Spread Of Grasses Research Articles

Grasses through space and time: An overview of the biogeographical and macroevolutionary history of Poaceae

AbstractGrasses are widespread on every continent and are found in all terrestrial biomes. The dominance and spread of grasses and grassland ecosystems have led to significant changes in Earth′s climate, geochemistry, and biodiversity. The abundance of DNA sequence data, particularly chloroplast sequences, and advances in placing grass fossils within the family allows for a reappraisal of the family′s origins, timing, and geographic spread and the factors that have promoted diversification. We reconstructed a time‐calibrated grass phylogeny and inferred ancestral areas using chloroplast DNA sequences from nearly 90% of extant grass genera. With a few notable exceptions, the phylogeny is well resolved to the subtribal level. The family began to diversify in the Early–Late Cretaceous (crown age of 98.54 Ma) on West Gondwana before the complete split between Africa and South America. Vicariance from the splitting of Gondwana may be responsible for the initial divergence in the family. However, Africa clearly served as the center of origin for much of the early diversification of the family. With this phylogenetic, temporal, and spatial framework, we review the evolution and biogeography of the family with the aim to facilitate the testing of biogeographical hypotheses about its origins, evolutionary tempo, and diversification. The current classification of the family is discussed with an extensive review of the extant diversity and distribution of species, molecular and morphological evidence supporting the current classification scheme, and the evidence informing our understanding of the biogeographical history of the family.

Preliminary Multi-Proxy 40 Ma Record of the Rise and Spread of Grasses in Montana

Preliminary Multi-Proxy 40 Ma Record of the Rise and Spread of Grasses in Montana

Historical perspectives on invasive grasses and their impact on wildlife in Australia

In recent years, there have been declines of varying severity in many vertebrate species across much of the sparsely populated savannas of northern Australia, and adding to the dismal record of extinctions from arid and semi-arid central Australia since European colonization. It is likely that multiple factors are responsible for the current wave of extinctions, but they are occurring in areas of sparse human population in extensive, seemingly unmodified landscapes. Habitat change is one likely contributing factor, with invasive exotic grasses an important component in some regions. Historically, conservation of native vertebrates has been poor in Australia, with many species being considered vermin under legislation. As late as the 1960s much scientific research was aimed at controlling species that are now considered threatened under legislation. Through the 20th century substantial efforts to introduce exotic pasture species saw the introduction for trial of twice as many species of grasses and legumes as occur naturally on the whole Australian continent. The legacy of these programs is the spread of grasses that, through a range of processes, lead to simplification of floristic structure and reduction in plant species diversity and habitat suitability for many native mammals. Management of these invasive species should focus on preventing their spread into and establishment in new regions, and controlling them where they are established. State and transition models may provide a framework for considering the management and environmental triggers that could lead to re-establishment of native grasses. © 2013 The Wildlife Society.

Effect of fertilization and harvest frequency on floristic composition and yields of meadow stand

The effect of fertilization and the harvest frequency on production and floristic characteristics of a meadow stand were assessed in a small plot trial established in 2003 in Vatín, Vysočina Region, the Czech Republic. Four levels of fertilization (none; N0 + P30 + K60 kg∙ha−1; N90 + P30 + K60 kg∙ha−1; N180 + P30 + K60 kg∙ha−1) were combined with four treatments of exploitation intensity (4 cuts per year, first cut on 15th May, every next after 45 days; 3 cuts per year, first cut on 30th May, every next after 60 days; 2 cuts per year, first cut on 15th June, next after 90 days; 2 cuts per year, first cut on 30th June, next after 90 days). Production of dry matter and proportions of guilds (grasses, legumes, and other species) were evaluated. Data from 2009–2011 were used in this paper. Yields of the dry matter increased along with increasing amounts of nutrients supplied and ranged from 3.8 t∙ha−1 (non-fertilized) to 9.1 t∙ha−1 (N180PK). The nutrition level had a significant effect on spread of grasses, which reached maximal proportion of 52.3 % under N180PK fertilization compared to 42.1% on non-fertilized plots. On the contrary, legumes flourished well in treatments without N-supply, attaining proportion of 6.8 % and 5.1 % on PK-fertilized and non-fertilized plot, respectively. With regard to the exploitation intensity grasses profited from extensive management by contrast to the group of other species which reached its maximum in swards harvested four times a year. Proportions of legumes did not show significant dependence on the cutting frequency.

