High Grazing Intensity Research Articles

Conditioning cattle to graze broom snakeweed (Gutierrezia sarothrae).

Broom snakeweed (Gutierrezia sarothrae) is the most widespread range weed in North America. We attempted to positively condition cattle to graze broom snakeweed to create a biological tool to decrease the competitive ability of snakeweed in a plant community. Fifteen yearling heifers were divided into three treatment groups receiving different supplements: 1) cornstarch, 2) starch with ground snakeweed, and 3) a control (no supplements). Heifers were fed fresh snakeweed, and then were gavaged with the respective supplements to provide positive feedback to enhance their acceptance of snakeweed. The starch group consumed more snakeweed in the pen conditioning trial (P = 0.02). The starch and control groups were then taken to the field for two grazing trials. In the spring grazing trial, there was no snakeweed consumed in the free-ranging part of the trial; however, when the pasture size was decreased, the heifers started to consume snakeweed as alternative forages became less abundant. In the second small pasture trial, heifers in the positively conditioned group consumed more snake-weed than those in the control group (16 vs. 5% of bites, P < 0.001). In the fall grazing trial, little snakeweed was consumed in the free-ranging part of the trial. When the pasture size was decreased, both positively conditioned and control groups increased snakeweed consumption up to 35% of bites. In the small pastures of both the spring and fall grazing trials, 36 to 59% of snakeweed plants were grazed. Cattle can be forced to graze snake-weed in a short-duration, high-intensity grazing strategy.

Performance of cultivated perennial grass mixtures under different grazing intensities in the alpine region of the Qinghai‐Tibetan Plateau

AbstractIn 1998, seeds of four cultivated native perennial grasses, Bromus inermis (B), Clinelymus nutans (C), Elymus nutans (E) and Agropyron cristatum (A), were sown as mixtures with different seed rates in three combinations (B + C, B + E + A and B + E + C + A) in a field study in the north‐eastern part of the Qinghai‐Tibetan Plateau, China. A grazing experiment was conducted in 2000 to investigate the performance of these grass mixtures at leaf, plant and sward scales under different grazing intensities (GI). Four GIs, expressed as the proportion of herbage consumed by Tibetan lambs in relation to the available biomass (IP), were applied in the summer: no grazing, and 0·30, 0·50 and 0·70 of IP. Tiller numbers of the grasses increased and leaf photosynthetic rate, sward leaf area index (LAI) and herbage mass declined with increase in GI. No effect of GI on specific leaf area was observed. Interactions between GI and grass mixtures on the dynamics of species composition, swards’ LAI and herbage mass were found. Large fluctuations in species composition with different GIs showed the poor species compatibility and sward persistence of these grass mixtures under high GI by sheep.

Long-term management impacts on soil carbon and nitrogen dynamics of grazed bermudagrass pastures

Managed pastures have potential for C and N sequestration in addition to providing forage for livestock. Our objectives were to investigate changes in soil organic C (SOC) and soil organic N (SON) concentrations and mineralizable C and N in cattle (Bos indicus) grazed bermudagrass [Cynodon dactylon (L.) Pers.] pastures up to 32 y after establishment. Management included low- and high-grazing intensity, fertilization, and winter overseeding with annual ryegrass (Lolium multiflorum Lam.) and clover (Trifolium sp.). Soil (0–15cm) was sampled 7, 15, 26, and 32 y after establishment of Coastal and common bermudagrass pastures. No significant differences in SOC or SON concentrations were observed between Coastal and common bermudagrass pastures. Grazing strategies played important roles in C and N sequestration, as high-grazing intensity resulted in a lower increase in SOC and SON concentrations over time compared to low-grazing intensity. Increases in SOC were observed up to 26 y, while increases in SON were observed up to 32 y after establishment of bermudagrass pastures. Soil organic C increased 67 and 39% from 7 to 26 y at low-grazing intensity for bermudagrass+ryegrass and bermudagrass+clover pastures, respectively. SOC and SON concentrations did not increase beyond 15 y after bermudagrass establishment at high-grazing intensity. An exception was the Coastal bermudagrass+ryegrass pastures, which exhibited higher SON at 32 y than at 7 y at both grazing intensities. By 32 y, SON increased 83 and 45% in Coastal bermudagrass+ryegrass pastures at low- and high-grazing intensity, respectively, compared to 7 y. The introduction of clover to pastures decreased SOC and SON relative to ryegrass at high- but not at low-grazing intensity. Potentially mineralizable C increased from 7 to 15 y, while mineralizable N increased from 7 to 32 y. Potentially mineralizable N was also greater for bermudagrass+clover than bermudagrass+ryegrass pastures. Long-term increases in SOC and SON concentrations suggest that managed and grazed pastures have strong potential for C and N sequestration.

