Using Precision Prairie Reconstruction to Drive the Native Seeded Species Colonization Process

Restoring forb richness to the northern tallgrass prairie (U.S.A.) is often problematic. A potential solution is the establishment of native forb‐seeded patches that can serve as colonization sites. This study was designed to determine the following: (1) the success at which native forbs sown in small patches can colonize the surrounding vegetation matrix and (2) whether soil amendments (C additions, P fertilization, and seed bank reduction) applied to the seeded sites can facilitate such colonization (patch quality). Colonization was investigated at (1) the immediate surrounding (1 m belt transect, BT) of the seeded sites and (2) in disturbed but not seeded patches located 3 m from the seeded site (out‐plots). Soil amendments did not affect colonization, but native forb density in the BT and out‐plots was correlated to the density of forbs in the seeded sites (r² = 0.3, p < 0.01). Seeded native forb density in the out‐plots was higher than in the adjacent BT (19 vs. 5 plants/m²), suggesting that competition from the matrix vegetation may be more important in forb colonization than distance from the source. Taller forbs with larger seeds showed advantages in colonization success. This study showed that the colonization of matrix vegetation with native forbs from seeded patches is a viable method for prairie reconstruction but requires the availability of disturbed sites. In most prairies, animal‐generated soil disturbances are common. In their absence, disturbances of the vegetation matrix will need to be added to the management plan.     

Patch dynamics in grazed subtropical native pastures in south‐east Queensland

Abstract Patch formation is common in grazed grasslands but the mechanisms involved in the formation and maintenance of patches are not clear. To increase our knowledge on this subject we examined possible reasons for patch formation and the influence of management on changes between patch states in three experiments in native pasture communities in the Crows Nest district, south‐east Queensland. In these communities, small‐scale patches (tall grassland (dominated by large and medium tussock grasses), short swards (dominated by short tussock grasses and sedges), and lawns (dominated by stoloniferous and/or rhizomatous grasses)) are readily apparent. We hypothesized that the formation of short sward and lawn patches in areas of tall grassland was due to combinations of grazing and soil fertility effects. This was tested in Experiment 1 by applying a factorial combination of defoliation, nutrient application and transplants of short tussock and stoloniferous species to a uniform area of tall grassland. Total species density declined during the experiment, was lower with high nutrient applications, but was not affected by defoliation. There were significant changes in abundance of species that provided support for our hypotheses. With light defoliation and low nutrients, the tall grassland remained dominated by large tussock grasses and contained considerable amounts of forbs. With heavy defoliation, the pastures were dominated by medium tussock grasses and there were significant decreases in forbs and increases in sedges (mainly with low nutrients) and stoloniferous grasses (mainly with high nutrients). Total germinable seed densities and those of most species groups were significantly lower in the heavy defoliation than the light defoliation plots. Total soil seed numbers were not affected by nutrient application but there were fewer seeds of the erect forbs and more sedge seeds in plots with high nutrients. The use of resting from grazing and fire to manage transitions between patches was tested. In Experiment 2 , changes in species density and abundance were measured for 5 years in the three patch types with and without grazing. Experiment 3 examined the effects of fire, grazing and resting on short sward patches over 4 years. In Experiment 2 , total species density was lower in lawn than short sward or tall grassland patches, and there were more species of erect forbs than other plant groups in all patch types. The lawn patches were originally dominated by Cynodon spp. This dominance continued with grazing but in ungrazed patches the abundance of Cynodon spp. declined and that of forbs increased. In the short sward patches, dominance of short tussock grasses continued with grazing but in ungrazed plots their abundance declined while that of large tussock grasses increased. The tall grassland patches remained dominated by large and medium tussock species. In Experiment 3 , fire had no effect on species abundance. On the grazed plots the short tussock grasses remained dominant but where the plots were rested from grazing the small tussock grasses declined and the large tussock grasses increased in abundance. The slow and relatively small changes in these experiments over 4 or 5 years showed how stable the composition of these pastures is, and that rapid changes between patch types are unlikely.     