The ecological impact of oceanic island colonization – a palaeoecological perspective from the Azores

AbstractAim In many cases, human colonization drastically modified the ecosystems of remote oceanic islands before scientists arrived to document the changes. Palaeoecological records before and after human colonization provide insights into the original ecosystems and an assessment of subsequent human impact. We used pollen analysis to compare the impact of 15th century colonization of the Azores with that of natural disturbances such as volcanic eruptions and climate changes.Location Azores archipelago, Atlantic Ocean.Methods Sediment records from three highland sites in the Azores (on the islands of Pico and Flores) were dated radiometrically and analysed palynologically. Pollen taxa were classified as native, endemic or introduced based on comparison with flora lists. Data were statistically zoned and temporal trends identified using detrended correspondence analysis.Results Human colonization of the Azores resulted in rapid, widespread, persistent vegetation changes on a scale unprecedented in the last 2700 years, detectable through the decline of dominant trees, the spread of grasses and fire‐tolerant species, the introduction of exotic plants, evidence for grazing and fire, and changes to soils and moisture availability. During the same period, volcanic eruptions appear to have had more localized impacts on the vegetation, lasting 500–1000 years and favouring endemic taxa. The effect of late Holocene climatic changes on the highland vegetation of the Azores seems to have been minor. Palaeoecological data indicate that at least two plant species went extinct on Pico after human colonization and that some plants regarded as introduced were almost certainly part of the original flora of the islands. Despite a consistent signal of human impact, compositional differences between Juniperus brevifolia communities on Pico and Flores remained after colonization.Main conclusions Human colonization had a greater impact on the pristine vegetation of Pico and Flores than climatic changes and volcanic activity during recent millennia. The similarity between post‐colonization changes on the Azores and other oceanic islands suggests a consistent pattern and scale to historical‐era human impact on otherwise pristine ecosystems. These characteristics could be used to further elaborate biogeographical theory and direct conservation efforts towards species that appear most susceptible to human activity.

A pollen-based record of late glacial–Holocene climatic variability in the southern lake district, Chile

A pollen record from Puyehue area (40°S; 72°W) in the southern Lake District, Chile, indicates that prior to 13,410 14C yr BP (ca. 16,500–15,200 cal yr BP), cold resistant and hygrophilous vegetation, particularly Nothofagus forest and myricaceous vegetation, covered the area. From ca. 15,000 cal yr BP onward, the forest became increasingly dense. Between 10,010 and 7450 14C yr BP (ca. 11,000–8000 cal yr BP), the expansion of Nothofagus obliqua and the spread of grasses suggests the climate became warmer and semi-arid. Lowland deciduous forest (Nothofagus obliqua, Aextoxicon punctatum, Laurelia sempervirens) and Valdivian rainforest (Nothofagus dombeyi, Eucryphia cordifolia, Caldcluvia paniculata, Aextoxicon punctatum, Laureliopsis philippiana) were abundant. During the next two thousand years, stable warm climatic conditions prevailed, and the diversity of the vegetation increased. From 5760 to 1040 14C yr BP (ca. 6500–900 cal yr BP), the North Patagonian rainforest expanded. The presence of Pilgerodendron/Fitzroya, together with Nothofagus forest, suggests that humid conditions prevailed. During the last millennium, human impact intensified and regional vegetation was disturbed, particularly the lowland deciduous forest and Valdivian rainforest. North-Patagonian and subantartic taxa, such as Podocarpus nubigena, Pilgerodendron/Fitzroya, Nothofagus dombeyi type, Austrocedrus chilensis and Drimys winteri, occupied the low and high-altitude parts of the Cordillera. Five hundred years ago, shrub and grasses expanded in the Nothofagus forest, suggesting that forest became more open under cool–cold, and humid climatic conditions. These conditions prevail to the present day.

