Exotic Buffelgrass Research Articles

Contrasting effects of native and exotic vegetation on soil infiltrability in the Sonoran Desert

Invasion by exotic grasses is transforming drylands across the planet, but the ecohydrological feedbacks of such invasions are not fully understood. For example, in the Sonoran Desert, previous studies have shown that buffelgrass (Cenchrus ciliaris) alters the spatial patterns of soil moisture, leading researchers to hypothesize that such alterations are related to the plants' effects on soil infiltrability. To evaluate this hypothesis, we compared field-saturated hydraulic conductivity (Kfs) in a native shrubland with that in a neighboring savanna extensively dominated by exotic buffelgrass. We measured Kfs during the dormant and growing seasons in both canopy and intercanopy zones. We found that Kfs was generally lower during the dormant season than during the growing season. There were no significant differences between sites during the dormant season, and at both sites, Kfs was 6–7 times higher under shrubs than in the intercanopies. During the growing season, Kfs for the exotic intercanopy was comparable to that for shrub cluster edges (140 mm h−1) and was more than twice that for the native intercanopy. Both shrubs and buffelgrass improved Kfs by reducing soil bulk density (thus increasing porosity). Additionally, surface roughness in the exotic intercanopy was nearly 3 times higher than in the native intercanopy. The combination of greater surface roughness and higher infiltration rates during the growing season most likely alters hydrological connectivity in savannas invaded by exotic grasses such as buffelgrass. By capturing portions of the runoff generated in the intercanopy, these grasses reduce runon into shrub patches, with potentially substantial impacts on native vegetation dynamics and stability.

Effect of buffelgrass fires on two Sonoran Desert trees: Bark and structural analyses

The introduction of exotic buffelgrass (Pennisetum ciliare) to the Sonoran Desert has modified the structure and fuel loads of desert scrub, creating a continuous fuel bed and altering fire frequencies and intensities. The damage to native vegetation has been widely acknowledged, but the mechanisms underlying the response have been little studied. Considering bark as one of the important characteristics to protect stems from fire, this study aimed to compare bark traits of two native Sonoran desert trees (Bursera microphylla and Olneya tesota) that may promote cambium survival from fire. Physical features of trees and fuel that influence fire behavior were analyzed, and bark characteristics were examined, including anatomy and chemical composition, to determine how these properties may influence their survival to fire. Surprisingly, drought-resistant traits of Bursera microphylla, such as thicker inner bark and greater stem water reserves make this species better able to survive fires, providing up to ten times more resistance to heat inputs from buffelgrass. In contrast, Olneya tesota has a dry and narrow inner bark, a flammable outer bark, fuel material accumulation under its crown, and large branches close to the soil surface, characteristics that increase fire intensity and give less protection to stem live tissues.

Factors influencing nesting phenology and nest success of the Rufous-winged Sparrow (Peucaea carpalis) at the center of its distribution in Sonora, Mexico

We determined the effect of the seasonal distribution of summer rainfall and associated seasonal changes in vegetation on the timing of reproduction and reproductive success of the Rufous-winged Sparrow (Peucaea carpalis) in the plains of central Sonora, Mexico, and influence of exotic buffelgrass (Pennisetum ciliare). We monitored 302 nests twice weekly from early July to early October of 2012–2014. We fitted Bayesian logistic-exposure models for nest survival data using covariables year, nest stage, date, normalized difference vegetation index, shrub cover, buffelgrass cover, and nest height. Mean daily nest survival probability equaled 95.9% (95% CRI 95.1%–96.1%), with nest survival probability averaging 36.3% (95% CRI 30.2%–42.5%) during the nesting season.We found evidence that daily nest survival probability differed between nest stages but variation in environmental explanatory variables among nests did not explain variation in daily nest survival probability, despite suggestive evidence of a positive association between NDVI and daily nest survival probability. Daily nest survival probability seemed unaffected by the habitat alteration in buffelgrass prairies, suggesting that the Rufous-winged Sparrow may be resilient to habitat transformation in the center of its distribution.

