Shrub Encroachment

The ingression of woody plants into savannas, known as bush or shrub encroachment, has become a global
concern. Fire has been acknowledged as a key factor in managing woody vegetation in savannas. This study
assessed the role of fire in determining the total density, structure and composition of woody vegetation in Ithala
Game Reserve, northern KwaZulu-Natal, South Africa. We surveyed woody vegetation in comparable areas with
different fire frequencies. In Combretum-dominated woodlands, there was no significant effect of fire frequency
on the total density of woody individuals. In old field grasslands, the density of woody plants was greater in
areas burnt annually and in areas burnt once every 10 years, compared to areas burnt once every 2–4 years.
In these grasslands, areas burnt annually were dominated by woody plants 2 m in height. Herbivore and fire
interactions may explain these results. Multivariate analyses also indicated a significant effect of fire frequency
on woody vegetation composition. To control dominant encroaching trees such as Dichrostachys cinerea and
Acacia karroo (Vachellia karroo), and the development of macrophyllous thickets, an intermediate fire frequency
is required (one burn every 2–4 years).

A dehesa is a multipurpose agroforestry system with scattered oaks. This study focuses on the influence of trees on soil chemical fertility and on the consequences of dehesa land use for soil fertility and nutritional status of trees. To achieve that we have studied the content of several nutrients in soils and tree leaves in four Spanish dehesas, considering three types of land use: scattered holm oak with an understorey of either native grasses (G), shrubs (E) or crop (C: either fertilized or unfertilized). We randomly selected six oaks per farm and land use for soil and tree leaf sampling. Soil samples were taken at five distances from each tree trunk (2, 5, 10, 15, and 20 m) at a depth of 0–30 cm. SOM, CEC, total and mineral-N, available-P, and exchangeable Ca, Mg and K were analysed. Foliar samples were collected from every tree in two consecutive years (2002 and 2003) at leaf maturity. The total content of N, P, K, Ca, and Mg was determined. Soils of C plots showed significantly higher contents for most of the nutrients studied than G ones. Cropping also affected trees positively, with higher foliar contents of N and K in C plots than in G ones. Foliar content did not decrease for any nutrient, and tree-crop interaction is interpreted as a mechanism of complementarity in terms of nutrient use. Shrub encroachment led to a higher content of organic-N and exchangeable cations in soils, but to a decrease in mineral N and available-P. The tree foliar contents of N, Mg, and Ca were lower in E plots than in G plots, probably as a consequence of the tree-shrub competition for those nutrients. By contrast, P content of tree leaves increased significantly in E plots compared to G plots.

Woody plant encroachment is frequent in dry savannas. Grazing is often considered to be a major cause of encroachment in dry savannas because grasses are removed by livestock, leaving bare areas for trees to colonise in wetter years. Earlier experiments conducted in the Kimberley area of the Northern Cape showed that neither fire nor grazing was important for woody plant encroachment. We used aerial and fixed-point repeat ground
photographs, including historical photographs taken at the time of the Second Anglo-Boer War of 1899–1902, to assess the scale and timing of woody plant encroachment in the dry savannas near Kimberley in South Africa (mean annual rainfall = 300–400 mm). There were large increases in woody plant encroachment in most areas. Even at the battlefield of Magersfontein, where grazing has been virtually absent since its protection in 1960, we
found that encroachment by trees and shrubs has occurred. Using aerial photographs, we found that the rate of encroachment has increased substantially since 1993. However, repeated photographs at certain sites indicate that
encroachment produced cohorts of trees. We show that global drivers are perhaps of greater importance than local drivers such as heavy grazing and absence of fire.

