Interactive effects of pasture management intensity, release from grazing and prescribed fire on forty subtropical wetland plant assemblages

Abstract

Summary Pasture management intensity, livestock grazing and prescribed fire are three widespread agricultural practices that affect small, isolated wetlands, but few studies have investigated their individual and interactive effects. Pasture management intensity refers to the degree of human alteration of grassland, ranging from intensively managed pastures planted with introduced forage, fertilizer/lime additions and artificial drainage to semi‐natural pastures with mixed native and non‐native vegetation, no fertilizer/lime additions and little or no artificial drainage. We examined individual and interactive effects of these three agricultural practices on individual, isolated wetlands using a replicated, full‐factorial experiment on 40 entire wetlands in south Florida, USA. Wetlands were embedded in two pasture management intensities: intensively managed and semi‐natural. After three years of treatment initiation, vegetation of wetlands released from grazing and unburned embedded in semi‐natural pastures had significantly lower evenness and coefficient of conservatism scores compared to wetlands released from grazing and burned, grazed unburned wetlands and grazed burned wetlands in the same pasture management intensity. For wetlands embedded in intensively managed pastures, evenness and coefficient of conservatism scores did not differ among treatments. Release from grazing increased abundance of the native, weedy herb, Eupatorium capillifolium. Grazing interacted with prescribed fire to affect shrub abundance and non‐native richness; relative abundance of shrubs and non‐native richness were greater in wetlands released from grazing and burned and did not differ among burn treatments in grazed wetlands. Interactive effects, especially three‐way interactions, were uncommon and not as important as differences between the two pasture management intensities. Synthesis and applications. Vegetation diversity and floristic quality of wetlands embedded in intensively managed pastures resisted common restoration management techniques such as release from grazing and prescribed fire, at least in the short term. In contrast, removing all top‐down disturbances from wetlands embedded in semi‐natural grasslands can negatively affect vegetation species diversity and floristic quality. Future studies should examine how intensity and seasonality of grazing and prescribed fire affect wetland vegetation, and track long‐term responses to evaluate lag effects.

The Role of Management on Methane Emissions From Subtropical Wetlands Embedded in Agricultural Ecosystems

“…Improved pastures have been agronomically improved since the 1940s. They are composed primarily of introduced forage, Bahia grass ( Paspalum notatum Flüggé), are typically fertilized annually or semiannually with nitrogen (56 kg/ha; Swain et al, ), were historically fertilized with NPK (nitrogen, phosphorus, potassium; 1970s to 1986) at a rate of 56‐kg/ha NH 4 SO 4 and NH 4 NO 3 and 34–90 kg/ha of P 2 O 5 and K 2 O, grazed more intensely during the summer wet season, and have numerous drainage ditches coupled with water management (Boughton et al, ). Seminative pastures have mostly intact natural vegetation and represent less intensely managed systems.…”

“…Both pasture types contain high and low elevations. During the study (2013–2015) and for over 30 years the average stocking rate ranged from 0.57 to 1.7 animal units (AU)/ha in improved pastures and 0.15–1.12 AU/ha in seminative pastures (Boughton et al, ). AU is a standard unit of measure where it is assumed that one cow is approximately 450 kg that consumes 12 kg · day · ha of dry matter.…”

“…Because they are generally the lowest‐lying areas in a landscape, land management decisions at the landscape scale may dramatically impact these systems. For example, management decisions in the surrounding land are shown to impact the plant biomass (Boughton et al, ), plant diversity (Boughton et al, ), soil characteristics (Ho et al, ; Verhoeven & Setter, ), and soil hydrology (Collins et al, ) of the wetlands themselves. Previous work shows that conversion of wetlands to new ecosystem types can lead to significant changes in CH 4 emissions.…”

Agricultural intensification and drought frequency increases may have landscape‐level consequences for ephemeral ecosystems

“…The little work that has been carried out in this regard has shown that agricultural practices such as livestock grazing, pasture management and prescribed fires affect ephemeral wetlands, in both positive and negative ways. For example, results from field experiments in Australia (Brock et al ., ), America (Marty, ; Pyke & Marty, ; Boughton et al ., ) and China (Wu et al ., ) have shown that agricultural practices such as grazing regimes play an important role in maintaining hydrologically suitable ephemeral habitats. Furthermore, grazing and prescribed fire interactions have also been shown to affect plant richness around wetlands (Boughton et al ., ).…”

“…For example, results from field experiments in Australia (Brock et al ., ), America (Marty, ; Pyke & Marty, ; Boughton et al ., ) and China (Wu et al ., ) have shown that agricultural practices such as grazing regimes play an important role in maintaining hydrologically suitable ephemeral habitats. Furthermore, grazing and prescribed fire interactions have also been shown to affect plant richness around wetlands (Boughton et al ., ). Understanding the various processes that affect wetlands in these landscapes is, therefore, key in determining how agricultural practices maintain plant evenness and floristic quality around wetlands within the developing world and globally.…”