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Woody Cover (woody + cover)

Distribution by Scientific Domains
Life Sciences70%
Humanities and Social Sciences30%

Selected Abstracts

Leichhardt's maps: 100 years of change in vegetation structure in inland Queensland

JOURNAL OF BIOGEOGRAPHY, Issue 1 2008
R. J. Fensham
Abstract Aim, To address the hypothesis that there has been a substantial increase in woody vegetation cover (,vegetation thickening') during the 100 years after the burning practices of aboriginal hunter-gatherers were abruptly replaced by the management activities associated with pastoralism in north-east Australia. Location, Three hundred and eighty-three sites on 3000 km transect, inland Queensland, Australia. Methods, Vegetation structure descriptions from the route notes of the first European exploration of the location by Ludwig Leichhardt in 1844,45 were georeferenced and compiled. Leichhardt's application of structural descriptors (e.g. ,scrub', ,open forest', ,plain') was interpreted as domains within a matrix of tall stratum and low stratum woody cover. Woody cover was also interpreted for the same locations using aerial photography that largely pre-dates extensive land clearing (1940s,1970s) and compared with their structural domain in 1844,45. The fire-sensitive tree, cypress-pine (Callitris glaucophylla) was singled out for case study because it has been widely proposed that the density of this tree has substantially increased under European pastoral management. Results, The coarse resolution of this analysis indicates that the structure of the vegetation has been stable over the first 100 years of pastoralism. For example treeless or sparsely treed plains described by Leichhardt (1844,45) had the same character on the aerial photography (1945,78). Leichhardt typically described vegetation that includes cypress-pine as having a ,thicket' structure suggesting dense regenerating stands of small trees, consistent with the signature typical on the aerial photography. Main conclusions, A large data set of geographically located descriptions of vegetation structure from the first European traverse of inland Australia compared with vegetation structure determined from aerial photography does not support the hypothesis that vegetation thickening has been extensive and substantial. On the contrary the study suggests that the structure of the vegetation has been relatively stable for the first 100 years of European settlement and pastoralism except for those areas that have been affected by broad-scale clearing. [source]

Changes in miombo woodland cover in and around Sengwa Wildlife Research Area, Zimbabwe, in relation to elephants and fire

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2002
Isaac N. Mapaure
Abstract One of the consequences of impacts of elephants and fire on woodlands is a change in woody cover, which often results in major challenges for wildlife managers. Changes in miombo woodland cover in and around Sengwa Wildlife Research Area (SWRA) between 1958 and 1996 were quantified by analyzing aerial photographs. Woody cover in SWRA decreazed from 95.2% in 1958 to 68.2% in 1996, with a lowest mean of 62.9% in 1983. The annual absolute rate of woody cover change in SWRA increazed from ,1.1% per annum between 1958 and 1964 to a recovery of 1.6% per annum between 1993 and 1996, while the annual relative rate increazed from ,1.1% per annum between 1958 and 1964 to 3.3% per annum between 1993 and 1996. There was a strong negative correlation between elephant densities and woody cover in SWRA, suggesting that loss of woody cover was mainly due to elephants. Woodland recovery after 1983 was due to reductions in elephant populations through legal and illegal off-take and reductions in fire frequency. Surrounding areas experienced less woody cover losses than SWRA, mainly due to tree removal by locals whose densities increazed after the eradication of tsetse fly in the 1970s. Résumé Une des conséquences de l'impact des éléphants et des feux sur les forêts s'exprime par un changement du couvert ligneux qui pose souvent de fameux défis pour les gestionnaires de la faune. Les changements du couvert forestier à Miombo, qui sont survenus à l'intérieur et aux alentours de l'Aire de Recherche sur la Faune de Sengwa (SWRA) entre 1956 et 1996, ont été quantifiés grâce à l'analyse de photos aériennes. Le couvert forestier de la SWRA a diminué de 95.2% en 1958 à 68.2% en 1996, la moyenne la plus basse étant observée en 1983, avec 62.9%. Le taux annuel absolu de changement du couvert forestier dans la SWRA est passé de , 1.1% par an entre 1958 et 1964 à une restauration de 1.6% par an entre 1993 et 1996, tandis que le taux annuel relatif augmentait de , 1.1% par an entre 1958 et 1964 à 3.3% par an entre 1993 et 1996. Il existait une forte corrélation négative entre la densité des éléphants et le couvert forestier de la SWRA, ce qui laisse supposer que la perte de couvert forestier était due principalement aux éléphants. La restauration de la forêt après 1983 était due à des réductions des populations d'éléphants suite à des prélèvements, légaux ou non, et à une baisse de la fréquence des feux. Les zones adjacentes ont subi de moins fortes pertes du couvert forestier que la SWRA, et celles-ci étaient principalement dues à des coupes faites par les locaux dont la densité a augmenté suite à l'éradication de la mouche tsé-tsé dans les années 1970. [source]

