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Climate was also found to be a significant variable and it was hypothesized that landscape patterns may influence important microclimate conditions that have an affect on the reproduction and survival of pathogens. For example, temperature has been found be related to structural aspects of the landscape such as overstorey canopy,
The central hypothesis that was tested was that, "...small isolated forest fragments have lower levels of P. ramorum infection, owing to an associated larger grassland dispersal barrier and less suitable microclimate conditions." 7
In general it as found that landscape-scale configuration as well as local composition of host habitats are both linked to the degree of destructiveness of the disease. The result showed that the structure and composition of the forest or woodland was severely affected by the disease, which in turn had a serious effect on both host and pathogen. 5 More specifically it was found that; "P. ramorum disease severity was greatest in plots surrounded by a high proportion of contiguous forest, after accounting for plot-level variables of host abundance, elevation, canopy cover and microclimate. 5
In other words the more contiguous or uninterrupted the forest was, the more severe the disease tended to be. Foliar hosts such as evergreen tree bay laurel (Umbellularia california) are also considered to play a central role in the transmission of the disease. 6
In general it way found that the severity of Phytophthora ramorum disease was most severe in plots or areas where there were a high percentage of woodland habitats. 8 Another finding was that landscape patterns affected the severity of the disease in terms of scale. Microclimatic conditions for the reproduction of the pathogen were influenced more by topography than by landscape patterns.
Therefore the "...response of P. ramorum to habitat conditions depended on landscape pattern and the spatial scale of the observation." 8
Conversely, an important factor was that "...P. ramorum had no response to landscape pattern at small scales..." 8 significant finding was that;
As the amount of woodland surrounding a plot increases, it is likely that the abundance of inoculum-producing hosts (e.g. bay laurel) also increases. Therefore, high disease severity in areas surrounded by the continuous forest is probably due to a greater available inoculum reservoir. 8
The study also shows that extensive and contiguous forest areas provide a greater surface area which can intercept propagules or plant material used for the purpose of plant propagation. This means that the chances of the colonization of pathogens in an area are directly related to the size of that area. This in turn means that the greater the amount of possible hosts increases the extent and severity of the disease; and this results in "....the potential for higher inoculum production within contiguous woodland and a lower probability of disease extinction." 9
As a consequence these areas became more amendable to the pathogen and over a period of time they maintained more serious and resilient levels of the disease than would be the case in smaller areas of forest.
Another important aspect of these findings is that the fragmentation of the forest or woodlands can reduce the spread of the pathogens. Consequently the pathogens become less mobile and distance was found to reduce the transmission probability of the disease from infected hosts.
This study is important to the extent that it emphasizes the value of, "Determining the spatial scale of a species' response to habitat... For understanding movement ranges and dispersal of invasive organisms such as P. ramorum." 10
On a more general level the study is important as a contribution to the understanding of how ecology and the physical environment affects and influences the spread, reproduction and severity of this particular pathogen. These findings therefore suggest that solutions to this problem lie in an intensive and extensive understanding of the variables, such as landscape that contribute to the proliferation of this pathogen.
In summary these findings suggest a number of important outcomes. In general the research strongly indicates that landscape and the local physical and topological characteristics of habitat are related and influence the development and distribution of pathogens.
Comparison of articles
The first article discussed Sudden oak death: endangering California and Oregon forest ecosystems provides more of a general overview of the disease and the pathogen in question. The second article, Effects of landscape heterogeneity on the emerging forest disease sudden oak death, is more focused on specific aspects of the development and the reproduction of the pathogen and is therefore more directed and intensive in its analysis and methodology.
While the first article is discursive and general it also provides a fairly comprehensive and detailed overview of certain aspects that are seen to be important in the study of this disease. The two articles, while they differ in terms of their focus, complement one another to a great extent and have many points of concurrence.
One do the most obvious points of similarity between the two articles is the view that relates the range and the severity of the disease to human involvement and especially to the human interface in relation to the ecology of the regions involved. As the second article emphasizes;" a major consequence of human expansion and global movement is the number of emerging and re-emerging infectious diseases." 5 the first article by Rizzo and Matteo Garbelotto also describes the effect and the result of human involvement in the spread of the development and spread of the pathogens.
Both articles emphasize the relative importance of different variables and in particular the significance of the different host plants in the importation of the pathogen. This is seen to be an important aspect of the general problem. For example, the second article draws attention to the importance of heterogeneous spatial patterns of habitat in the spread of forest pathogens and the way that this aspect is related to regional outbreaks of the disease. 6
The findings of both articles stress the importance of understanding the complexities and the vicissitudes of the relevant ecological systems. This is seen as an essential aspect that is necessary if the disease is to be understood and combated. Another important aspect that is referred to, especially in the second article, is the role of microclimate and the way that this aspect affects the spread of the pathogens.
In general both studies find that preventing the spread of these pathogens and denying them access to other areas is heavily dependent on the facets that influence the ecology of the areas concerted. The numerous variables such as topography, climate and landscape are elements that are inextricably linked and which have varying effects on the spread an the severity of the disease.
Finally, one of the most important aspects that both articles stress is the importance of further research and study in this area of concern. In both articles there is a realization which is reiterated a number of times, that the research that has been undertaken represents a comparatively early stage in the understanding of these pathogens and that a more integrated and cohesive body of research is needed if the problem is to be dealt with realistically.
Rizzo D., Garbelotto M. Sudden oak death: endangering California and Oregon forest ecosystems. Frontiers in Ecology and the Environment. 2003. 1 (4): 198.
Rizzo D., Garbelotto M. Sudden oak death: endangering California and Oregon forest ecosystems. Frontiers in Ecology and the Environment. 2003. 1 (4): 199.
Rizzo D., Garbelotto M. Sudden oak death: endangering California and Oregon forest ecosystems. Frontiers in Ecology and the Environment. 2003. 1 (4): 200.
Rizzo D., Garbelotto M. Sudden oak death: endangering California and Oregon forest ecosystems. Frontiers in Ecology and the Environment. 2003. 1 (4): 203.
CONDESO T., ROSS K. MEENTEMEYER. Effects of landscape heterogeneity on the emerging forest disease sudden oak death. Journal of Ecology. 2007. 95 (2), 365.
CONDESO T., ROSS K. MEENTEMEYER. Effects of landscape heterogeneity on the emerging forest disease sudden oak death. Journal of Ecology. 2007. 95 (2), 366.
CONDESO T., ROSS K. MEENTEMEYER. Effects of landscape heterogeneity on the emerging forest disease sudden oak death. Journal of Ecology.…[continue]
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