The Experts below are selected from a list of 13599 Experts worldwide ranked by ideXlab platform
Richard M Cowling - One of the best experts on this subject based on the ideXlab platform.
-
multi decadal vegetation change in dune vegetation of the south eastern cape floristic region is Thicket expansion without fire inevitable
South African Journal of Botany, 2021Co-Authors: Richard M Cowling, M T HoffmanAbstract:Abstract It is hypothesized that in the Holocene dune fynbos-Thicket mosaics of the Cape, decades-long absence of fire results in closed-canopy Thicket replacing more open fynbos shrublands. We tested this hypothesis by analyzing repeat photographs from 16 sites at Cape St Francis in the south-eastern Cape Floristic Region. The period of monitoring ranged from 55 to 17 year and most sites had been last burnt between 30 and 50 years ago. We divided the sites into coastal (salt wind-exposed) and inland zones and computed, for each pair of photographs, the rate of change of four plant types, namely Thicket shrubs, fynbos woody, fynbos herbaceous and grass. Coastal zone sites showed a significant increase in Thicket shrub cover and a significant decline in both grass and fynbos herbaceous cover. Fynbos woody cover declined in the face of Thicket invasion, but increased in grassy sites, most likely due to a decline in herbivory intensity. No significant changes in plant types were observed in the inland sites, although Thicket shrub cover did increase marginally at the expense of fynbos woody plants. However, Thicket invasion was restricted to swales and lower dune slopes; the dune fynbos of the upper slopes and crests remains uninvaded by Thicket and surprisingly vigorous after 30–50 year without fire. This is consistent with the notion that fynbos species occupy drier sites than Thicket in these dune landscapes and regular fire is not a prerequisite for its persistence. Overall, we showed a large increase in woody plant cover throughout the study area. While this pattern is consistent with predictions for vegetation change in response to atmospheric [CO2] pollution, it can also be explained by land use changes experienced in the study area, starting in the early 1960s, involving a shift from subsistence agriculture to holiday resort development and tourism.
-
the short term response of coastal Thicket bird communities to fire in the southeastern cape south africa
African Journal of Wildlife Research, 2019Co-Authors: Tiaan Strydom, Tineke Kraaij, Mark Brown, Richard M CowlingAbstract:Fire ecological research within the Cape Floristic Region is largely restricted to fynbos vegetation and, amongst fauna, birds. Nothing is known about post-fire responses of birds in subtropical Thicket, which burns on much longer cycles than fynbos. Extensive fires in subtropical Thicket along the southeastern Cape coast (in the Knysna area during June 2017) presented the opportunity to assess the response of these birds to fire. We predicted that (1) fire reduces bird species diversity, richness and abundance in Thicket during the first two years post-fire; and (2) fire changes feeding guild composition and results in the loss of frugivorous birds. Bird surveys (point counts) were undertaken between 12- and 21-months post-fire in burnt (n =7) and unburnt (n = 7) Thicket sites to determine bird community structure and abundance. A total of 66 bird species and 2404 individuals were recorded of which 52 species and 1176 individuals were recorded in burnt Thicket and 60 species and 1228 individuals in unburnt Thicket. Ten species occurred only in burnt Thicket and 13 species only in unburnt Thicket. There was a 21% loss of bird species (mainly forest birds) after fire. The Sorenson similarity coefficient was 60% for bird species composition between burnt and unburnt Thicket. The most common feeding guilds in terms of richness and abundance in both burnt and unburnt Thicket were insectivores and generalists. Frugivores were most abundant in unburnt Thicket, whereas granivores were most abundant in burnt Thicket. Changes in Thicket bird community composition following the fire were minor and are likely to be short-lived as Thicket shrubs re-sprout vigorously after fire resulting in rapid recovery of vegetation and thus bird habitat structure.