Responses of Leymus chinensis (Poaceae) to long‐term grazing disturbance in the Songnen grasslands of north‐eastern China

AbstractA field study was conducted to test the responses of Leymus chinensis to long‐term grazing disturbance on a native grassland in the Songnen plain, north‐eastern China. Six grazing intensities were examined using thirty random sample plots in each. Components of biomass, and shoot and tiller densities of L. chinensis decreased significantly (P &lt; 0·05) with increased grazing intensity, especially at the extremely high grazing intensity. Conversely, the proportion of the total biomass as rhizomes increased considerably with increased grazing intensity, and peaked on the extremely high grazing treatment (at 0·91 of the total biomass). Shoot and tiller densities, and the proportion of the total biomass as rhizomes were strongly negatively correlated with soil organic matter content and soil moisture content and negatively correlated with soil pH and soil bulk density along the grazing gradient, indicating that the responses of L. chinensis to the canopy removal by long‐term grazing are likely to have influenced changes in the soil.

Changes in population biology of two succulent shrubs along a grazing gradient

Summary Heavy livestock grazing in Namaqualand, South Africa, is threatening the region's unique diversity of succulent shrubs. This is especially true in the communally managed lands, where grazing is centred around fixed enclosures (stockposts) in which animals stay overnight. In this study we set out to determine the effects of a semi‐permanent stockpost on the composition of the surrounding vegetation and the mechanisms by which grazing limits the persistence of leaf‐succulent shrub populations. We used the grazing gradient created by a stockpost to examine the impacts of grazing on vegetation composition and changes in mortality, reproductive output and seedling establishment for the leaf‐succulent species Ruschia robusta and Cheiridopsis denticulata. Vegetation composition was found to change from a community dominated by the unpalatable shrub Galenia africana at high grazing intensities to a community dominated by the palatable leaf‐succulent shrub R. robusta at lower grazing intensities. Mortality of the leaf‐succulents R. robusta and C. denticulata was high at the sites closest to the stockpost, while fruit production and seedling germination were substantially reduced over distances of 800 m and 2 km for the two species, respectively. Seedling establishment was not limited by either grazing or microsite availability. Thus reduction in reproductive output is the greatest impact of heavy grazing on these two species. Synthesis and applications. This study demonstrates that marked zonation in vegetation composition and population biology can develop around a fixed stockpost and that the greatest impact of grazing on the two leaf‐succulent species studied is the suppression of flower and fruit production. Consistent suppression of reproductive output could have long‐term consequences for the persistence of succulent shrub populations in the heavily grazed communal lands of Namaqualand. We recommend that (i) herders should be encouraged to relocate their stockposts regularly to prevent the development of centres of degradation, and (ii) areas should be relieved periodically of all grazing pressure to allow for successful seed set of native shrubs.

Effects of grazing on soil seed bank dynamics: An approach with functional groups

Abstract. The relationship between intensity and timing of cattle grazing on changes in the size and composition of the soil seed bank were investigated in a 3‐yr study in a Mediterranean grassland in northeastern Israel. Treatments included manipulations of stocking rates and of grazing regimes, in a factorial design.The retrieved soil seed bank community was rich in species, with 133 species accounting for 80% of the 166 species recorded at the site. Within the seed bank, 89% of the species were annuals. Seed bank dynamics was analysed in terms of plant functional groups and germination strategies. In terms of total seed bank density and including all functional groups, 42% of the seeds present in the soil did not germinate under watering conditions. The dormancy level differed greatly among functional groups. The seed bank of annual legumes, crucifers, annual thistles and annual forbs had a large fraction of non‐germinated seeds and characterized areas grazed early in the growing season under high and very high grazing intensity. These functional groups were considered to have a higher potential for persistent seed banks production. In contrast, short and tall annual grasses and tall perennial grasses, that were dominant in ungrazed or moderately grazed paddocks, generally had seed banks with a very small fraction of non‐germinated seeds. Seed bank densities varied widely between grazing treatments and years. Under continuous grazing, heavy grazing pressure reduced seed bank densities of grasses and crucifers in comparison to moderate grazing. The greatest reduction on the seed bank densities resulted from heavy grazing concentrated during the seed‐set stages.