Effects of Frequent Mowing on Survival and Persistence of Forbs Seeded into a Species-Poor Grassland

Many early attempts at tallgrass prairie reconstruction failed to achieve the high species diversity of remnant prairies, and instead consist primarily of C₄ grasses. We hypothesized that frequent mowing of established prairie grasses could create sufficient gaps in the aboveground and belowground environment to allow for the establishment of native forbs from seed. We studied forb seedling establishment in a 25‐year‐old prairie planting in northern Iowa that was dominated by native warm‐season grasses. In winter 1999, 23 species of native forbs were broadcast into the recently burned sod at a rate of 350 viable seeds/m². Treatment plots were mowed weekly for either one or two growing seasons, and control plots were unmowed. Mowed plots had greater light availability than controls, especially when warm‐season grasses began to flower. Overwinter seedling mortality was 3% in mowed treatments compared to 29% in the controls. Forbs in mowed plots had significantly greater root and shoot mass than those in control plots in the first and second growing seasons but were not significantly more abundant. By the fourth growing season, however, forbs were twice as abundant in the mowed treatments. No lasting negative impacts of frequent mowing on the grass population were observed. Mowing a second year influenced species composition but did not change total seedling establishment. Experimental evidence is consistent with the idea that mowing reduced competition for light from large established grasses, allowing forb seedlings the opportunity to reach sufficient size to establish, survive, and flower in the second and subsequent years.     

Silvopastoralism in the Alps: Native plant species selection under different grazing pressure

To evaluate the suitability of wood pastures as a managing tool in subalpine regions it is essential to know more about the influence of grazing on the ground vegetation. This study assessed native plant species selection by cattle at different stocking rates, feeding habits and site preferences of cattle. Based on the results, conclusions concerning the value of silvopastoral systems in the Alps were drawn. A field study on six different wood pasture areas, grazed by cattle at different stocking rates, was accompanied by an experiment on three adjoining areas of 0.51 ha each, stocked with either three, six, or nine heifers. Plant species were recorded in plots of 20 cm × 20 cm before and after grazing, and the intensity of grazing on each species was assessed. At low stocking rates, grasses and tall species were most intensely grazed, while at higher stocking rates the intake of forbs and small species increased. Since no relationship was found between nutritional value and species preference, other factors such as accessibility of a plant seem to be important for the feeding preferences of cattle. The preference for grasses at low and medium stocking rates suggests that an increased growth of forbs might lead to an increase in plant species diversity.     

Diets of prairie dogs (Cynomys mexicanus) co-existing with cattle or goats

Diets of prairie dogs (Cynomys mexicanus) co-existing with goats or cattle were examined using microhistological fecal analysis in a 1-year study on a grassland of northern Mexico. Consumption of forbs was generally higher (33% versus 21% across all seasons; P< 0.05) in prairie dog diets co-existing with cattle compared to prairie dogs co-existing with goats. The diet of prairie dogs grazing with goats was based around grasses (79% of total forage ingested versus 68% for prairie dogs on the pasture grazed by cattle all seasons; P<0.05). In general, prairie dogs showed a higher preference for forbs in the pasture grazed by cattle than in the pasture grazed by goats. Data for dietary overlap (69% across all seasons) pointed to a moderate diet similarity between prairie dogs grazing with goats or cattle. Prairie dogs co-existing with goats had a higher (P<0.05) fecal N concentration in the fall than prairie dog co-occurring with cattle (2.4±0.1 versus 2.1±0.1). In spring and summer, prairie dogs in the pasture shared with goats had higher (P<0.05) fecal P concentrations than prairie dog co-existing with cattle (3.0±0.4 versus 2.5±0.2 and 1.6±0.1 versus 1.0±0.1, respectively). The results of this study indicate distinct differences in diets of prairie dogs co-existing with goats or cattle, although these foraging differences did not affect negatively the diet quality of prairie dogs (based on fecal N and P data) grazing with goats, despite the highly degraded range in this site. Prairie dogs showed a high feeding adaptability, which allowed them to meet their nutritional needs in a highly degraded site around the goat's pens in a settlement with communal grazing land.     

How season of grazing and herbivore selectivity influence monsoon tall-grass communities of northern Australia

Abstract. The hypothesis that season of defoliation and herbivore selectivity may be as important as level of use in determining plant community response to grazing was tested in a monsoon grassland in northern Australia. Plots, dominated by the tussock grasses Themeda triandra and Chrysopogon fallax, were grazed by cattle at low, medium and high rates of utilization in either the early wet, late wet or dry seasons. Effects of grazing on species composition were greatest in the early wet season when high rates of utilization significantly reduced the proportion and occurrence of Themeda and increased the proportion of forbs. Grazing in the dry season had no significant effect on composition. At medium and high levels of utilization in the early wet season, the pasture responded negatively to defoliation, only partially compensating for plant tissue lost to herbivory. The negative response to defoliation carried over to the next wet season when these same medium and high-grazing treatments produced only 80 % and 60 % growth, respectively, of that in treatments grazed at low levels of utilization or those grazed during the dry season. The frequency of Themeda was still lower, and that of annual grasses and non-leguminous forbs higher, in plots that had been grazed at a high rate of utilization for just eight weeks in the early wet season two years previously. Species richness and diversity were also significantly affected by this grazing disturbance. If species composition is to be maintained in these grasslands then stocking rates must be set at low levels to cope with the combined effect of undercompensation in response to defoliation in the wet season and strong dietary preferences for grazing sensitive species.     