Remote sensing, together with geographic information systems (GISs), provide a powerful tool for monitoring environmental processes. Aerial and satellite photographs enable the analysis of an entire landscape and, using multi-temporal sets of photographs, one is able to follow processes over time. In our study, we used multi-temporal sets of aerial photographs, taken between 1944 and 2005, to observe the phenomenon of woody plant encroachment in four neighbouring study sites in northern KwaZulu-Natal, South Africa. We also analysed rainfall and temperature trends. Woody plant encroachment was evident in all sites. We suggest possible drivers behind the bush encroachment; in particular, climatic trends. However, encroachment did not relate directly to rainfall and temperature trends. We also speculate on the effects of herbivory and fire, as well as rising atmospheric CO2 concentrations and its effect on C3 and C4 plants. We suggest that increasing atmospheric CO2 concentrations could be the overriding driver of woody plant encroachment in our study area, with other drivers, such as rainfall, temperature, fire, herbivory, and land use, playing a modifying role.

This study was amid to investigate animal response to replacement 15% of concentrate feed mixture (CFM) with ground mesquite pods without and with 4% Polyethylene glycol (PEG) 4000 in invitro and invivo experiments. In vitro rumen gas production values at 24h were 58.67, 55.0 and 61.67 ml/400mg for CFM1, CFM2 (15% mesquite pods) and CFM3(15% mesquite pods + 4%PEG4000) respectively. Dry matter digestibility (DMD %) was 63.58, 64.50 and 66.65% for CFM1, CFM2 and CFM3, respectively. In vivo experiment was done using 15 growing goat kids (10.49±1.29 Kg) which were randomly divided into three groups. Group one (G1) was fed on concentrate feed mixture (CFM) and pasture (desert grass, Panicumtidrgium), group two (G2) was fed on CFM with 15% ground mesquite pods and pasture and group three (G3) was fed on with 15% ground mesquite pods plus 4% PEG 4000. Using PEG 4000 in G3 resulted in increasing intake from pasture by 19.45 and 30.51% from pasture intake in G1 and G2, respectively. Digestibility coefficients were very close to each other's. Values of NDF and ADF digestibility tended to increase in mesquite pods groups (G2 and G3) compared to control group (G1). Also, TDN% values were 74.46, 77.69 and 77.68% for G1, G2, and G3, respectively. Using PEG 4000 (G3) with mesquite pods had the best values over all groups in average daily gain (60.13 g/day),body weight gain (9.02 Kg) and final body weight (19.5 Kg).Serum parameters were under normal range of healthy goats. In general, using mesquite pods decreased feed cost per day by about 21% from control diet and PEG group as well.

The worldwide phenomenon of shrub encroachment in grass-dominated dryland ecosystems is commonly associated with desertification. Studies of the purported desertification effects associated with shrub encroachment are often restricted to relatively few study areas, and document a narrow range of possible impacts upon biota and ecosystem processes. We conducted a study in degraded Mediterranean grasslands dominated by Stipa tenacissima to simultaneously evaluate the effects of shrub encroachment on the structure and composition of multiple biotic community components, and on various indicators of ecosystem function. Shrub encroachment enhanced vascular plant richness, biomass of fungi, actinomycetes and other bacteria, and was linked with greater soil fertility and N mineralization rates. While shrub encroachment may be a widespread phenomenon in drylands, an interpretation that this is an expression of desertification is not universal. Our results suggest that shrub establishment may be an important step in the reversal of desertification processes in the Mediterranean region.

Silvopastoral systems are threatened worldwide by progressive loss of either tree cover or herbaceous cover due to lack of tree regeneration and shrub encroachment, respectively. Grazed Mediterranean open woodlands, as Iberian dehesa, are an outstanding example of silvopastoral system where shrub encroachment has been proposed as an effective means to facilitate tree seedling recruitment and ensure the system persistence. Shrubs