Trends in woody vegetation cover in the Kruger National Park, South Africa, between 1940 and 1998

AFRICAN JOURNAL OF ECOLOGY, Issue 2 2000
H. C. Eckhardt
Changes in the cover and density of shrubs and trees were assessed from aerial photographs (1940, 1974 and 1998) as well as from fixed-point photographs taken in 1984 and 1996 in the Kruger National Park, South Africa. Woody cover (trees and shrubs combined) increased by 12% on granite substrates but decreased by 64% on basalt substrates over the past 58 years. Both these figures are expressed in terms of the initial values, respectively. The density of the large tree component of woody vegetation decreased on both substrates. Woody vegetation cover declined as fire return periods became shorter, but the relationship was weak. The increases in woody plant density and cover on granite are thought to be the result of decreased competition from grasses, which in turn is a result of overgrazing by wild herbivores whose numbers have been kept high through the provision of surface water. These effects were not seen on the relatively nutrient-rich basalts, where grasses can recover rapidly even after heavy grazing. The decline in overall woody cover on basalts is interpreted as a result of regular, short-interval prescribed burning over the past 40 years, while the universal decline in large trees seems to result from an interaction between regular, frequent fires and utilization by elephants. The implications for management are discussed. Résuné On a évalué les changements du couvert et de la densité des arbustes et des arbres à partir de photos aériennes (1940, 1974 et 1998) et de photos prises d'un endroit fixe en 1984 et en 1996 dans le Parc National Kruger, en Afrique du Sud. Le couvert boisé (arbustes et arbres pris ensemble) a augmenté de 12% sur les substrats granitiques mais diminué de 64% sur les substrats basaltiques, au cours des 58 dernières années. Ces deux chiffres sont exprimés en termes de valeurs initiales, respectivement. La densité de la composante de grands arbres de la végétation boisée a diminué sur les deux substrats. Le couvert végétal boisé a diminué alors que les périodes de récupération entre les feux raccourcissaient, mais la relation est faible. On pense que l'augmentation de la densité et du couvert boisés sur le granite est le résultat d'une diminution de la compétition exercée par les herbes qui elle, résulte d'un surpâturage des herbivores sauvages dont le nombre a été maintenu élevé par l'apport d'eau de surface. On n'a pas observé ces effets sur les basaltes relativement riches en nutriments, car les herbes peuvent y repousser rapidement même après un pâturage intense. On interprète le déclin du couvert boisé global sur le basalte comme le résultat des feux provoqués régulièrement et avec de brefs intervalles depuis 40 ans, alors que le déclin général des grands arbres semble être le résultat d'une interaction entre les feux, réguliers et fréquents, et la présence des éléphants. On discute de ce que cela implique pour la gestion. [source]

Adaptive restoration of sand-mined areas for biological conservation

JOURNAL OF APPLIED ECOLOGY, Issue 1 2005
JASON CUMMINGS
Summary 1Adaptive management approaches to ecological restoration are current best practice. The usefulness of such an approach was tested in this study by implementing repeated experiments that examined restoration options for derelict sand mine sites dominated by Imperata cylindrica. Reclamation of degraded land that is dominated by I. cylindrica is a common problem throughout the tropics. 2Initially, the hypothesized barrier to regeneration was limited seedling establishment because of I. cylindrica competition. After burning the grassland, woody weed control and planting of seedlings were implemented in factorial combination. 3Seedling survival 28 months after planting averaged 26%, with < 1% of all seedlings establishing to a height > 1 m. The hypothesis that a transition barrier comprising solely biotic interactions restricted regeneration of native woody cover was rejected after seedlings and natural regeneration failed to thrive in this experiment. 4A revised hypothesis, that the transition barrier comprised a combination of abiotic limitations (soil deficiencies) and biotic interactions (Wallabia bicolor browsing and I. cylindrica competition), was developed. A second experiment tested this hypothesis by removing W. bicolor (fencing), slashing the I. cylindrica, adding organic mulch and planting a mixture of native pioneer and secondary successional woody species in factorial combination. 5Seedling survival was 61% in the second experiment and mulching significantly enhanced the survival and growth of all planted species. Planting alone reduced the regeneration of I. cylindrica after slashing. Native woody cover establishment was maximized by planting seedlings in mulched treatments. 6Synthesis and applications. Taken together, these experiments support the hypothesis that there is a barrier restricting regeneration of native woody cover, and the barrier probably comprises both abiotic and biotic components. By adopting an adaptive management approach to the ecological restoration of sites, significant insights into their management requirements have been gained, supporting the current best practice restoration framework. Insights gained through monitoring and adaptation will be used to update the reserve plan of management, enhancing restoration of this severely degraded area and promoting connectivity of native woody cover within the conservation estate. [source]