Effects of grazing and invasive grasses on desert vertebrates in California

Much of California's San Joaquin Valley is a desert and, like portions of other North American deserts, is experiencing an ecological shift from being dominated by ephemeral native forbs, with widely spaced shrubs, to fire-prone non-native annual grasses. Small terrestrial vertebrates, many of which are adapted to open desert habitats, are declining. One hypothesis is that the invasive plants contribute to the decline by altering vegetative structure. Although cattle may have originally been a factor in the establishment of these non-native plants, their grazing may benefit the terrestrial vertebrates by maintaining an open structure, especially during average or wet winters when the exotic grasses grow especially dense. We experimentally tested the effect of cattle grazing on invasive plants and a community of small vertebrates at a site in the southwestern San Joaquin Desert. We established and monitored 4 treatment (grazed) and 4 control (ungrazed) plots from 1997 to 2006, and assessed the abundances of blunt-nosed leopard lizards (Gambelia sila), giant kangaroo rats (Dipodomys ingens), short-nosed kangaroo rats (Dipodomys nitratoides nitratoides), and San Joaquin antelope squirrels (Ammospermophilus nelsoni), all of which are listed as threatened or endangered by state or federal agencies. We also recorded abundances of the non-protected western whiptail lizards (Aspidoscelis tigris), side-blotched lizards (Uta stansburiana), San Joaquin pocket mice (Perognathus inornatus inornatus), and Heermann's kangaroo rats (Dipdomys heermanni). Based on repeated measures analysis of variance (ANOVA) and a 0.05 alpha level, only Heermann's kangaroo rats showed a treatment effect; they were more abundant on the control plots. However, this effect could be accounted for by the natural re-establishment of saltbush (Atriplex spp.) on part of the study site. Saltbush return also favored western whiptail lizards and San Joaquin antelope squirrels. A regression analysis indicated that populations of blunt-nosed leopard lizard and giant kangaroo rat increased significantly faster in grazed plots than the ungrazed controls, and abundances of 6 of 8 species were negatively correlated with increased residual dry matter. With relaxed alpha values to decrease Type II error, populations of blunt-nosed leopard lizards (500% greater), San Joaquin antelope squirrels (85% greater), and short-nosed kangaroo rats (73% greater) increased significantly on grazed plots over the course of the study compared to ungrazed plots. We did not find grazing to negatively affect abundance of any species we studied. When herbaceous cover is low during years of below average rainfall in deserts and other arid areas, grazing may not be necessary to maintain populations of small vertebrates. However, if cattle grazing is closely monitored in space and time to minimize adverse effects on the habitat, it could be an effective tool to control dense stands of non-native grasses and benefit native wildlife. © 2011 The Wildlife Society.     

Contrasting impacts of grass species on nitrogen cycling in a grazed Sudanian savanna

We investigated the impact of perennial and annuals grass species on nitrogen cycling in a Sudanian savanna of Burkina Faso. We also analysed how the local context in terms of grazing and soil properties modifies these impacts. We selected four plots differing both by the intensity of grazing by cattle and soil depth, and used soil and grass biomass ¹⁵N as integrative indicators of N cycle. If perennials are able to foster a more efficient nitrogen cycling there should be lower ¹⁵N abundances in their biomass and soil. If soil depth and cattle pressure significantly modify nitrogen fluxes, soil depth and cattle pressure should influence ¹⁵N signatures. Our results suggest that perennial grasses are more conservative for nitrogen (inhibition of nitrification, less leaching via a perennial root system, slower cycling). The increase in leaf δ¹⁵N with N concentration is steeper in Loudetia togoensis than in the three other grasses. No significant difference was found between the ¹⁵N signatures of the four plots. Our results on ¹⁵N signatures and the fact that perennial grasses are much more abundant in the plots that are less grazed and have deeper soils, confirm that the switch from perennial to annual grasses is linked to a degradation in soil fertility and pasture quality. This suggests that ¹⁵N signatures can be used as indicators of fertility.     

