Limits to recruitment of tall fescue plants in poplar silvopastoral systems of the Pampas, Argentina

Abstract

Forage production in silvopastoral systems of the Flooding Pampa is based on cool season grasses with a relatively asynchronous phenology regarding their accompanying deciduous trees. However, the productivity of cool season grasses in these systems is usually low. The hypothesis of this work is that the low productivity of cool season grasses is caused by tree litter constraining plant recruitment. Emergence and establishment (reproductive propagation), and tillering (vegetative propagation) patterns of tall fescue, a cool season grass in the region, were studied in two pairs of adjacent non-afforested and afforested poplar stands (tree age 26-28 years, tree density 453-797 plants ha -1 ). Observational and manipulative (i.e. addition of seeds, leaf litter removal) experiments indicated that the recruitment of tall fescue plants is strongly limited by the fall of poplar leaves over emerged seedlings, during autumn. Results suggest that any management practice capable of removing poplar litter, either through grazing or machinery, could neutralize this limitation enhancing the herbaceous primary production of the system.

Forage production in natural and afforested grasslands of the Pampas: ecological complementarity and management opportunities

“…The original purpose of these plantations was timber production, yet they were never harvested, nor thinned or pruned. By the time of our study full canopy closure was observed (see Clavijo et al 2010). At the time of our study, 28 years after tall fescue was sown, this species was still abundant in the grassland stands (10-20% cover), although they were dominated by native species (62% cover, 71% species number) (Clavijo et al 2005).…”

“…Moreover, light incidence is reduced and day temperatures tend to be lower under the canopy (Lin et al 2001 Syst (2011) 83:201-211 207 under which C3 species performance and fitness are relatively less affected (Jose et al 2004). After several years of interaction, the abundance of summer grasses in the understory of our stands is low whereas winter grasses dominate (Clavijo et al 2005(Clavijo et al , 2010. It is these differences in relative abundance, rather than changes in the seasonality of any functional group itself, what dictates the observed changes in the seasonal dynamics of productivity.…”

“…As opposed to pines and eucalypts, winter deciduous species leave a temporal window for herbaceous growth during the mild cool season of the Pampas that allows the maintenance of a grass understory even under high plantation densities (Clavijo et al 2005(Clavijo et al , 2010Benavides et al 2009). We expect that these tree plantations will enhance total ecosystem ANPP, like their evergreen counterparts, but will sustain an herbaceous ANPP component, serving as the basis for combined forestry-ranching schemes that diversify outputs and risks (von Maydell 1985;Pearson and Ison 1997).…”

Effects of low‐density Pinus elliottii (Slash pine) afforestation on environmental conditions and native plant diversity, in the mountains of central Argentina

“…Clavijo et al. () have documented that under trees of most forests and plantations (UC), understorey recruitment is limited by litter accumulated on the ground.…”

“…In general, silvicultural practices such as thinning (which tends to open the canopy cover and reduce competition) promote an increase in diversity of plant species in the ground vegetation (French et al., ). Besides reducing competition, thinning may also reduce litter accumulation and soil acidification, since these processes intensify as canopy cover increases (Amiotti et al., ; Clavijo, Cornaglia, Gundel, Nordenstahl, & Jobbagy, ).…”