Leichhardt's maps: 100 years of change in vegetation structure in inland Queensland

JOURNAL OF BIOGEOGRAPHY, Issue 1 2008
R. J. Fensham
Abstract Aim, To address the hypothesis that there has been a substantial increase in woody vegetation cover (,vegetation thickening') during the 100 years after the burning practices of aboriginal hunter-gatherers were abruptly replaced by the management activities associated with pastoralism in north-east Australia. Location, Three hundred and eighty-three sites on 3000 km transect, inland Queensland, Australia. Methods, Vegetation structure descriptions from the route notes of the first European exploration of the location by Ludwig Leichhardt in 1844,45 were georeferenced and compiled. Leichhardt's application of structural descriptors (e.g. ,scrub', ,open forest', ,plain') was interpreted as domains within a matrix of tall stratum and low stratum woody cover. Woody cover was also interpreted for the same locations using aerial photography that largely pre-dates extensive land clearing (1940s,1970s) and compared with their structural domain in 1844,45. The fire-sensitive tree, cypress-pine (Callitris glaucophylla) was singled out for case study because it has been widely proposed that the density of this tree has substantially increased under European pastoral management. Results, The coarse resolution of this analysis indicates that the structure of the vegetation has been stable over the first 100 years of pastoralism. For example treeless or sparsely treed plains described by Leichhardt (1844,45) had the same character on the aerial photography (1945,78). Leichhardt typically described vegetation that includes cypress-pine as having a ,thicket' structure suggesting dense regenerating stands of small trees, consistent with the signature typical on the aerial photography. Main conclusions, A large data set of geographically located descriptions of vegetation structure from the first European traverse of inland Australia compared with vegetation structure determined from aerial photography does not support the hypothesis that vegetation thickening has been extensive and substantial. On the contrary the study suggests that the structure of the vegetation has been relatively stable for the first 100 years of European settlement and pastoralism except for those areas that have been affected by broad-scale clearing. [source]

Impact of habitat disturbance in the wetland forests of East Usambara, Tanzania

AFRICAN JOURNAL OF ECOLOGY, Issue 2 2010
Ramadhani Senzota
Abstract We evaluated habitat characteristics of East Usambara wetland forests. The abundance and species composition in the tree, shrub and herbaceous layers were enumerated in two sets of nested plots, one set in a natural wetland forest and the second in a wetland forest that had been disturbed by small-scale gold mining activities. Each set had thirty-six 1 m × 1 m plots for herbs, inside nine 5 m × 5 m plots for shrubs, in three 20 m × 20 m plots for trees. The habitat profile of herbaceous , shrub , tree layers was found to be sharply different from one obtained in previous studies at the surrounding nonwetland forests as were species composition and abundance. Unlike in the nonwetland forests, the herbaceous layer was thick, the shrub layer very thin and the woody species density and richness much lower. Disturbance significantly reduced woody cover and changed species composition in the herbaceous layer. Recovery of the woody vegetation was low. Wetland forests in the East Usambaras form a small fraction of the total area, but they are a unique biodiversity repository, they appear to be an important carbon dioxide sink and to reserve and purify water. They are sensitive to disturbance and need protection. Résumé Nous avons évalué les caractéristiques de l'habitat des forêts humides d'East Usambara. L'abondance et la composition des espèces dans les étages d'arbres, d'arbustes et d'herbes furent dénombrées dans deux ensembles de parcelles emboitées, un situé dans une forêt humide naturelle, l'autre dans une forêt humide qui avait été perturbée par les activités d'orpaillage à petite échelle. Chaque ensemble se composait de 36 carrés de 1 m² pour les herbes, situés dans neuf carrés de 5 m × 5 m pour les buissons, eux-mêmes situés à l'intérieur de trois carrés de 20 m × 20 m pour les arbres. Le profil des habitats pour les trois couches d'herbes , d'arbustes , d'arbres s'est révélé très différent de celui qui avait été obtenu lors d'études précédentes réalisées dans des forêts environnantes non humides; il en était de même pour la composition et l'abondance des espèces. Contrairement aux forêts non humides, la couche herbeuse était épaisse, la couche des arbustes très claire et la densité et la richesse des espèces ligneuses étaient beaucoup plus faibles. La perturbation avait significativement réduit le couvert ligneux et changé la composition des espèces de l'étage herbacé. La restauration de la végétation ligneuse était faible. Les forêts humides des East Usambara ne constituent qu'une petite fraction de la superficie totale, mais elles sont un sanctuaire unique pour sa biodiversité, elles semblent être un puits de carbone important et aussi retenir et purifier l'eau. Elles sont sensibles à toute perturbation et doivent être protégées. [source]

