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Small-scale Disturbance (small-scale + disturbance)
Selected AbstractsNassella pulchra Survival and Water Relations Depend More on Site Productivity Than on Small-Scale DisturbanceRESTORATION ECOLOGY, Issue 2 2007Keith Lombardo Abstract We found no significant effect (p > 0.38) of clipping surrounding non-native annuals on the performance or survival of plantings of the native Nassella pulchra. However, the preplanting productivity of the three sites had a significant effect (p < 0.001) on the demography and water relations of Nassella. Survival was 85% on the lowest productivity site and it decreased by 6% for each additional 100 kg in average aboveground productivity between 2,400 and 3,600 kg/ha. Plants experienced greater water stress in higher productivity sites. Together, these results suggest that the original habitat of N. pulchra may have been in more marginal ecological sites rather than the more fertile soils of the Central Valley. [source] Influence of nests of leaf-cutting ants on plant species diversity in road verges of northern PatagoniaJOURNAL OF VEGETATION SCIENCE, Issue 3 2000A.G. Farji-Brener Correa (1969,1998) Abstract. It has been suggested that ant nests are the most frequent small-scale disturbance that affect vegetation patterns. However, their effects on plant diversity are little studied. We document effects of nests of the leaf-cutting ant Acromyrmex lobicornis on physical-chemical soil properties and their influence on plant diversity near road verges in a desert steppe in NW Patagonia, Argentina. We analysed nest soils and controls for nitrogen, phosphorus, organic matter, moisture retention capacity and texture. We also analysed the vegetation on 42 nests (30 active and 12 abandoned or without life) and 42 areas without nests. Soil around nests had a greater nutrient content and capacity to retain moisture than control soils, which is mainly due to the presence of organic waste that the ants deposit on the soil surface. We found no association between the occurrence of nests and specific groups of plants, but plant diversity was higher at nest-sites than at nearby non-nest sites. This increased diversity , which is also found on abandoned nests , is mainly due to the occurrence of a larger number of native and exotic plant species on nest-sites that are uncommon elsewhere in the study area. The most abundant plant species showed similar cover values at nest and non-nest sites. This suggests that changes in diversity are associated to edaphic changes caused by nests rather than by changes in competitive balance caused by dominant species exclusion. We propose that the nests of Acromyrmex lobicornis, through increasing the availability of resources, generate favourable microsites that can function both as ,refuges' for less frequent native species, and as,stepping stones' for less frequent exotic plant species. [source] Factors determining the centrifugal organization of remnant Festuca grassland communities in AlbertaJOURNAL OF VEGETATION SCIENCE, Issue 1 2000K. Vujnovic Moss (1983); Pavlick & Looman (1984) Abstract. This paper describes the species composition of remnant grasslands in the aspen parkland region of Alberta and its relation to soil characteristics and small-scale disturbance. Our findings are consistent with the centrifugal model of communities with Festuca hallii dominating undisturbed ,core' habitat and the composition of more ,peripheral' habitats varying in soil properties and in the magnitude of disturbance. Invasive non-native species are not present in the core habitat and are present only in the disturbed sites, most abundantly in those with the highest soil nitrogen. The centrifugal model, as it applies to these remnant grasslands, differs from its previous application to wetlands and forests in that the core communities are not on the most fertile sites, but on the least disturbed. These findings have implications for the management of prairie remnants to exclude invasive exotic species. [source] The role of successional stage and small-scale disturbance for establishment of pioneer grass Corynephorus canescensAPPLIED VEGETATION SCIENCE, Issue 3 2010Okka Tschöpe Abstract Question: Which mechanisms promote the maintenance of the protected pioneer grass Corynephorus canescens in a mosaic landscape? Which are the interactive effects of small-scale disturbances, successional stage and year-to-year variation on early establishment probabilities of C. canescens? Location: Brandenburg, NE Germany. Methods: We measured emergence and survival rates over 3 yr in a sowing-experiment conducted in three successional stages (C. canescens -dominated site, ruderal forb site and pioneer forest) under two different regimes of mechanical ground disturbance (disturbed versus undisturbed control). Results: Overall, disturbance led to higher emergence in a humid year and to lower emergence in a very dry year. Apparently, when soil moisture was sufficient, the main factor limiting C. canescens' establishment was competition, while in the dry year, water became the limiting factor. Survival rates were not affected by