Restoration of Native Perennials in a California Annual Grassland after Prescribed Spring Burning and Solarization

Grasslands dominated by exotic annual grasses have replaced native perennial vegetation types in vast areas of California. Prescribed spring fires can cause a temporary replacement of exotic annual grasses by native and non‐native forbs, but generally do not lead to recovery of native perennials, especially where these have been entirely displaced for many years. Successful reintroduction of perennial species after fire depends on establishment in the postfire environment. We studied the effects of vegetation changes after an April fire on competition for soil moisture, a key factor in exotic annual grass dominance. As an alternative to fire, solarization effectively kills seeds of most plant species but with a high labor investment per area. We compared the burn to solarization in a study of establishment and growth of seeds and transplants of the native perennial grass Purple needlegrass (Nassella pulchra) and coastal sage species California sagebrush (Artemisia californica). After the fire, initial seed bank and seedling densities and regular percent cover and soil moisture (0–20 cm) data were collected in burned and unburned areas. Burned areas had 96% fewer viable seeds of the dominant annual grass, Ripgut brome (Bromus diandrus), leading to replacement by forbs from the seed bank, especially non‐native Black mustard (Brassica nigra). In the early growing season, B. diandrus dominating unburned areas consistently depleted soil moisture to a greater extent between rains than forbs in burned areas. However, B. diandrus senesced early, leaving more moisture available in unburned areas after late‐season rains. Nassella pulchra and A. californica established better on plots treated with fire and/or solarization than on untreated plots. We conclude that both spring burns and solarization can produce conditions where native perennials can establish in annual grasslands. However, the relative contribution of these treatments to restoration appears to depend on the native species being reintroduced, and the long‐term success of these initial restoration experiments remains to be determined.     

Mowing Reduces Exotic Annual Grasses but Increases Exotic Forbs in a Semiarid Grassland

Cheatgrass (Bromus tectorum) and other exotic winter‐active plants can be persistent invaders in native grasslands, growing earlier in the spring than native plants and pre‐empting soil resources. Effective management strategies are needed to reduce their abundance while encouraging the reestablishment of desirable native plants. In this 4‐year study, we investigated whether mowing and seeding with native perennial grasses could limit growth of exotic winter‐actives, and benefit growth of native plants in an invaded grassland in Colorado, United States. We established a split‐plot experiment in October 2008 with 3 mowing treatments: control, spring‐mowed, and spring/summer‐mowed (late spring, mid‐summer, and late summer), and 3 within‐plot seeding treatments: control, added B. tectorum seeds, and added native grass seeds. Cover of plant species and aboveground biomass were measured for 3 years. In March and June of 2010, 2011, and March of 2012, B. tectorum and other winter‐annual grasses were half as abundant in both mowing treatments as in control plots; however, cover of non‐native winter‐active forbs increased 2‐fold in spring‐mowed plots and almost 3‐fold in spring/summer‐mowed plots relative to controls. These patterns remained consistent 1 year after termination of treatments. Native cool‐season grasses were most abundant in spring‐mowed plots, and least abundant in control plots. There was higher cover of native warm‐season grasses in spring/summer‐mowed plots than in control plots in July 2011 and 2012. The timing of management can have strong effects on plant community dynamics in grasslands, and this experiment indicates that adaptive management can target the temporal niche of undesirable invasive species.     

The Role of White Clover in the Loss of Diversity in Grassland Habitat Restoration

A field experiment was designed to recreate a species‐rich mesotrophic grassland community of conservation worth. Trifolium repens (white clover) was observed to increase significantly in both frequency and abundance in sown plots grazed by cattle, but not in plots cut in June and subsequently grazed by cattle. In both these treatments permanent quadrats containing clover patches were found to be lower in species richness than were quadrats without clover. In both treatments botanical diversity was seen to decline over time. In the grazed‐only treatment the loss of diversity may be linked to the increase in clover. In the cut and grazed plots, T. repens did not become so abundant but diversity was still seen to decline, possibly due to the loss of low growing species from the taller sward. A pot experiment which varied the sowing density of a mix of seven wild flower species in full factorial combination with cutting frequency was established on soils from an arable field also sown with a single density of clover. T. repens was seen to decline from initial high cover estimates in infrequently cut and uncut treatments. In the pot experiment where a grass component to the vegetation was absent, clover was seen to have less impact on the other forbs than it did in the field. It is suggested that, being a nitrogen fixer, T. repens may have a competitive edge in ex‐arable soils low in available nitrogen. The observed reduction in botanical diversity may be a result of this increase in available nitrogen, facilitating the spread of the sown grasses and preventing the recovery of the sown forbs that were excluded by the invasion of T. repens. It is suggested that reducing the proportion of grass in the seed mixtures during grassland habitat creation on these soils may help reduce or delay this effect.     

