Plant Functional Type Composition Research Articles

Responses of leaf traits to climatic gradients: adaptive variation versus compositional shifts

Abstract. Dynamic global vegetation models (DGVMs) typically rely on plant functional types (PFTs), which are assigned distinct environmental tolerances and replace one another progressively along environmental gradients. Fixed values of traits are assigned to each PFT; modelled trait variation along gradients is thus driven by PFT replacement. But empirical studies have revealed "universal" scaling relationships (quantitative trait variations with climate that are similar within and between species, PFTs and communities); and continuous, adaptive trait variation has been proposed to replace PFTs as the basis for next-generation DGVMs. Here we analyse quantitative leaf-trait variation on long temperature and moisture gradients in China with a view to understanding the relative importance of PFT replacement vs. continuous adaptive variation within PFTs. Leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC) and nitrogen content of dry matter were measured on all species at 80 sites ranging from temperate to tropical climates and from dense forests to deserts. Chlorophyll fluorescence traits and carbon, phosphorus and potassium contents were measured at 47 sites. Generalized linear models were used to relate log-transformed trait values to growing-season temperature and moisture indices, with or without PFT identity as a predictor, and to test for differences in trait responses among PFTs. Continuous trait variation was found to be ubiquitous. Responses to moisture availability were generally similar within and between PFTs, but biophysical traits (LA, SLA and LDMC) of forbs and grasses responded differently from woody plants. SLA and LDMC responses to temperature were dominated by the prevalence of evergreen PFTs with thick, dense leaves at the warm end of the gradient. Nutrient (N, P and K) responses to climate gradients were generally similar within all PFTs. Area-based nutrients generally declined with moisture; Narea and Karea declined with temperature, but Parea increased with temperature. Although the adaptive nature of many of these trait-climate relationships is understood qualitatively, a key challenge for modelling is to predict them quantitatively. Models must take into account that community-level responses to climatic gradients can be influenced by shifts in PFT composition, such as the replacement of deciduous by evergreen trees, which may run either parallel or counter to trait variation within PFTs. The importance of PFT shifts varies among traits, being important for biophysical traits but less so for physiological and chemical traits. Finally, models should take account of the diversity of trait values that is found in all sites and PFTs, representing the "pool" of variation that is locally available for the natural adaptation of ecosystem function to environmental change.

Evaluating restoration potential of transferred topsoil

AbstractQuestionsTranslocation of topsoil and its seed bank for ecological restoration is increasingly popular. How representative is the soil seed bank of the extant vegetation at the source site? What influence does the transfer process have on germinant density, species and plant functional type composition? Does smoke and heat treatment of transferred topsoil enhance germination and potential for restoration success?LocationBanksia woodland of the Swan Coastal Plain, Western Australia.MethodsTo assess the efficacy of topsoil transfer for return of native plant species, we measured topsoil seed bank characterisitcsin situproir to vegetation clearing, and immediately after transfer of the topsoil to an adjacent, degraded mediterranean‐type woodland in southwest Australia. Glasshouse germination of topsoil samples from 24 pre‐ and 24 post‐transfer plots was used to quantify the effects of transfer and soil depth on germinant density, species richness, plant functional types and seed bank similarity toin situvegetation. Application of germination cues (heat + smoke) was used to explore the impact of topsoil transfer on seed germination and emergence.ResultsTopsoil transfer significantly reduced germinant densities (pre‐transfer 1692–4239 germinants·m−2, post‐transfer 795–1016 germinants·m−2;t = 6.7,P < 0.001) and shifted community structure (MRPP:A = 0.13,P < 0.001), including a reduction of woody species density by 81%. For the majority of functional types, heat and smoke failed to stimulate additional germination post‐transfer, suggesting soil transfer simulated the effect of fire‐related germination cues.ConclusionAlthough topsoil transfer translocated many viable native seeds, potential restoration success was hindered by reduced germinant densities. This was mostly attributable to a dilution effect associated with mixing of transferred topsoil, so that many seeds were buried too deep to emerge. However, total reductions were greater than expected based on dilution alone, suggesting some seed mortality during the transfer process. Transfer shifted composition towards dominance by annual species, suggesting the need for topsoil transfer to be supplemented by other restoration techniques.