-
frost portulacaria afra jacq and the boundary between the albany subtropical Thicket and nama karoo biomes
South African Journal of Botany, 2015Co-Authors: Robbert Duker, Richard M Cowling, D Du Preez, Alastair J PottsAbstract:Abstract Numerous shrublands exist in areas where soil moisture should support tree growth. In South Africa, the dwarf shrublands of the Nama-Karoo biome and tree-dominated vegetation of the Albany Subtropical Thicket biome share a boundary that is often abrupt. This boundary is not associated with edaphic or rainfall transitions. Field observations and leaf-level experiments suggest that the vulnerability of Thicket species to frost damage is responsible for this Thicket–shrubland boundary. We tested this hypothesis by establishing cuttings of Portulacaria afra (spekboom) – a dominant Thicket succulent shrub that is a keystone species in arid forms of Thicket – in two separate transplant experiments. Firstly across a topographic gradient from frost-free, Thicket clad slopes to frost-prone, karoo shrubland dominated valley floor; and secondly, inside and outside a Thicket clump in the frost-prone valley floor. We quantified the effects of frost on spekboom by measuring photosynthetic efficiency (Fv / Fm), leaf number, estimating the percentage of healthy stem before and after frost events in June 2013. Frost-exposed spekboom cuttings rapidly underwent declines in photosynthetic efficiency, followed by severe leaf and stem necrosis; herbivores played no role in these declines. Those planted on the frost-free valley slopes or under the frost-protecting Thicket canopy on the valley floor remained largely unaffected. This supports the hypothesis that frost-exposure is likely to be the main factor determining the growth rates, and ultimately survival of spekboom. These results suggest that frost occurrence is an important factor involved in determining the boundaries between the arid, and spekboom-rich subtypes of Albany Subtropical Thicket, and the frost tolerant shrublands of the Nama-Karoo.
-
how fast can carbon be sequestered when restoring degraded subtropical Thicket
Restoration Ecology, 2014Co-Authors: Anthony Mills, Richard M CowlingAbstract:Is the maximum rate of carbon sequestration reported for the CAM-C 3 plant Portulacaria afra (spekboom), viz. 15.4 t CO2 ha −1 yr −1 , unusual in comparison with other plants with similar physioliogies, or could such rates be expected routinely in restoration with P. afra ? Private sector investors in Thicket restoration need an answer to this question in order to assess the feasibility of using carbon finance as the main income stream from their investments. A literature review showed that 15.4 t CO2 ha −1 yr −1 is not an unusual rate of carbon sequestration for CAM plants in arid and semi-arid environments, which suggests that investors in Thicket restoration should not consider this an outlier value. The results also suggest that carbon finance could be used to fund restoration using other CAM plants in degraded xeric Thickets in countries such as Argentina, Chile, Mexico, and Madagascar.
-
a mismatch between germination requirements and environmental conditions niche conservatism in xeric subtropical Thicket canopy species
South African Journal of Botany, 2014Co-Authors: V Wilman, Alastair J Potts, Eileen E Campbell, Richard M CowlingAbstract:Seedlings of woody canopy species in the xeric forms of subtropical Thicket are rare. Here we argue that the low number of seedlings is a consequence of niche conservatism where Thicket species have retained germination and seedling establishment requirements associated with their ancestral origins in the warm, wet forests of the early Cenozoic. We test this hypothesis by evaluating the germination success of 12 arid and valley Thicket species – representing a range of growth forms and dispersal modes – using a factorial germination experiment that sought to simulate permanently moist and deeply-shaded conditions (i.e. a wet forest environment) and sparsely-shaded and intermittently dry conditions (i.e. open microsites during the rainy season) in contemporary Thicket environments. Germination success was significantly higher under the more mesic soil-moisture conditions for all species except Pappea capensis and Jatropha capensis. These results suggest that germination of Thicket species requires long periods of high soil moisture supporting the niche conservatism hypothesis.
Young Hee Yoon - One of the best experts on this subject based on the ideXlab platform.
