Local Vegetation Composition Research Articles

Seasonal biogenic volatile organic compound emission factors in temperate tree species: Implications for emission estimation and ozone formation

Variability in biogenic volatile organic compound (BVOC) emissions across species and seasons poses challenges for accurate regional emission estimates and effective ozone (O3) control policies. To address this issue, we conducted in-situ measurements of emission factors for six dominant tree species in Beijing across four seasons. Subsequently, we developed monthly dynamic standard emission factors (SER-MDs) to model monthly BVOC emissions and their impacts on O3 formation at citywide and district levels. Our observations revealed pronounced seasonal differences in the BVOC composition and emission rates, as well as their responsiveness to monthly average temperature. By introducing the SER-MDs, we estimated BVOC emissions from the dominant tree species in Beijing to be 38.2 Gg yr−1, with monoterpenes and isoprene contributing 49% and 11%, respectively. This calculation reduced the overestimation associated with constant standard emission factors by 31%–38% at district level. The estimates also revealed regional differences in plant compositions rather than simple feedback from regional temperature and photosynthetically active radiation periods. Under these conditions, the maximum monthly BVOC-induced O3 concentration occurred in August and ranged from 4 to 17 μg m−3 across districts, with isoprene being the dominant contributor. Quercus mongolica and Populus tomentosa played significant roles in the formation of BVOC-induced O3 due to their strong isoprene emitting potential in July–August. These results indicate the necessity of introducing species-specific rhythms of BVOC emissions from dominant species in the development of urban BVOC emission inventories. This approach could inform the development of air pollution management policies that are consistent with the local vegetation composition and O3 pollution characteristics. For Beijing and other similar northern cities, reducing the use of tree species emitting substantial amounts of isoprene during periods of regional peak ambient O3 concentrations could constitute an effective nature-based solution for improving urban air quality in the future.

Modelling the ecological impact of invasive weed Verbesina encelioides on vegetation composition across dryland ecosystems of Punjab, northwestern India.

Events of climate change have led to increased aridification, which alters local vegetation patterns and results in the invasion of opportunistic species. Though many studies assess the impact of invasive weeds and aridification at the agronomic level, studies investigating changes in local vegetation are severely lacking. We investigated the impact of the invasive plant Verbesina encelioides (Asteraceae) on the local vegetation composition across different dryland ecosystems in Punjab, northwestern India. Based on the aridity index for the period of 1991-2016, three major dryland ecosystems, i.e., arid, semi-arid, and sub-humid, were found in Punjab. The impact of V. encelioides on local biodiversity was measured in terms of species diversity (using Shannon's diversity index, Simpson's dominance index, Hill's evenness index, and Margalef's richness index), species composition (using non-metric multidimensional scaling based on Bray-Curtis's dissimilarity index), and species proportion in the two invasion classes (uninvadedandinvaded) and across the three aridity zones (arid, semi-arid, and sub-humid). The vegetation survey depicted the presence of 53 flowering species belonging to 22 families, including 30 exotics and 23 natives. Verbesina encelioides decreased species diversity and proportion, with a more pronounced impact in arid and semi-arid ecosystems. In contrast, species composition varied between uninvaded and invaded classes only in arid ecosystems. Ecological parameters derived from population statistics (number of individuals) were more drastically affected than those from species abundance data. Since the ecological impacts of V. encelioides were manifested with increased aridification, it is a matter of apprehension under the potential climate change scenario.

Perennial woodlands benefit parasitoid diversity, but annual flowering fallows enhance parasitism of wheat aphids in an agricultural landscape