Ecohydrology of Dry Regions: Storage versus Pulse Soil Water Dynamics

Although arid and semiarid regions are defined by low precipitation, the seasonal timing of temperature and precipitation can influence net primary production and plant functional type composition. The importance of precipitation seasonality is evident in semiarid areas of the western U.S., which comprise the Intermountain (IM) zone, a region that receives important winter precipitation and is dominated by woody plants and the Great Plains (GP), a region that receives primarily summer precipitation and is dominated by perennial grasses. Although these general relationships are well recognized, specific differences in water cycling between these regions have not been well characterized. We used a daily time step soil water simulation model and twenty sites from each region to analyze differences in soil water dynamics and ecosystem water balance. IM soil water patterns are characterized by storage of water during fall, winter, and spring resulting in relatively reliable available water during spring and early summer, particularly in deep soil layers. By contrast, GP soil water patterns are driven by pulse precipitation events during the warm season, resulting in fluctuating water availability in all soil layers. These contrasting patterns of soil water—storage versus pulse dynamics—explain important differences between the two regions. Notably, the storage dynamics of the IN sites increases water availability in deep soil layers, favoring the deeper rooted woody plants in that region, whereas the pulse dynamics of the Great Plains sites provide water primarily in surface layers, favoring the shallow-rooted grasses in that region. In addition, because water received when plants are either not active or only partially so is more vulnerable to evaporation and sublimation than water delivered during the growing season, IM ecosystems use a smaller fraction of precipitation for transpiration (47%) than GP ecosystems (49%). Recognizing the pulse-storage dichotomy in soil water regimes between the IM and GP regions may be useful for understanding the potential influence of climate changes on soil water patterns and resulting dominant plant functional groups in both regions.

Plant functional diversity drives niche‐size‐structure of dominant microbial consumers along a poor to extremely rich fen gradient

Summary Plant community composition is recognized more and more for playing an important role in ecosystem processes, such as C cycling. In particular, plant functional type (PFT) composition seems to have a key regulatory role, yet the underlying mechanisms in the interaction between PFTs and ecosystem processes are still to be identified. Here, we assess the link between PFTs and dominant microbial consumers along a calcareous poor to extremely rich fen gradient in western Poland. We particularly focussed on dominant microbial consumers (testate amoebae), which can exert large effects on the functioning of peatlands. Using moving‐window analyses and path‐relation networks subjected to structural equation modelling (SEM), we investigated linkages among abiotic factors, PFTs and testate amoebae. We show that along the poor to extremely rich fen gradient, the dependence of testate amoebae to PFTs is higher than their dependence to abiotic factors. We also found that the link between testate amoebae and PFTs differs between size assemblages of testate amoebae. While large testate amoeba species (i.e. high trophic level) were highly linked to Sphagnum mosses cover, small species (i.e. low trophic level) were linked to brown mosses. Distinction between shallow‐rooted and deep‐rooted vascular plants also showed that shallow‐rooted plants play a role on testate amoeba community structure at the ‘poor’ side of the gradient. Our results further show a dominant role for calcium content and the structure of the bryophyte community on testate amoeba size assemblages at the poor to extremely rich fen scale, both for diversity and abundance of testate amoebae. Synthesis. Variations in plant functional type composition drive niche‐size‐structure of testate amoebae along the (calcareous) poor to extremely rich fen gradient. Furthermore, strong relationships between moss types and testate amoeba size‐structure suggest that mosses specifically influence testate amoeba development through autogenic effects. Therefore, moss cover composition is key to microbial consumers and may be the driving factor determining microbial network structure and associated ecosystem processes, such as carbon cycling.

Woody Plant Encroachment into Grasslands: Spatial Patterns of Functional Group Distribution and Community Development

Woody plant encroachment into grasslands has been globally widespread. The woody species invading grasslands represent a variety of contrasting plant functional groups and growth forms. Are some woody plant functional types (PFTs) better suited to invade grasslands than others? To what extent do local patterns of distribution and abundance of woody PFTs invading grasslands reflect intrinsic topoedaphic properties versus plant-induced changes in soil properties? We addressed these questions in the Southern Great Plains, United States at a subtropical grassland known to have been encroached upon by woody species over the past 50-100 years. A total of 20 woody species (9 tree-statured; 11 shrub-statured) were encountered along a transect extending from an upland into a playa basin. About half of the encroaching woody plants were potential N2-fixers (55% of species), but they contributed only 7% to 16 % of the total basal area. Most species and the PFTs they represent were ubiquitously distributed along the topoedaphic gradient, but with varying abundances. Overstory-understory comparisons suggest that while future species composition of these woody communities is likely to change, PFT composition is not. Canonical correspondence analysis (CCA) ordination and variance partitioning (Partial CCA) indicated that woody species and PFT composition in developing woody communities was primarily influenced by intrinsic landscape location variables (e.g., soil texture) and secondarily by plant-induced changes in soil organic carbon and total nitrogen content. The ubiquitous distribution of species and PFTs suggests that woody plants are generally well-suited to a broad range of grassland topoedaphic settings. However, here we only examined categorical and non-quantitative functional traits. Although intrinsic soil properties exerted more control over the floristics of grassland-to-woodland succession did plant modifications of soil carbon and nitrogen concentrations, the latter are likely to influence productivity and nutrient cycling and may, over longer time-frames, feed back to influence PFT distributions.

