气候变化对森林演替的影响

森林演替是森林生态动力源驱动下森林再生的生态学过程,自20世纪初建立群落演替理论以来,演替研究成为生态学研究中的热点．客观准确地认识森林演替规律,研究森林演替动力学机理及其模型,是科学管理森林生态系统的需要;对于天然林保护工程与森林植被的恢复重建,具有重要的理论与实际意义．干扰是森林循环的驱动力,导致森林生态系统时空异质性,是更新格局和生态学过程的主要影响因素．它可改变资源的有效性,干扰导致的林隙是森林循环的起点．回顾了目前演替研究的几种方法,即马尔科夫模型、林窗模型(GAP)、陆地生物圈模型(BIOME)和非线性演替模式．介绍了气候变化对森林演替的影响;并在已有成果的基础上,提出了目前研究存在的问题及未来的发展方向．     

Plant functional types and climate in a southern African savanna

Abstract. A system of easily defined plant functional types for a dry savanna is presented and related to climate data. To predict possible changes of vegetation in response to climate change, a system of functional attributes is developed. The attributes are based on both structural and functional characteristics and are chosen to be related to climatic conditions. plant functional types are defined as assemblages of plant species having similar combinations of plant functional attributes. Direct and indirect gradient analyses of a test data set show that the plant functional types as well as the vegetation described from them are strongly associated with total annual precipitation, precipitation of the wettest month and a moisture index (all related to soil moisture) and with temperature of the coldest month.     

Modelling the potential effects of climate change on calcareous grasslands in Atlantic Europe

Aim This study aims to assess the sensitivity of calcareous grassland vegetation to climate change and to indicate the most probable direction of change. Location The study area was a region of Britain, Ireland, France and Spain, centred on the Bay of Biscay, which was defined using a land classification based on climatic criteria. Methods Vegetation was sampled in the field, with additional data collected on soils, climate, management and land cover. The vegetation samples were ordinated by detrended correspondence analysis in order to explore the main gradients present and as a basis for modelling changes. Environmental data were summarized by ordination techniques, with the scores generated used to predict the current vegetation score on the first two ordination axes by multiple regression. The model was then manipulated to represent a 2 °C increase in temperature and resulting shifts in the vegetation samples in terms of their species composition assessed. Results There was a good general agreement between the original vegetation ordination axis scores and those predicted by the model, the latter of which were based on environmental data alone. Following a 2 °C increase in temperature, the predicted changes in the ordination space were demonstrated to be subtle, consisting of small shifts towards vegetation associated with warmer conditions, representing distances 100 km or less on the ground. Main conclusions The models are simple but nevertheless provide a useful basis for the investigation of potential vegetation change. The shifts in the ordination space represent more minor changes than those predicted in previous studies. This suggests that the potential for major change is lower when environmental factors such as soil and management are considered in addition to climate. The potential for change is also reduced when vegetation is considered as a whole rather than on an individual species basis, due to both interspecific interactions and interactions with environmental factors acting as constraints.     

Morphological and reproductive responses of dominant plant species to local conditions in herbaceous successional stages of a calcareous hillside

Secondary succession on calcareous hillsides, initiated following the abandonment of agro-pastoral practices, is characterized by the transformation of initial short sward into tall herbaceous vegetation and finally woody formations. These structural changes are accompanied by modifications in ecological conditions but some species are able to persist and flower along the successional gradient. In this study, we compare reproductive and morphological traits of seven perennial species present in three successional stages [short grassland (SG), tall grassland (TG), and encroached grassland (EG)] to test if plant species present modifications along the successional gradient. The results show that morphological traits as height, leaf area and leaf dry mass increase for all studied species. Along the successional gradient, Teucrium chamaedrys increases ramet biomass more than twice (+145%) while Brachypodium pinnatum increases it even more (+340%). Maximum specific leaf area was observed in Brachypodium pinnatum (SLA = 20.4 mm² mg⁻¹) in SG, whereas Helianthemum nummularium and Teucrium chamaedrys have both rising SLA and falling leaf dry matter content in TG and EG. Concurrently, Helianthemum nummularium, Hippocrepis comosa and Teucrium chamaedrys show a clear decrease in sexual reproduction, with between 18 and 40% fewer flowers during the progress of succession. By contrast, Festuca lemanii, Sesleria caerulea and Brachypodium pinnatum increase their flower numbers per inflorescence (×3.6, ×3.3, and ×3.5, respectively). Festuca lemanii and Sesleria caerulea increase seed production to a maximum in TG, and Brachypodium pinnatum and Carex flacca increase seed output in TG and EG (×4.5, ×5.5, respectively). Changes in plants traits underscore the idea that species allocate resources differently probably because of increasing competition and decreasing edaphic constraints. This study also implies the potential existence of specific responses allowing plants to maintain existence within a plant community and explaining their contrasting performance during the succession.     