Agriculture intensification poses serious threats to natural enemy biodiversity and associated ecological services. The conservation or reestablishment of semi-natural habitats is used to counteract negative effects of agriculture intensification on natural enemies. Understanding specific functions of different habitats for natural enemies from a landscape perspective is an important step needed for the development of sustainable agriculture. Here, focusing on parasitoids of wheat aphids, we examined effects of the proportion and connectivity of two main semi-natural habitats (woodlands and fallows) present in landscapes, measured within circular buffer radii of 0.5, 1.0, 1.5, and 2.0 km around sampling sites, on parasitoid (mummy) density, biodiversity (Shannon diversity) and associated services (parasitism rate) in 35 wheat fields. We also compared local vegetation communities of these two semi-natural habitats to test whether plant characteristics can shed light on the potential mechanisms driving parasitoids responses to different landscape habitats. We found that the parasitoid diversity was much higher in landscapes dominated by woodlands, while fallows in the landscape promoted parasitoid density and parasitism. Woodlands connectivity at larger scales (such as 1.5 or 2.0 km) displayed positive effects on parasitoid activities, fallows connectivity at the smaller scale (0.5 km) had a positive effect on the hyperparasitism rate. In terms of vegetation characteristics, fallows provided more flowering plants and floral resources, while woodlands suffered less disturbance across years. Local vegetation composition of the semi-natural habitats indeed help explain their different effects on parasitoids at larger landscape scales. We suggested that future research should investigate the role of different types of semi-natural habitats. Conservation management should combine different habitats, such as perennial and annual habitats, to promote the functional complementarity for beneficial organisms. Based on results from local vegetation survey, we also suggested native flowering plants such as Capsella bursa-pastoris L., Lagopsis supina Steph., and Calystegia hederacea Wall. in fallows could be used as functional plants to conserve wheat aphid parasitoids.

Investigation of factors affecting surface pollen assemblages in the Balikun Basin, central Asia: Implications for palaeoenvironmental reconstructions

To interpret pollen assemblages in terms of past vegetation, it is important to consider the source of pollen for any given lake profile containing sufficient pollen, and the way it arrives at its preservation site. It is of value to know the proportion of the pollen assemblage derived from the lake catchment and that which was airborne. This has been a long-neglected issue for lakes from arid areas of central Asia. In this study, we used two modified Cour (M-Cour) traps in different biomes (steppe and desert) to collect airborne pollen in the enclosed Balikun Basin during the non-flowering season (late autumn to early winter). The pollen assemblages from the traps are similar with large proportions of herbaceous and (sub-)shrub taxa such as Artemisia and Chenopodioideae. This implies a shared long-distance transport component, in addition to pollen derived from the local vegetation. These xeromorphic species are ubiquitous in the inland desert and/or steppe areas beyond the lake basin, and their pollen is likely to be carried by the wind into lake sediments from a broad area, leading to high percentages of Artemisia and Chenopodioideae pollen in lake surface-sediments. Pollen types from upstream areas (e.g. Picea, Cyperaceae, Leguminosae) are barely found in samples from the river mouth and lake surface-sediments. Thus, we speculate that the transport of pollen by inflow streams makes little contribution to the overall pollen budget in Balikun Lake. This is probably related to the low transport capacity of the surface runoff into the lake, as precipitation is low and there is limited meltwater from snow and glaciers in the surrounding mountains. Pollen assemblages from the near-shore lakebed, which have a high percentage of Chenopodioideae pollen (74.8%), represent only the very local environment, reflecting the expansion of saline-alkali habitats rather than desert. Sedimentary archives from the near-shore lakebed will thus overestimate the desert Chenopodioideae pollen component and hence cause unreliable vegetation or climate reconstructions. We also found the local vegetation composition and pollen depositional processes could significantly bias the ratio of Artemisia/Chenopodioideae (A/C), reducing its effectiveness as an index to distinguish steppe from desert. We suggest using A/C ratios from lake surface-sediments which have a large airborne pollen source area in arid areas, as a better reference for down-core fossil pollen.

New insights into island vegetation composition and species diversity-Consistent and conditional responses across contrasting insular habitats at the plot-scale.