Ecohydrological changes in semiarid ecosystems transformed from shrubland to buffelgrass savanna

AbstractIn arid and semiarid lands worldwide, vegetation cover is being transformed to savannas dominated by exotic grasses. However, the ecohydrological and biogeochemical changes associated with this process remain little understood. For more than 3 years, we studied soil moisture dynamics in natural semiarid shrubland patches and compared those with changes in an adjacent site that had been transformed to an exotic buffelgrass (Cenchrus ciliaris) savanna. We found that volumetric soil moisture was higher in patches with some kind of cover. For both tree and bare patches, volumetric soil moisture and plant‐available water in the 60‐ to 100‐cm depth interval were significantly lower in the savanna than in the natural site. In buffelgrass patches, volumetric soil moisture and plant‐available water were higher at almost all depths and in wet years and increased significantly during the summer monsoon season, suggesting rapid infiltration mechanisms under buffelgrass. During years with wet winters, these mechanisms also led to brief accumulations of water in the soil profile (0–200 cm). Such changes in soil profile water dynamics brought about adaptive responses in perennial plant species. The ability of species to change their patterns of soil water use in the profile may be an important mechanism enabling them to compete when novel tree–grass interactions are established by invasion of grasses. Our results provide new insights for understanding the changes caused by grass invasion in arid and semiarid lands, as well as how these changes may impact ecohydrological dynamics in global change scenarios. Copyright © 2016 John Wiley & Sons, Ltd.

Carbon and Water Fluxes in an Exotic Buffelgrass Savanna

Buffelgrass savanna is becoming widespread in aridland ecosystems around the world following invasion or deliberate land conversion for cattle forage. There is still a gap of information regarding functional and ecohydrological aspects such as carbon, water, and greenhouse gas exchanges in these highly productive novel ecosystems where buffelgrass is an exotic species. We measured net ecosystem CO2 exchange (NEE), ecosystem respiration (Reco), gross primary production (GPP), and evapotranspiration (ET) with eddy covariance techniques over a buffelgrass savanna established for cattle grazing, approximately 30 yr ago within the Sonoran Desert. The savanna was a net carbon sink (NEE −230 g C/m2/yr) during both a year with above average and one with below-average precipitation (NEE −84 g C/m2/yr). Water loss through evapotranspiration (ET) was similar to total annual rainfall input. Up to 62% of the annual fixed carbon and 75% of ET occurred during the summer monsoon season, when 72−86% of annual rainfall occurred and buffelgrass was active. ET from summer months explained 73% of variation in NEE, with an average ET of 50 mm H2O/month needed to turn the ecosystem into a net carbon sink during this season. Other seasons in the year, when buffelgrass was dormant, contributed with up to 48% of annual fixed carbon but with higher water use efficiency (−NEE/ET). We discuss the importance of the seasonal variability in Reco, GPP, and ET processes and the phenology of native plant species for the net carbon uptake through the year for this managed novel ecosystem.

Introduced and native grass-derived smoke effects on Cymbopogon obtectus germination

Introduced grasses, such as buffel, alter the dynamics of grassy ecosystems by replacing native species and influencing recruitment. Several different smoke-derived chemicals are separately responsible for the promotion and inhibition of germination of various plant species. We tested whether smoke derived from the introduced buffel grass (Cenchrus ciliaris) produced the same density of germination as provided by smoke derived from a native spinifex grass (Triodia brizoides). Smoke from both spinifex and buffel grass significantly enhanced the germination of a native lemon grass (Cymbopogon obtectus) in comparison to untreated seed, reflecting the significant role of fire in woodlands across northern Australia. This is the first record of smoke-promoted germination in a species of Cymbopogon. However, smoke from the exotic buffel grass provided the same level of germination as that from the native spinifex, suggesting similarity in smoke chemicals involved. Further research is required to test the effect of buffel smoke on the germination of other species and whether exotics such as buffel grass provide the same temperature profile in the topsoil as does spinifex, and therefore equivalent germination cues to heat-shock responsive native plants.