Effects of grazing on soil seed bank dynamics: An approach with functional groups

Abstract. The relationship between intensity and timing of cattle grazing on changes in the size and composition of the soil seed bank were investigated in a 3-yr study in a Mediterranean grassland in northeastern Israel. Treatments included manipulations of stocking rates and of grazing regimes, in a factorial design. The retrieved soil seed bank community was rich in species, with 133 species accounting for 80% of the 166 species recorded at the site. Within the seed bank, 89% of the species were annuals. Seed bank dynamics was analysed in terms of plant functional groups and germination strategies. In terms of total seed bank density and including all functional groups, 42% of the seeds present in the soil did not germinate under watering conditions. The dormancy level differed greatly among functional groups. The seed bank of annual legumes, crucifers, annual thistles and annual forbs had a large fraction of non-germinated seeds and characterized areas grazed early in the growing season under high and very high grazing intensity. These functional groups were considered to have a higher potential for persistent seed banks production. In contrast, short and tall annual grasses and tall perennial grasses, that were dominant in ungrazed or moderately grazed paddocks, generally had seed banks with a very small fraction of non-germinated seeds. Seed bank densities varied widely between grazing treatments and years. Under continuous grazing, heavy grazing pressure reduced seed bank densities of grasses and crucifers in comparison to moderate grazing. The greatest reduction on the seed bank densities resulted from heavy grazing concentrated during the seed-set stages.

Species richness of annual legumes in relation to grazing in Mediterranean vegetation in northern Israel

Species richness of annual legumes in step-point transects was analyzed for 79 pairs of grazed and ungrazed sites of Mediterranean vegetation in northern Israel. Seventy-eight species of annual legumes belonging to 17 genera were sampled. Species richness of all annual legumes of Medicago and Trifolium was significantly greater, by 25-42%, on the grazed compared to the ungrazed site of site-pairs. Legume richness was significantly greater on Cretaceous and Eocene sedimentary rocks compared to younger Neogene and Pleistocene sediments, with intermediate richness on basalt. It was significantly lower in sites with 400-500 mm rainfall compared to 500-900 mm, and in wetland compared to grassland, shrubland, and woodland. Species richness of annual legumes, Medicago and Trifolium, increased significantly from zero or low grazing intensity to high intensity. A consistent, not significant reduction of species richness was observed at extremely high grazing intensity. Many species of small annual legumes increased in cover with grazing intensity. Erect or twining species did not show this response. The tendency of increased richness of annual legumes with grazing was confirmed for subhumid Mediterranean communities, but it may be reversed at extremely high grazing intensities, or in semiarid communities grazed by sheep, and for some legume taxa. Management for in situ conservation of the entire annual legume flora in productive Mediterranean vegetation requires, in different parts of the landscape, continuation of intense grazing and relative protection from grazing.

Effects of frequent fires and grazing on stable nitrogen isotope ratios of vegetation in northern Australia

AbstractThe ratios of stable nitrogen isotopes expressed as δ15N values can indicate the openness of nitrogen cycles in ecosystems. Southwards through the Northern Territory, values of foliar δ15N in savanna trees increase as mean annual rainfall decreases from approximately 1800 mm to approximately 750 mm, with foliar δ15N thereafter decreasing toward arid central Australia. Recent literature argues that this pattern is caused by higher grazing intensity in semi‐arid savannas, but counter views have attributed the pattern more directly to variations in aridity. In this paper, grazed and ungrazed sites in a semi‐arid savanna are compared, and it is shown that grazing has a relatively small effect on the positive foliar δ15N values of grasses, but no effect on δ15N values of trees. This gives little support to the argument that variations in grazing pressure at the scale of hundreds of kilometres could result in detectable differences in the foliar δ15N values of trees. I then compare the semi‐arid savannas with mesic savannas, where fires are frequent, and with mesic rainforests, which are rarely burnt. Greater foliar δ15N values in rainforest and fire‐excluded mesic savannas than in frequently burnt savannas suggests that fire regimes affect foliar δ15N. The previously observed pattern in δ15N values along the rainfall gradient in the Northern Territory is consistent with trends in fire frequency and possible direct effects of fire, but further work is required to determine the relative impacts of aridity and fire. Within a particular rainfall regime, foliar δ15N values may indicate historical fire frequencies.