Lasting effects of climate disturbance on perennial grassland above‐ground biomass production under two cutting frequencies

Climate extremes can ultimately reshape grassland services such as forage production and change plant functional type composition. This 3-year field research studied resistance to dehydration and recovery after rehydration of plant community and plant functional types in an upland perennial grassland subjected to climate and cutting frequency (Cut+, Cut-) disturbances by measuring green tissue percentage and above-ground biomass production (ANPP). In year 1, a climate disturbance gradient was applied by co-manipulating temperature and precipitation. Four treatments were considered: control and warming-drought climatic treatment, with or without extreme summer event. In year 2, control and warming-drought treatments were maintained without extreme. In year 3, all treatments received ambient climatic conditions. We found that the grassland community was very sensitive to dehydration during the summer extreme: aerial senescence reached 80% when cumulated climatic water balance fell to -156mm and biomass declined by 78% at the end of summer. In autumn, canopy greenness and biomass totally recovered in control but not in the warming-drought treatment. However ANPP decreased under both climatic treatments, but the effect was stronger on Cut+ (-24%) than Cut- (-15%). This decline was not compensated by the presence of three functional types because they were negatively affected by the climatic treatments, suggesting an absence of buffering effect on grassland production. In the following 2years, lasting effects of climate disturbance on ANPP were observable. The unexpected stressful conditions of year 3 induced a decline in grassland production in the Cut+ control treatment. The fact that this treatment cumulated higher (45%) N export over the 3years suggests that N plays a key role in ANPP stability. As ANPP in this mesic perennial grassland did not show engineering resilience, long-term experimental manipulation is needed. Infrequent mowing appears more appropriate for sustaining grassland ANPP under future climate extremes.

Plant competition, temporal niches and implications for productivity and adaptability to climate change in water‐limited environments

Summary We review plant competition in water‐limited environments with focus on temporal niche dynamics and examine implications for diversity–productivity relationships and the response of ecosystem productivity to changes in water availability. The main theses under examination are that (i) plant functional types (PFTs) have distinct resource pulse use and coexist through mechanism of temporal resource use complementarity; and (ii) species of same PFT (functionally redundant species) coexist through distinct recruitment niches. In water‐limited systems, opportunities for plant resource uptake and growth fluctuate through time, dependent on precipitation patterns. Species differ in the sensitivities of germination, seedling mortality and adult productivity to pulses of water availability, and this generates opportunity for temporal niche diversification. We illustrate this in two case studies. Case study I. Savannas: This is an example of niche separation between two distinct plant functional types (PFTs), trees and grasses. Several models suggest that the two PFTs have complementary resource pulse use, which regulates their abundances, but other models suggest that tree abundance is regulated by the narrow recruitment niche of trees. Overly restrictive recruitment niches can cause a mismatch between resource availability, PFT composition and ecosystem productivity. Case study II. The tropical dry forest: Here, we examine niche separation between closely related species of same PFT. These species commonly have distinct temporal recruitment niches based on differences in seed and seedling traits. A diversification of recruitment niches may be necessary for sympatric speciation and has the effect of broadening of the recruitment ‘portfolio’ of a phylogenetic lineage and PFT. Synthesis: Functional diversity, characterized by differences in adult resource use, optimizes ecosystem function in a pulsed resource environment only if PFT abundances are regulated by adult resource use. Regulation through recruitment niches tends to uncouple plant productivity from resource availability. However, we hypothesize that a diversification of recruitment niches within PFTs may help alleviate recruitment limitations and help communities attain a PFT composition that optimizes resource use and permits adaptation to climate change.

Energy exchange and water budget partitioning in a boreal minerogenic mire

This study investigated patterns and controls of the seasonal and inter‐annual variations in energy fluxes (i.e., sensible heat, H, and latent heat, λE) and partitioning of the water budget (i.e., precipitation, P; evapotranspiration, ET; discharge, Q; and soil water storage, ∆S) over five years (2001–2005) in a boreal oligotrophic fen in northern Sweden based on continuous eddy covariance, water table level (WTL), and weir measurements. For the growing season (May 1 to September 31), the 5 year averages (± standard deviation) of the midday (10:00 to 14:00 h) Bowen ratio (β, i.e., H/λE) was 0.86 ± 0.08. Seasonal and inter‐annual variability of β was mainly driven by λE which itself was strongly controlled by both weather (i.e., vapor pressure deficit, D, and net radiation, Rn) and physiological parameters (i.e., surface resistance). During the growing season, surface resistance largely exceeded aerodynamic resistance, which together with low mean values of the actual ET to potential ET ratio (0.55 ± 0.05) and Priestley‐Taylor α (0.89) suggests significant physiological constrains on ET in this well‐watered fen. Among the water budget components, the inter‐annual variability of ET was lower (199 to 298 mm) compared to Q (225 to 752 mm), with each accounting on average for 34 and 65% of the ecosystem water loss, respectively. The fraction of P expended into ET was negatively correlated to P and positively to Rn. Although a decrease in WTL caused a reduction of the surface conductance, the overall effect of WTL on ET was limited. Non‐growing season (October 1 to April 30) fluxes of H, λE, and Q were significant representing on average −67%, 13%, and 61%, respectively, of their growing season sums (negative sign indicates opposite flux direction between the two seasons). Overall, our findings suggest that plant functional type composition, P and Rn dynamics (i.e., amount and timing) were the major controls on the partitioning of the mire energy and water budgets. This has important implications for the regional climate as well as for ecosystem development, nutrient, and carbon dynamics.

