Woodland Plants Research Articles

Managing intensive and extensive land uses to conserve grassland plants in sub-tropical eucalypt woodlands

We sampled grasslands at 108 sites, representing five combinations of soil disturbance and enrichment that occurred in eucalypt grassy woodlands in eastern Australia. Intensive land use was represented as a combination of cultivation and fertilizer addition. Other disturbances were represented as various combinations of moderate or no soil disturbance and water enrichment or no enrichment. We identified disturbance response groups that were broadly summarized as Generalists, Tolerant species, Specialists and Intolerant species. The exotic component of the grasslands differs from the native in that there were more Intolerant species amongst natives and more Disturbance Specialist species amongst exotics. However, there were strong similarities, with the majority of exotics (66%) and of natives (60%) being either Generalists or Disturbance Tolerators. The evidence from this study suggests that significant expansion of intensive land use in the district, combining cultivation and fertilization, would pose a major threat to grassland vegetation and would threaten 69 of the 121 native species analysed.

Vegetation of the Tembe Elephant Park, Maputaland, South Africa

A hierarchical classification, vegetation map, description and ecological interpretation of the plant communities of the Tembe Elephant Park and surrounding areas are presented. The study area falls within the Maputaland Centre of Endemism, which is part of the Maputaland-Pondoland Region, a centre of plant diversity rich in endemic plants and animals. Sixty-four sample plots were distributed in a stratified manner throughout the study area. A TWINSPAN classification, refined by Braun-Blanquet procedures, revealed eight distinct, mainly woodland plant communities. Much of the vegetation distribution can be ascribed to vegetation dynamics and the geomorphological evolution of the region. Dynamics of water in the landscape either directly or indirectly, through its role in moisture levels and soil formation, plays a role in the determination of plant communities at the higher levels. The proposed classification and general descriptions can be used for nature reserve management, land-use planning and further research. Ordinations based on floristic data give an indication of floristic and associated habitat and environmental relationships. Soil character and moisture differences are usually slight, hence the sand-based communities do not have distinct boundaries, except for Sand Forest. Indications are that in the case of Sand Forest the distinct boundary zone of nearly bare soil may well be the result of allelopathy Eighty-four Maputaland Centre plant endemics/near-endemics were recorded for the study area, with Sand Forest being the most prolific habitat for such taxa, many which appear to be neoendemics. Because of its hypothesised origin (especially lack of specific historic events) and vegetation dynamics, the inclusion of Sand Forest in conservation areas is no guarantee of the future persistence of this rare vegetation type.

Darwin's Naturalization Hypothesis Revisited

In The Origin of Species, Darwin (1859) drew attention to observations by Alphonse de Candolle (1855) that floras gain by naturalization far more species belonging to new genera than species belonging to native genera. Darwin (1859, p. 86) goes on to give a specific example: “In the last edition of Dr. Asa Gray’s ‘Manual of the Flora of the United States’ ... out of the 162 naturalised genera, no less than 100 genera are not there indigenous.” Darwin used these data to support his theory of intense competition between congeners, described only a few pages earlier: “As the species of the same genus usually have, though by no means invariably, much similarity in habits and constitution, and always in structure, the struggle will generally be more severe between them” (1859, p. 60). Darwin’s intriguing observations have recently attracted renewed interest, as comprehensive lists of naturalized plants have become available for various regions of the world. Two studies (Mack 1996; Rejmanek 1996, 1998) have concluded that naturalized floras provide some support for Darwin’s hypothesis, but only one of these studies used statistical tests. Analyses of additional floras are needed to test the generality of Darwin’s naturalization hypothesis. Mack (1996) tabulated data from six regional floras within the United States and noted that naturalized species more often belong to alien genera than native genera, with the curious exception of one region (New York). In addition to the possibility of strong competition between native and introduced congeners, Mack (1996) proposed that specialist native herbivores, or pathogens, may be

A method for estimating changes in the visibility of land cover

An inventory of resources that includes the contribution made by land cover to the visual landscape can be used in monitoring and assessing the impacts of change in land cover on the visual landscape of an area. A method is presented for assessing the visual resources of the landscape as applied to a case study area in the western part of the proposed Cairngorm National Park in Scotland. The method is based upon measuring the extent of the land from which different land cover types may be visible, on a cell-by-cell basis, using high resolution Digital Elevation Models combined with interpreted land cover data as inputs. The results show a reduction in the overall contribution of scattered, natural woodland to the visual landscape, and an increase in the visual contribution of plantation woodland at the expense of heather moorland. The geographical distribution of the changes in visibility of land cover types is shown and the potential of the method for providing a spatial context for expressing the results of landscape preference modelling is discussed.