Managing Orchard Floor Vegetation in Flood-irrigated Citrus Groves

Several orchard floor management strategies were evaluated beginning in Fall 1993 in a `Limoneira 8A Lisbon' lemon (Citrus limon) grove on the Yuma Mesa in Yuma, Ariz. and in a `Valencia' orange (Citrus sinensis) grove at the University of Arizona Citrus Agricultural Center, Waddell, Ariz. At Yuma, disking provided acceptable weed control except underneath the tree canopies where bermudagrass (Cynodon dactylon), purple nutsedge (Cyperus rotundus), and other weed species survived. Mowing the orchard floor suppressed broadleaf weed species allowing the spread of grasses, primarily bermudagrass. Preemergence (norflurazon and oryzalin) and postemergence (glyphosate and sethoxydim) herbicides were used to control weeds in the clean culture treatment in Yuma. After three harvest seasons (1994-95 through 1996-97), the cumulative yield of the clean culture treatment was 385 kg (848.8 lb) per tree, which was significantly greater than the 332 kg (731.9 lb) and 320 kg (705.5 lb) per tree harvested in the disking and mowing treatments, respectively. In addition, the clean culture treatment had a significantly greater percentage of fruit in the 115 and larger size category at the first harvest of the 1995-96 season than either the disk or mow treatments. At Waddell, the management strategies compared were clean culture (at this location only postemergence herbicides were used), mowing of resident weeds with a vegetation-free strip in the tree row, and a `Salina' strawberry clover (Trifolium fragiferum) cover crop with a vegetation-free strip. The cumulative 3-year yield (1994-95 through 1996-97) of the clean culture treatment was 131 kg (288.8 lb) per tree, which was significantly greater then the 110 kg (242.5 lb) per tree yield of the mowed resident weed treatment. The yield of the strawberry clover treatment, 115 kg (253.5 lb) of oranges per tree, was not significantly different from the other two treatments. The presence of cover crops or weeds on the orchard floor was found to have beneficial effects on soil nitrogen and soil organic matter content, but no effect on orange leaf nutrient content. The decrease in yield in the disked or mowed resident weed treatments compared to the clean culture treatment in both locations was attributed to competition for water.

Comparative nutritional ecology of grass-feeding in a sub-Antarctic beetle: the impact of introduced species on Hydromedion sparsutum from South Georgia.

South Georgia has many introduced plant and animal species, a consequence of its long history of human habitation. Introduced reindeer have a strong effect on the vegetation of the Stromness Bay area by causing the replacement of indigenous species by grazing-tolerant grasses such as the exotic Poa annua, and in certain circumstances, the indigenous Festuca contracta. Recently it has been argued that an introduced predatory carabid has contributed to declines in the abundance and an increase in the body size of adults of the indigenous perimylopid beetle Hydromedion sparsutum. However, it also appears that body size of these beetles is smaller in areas where exotic grasses predominate compared to undisturbed areas. Here we test the hypothesis that by causing the spread of poorer quality grasses, especially the exotic Poa annua, reindeer may be having an indirect effect on H. sparsutum. To do this we examined the nutritional ecology of H. sparsutum larvae on four grass species which form a major part of its diet, viz. the indigenous Parodiochloa flabellata, Phleum alpinum and Festuca contracta, and the exotic Poa annua. Larvae showed the highest growth rate on Parodiochloa flabellata, followed by Phleum alpinum, F. contracta and Poa annua. These differences are due to poorer absorption of the exotic grass, and poorer utilization of the absorbed material in the case of F. contracta. Poor growth of larvae on F. contracta appears to be due to its low water and nitrogen contents, whereas in the case of P. annua a combination of low water content and high nitrogen content may be responsible for low growth rates. Low growth rates associated with poor-quality food may lead either to a prolongation of the life cycle or of the length of feeding bouts of an insect. Neither option appears to be feasible for H. sparsutum, and this means that the outcome of feeding on poorer-quality foods would be a reduction in final adult size. This has fitness consequences for the beetle. Hence it appears that by causing the spread of grasses that are unsuitable for growth of H. sparsutum, reindeer may be having an indirect effect on this beetle species.