ASSESSMENT OF PLANT FUNCTIONAL TYPES IN TROPICAL ARID AND SEMI-ARID ECOSYSTEMS OF INDIA USING REMOTE SENSING DATA AND GIS

Abstract. Tropical ecosystems undergo changes caused by season, climate or multiple anthropogenic impacts. Such changes may cause gradual or rapid shifts from one state to another. There has been a focus on functional classifications of plants to find tools for monitoring and assessing species status in changing environments. It has been recognised that plant biological characteristics can be related to their response to predominant environmental factors and interactions between other organisms. These findings have resulted in a search for plant functional types (PFTs) that are user-defined groups of species with similar response to environmental resources and disturbance associated to common biological traits. Now, identification of plant functional types is priority area in the climate change research. Satellite Earth observation data is an important tool in providing considerable information on extracting PFT information at global and regional levels. From the modelling perspective, some of the current needs are the refinement of processes that govern community assembly, such as natural and anthropogenic disturbances. PFTs used in large-scale models are insufficient to represent the diversity of responses in natural plant communities. The currently available MODIS PFT map was generated by re-labeling the IGBP land cover type classes. However, the error magnitudes of the MODIS PFT product and their spatial and temporal distributions have not been fully characterized. Remotely sensed derived information of the phenology, community composition and vegetation structure are the key inputs to integrate with the variability in precipitation and temperature to map the spatial distribution of Plant functional types. PFTs allows accurate representation of the land surface by separately specifying the composition and structure of PFTs within a grid cell. Very little research efforts are discernible in India that explicitly address the PFTs. In the present study five natural vegetation systems were studied along arid, semi-arid and sub-humid regions of Indian Desert and Aravallis of Rajasthan, India, with a distance of 600 km. The annual precipitation decreases from as high as 1600 mm in the south to 700 mm in the north-east and 100 mm in the west. The study is based on the integrated approach of remote sensing, GIS, and phytosociology. In the step 1, vegetation type map was prepared using multi-season IRS P6 LISS III data. Screening of plant traits was done based on field observations and literature. Phytosociological data pertains to 500 sample plots was used to identify plant functional traits of 900 species at morphological level. The vegetation classification scheme at regional level identified thorn forest, dry deciduous forest, broad leaved forest, woodland, shrubland and grasslands. Five plant traits selected in the study were significant for tropical environments. Attributes such as leaf size, leaf texture, spinescence, stem diameter and bark consistency were categorized systematically. Ordination analysis was carried out across the environmental gradient. Plant functional traits were measured on 20 individuals per species at each site. Environmental information was integrated to identify plant trait response. The spatial trends in PFTs were analysed and compared across the vegetation types, along the gradient of land surface temperature, climate, elevation and time integrated NDVI. Results established the occurrence of recurrent patterns of association among selected plant traits. Functional response groups were identified by summarizing results and relating them to individual species. Finally phytoclimatic map was prepared to represent spatial distribution of PFTs. The species with of functional traits of representing microphylls, sclerophyll, rough bark, spinescence and therophyte are demarcated as drought tolerant traits. Drought Intolerant PFTs are represented by macrophyll, malacophyll, smooth Bark, non spinescent stems and leaves. Biological spectrum of Desert national park, Jaisalmer and and Ajmer represents therophytic climate (below 600mm rainfall) while Sariska and Mt. Abu are of therophanerophytic (>600mm rainfall). The higher proportion of microphylls and therophytes are distributed within tropical arid environments. The dominance of the drought tolerant PFTs increased towards west while the dominance of the drought intolerant PFTs increased in southern and northern parts of Rajasthan. Detecting the change of spatial characteristics of plant species under precipitation gradients would be helpful to study species dynamics in a large region under environmental gradient. On the basis of easily-measured plant traits and phytosociological surveys, the present approach summarized the complexity of tropical vegetation into a relatively few PFTs. The present study open up new possibilities for understanding plant trait and environment relationship and developing PFT classification in tropical regions.

Changes in plant species and functional composition with time since fire in two mediterranean climate plant communities