Relationships Between Climate and Flowering of Eight Herbs in a Swedish Deciduous Forest

Effects of annual variation in rainfall, temperature and humidity on flowering abundance of eight temperate woodland plants (Anemone nemorosa, Cardamine bulbifera, Lamiastrum galeobdolon,Oxalis acetosella , Ranunculus ficaria, Stellaria holostea, Viola reichenbachiana and Viola riviniana) were studied during 12 consecutive years (1989–2000) in a hornbeam (Carpinus betulus) forest in southeast Sweden. Above-average rainfall/humidity in late summer to early autumn of the preceding year increased flowering abundance in L. galeobdolon, O. acetosella, V. reichenbachiana, V. riviniana and, especially, in R. ficaria, but not in S. holostea and A. nemorosa. Moreover, flowering of R. ficaria and O. acetosella was positively related to rainfall/humidity during several parts of, or the entire, preceding year. On the contrary, flowering of S. holostea and A. nemorosa was closely related to low values of rainfall/humidity in autumn and/or winter of the preceding year and also to low humidity in the current year in A. nemorosa. Two long periods (3–4 years) of increasing rainfall deficit coincided with decreasing flowering abundance in most of the species, but not with decreasing vegetative development. Temperature variability was less consistently related to flowering. A cool period during the preceding summer or autumn seemed important for flowering in L. galeobdolon, O. acetosella and the Viola species, although these relations were, at least partly, caused by interactions with rainfall/humidity. No significant (P<0.05) correlations were found between flowering and the conditions prevailing in April to May—the main flowering season—of the current year.

Developing an ecosystem perspective from experimental monitoring programs: II. Ecophysiological responses of a rare geothermal grass to soil water.

Measurements of xylem water potential, leaf conductance, and leaf pressure-volume characteristics on the geothermal endemic Dichanthelium lanuginosum var. thermale (DILA) were used to delineate operational ranges during wet and dry years and among several microsites at Little Geysers, Sonoma County, California, USA. Plants seldom experienced water potentials more negative that -1.5 MPa. Other nongeothermal, widespread species experienced the lower water potentials typical of chaparral and woodland plants. DILA was able to effectively utilize geothermal water while the widespread species could not and was able to keep stomata open during most of the year. There was evidence to suggest that DILA had some ability to acclimate with significant shifts in Pio and psio during the dry 1994 summer, especially in the upland microhabitat. Nevertheless, minimum leaf turgor values in the upland came very close to, or dropped below, the 0.2-0.3 MPa threshold thought necessary to maintain stomatal opening and photosynthesis. DILA thus depends upon the unique water status of fumarole soils in the vicinity of the Little Geysers to persist in an otherwise lethal regional mosaic of climate, soil, and vegetation. The physiological data were used to derive reference ranges for subsequent monitoring of DILA at Little Geysers. Such ranges are required to determine the future impact, if any, of geothermal development on the persistence of this rare grass and its complex ecosystem.

Center Parcs UK: leisure development which achieves biodiversity gains

There is a growing consensus that land management for nature conservation in the UK must move from being a negative, essentially protectionist, activity to being a positive, creative, managerial one. Maintaining and enhancing biodiversity is the driving force for both statutory and voluntary nature conservation organisations. Leisure development is often associated with a change of land use to a 'less natural' environment, which threatens nature conservation interests. However, this does not have to be the case. Environmental assessments for some leisure developments which involve large areas of land, including areas marginal to the main focus of recreational activity, have suggested, at the planning stage, that such developments can result in environmental improvements. This paper examines the three Center Parcs UK Holiday Villages established in coniferous woodland plantations and illustrates the biodiversity gains, which can be achieved. Careful site selection, environmentally sensitive design and construction, and management regimes that foster target species and habitats are important. Ecological monitoring is vital both to quantify and substantiate biodiversity gains and to raise awareness and confirm expectations.