ECOLOGY OF WILD EMMER WHEAT IN MEDITERRANEAN GRASSLANDS IN GALILEE

Aaronsohn in 1909 noted that Triticum dicoccoides was found mainly in rocky habitats. Recent research in Mediterranean grasslands in Galilee supports the hypothesis that rocks served as refuges from intensive grazing. Although proximity of rocks enhances early germination of Triticum, cattle grazing intensity is the major factor determining its abundance. At high grazing intensity, it is absent or survives only among rocks. At moderate grazing intensity it is common not only near rocks. In ungrazed sites it sometimes becomes dominant, but in the long term is often suppressed by perennial grasses. Fitness of Triticum plants in intensively grazed populations was only half that of plants in ungrazed populations, mainly because of damage to maturing ears. After grass fires, Triticum cover increased in ungrazed grasslands, as the cover of perennials was reduced. In ungrazed or lightly grazed grasslands, severe reductions of Triticum populations were observed during population eruptions of the Levant vole, foll...

Spatial distribution of soil seed banks of three African savanna woody species at two contrasting sites

In southern African savannas, bush encroachment is a major problem for range managers. However, little is understood of the actual regeneration processes leading to it, and in particular the role of soil seed banks. The horizontal (between microsites) and vertical (with depth in litter and soil) distribution of soil seed banks of the microphyllous woody species, Acacia tortilis, A. nilotica and Dichrostachys cinerea (all legumes of the Mimosoideae), were quantified in an area with low intensity grazing (reserve), and a bordering cattle farm with high intensity grazing (farm). Species differed in seed bank densities between microsites and sites. Seed densities for all species were highest below parent tree canopies and decreased with distance beyond the canopy, and with soil depth. D. cinerea had the smallest seed bank associated with parent trees, particularly on the farm (8 vs. 1643 seeds/tree on the reserve), A. tortilis had the largest (6357, 31910), with A. nilotica intermediate (1789, 1906). The proportion of current (recently fallen) versus old (≥1 year old) seeds differed between species and sites. These species form at least short-term persistent seed banks with the old seeds largely representing the persistent seed bank. Seed densities in the open (inter-canopy) and those dispersed under either of the other two (non-parental) study species were much lower than those associated with parent trees. The latter were mostly found under the acacias (single-stemmed) rather than D. cinerea (multistemmed). Total seed store per parent plant increased with plant size (best fits were mostly power curves of canopy area). A large proportion of intact seeds were viable, namely 81–84% for A. tortilis, 68–77% for A. nilotica and 63–78% for D. cinerea, with no differences between sites. Viability tended to increase with depth of burial, except for A. nilotica seeds at the 3–5 cm depths on the farm. At the landscape scale there were 1.5 million and 140 000 A. tortilis seeds/ha on the reserve and farm respectively, with corresponding values of 2000 and 31 000 for D. cinerea, and 23 000 and 86 000 for A. nilotica.

Modelling the Effects of Patch Size on Vegetation Dynamics: Bracken 6 Pteridium aquilinum(L.) Kuhn9 under Grazing

Abstract A new spatial simulation model of vegetation dynamics, called ‘VegeTate’, was applied to relationships between expansion of bracken (Pteridium aquilinum(L.) Kuhn) patches and grazing. VegeTate simulates multispecies dynamics within each cell of its grid, including localized apparent competition mediated by grazing and trampling. It can be parameterized to simulate various plant communities and species, includes seasonality and uses a hexagonal grid. Dynamics of individual bracken patches in grassland, and of heathland initially containing sparse grass and bracken were simulated. Mixtures of grass and bracken formed mosaics, in which locally high grass densities were associated with low standing mass and high grazing intensity, whereas high bracken densities were associated with high standing mass and low grazing intensity. Control of bracken by grazing depended on the impact of trampling. In simulations, small bracken patches occupying one or a few cells could be controlled by grazing, but not the expansion of large patches. In a sensitivity analysis, this phenomenon was reproduced after substantial changes in parameter values and environmental conditions, suggesting that it should be observable in the field. Interaction between patch size and grazing impact strongly influenced the spatial dynamics of simulated vegetation. The size of bracken patches became bimodal, so that most of the area of bracken was within a few large patches. Both spatial and temporal vegetation dynamics became non-linear. These results are consistent with observations that some bracken patches contain several genets and some genets occupy several patches. The hexagonal grid and trampling were important factors in the simulation results.