disturbance. In humid years, C. canescens emerged in higher numbers in open successional stages while in the dry year, emergence rates were higher in late stages, suggesting an important role of late successional stages for the persistence of C. canescens. Conclusions: Our results suggest that small-scale disturbances can promote germination of C. canescens. However, disturbances should be carefully planned. The optimal strategy for promoting C. canescens is to apply disturbances just before seed dispersal and not during dry years. At the landscape scale, a mosaic of different vegetation types is beneficial for the protected pioneer grass as facilitation by late-successional species may be an important mechanism for the persistence of C. canescens, especially in dry years. [source] Interactions of multiple disturbances in shaping boreal forest dynamics: a spatially explicit analysis using multi-temporal lidar data and high-resolution imageryJOURNAL OF ECOLOGY, Issue 3 2010Udayalakshmi Vepakomma Summary 1.,Mixed-wood boreal forests are often considered to undergo directional succession from shade-intolerant to shade-tolerant species. It is thus expected that overstorey gaps should lead to the recruitment of shade-tolerant conifers into the canopy in all stand development stages and that the recruitment of shade-intolerant hardwoods would be minimal except in the largest gaps. 2.,We analysed short-term gap dynamics over a large 6-km2 spatial area of mixed-wood boreal forest across a gradient of stands in different developmental stages with different times of origin since fire (expressed as stand ,age') that were affected differentially by the last spruce budworm (SBW) outbreak. Structural measurements of the canopy from lidar data were combined with spectral classification of broad species groups to characterize the gap disturbance regime and to evaluate the effect of gap openings on forest dynamics. 3.,Estimated annual gap opening rates increased from 0.16% for 84-year-old stands to 0.88% for 248-year-old stands. Trees on gap peripheries in all stands were more vulnerable to mortality than interior canopy trees. 4.,Due to recovery from the last SBW outbreak 16 years previously, gap closure rates were higher than opening rates, ranging from 0.44% to 2.05% annually, but did not show any relationship with stand age. There was, however, a continuing legacy of the last SBW outbreak in old-conifer stands in terms of a continued high mortality of conifers. In all stands, the majority of the openings were filled from below, although a smaller but significant proportion filled from lateral growth of gap edge trees. 5.,Synthesis. The forest response to moderate- to small-scale disturbances in old-growth boreal forest counters the earlier assumption that the transition from one forest state to the next is slow and directional with time since the last fire. Overall, a small 6% increase in hardwoods was observed over 5 years, largely due to regeneration in-filling of hardwoods in gaps instead of successional transition to more shade-tolerant conifers. Gaps are vital for hardwood maintenance while transition to softwoods can occur without perceived gap-formation as overstorey trees die, releasing understorey trees. [source] The role of successional stage and small-scale disturbance for establishment of pioneer grass Corynephorus canescensAPPLIED VEGETATION SCIENCE, Issue 3 2010Okka Tschöpe Abstract Question: Which mechanisms promote the maintenance of the protected pioneer grass Corynephorus canescens in a mosaic landscape? Which are the interactive effects of small-scale disturbances, successional stage and year-to-year variation on early establishment probabilities of C. canescens? Location: Brandenburg, NE Germany. Methods: We measured emergence and survival rates over 3 yr in a sowing-experiment conducted in three successional stages (C. canescens -dominated site, ruderal forb site and pioneer forest) under two different regimes of mechanical ground disturbance (disturbed versus undisturbed control). Results: Overall, disturbance led to higher emergence in a humid year and to lower emergence in a very dry year. Apparently, when soil moisture was sufficient, the main factor limiting C. canescens' establishment was competition, while in the dry year, water became the limiting factor. Survival rates were not affected by disturbance. In humid years, C. canescens emerged in higher numbers in open successional stages while in the dry year, emergence rates were higher in late stages, suggesting an important role of late successional stages for the persistence of C. canescens. Conclusions: Our results suggest that small-scale disturbances can promote germination of C. canescens. However, disturbances should be carefully planned. The optimal strategy for promoting C. canescens is to apply disturbances just before seed dispersal and not during dry years. At the landscape scale, a mosaic of different vegetation types is beneficial for the protected pioneer grass as facilitation by late-successional species may be an important mechanism for the persistence of C. canescens, especially in dry years. [source] | |||||||||||||