Hedgerows as habitat for woodland plants

For hedgerows to act as corridors for woodland plants they must provide habitat conditions to suit species’ autecological requirements. This supposition was tested by examining differences in the habitat and autecological characteristics of woodland plants according to their relative frequency in hedgerows and woodlands using a novel Habitat Preference Index (HPI). Indicator values for habitat and autecological characteristics of plant species were derived from Ellenberg and other published sources. Analyses were done separately for three main types of landscape in which hedgerows are found in Britain: (1) Lowland Arable; (2) Lowland Pastural; and (3) Marginal Upland. The relative frequency of plant species across all three landscape types was similar and significant differences between HPIs and environmental indicators were found for all three landscape types. Plants more frequently found in hedgerows had significantly higher indicator scores for soil fertility, temperature, continentality together with reduced soil acidity, in comparison to those species more frequent in woodlands. Analyses of autecological indicators failed to show similar consistent trends across landscape types except for the number of woodland types of the National Vegetation Classification (NVC) in which species occur. Plants more frequently found in hedgerows were associated with fewer woodland communities suggesting that hedgerows contain only a narrow range of recognised woodland NVC stand types. Also, a significantly higher proportion of ancient woodland indicators were found in the group of plants that were more frequent in woodlands. Overall, results suggested that the environments of hedgerows are more similar to woodland edges than interiors. Qualitative differences between the environmental characteristics of hedgerows and woodlands are such that certain woodland plant species are highly likely to be limited in their capacity to use hedgerow networks. Implications for conservation of biodiversity are considered.

Interactions by vascular plants and birds between isolated ancient oak–hazel woods and a matrix of conifer plantations

Ecosystem interactions were considered for the interface between ancient and rare woodland habitats in Sweden and surrounding extensive conifer plantations. Vascular plant and bird distributions were examined in the centres and edges of the woodlands, in adjoining conifer forest and in random locations within the conifer forest. Plant species abundances did not usually vary within woodlands but many woodland plants had settled in the nearby conifer forest. Birds, instead, moved from conifer forest to woodland areas, particularly into small woodland areas. Multivariate analyses confirmed the different directions of movement of the two taxa between the adjoining ecosystems. The reason appears to be opportunistic and extensive resource capture by mobile organisms and temporary use of a particular resource, viz. empty ground or substrate, by sedentary organisms. Such interplay with adjoining ecosystems emphasises the need for conservation of large woodland sites and conservation of suitable landscapes with remnant woodlands and surrounding grasslands.

Edge structures and edge effects on plants and birds in ancient oak-hazel woodlands

Structural differences between centres and edges of ancient oak-hazel woodlands within a conifer forest matrix were established and significant differences were related to the occurrence and abundance of vascular plants and birds. The edges did not demonstrate any higher abundance of dead trees, fallen limbs or branches or stumps. However, edges kept a higher proportion of young deciduous trees. The frequencies of invading plant species from the conifer forest were negatively, and of total bird species positively, related to the proportion of large old trees in the edges. Total number of plant species, woodland plants, or breeding pairs of birds were not clearly related to the proportion of old trees. Light-excluding bushes and young trees may favour conifer forest plants adapted to a similar dark environment. Old trees may provide more niches for temporary exploitation by mobile birds. Thus, the more rapid tree regeneration at forest edges should be circumvented by selection of large reserves, suitable juxtaposition of similar habitat types or by management particularly directed against excessive tree regeneration.

Stable isotopes in ecosystem science: structure, function and dynamics of a subtropical Savanna.