Grazing intensity effects on weed populations in annual and perennial pasture systems

Abstract Few studies report animal grazing effects on weed populations. A study was conducted to assess weed populations in annual and perennial forage grasses grazed at various intensities by cattle over a 4-yr period. The perennial forages were Bromus inermis and Bromus riparius, and the annual forages were winter Triticosecale and a mixture of Hordeum vulgare and winter Triticosecale. With few exceptions, results from the two annual pastures could be adequately described as a group, as could the results from the two perennial pastures. The two most prevalent weed species were Capsella bursa-pastoris and Taraxacum officinale; other species encountered over the course of the study were analyzed as a group. Tillage (seedbed preparation) in the annual system supported a proliferation of annual weeds in the spring. In the perennial pasture system, a lack of tillage and spring MCPA allowed T. officinale to increase as the study progressed, especially at the highest grazing intensity. In the perennial pasture...

Plant quality and harvest in old meadows grazed by reindeer in spring

Dry matter (DM) production and nutritional quality of plants were recorded on an old meadow before, during and after it was grazed by reindeer (Rangifer tarandus tarandus; 15 reindeer ha -1 ) in the spring of 1996 and 1997 in northern Norway. Mean herbage harvest after 54 and 50 days of growth including 25 and 24 days of reindeer grazing was 1217 ± 320 kg DM ha -1 in 1996 and 2297 ± 495 kg DM ha -1 in 1997 respectively. On ungrazed old meadow, in contrast (P 0.05). Crude protein content (% of DM) was 25% early in the growing season in both 1996 and 1997. After 54 and 50 days of growth including 25 and 24 days of reindeer grazing, crude protein content was about 17% of DM in both 1996 and 1997 respectively, compared with about 12% of DM in ungrazed old meadow in both years. In 1997, crude protein content was 13.3% of DM after 50 days of growth including 7 days of reindeer grazing. The grazed and ungrazed old meadow contained about 20% (of DM) water-soluble carbohydrates throughout the summer in both years. Mean plant cell wall content in ungrazed plants harvested after about 50 days was higher (51.5 and 49.1% of DM; P > 0.05) compared with plant cell wall content in grazed meadow (49.0 and 46.4% of DM) in 1996 and 1997 respectively. In vitro dry matter digestibility (%) of herbage harvest using rumen fluid from domestic ruminants was about 10% higher (73.4 ± 0.30 and 75.7 ± 0.28) in samples from grazed meadow compared with ungrazed meadow (66.2 ± 0.93 and 65.4 ± 1.19) in 1996 and 1997 respectively. Reindeer grazing of old meadow in spring maintains the vegetation at a younger phenological stage during the growing season when compared with ungrazed meadow. Therefore grazing increased the quality of the herbage, but decreased herbage harvest under conditions of high grazing intensity.

Laboratory experiments on sequential scour/deposition and their application to the development of banded vegetation