Most island-ecology studies focus on the properties of entire island communities, thus neglecting species-environment relationships operating at the habitat-level. Habitat-specific variation in the strength and sign of these relationships will conceal patterns observed on the island scale and may preclude a mechanistic interpretation of patterns and processes. Habitat-specific species-environment relationships may also depend on the descriptor of ecological communities. This paper presents a comprehensive plot-based analysis of local vegetation composition and species diversity (species richness and species evenness) of (i) rocky shore, (ii) semi-natural grassland and (iii) coniferous forest habitats in three Baltic archipelagos in Sweden. To identify differences and consistencies between habitats and descriptors, we assessed the relative contributions of the variable-sets “region”, “topography”, “soil morphology”, “soil fertility”, “soil water”, “light availability”, “distance” and “island configuration” on local vegetation composition, species richness and species evenness. We quantified the impact of “management history” on the descriptors of local grassland communities by a newly introduced grazing history index (GHI). Unlike species diversity, changes in vegetation composition were related to most of the variable-sets. The relative contributions of the variable-sets were mostly habitat-specific and strongly contingent on the descriptor involved. Within each habitat, richness and evenness were only partly affected by the same variable-sets, and if so, their relative contribution varied between diversity proxies. Across all habitats, soil variable-sets showed highly consistent effects on vegetation composition and species diversity and contributed most to the variance explained. GHI was a powerful predictor, explaining high proportions of variation in all three descriptors of grassland species communities. The proportion of unexplained variance was habitat-specific, possibly reflecting a community maturity gradient. Our results reveal that species richness alone is an incomplete representation of local species diversity. Finally, we stress the need of including habitat-based approaches when analyzing complex species-environment relationships on islands.

Heterogeneous vegetation sensitivity at local and regional scales: Implications for pollen-based climate reconstruction

Vegetation–climate relationships are often different at varying spatial scales, which is seldom taken into account in reconstructing past climate changes from fossil pollen spectra represent more local vegetation composition but using regional or extra-regional modern pollen–climate calibration set. In this paper, we employ 2620 surface pollen spectra and six pollen sequences from continental East Asia to reconstruct Holocene climate with modern analogue technique. A novel data set of vegetation sensitivity index (VSI) is introduced to examine vegetation–climate relationships in 0.5° search windows around the fossil sites (local) and in the tailored calibration sets (regional). Then, we compare them to the explanatory abilities of (reconstructed) climate variables on explaining the pollen variance in calibration sets and in the fossil pollen data sets using constrained ordination, cross-validation and significance test. By this procedure that we called local–regional–fossil comparison, we can better determine which variable reconstruction is valid and useful. In our cases, moisture variable reconstructions in temperate forest-steppe ecotone at the East Asian summer monsoon margin are reliable. Consistent Holocene moisture variations with a strong monsoon influence during 8.6–4.0 cal ka BP which can help us to better interpret human adaptations along the Great Wall. However, quantitative climate reconstructions at some sites are less reliable due to highly heterogeneous vegetation sensitivities surrounding the site, particularly for areas with complicated topographical contexts. We stress that vegetation sensitivities at local and regional scales both need to be investigated before conducting quantitative climate reconstruction.

Drivers of peat accumulation rate in a raised bog: impact of drainage, climate, and local vegetation composition

Drivers of peat accumulation rate in a raised bog: impact of drainage, climate, and local vegetation composition

A 12,000 year record of changes in herbivore niche separation and palaeoclimate (Wonderwerk Cave, South Africa)

The large mammalian fauna of southern Africa is characterised by strong niche separation into grazer and browser species, with few falling into the intermediate mixed-feeder niche. Moreover, the modern fauna is reduced in species diversity compared to the Pleistocene, following the extinction of several specialized grazers in the late Pleistocene and early Holocene. How did this state develop, and how might it be connected to climatic change during the Holocene? To better understand this development, we obtained extensive carbon and oxygen stable light isotope data from herbivore tooth enamel samples from Wonderwerk Cave, South Africa, spanning about 12,000–500 cal. BP. This is a unique dataset since it is the only site in the southern Kalahari with a robust chronometric record and well-preserved faunal remains for the last 12,000 years without significant gaps. Combining the stable isotopes with pollen and micromammal data from Wonderwerk Cave, we have explored shifts in the proportions of C3 and C4 plants and moisture availability. Although climate remained generally semi-arid for much of this period, the results show significant hydrological and vegetation shifts in the sequence, particularly with the strengthening of summer rainfall in the mid-Holocene. The results for the sixteen herbivore species reveal a reinforcement of the grazer-browser niche partitioning through the Holocene and shows how niche specialization follows changes in local vegetation composition. In the light of this reconstruction of the local ecology we discuss grazer extinctions, human adaptations, and the drivers behind climatic changes in the summer rainfall zone of southern Africa.