AbstractQuestionDo floristic composition and plant functional type (PFT) richness and dominance change with time since fire, in the directions predicted through consideration of their fire response traits?LocationTwo vegetation communities in the globally significant biodiversity hotspot of south‐western Australia: mallee, dominated by resprouters, and mallee‐heath, dominated by non‐resprouters.MethodsSpecies richness and cover were sampled in replicated plots across a time since fire gradient ranging from 2 to >55 yr post‐fire, using a space‐for‐time approach. Species were allocated to PFTs according to traits relevant to the processes of vegetation change underpinning the initial floristic composition model of vegetation assembly: their capacity to resprout, the location and persistence of the seed bank, competitive stratum and longevity. Ordination and ANOVA were used to test for differences in floristic and PFT composition between young (<10 yr post‐fire), mature (18–35 yr) and old (>40 yr) vegetation in each community.ResultsPlant functional type and floristic analyses were similar, showing substantial changes in the composition of mallee‐heath vegetation with time since fire, but not in mallee. The direction of change in PFT composition in mallee‐heath was consistent with predictions, with increasing cover of non‐resprouting, serotinous PFTs, an intermediate peak in cover of PFTs with persistent soil‐stored seed banks, and decreasing cover of post‐fire ephemerals and non‐resprouting, non‐serotinous dwarf shrubs, herbs and graminoids with increasing time since fire. Success in predicting changes in PFT dominance in mallee was lower.ConclusionsThe similarity of floristic and PFT analyses suggest that these approaches are interchangeable for characterizing vegetation change with increasing time since fire. PFTs were more effective for predicting fire response trajectories in the vegetation community dominated by non‐resprouting, serotinous shrubs (mallee‐heath) than that dominated by resprouting, serotinous trees (mallee). The underlying vegetation assembly model and PFTs used appear suitable for broader application in fire‐prone communities with competitive dominance by non‐resprouting, serotinous shrubs, but less so in communities dominated by other PFTs.

Seasonal dynamics of biomass production and herbage quality of three grasslands with contrasting functional compositions

AbstractClassifying grasses into plant functional types (PFT) according to their strategy of nutrient capture (PFT A, B and b) or nutrient conservation (PFT C) is claimed to predict variability in biomass production and herbage quality in grasslands. PFT A, B and b are characterized by higher production than PFT C, with higher nutritive value, which decreases rapidly. PFT C is characterized by lower nutritive value, which remains more stable in time. The aim of this study was to quantify the consequences of PFT composition at the community level on the seasonal dynamics of biomass and herbage quality for livestock feed. We studied three grasslands located in the same area with contrasting PFT composition and classified PFT A, PFT Bb and PFT C. The dynamics of vegetation stages, dry‐matter yield and nutritive value were followed over three vegetation cycles in 2007–2008. In the first cycle, biomass accumulation was high for the PFT A and PFT Bb grasslands and the high quality of herbage declined rapidly with the reproductive development. By contrast, biomass accumulation was slow in the PFT C grassland, with a lower quality that declined slowly, consistent with the later reproductive development. For regrowth cycles, the same ranking of grasslands was observed for biomass accumulation, and differences in digestibility were similar to those observed at the beginning of the first vegetation cycle. Combining type of grassland with sum of temperature for the first cycle and regrowth days for the second and third vegetation cycles provided quantitative models of herbage biomass and quality.

Alpine steppe plant communities of the Tibetan highlands

AbstractAim: To present a first description of plant communities of the Tibetan alpine steppes based on floristically complete vegetation records as a baseline reference for future ecological and palaeoecological studies. These constitute the world's largest alpine biome, but their vegetation is virtually unknown. Due to their vast extent, they are relevant for functioning of large‐scale climatic systems. In turn, arid and alpine biomes are suspected to be highly sensitive to ongoing climate change, underwent climate‐driven changes during the Last Glacial Maximum and have been subject to overgrazing and desertification.Location: Northwestern Tibetan highlands (China: Xizang, Qinghai), 4200 to 5400 m a.s.l., total area ca. 800 000 km2.Methods: Two hundred and fifty‐three vegetation records with absolute percentage cover were classified based on expert knowledge and analysed by DCA; composition of plant functional types related to grazing resilience was also assessed.Results: Ten communities of alpine steppe were distinguished. A set of 11 alpine steppe species is distributed throughout the highlands, with a precipitation gradient between 350 mm yr−1 (southeast) and 20 to 50 mm yr−1 (northwest). The elevational range of more than 80% of species is larger than 1000 m. The data set comprises 30% endemic species, with ten endemic genera.Conclusions: The wide thermal and hygric range of many species and high rate of endemism do not support the idea of high sensitivity to climate change or occurrence of past climate‐driven extinctions. The prevailing plant functional types are grazing resilient, and evidence for overgrazing is very limited. Cushion plants and dwarf shrubs, however, become increasingly rare around settlements, because they are uprooted for fuel. Hence, the world's largest arid alpine biome is apparently resilient to climatic changes and grazing. This contradicts common perceptions about arid and alpine ecosystems and therefore deserves intense multi‐disciplinary research efforts.

