Higher Establishment Success Research Articles

Can artificial introductions of diaspore fragments work as a conservation tool for maintaining populations of the rare peatmoss Sphagnum angermanicum?

Species can become regionally rare when limited by the availability of suitable habitats or by limited dispersal ability. We tested if the presence of a rare bryophyte species ( Sphagnum angermanicum) was dispersal or habitat limited and at the same time investigated the possibility of establishing new populations of this rare species. Further, we tested how propagule (fragment) size and small scale disturbances affected establishment success. All field experiments were performed by artificially transporting propagules (of various sizes) to new and old sites for the species in Sweden. We show that S. angermanicum is dispersal limited on a regional scale, as no significant differences in establishment success were found between new suitable sites and old occupied sites. The larger the propagule the better was the establishment success; the best establishment success was found when transplanting whole shoots. Disturbances did not increase establishment success, in contrary, when compared to controls success was reduced by the more intensive disturbance treatments. We suggest that disturbance maybe more important for increasing direct dispersal than for making the microhabitat more advantageous for establishment. However, an intermediate disturbance, which slightly reduces the Sphagnum-community length increment, might also be beneficial for the establishment success of S. angermanicum propagules. The reasonably high establishment success of S. angermanicum propagules in new suitable sites suggests that artificial introductions of fragments could be considered as an active management regime for the species if the number of localities continues to decrease.

Establishment and Growth of Living Fence Species: An Overlooked Tool for the Restoration of Degraded Areas in the Tropics

Abstract Numerous tree species can establish by vegetative means in the tropics. Many are used in agriculture as living fences and in alley cropping and could also be used in a restorational setting. However, little is known about their establishment ability. This study evaluated the establishment ability and cover development of multiple species in three separate field trials in northern Honduras. First, 11 species were evaluated for their ability to establish in a common garden experiment. Second, of the former species, Bursera simaruba and Gliricidia sepium were evaluated for 2 years for their ability to establish vegetatively and develop cover at three deforested sites. Lastly, a study examined whether greater initial stake height and diameter at breast height increased the establishment success and crown development of G. sepium stakes. First, five species, Erythrina berteroana, Erythrina fusca, Jatropha curcas, G. sepium, and B. simaruba, had high establishment success. Others showed promise but may have been planted in the wrong season. Second, establishment for G. sepium was nearly 100% at all sites, whereas B. simaruba ranged from 30–50%. Gliricidia sepium stakes developed more rapidly and attained greater cover than B. simaruba. Dry season planting may increase the establishment success of both species. Lastly, greater initial stake height and diameter at breast height each resulted in greater crown development for G. sepium. The use of living fence species as a restorational tool has been overlooked. Aside from the advantages of planting tree species vegetatively, species can act as seed recruitment foci by attracting seed dispersers and provide shade to improve microclimatic conditions for seedling establishment. The technique described is simple and could have broad application throughout tropical regions.

Seasonal and ontogenetic dynamics in trophic transmission of parasites

Transmission rates from the intermediate (amphipods) to the definitive hosts (fish) were quantified for two helminth species (Cyathocephalus truncatus, Cestoda, and Cystidicola farionis, Nematoda) both seasonally and through the ontogeny of the final hosts (arctic charr, Salvelinus alpinus, and brown trout, Salmo trutta). Amphipods (Gammarus lacustris) were important prey for both fish species, especially in the autumn. Both parasite species had low infection levels in amphipods compared to high abundance in fish. The seasonal variations in transmission rate of C. truncatus procercoids from amphipods to fish were in accordance with the observed abundance in fish hosts, being highest in the autumn and lowest during late winter and early summer. During summer, however, the estimated monthly transmission rates of C. truncatus were higher than the observed infection levels in the fish, suggesting restricted establishment success and shorter development time and longevity of the cestode in fish at higher temperatures. The accumulated transmission of C. farionis over the ontogeny of arctic charr was similar to the observed age‐specific infection levels, reflecting a high establishment success and longevity of this parasite in charr. In contrast, brown trout exhibited an infection level that was much lower than the estimated transmission rates, suggesting a high resistance against C. farionis in these fish. The magnitudes of the estimated transmission rates were sufficient to explain the paradoxical contrast between low infection levels in the intermediate and high in the final hosts.

Establishment of Native Grass Seedlings along a Topographic/Moisture Gradient in the Nebraska Sandhills

-This study examines the effect of differential survival of seedlings on the distribution of native grasses along topographic gradients in the Nebraska Sandhills. In 1981, seeds of three ridge species (Andropogon hallii, Sorghastrum nutans, Panicum virgatum) were planted into rototilled, irrigated, rototilled and irrigated, or untreated soils on three sites: one ridge site (ridge) and two valley sites (valley and lowland). The three sites represented a gradient of topography and soil moisture-holding capacity. For all species, seedling survival was greatest (86%) in the rototilled and irrigated treatment on the lowland site. No seedlings survived in untreated plots along the gradient. In 1982 and 1983, seeds of a ridge species (Andropogon hallii) and a valley species (Bouteloua gracilis) were planted in replicated ridge and valley plots. Seeds were planted into either untreated plots, or plots where plants received weekly clipping treatments around seedlings. Although clipping significantly increased survival of both species in both sites, it had a significantly greater effect in valley sites. In untreated plots, seedling survival was greatest (20%) in ridge sites in a year of average precipitation (1982) and in valley sites (49%) in a year that was exceptionally wet (1983). In 1983, soil moisture explained 98% of the variation in the survival of A. hallii seedlings and 82% in B. gracilis seedlings. Competition from existing vegetation severely limited the probability of seedling establishment. The distribution pattern of ridge species likely results from differential survival of juveniles and adults along the gradient, rather than the ability of seedlings to have higher establishment success on ridge sites. Significant establishment of the valley species (Bouteloua gracilis) occurred only during an exceptionally wet year when the pattern of survival of seedlings reflected the distribution pattern of adult plants. Establishment of prairie grass seedlings appears to depend on the availability of soil moisture, which may only be adequate in relatively large disturbance areas (> 1 m2), or in years of higher than normal precipitation.