Life expansion in Sørkapp Land, Spitsbergen, under the current climate warming

Terrestrial life response to climate warming in Sørkapp Land after the Little Ice Age is described. Plant succession starts in the areas abandoned by glaciers and continues in the areas which have been outside glaciers. Continuous tundra becomes denser in many places of the west and south. A denser tundra attracts animal species feeding on plants. Vegetation of non-glaciated areas in the north-east is very sparse until now in spite of persisting development. Scarce fauna of the NE Sørkapp Land consists mainly of several bird species feeding on the sea. They are of great importance in plant and soil development, delivering organic matter to the land by fertilizing. Persisting warming leads an increase of the landscape heterogenity.     

Salt stress limitation of seedling recruitment in a salt marsh plant community

Summary Seedling recruitment in salt marsh plant communities is generally precluded in dense vegetation by competition from adults, but is also relatively rare in disturbance-generated bare space. We examined the constraints on seedling recruitment in New England salt marsh bare patches. Under typical bare patch conditions seed germination is severely limited by high substrate salinities. We examined the germination requirements of common high marsh plants and found that except for one notably patch-dependent fugitive species, the germination of high marsh plants is strongly inhibited by the high soil salinities routinely encountered in natural bare patches. Watering high marsh soil in the greenhouse to alleviate salt stress resulted in the emergence of up to 600 seedlings/225 cm². The vast majority of this seed bank consisted of Juncus gerardi, the only common high marsh plant with high seed set. We tested the hypothesis that salt stress limits seedling contributions to marsh patch secondary succession in the field. Watering bare patches with fresh water partially alleviated patch soil salinities and dramatically increased both the emergence and survival of seedlings. Our results show that seedling recruitment by high marsh perennial turfs is limited by high soil salinities and that consequently their population dynamics are determined primarily by clonal growth processes. In contrast, populations of patch-dependent fugitive marsh plants which cannot colonize vegetatively are likely governed by spatially and temporally unpredictable windows of low salinities in bare patches.     

Effective crop structure adjustment under climate change

Choosing effective responses to the adverse impacts of climate change is a challenging issue worldwide. Crop structure adjustment is a primary strategy to effectively respond to climate change and maximize climatic resources. However, quantitative analysis of crop structure adjustment is a difficult process. This study proposes an effective evaluation method for crop structure adjustment that combines vulnerability and contribution rate assessment. Selection of prior crop with lower vulnerability, higher climate change contribution rate, and lower agricultural technology contribution rate can effectively address the adverse impacts of climate change and maximize climatic resources at a lower cost. A case study comparing spring wheat, potato and naked oat in Wuchuan County of Inner Mongolia, China determined the feasibility and practicality of this method.     

Biodiversity change under adaptive community dynamics

Compositional change is a ubiquitous response of ecological communities to environmental drivers of global change, but is often regarded as evidence of declining “biotic integrity” relative to historical baselines. Adaptive compositional change, however, is a foundational idea in evolutionary biology, whereby changes in gene frequencies within species boost population-level fitness, allowing populations to persist as the environment changes. Here, we present an analogous idea for ecological communities based on core concepts of fitness and selection. Changes in community composition (i.e., frequencies of genetic differences among species) in response to environmental change should normally increase the average fitnessof community members. We refer to compositional changes that improve the functional match, or “fit,” between organisms' traits and their environment as adaptive community dynamics. Environmental change (e.g., land-use change) commonly reduces the fit between antecedent communities and new environments. Subsequent change in community composition in response to environmental changes, however, should normally increase community-level fit, as the success of at least some constituent species increases. We argue that adaptive community dynamics are likely to improve or maintain ecosystem function (e.g., by maintaining productivity). Adaptive community responses may simultaneously produce some changes that are considered societally desirable (e.g., increased carbon storage) and others that are undesirable (e.g., declines of certain species), just as evolutionary responses within species may be deemed desirable (e.g., evolutionary rescue of an endangered species) or undesirable (e.g., enhanced virulence of an agricultural pest). When assessing possible management interventions, it is important to distinguish between drivers of environmental change (e.g., undesired climate warming) and adaptive community responses, which may generate some desirable outcomes. Efforts to facilitate, accept, or resist ecological change require separate consideration of drivers and responses, and may highlight the need to reconsider preferences for historical baseline communities over communities that are better adapted to the new conditions.     