Novel ecosystems created by coal mines in central Queensland’s Bowen Basin

Open-cut coal mining began in central Queensland’s Bowen Basin approximately 50 years ago. Over this period of time, mine rehabilitators have used a variety of tree, shrub, and groundcover species to create ‘novel ecosystems’ to stabilise soils and provide vegetative cover for pre-supposed final end-land uses. We examine post-mining rehabilitation from multiple soil and vegetation monitoring activities in the Bowen Basin to assess the similarity of landforms, plant composition, and trends in plant diversity compared to unmined reference communities. Rehabilitated spoil dumps and reference sites were assessed using soil and vegetation data contained in compliance monitoring reports from Goonyella Riverside, Moura, Oaky Creek, Rolleston, and Blackwater mines. Slopes, soil chemistry, and plant species mixes of rehabilitation aged from 2 to 22 years were compared to selected reference communities. Mines in this region have generally proposed one of two post-rehabilitation end-land uses: either pasture for cattle grazing or reconstructed native communities which potentially provide native fauna habitat. Landform data from a selection of these mine sites suggest that when their rehabilitation was compared to nearby reference sites median slope values were between 2.5 and 7 times steeper and soil pH, electrical conductivity, and phosphorus levels were significantly higher. The steeply sloped landforms, poor soil characteristics, depauperate native species pool, and uniform presence of exotic pasture grasses in the rehabilitation indicate that most of these newly created ecosystems should not be used for cattle grazing and also have few natural values. Legislative and community expectations have changed progressively over time and, although much of the rehabilitation is currently dominated by an assemblage of exotic buffel grass (Cenchrus ciliaris) and Acacia spp., recent environmental authorities suggest these ‘novel ecosystems’ will be judged against native reference sites. Upon completion of mining activities the resilience of these new ecosystems to drought, fire, and grazing will need to be demonstrated prior to lease relinquishment.

Buffelgrass (Pennisetum ciliare) Invades Lands Surrounding Cultivated Pastures in Sonora, Mexico

AbstractWe examined relationships between land disturbance and the extent and abundance of exotic buffelgrass (Pennisetum ciliare) at the interface of cultivated pastures and native desert lands in Sonora, Mexico. Plot and transect surveys of lands inside and outside pasture fences and general linear mixed models revealed complex relationships among buffelgrass, native vegetation, distance from pasture fences, and three categories of land disturbance (undisturbed, moderate, and severe). Results illustrate that buffelgrass invasion is extensive in lands surrounding pastures, and that buffelgrass abundance declines steeply with distance from pasture fences. The role of disturbance is weak but significant in its interaction with distance from the fence. Buffelgrass is more successful at colonizing severely disturbed lands than native vegetation, and its decline in abundance on severely disturbed lands is relatively more gradual than on other disturbance regimes, so landscapes where severely disturbed lands are interspersed with buffelgrass pastures could become centers of extensive buffelgrass invasion. In light of its potential to transform the Sonoran Desert, buffelgrass outside pastures warrants attention in a region-wide control scheme, as well as in future research, which ideally would involve remote sensing.

Segmentation of Landsat Thematic Mapper imagery improves buffelgrass (Pennisetum ciliare) pasture mapping in the Sonoran Desert of Mexico

The invasive exotic buffelgrass (Pennisetum ciliare) is a principal threat to the Sonoran Desert of southwestern North America. Buffelgrass is cultivated in cattle pastures throughout Mexico's northwestern state of Sonora, where it poses an invasion threat to surrounding desert lands. Automated remote sensing methods to detect buffelgrass pasture conversion at a regional scale have shown limited success, due in part to variable land-cover conditions, and in part to intrinsic heterogeneity in desertscrub land-cover. This paper discusses a novel technique for delineating and mapping buffelgrass pastures based on vector-based satellite image segmentation followed by pixel-based classification using ancillary spatial environmental data. Based on quantitative accuracy metrics and visual inspection of known pasture sites, we report that segmentation considerably improved the mapping process, in particular the detection and delineation of pastures. Comparisons of paired classifications with segmented and nonsegmented imagery revealed higher overall map accuracies and higher buffelgrass class accuracies, as well as lower errors of commission and omission for buffelgrass in segmented maps. This new application of object-based image analysis has promising implications for ongoing efforts to map and monitor buffelgrass expansion region-wide and other similar changes in land-cover type and condition across human-modified landscapes.