Present‐day and future contribution of climate and fires to vegetation composition in the boreal forest of China

AbstractClimate is well known as an important determinant of biogeography. Although climate is directly important for vegetation composition in the boreal forests, these ecosystems are strongly sensitive to an indirect effect of climate via fire disturbance. However, the driving balance of fire disturbance and climate on composition is poorly understood. In this study, we quantitatively analyzed their individual contributions for the boreal forests of the Heilongjiang Province, China, and their response to climate change using four warming scenarios (+1.5°, 2°, 3°, and 4°C). This study employs the statistical methods of Redundancy Analysis (RDA) and variation partitioning combined with simulation results from a SErgey VERsion Dynamic Global Vegetation Model (SEVER‐DGVM), and remote sensing datasets of global land cover (GLC2000) and the third version of Global Fire Emissions Database (GFED3). Results show that the vegetation distribution for the present day is mainly determined directly by climate (35%) rather than fire (1–10.9%). However, with a future global warming of 1.5°C, local vegetation composition will be determined by fires rather than climate (36.3% > 29.3%). Above 1.5°C warming, temperature will be more important than fires in regulating vegetation distribution although other factors such as precipitation can also contribute. The spatial pattern in vegetation composition over the region, as evaluated by Moran's Eigenvector Map (MEM), has a significant impact on local vegetation coverage; for example, composition at any individual location is highly related to that in its neighborhood. It represents the largest contribution to vegetation distribution in all scenarios, but will not change the driving balance between climate and fires. Our results are highly relevant for forest and wildfires' management.

Dental mesowear reflects local vegetation and niche separation in Pleistocene proboscideans from Britain

ABSTRACTProboscideans, and elephants in particular, played a key role in Pleistocene mammal communities in Europe. The British Pleistocene fossil record provides a unique opportunity to study changes in proboscidean feeding ecology associated with environmental proxy data such as pollen records and the presence of competitors. Here we utilize a recently introduced dietary analysis method, mesowear angle analysis, for studying relationships between dietary variation in proboscideans, changes in available vegetation and the presence of sympatric proboscidean species. The method is based on recording the relief of worn molar surfaces as angle measurements, which reflect attrition‐ vs. abrasion‐dominated feeding and serve as a proxy for grazing vs. browsing diets. By comparison with pollen records, we show that blunt mesowear angles specifically reflect grass eating rather than open‐ground feeding in general. We further find that all British Pleistocene proboscidean species were relatively flexible feeders able to shift their dietary preference according to local vegetation composition. Nonetheless, when more than one proboscidean species occurred in the same environment, they always show significantly different mean mesowear signal, suggesting dietary niche separation.

Leaf wax n-alkane distributions in Chinese loess since the Last Glacial Maximum and implications for paleoclimate

Leaf wax n-alkanes have been recently introduced into loess deposits for paleovegetation and paleoclimate reconstruction. However, the paleoclimate significance of some n-alkane parameters such as chain-length ratios (L/H, C27/C31, C29/C31, and (C27+C29)/(C31+C33)) remains to be clarified. In order to evaluate the validity of those proxies in loess deposits, leaf wax n-alkanes were analyzed from a northwest-southeast transect on the Chinese Loess Plateau since the Last Glacial Maximum (LGM). The n-alkanes show a bimodal distribution between C14 and C33 with Carbon number maxima (Cmax) at C14 or C16, and at C31 or C33, indicative of both terrestrial plant and microbial origin. L/H variations are in good agreement with climate changes both temporally and spatially, i.e. the higher L/H ratio the warmer and wetter climate and vice versa. Therefore, the L/H ratio in Chinese loess can serve as an efficient proxy for paleoclimate. By comparing long-chain n-alkane ratios with pollen records, we suggest that the generally used woody plant proxies (C27 and C29) and grass proxies (C31 and C33) are not applicable to Chinese loess. As the Chinese Loess Plateau was dominated by herbs in both the LGM and the Holocene, the long-chain n-alkane ratios may mainly reflect changes in the species composition of local vegetation. For a better understanding of leaf wax n-alkanes in Chinese loess, further studies are required to investigate the n-alkane distributions in both the major plant species and their associated surface soils on the Chinese Loess Plateau.