Alternating bands of vegetation and bare soil, reported from many dryland regions, have been identified as indicators of rangeland deterioration triggered by overgrazing, cattle trampling or climatic change. Banded vegetation occurs at a range of scales and although it has been reported from a number of different environments, it is not characteristic of all degraded rangelands. It does appear particularly frequently on low angle, smooth slopes over soils of high erodibility but low permeability, where scant rainfall is sporadic or highly seasonal. It has been attributed both to wind and to water erosion, but few data on the processes active or their specific response to limiting environmental variables are available. Small-scale banded vegetation associated with small scour steps occurs on low angle alluvio-lacustrine flats surrounding Lake Baringo in semi-arid northern Kenya. In this area of strong moisture deficit, the dominant factor controlling the incidence of ground vegetation is variation in near-surface moisture storage. The regular spacing of the small-scale vegetation bands reflects preferential moisture storage in regularly-spaced sediment deposits. Field and laboratory runon and rainfall simulation experiments, previously reported, provided some data on the processes and conditions involved in formation of these deposits. This paper describes more closely-controlled laboratory rainfall simulation and runon experiments, carried out to identify the sequential scour and deposition processes involved, which are ultimately responsible for the regular variations in moisture storage capacity. These experiments, carried out in an 8.5 m long flume, show critical stream power ( Ω) conditions in sheetwash and rain-impacted sheetflow required for sequential scour/deposition as 0.020–0.025 W m −2 and between 0.043 and 0.055 W m −2, respectively. Experimental results indicate that vegetation bands at the scale observed at Baringo are consistent with development by sequential scour and deposition, caused by some combination of sheetwash, rainsplash and rainflow. The vegetation bands are composed primarily of unpalatable low herbaceous plants, dominated by Trianthema triquetra. These plants colonize or survive better on deposition zones because of better soil moisture status. The vegetation bands can therefore indicate an initial stage in vegetation recovery rather than continuing rangeland deterioration, but at Baringo further development of vegetation appears to be restricted by high grazing intensities or by allelopathy.

The impact of grazing on spatial variability of humus profile properties in a grass-encroached Scots pine ecosystem

Grazing is often used in management of grass-encroached Scots pine ( Pinus sylvestris) forests in The Netherlands, because it is thought to increase diversity of vegetation and humus profiles. To test this hypothesis, two 1 ha plots in a primary pine stand on drift sand were grazed for 7 years at high and moderate intensities. The humus profiles of these two sites and of a control site were sampled at various scales to assess changes in grass biomass, thickness of ectorganic horizons, organic matter stocks, root stocks, and pH. Whether grazed or not, site factors such as slope angle and aspect, distance to trees and parent material did not explain the spatial variability of the plots. Spatial variability could be linked to the tussock structure of the grass layer. With continued grazing, ectorganic horizons became more compact (particularly the F horizon), stocks of organic matter increased, grass biomass decreased, variances tended to decrease and ranges tended to increase. These results suggest that at the landscape scale, where much variation in grazing intensity can be expected, spatial variability of humus profile properties and thus site diversity will increase. However, grazing intensities in the experiment were far greater than those normally employed in management of grass-encroached forests. Therefore grazing will scarcely affect site diversity, unless grazing variability is enhanced by special treatments, such as temporary fencing to create locally high grazing intensities.

Carbon (13C) uptake and allocation in pasture plants following field pulse-labelling

The allocation of carbon (C) to plant roots and conversion to soil organic matter is a major determinant of the size of the terrestrial C pool in pastoral ecosystems. The aim was to quantify C allocation to roots in contrasting pastoral ecosystems. Pastures on long-term research sites in Canterbury, New Zealand were pulse-labelled using 13CO2 within portable gas-tight enclosures. Sites included Winchmore (with or without superphosphate fertiliser, and with or without irrigation) and Tara Hills (low, medium or high grazing intensity with continuous or alternating grazing). Separate micro-plots were labelled in late spring, summer and autumn at Winchmore and in spring at Tara Hills. Herbage label 13C recoveries were greatest one hour after pulse labelling and declined by 21 days, whereas in roots they were initially lower but generally continued to increase until 21 days. The greatest recoveries of 13C in roots, one hour and 21 days after labelling, were in summer and autumn respectively. The proportion of label 13C allocated to roots by 21 days was 0.50 in the absence of superphosphate and 0.41 in the superphosphate treatment, and was 0.39, 0.43 and 0.51 respectively in spring, summer and autumn. Irrigation had no significant effect on root allocation. The low stocking rate at Tara Hills, which had the greatest herbage biomass, also had greater total 13C, tussock herbage 13C and root 13C recoveries than the higher stocking rate treatments. Inter-tussock root recovery and allocation of 13C to roots increased with increasing stocking rate, whereas tussock root allocation was greatest in the high and least in the medium stocking rate treatment. By 21 days there was a greater inter-tussock and tussock root recovery and lower inter-tussock herbage recovery in the continuous than in the alternating grazing management treatment. The root allocation was generally greater in the continuous than in alternating grazed treatments, except for tussocks one hour after labelling where the reverse was the case. In conclusion the 13C pulse labelling showed pasture plants allocate more C to roots with low soil fertility, high grazing intensity, continuous grazing, and in autumn.