Desertification alters the response of vegetation to changes in precipitation

Summary 1. Desertification is of critical concern because it may affect 40% of the global land area inhabited by more than 1 billion people. During the process of desertification, defined as land degradation in arid, semi‐arid and dry subhumid areas, drylands shift to a state of reduced biological productivity that may lead to widespread loss of human well‐being. Despite recent advances, we need a better understanding of the response of ecosystems to desertification to improve the assessment and monitoring of desertification. 2. We used a published physiognomic description, MODIS monthly NDVI data for 2000–2005 and rain gauge data to characterize the long‐term effects of degradation for an area of 128 000 ha located in western Patagonia. 3. We focused on three aspects of vegetation dynamics: radiation interception, precipitation use efficiency (PUE) and the sensitivity of vegetation to interannual changes in precipitation (i.e. the slope of the relationship between the above‐ground net primary productivity and precipitation, the precipitation marginal response, PMR). In particular, we analysed the response of PMR and PUE to long‐term changes in vegetation structure due to grazing. 4. On average, NDVI decreased by 28%, ranging between 35% (grass or grass–shrub steppes to semi‐deserts) and 22% (grass or grass‐shrub steppes to low cover grass steppes) suggesting that, in Patagonia, desertification may imply a reduction in the above‐ground net primary productivity. 5. Additionally, PMR and PUE captured the functional modifications associated with vegetation structure caused by desertification. In general, grass and grass‐shrub steppes had the highest average PUE and PMR. Shrub steppes and semi‐deserts had the lowest PMR and PUE. These results support the hypothesis that PUE is more sensitive to changes in total plant cover and PMR to changes in plant functional type composition. 6. Synthesis and applications. Our results indicate that the precipitation marginal response could complement current desertification assessments based only on precipitation use efficiency thereby improving our ability to monitor desertification. Enhanced monitoring programmes could provide an early warning signal for the onset of desertification allowing for timely management action.

광릉 활엽수림에서 Community Land Model 3.5-Dynamic Global Vegetation Model의 평가

본 연구에서는 광릉의 활엽수림에서 관측된 생태자료들을 이용하여 CLM3.5-DGVM(Community Land Model 3.5-Dynamic Global Vegetation Model)의 탄소교환과정에 대한 모의능력을 평가하고 탄소수지를 계산하였다. 또한 식생 종의 구성과 식물계절학, 그리고 기후 변동성이 탄소수지에 미치는 영향을 조사하기 위하여 민감도 실험을 수행하였다. 모델의 식물계절학은 잎의 출현과 낙하의 시기를 잘 모의하지 못하였으며, 특히 낙엽은 관측보다 한달 이상 지연되어 생장기간을 과대모의 하였다. 모의된 최대 엽면적지수(leaf alea index, LAI)는 5.8이며 관측값(4.5)에 비해 과대모의 되었다. 과대 모의된 LAI는 광합성량과 잎의 자가영양호홉의 과대모의를 야기하였으며, 이를 통해 연간 총 일차 생산량(gross primary producing, GPP)과 생태 호흡량(ecosystem respiration, <TEX>$R_e$</TEX>)의 과대모의에 기여하였다. 관측과 모델간의 LAI의 차이에도 불구하고 모의된 식생 탄소 저장항의 크기는 관측 보고된 값과 유사하였다. 모델의 식물계절학함수를 사용하는 대신 관측된 PAI로부터 유도된 식물계절학을 사용하면 생육 기간이 감소함에 따라 GPP와 <TEX>$R_e$</TEX>의 과대 모의는 완화되었다. 하지만 관측 보고된 값과 비교할 때 여전히 큰 값을 보였다. 모의된 탄소수지는 식생 종의 구성에는 유의한 민감도를 가지지 않았다. 모델입력자료에 기후변동성의 고려 유무에 따른 평형상태의 탄소저장량의 차이는 10%이하로 낮았으며 기후변동성이 평형상태의 탄소저 장량에 미치는 영향은 유의할 수준이 아니라고 사료된다. 모델에서 모의된 GPP와 <TEX>$R_e$</TEX>의 1994년부터 2003년간의 연간 변동성은 연 평균 대기온도와 일사량에 의존하였다. 모델의 다른 문제점들에 관해서도 본문에서 논의되었다. The performance of Community Land Model version 3.5 - Dynamic Global Vegetation Model (CLM-DGVM) was evaluated through a comparison with the observation over temperate deciduous forest in Gwangneung, Korea. Influence of plant phenology, composition of plant functional type, and climate variability on carbon exchanges was also examined through sensitivity test. To get equilibrium carbon storage, the model was run for 400 years driven by the observed atmospheric data at the deciduous forest of the year 2006. We run the model for 2006 with the equilibrium carbon storage at Gwangneung forest and compared the model output with the observation. A comparison of leaf area index (LAI) between the model and observation indicated that the simulated phenology poorly represented the timing of budburst, leaf-fall, and evolution of LAI. Senescence of the phenology was delayed about four weeks and the simulated maximum LAI (of 5.8 <TEX>$m^2$</TEX> <TEX>$m^{-2}$</TEX>) was greater than the observed value (of 4.5 <TEX>$m^2$</TEX> <TEX>$m^{-2}$</TEX>). The overestimated LAI contributed to overestimation of both gross primary productivity (GPP) and ecosystem respiration <TEX>$(R_e)$</TEX> through increased photosynthesis and foliar autotropic respiration <TEX>$(R_a)$</TEX>, respectively. Despite the discrepancy between the simulated and observed LAI, the simulated tree carbon storage amounts were comparable with the reported values at the site. Change in plant phenology from the simulated to the observed reduced more than six weeks of the plant growth period, resulting in the decreased amount of GPP and <TEX>$R_e$</TEX>. These values, however, were still higher (~10% of GPP and 40% of <TEX>$R_e$</TEX>) than the observed values. The effect of change in plant functional type composition (from dominant temperate deciduous forest to the coexistence of temperate deciduous and needle leaf forests) on the estimated amount of GPP and <TEX>$R_e$</TEX> was marginal. The influence of climate variability on carbon storage amounts was not significant. The simulated inter-annual variation of GPP and <TEX>$R_e$</TEX> from 1994 to 2003 depended on annual mean air temperature and total radiation but not on precipitation. Other deficiencies of CLM3.5-DGVM have been discussed.

