Vegetation Turnover Research Articles

Species turnover differentiates diversity–disturbance relationships between aboveground vegetation and soil seedbank

An understanding of relationships between species diversity and disturbance gradient is important to comprehend the role of disturbances in the structure of plant communities. Although some studies have demonstrated incongruence in diversity–disturbance relationships (hereafter DDRs) between aboveground vegetation and soil seedbank, the process that causes the difference remains unclear. This incongruence between the two DDRs could result in the decrease in the source of recovery of aboveground vegetation following disturbances being overlooked when only aboveground vegetation is surveyed. Here, we verified a process that species turnover across the disturbance gradient causes the incongruence. Based on a vegetation and seedbank survey, we examined DDRs and species turnover of aboveground vegetation and seedbank along disturbance duration (i.e., excluding years of ungulate grazing). The degree of species turnover was considerably greater in aboveground vegetation than in seedbank; thus, the degree of species turnover along a disturbance gradient caused the difference in DDR between aboveground vegetation and seedbank.

Interaction between climate and management on beta diversity components of vegetation in relation to soil properties in arid and semi-arid oak forests, Iran

This study aimed to investigate the interaction between regions with different climatic conditions (arid vs. semi-arid) and management (protected vs. unprotected) on the turnover and nestedness of vegetation in relation to physical, chemical and biological properties of soils in the Ilam Province of Iran. In each of the two regions, we sampled 8 sites (4 managed and 4 unmanaged sites) within each of which we established 4 circular plots (1000 m2) that were used to investigate woody species, while two micro-plots (1 m×1 m) were established in each 1000-m2 plot to analyze herbaceous species. In each sample unit, we also extracted three soil samples (0–20 cm depth) for measuring soil properties. The results indicated that the interaction between region and conservational management significantly affected the percent of canopy cover of Persian oak (Quercus brantii Linddl), soil respiration, substrate-induced respiration, as well as beta and gamma diversities and turnover of plant species. The percent of oak canopy cover was positively correlated with soil silt, electrical conductivity, available potassium, and alpha diversity, whereas it was negatively correlated with plant turnover. In addition, plant turnover was positively related to available phosphorus, while nestedness of species was positively related to organic carbon and total nitrogen. According to these results, we concluded that physical, chemical, and biological characteristics of limited ecological niche generally influenced plant diversity. Also, this study demonstrated the major contribution of the beta diversity on gamma diversity, especially in semi-arid region, because of the higher heterogeneity of vegetation in this area.

Dynamics of understorey biomass, production and turnover associated with long-term overstorey succession in boreal forest of Canada

Understorey vegetation hosts the most species diversity in temperate and boreal forests and contributes substantially to ecosystem functions. Despite its ecological importance, the dynamics of understorey biomass, production and turnover rates following stand-replacing disturbance and throughout forest succession remain poorly understood. Using a replicated chronosequence spanning 8, 16, 34, 98, 146 and 210 years following fire, we examined the dynamics of understorey biomass, production and turnover associated with stand development and overstorey types (broadleaf, mixedwood, and conifer) in the central boreal forest of Canada. Across all ages and overstorey types, biomass, production and turnover rates of woody plants, herbs, and bryophytes were on average 2.71, 0.10, and 0.13 Mg ha−1; 0.24, 0.13, and 0.08 Mg ha−1 year−1 and 9.7%, 127.3%, and 67.6% year−1, respectively. Total understorey biomass and production increased continuously with stand age and reached the maximum in 146-year-old stands. Herbaceous biomass and production, peaked in 16-year-old stands, and remained stable thereafter with a slight increase in 146-year-old stands; in contrast, woody plant and bryophyte biomass and production peaked in 98- and 146-year-old stands. Herbaceous and woody vegetation turnover rates were higher in young stands, and those of bryophytes were higher in older stands. Total, woody and herbaceous biomass, production and turnover rates were higher under deciduous broadleaf overstorey, while values for bryophytes were higher in conifer stands, with mixedwood being intermediate. Overstorey mixture had no overall effect on total, woody, herbaceous biomass and production other than the expected from the averages of their broadleaf and conifer stands, but reduced bryophyte biomass and woody turnover. Our findings suggest that understorey biomass, production and turnover rates in the boreal forest are mainly driven by time since colonization and the resource availability and heterogeneity mediated via overstorey composition. Our results highlight the roles of stand development and overstorey composition in understorey biomass, production and turnover and their importance for modeling total forest ecosystem contribution to the global forest carbon.