-
changes in choroidal thickness in relation to the severity of retinopathy and macular edema in type 2 diabetic patients
Investigative Ophthalmology & Visual Science, 2013Co-Authors: Jee Taek Kim, Dong Hoon Lee, Soo Geun Joe, Junegone Kim, Young Hee YoonAbstract:PURPOSE: To assess changes in choroidal thickness in type 2 diabetic patients with diabetic retinopathy (DR) and diabetic macular edema (DME) using enhanced-depth imaging spectral domain optical coherence tomography (EDI-OCT). METHODS: Among 235 eyes from 145 patients, 195 treatment-naive eyes were divided into no DR, mild/moderate nonproliferative DR (NPDR), severe NPDR, proliferative DR (PDR), and 40 eyes having a history of laser panretinal photocoagulation (PRP) were classified as PRP-treated DR. Eyes with no ocular treatment (195 eyes) were divided according to the presence of and to the subtypes of DME. Subfoveal choroidal thickness (SFChT) and parafoveal choroidal thickness (PFChT) at 1500 μm were measured using EDI-OCT. RESULTS: Mean age was 62.6 ± 12.4 years, and mean duration of DM was 15.1 ± 7.2 years. Mean SFChT in groups with no DR (40 eyes), mild/moderate NPDR (47 eyes), severe NPDR (72 eyes), PDR (36 eyes), and PRP-treated DR (40 eyes) was 262.3 ± 68.4 μm, 244.6 ± 77.0 μm, 291.1 ± 107.7 μm, 363.5 ± 74.9 μm, and 239.9 ± 57.4 μm, respectively. Mean SFChT was significantly greater in eyes with PDR than in those with no DR (P < 0.01), mild/moderate NPDR (P < 0.01), or severe NPDR (P < 0.05). Mean SFChT decreased significantly in PRP-treated DR compared with PDR (P < 0.01). Eyes with DME (67 eyes) had a thicker subfoveal choroid than eyes without DME (128 eyes; P < 0.05) and, compared with cystoid or diffuse types, SFChT was thickest in subretinal detachment (SRD)-type DME (P < 0.05). CONCLUSIONS: Choroidal thickness increased significantly as the severity worsened from mild/moderate/NPDR to PDR, and decreased in PRP-treated eyes. The subfoveal choroid was thicker in eyes with DME than in those without, and was thickest in eyes with SRD-type DME.
-
changes in choroidal thickness in relation to the severity of retinopathy and macular edema in type 2 diabetic patients
Investigative Ophthalmology & Visual Science, 2013Co-Authors: Young Hee YoonAbstract:PURPOSE: To assess changes in choroidal thickness in type 2 diabetic patients with diabetic retinopathy (DR) and diabetic macular edema (DME) using enhanced-depth imaging spectral domain optical coherence tomography (EDI-OCT). METHODS: Among 235 eyes from 145 patients, 195 treatment-naive eyes were divided into no DR, mild/moderate nonproliferative DR (NPDR), severe NPDR, proliferative DR (PDR), and 40 eyes having a history of laser panretinal photocoagulation (PRP) were classified as PRP-treated DR. Eyes with no ocular treatment (195 eyes) were divided according to the presence of and to the subtypes of DME. Subfoveal choroidal thickness (SFChT) and parafoveal choroidal thickness (PFChT) at 1500 μm were measured using EDI-OCT. RESULTS: Mean age was 62.6 ± 12.4 years, and mean duration of DM was 15.1 ± 7.2 years. Mean SFChT in groups with no DR (40 eyes), mild/moderate NPDR (47 eyes), severe NPDR (72 eyes), PDR (36 eyes), and PRP-treated DR (40 eyes) was 262.3 ± 68.4 μm, 244.6 ± 77.0 μm, 291.1 ± 107.7 μm, 363.5 ± 74.9 μm, and 239.9 ± 57.4 μm, respectively. Mean SFChT was significantly greater in eyes with PDR than in those with no DR (P < 0.01), mild/moderate NPDR (P < 0.01), or severe NPDR (P < 0.05). Mean SFChT decreased significantly in PRP-treated DR compared with PDR (P < 0.01). Eyes with DME (67 eyes) had a thicker subfoveal choroid than eyes without DME (128 eyes; P < 0.05) and, compared with cystoid or diffuse types, SFChT was thickest in subretinal detachment (SRD)-type DME (P < 0.05). CONCLUSIONS: Choroidal thickness increased significantly as the severity worsened from mild/moderate/NPDR to PDR, and decreased in PRP-treated eyes. The subfoveal choroid was thicker in eyes with DME than in those without, and was thickest in eyes with SRD-type DME.