Stable isotopes are often utilized as intrinsic tracers to study the effects of human land uses on the structural and functional characteristics of ecosystems. Here, we illustrate how stable isotopes of H, C, and O have been utilized to document changes in ecosystem structure and function using a case study from a subtropical savanna ecosystem. Specifically, we demonstrate that: (1) delta 13C values of soil organic carbon record a vegetation change in this ecosystem from C4 grassland to C3 woodland during the past 40-120 years, and (2) delta 2H and delta 18O of plant and soil water reveal changes in ecosystem hydrology that accompanied this grassland-to-woodland transition. In the Rio Grande Plains of North America, delta 13C values of plants and soils indicate that areas now dominated by C3 subtropical thorn woodland were once C4 grasslands. delta 13C values of current organic matter inputs from wooded landscape elements in this region are characteristic of C3 plants (-28 to -25/1000), while those of the associated soil organic carbon are higher and range from -20 to -15/1000. Approximately 50-90% of soil carbon beneath the present C3 woodlands is derived from C4 grasses. A strong memory of the C4 grasslands that once dominated this region is retained by delta 13C values of organic carbon associated with fine and coarse clay fractions. When delta 13C values are evaluated in conjunction with 14C measurements of that same soil carbon, it appears that grassland-to-woodland conversion occurred largely within the past 40-120 years, coincident with the intensification of livestock grazing and reductions in fire frequency. These conclusions substantiate those based on demographic characteristics of the dominant tree species, historical aerial photography, and accounts of early settlers and explores. Concurrent changes in soil delta 13C values and organic carbon content over the past 90 years also indicate that wooded landscape elements are behaving as sinks for atmospheric CO2 by sequestering carbon derived from both the previous C4 grassland and the present C3 woody vegetation. Present day woodlands have hydrologic characteristics fundamentally different from those of the original grasslands. Compared to plants in remnant grasslands, tree and shrub species in the woodlands are rooted more deeply and have significantly greater root biomass and density than grasslands. delta 18O and delta 2H values of plant and soil water confirm that grassland species acquire soil water primarily from the upper 0.5 m of the soil profile. In contrast, trees and shrubs utilize soil water from throughout the upper 4 m of the profile. Thus, soil water that formerly may have infiltrated beyond the reach of the grassland roots and contributed to local groundwater recharge or other hydrologic fluxes may now be captured and transpired by the recently formed woodland plant communities. The natural abundances of stable isotopes revealed fundamental information regarding the impacts of human land use activities on the structure and function of this subtropical savanna. Stable isotopes provided direct, spatially explicit evidence for dramatic changes in ecosystem physiognomy and demonstrated some functional consequences for the hydrologic cycle. Furthermore, grassland-to-woodland conversion has been geographically extensive in the worlds' drylands, suggesting that these ecosystem-level changes in vegetation structure, carbon cycling, and hydrology may have implications for regional/global biogeochemistry and climate.

Progressive plant invasion and colonization of an area adjacent to ancient woodland at Edford Wood, Somerset, England

Edford Wood, near Holcombe in Somerset, England has a rich and varied flora. Topography and species composition indicate that much of the woodland is of ancient origin. The history of the site is complex, with the woodland long subjected to considerable human disturbance from surface mining of coal, drainage and the felling of larger trees. Documentary and other evidence has revealed that part of the wood has developed from grassland during the present century. This area of secondary woodland illustrates processes of succession as woodland plants invade.

Recent landscape change and landscape restoration in Northern Ireland; a tephra-dated pollen study

Tephra-dated palynological investigations of lowland peats which have accumulated over the last millennium, provide an excellent means of tracing recent landscape change. Pollen analytical investigations of lowland raised bogs in the northern and western counties of the province show past regional variations. At one extreme northern lowland site, the landscape has remained relatively unchanged over much of the last millennium, while in the western county agricultural expansion linked to the rise of the great estates in the 18th century is observed. These findings provide those concerned with conservation and landscape restoration with information on which to base woodland planting.

Progressive plant invasion and colonization of an area adjacent to ancient woodland at Edford Wood, Somerset, England

Edford Wood, near Holcombe in Somerset, England has a rich and varied flora. Topography and species composition indicate that much of the woodland is of ancient origin. The history of the site is complex, with the woodland long subjected to considerable human disturbance from surface mining of coal, drainage and the felling of larger trees. Documentary and other evidence has revealed that part of the wood has developed from grassland during the present century. This area of secondary woodland illustrates processes of succession as woodland plants invade.