Variation in the diversity and richness of parasitoid wasps based on sampling effort.

Parasitoid wasps are a mega-diverse, ecologically dominant, but poorly studied component of global biodiversity. In order to maximise the efficiency and reduce the cost of their collection, the application of optimal sampling techniques is necessary. Two sites in Auckland, New Zealand were sampled intensively to determine the relationship between sampling effort and observed species richness of parasitoid wasps from the family Ichneumonidae. Twenty traps were deployed at each site at three different times over the austral summer period, resulting in a total sampling effort of 840 Malaise-trap-days. Rarefaction techniques and non-parametric estimators were used to predict species richness and to evaluate the variation and completeness of sampling. Despite an intensive Malaise-trapping regime over the summer period, no asymptote of species richness was reached. At best, sampling captured two-thirds of parasitoid wasp species present. The estimated total number of species present depended on the month of sampling and the statistical estimator used. Consequently, the use of fewer traps would have caught only a small proportion of all species (one trap 7–21%; two traps 13–32%), and many traps contributed little to the overall number of individuals caught. However, variation in the catch of individual Malaise traps was not explained by seasonal turnover of species, vegetation or environmental conditions surrounding the trap, or distance of traps to one another. Overall the results demonstrate that even with an intense sampling effort the community is incompletely sampled. The use of only a few traps and/or for very short periods severely limits the estimates of richness because (i) fewer individuals are caught leading to a greater number of singletons; and (ii) the considerable variation of individual traps means some traps will contribute few or no individuals. Understanding how sampling effort affects the richness and diversity of parasitoid wasps is a useful foundation for future studies.

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Late-Quaternary spatiotemporal dynamics of vegetation in Central Mexico

Central Mexico exhibits a complex environment with wide topographic, climatic, and biological gradients. Lacustrine basins distributed along the region have been the source for numerous paleoenvironmental reconstructions, representing an exceptional opportunity for studying vegetation turnover dynamics across time and space. A total of 1397 fossil and modern pollen samples were ordinated through a Detrended Correspondence Analysis (DCA) to characterize the regional ecological space. Resulting DCA Axis 1 scores were related to a forest cover gradient. Aiming to generalize the interpretation of the analyzed records and given the clear altitudinal pattern shown by modern samples, paleoenvironmental interpretations were performed grouping fossil records according to their elevation. Euclidean distances among sites scores were used as estimators of ecological distance and summarized from two different approaches to observe turnover dynamics at different spatial scales: i) local turnover through time, and ii) ecological versus geographic distance. The regional late Quaternary vegetation dynamics were found mostly driven by global climatic events, whereas the Holocene was marked by more local factors such as precipitation regime and human occupation patterns. Strong local modulation in turnover dynamics was observed in the region. Additionally, we conclude that a palynological record produces results that are repeatable within 50km, considering a maximum compositional turnover of 50%.

Estimates of grassland biomass and turnover time on the Tibetan Plateau

The grassland of the Tibetan Plateau forms a globally significant biome, which represents 6% of the world’s grasslands and 44% of China’s grasslands. However, large uncertainties remain concerning the vegetation carbon storage and turnover time in this biome. In this study, we quantified the pool size of both the aboveground and belowground biomass and turnover time of belowground biomass across the Tibetan Plateau by combining systematic measurements taken from a substantial number of surveys (i.e. 1689 sites for aboveground biomass, 174 sites for belowground biomass) with a machine learning technique (i.e. random forest, RF). Our study demonstrated that the RF model is effective tool for upscaling local biomass observations to the regional scale, and for producing continuous biomass estimates of the Tibetan Plateau. On average, the models estimated 46.57 Tg (1 Tg = 1012g) C of aboveground biomass and 363.71 Tg C of belowground biomass in the Tibetan grasslands covering an area of 1.32 × 106 km2. The turnover time of belowground biomass demonstrated large spatial heterogeneity, with a median turnover time of 4.25 years. Our results also demonstrated large differences in the biomass simulations among the major ecosystem models used for the Tibetan Plateau, largely because of inadequate model parameterization and validation. This study provides a spatially continuous measure of vegetation carbon storage and turnover time, and provides useful information for advancing ecosystem models and improving their performance.