Ecology of Sandalwood (Santalum Spicatum) Near Paynes Find and Menzies, Western Australia: Size Structure and Dry-Sided Stems.

Population size structure of sandalwood (Santalum spicatum) was studied on four pastoral leases near Paynes Find and Menzies, in semi-arid Western Australia. Stem diameter, height, height to crown and the orientation of dry-sided stems were recorded for 1017 individual sandalwood. Populations of S. spicatum at Paynes Find contained only mature trees, indicating no successful recruitment for at least 30 years. In contrast, populations of S, spicatum at Menzies had a high proportion of seedlings and saplings. Crown measurements of mature S. spicatum trees indicated high grazing intensity at Paynes Find: mean height to crown at Paynes Find (147-148 cm) was significantly higher than Menzies (92-94 cm). Dry-side percentage differed significantly between directional faces, consistent with sun damage. Highest mean dry-side percentages were on stem sides facing the sun between midday and late afternoon: west, north-west, south-west and north. This directional pattern was the same between pastoral leases, and there was no interaction between pastoral lease and dry-side direction. Mean percentage of mature trees with a dry-sided stem was also significantly higher at Paynes Find (76-82%) than at Menzies (42-46%). Significantly less foliage low to the ground on mature trees at Paynes Find may have exposed the stems to more sun damage. Land systems did not significantly influence dry-side direction on Burnerbinmah or Goongarrie. No S. spicatum seedlings or saplings had a dry-sided stem. Key words: Santalum spicatum, size structure, dry-sided stems

Conservation value of road verges in the semi-arid Karoo, South Africa: ants (Hymenoptera: Formicidae) as bio-indicators

Ground-foraging ants (Hymenoptera: Formicidae) were used to assess the conservation value of road verges in a semi-arid region around Prince Albert, Western Cape Province, South Africa. Ant communities were sampled using pitfall traps on 50 sites along two roads. Four transects were sampled at each site, two in the road verge and two in adjacent rangeland. A total of 43,298 individual ants of 34 species were caught, with 31 and 32 species in the road verge and adjacent rangeland respectively, but on average road verges were the more species-rich. Road verges also contained relatively more rare species (i.e. those species that occurred in <10% of the traps. Ant species richness appeared to be influenced by food availability. Although ants appeared to be negatively impacted by higher grazing intensities in the rangeland, there was no difference in species richness between fenced and unfenced road verges. Species in the road verge may benefit directly from road kills, and indirectly from lower grazing pressure on plants, increased surface run-off and differences in soil surface temperatures. No alien ant species were observed or captured at any of the sites.

Reconstruction of long‐term successional dynamics of temperate woodland in Białowieża Forest, Poland

1 Białowieża Forest contains the most extensive stands of old‐growth temperate woodland in Europe. It therefore has the potential to provide a model for near‐natural woodland, which is a conservation aim for many sites in western Europe. 2 Pollen analyses from two small hollow sites in the northern part of Białowieża Forest National Park are reported here. The records cover the last 1200–1500 years. The pollen data of the principal tree taxa were converted into vegetation data using previously published pollen:vegetation correction factors. 3 These data were used to reconstruct long‐term vegetation dynamics in the Tilio–Carpinetum and Pino–Quercetum communities that dominate the forest. Changes in forest composition have occurred as a result of both autogenic and allogenic processes. High grazing intensities in recent centuries have been particularly significant, although the forest is often considered to be undisturbed. 4 The larger hollow (site I) initially sampled across Peucedano–Pinetum, Carici elongatae–Alnetum and Tilio–Carpinetum communities. Since 1750, the Peucedano–Pinetum community has dominated, but with an increased Picea component. This has recently been replaced by the Pino–Quercetum community following the reduction of grazing pressure. These recent changes are largely consistent with published successional models for Białowieża Forest. 5 Site II recorded a relatively stable balance between the Tilio–Carpinetum and Pino–Quercetum communities until 750 years ago. The Tilio–Carpinetum community then expanded. The continued dominance of Quercus in this community is inconsistent with previous models. 6 The long time perspective available with pollen data permits the exploration of forest dynamics beyond the temporal range of existing models for Białowieża Forest. Comparison of recent and older records revealed that anthropogenic impact on forest composition has been greatest in recent centuries. 7 This investigation highlights the significant role of history in determining forest stand structure and composition.