Physiognomic responses of páramo tussock grass to time since fire in northern Ecuador

Abstract

Ecologically-sound management plans for high-altitude grasslands of the Andes depend on an understanding the responses of plants to fire, especially the dominant tussock grasses. This study considers physiognomic responses of tussock grass in 13 sites in northern Ecuador with a known fire history, with time since fire 0.5–10 y, and a control site which had not been burned for at least 40 y. At each site, we assessed vegetation height, basal cover of the tussocks, and the ratio of dead:live leaves in tussocks. We also measured light at ground level. As recovery time increased, tussock cover and number decreased, while tussock height increased. Light levels fell sharply below the tussock canopies as recovery took place, and dead leaves accumulated quickly, reaching 60 – 70% by just two years after fire. The modification of physical tussock structure is likely to influence a much wider ecosystem response to fire, and determines directly the fuel load for future fires. Despite these clear changes in tussock characteristics, they were too variable to be used as a reliable bioindicator of time since fire. However, a better understanding of the responses of tussock grasses to fire and particularly its impact on other species should become the focus of further attention in future.

Post‐fire changes in plant growth form composition and diversity in Andean páramo grassland

“…In this second phase, tussock grasses increase their dominance. Gutiérrez‐Salazar and Ramsay (2020) have shown that the height of the tussocks increases steadily during this phase, resulting in a consistent shading effect and decline in temperature at ground level. The dominance‐controlled plant community during phase 2 is thus characterised by the suppression of potential competitors by the tussocks.…”

“…Tussock plants are rarely killed by fires (Hofstede et al, 1995) as their deeply‐seated shoot apices and buds are protected against heat in the centre of the tussock base (Laegaard, 1992; Ramsay & Oxley, 1996). Nevertheless, partial mortality is often observed, leading to fragmentation of plants and a smaller basal area (Laegaard, 1992; Ramsay, 1999; Suárez & Medina, 2001; Gutiérrez‐Salazar & Ramsay, 2020). In the initial recovery phase after a fire, there is a tussock‐building phase caused by the growth of surviving fragments and recruitment of new seedlings in open areas (Ramsay & Oxley, 1996; Vargas‐Ríos, 1997; Ramsay, 2001; Vargas Ríos, 2011).…”

“…In the initial recovery phase after a fire, there is a tussock‐building phase caused by the growth of surviving fragments and recruitment of new seedlings in open areas (Ramsay & Oxley, 1996; Vargas‐Ríos, 1997; Ramsay, 2001; Vargas Ríos, 2011). During this period, the height of tussocks is restricted, permitting more light at ground level and increased soil temperatures (Gutiérrez‐Salazar & Ramsay, 2020). This allows other growth forms time and space to recover after the fire.…”

“…Rates of tussock grass regeneration have been observed to be high (Gutiérrez‐Salazar & Ramsay, 2020), but the impact of fire on other páramo life forms varies widely (Janzen, 1973; Horn, 1989; Horn, 1997; Keating, 1998). Most páramo species have adaptations that help them to survive fires (Laegaard, 1992), but the mechanisms vary among species, making the recognition of community‐level successional trends at this taxonomic level difficult.…”