Demography of Grazed Tussock Grass Populations in Patagonia
The cover of Festuca gracillima (coirón fueguino), a native tussock grass that dominates grass steppes of Southern Patagonia and Tierra del Fuego, has diminished under continuous sheep grazing. This loss is a concern, because it also reduces forage availability in winter, biodiversity, and soil stab...
| Autores principales: | , , |
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| Formato: | info:ar-repo/semantics/artículo |
| Lenguaje: | Inglés |
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Elsevier
2025
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| Materias: | |
| Acceso en línea: | http://hdl.handle.net/20.500.12123/22405 https://www.sciencedirect.com/science/article/abs/pii/S1550742405500745 https://doi.org/10.2111/1551-5028(2005)58[466:DOGTGP]2.0.CO;2 |
| _version_ | 1855038564085006336 |
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| author | Oliva, Gabriel Esteban Collantes, Marta Beatriz Humano, Gervasio |
| author_browse | Collantes, Marta Beatriz Humano, Gervasio Oliva, Gabriel Esteban |
| author_facet | Oliva, Gabriel Esteban Collantes, Marta Beatriz Humano, Gervasio |
| author_sort | Oliva, Gabriel Esteban |
| collection | INTA Digital |
| description | The cover of Festuca gracillima (coirón fueguino), a native tussock grass that dominates grass steppes of Southern Patagonia and Tierra del Fuego, has diminished under continuous sheep grazing. This loss is a concern, because it also reduces forage availability in winter, biodiversity, and soil stability. In the present study, the hypothesis that tussock grass birth and mortality rates are balanced only under moderate-grazing or exclusion regimes was tested with two 5-year records of demographic data obtained from 3 sheep grazing regimes: exclosure (no grazing), low (0.0348 AU·ha−1·y−1, where AU represents animal units equivalent to the consumption of a 450-kg cow), and high (0.1043 AU·ha−1·y−1). Tussocks were outlined in photographs and marked in the field at two 5-year intervals. The initial total number of plants for the 3 grazing regimes (n = 358) increased to 384 plants at the end of the 10-year period. No recruitment from seed was observed; plant number changed as a balance of yearly rates of tussock mortality (1.48%), amalgamation (0.75%), and subdivision (2.04%). Intensely grazed populations showed greater (2.13%) mortality rates than ungrazed (1.20%) or moderately grazed (0.78%) populations. Tussocks in intensely grazed populations were smaller (167 cm2·plant−1) than those in moderately grazed (197 cm2·plant−1) or ungrazed (300 cm2·plant−1) populations. Transition matrices showed eigenvalues of 0.701 (high grazing), 0.794 (exclosure), and 0.876 (low grazing). All growth rates of demographic models were negative; the largest rate of population decrease was found under high-intensity grazing, for which projections show that half the tussocks would be lost in 37 years. Under low-intensity grazing and exclosure, a similar tussock loss would take place in 87 and 74 years, respectively. Results show 1) the importance of vegetative processes for tussock demography, 2) the extremely slow dynamics of population changes, and 3) that tussocks may suffer increased mortality as a consequence of subdivision or fragmentation, a process that can be viewed as a small-scale example of the generalized effect of patch subdivision under grazing. |
| format | info:ar-repo/semantics/artículo |
| id | INTA22405 |
| institution | Instituto Nacional de Tecnología Agropecuaria (INTA -Argentina) |
| language | Inglés |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Elsevier |
| publisherStr | Elsevier |
| record_format | dspace |
| spelling | INTA224052025-05-23T12:32:42Z Demography of Grazed Tussock Grass Populations in Patagonia Oliva, Gabriel Esteban Collantes, Marta Beatriz Humano, Gervasio Grasslands Demography Steppes Drylands Sheep Biomass Praderas Demografía Rangelands Tierras de Pastos Estepas Tierras Secas Ovinos Biomasa Santa Cruz (Argentina) Grassland Ecology Arid Ecosystems Matrix Population Model Ecología de Pastizales Festuca gracillima Ecosistemas Aridos Modelo Matricial de Población Región Patagónica The cover of Festuca gracillima (coirón fueguino), a native tussock grass that dominates grass steppes of Southern Patagonia and Tierra del Fuego, has diminished under continuous sheep grazing. This loss is a concern, because it also reduces forage availability in winter, biodiversity, and soil stability. In the present study, the hypothesis that tussock grass birth and mortality rates are balanced only under moderate-grazing or exclusion regimes was tested with two 5-year records of demographic data obtained from 3 sheep grazing regimes: exclosure (no grazing), low (0.0348 AU·ha−1·y−1, where AU represents animal units equivalent to the consumption of a 450-kg cow), and high (0.1043 AU·ha−1·y−1). Tussocks were outlined in photographs and marked in the field at two 5-year intervals. The initial total number of plants for the 3 grazing regimes (n = 358) increased to 384 plants at the end of the 10-year period. No recruitment from seed was observed; plant number changed as a balance of yearly rates of tussock mortality (1.48%), amalgamation (0.75%), and subdivision (2.04%). Intensely grazed populations showed greater (2.13%) mortality rates than ungrazed (1.20%) or moderately grazed (0.78%) populations. Tussocks in intensely grazed populations were smaller (167 cm2·plant−1) than those in moderately grazed (197 cm2·plant−1) or ungrazed (300 cm2·plant−1) populations. Transition matrices showed eigenvalues of 0.701 (high grazing), 0.794 (exclosure), and 0.876 (low grazing). All