Effects of fencing on forage biomass and quality through livestock exclusion from a protected area in the southern Kalahari

The substitution of wild herbivores by livestock has led to substantial degradation of many southern African grazing systems. As a result, bush and shrub encroachment has led to a reduction of grasslands, invasion of thorn shrubs, reduced carrying capacity of range land, and desertification. These changes often raise socio-economic challenges for rural communities in arid and semi-arid regions, as previously profitable areas may become no longer economically viable. This study aims to compare biomass and key chemical characteristics of grassy vegetation between sites experiencing low vs. high grazing pressures. Furthermore, we estimate the recovery time needed for pasture in heavily grazed areas to reach properties of similar sites under low grazing pressure. In heavily grazed areas, grass was of higher quality than in areas with low grazing pressure, as the remaining or re-growing grass contains higher percentages of protein and lower concentrations of fiber. However, as heavy grazing led to reduced grass biomass, the absolute amount of protein available per unit area was lower in areas with high compared to areas with low grazing pressure. Furthermore, at the heavily grazed area we recorded a high proportion of unpalatable plant species. The exclusion of livestock through fencing resulted in a rapid increase of grass biomass and therefore higher amounts of fibre, protein and hemicellulose contents per unit area after one wet season, whereas the chemical concentrations of plant compounds changed remarkably little after elimination of livestock grazing pressure. In areas where cattle substitute wild-ranging herbivores we recommend livestock managers consider transitioning to sustainable grazing systems through grazing rotation, diversification of herbivore species, and reduction in stocking rates. This would secure sustainable livestock-based livelihoods while avoiding permanent rangeland degradation due to bush encroachment and desertification

Long-term effect of sheep and goat grazing on plant diversity in a semi-natural dry grassland habitat

Semi-natural dry grassland sites are of great importance for nature conservation because they support high species diversity and the abundance of “Red-List” species. Grazing has proved to be a successful management tool in terms of maintenance and restoration of biodiversity. For a deeper understanding of the effects of different grazers on species biodiversity in dry grasslands, it is necessary to study the long-term effects of major changes in grazing management. In a semi-natural dry grassland habitat, which was formerly grazed by cattle, we investigated the changes in plant species composition due to long term grazing by sheep and goats. Specifically we asked: a) How does long-term grazing by sheep and goats change the composition of all plant species and particularly those that are on the Red-List? Are changes caused mainly by species turnover? b) How does long-term grazing by sheep and goats influence the fertility and acidity of the soil? To address these questions, we compared the composition and diversity of plants as well deriving Ellenberg indicator values of the species. Long-term grazing by sheep and goats subsequent to a year-round cattle grazing changed the plant species composition of the dry grasslands resulting in a high species turnover rate. It did not, however, lead to an increase in plant species diversity even though Red-List species were considerably more abundant in 2013. Overall, the grazing regime studied positively influenced vegetation composition. The effects on local species composition due to species turnover might further be influenced by local factors like soil nitrogen availability

Near infrared reflectance spectroscopy (NIRS) analyses of nutrient composition and condensed tannin concentrations in carolina willow ( Salix caroliniana

Iron overload disorder has been described in a number of zoo-managed species, and it has been recommended to increase the tannin composition of the diet as a safe way to minimize iron absorption in these iron-sensitive species. The goal of this study was to examine the potential of near infrared reflectance spectroscopy (NIRS) as a rapid and simple screening tool to assess willow (Salix caroliniana) nutrient composition (crude protein: CP; acid detergent fiber: ADF; neutral detergent fiber: NDF; lignin, gross energy: GE) and condensed tannin (CT) concentrations. Calibration equations were developed by regression of the lab values from 2 years using partial least squares on n=144 NIRS spectra to predict n=20 independent validation samples. Using the full 2-year dataset, good prediction statistics were obtained for CP, ADF, NDF, and GE in plant leaves and stems (r2\u3e0.75). NIRS did not predict lignin concentrations reliably (leaves r2=0.52, stems r2=0.33); however, CTs were predicted moderately well (leaves r2=0.72, stems r2=0.67). These data indicate that NIRS can be used to quantify several key nutrients in willow leaves and stems including concentrations of plant secondary compounds which, depending on the bioactivity of the compound, may be targeted to feed iron-sensitive browsing animals

