Persistence and colonization of gaps in sown swards of grass and clover under different sward managements

Abstract

The effects of extensive sward management and patch size on the persistence and colonization of gaps in sown swards was examined by creating gaps of five different sizes (2·3, 7, 10, 14 and 19 cm in diameter) in four different sward treatments: a fertilized sward grazed to 4 cm, i.e. relatively intensive management, and three extensively managed unfertilized swards, which were not grazed or grazed to 4 cm or 8 cm. The swards were originally sown with ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.), but had developed differences in species composition as a result of the management treatments imposed 2 years before and during the experiment. Light quality measurements, i.e. red‐far red (R/FR) ratio, were used to determine when the light environment in the gaps no longer differed from that in control, uncut patches and this was used as an estimate of gap persistence. Persistence of gaps depended on both sward management and gap size. Gaps disappeared most rapidly in the ungrazed sward and fertilized 4‐cm sward, and most slowly in the unfertilized 8‐cm sward. Small gaps persisted for up to 2 weeks in all but 8‐cm swards, whereas larger gaps were estimated to persist for up to 20–25 weeks in unfertilized, grazed swards. There was no evidence that the number of grass or dicotyledonous species increased in the gaps compared with the control areas. There were significant positive linear relationships between the vegetation that developed in gaps and that in the control, uncut patches, reflecting the different species composition of the established sward of the grazed (grass‐dominant) and ungrazed (Ranunculus repens‐dominant) treatments. For total grass dry matter and tiller numbers, as well as L. perenne tiller numbers, there was a small, but significant, effect of both patch size and sward management on the slopes of the regressions between the controls and gaps. The results are discussed in relation to the potential for species composition of sown swards to change as a result of gap creation.

Effect of cattle activities on gap colonization in mountain pastures

“…By contrast, in wet grassland, MILBERG (1993) concluded that the seed bank was the main source of seedlings emerging after gap creation but these seedlings contributed very little to the colonization, which was clearly dominated by vegetative regrowth. In our case and as reported from perennial grasslands elsewhere (RAPP & RABINOWITZ 1985, MILBERG 1993, KOTANEN 1997, MARIOTT et al 1997, rapid vegetative spread was also a characteristic trait of species present in gaps. The importance of this trait was not surprising considering the high proportion of species using this strategy in perennial grasslands (KLIMEŠ et al 1997, MACEK & LEPŠ 2003.…”

“…Traits that provide advantages in a closed canopy are not necessarily an advantage for gap colonization. In perennials grasslands rapid vegetative spread (KOTANEN 1997, MARIOTT et al 1997) and smaller seed mass (KALAMEES & ZOBEL 2002, SUDING et al 2003 generally characterize gap colonizers. Consequently, plant species often occur with different relative frequencies in recently colonized gaps than they do in the surrounding vegetation (MARTINSEN et al 1990, BULLOCK et al 1995.…”

Communautés de sous-bois des peupleraies artificielles : relation entre phytomasse, richesse spécifque et perturbations

“…C'est ce qu'on observe lorsqu'il y a arrêt des entretiens de la peupleraie ; où les espèces, initialement herbacées, cèdent la place à des ligneux. La quantité de lumière, de moins en moins disponible au fur et à mesure du vieillissement d'une peupleraie, joue un rôle important dans l'établissement et la croissance des espèces végétales [32]. En raison des résultats obtenus en P1, ce modèle n'est pas en liaison avec les observations d'Odum [33] qui indiquent que la plus forte diversité en espèces s'observe à des taux modérés de gradients physiques.…”

Assessment of seasonal dry‐matter yield and quality of grass swards with imaging spectroscopy

“…Dung and urine may also create gaps in the canopy (Lantinga, 1986), especially under high stocking rates (Wolton, 1978). Small-and medium-sized gaps in the canopy are rapidly filled by vegetative expansion or seedlings (Marriott et al, 1997). Therefore, the dynamics of heterogeneity should be incorporated in a sward quality assessment, and this requires repeated measurements during the growing season.…”

“…Keuning and Vellinga, 1986;Deenen, 1994). Local tiller or plant death creates gaps which may be filled with weeds (Keuning and Vellinga, 1986;Marriott et al, 1997). This leads to heterogeneous swards in terms of DM yield and feeding quality.…”