthropods) and found that they responded to increased productivity both at the guild and whole assemblage levels. However, the population response of arthropod prey (almost simultaneous) and of different small mammal prey (delayed by 1 or 2 years) to productivity imposed a degree of asynchrony in prey availability and in the response of predators. This resulted in the between‐guilds exchange of predator species depending on mammal prey scarcity or abundance. As a consequence, the observed pattern was an apparent lack of response at the assemblage level. Despite differences in the perception of prey levels by predators, we conclude that each one of them responded accordingly to theoretical predictions following a simple rule: if prey resources are not limiting, predators behave opportunistically converging over the most abundant resources, thus increasing niche overlap; if prey shortages occur, predators specialize on those prey resources that they gather most efficiently, thus lowering niche overlap; if resources become even scarcer, all predators converge again upon the few prey resources still available, thus increasing overlap – out of necessity.     

Increase in CO2 concentration could alter the response of Hedera helix to climate change

Increasing CO₂ concentration ([CO₂]) is likely to affect future species distributions, in interaction with other climate change drivers. However, current modeling approaches still seldom consider interactions between climatic factors and the importance of these interactions therefore remains mostly unexplored. Here, we combined dendrochronological and modeling approaches to study the interactive effects of increasing [CO₂] and temperature on the distribution of one of the main European liana species, Hedera helix. We combined a classical continent‐wide species distribution modeling approach with a case study using H. helix and Quercus cerris tree rings, where we explored the long‐term influence of a variety of climate drivers, including increasing [CO₂], and their interactions, on secondary growth. Finally, we explored how our findings could influence the model predictions. Climate‐only model predictions showed a small decrease in habitat suitability for H. helix in Europe; however, this was accompanied by a strong shift in the distribution toward the north and east. Our growth ring data suggested that H. helix can benefit from high [CO₂] under warm conditions, more than its tree hosts, which showed a weaker response to [CO₂] coupled with higher cavitation risk under high temperature. Increasing [CO₂] might therefore offset the negative effects of high temperatures on H. helix, and we illustrate how this might translate into maintenance of H. helix in warmer areas. Our results highlight the need to consider carbon fertilization and interactions between climate variables in ecological modeling. Combining dendrochronological analyses with spatial distribution modeling may provide opportunities to refine predictions of how climate change will affect species distributions.     

Historical changes in the distributions of invasive and endemic marine invertebrates are contrary to global warming predictions: the effects of decadal climate oscillations

Aim We tested whether a hybrid zone that has formed between an endemic and an invasive species of marine mussel has shifted poleward as expected under a general hypothesis of global warming or has responded instead to decadal climate oscillations. Location We sampled 15 locations on the coast of California, USA, that span the distributions of the two species of marine mussels and their hybrids. Methods Mussels were sampled in 2005–08 and analysed at three nuclear gene loci using methods identical to those used in a study a decade earlier in order to document the genetic architecture of this system. Change in the system was determined by comparing the frequency of species‐specific alleles and multi‐locus genotypes over the intervening decade. Climate variation over the same period was examined by comparing the Pacific Decadal Oscillation (PDO), El Niño/Southern Oscillation (ENSO), upwelling indices and sea surface temperature (SST) during and prior to the study period. Results Contrary to the general expectations of global warming we show that the highly invasive warm‐water mussel Mytilus galloprovincialis and the hybrid zone formed with the endemic species Mytilus trossulus has rapidly contracted southwards. Mytilus galloprovincialis declined in abundance over the northern third of its geographic range (c. 540 km) and has become rare or absent across the northern 200 km of the range it previously colonized during its initial invasion. The distribution of the native species M. trossulus has remained unchanged over the same time period. Main conclusions The large‐scale range shift in the warm‐water invasive species M. galloprovincialis and the hybrid zone it forms with M. trossulus has been exceptionally rapid and is in the opposite direction to that predicted by the global warming hypotheses. This shift, however, is consistent with decadal climate variation associated with the ENSO and the PDO. Since the biogeography of this system was first described in 1999, the PDO has shifted from a warm phase, dominated by frequent and large El Niño events, to a cold‐phase period, with minimal ENSO activity. Thus recent decadal climate variation can oppose global trends in average temperature and this study illustrates the need to integrate the effects of climate change across multiple time‐scales.     

Long‐term forest resilience to climate change indicated by mortality,regeneration, and growth in semiarid southern Siberia

Several studies have documented that regional climate warming and the resulting increase in drought stress have triggered increased tree mortality in semiarid forests with unavoidable impacts on regional and global carbon sequestration. Although climate warming is projected to continue into the future, studies examining long‐term resilience of semiarid forests against climate change are limited. In this study, long‐term forest resilience was defined as the capacity of forest recruitment to compensate for losses from mortality. We observed an obvious change in long‐term forest resilience along a local aridity gradient by reconstructing tree growth trend and disturbance history and investigating postdisturbance regeneration in semiarid forests in southern Siberia. In our study, with increased severity of local aridity, forests became vulnerable to drought stress, and regeneration first accelerated and then ceased. Radial growth of trees during 1900–2012 was also relatively stable on the moderately arid site. Furthermore, we found that smaller forest patches always have relatively weaker resilience under the same climatic conditions. Our results imply a relatively higher resilience in arid timberline forest patches than in continuous forests; however, further climate warming and increased drought could possibly cause the disappearance of small forest patches around the arid tree line. This study sheds light on climate change adaptation and provides insight into managing vulnerable semiarid forests.