David T Felson - One of the best experts on this subject based on the ideXlab platform.
-
reference values and z scores for subregional femorotibial cartilage thickness results from a large population based sample framingham and comparison with the non exposed osteoarthritis initiative reference cohort
Osteoarthritis and Cartilage, 2010Co-Authors: F Eckstein, Mei Yang, Ali Guermazi, Frank W Roemer, M Hudelmaier, Kristen Picha, Frdric Baribaud, W Wirth, David T FelsonAbstract:Summary Objective To establish sex-specific (subregional) reference values of cartilage thickness and potential maximal Z-scores in the femorotibial joint. Methods The mean cartilage thickness (ThCtAB.Me) in femorotibial compartments, plates and subregions was determined on coronal magnetic resonance imaging (MRI) from a population-based sample (Framingham) and from a healthy reference sample of the Osteoarthritis Initiative (OAI). Results 686 Framingham participants (309 men, 377 women, age 62±8 years) had no radiographic femorotibial osteoarthritis (OA) ("normals") and 376 (156 men, 220 women) additionally had no MRI features of cartilage lesions ("supernormals"). The Framingham "normals" had thinner cartilage in the medial (3.59mm) than in the lateral femorotibial compartment (3.86mm). Medially, the femur displayed thicker cartilage (1.86mm) than the tibia (1.73mm), and laterally the tibia thicker cartilage (2.09mm) than the femur (1.77mm). The thickest cartilage was observed in central, and the thinnest in external femorotibial subregions. Potential maximal Z-scores ranged from 5.6 to 9.8 throughout the subregions; men displayed thicker cartilage but similar potential maximal Z-scores as women. Mean values and potential maximal Z-scores in Framingham "supernormals" and non-exposed OAI reference participants (112 participants without symptoms or risk factors of knee OA) were similar to Framingham "normals". Conclusions We provide reference values and potential maximal Z-scores of cartilage thickness in middle aged to elderly non-diseased populations without radiographic OA. Results were similar for "supernormal" participants without MRI features of cartilage lesions, and in a cohort without OA symptoms or risk factors. A cartilage thickness loss of around 27% is required for attaining a Z-score of −2.
Xiulan Zhang - One of the best experts on this subject based on the ideXlab platform.
-
topographic profile of choroid in eyes after acute primary angle closure
Canadian Journal of Ophthalmology-journal Canadien D Ophtalmologie, 2016Co-Authors: Xinbo Gao, Minwen Zhou, Wei Wang, Wenbin Huang, Shida Chen, Jiawei Wang, Xiulan ZhangAbstract:Abstract Objective To characterize and compare the topographic profile of choroid in eyes after acute primary angle-closure (APAC) and in normal controls. Design, Setting, and Participants A prospective observational study was conducted. Forty-four consecutive patients who had experienced unilateral APAC that was resolved by treatment were recruited. Seventy age- and sex-matched normal individuals were recruited as controls. Methods Enhanced depth imaging–optical coherence tomography was used to measure choroidal thickness (CT) in 9 diffuse locations of macular region. The average CT was compared among each location in the APAC and control groups and between the same locations in the 2 groups. Results Variants of CT at different macular locations were found in both groups; it was greatest at subfoveal locations and spread thinner around them, to reach a significant decrease (all p ≤ 0.05) 3 mm away in all directions from the fovea except for the superior direction in normal controls ( p = 0.472). Among the 4 directions, the superior had the thickest CT in both groups, followed by the temporal, inferior, and nasal directions in both groups, whereas the APAC had a thicker choroid profile at each location (all p p p ≤ 0.05). Conclusions APAC eyes have a thicker choroid than normal eyes in the macular region, and the increase in CT in APAC eyes follows topographic distribution as in normal control eyes.