Regional environmental change can be assessed using remote sensing in two ways: by looking for trends in image time series in terms of spectral indices, like the normalized difference vegetation index (NDVI), or through post-classification change analysis to identify land cover change (LCC). Here we demonstrate the efficacy of combined trend-LCC analysis using the Northern Eurasian grain belt (NEGB) and Aral Basin (AB) as examples. NDVI time series from 2001-2008 were derived from 500m MODIS NBAR 8-d composites spanning the growing season from March to October of each year. LCC analysis was based on the 500m MODIS Global Land Cover product for the years 2001 and 2008. Seasonal Kendall trend tests showed, on a per-pixel basis, that statistically significant (p<0.05) NDVI trends were largely negative, with declining seasonal NDVI covering 57% of the NEGB’s land area and 15% of the AB. Among pixels exhibiting negative NDVI trends, we found elevated LCC rates (relative to pixels exhibiting no trend) from: (1) cropland mosaic to pure cropland in the northern portion of the NEGB, largely in Russia (RU); (2) cropland to grassland in the southern portion of the NEGB, largely in Kazakhstan (KZ); (3) cropland to grassland, and shrub to grassland, in the AB. Statistically significant (p<0.05) positive NDVI trends were rare, covering less than 1% of the NEGB and AB. Among pixels exhibiting positive NDVI trends, we found elevated LCC rates from: (1) cropland to cropland mosaic in relatively small clusters of pixels in the northern NEGB, mostly in RU; (2) grassland to cropland in the southern NEGB, largely in KZ, and also in small clusters; (3) grassland to cropland (largely along the Amu Darya river), in addition to more widespread conversion of grassland and barren classes to shrub, in the AB. In the NEGB, the overall direction of regional change was toward agricultural de-intensification in KZ, likely reflecting persistent drought, in contrast with agricultural intensification in RU - perhaps due to overriding effects of socioeconomic forces, relative to climatic drivers, on land use decisions in RU. In the AB, we find agricultural intensification (grassland to cropland conversion) associated with positive NDVI trends; concentration of positive trends along the Amu Darya in Karakalpakstan suggests an expansion of irrigation. We also find both shrub decline and shrub encroachment in the AB, with likely effects on ecosystem function reflected in negative NDVI trends (declining GPP) where shrubs are declining and positive NDVI trends (increasing GPP) where shrubs are increasing. In sum, LCC analysis complements NDVI trend analyses. LCC analysis focuses on discrete, abrupt, and principally human-caused change. NDVI trend analysis is better suited to identifying continuous, gradual change, primarily driven by climatic conditions. However, land surface changes are both discrete and continuous, depending on perspective, and can be mutually reinforcing. Here we find that LCC results inform our interpretation of NDVI trends and vice versa. Each analysis, alone, provides an incomplete picture of the complexities of land surface change.

The massive decline of calcareous grasslands in the Franconian Jura is caused mainly by land use abandonment and afforestation. In the district Lichtenfels, the northernmost part of the Franconian Alb, management measures were put in action since the middle of the 1980s to conserve or restore those threatened ecosystems. Important actions were removal of trees (mainly Pinus sylvestris) and shrubs as well as reintroduction of sheep grazing. This study analyses the success of restoration measures taken at two Natura 2000 sites. Based on vegetation releves from 70 sites with different land use histories, we investigate the influence of the successional status of the woodlands prior to clear-cutting and the time period of subsequent grazing on the actual vegetation. The results suggest that both factors influence species composition. On formerly dense pine woodland sites, it takes at least five years of grazing until the number of target species increases. On formerly more sparsely wood...

Ungulate abundance has increased dramatically worldwide, having strong impacts on ecosystem functioning. High ungulate densities can reduce the abundance, diversity and/or body condition of small mammals, which has been attributed to reductions in cover shelter and food availability by ungulates. The densities of wild ungulates have increased recently in high-diversity Mediterranean oak ecosystems, where acorn-dispersing small rodents are keystone species. We analysed experimentally ungulate effects on seed-dispersing ...

In European mountain areas, shrub encroachment resulting from farmland abandonment is most often managed by mechanical operations such as roller chopping or controlled burning, which have proved to be ineffective and unsustainable. Recent agroecological findings highlight the potential impact of grazing on long-term shrub dynamics. We thus explored the potential contribution of livestock farms to the management of shrub encroachment. We studied the diversity of livestock practices and strategies on the scale of a small mountain valley in France where a land-use management plan was initiated. We interviewed 33 livestock farmers with a comprehensive approach and analysed the data in partnership with local land-use managers. To categorise farming practices, we used an innovative constructivist method based on knowledge engineering techniques and tools such as repertory grids. Our results show that the diversity of land-use practices can be summed up by ten practices related to three ma...