Bush encroachment under three contrasting land-use practices in a mesic South African savanna

AFRICAN JOURNAL OF ECOLOGY, Issue 2009
B. J. Wigley
Abstract This study determined the effects of land-use practice had on the rate and extent of bush encroachment in a mesic savanna in KwaZulu-Natal, South Africa. Changes in woody cover were measured for 1 km2 sites in areas under communal, commercial and conservation land-use systems for the period between 1937 and 2000. Land users from each area were interviewed to gain the histories of each area and to determine how the changes in woody cover had impacted them and whether anything was being done to counteract the spread of trees and shrubs on their land. Bush encroachment occurred across all three of the land-use types in the 67-year period between 1937 and 2000. The results showed that land-use practice had enormous impacts on the process of bush encroachment. The communal site showed a decrease in grass (21%) and tree (5%) cover and an increase in shrub cover (13%). At the commercial site, there was a considerable decrease in grass cover (46%) and moderate increase in shrub cover (10%) and a massive increase in tree cover (36%). The area under conservation showed a substantial decrease in grass cover (47%), a slight decrease in shrub cover (19%) and a massive increase in tree cover (66%). The perceived causes of these changes were fairly similar amongst the different land users. The changes were mostly not perceived to be a problem for the communal land users. The main advantages mentioned were increased woody resources for building and firewood and increased browse availability. The commercial and conservation land users perceived the changes to have significant negative connotations including the loss of grazing land and biodiversity and secondary invasion of encroached areas by alien plant species. Despite these perceptions, very little has been done to combat bush encroachment in the commercial and conservation land use systems. [source]

Changes in miombo woodland cover in and around Sengwa Wildlife Research Area, Zimbabwe, in relation to elephants and fire

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2002
Isaac N. Mapaure
Abstract One of the consequences of impacts of elephants and fire on woodlands is a change in woody cover, which often results in major challenges for wildlife managers. Changes in miombo woodland cover in and around Sengwa Wildlife Research Area (SWRA) between 1958 and 1996 were quantified by analyzing aerial photographs. Woody cover in SWRA decreazed from 95.2% in 1958 to 68.2% in 1996, with a lowest mean of 62.9% in 1983. The annual absolute rate of woody cover change in SWRA increazed from ,1.1% per annum between 1958 and 1964 to a recovery of 1.6% per annum between 1993 and 1996, while the annual relative rate increazed from ,1.1% per annum between 1958 and 1964 to 3.3% per annum between 1993 and 1996. There was a strong negative correlation between elephant densities and woody cover in SWRA, suggesting that loss of woody cover was mainly due to elephants. Woodland recovery after 1983 was due to reductions in elephant populations through legal and illegal off-take and reductions in fire frequency. Surrounding areas experienced less woody cover losses than SWRA, mainly due to tree removal by locals whose densities increazed after the eradication of tsetse fly in the 1970s. Résumé Une des conséquences de l'impact des éléphants et des feux sur les forêts s'exprime par un changement du couvert ligneux qui pose souvent de fameux défis pour les gestionnaires de la faune. Les changements du couvert forestier à Miombo, qui sont survenus à l'intérieur et aux alentours de l'Aire de Recherche sur la Faune de Sengwa (SWRA) entre 1956 et 1996, ont été quantifiés grâce à l'analyse de photos aériennes. Le couvert forestier de la SWRA a diminué de 95.2% en 1958 à 68.2% en 1996, la moyenne la plus basse étant observée en 1983, avec 62.9%. Le taux annuel absolu de changement du couvert forestier dans la SWRA est passé de , 1.1% par an entre 1958 et 1964 à une restauration de 1.6% par an entre 1993 et 1996, tandis que le taux annuel relatif augmentait de , 1.1% par an entre 1958 et 1964 à 3.3% par an entre 1993 et 1996. Il existait une forte corrélation négative entre la densité des éléphants et le couvert forestier de la SWRA, ce qui laisse supposer que la perte de couvert forestier était due principalement aux éléphants. La restauration de la forêt après 1983 était due à des réductions des populations d'éléphants suite à des prélèvements, légaux ou non, et à une baisse de la fréquence des feux. Les zones adjacentes ont subi de moins fortes pertes du couvert forestier que la SWRA, et celles-ci étaient principalement dues à des coupes faites par les locaux dont la densité a augmenté suite à l'éradication de la mouche tsé-tsé dans les années 1970. [source]