Carbon isotope signatures from land snail shells: Implications for palaeovegetation reconstruction in the eastern Mediterranean

In this study we compare carbon isotope values in modern Helix melanostoma shell carbonate (δ13Cshell) from the Gebel al-Akhdar region of Libya with carbon isotope values in H. melanostoma body tissue (δ13Cbody), local vegetation (δ13Cplant) and soil (δ13Csoil). All vegetation in the study area followed the C3 photosynthetic pathway. However, the δ13Cplant values of different species formed two distinct isotopic groups. This can be best explained by different water use efficiencies with arid adapted species having significantly more positive δ13Cplant values than less water efficient species. The ranges and means of δ13Cbody and δ13Cplant were statistically indistinguishable from one another suggesting that δ13Cbody was primarily a function of local vegetation composition. H. melanostoma δ13Cshell reflected the δ13Cplant of local vegetation with a positive offset between body/diet and shell of 14.5 ± 1.4‰. Therefore, in the Gebel al-Akhdar where only C3 plants are present, higher mean δ13Cshell values likely reflect greater abundances of water-efficient C3 plants in the snails diet and therefore in the landscape, whilst lower mean δ13Cshell values likely reflect the consumption of less water-efficient C3 plants. The distribution of these plants is in turn affected by environmental factors such as rainfall. These findings can be applied to archaeological and geological shell deposits to reconstruct late Pleistocene to Holocene vegetation change in the southeast Mediterranean.

A charcoal record of Holocene woodland succession from sandstone rock shelters of North Bohemia (Czech Republic)

Archaeological excavations at North-Bohemian sandstone rock shelters have uncovered complex evidence of intermittent human presence since the Late Palaeolithic to recent times. In this paper, we investigate the history of Holocene woodlands based on charcoal assemblages from stratified sandy accumulations under archaeologically investigated rock shelters. In total, we carried out anthracological analyses of eight profiles excavated under rock shelters.Our study shows that the number of charcoal taxa correlated with local environmental diversity around the rock shelters. Charcoals of Pinus sylvestris were abundant in all the profiles analysed. Profiles in bottom parts of valleys recorded a higher abundance of broadleaf tree charcoal. The abundance of oak gradually decreased from the Bronze Age onwards, as oak got replaced by pine, and locally beech, fir and spruce. Today, several of the recorded woody species are rare or even absent in the sandstone region under study.We focused on comparing anthracological results with results of pollen analyses carried out in the same areas. Our results demonstrate that when results from different types of archives are compared, it is possible to gain a more differentiated insight into local vegetation composition. This may carry wide methodological implications.

Preliminary environmental historical results to reconstruct prehistoric human-environmental interactions in Eastern Hungary

AbstractPalaeoenvironmental research is playing an important role in recent archaeological investigations. We present preliminary results of geoarchaeological analyses conducted at a palaeochannel located between two prehistoric archaeological sites in eastern Hungary. The study area lies within the Körös River Basin in Békés County, a region of intensive human occupation beginning in the Neolithic, ca. 7550 BP, and represents only the second palynological analysis done in conjunction with archaeological investigations and adjacent to an archaeological site in the Körös region. Pollen from an environmental monolith was used to reconstruct the local vegetation composition and the human impact on arboreal and non-arboreal vegetation near the archaeological sites. Sediment analyses helped to reconstruct hydrological activity and human impact on the local palaeochannel. Results indicate that activity from the Neolithic onwards played an important role in local environmental change, including increasing sedimentation and deposition of organic matter in the local waterway, some forest clearance and a shift from primarily arboreal vegetation to more grasses on elevated surfaces. The trophic status of the local channel changed several times during the Holocene. In addition, indications that groundwater levels may have been fluctuating during the period of human occupation, when combined with the other changes in the area, provide a possible partial explanation for changing settlement patterns.