Influence of flood regime on riparian vegetation dynamics in rivers with alternate bars

Throughout the 20th century, many rivers worldwide have undergone important riparian vegetation encroachment, which can be problematic in terms of flood risks and biodiversity. Nowadays, controlled floods is often considered as a management option in anthropized rivers, with the aim of limiting vegetation encroachment within river channels, as well as maintaining a diverse habitat by reactivating natural channel dynamics. In this context, this study aims at investigating the influence of different flood regimes on river bar vegetation development and dynamics, focussing on alternate bar systems which are typically found in embanked streams. This question has been addressed through two-dimensional bio-morphodynamic modeling of a simplified gravel bed river reach. Four hydrological scenarios with different flood peak discharges have been run for 50 years. For all scenarios, a steady increase in vegetation cover strongly impacts the evolution of bar morphology, until a relatively stable equilibrium is reached after one to three decades. Numerical results suggest that vegetation development on bars is associated to an increase in bar wavelength and a decrease in bar width. Higher peak flood discharges lead to narrower and longer bars, and a longer adjustment duration. When vegetation cover is fully developed, interannual flood variability seems crucial to maintain bedform and vegetation turnover.

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

Riparian zones are formed by interactions between fluvio-geomorphological processes, such as sediment deposition, and biota, such as vegetation. Establishment of invasive alien plant (IAP) species along rivers may influence vegetation dynamics, evidenced as higher seasonal or inter-annual fluctuations in native plant diversity when IAP cover is high. This could impact the overall functioning of riparian ecosystems. Conversely, fine sediment deposited in riparian zones after floods may replenish propagule banks, thus supporting recruitment of native species. The interactive effects of invasion and fine sediment deposition have hitherto, however, been ignored. Vegetation surveys across rivers varying in flow regime were carried out over 2 years to assess changes in community composition and diversity. Artificial turf mats were used to quantify over-winter sediment deposition. The viable propagule bank in soil and freshly deposited sediment was then quantified by germination trials. Structural Equation Models were used to assess causal pathways between environmental variables, IAPs and native vegetation. Greater variation in flow increased the cover of IAPs along riverbanks. An increased in high flow events and sediment deposition were positively associated with the diversity of propagules deposited. However, greater diversity of propagules did not result in a more diverse plant community at invaded sites, as greater cover of IAPs in summer reduced native plant diversity. Seasonal turnover in the above-ground vegetation was also accentuated at previously invaded sites, suggesting that a legacy of increased competition in previous years, not recent sediment deposition, drives above-ground vegetation structure at invaded sites. The interaction between fluvial disturbance via sediment deposition and invasion pressure is of growing importance in the management of riparian habitats. Our results suggest that invasion can uncouple the processes that contribute to resilience in dynamic habitats making already invaded habitats vulnerable to further invasions.

Urban riparian systems function as corridors for both native and invasive plant species

Riparian areas are often the only green areas left in urban and suburban landscapes, providing opportunities for conservation and connectivity of both aquatic and terrestrial organisms. While city planners and land managers often tout the importance of riparian networks for these uses, it is not well established if urban riparian plant communities are actually functioning as connected assemblages. Furthermore, urban riparian zones are well known to be highly invaded by non-native plant species and may be functioning to increase the spread of non-native species across the landscape. Here we examine connectivity of plant assemblages in riparian networks within an extensively urbanized landscape. We sampled riparian plant communities at 13 sites along three second-order streams of the Rahway River watershed, New Jersey. We also characterized propagule dispersal at each site by sampling litter packs on the river banks five times between March–October 2011 and identifying germinants from litter packs after cold stratification. Species turnover of both riparian and litter vegetation was more strongly associated with flow distance, particularly for native species, indicating that riverine systems are important for promoting connectivity of native plant assemblages in urban landscapes. However, non-native germinants significantly dominated propagule dispersal along the stream reaches, particularly early in the growing season, suggesting spread utilizing the river system and preemption may be an important mechanism for invasion success in this system. Our data show that management of invasive species should be planned and implemented at the watershed scale to reduce spread via the river system.