-
choroidal thickness in fellow eyes of patients with acute primary angle closure measured by enhanced depth imaging spectral domain optical coherence tomography
Investigative Ophthalmology & Visual Science, 2013Co-Authors: Minwen Zhou, Wei Wang, Xiaoyan Ding, Wenbin Huang, Shida Chen, Alan M Laties, Xiulan ZhangAbstract:PURPOSE: We evaluated choroidal thickness in the fellow eyes of patients with acute primary angle-closure (APAC) and compared findings to those of normal controls. METHODS: The study group comprised 44 fellow eyes defined as primary angle-closure suspect (PACS) of 44 subjects who had experienced APAC and 43 eyes of 43 healthy volunteers. Using enhanced depth imaging optical coherence tomography (EDI-OCT), the peripapillary and macular choroidal thickness of the PACS eyes and the control eyes were measured and compared at each location or segment. Pearson correlation analysis and a multivariable regression model were used to evaluate the relationships between choroidal thickness and related factors. RESULTS: At all the macular locations, the choroidal thickness was thickest at the subfovea. The PACS eyes had a thicker choroid than the control eyes at all macular locations (all P 0.05). CONCLUSIONS: PACS eyes that had a fellow eye experience of APAC had a thicker macular choroid than the control eyes. The potential role of a thicker choroid as a risk factor for APAC must be investigated further.
F Eckstein - One of the best experts on this subject based on the ideXlab platform.
-
reference values and z scores for subregional femorotibial cartilage thickness results from a large population based sample framingham and comparison with the non exposed osteoarthritis initiative reference cohort
Osteoarthritis and Cartilage, 2010Co-Authors: F Eckstein, Mei Yang, Ali Guermazi, Frank W Roemer, M Hudelmaier, Kristen Picha, Frdric Baribaud, W Wirth, David T FelsonAbstract:Summary Objective To establish sex-specific (subregional) reference values of cartilage thickness and potential maximal Z-scores in the femorotibial joint. Methods The mean cartilage thickness (ThCtAB.Me) in femorotibial compartments, plates and subregions was determined on coronal magnetic resonance imaging (MRI) from a population-based sample (Framingham) and from a healthy reference sample of the Osteoarthritis Initiative (OAI). Results 686 Framingham participants (309 men, 377 women, age 62±8 years) had no radiographic femorotibial osteoarthritis (OA) ("normals") and 376 (156 men, 220 women) additionally had no MRI features of cartilage lesions ("supernormals"). The Framingham "normals" had thinner cartilage in the medial (3.59mm) than in the lateral femorotibial compartment (3.86mm). Medially, the femur displayed thicker cartilage (1.86mm) than the tibia (1.73mm), and laterally the tibia thicker cartilage (2.09mm) than the femur (1.77mm). The thickest cartilage was observed in central, and the thinnest in external femorotibial subregions. Potential maximal Z-scores ranged from 5.6 to 9.8 throughout the subregions; men displayed thicker cartilage but similar potential maximal Z-scores as women. Mean values and potential maximal Z-scores in Framingham "supernormals" and non-exposed OAI reference participants (112 participants without symptoms or risk factors of knee OA) were similar to Framingham "normals". Conclusions We provide reference values and potential maximal Z-scores of cartilage thickness in middle aged to elderly non-diseased populations without radiographic OA. Results were similar for "supernormal" participants without MRI features of cartilage lesions, and in a cohort without OA symptoms or risk factors. A cartilage thickness loss of around 27% is required for attaining a Z-score of −2.