Nutrient relations in calcareous grassland under elevated CO2

Plant nutrient responses to 4 years of CO₂ enrichment were investigated in situ in calcareous grassland. Beginning in year 2, plant aboveground C:N ratios were increased by 9% to 22% at elevated CO₂ (P < 0.01), depending on year. Total amounts of N removed in biomass harvests during the first 4 years were not affected by elevated CO₂ (19.9 ± 1.3 and 21.1 ± 1.3 g N m⁻² at ambient and elevated CO₂), indicating that the observed plant biomass increases were solely attained by dilution of nutrients. Total aboveground P and tissue N:P ratios also were not altered by CO₂ enrichment (12.5 ± 2 g N g⁻¹ P in both treatments). In contrast to non-legumes (>98% of community aboveground biomass), legume C/N was not reduced at elevated CO₂ and legume N:P was slightly increased. We attribute the less reduced N concentration in legumes at elevated CO₂ to the fact that virtually all legume N originated from symbiotic N₂ fixation (%N_dfa ≈ 90%), and thus legume growth was not limited by soil N. While total plant N was not affected by elevated CO₂, microbial N pools increased by +18% under CO₂ enrichment (P = 0.04) and plant available soil N decreased. Hence, there was a net increase in the overall biotic N pool, largely due increases in the microbial N pool. In order to assess the effects of legumes for ecosystem CO₂ responses and to estimate the degree to which plant growth was P-limited, two greenhouse experiments were conducted, using firstly undisturbed grassland monoliths from the field site, and secondly designed `microcosm' communities on natural soil. Half the microcosms were planted with legumes and half were planted without. Both monoliths and microcosms were exposed to elevated CO₂ and P fertilization in a factored design. After two seasons, plant N pools in both unfertilized monoliths and microcosm communities were unaffected by CO₂ enrichment, similar to what was found in the field. However, when P was added total plant N pools increased at elevated CO₂. This community-level effect originated almost solely from legume stimulation. The results suggest a complex interaction between atmospheric CO₂ concentrations, N and P supply. Overall ecosystem productivity is N-limited, whereas CO₂ effects on legume growth and their N₂ fixation are limited by P. Received: 12 July 1997 / Accepted: 15 April 1998     

Effects of vegetation canopy and climate on seedling establishment in Mediterranean shrubland

Abstract. Question: Does the influence of plant canopy on seedling establishment interact with climate conditions, and particularly, do intensified drought conditions, enhance a positive effect of the vegetation canopy on seedlings in Mediterranean‐type ecosystems. Location: Mediterranean shrubland near Barcelona, Spain at 210 m a.s.l. Methods: Over the course of four years we recorded seedling emergence and survival in open areas and below vegetation under control, drier and warmer experimental climatic conditions. Results: Seedling emergence is more sensitive to climate conditions than later stages of growth. When considering the whole set of species, the total number of established seedlings at the end of the experiment was lower in the drought and warming stands than in control ones, and vegetation canopy increased the number of these seedlings in the drought stands. Drought reduced seedling emergence but not warming, while the interaction between climate treatments and vegetation canopy was not significant. Seedling survival was lower in the warming treatment than in the control. Under drought conditions, vegetation canopy increased seedling emergence of the dominant Globularia alypum. In control stands, vegetation canopy reduced their survival. Vegetation canopy increased the survival of the dominant Erica multiflora in warming stands, and it reduced the survival of G alypum in drought stands. No significant effects of drought and warming were observed in the seed rain of these two species. Conclusions: The balance of the facilitation‐competition interactions between vegetation canopy and seedling establishment in Mediterranean‐type ecosystems determined by water availability, and drought conditions enhance the positive effect of vegetation canopy. This interaction is species‐specific and shows important between‐year variability.     