Response of spatial vegetation distribution in China to climate changes since the Last Glacial Maximum (LGM).

Analyzing how climate change affects vegetation distribution is one of the central issues of global change ecology as this has important implications for the carbon budget of terrestrial vegetation. Mapping vegetation distribution under historical climate scenarios is essential for understanding the response of vegetation distribution to future climatic changes. The reconstructions of palaeovegetation based on pollen data provide a useful method to understand the relationship between climate and vegetation distribution. However, this method is limited in time and space. Here, using species distribution model (SDM) approaches, we explored the climatic determinants of contemporary vegetation distribution and reconstructed the distribution of Chinese vegetation during the Last Glacial Maximum (LGM, 18,000 14C yr BP) and Middle-Holocene (MH, 6000 14C yr BP). The dynamics of vegetation distribution since the LGM reconstructed by SDMs were largely consistent with those based on pollen data, suggesting that the SDM approach is a useful tool for studying historical vegetation dynamics and its response to climate change across time and space. Comparison between the modeled contemporary potential natural vegetation distribution and the observed contemporary distribution suggests that temperate deciduous forests, subtropical evergreen broadleaf forests, temperate deciduous shrublands and temperate steppe have low range fillings and are strongly influenced by human activities. In general, the Tibetan Plateau, North and Northeast China, and the areas near the 30°N in Central and Southeast China appeared to have experienced the highest turnover in vegetation due to climate change from the LGM to the present.

Vegetation assemblages of central Mexico through the late Quaternary: modern analogs and compositional turnover

AbstractQuestionWhen did vegetation assemblages that occupy modern central Mexico appear within the context of the late Quaternary?LocationCentral Mexico.MethodsWe used modern and fossil pollen data sets from central Mexico to explore the evolution of regional vegetation through the late Quaternary. A total of 1397 samples (1357 fossil samples distributed in 17 records and 40 modern samples) were analysed through detrended correspondence analysis to evaluate the degree of analogy between modern and past vegetation assemblages, and regional vegetation compositional turnover through time.ResultsThere was a high degree of analogy between modern and glacial vegetation, whereas the early and mid‐Holocene were characterized by a high frequency of no‐modern‐analogue pollen assemblages. Vegetation turnover during the glacial time was characterized by both pulses of abrupt change and episodes of stability. In contrast, vegetation turnover was high through most of the Holocene. Both vegetation turnover and past vegetation analogy to modern were not synchronous in altitudinal zones, except for the past 2000 yrs, when pollen assemblages suggest a high vegetation analogy to modern‐day throughout the region.ConclusionsHuman impacts on central Mexico regional vegetation were consistently evident during the last 2000 yrs, suggesting that biodiversity expressed in the modern vegetation assemblages incorporates a high anthropogenic imprint. High resemblance of glacial and modern landscapes suggests that the effect of human occupation on the landscape is similar to that exerted by glacial time environmental stress. However, loss of ecosystem connectivity under the modern pattern of landscape homogenization represents an unprecedented threat for regional biodiversity.

Biomass turnover time in terrestrial ecosystems halved by land use

Biomass turnover time is a key parameter in the global carbon cycle. An analysis of global land-use data reveals that biomass turnover is almost twice as fast when the land is used to enhance terrestrial ecosystem services. The terrestrial carbon cycle is not well quantified1. Biomass turnover time is a crucial parameter in the global carbon cycle2,3,4, and contributes to the feedback between the terrestrial carbon cycle and climate2,3,4,5,6,7. Biomass turnover time varies substantially in time and space, but its determinants are not well known8,9, making predictions of future global carbon cycle dynamics uncertain5,10,11,12,13. Land use—the sum of activities that aim at enhancing terrestrial ecosystem services14—alters plant growth15 and reduces biomass stocks16, and is hence expected to affect biomass turnover. Here we explore land-use-induced alterations of biomass turnover at the global scale by comparing the biomass turnover of the actual vegetation with that of a hypothetical vegetation state with no land use under current climate conditions. We find that, in the global average, biomass turnover is 1.9 times faster with land use. This acceleration affects all biomes roughly equally, but with large differences between land-use types. Land conversion, for example from forests to agricultural fields, is responsible for 59% of the acceleration; the use of forests and natural grazing land accounts for 26% and 15% respectively. Reductions in biomass stocks are partly compensated by reductions in net primary productivity. We conclude that land use significantly and systematically affects the fundamental trade-off between carbon turnover and carbon stocks.