Migration of vascular plants to secondary woodlands in southern Sweden

1 We studied the migration of field layer plants across ecotones between ancient woodlands and recent deciduous woods on former arable land varying in age between 30 and 75 years. 2 Number and percentage cover of woodland species in recent woods decreased with increasing distance to the ancient woods, and increased with the age of the recent woods, indicating dispersal limitation during secondary succession. 3 Colonization by typical woodland plants was observed in 183 of 200 species × site combinations. In 72 combinations, a colonization front was characterized by logarithmic or linear decrease in species cover, indicating establishment of isolated individuals and gradual infill of gaps. This pattern was most common in ant‐dispersed species and less frequent in species with adhesive or ingested seeds. 4 Migration rates were calculated for 49 woodland species. Mean migration rates based on maximum cover in recent woods varied from 0.00 to 1.00 m year−1 between species, with a median migration rate of 0.30 m year−1. Migration rates calculated on occurrence of the farthest individual ranged from 0.00 to 1.25 m year−1, with a median rate of 0.53 m year−1. 5 Ant‐dispersed species had lower migration rates based on maximum cover compared with species with adhesive or ingested seeds. No differences between dispersal modes were found when comparing migration rates based on the farthest individuals. Most of the calculated migration rates (84%) exceeded the rate of possible vegetative spread of woodland species. 6 Establishment of a field layer vegetation in secondary woods comparable to that of the adjacent ancient stands proceeded at a rate of c. 0.3–0.5 m year−1. We conclude that scale and intensity of temperate forest management should be adjusted to the relatively slow migration of the field layer flora in order to enable complete recovery during a management cycle.

Effects of livestock exclusion on the ground flora and regeneration of an upland Alnus glutinosa woodland

Summary Vegetation composition and tree regeneration were compared between grazing exclosures and unfenced areas of an hillside alder (Alnus glutinosa) woodland, at Coedydd Aber, North Wales. Sheep and ponies have had unrestricted access to the unfenced woodland throughout the 20 years since the exclosures were erected. The exclosures had a well developed field layer with significantly higher cover of plant litter, dead wood, bryophytes and woodland species; the unfenced woodland had a sparse field layer and significantly higher cover of bare soil, grasses and wet pasture species. These changes appear to be a consequence of the removal of both herbivory and physical disturbance caused by large herbivores. Tree regeneration from seed was virtually absent from the unfenced areas, and no alder regeneration was recorded in the woodland study plots. The exclosures contained high densities of young ash (Fraxinus excelsior), and it is possible that, in the long term, ash will replace alder as the dominant tree in these stands.

On the Relationship between Shade Tolerance and Shade Avoidance Strategies in Woodland Plants

Decreasing light availability with time is one of the primary factors that drives autogenic succession in woodland communities. In many successions, the pattern of species replacement appears to be largely a consequence of a negative correlation across species between adaptation to high irradiance and adaptation to low irradiance (Bazzaz 1979, Oliver and Larson 1990, Kobe et al. 1995). The mechanistic basis for this negative correlation can be explained with respect to at least two distinct fitness components: 1) the maximization of light interception and 2) the maximization of net carbon fixation per unit leaf protein (Givnish 1988). A plant grown under high irradiance can maximize light interception through a highly branched, bushy growth form (Steingraeber et al. 1979, Shukla and Ramakrishnan 1986). Maximum net carbon fixation under high irradiance is achieved through sun-adapted leaf physiology (Bj6rkman 1981). In contrast, for a plant grown under low irradiance, light interception is maximized through strong vertical growth (King 1990), and net carbon fixation is maximized through shadeadapted leaf physiology (Bjdrkman 1981). The term has long been used to describe the suite of leaf-level traits that afford maximal net carbon fixation under low irradiance. Less commonly, the analogous term has been used to describe the suite of architectural traits that contribute to strong vertical growth in plants grown under low irradiance (Grime 1966, Smith 1986, 1994). Although many components of shade tolerance and shade avoidance have been studied along light gradients, the relationship between these strategies has received very little theoretical and empirical attention (Kuppers 1994). Do they represent alternative adaptations to light limitation with patterns of covariance that reflect tradeoffs through life history or phylogenetic constraints (Smith 1986)? Alternatively, are the distributions across taxa, of shade avoidance and shade tolerance, independent of each other? In this paper, we briefly review the mechanistic basis of shade tolerance and shade avoidance to illustrate that both of these strategies can be expected to impose costs (trade-offs) to a plant in terms of reduced relative growth rate under high irradiance (Fig. 1). By interpreting these costs in the context of different selection regimes within vegetation, we arrive at the prediction that shade tolerance and shade avoidance strategies should be generally negatively correlated along light gradients.