Browser selectivity alters post-fire competition between Erica arborea and E. trimera in the sub-alpine heathlands of Ethiopia

Mammalian herbivores have the potential to alter the competitive relations of woody species, if consumption is unevenly distributed between species. At elevations above 3500 m in the southern Ethiopian highlands, vegetation is dominated by Erica arborea and Erica trimera. Both species can potentially grow into short trees, but are burnt on a rotation of 6 to 10 years, and regenerate by re-sprouting from belowground lignotubers. The regenerating scrub is heavily browsed by cattle. We set up browsing exclosures at three burnt sites to quantify the impact of browsing over a three-year period. When protected from browsing, E. trimera had similar or better height growth than Erica arborea, but in browsed vegetation, Erica arborea instead grew taller. Browsing was more intense on E. trimera in the first years after fire, indicating a difference in palatability between the species. We checked if browse quality differed, by analysing shoot contents of acid detergent fibre, protein, phenolics and tannins. Contrary to expectations the preferred E. trimera contained more acid detergent fibre, less protein and had a higher tannin activity than E. arborea. Although the vegetative growth of E. arborea is favoured relative to E. trimera under high browsing pressure, rapid change in abundance would not be expected, since short-interval fire will repeatedly eradicate any gains in vegetative growth. However, within the typical fire return interval of less than 10 years, E. trimera barely reach a reproductive state, whereas E. arborea flower profusely. Under the current regime of fire and browsing this may in the long run be more important than differences in height growth, leading to a gradual increase in the proportion of E. arborea

Compositional Changes in Foliage Phenolics with Plant Age, a Natural Experiment in Boreal Forests

The composition of plant secondary metabolites (PSMs) extensively impacts ecosystem functioning. It is vital that we understand temporal patterns in the plants’ allocation of resources to PSMs, particularly those influenced by human activity. Existing data are insufficient in the long-term perspective of perennial plants (age or ontogeny). We analysed phenolic concentrations in foliage from birch (Betula pubescens Ehr.) considered to be undamaged and growing on 5, 10 and 15 years old clear-cuts in two boreal forest landscapes in Norway, sampled at the peak of the growing season. In sum, low molecular weight phenolic concentrations decreased with age. Apart from one apigenin glycoside, the low molecular weight phenolics co-varied similarly at all ages, suggesting a lack of temporal compound-specific prioritisation of this group. In contrast, the concentration of MeOH-soluble condensed tannins increased with age. The compositional shift fits well with several hypotheses that may provide proximate explanations for age patterns in PSM allocations, including both resource constraints and external pressures. Regardless of these explanations, our study adds an important perennial perspective (plant age) to temporal PSM patterns already well-known in boreal plant phenology (foliage age).publishedVersio

Simulated winter browsing may lead to induced susceptibility of willows to beavers in spring

Browsing may lead to an induced resistance or susceptibility of the plant to the herbivore. We tested the effect of winter browsing by Eurasian beavers (Castor fiber L., 1758) on food quality of holme willows (Salix dasyclados Wimm.) in and after the following growth season. Shrubs were pruned in February, and new shoots from these (cut) shrubs were compared with those of untreated (uncut) ones in May and November. The shoots were analysed for dry matter, nitrogen, acid detergent fibre, and total phenolics. In May, the leaves from the cut treatment had a better food quality (more water, more nitrogen, and less phenolics) than those from the uncut one. There was in part also a systemic response, with lower total phenolics in both the cut and untreated parts of pruned shrubs (uncut–cut) than in the uncut shrubs. In November, we did not find significant differences in biochemistry of bark among cut, uncut, or uncut–cut treatments. These results are in accordance with a cafeteria experiment in the field: in May the beavers preferred shoots from the cut treatment, but in November they showed no preference. The results suggest that willows invest in compensatory growth rather than a defence response early in the regrowing phase.