Pliocene reversal of late Neogene aridification

The Pliocene epoch (5.3-2.6 Ma) represents the most recent geological interval in which global temperatures were several degrees warmer than today and is therefore considered our best analog for a future anthropogenic greenhouse world. However, our understanding of Pliocene climates is limited by poor age control on existing terrestrial climate archives, especially in the Southern Hemisphere, and by persistent disagreement between paleo-data and models concerning the magnitude of regional warming and/or wetting that occurred in response to increased greenhouse forcing. To address these problems, here we document the evolution of Southern Hemisphere hydroclimate from the latest Miocene to the middle Pliocene using radiometrically-dated fossil pollen records preserved in speleothems from semiarid southern Australia. These data reveal an abrupt onset of warm and wet climates early within the Pliocene, driving complete biome turnover. Pliocene warmth thus clearly represents a discrete interval which reversed a long-term trend of late Neogene cooling and aridification, rather than being simply the most recent period of greater-than-modern warmth within a continuously cooling trajectory. These findings demonstrate the importance of high-resolution chronologies to accompany paleoclimate data and also highlight the question of what initiated the sustained interval of Pliocene warmth.

Species turnover of wetland vegetation in northeastern China: Disentangling the relative effects of geographic distance, climate, and hydro-geomorphology

Species turnover is a central issue in plant ecology and has a high significance in conservation of biodiversity and ecosystem management. Niche differentiation and dispersal limitation are the two main processes controlling species turnover of upland vegetation. However, our understanding of the drivers of plant species turnover in wetlands remains poor. To comprehensively disentangle the influences of niche differentiation and dispersal limitation on the plant species turnover in wetlands of the Great Hing’an Mountain valleys, we not only considered two plant functional groups (herbs and shrubs), but also took hydro-geomorphological variables into account when quantifying the effect of environmental differences on species turnover. We found that species similarity, measured by the Jaccard similarity index, decreased with geographic distance for both herbs and shrubs with a decay rate being −0.39 and −0.49, respectively. We then partitioned the variance of species similarity based on type III sums of squares in partial correlations. Results showed that geographic distance and the joint effect were the most important factor explaining the species turnover of herbs and shrubs respectively when representing environmental constraints with climatic variables only. The total explained variances were improved by 15.93% for herbs and 24.69% for shrubs after including hydro-geomorphologic measurements. Our study showed that both dispersal limitation (represented by geographic distance effects) and niche differentiation (represented by climate and hydro-geomorphology) played important roles in shaping wetland species turnover, but their relative effects differed by plant functional groups. Considering hydro-geomorphological characteristics can better elucidate the role of the environment in shaping species turnover in wetland systems than using climatic variables alone.

Ground ice melt in the high Arctic leads to greater ecological heterogeneity

Summary The polar desert biome of the Canadian high Arctic Archipelago is currently experiencing some of the greatest mean annual air temperature increases on the planet, threatening the stability of ecosystems residing above temperature‐sensitive permafrost. Ice wedges are the most widespread form of ground ice, occurring in up to 25% of the world's terrestrial near‐surface, and their melting (thermokarst) may catalyse a suite of biotic and ecological changes, facilitating major ecosystem shifts. These unknown ecosystem shifts raise serious questions as to how permafrost stability, vegetation diversity and edaphic conditions will change with a warming high Arctic. Ecosystem and thermokarst processes tend to be examined independently, limiting our understanding of a coupled system whereby the effect of climate change on one will affect the outcome of the other. Using in‐depth, comprehensive field observations and a space‐for‐time approach, we investigate the highly structured landscape that has emerged due to the thermokarst‐induced partitioning of microhabitats. We examine differences in vegetation diversity, community composition and soil conditions on the Fosheim Peninsula, Ellesmere Island, Nunavut. We hypothesize that (i) greater ice wedge subsidence results in increased vegetation cover due to elevated soil moisture, thereby decreasing the seasonal depth of thaw and restricting groundwater outflow; (ii) thermokarst processes result in altered vegetation richness, turnover and dispersion, with greater microhabitat diversity at the landscape scale; and (iii) shifts in hydrology and plant community structure alter soil chemistry. We found that the disturbance caused by melting ice wedges catalysed a suite of environmental and biotic effects: topographical changes, a new hydrological balance, significant species richness and turnover changes, and distinct soil chemistries. Thermokarst areas favour a subset of species unique from the polar desert and are characterized by greater species turnover (β‐diversity) across the landscape. Synthesis. Our findings suggest that projected increases of thermokarst in the polar desert will lead to the increased partitioning of microhabitats, creating a more heterogeneous high arctic landscape through diverging vegetation communities and edaphic conditions, resulting in a wetland‐like biome in the high Arctic that could replace much of the ice‐rich polar desert.