Links between plant community composition, soil organic matter quality and microbial communities in contrasting tundra habitats

Plant communities, soil organic matter and microbial communities are predicted to be interlinked and to exhibit concordant patterns along major environmental gradients. We investigated the relationships between plant functional type composition, soil organic matter quality and decomposer community composition, and how these are related to major environmental variation in non-acid and acid soils derived from calcareous versus siliceous bedrocks, respectively. We analysed vegetation, organic matter and microbial community compositions from five non-acidic and five acidic heath sites in alpine tundra in northern Europe. Sequential organic matter fractionation was used to characterize organic matter quality and phospholipid fatty acid analysis to detect major variation in decomposer communities. Non-acidic and acidic heaths differed substantially in vegetation composition, and these disparities were associated with congruent shifts in soil organic matter and microbial communities. A high proportion of forbs in the vegetation was positively associated with low C:N and high soluble N:phenolics ratios in soil organic matter, and a high proportion of bacteria in the microbial community. On the contrary, dwarf shrub-rich vegetation was associated with high C:N and low soluble N:phenolics ratios, and a high proportion of fungi in the microbial community. Our study demonstrates a strong link between the plant community composition, soil organic matter quality, and microbial community composition, and that differences in one compartment are paralleled by changes in others. Variation in the forb-shrub gradient of vegetation may largely dictate variations in the chemical quality of organic matter and decomposer communities in tundra ecosystems. Soil pH, through its direct and indirect effects on plant and microbial communities, seems to function as an ultimate environmental driver that gives rise to and amplifies the interactions between above- and belowground systems.

Relevance of Plant Functional Types based on Leaf Dry Matter Content for Assessing Digestibility of Native Grass Species and Species‐Rich Grassland Communities in Spring

Little research has been done on the nutritive value of species‐rich permanent grasslands in spite of their recognized ecological value. We proposed a new method based on the concept of plant functional type (PFT) to rank grass species and grasslands according to the organic matter digestibility (OMD) of the plant material. The PFTs are based on leaf dry matter content (LDMC). The objectives of this study were: (i) to see if there were significant differences between PFTs for the three components of plant OMD (leaf and stem digestibility and leaf proportion [L%]) in a set of 19 grasses growing in pure stand under two contrasting levels of N supply (Exp. 1); (ii) to see whether grassland vegetation types (GVT) differing in their PFT composition have different digestibility values; investigations being made on the leaf, stem, and whole plant OMD of five and eight plant communities (Exp. 2 and 3, respectively). In pure grass stands (Exp. 1) as well as in grassland communities (Exp. 2 and 3), there was a significant effect of PFT or GVT on leaf and stem OMD. The greatest differences in L% were observed when there were large differences in nutrient availability. At the leafy stage, the whole plant digestibility was higher for GVTs composed of PFTs with a low LDMC. However around the time of flowering there was a convergence in whole‐plant OMD between all grassland communities because L% decreased faster for those composed of PFTs having the lowest LDMC. At this stage, plots with low LDMC had higher plant component digestibility but lower L%. Our results show that the decrease in plant digestibility over time is the result of two processes, an ontogenic one, due to a decrease in leaf proportion, and an ageing one. For the latter, we show that PFT had an effect of leaf and stem digestibility at an early stage of plant development, then they decreased at a rate depending on plant development. Both processes explained the convergence between GVTs in plant digestibility at flowering time.

Modelling above-ground herbage mass for a wide range of grassland community types

Whereas it is recognized that management of plant diversity can be the key to reconciling production and environmental aims, most grassland models are tailored for high-value grass species. We proposed to adapt a mono-specific grass model to take into account specific features of species-rich permanent grasslands, especially over the reproductive phase. To this end, we used the concept of plant functional type (PFT), i.e. the grouping of plant species according to plant traits determined by the response of plant species to different management practices (land use and fertilization) and characterizing of agronomic properties of the corresponding species. In the model, weather and nutrient availability act upon rates of biophysical processes (radiation capture and use, plant senescence). These rates are modified over times due to PFT-specific parameters determined experimentally which represent the different strategies of plant species regarding growth. The integration of these parameters into the model made it possible to predict herbage biomass accumulation rate under different management practices for a wide range of plant communities differing in their PFT composition. The model was evaluated in two steps, first by analyzing separately the effects of PFT and an indicator of nutrient availability on herbage accumulation and then by conducting a sensitivity analysis. It was validated using two independent datasets; a cutting experiment running over the whole growing season to examine the consistency of the model outputs under different cutting regimes, and a monitoring of meadows and pastures in spring over a whole growth cycle to assess the model’s ability to reproduce growth curves. Although a good fit was observed between the simulated and observed data, the few discrepancies noticed between field data and predicted values were attributed mainly to the potential presence of non-grass species. More specifically, we noticed that nutrient (mainly nitrogen) availability is the main driver of plant growth rate, and that PFT determines the times at which this rate changes in relation to the phenological characteristics of species present. We concluded that integration of the PFT concept into the initial mono-specific growth model is especially suited to evaluating the consequences of management practices on species-rich permanent grasslands to meet feed production targets.

