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Cypress canker is a branch and stem canker disease of Cupressaceae trees, particularly those in the genera Cupressus and Hesperocyparis. These trees have been planted in many parts of the world as ornamentals and the Seiridium species that cause the disease, consequently, also have an almost global distribution. The taxonomy of Seiridium species causing cypress canker has recently been revised and numerous species are now believed to cause the disease. This study describes, for the first time, cypress canker on the native South African Cupressaceae tree, Widdringtonia nodiflora. The aim was to identify the causal agent and confirm its pathogenicity. Phylogenetic analyses of sequence data for four regions identified the fungus as Seiridium neocupressi, a species previously known only from Australia, New Zealand and Italy. Field inoculations of W. nodiflora branches resulted in distinct cankers within 6 weeks and the fungus could be reisolated from the treated trees. Cypress canker has been known in South Africa for many decades, where it causes a serious disease on nonnative species of Cupressus, but it has never been found on native Cupressaceae. The newly discovered disease caused by a probable alien pathogen is of particular concern because only three species of Widdringtonia occur in South Africa and are important components of the native flora. The two other species, W. wallichii and W. schwartzii, occur in small endemic and threatened populations. The origin of S. neocupressi in South Africa and the relative susceptibility of the three Widdringtonia species, consequently, requires urgent attention. [ABSTRACT FROM AUTHOR]

Aim To maintain biodiversity in plantation forest ecosystems it is important to understand the community assembly process. Canopy thinning effectively increases understorey diversity in plantation forests. However, the process of understorey community assembly after canopy thinning remains unclear. We compared the relative importance of two mechanisms that could affect the assembly of understorey woody communities after thinning: (1) environmental filtering due to competition from canopy trees, and (2) stochastic immigration. If the latter is dominant, the effectiveness of local treatment might be unpredictable because of the variable probability of immigration at each location. Location Yamagata Prefecture, Japan. Methods We censused the understorey tree communities in 18 quadrats (each 1 m × 1 m) in each of 49 stands of Japanese cedar plantations. The mean species richness of the 18 quadrats (alpha-diversity), variation in community composition among them (beta-diversity), deviation of beta-diversity from that of a random community (beta-deviation) and total species richness of the plots (gamma-diversity) were compared among censuses (before thinning, 2 and 5 yr after thinning). The relative contributions of two explanatory variables to the various diversities were examined: (1) basal area of canopy trees (overstorey BA, an index of environmental filtering), and (2) available seed source in the surrounding landscape (landscape effect; an index of the probability of immigration). Results Although neither beta-diversity nor gamma-diversity changed throughout the censuses, the alpha-diversity, stem abundance and beta-deviation were affected by thinning. beta-deviation increased after thinning. Overstorey BA limited alpha- and gamma-diversity throughout the censuses. The landscape effect was more significant in terms of beta-deviation after than before thinning. In addition, the effective scale of the landscape effect increased after thinning. Conclusion Our results indicate that both processes are important: thinning brought about an increase in the relative importance of stochastic immigration as well as a reduction in competitive pressure from canopy trees. These results suggest that while local treatment can increase understorey diversity, stochastic immigration from seed sources is the direct driver after thinning. Although local treatment is effective, its efficiency depends on the seed source availability in the surrounding landscape. [ABSTRACT FROM AUTHOR]

We studied how the dominant factor affecting stem volume growth changes during stand development in a monoclonal stand of Cryptomeria japonica D. Don. Stem analysis was used to compare growth history of trees in an unthinned plot (closed canopy) and a thinned plot (open canopy). In the unthinned plot, the dominant factor affecting stem volume growth was basal area (BA) before canopy closure, whereas neighborhood competition index (CI) was the dominant factor after canopy closure. In contrast, the dominant factor affecting stem volume in the thinned plot was BA throughout stand development. Spearman’s rank correlation coefficient between BA and CI continued to increase after canopy closure and size rank among individuals became increasingly fixed. Our results indicated that stem volume growth shifts from size-dependent to competition-dependent growth at canopy closure. The apparent correlation between tree size and growth rate observed in many previous studies may be the result of competition-mediated positive feedback between size and growth. [ABSTRACT FROM AUTHOR]

Cedrus atlantica (Pinaceae) is a large and exceptionally long-lived conifer native to the Rif and Atlas Mountains of North Africa. To assess levels and patterns of genetic diversity of this species, samples were obtained throughout the natural range in Morocco and from a forest plantation in Arbùcies, Girona (Spain) and analyzed using RAPD markers. Within-population genetic diversity was high and comparable to that revealed by isozymes. Managed populations harbored levels of genetic variation similar to those found in their natural counterparts. Genotypic analyses of molecular variance (AMOVA) found that most variation was within populations, but significant differentiation was also found between populations, particularly in Morocco. Bayesian estimates of FST corroborated the AMOVA partitioning and provided evidence for population differentiation in C. atlantica. Both distance- and Bayesian-based clustering methods revealed that Moroccan populations comprise two genetically distinct groups. Within each group, estimates of population differentiation were close to those previously reported in other gymnosperms. These results are interpreted in the context of the postglacial history of the species and human impact. The high degree of among-group differentiation recorded here highlights the need for additional conservation measures for some Moroccan populations of C. atlantica. [ABSTRACT FROM AUTHOR]

The article focuses on a study related to the establishment of Widdringtonia Cedarbergensis or clanwilliam cedar. It refers to a is a tree species endemic in Cederberg mountains, Cape Province, South Africa. A decline has been noted in their numbers, due to exploitation, stock grazing and modifications in fire regime. In this study, the impact of sowing method, seed density and granivory on the germination and establishment of cedar seedlings, were assessed. It is stated in the conclusion that granivory plays a major role in cedar regeneration, but does not preclude successful reestablishment.