What limits herb biomass in grasslands: competition or herbivory?

Abstract

Competition and herbivory are two of the main forces shaping plant communities. Although several studies have investigated their impact on plant populations separately, few investigations have examined how they might interact. With the purpose of clarifying the combined roles of competition and herbivory on herb biomass in a grassland, we assessed the effects of different herbivores with reduced grass competition. We conducted a field experiment in 2000-2001 in a British acid grassland (Oak Mead), where we experimentally reduced grass biomass and excluded rabbits, insects and molluscs in a factorial design. Removing the grasses from Oak Mead dramatically increased herb biomass and total above-ground biomass. Herbivore exclusions (i.e. rabbits, insects and molluscs) did not affect total above-ground biomass, but they altered relative abundance of several species. Grass removal and rabbit exclusion had positive interactions on biomass of several herb species, and there were some subtle interactions between different herbivore groups: monocots benefitted when both rabbits and molluscs were excluded, and some herb species had greater biomass when insects and rabbits were absent. We then compared the results with a 10-year experiment that manipulated similar variables in neighbouring grassland (Nash's Field). The comparison between Oak Mead and Nash's Field showed that cessation of herbicide application returns the system to its previous state of grass dominance after 3 years. Therefore, even when herbs were more abundant, they could not prevent reinvasion of the grasses once external factors were removed.

The variable effects of soil nitrogen availability and insect herbivory on aboveground and belowground plant biomass in an old-field ecosystem

“…A recent meta-analysis by Coupe and Cahill (2003) suggested that, on average, insects reduce NPP by 13% in temperate herbaceous plant communities. But there was considerable variation among studies--some showed increases in, or no eVects of, insect herbivory on NPP (Carson and Root 2000;Coupe and Cahill 2003;Chapman et al 2003;Del-Val and Crawley 2005;Gao et al 2008).…”

Aboveground vertebrate and invertebrate herbivore impact on net N mineralization in subalpine grasslands

“…They alter plant species composition (e.g., Del-Val andCrawley 2005, Bakker et al 2006) and directly and indirectly affect belowground properties (e.g., Bardgett and Wardle 2003). Direct impacts such as trampling or burrowing can alter soil structure or permeability (e.g., Binkley et al 2003, Schrama et al 2013, Barth et al 2014.…”

Limitations for seedling establishment in volcanic tephra deposits

“…El efecto de la herbivoría podría ser fácilmente determinado al controlar el acceso a herbívoros mediante la colocación de cercas. Se ha documentado que el crecimiento y/o supervivencia de las plántulas pueden ser incrementados signifi cativamente por la colocación de cercas (Shelton y Intuye, 1995;Case y Kauffman, 1997;Opperman y Merenlender, 2000;Sweeney et al, 2002;Frankland y Nelson, 2003;del-Val y Crawley, 2005;del-Val et al, 2007;Howe, 2008).…”