Positive relationship between fruit removal by animals and seedling recruitment in a tropical forest

Fleshy-fruited plants rely on animal frugivores to disperse their seeds, and seed removal by frugivores may leave an imprint on seedling recruitment. However, to what extent plant–frugivore interactions are related to seedling recruitment has rarely been quantified at the community level, especially in species-rich tropical forests. In this study, we tested the effect of different plant traits on fruit removal by frugivores and tested the relative importance of fruit removal, plant traits and abiotic factors for seedling recruitment. We quantified plant–frugivore interactions of 22 fleshy-fruited plant species consumed by 56 diurnal frugivore species, and counted the number of seedlings that emerged along an elevational gradient in the Colombian Andes. We measured a set of plant traits (i.e., crop size; fruit size; seed load and mass; fruit nutritional contents), estimated the density of adult plants and recorded relevant abiotic factors (light, temperature and humidity). We found that fruit removal by frugivores was positively associated with crop size, but negatively associated with fruit length and unrelated to seed load and fruit nutritional content. Seedling densities were positively related to the density of adult plants, seed mass and fruit removal by animals. We found no relationship between abiotic factors and seedling recruitment. Our results indicate that fruit abundance and morphology are important determinants of fruit removal and that fruit removal is positively associated with seedling recruitment accounting for effects of species abundance and plant traits. We conclude that plant traits shape fruit removal and seedling recruitment at the community level, while these two crucial processes of forest regeneration are directly linked by seed dispersal of animals.     

Seed–litter–position drives seedling establishment in grassland species under recurrent drought

Changes in land use and climate interfere with grassland ecosystem processes. Here I experimentally investigated the combined effects of land‐use change related litter cover and contrasting water supply on seedling emergence. In this context, the role of the initial relative position of seeds, i.e. seeds on top of the litter versus seeds beneath the litter in interaction with water supply has not been investigated so far. I hypothesised that facilitative effects of litter on seedling emergence occur when seeds are covered by litter and deteriorate when litter covers the ground and seeds fall on it (seeds on top of the litter). Further, I hypothesised that the importance of seed position for seedling emergence will increase under conditions of recurrent drought. I performed a controlled pot experiment on seedling emergence of three common European grassland species (Pimpinella saxifraga, Leontodon autumnalis, Sanguisorba officinalis) by experimental manipulations of litter and water availability. Seedling emergence under moist conditions showed no significant differences between each litter position compared to the control across species. In contrast, under recurrent drought, seedling emergence was significantly higher below the litter compared to seeds on top of the litter and the control (i.e. no litter). In abandoned land, seedling emergence may be limited when seeds fall on ground‐covering litter. In contrast, in grasslands with regular low‐intensity land use, seedling emergence may be enhanced when a moderate level of litter covers seeds at the end of the growing season. Protective mechanisms that occur with seeds positioned beneath litter are particularly important under recurrent drought.     

Implications of climate warming on seedling emergence and mortality of African savanna woody plants

Seedling emergence from scarified seeds and mortality of different seedling cohorts of five African savanna woody species (Acacia polyacantha, A. sieberana, Bauhinia thonningii, Dichrostachys cinerea and Ziziphus abyssinica) were studied under field conditions at a site in central Zambia. The study was conducted over a 4-year period, from 2003 to 2007. The objectives of the study were to determine climate factors that significantly influence seedling emergence rate and mortality in order to assess likely responses of the studied species to a warmer climate. Mean seedling emergence rate was 12% in D. cinerea and Z. abyssinica, 17% in B. thonningii, 47% in A. poyacantha and 62% in A. sieberana. Climate factors did not significantly affect seedling emergence in A. sieberana while temperature significantly influenced seedling emergence rate in the other species. Under a 1° warmer climate, seedling emergence rate was predicted to decline in A. polyacantha, B. thonningii and Z. abysssinica but is likely to increase slightly in D. cinerea. Time of seedling emergence during the wet season did not appear to affect seedling survival. Temperature also significantly influenced seedling mortality in all the studied species such that under a warmer climate, mortality was predicted to increase in A. sieberana and D. cinerea but decrease in A. polyacantha, B. thonningii and Z. abyssinica. As the studied species exhibited differential optimum temperature conditions for seedling emergence and seedling survival, they are likely to respond to climate warming in different but predictable ways. The results of the study are useful to forest management and development of climate change adaptation strategies in southern Africa.     