Bird abundance and diversity across a hardwood gradient within early seral plantation forest

The extensive removal of competing broadleaved shrubs in forest plantations typically results in structural and compositional simplification of early seral habitat. However, information on the tradeoffs between such intensive forestry practices and biodiversity is scant. Here we assess the magnitude and direction of potential impacts of intensive forest management on populations of early seral-associated breeding birds. Observed population declines of several Neotropical migrant bird species are hypothesized to be linked to the loss of early seral habitat on the breeding grounds. We investigated the association between broadleaved hardwood cover and avian abundance and diversity in intensively managed early seral Douglas-fir ( Pseudotsuga menziesii) stands of the Pacific Northwest. Bird species richness decreased across an elevational gradient, but did not vary as a function of either local vegetation composition or structure. In contrast, bird abundance was strongly associated with hardwood cover at local and landscape scales, especially for foliage-gleaning species. We found strong support for the existence of a threshold in relative bird abundance as a function of hardwood at the stand scale; abundance doubled with an increase from 1% to ∼6% hardwood and then reached a plateau. Though abundance of leaf-gleaners increased even more strongly across a gradient in hardwood cover, evidence for a distinct threshold was less clear. We conclude that when early seral hardwood forest is scarce, even small increases in hardwood may provide substantial conservation benefits. However, for some species (i.e., foliage gleaners), there may be more direct trade-offs in abundance and juvenile recruitment with hardwood management intensity.

Experimental test of the impacts of feral hogs on forest dynamics and processes in the southeastern US

The foraging activities of nonindigenous feral hogs (Sus scrofa) create widespread, conspicuous soil disturbances. Hogs may impact forest regeneration dynamics through both direct effects, such as consumption of seeds, or indirectly via changes in disturbance frequency or intensity. Because they incorporate litter and live plant material into the soil, hogs may also influence ground cover and soil nutrient concentrations. We investigated the impacts of exotic feral hogs in a mixed pine-hardwood forest in the Big Thicket National Preserve (Texas, USA) where they are abundant. We established sixteen 10m×10m plots and fenced eight of them to exclude feral hogs for 7 years. Excluding hogs increased the diversity of woody plants in the understory. Large seeded (>250mg) species known to be preferred forage of feral hogs all responded positively to hog exclusion, thus consumption of Carya (hickory nuts), Quercus (acorns), and Nyssa seeds (tupelo) by hogs may be causing this pattern. The only exotic woody species, Sapium sebiferum (Chinese tallow tree), was more than twice as abundant with hogs present, perhaps as a response to increased disturbance. Hogs increased the amount of bare soil by decreasing the amounts of plant cover and surface litter. Plots with hogs present had lower soil C:N, possibly due to accelerated rates of nitrogen mineralization. These results demonstrate that hogs may influence future overstory composition and reduce tree diversity in this forest. Management of hogs may be desirable in this and other forests where large-seeded species are an important component of the ecosystem. Further, by accelerating litter breakdown and elevating nitrogen in the soil, hogs have the potential to impact local vegetation composition via nitrogen inputs as well.

COMPARISON OF POLLEN AND STOMATA IN LATE-GLACIAL AND EARLY-HOLOCENE LAKE SEDIMENTS FROM EASTERN MASSACHUSETTS

The analysis of stomata in lake-sediment cores is increasingly used as a paleoecological tool. Stomata are less likely than pollen grains to be dispersed over long distances, and thus stomate records supplement and enhance interpretations based on pollen data by providing information about patterns and composition of local vegetation (e.g., Froyd 2005; Hansen 1995; Parshall 1999; Pisaric et al. 2000, 2003; Yu 1997). Stomata have been analyzed in modern and fossil sediments in many regions, oftentimes to gain a better understanding of past changes in the position of boreal treeline (e.g., Clayden et al. 1996, 1997; Gervais and MacDonald 2001; Gervais et al. 2002; Hansen et al. 1996; Leitner and Gajewski 2004; Pisaric et al. 2001). We have conducted the first study of this type in New England, analyzing conifer stomata in the late-glacial and early-Holocene sediments of Berry Pond, Massachusetts. Compar ison of the stomate record with pollen data tests the ability of both approaches to reflect the history of vegetation at the study site.