Pasture Conversion, Private Ranchers, and the Invasive Exotic Buffelgrass (Pennisetum ciliare) in Mexico's Sonoran Desert

This research examines the role of private ranchers in Sonora, Mexico, in regional-scale landscape change involving an invasive species. The arid rangelands of Sonora are a center of modern commercial cattle ranching, where the exotic buffelgrass (Pennisetum ciliare) is the favored species for the extensive conversion of native range vegetation to pasture. The land management decisions of private ranchers, the primary agents of pasture conversion, are examined amid peculiar challenges and opportunities presented by buffelgrass in the context of the modernization of Sonoran ranching. An environmental history of buffelgrass in the region is coupled with qualitative and quantitative interview data, which are subjected to binary logistic regression modeling. Statistical results show rotational grazing as the strongest driver of pasture conversion, followed by native forage scarcity. Land entitlement, government support, hobbyism, and belief in buffelgrass as long-term drought mitigation are insignificant. Interview data reveal diverse expressions of agency among Sonoran private ranchers, and historical research illustrates the structural context that conditions land-use decisions. Ultimately, pasture conversion arises not from state sponsorship but from complex interactions among desert ecosystems, ranchers, and the institutions that mediate their engagements with the state and an international political economy. This research confirms the utility of analyzing changing landscapes as coupled human–environment systems and questions the utility of an agency–structure dichotomy in land-use change explanations.

What Drives the Conversion of Native Rangeland to Buffelgrass (Pennisetum ciliare) Pasture in Mexico’s Sonoran Desert?: The Social Dimensions of a Biological Invasion

The introduction of invasive exotic plants has many social dimensions. Although a diverse literature identifies some of the social drivers of exotic plant introduction and subsequent invasion, relatively little attention has been given to the motives of individuals involved. This research focuses on the extensive conversion of native rangeland to exotic buffelgrass (Pennisetum ciliare) pasture by ranchers in Mexico’s Sonoran Desert using data gathered through systematic interviews and ordinary least squares regression modeling to demonstrate how a few social variables determine the extent of buffelgrass introductions. Results show that land allocation to pasture is determined chiefly by ranch size, with significant roles also played by rotational grazing, buffelgrass seed harvest, and exposure to government research. Results are contextualized and explored in depth, illustrating how the extent of rangeland-to-pasture conversion in this part of the Sonoran Desert is determined by direct and indirect social factors. The study also highlights implications for buffelgrass invasion.

Clearing savannas for use as rangelands in Queensland: altered landscapes and water-erosion processes

This paper presents a framework and some examples of how tree clearing alters landscapes (vegetation structure and faunal habitat) and processes (run-off and soil erosion) for eucalypt savannas in Queensland. Unaltered savannas have a tree-layer and a well-covered ground-layer of perennial grasses, and they provide habitats favoured by a variety of open woodland birds, reptiles and small mammals. Because unaltered savannas have a high ground-cover, they have low rates of run-off and erosion. When savannas are chained, but otherwise unaltered, trees rapidly regrow and increase in canopy cover. The exotic buffel grass often establishes in chained regrowth (especially if grazed), although the cover of native grasses such as black speargrass remains high (unless heavily grazed). We found that open woodland birds declined on these chained regrowth sites, except for the Weebill, which increased in abundance. When savannas are cleared of trees and woody debris and developed as improved pasture systems, both exotic and native perennial grass increased in cover. However, open woodland fauna abundance declined whereas grassland fauna such as the Red-backed Fairy-wren and the House Mouse increased in abundance. If these pasture sites are heavily utilised by livestock so that ground-cover is reduced, rates of run-off and soil loss are likely to rapidly increase, especially as cover declines below 40%. These run-off and erosion findings suggest that the manner in which savanna landscapes are cleared and subsequently used will have flow-on effects at catchment scales.