Surrogate species protection in Bolivia under climate and land cover change scenarios

The Amazon rainforest covers more than 60% of Bolivia’s lowlands, providing habitat for many endemic and threatened species. Bolivia has the highest rates of deforestation of the Amazon biome, which degrades and fragments species habitat. Anthropogenic habitat changes could be exacerbated by climate change, and therefore, developing relevant strategies for biodiversity protection under global change scenarios is a necessary step in conservation planning.In this research we used multi-species umbrella concept to evaluate the degree of habitat impacts due to climate and land cover change in Bolivia. We used species distribution modeling to map three focal species (Jaguar, Lowland Tapir and Lesser Anteater) and assessed current protected area network effectiveness under future climate and land cover change scenarios for 2050.The studied focal species will lose between 70% and 83% of their ranges under future climate and land-cover change scenarios, decreasing the level of protection to 10% of their original ranges. Existing protected area network should be reconsidered to maintain current and future biodiversity habitats.     

Terrestrial gastropods and experimental climate change: A field study in a calcareous grassland

The impact of field manipulations of local climate on terrestrial gastropod populations and how they may affect the dynamics of the plant community were studied in a calcareous grassland. The experimental site was located in a grassland at the Wytham estate, Oxfordshire, UK. Manipulations representing two climate change scenarios in a factorial combination were used, these were warmer winters with increased summer rainfall, and warmer winters with summer drought. The climate manipulations had a significant effect on the relative abundance of molluscs. However, no important changes in species composition were found. Distribution and densities of snails and slugs were affected because of changes in the physical environment and the vegetation in the grassland. The responses of different species to the climate manipulations were strongly influenced by their phenological traits and food preferences. Potential responses of mollusc populations to a changing climate are discussed.     

Identifying drivers of species compositional change in a semi‐natural upland grassland over a 40‐year period

Question: Few long‐term studies exist with integrated vegetation and soil composition data, coupled with detailed environmental driver records. Can changes in community composition in an upland grassland be identified by revisitation after a 40‐year period and allow the main environmental drivers of change to be identified? Location: Snowdon, Wales, UK. Methods: Changes in plant community and soil composition were assessed by resurveying an upland Agrostis–Festuca grassland in 2008, 40 years after the original survey. PCA and ecological indicators were used to determine changes in plant community composition. Redundancy analysis (RDA) allowed the impact of soil chemical composition on the vegetation community to be assessed. Results: A significant shift in community composition was found between years. A 35% reduction in species richness and an increase in the grass:forb ratio, suggest significant ecosystem degradation. Indicator values suggest acidification of the community with an increased acidity preference of species recorded in 2008. However, soil pH measurements showed that soil pH had increased. RDA suggested that the main shifts in species composition were correlated with an increase in pH and a reduction in soil exchangeable base cation concentration. Clear ecosystem responses to climate, land‐use change or nitrogen enrichment were not observed. Conclusions: Shifts in vegetation and soil composition are clearly identifiable after 40 years. The shifts in community composition are consistent with ecosystem degradation due to acidification during the period between surveys. Ecological indicator values and soil chemical composition displayed differing degrees of change. Whilst soils appear to be recovering from historic effects of sulphur deposition, vegetation community composition changes appear to lag behind those in soil chemistry.     

Mid-season gas exchange of an alpine grassland under elevated CO2

Ecosystem net CO₂ uptake, evapotranspiration (ET) and night-time CO₂ efflux were measured in an alpine grassland dominated by Carex curvula, treated with doubled ambient partial pressure of CO₂ via open-top chambers. One quarter of the plots were treated with mineral nutrients to simulate the effect of lowland nitrogen deposition rates. Depending upon fertilizer supply, ecosystem net CO₂ uptake per ground area in full sunlight (NCE_max) was 41–81% higher in open-top chambers supplied with doubled ambient partial pressure (p _a) of CO₂ than in plots receiving ambient CO₂. Short-term reversals of the CO₂ level suggest that the extent of downward adjustment of canopy photosynthesis under elevated CO₂ was 30–40%. ET tended to decline, while water use efficiency (WUE), expressed as the NCE_max:ET ratio, increased more than twofold under elevated CO₂. Night-time ecosystem CO₂ efflux did not respond to changes in CO₂ p _a. NCE_max and night-time CO₂ efflux were more responsive to mineral fertilizer than the doubling of CO₂. This suggests that in these alpine plant communities, atmospheric nutrient input may induce equal or greater effects on gas exchange than increased CO₂.