IFEVA, Departamento de Recursos Naturales y Ambiente, Facultad de Agronomía, Universidad de Buenos Aires, CONICET, Av. San Martín 4453, Buenos Aires, C1417DSE, Argentina.
IFEVA, Departamento de Recursos Naturales y Ambiente, Facultad de Agronomía, Universidad de Buenos Aires, CONICET, Av. San Martín 4453, Buenos Aires, C1417DSE, Argentina.
J Environ Manage. 2019 Apr 1;235:42-50. doi: 10.1016/j.jenvman.2019.01.037. Epub 2019 Jan 19.
Ecological modeling that includes plant population processes as a critical determinant of vegetation dynamics is useful for sustainable rangeland management. However, we know little about how long-term sheep grazing pressure drives the plant community structure through changes in different native grass species at both individual and population levels. In this study, we hypothesized that plant populations perform differently under different grazing management due to their specified preference by livestock animals. We also tested whether grazing-rest management, aimed at increasing long-term rangeland sustainability, improves the plant growth of forage grass species. We evaluated plant density, individual morphology and plant-size distribution of dominant grass populations in permanent exclosures and open fields under moderate and intensive grazing pressures in Patagonian steppes (South America). We also examined the effects of seasonal grazing-rest managements on the growth and tillering (asexual reproduction) of forage species plants, using temporary mobile exclosures. Grazing intensity changed population density and structure according to species. Compared to permanent exclosures, moderate grazing maintained the plant density of palatable species highly preferred by sheep, reduced the standing-dead biomass proportion of individual plants, and promoted the green biomass of tussocks. Conversely, intensive grazing (double stocking rates) decreased the plant density and individual size of species highly preferred by sheep, and increased the plant density of non-preferred species. Grazing-rest enhanced forage grass species growth and reproduction compared with year-round grazing management, especially during the growing season of a wet year. Our studies support that sheep can be managed to control the plant-size distribution of dominant grass species, their population dynamics, and thereby the overall forage availability at the community level. Both moderate grazing and grazing-rest management can improve the forage availability and preserve the dominant native grasses. We suggest applying a plant population dynamics perspective to facilitate sustainable management of global rangelands.
将植物种群过程作为植被动态的关键决定因素纳入生态模型，对于可持续的牧场管理非常有用。然而，我们对于长期绵羊放牧压力如何通过不同原生草种在个体和种群水平上的变化来驱动植物群落结构知之甚少。在这项研究中，我们假设由于牲畜动物的特定偏好，植物种群在不同的放牧管理下会表现出不同的行为。我们还测试了旨在提高长期牧场可持续性的放牧休息管理是否会改善饲料草种的植物生长。我们评估了永久性围栏和开放田野中主要草种群的植物密度、个体形态和植物大小分布，这些围栏处于巴塔哥尼亚草原（南美洲）的中度和重度放牧压力下。我们还使用临时移动围栏，研究了季节性放牧休息管理对饲料物种植物生长和分蘖（无性繁殖）的影响。放牧强度根据物种改变了种群密度和结构。与永久性围栏相比，中度放牧维持了绵羊高度偏好的可食用物种的植物密度，降低了个体植物的立枯生物量比例，并促进了草丛的绿色生物量。相反，重度放牧（双倍放牧率）降低了绵羊高度偏好的物种的植物密度和个体大小，并增加了非偏好物种的植物密度。与全年放牧管理相比，放牧休息可促进饲料草种的生长和繁殖，尤其是在多雨年份的生长季节。我们的研究表明，可以通过管理绵羊来控制主要草种的植物大小分布、种群动态，从而控制群落水平的整体饲料供应。中度放牧和放牧休息管理都可以提高饲料供应并保留优势原生草种。我们建议采用植物种群动态的观点，以促进全球牧场的可持续管理。