Trends in woody vegetation cover in the Kruger National Park, South Africa, between 1940 and 1998

AFRICAN JOURNAL OF ECOLOGY, Issue 2 2000
H. C. Eckhardt
Changes in the cover and density of shrubs and trees were assessed from aerial photographs (1940, 1974 and 1998) as well as from fixed-point photographs taken in 1984 and 1996 in the Kruger National Park, South Africa. Woody cover (trees and shrubs combined) increased by 12% on granite substrates but decreased by 64% on basalt substrates over the past 58 years. Both these figures are expressed in terms of the initial values, respectively. The density of the large tree component of woody vegetation decreased on both substrates. Woody vegetation cover declined as fire return periods became shorter, but the relationship was weak. The increases in woody plant density and cover on granite are thought to be the result of decreased competition from grasses, which in turn is a result of overgrazing by wild herbivores whose numbers have been kept high through the provision of surface water. These effects were not seen on the relatively nutrient-rich basalts, where grasses can recover rapidly even after heavy grazing. The decline in overall woody cover on basalts is interpreted as a result of regular, short-interval prescribed burning over the past 40 years, while the universal decline in large trees seems to result from an interaction between regular, frequent fires and utilization by elephants. The implications for management are discussed. Résuné On a évalué les changements du couvert et de la densité des arbustes et des arbres à partir de photos aériennes (1940, 1974 et 1998) et de photos prises d'un endroit fixe en 1984 et en 1996 dans le Parc National Kruger, en Afrique du Sud. Le couvert boisé (arbustes et arbres pris ensemble) a augmenté de 12% sur les substrats granitiques mais diminué de 64% sur les substrats basaltiques, au cours des 58 dernières années. Ces deux chiffres sont exprimés en termes de valeurs initiales, respectivement. La densité de la composante de grands arbres de la végétation boisée a diminué sur les deux substrats. Le couvert végétal boisé a diminué alors que les périodes de récupération entre les feux raccourcissaient, mais la relation est faible. On pense que l'augmentation de la densité et du couvert boisés sur le granite est le résultat d'une diminution de la compétition exercée par les herbes qui elle, résulte d'un surpâturage des herbivores sauvages dont le nombre a été maintenu élevé par l'apport d'eau de surface. On n'a pas observé ces effets sur les basaltes relativement riches en nutriments, car les herbes peuvent y repousser rapidement même après un pâturage intense. On interprète le déclin du couvert boisé global sur le basalte comme le résultat des feux provoqués régulièrement et avec de brefs intervalles depuis 40 ans, alors que le déclin général des grands arbres semble être le résultat d'une interaction entre les feux, réguliers et fréquents, et la présence des éléphants. On discute de ce que cela implique pour la gestion. [source]

Natural and human dimensions of environmental change in the proximal reaches of Botswana's Okavango Delta

THE GEOGRAPHICAL JOURNAL, Issue 1 2010
HAMISAI HAMANDAWANA
Though wetlands are vital for the proper functioning of terrestrial ecosystems and provisioning of a wide range of goods and services, their sustainability is being threatened by inappropriate human resource use practices due to our limited understanding of how these systems operate and lack of appropriately informed interventions. We attempt to address these limitations by using historical CORONA photographs of 1967, Landsat imagery of 1989, 1994 and 2001 and information from the literature to investigate the role of natural and human factors in influencing the direction of environmental change in the proximal reaches of Botswana's Okavango Delta. Results of this investigation point to fragmentation of natural habitats, localised degradation of areas close to perennial water supplies, significant increase in woody cover, significant decrease in open grassland, increase in scrub and shrubs, deterioration in the quality of grazing and depletion of specific woody species. With the direction of change pointing to persistent decrease in the environment's supporting potentials, there is urgent need to adopt intervention strategies potentially capable of enhancing sustainable utilisation of natural resources in this sub-region. [source]