Assessment of prescribed fire and cutting as means of controlling the invasion of sub‐alpine grasslands by Echinospartum horridum

Abstract

Aims: Sub-alpine grassland ecosystems have some of the highest biodiversity in Europe and constitute high-value natural resources. These grasslands are under threat because of the abandonment of traditional agro-pastoral activities and subsequent invasion by woody species. In the Central Pyrenees (Spain) several management techniques have been used to stop expansion of the highly encroaching shrub Echinospartum horridum. However, the ways in which these techniques affect recovery of sub-alpine grasslands are poorly understood. The final goal of this study is to gain information about the effects of E. horridum management practices and provide recommendations for the local stakeholders. Methods: This study evaluated the efficacy of controlled fires and mechanical removal of above-ground vegetation in controlling expansion of E. horridum into sub-alpine grasslands in the Central Pyrenees. E. horridum demography (germination and survival), soil seed bank and soil properties were recorded in two E. horridum stands where vegetation was previously removed by (1) fire (burning treatment) or (2) mechanical removal (cutting treatment) and (3) an undisturbed E. horridum stand (control). Results:The burning treatment increased germination and survival of E. horridum seedlings more than the cutting treatment, relative to the control. Therefore, cutting appeared to be a better option for controlling E. horridum. Soil seed density was higher in the management treatments than in the control, but it did not harbour sub-alpine grasslands species. E. horridum removal favoured recharge of the soil with seeds that arrived by dispersal. The soil seed bank in the burning treatment had higher seed abundance and seed diversity than in the cutting treatment; however, fire promoted a loss of soil nutrients. Conclusions:The soil seed bank composition (low abundance and diversity of native species) coupled with rapid regeneration rate of E. horridum would prevent recovery of the sub-alpine grassland based on the soil seed bank alone. Traditional shepherding has been reported to favour seed dispersal, and here we recommend E. horridum | 199 Applied Vegetation Science NUCHE Et al.

Clearing vs. burning for restoring Pyrenean grasslands after shrub encroachment

“…Mechanical removal is much more effective than fire because these two types of removal differently affect the seed establishment rates of E. horridum on bare soil (Nuche et al, 2018). Fire perturbation increased E. horridum seedling establishment more than clearing as also reported previously (Nuche et al, 2018).…”

“…Moreover, the influence of fire on soil fertility showed contradictory results. Some authors reported soil nutrient decreases after prescribed fire events (Martínez-Mena et al, 2001;San Emeterio et al, 2016;Nuche et al, 2018), while others reported neutral or even positive effects on soil nutrients (Fernandes et al, 2013).…”

“…It is among the most aggressive species encroaching Pyrenean grasslands and it is spreading rapidly (Komac et al, 2011a). Empirical studies reported increased seed germination and seedling survival of E. horridum after burning and in less extent under clearing treatment (Nuche et al, 2018). Thus, it is of major importance to understand the dynamics of this species if optimal management practices are to be applied in the Pyrenees.…”

Gestión activa frente a matorralización: buscando el equilibrio entre conservación y explotación en montaña

“…Badía et al (2017) concluded that burning E. horridum rejuvenates the community which, far from being eliminated, undergoes self-succession in time. Nuche et al (2018) also found that burning E. horridum increases its germination and helps to sow seeds that were not previously present in the rich sub-alpine pastures of the Pyrenees. Ruiz Mirazo et al (2011) state that the current low numbers of livestock in many mountain areas result in the failure of the fire-grazing balance.…”

Effects of prescribed burning on soil organic C, aggregate stability and water repellency in a subalpine shrubland: Variations among sieve fractions and depths

“…The mesophytic Pyrenean pastures are composed of subclimax species that require the grazing of shrubs to survive (Halada et al, 2011). As a consequence of grazing reduction, the Pyrenees have suffered shrub encroachment processes, dominated by the thorny cushion dwarf (Echinospartum horridum (Vahl) Rothm), among others (Komac et al, 2013;Nuche et al, 2018). This species forms large and dense monospecific covers (Komac et al,2011) that pose a threat to biodiversity and increase flammability risks (Caballero et al, 2010).…”