Late Quaternary climatic and environmental conditions of northern Spain: An isotopic approach based on the mammalian record from La Paloma cave

La Paloma cave (Asturias, northern Spain) stands out as one of the most notable prehistoric sites of the northern Iberian sector due to the richness of its archaeo-paleontological material, spanning a complete Magdalenian–Azilian sequence (~20,300–12,900calyears BP). The abundance, diversity and good preservation of mammalian remains make of La Paloma site an excellent location to characterize paleoclimatic, paleoecological and paleoenvironmental conditions from a biogeochemical standpoint. Stable isotope analyses performed on tooth enamel (δ13Cen, δ18OCO3, δ18OPO4) and bone collagen (δ13Ccoll, δ15N) of a suite of herbivore, carnivore and omnivore species did not yield significant variations across the stratigraphic sequence, likely pointing to prevalent and stable local conditions, with i) no major vegetation turnover, ii) maintenance of hydrological conditions, and iii) relatively constant soil activity, in spite of the synchrony of the La Paloma temporal context with global events, such as the end of the Last Glacial Maximum, the Heinrich Event 1 and the Bølling–Allerød oscillation. La Paloma δ13Cen and δ13Ccoll values are within the expected range for C3 mixed woodland–mesic C3 grassland conditions. Overall, bovids (large Bovidae, ibex and chamois) show higher δ13Cen, δ13Ccoll and δ15N values than cervids (red deer and roe deer), indicating a preference for more open environments in the former. Horse δ13C values are undistinguishable from those of red deer and point to a mixed-feeding behavior. Horse low δ15N values may be indicative of a diet with a low protein content. Bayesian mixing model results yielded differences in carnivore resource use, with wolf preying on all ungulates and red fox preferentially incorporating roe deer. Stable paleoenviromental conditions during the latest Pleistocene at the La Paloma area may have favored the persistence of a stable mammalian community structure, supporting the idea of the existence of refuge areas in the northern Iberian sector throughout the late Quaternary glacial–interglacial dynamics.

Vegetation stability and the habitat associations of the endemic taxa of the Olympic Peninsula, Washington, USA

Explanations for areas of endemism often involve relative climatic stability, or low climate ve- locity, over time scales ranging from the Pleistocene to the late Cenozoic. Given that many narrowly en- demic taxa in forested landscapes display discrete habitat associations, habitat stability should be simi- larly important for endemic persistence. Furthermore, while past climate variability is exceedingly diffi- cult to quantify on millennial time scales, past distributions of habitats may be robustly inferred from paleoecological records. The Olympic Peninsula, Washington, supports a biota with several insular fea- tures including 29 endemic plant and animal taxa. Here I present the geographic distribution and habitat of the endemic taxa, and then examine the vegetation stability of the past 14,300 years from five pollen records associated with discrete vegetation zones on the peninsula. I show that 11 endemics have distri- butions centered on dry alpine scree and rock in the northeastern quadrant of the peninsula, and nine occur in shaded riparian forests in the southwest. Vegetation turnover during the post -glacial period was smallest in these areas. However, another long pollen record from the western peninsula reveals existence of shrub tundra and greatly reduced forest cover, indicating southward displacement of shad- ed riparian habitats by perhaps as much as 100 km. Although this study supports an association of post - glacial vegetation stability with endemism, records spanning the glacial maximum indicate widespread tundra during long periods of the late Pleistocene and therefore suggest southern displacement of for- est-associated endemics. While some of the alpine scree-associated endemics may have persisted in situ, many others likely arrived via a variety of dispersal trajectories. These histories include dispersal from southern refugia towards ocean barriers preventing further northward dispersal, contraction from more widespread distributions, and recent divergence from sister taxa. This study shows that paleoeco- logical records can cast strong doubt on the inference that areas of endemism necessarily imply in situ glacial survival.