Climate change effects on organic matter decomposition rates in ecosystems from the Maritime Antarctic and Falkland Islands

AbstractAntarctic terrestrial ecosystems have poorly developed soils and currently experience one of the greatest rates of climate warming on the globe. We investigated the responsiveness of organic matter decomposition in Maritime Antarctic terrestrial ecosystems to climate change, using two study sites in the Antarctic Peninsula region (Anchorage Island, 67°S; Signy Island, 61°S), and contrasted the responses found with those at the cool temperate Falkland Islands (52°S). Our approach consisted of two complementary methods: (1) Laboratory measurements of decomposition at different temperatures (2, 6 and 10 °C) of plant material and soil organic matter from all three locations. (2) Field measurements at all three locations on the decomposition of soil organic matter, plant material and cellulose, both under natural conditions and under experimental warming (about 0.8 °C) achieved using open top chambers. Higher temperatures led to higher organic matter breakdown in the laboratory studies, indicating that decomposition in Maritime Antarctic terrestrial ecosystems is likely to increase with increasing soil temperatures. However, both laboratory and field studies showed that decomposition was more strongly influenced by local substratum characteristics (especially soil N availability) and plant functional type composition than by large‐scale temperature differences. The very small responsiveness of organic matter decomposition in the field (experimental temperature increase &lt; 1 °C) compared with the laboratory (experimental increases of 4 or 8 °C) shows that substantial warming is required before significant effects can be detected.

Are lianas increasing in importance in temperate floodplain forests in the southeastern United States?

Floodplain forests of the southeastern United States are species rich, often with a dense and diverse liana community. Long-term trends in the density and distribution of lianas may indicate shifts in the composition of plant functional types in these forests. Liana communities in non-fragmented forests in Panama and across the Neotropics have increased in size and density over the last two decades of the 20th century. Are similar changes occurring in temperate forests? Evidence from long-term studies of liana communities in two floodplain forests in South Carolina support the findings from tropical forests. In second-growth forests of the Savannah River system, data from five 1-ha plots established in 1979 and monitored for 22 years indicate a steady increase in liana size and density. Likewise, in old-growth floodplain forests of the Congaree National Park, liana density has increased over 12 years in six 1-ha plots after Hurricane Hugo disturbed the forests in 1989. The increase in liana density and size in these floodplain forests of the southeastern United States is of sufficient magnitude to suggest that lianas are likely influencing stand dynamics in these forests. Consequently, we argue that lianas should be included in models of temperate bottomland forest development of the southeastern United States.

Simulated ecosystem threshold responses to co‐varying temperature, precipitation and atmospheric CO2 within a region of Amazonia

ABSTRACTAim Using a Dynamic Global Vegetation Model (DGVM), we assessed the independent and co‐varying effects of temperature, precipitation and atmospheric CO2 on nonlinear (threshold) responses in carbon‐based processes, and evaluated whether these underlying process thresholds translate to the ecosystem‐scale.Location Amazon Basin, South America.Methods The Lund‐Potsdam‐Jena model (LPJ) was employed to determine responses in net primary production (NPP), heterotrophic respiration (RH), vegetation carbon (CV), soil carbon (CS), and plant functional type (PFT) composition to variations in temperature (± 9 °C relative to the control), precipitation (up to 80% reduction in rainfall relative to the control) and atmospheric CO2 (± 100 p.p.m.v. relative to the control).Results Our modelling experiments show that increases in temperature result in lower and steeper NPP and RH curves, indicating a thermal threshold at current temperature conditions. Under a combination of temperature and precipitation change, CV responds more to precipitation, while CS closely follows temperature gradients. Ecosystem thresholds, measured in terms of PFT composition stability, are surprisingly few. Simulations indicate an ecosystem threshold occurring at 80% reduction in rainfall; however, due to modelling limitations, this threshold is likely to occur at earlier drought stress conditions. Further empirical research on abiotic stress tolerance levels in tropical ecosystems must be performed in order to refine PFT descriptions used in DGVMs.Main conclusion In evaluating simulation scenarios that promote major changes in PFT assemblage, we conclude that the ‘natural’ Amazonian rain forest is resilient to environmental change, particularly to decreases in temperature and precipitation. Determining to what extent anthropogenic pressures have altered this resiliency is of utmost importance in predicting the future fate of the Amazon Basin.