growth rates of demographic models were negative; the largest rate of population decrease was found under high-intensity grazing, for which projections show that half the tussocks would be lost in 37 years. Under low-intensity grazing and exclosure, a similar tussock loss would take place in 87 and 74 years, respectively. Results show 1) the importance of vegetative processes for tussock demography, 2) the extremely slow dynamics of population changes, and 3) that tussocks may suffer increased mortality as a consequence of subdivision or fragmentation, a process that can be viewed as a small-scale example of the generalized effect of patch subdivision under grazing. Festuca gracillima (coirón fueguino) es una gramínea mediana dominante en los pastizales del sur de la Patagonia y norte de Tierra del Fuego que ha ido perdiendo cobertura bajo pastoreo continuo. El proceso implica también una reducción en el forraje disponible en invierno, en la estabilidad del suelo y en la biodiversidad. El presente trabajo analiza 10 años de demografía de poblaciones de coirones sujetos a pastoreo controlado con tres intensidades: clausura (sin pastoreo), alta (0.1043 AU·ha−1·año−1, AU son unidades animales equivalentes al consumo de una vaca de 450 kg), y baja (0.0348 AU·ha−1·año−1). Se puso a prueba la hipótesis de que las tasas de natalidad y mortalidad llegan al equilibrio solamente bajo pastoreo moderado o en exclusión. Los coirones fueron identificados en mapas fotográficos y marcados en el campo en dos períodos consecutivos de cinco años. La población inicial de 358 plantas cambió lentamente, dando lugar a 384 individuos al cabo de diez años. No se observó reclutamiento por semilla, y el número de individuos varió de acuerdo al balance entre tasas anuales de mortalidad (1.48%), fusión (0.75%) y subdivisión (2.04%) vegetativa. Las poblaciones bajo alta carga animal mostraron mayores tasas anuales de mortalidad (2.13%) que las de áreas clausuradas (1.20%) o las moderadamente pastoreadas (0.78%). Los coirones de áreas pastoreadas fueron más pequeños (167 cm2·planta−1) que los de áreas pastoreadas moderadamente (197 cm2·planta−1) o las clausuradas (300 cm2·planta−1). Las matrices de transición muestran autovalores de 0.701 (alta carga), 0.794 (clausura), y 0.876 (baja carga). Todas las tasas de crecimiento poblacional asociadas son negativas. Las proyecciones muestran caídas más marcadas en las poblaciones bajo altas cargas, que perderían un 50% de sus individuos en 37 años, mientras que las sujetas a bajas cargas animales y clausura llegarían a una caída similar en un plazo de 74 y 87 años, respectivamente. Los resultados señalan 1) la importancia de la reproducción vegetativa en la demografía de estos coirones, 2) una dinámica poblacional extremadamente lenta, 3) que los coirones pueden sufrir mayor mortalidad por fragmentación, un ejemplo en pequeña escala el efecto generalizado de subdivisión de parches que el pastoreo provoca en los ecosistemas. EEA Santa Cruz, INTA Fil: Oliva, Gabriel Esteban. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina. Fil: Oliva, Gabriel Esteban. Universidad Nacional de la Patagonia Austral. Unidad Académica Río Gallegos; Argentina. Fil: Collantes, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Estudios Farmacológicos y Botánicos; Argentina. Fil: Humano, Gervasio. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina. 2025-05-23T12:21:27Z 2025-05-23T12:21:27Z 2005-09 info:ar-repo/semantics/artículo info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion http://hdl.handle.net/20.500.12123/22405 https://www.sciencedirect.com/science/article/abs/pii/S1550742405500745 Oliva, G., Collantes, M., & Humano, G. (2005). Demography of grazed tussock grass populations in Patagonia. Rangeland Ecology & Management, 58(5), 466-473. https://doi.org/10.2111/1551-5028(2005)58[466:DOGTGP]2.0.CO;2 1550-7424 https://doi.org/10.2111/1551-5028(2005)58[466:DOGTGP]2.0.CO;2 eng info:eu-repo/semantics/restrictedAccess http://creativecommons.org/licenses/by-nc-sa/4.0/ Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) application/pdf Elsevier Rangeland Ecology & Management 58 (5) : 466-473. (September 2005) |
| spellingShingle | Grasslands Demography Steppes Drylands Sheep Biomass Praderas Demografía Rangelands Tierras de Pastos Estepas Tierras Secas Ovinos Biomasa Santa Cruz (Argentina) Grassland Ecology Arid Ecosystems Matrix Population Model Ecología de Pastizales Festuca gracillima Ecosistemas Aridos Modelo Matricial de Población Región Patagónica Oliva, Gabriel Esteban Collantes, Marta Beatriz Humano, Gervasio Demography of Grazed Tussock Grass Populations in Patagonia |
| title | Demography of Grazed Tussock Grass Populations in Patagonia |
| title_full | Demography of Grazed Tussock Grass Populations in Patagonia |
| title_fullStr | Demography of Grazed Tussock Grass Populations in Patagonia |
| title_full_unstemmed | Demography of Grazed Tussock Grass Populations in Patagonia |
| title_short | Demography of Grazed Tussock Grass Populations in Patagonia |
| title_sort | demography of grazed tussock grass populations in patagonia |
| topic | Grasslands Demography Steppes Drylands Sheep Biomass Praderas Demografía Rangelands Tierras de Pastos Estepas Tierras Secas Ovinos Biomasa Santa Cruz (Argentina) Grassland Ecology Arid Ecosystems Matrix Population Model Ecología de Pastizales Festuca gracillima Ecosistemas Aridos Modelo Matricial de Población Región Patagónica |
| url | http://hdl.handle.net/20.500.12123/22405 https://www.sciencedirect.com/science/article/abs/pii/S1550742405500745 https://doi.org/10.2111/1551-5028(2005)58[466:DOGTGP]2.0.CO;2 |
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