Vegetation stability and the habitat associations of the endemic taxa of the Olympic Peninsula, Washington, USA

Explanations for areas of endemism often involve relative climatic stability, or low climate velocity, over time scales ranging from the Pleistocene to the late Cenozoic. Given that many narrowly endemic taxa in forested landscapes display discrete habitat associations, habitat stability should be similarly important for endemic persistence. Furthermore, while past climate variability is exceedingly difficult to quantify on millennial time scales, past distributions of habitats may be robustly inferred from paleoecological records. The Olympic Peninsula, Washington, supports a biota with several insular features including 29 endemic plant and animal taxa. Here I present the geographic distribution and habitat of the endemic taxa, and then examine the vegetation stability of the past 14,300 years from five pollen records associated with discrete vegetation zones on the peninsula. I show that 11 endemics have distributions centered on dry alpine scree and rock in the northeastern quadrant of the peninsula, and nine occur in shaded riparian forests in the southwest. Vegetation turnover during the post-glacial period was smallest in these areas. However, another long pollen record from the western peninsula reveals existence of shrub tundra and greatly reduced forest cover, indicating southward displacement of shaded riparian habitats by perhaps as much as 100 km. Although this study supports an association of post-glacial vegetation stability with endemism, records spanning the glacial maximum indicate widespread tundra during long periods of the late Pleistocene and therefore suggest southern displacement of forest-associated endemics. While some of the alpine scree-associated endemics may have persisted in situ, many others likely arrived via a variety of dispersal trajectories. These histories include dispersal from southern refugia towards ocean barriers preventing further northward dispersal, contraction from more widespread distributions, and recent divergence from sister taxa. This study shows that paleoecological records can cast strong doubt on the inference that areas of endemism necessarily imply in situ glacial survival.

Decomposing uncertainties in the future terrestrial carbon budget associated with emission scenarios, climate projections, and ecosystem simulations using the ISI-MIP results

Abstract. We examined the changes to global net primary production (NPP), vegetation biomass carbon (VegC), and soil organic carbon (SOC) estimated by six global vegetation models (GVMs) obtained from the Inter-Sectoral Impact Model Intercomparison Project. Simulation results were obtained using five global climate models (GCMs) forced with four representative concentration pathway (RCP) scenarios. To clarify which component (i.e., emission scenarios, climate projections, or global vegetation models) contributes the most to uncertainties in projected global terrestrial C cycling by 2100, analysis of variance (ANOVA) and wavelet clustering were applied to 70 projected simulation sets. At the end of the simulation period, changes from the year 2000 in all three variables varied considerably from net negative to positive values. ANOVA revealed that the main sources of uncertainty are different among variables and depend on the projection period. We determined that in the global VegC and SOC projections, GVMs are the main influence on uncertainties (60 % and 90 %, respectively) rather than climate-driving scenarios (RCPs and GCMs). Moreover, the divergence of changes in vegetation carbon residence times is dominated by GVM uncertainty, particularly in the latter half of the 21st century. In addition, we found that the contribution of each uncertainty source is spatiotemporally heterogeneous and it differs among the GVM variables. The dominant uncertainty source for changes in NPP and VegC varies along the climatic gradient. The contribution of GVM to the uncertainty decreases as the climate division becomes cooler (from ca. 80 % in the equatorial division to 40 % in the snow division). Our results suggest that to assess climate change impacts on global ecosystem C cycling among each RCP scenario, the long-term C dynamics within the ecosystems (i.e., vegetation turnover and soil decomposition) are more critical factors than photosynthetic processes. The different trends in the contribution of uncertainty sources in each variable among climate divisions indicate that improvement of GVMs based on climate division or biome type will be effective. On the other hand, in dry regions, GCMs are the dominant uncertainty source in climate impact assessments of vegetation and soil C dynamics.