Theory of quantitative reconstruction of vegetation II: all you need is LOVE

This paper describes the LOVE (LOcal Vegetation Estimates) model for estimating local vegetation composition within the relevant source area of pollen. This model quantifies and then subtracts background pollen (ie, pollen coming from beyond the relevant source area) in order to arrive at a quantitative reconstruction of local vegetation. Parameters required for LOVE applications are pollen counts from target sites, the relevant source area of pollen of these sites, pollen productivity estimates and regional vegetation composition within 104 -105 km2. Regional vegetation composition is obtained using fossil pollen from large sites (≥102 ha) with the REVEALS (Regional Estimates of VEgetation Abundance from Large Sites) model, the first step of the Landscape Reconstruction Algorithm (LRA) specifically designed for LOVE applications. POLLSCAPE simulations demonstrate that (1) regional vegetation composition can be used to predict background pollen at and beyond the relevant source area of pollen for given-sized basins, (2) LOVE with the LRA framework provides a robust and accurate estimate of local vegetation composition much better than vegetation reconstruction using pollen percentages alone and (3) although the relevant source area of pollen is difficult to estimate particularly in past landscapes, a proposed method using backward modelling of LOVE is effective to estimate the relevant source area in landscapes of unknown vegetation patchiness and heterogeneity. Thus, the LRA will also be useful to estimate indirectly changes in spatial structure of past vegetation and landscape caused by natural and anthropogenic forcing.

Breeding bird communities in the upland margins (ffridd) of Wales in the mid-1980s

Capsule The bird communities in the Welsh marginal uplands were frequently distinct from those of adjacent habitats and consisted of heterogeneous mixtures of species strongly influenced by vegetation composition and land-use. Aims To provide a unique description of the influence of vegetation, altitude and regional position on the bird communities of upland margins and to create a baseline against which future changes in these communities may be assessed. Methods Survey data collected at 120 sites in 1985–87 were used to identify broad relationships between habitat and bird communities. This was complemented by habitat descriptions made at exact locations occupied by individual birds. Results Bird communities in Bracken-dominated sites, especially those with relatively high numbers of scattered trees and bushes, held more species than sites dominated by grassland and other moorland vegetation. Relationships between species and habitat were broadly consistent at both the scale of whole sites and the scale of patches occupied by individual birds. Abundance of scattered trees and bushes was important for a diverse range of passerines; extent of Gorse Ulex spp. scrub was important for several species. Geographical location and topography appeared to have secondary effects on bird communities relative to those of vegetation composition. Conclusions The Welsh marginal uplands hold diverse bird communities, strongly affected by local vegetation composition and usually different from those of adjacent moorland, woodland and farmland. Tree Pipit Anthus trivialis, Whinchat Saxicola rubetra, Linnet Carduelis cannabina and Yellowhammer Emberiza citrinella were among the species likely to be more abundant in the upland margins than in adjacent habitats. There is a need to assess whether these communities have changed since the mid-1980s, especially in relation to high sheep grazing pressure. However, agricultural abandonment of marginal areas may occur in the future which could eventually reduce habitat availability for several bird species and reduce avian diversity in the Welsh uplands.

A model of wetland vegetation dynamics in simulated beaver impoundments

Beavers alter environments to provide food and habitat necessary to support themselves, and consequently have a significant effect on vegetation structure at both the local and landscape scale. I constructed a simulation model of allogenic wetland vegetation succession as an initial step in exploring important factors affecting vegetation trends for areas disturbed by beaver impoundment. The model is based on general relationships of basic community life history traits, and how each responds to hydrologic disturbance. Vegetation succession takes place within the framework of a hypothetical beaver pond, characterized by a seasonally fluctuating hydrologic regime and periodic flood disturbance. A submodel of sediment accumulation is also included. Model results are consistent with past studies of beaver wetland change, which indicate that beaver impoundment may have long-lasting effects on local vegetation composition. Sensitivity analysis indicates that the model is particularly sensitive to outside seed sources. Based on the results of the model, parameters requiring additional quantification include local seed sources within riparian river drainages, and both growth and mortality functions for wetland vegetation elevated above the water table.