Stomatal density responses of temperate woodland plants over the past seven decades of CO2 increase: a comparison of Salisbury (1927) with contemporary data

We investigated the possible effect of recent (1927-1995) increases in the concentration of atmospheric CO2 on the stomatal densities of leaves of a wide range of tree, shrub, and herb species (N = 60) by making new measurements for comparison with corresponding data reported by E. J. Salisbury in 1927--a time when ice core studies indicate CO2 concentrations ~55 mL/L lower than present. A detailed intraspecific study of the herb Mercurialis perennis showed plants of M. perennis in a Cambridgeshire woodland in 1994 had significantly lower stomatal densities, irrespective of leaf insertion point, compared with their 1927 counterparts. Comparisons made across species using evolutionary comparative methods (independent contrasts) revealed a significant (P 2 increases have influenced leaf morphology in a manner consistent with recent experiments and the palaeoecological record. Further analyses suggested that the strength of the stomatal density response was independent of life form but dependent on "exposure" and the initial leaf stomatal density. Consequently, firmer predictions for future changes in stomatal density across all species, expected as a possible result of anthropogenically related CO2 increases, may now be possible.

Effects of soil extracts from repeated plantation woodland of Chinese-fir on microbial activities and soil nitrogen mineralization dynamics

Effects of soil extracts from repeated plantation woodlands of Chinese-fir on soil fungi growth, the activities of microbial communities, and rates of net soil nitrogen mineralization were investigated. Soil extracts from replanted woodlands significantly inhibited soil non-pathogenic fungi growth, reduced soil respiration activities, and net soil nitrogen mineralization rates. However, soil extracts from replanted woodland increased the growth of pathogenic fungi. The combination of soil extracts and pathogenic fungi did not significantly reduce the growth of Chinese-fir seedlings when compared to the soil extracts alone. The combination of soil extracts with pathogenic and non-pathogenic fungi significantly increased the growth of Chinese-fir seedlings when compared to the combination of soil extracts and pathogenic fungi. The results suggest that the allelochemicals from soil extracts, rather than pathogenic fungi, are the key factor regulating the productivity and nitrogen cycling in repeated plantation woodlands.

Fencerow and forest edge architecture in eastern Ontario farmland

In landscapes of fragmented forest, fencerows and similar linear patches of vegetation may provide movement corridors for woodland plants if they connect matching habitats. This will be expected where fencerow architecture has developed as a structural or functional extension of woodland, and thus offers low resistance to plant movement. A comparison was made of several architectural components of fencerows and forest edges to determine whether fencerows extend forest remnants structurally into the surrounding agricultural matrix. Horizontal foliage density and foliage profile diversity were greater in fencerows than in forest edges. Main contributors to the difference detected between edge types were greater frequencies of vines, trees and grasses in fencerows. Large trees were clustered at fencerow centres, but showed a polynodal distribution across forest edges. In fencerows, greater tree stem diameter and stem and branch frequencies resulted in infrequent and smaller sub-canopy gaps there relative to those in forest edges. Several individual elements (shrub density, the size and condition of coarse woody debris, rock size) were not detectably different between edge types, but the combination of these elements contributed to significantly greater architectural diversity in fencerows. The spatial distribution of architectural elements across edge widths indicated qualitative differences between edge types. It is concluded that habitat qualities that result from the architectural differences between fencerows and forest edges may constrain plant movement along fencerow corridors between isolated forest patches.