A hierarchical model for analysing the stability of vegetation patterns created by grazing in temperate pastures

Questions: Does vegetation structure display any stability over the grazing season and in two successive years, and is there any correlation between the stability of these spatial patterns and local sward composition? Location: An upland grassland in the French Massif Central. Method: The mosaic of short and tall vegetation stands considered as grazed and ungrazed patches respectively is modeled as the realization of a Boolean process. This method does not require any arbitrarily set sward‐height thresholds to discriminate between grazed and ungrazed areas, or the use of additional variables such as defoliation indexes. The model was validated by comparing empirical and simulated sward‐height distributions and semi‐variograms. Results: The model discriminated between grazed and ungrazed patches at both a fine (1 m²) and a larger (500 m²) scale. Selective grazing on legumes and forbs and avoidance of reproductive grass could partly explain the stability of fine‐scale grazing patterns in lightly grazed plots. In these plots, the model revealed an inter‐annual stability of large‐scale grazing patterns at the time peak biomass occurred. At the end of the grazing season, lightly grazed plots showed fluctuating patch boundaries while heavily grazed plots showed a certain degree of patch stability. Conclusion: The model presented here reveals that selective grazing at the bite scale could lead to the creation of relatively stable patches within the pasture. Locally maintaining short cover heights would result in divergent within‐plot vegetation dynamics, and thus favor the functional diversity of vegetation.     

Seed and microsite limitation in a late-successional old field: the effects of water, adults, litter, and small mammals on seeds and seedlings

Many plant communities are recruitment limited, which may occur because there are either too few seeds to fill available microsites, too few available microsites, or both. In a recruitment-limited, Minnesota, USA old field, we tested among these alternatives in a three-phase study. In phase 1, we estimated the production of late-successional forb and C4 grass seeds. In phase 2, we experimentally modified field establishment conditions with rainfall amendment, adult plant thinning, litter reduction, and small mammal exclusion. We then measured recruitment. On average, of the nearly 2,600 seeds produced m^?2, only 164 seeds m^?2 were present and living after overwintering, as measured by field and greenhouse germination. Furthermore, on average, only 9 of those 164 seeds m^?2 germinated in the field, even under the relaxed establishment conditions of our four experimental treatments. Although adults of C4 grasses dominate the field, surprisingly few C4 grass seedlings germinated. To understand why, in phase 3, we added seed of the three dominant C4 grasses into the same plots the following year. Their ability to recruit into control plots compared with treated plots was relatively lower than for the ambiently recruited forbs from phase 2, suggesting that the competitively dominant C4 grasses have greater difficulty establishing in the extant community. Of the seeds that did germinate in the field in phases 2 and 3, all four experimental treatments significantly improved at least one stage of establishment, with the rainfall amendment having the greatest overall effect across species. In total, our results suggest that seed limitation was exacerbated by microsite limitation via multiple mechanisms.     

Soil seed densities and emergence patterns in pastures in the seasonally dry tropics of northeastern Australia

Germinable seed densities in the surface (0–10 cm) soil of pasture communities growing at Lansdown, near Townsville, were measured during the late dry season before the first germinating rain and again during the following wet season after germination but before the input of new seed. Seedlings emerging in the field were counted at approximately weekly intervals during this period to determine emergence patterns. Twelve communities were sampled in 1980–81 and six were re-sampled in 1981–82. During the late dry season germinable seed densities ranged from 5000 to 40 000 seeds m^-2. Seeds of the introduced legume, Stylosanthes hamata, were present in all pastures. There were many seeds of annual grasses (Digitaria ciliaris and Brachiaria miliiformis) and sedges (Cyperus and Fimbristylis spp.) but only few seeds of perennial grasses (both native and introduced). Soil seed densities were much lower during the wet season than during the preceding dry season, particularly for the grasses. Emergence commenced and approximately 70% of all seedlings emerged on the first major rainfall of the wet season. The subsequent emergence pattern varied between years. In 1980–81 there was a gradual and continuous increase in seedling numbers under the continuously moist conditions which prevailed. In 1981–82 further emergence occurred in discrete events related to rainfall and intervening dry periods. Maximum seedling densities exceeded 34 000 seedlings m^-2 including 29 000 grass seedlings (mainly annual species). The implications of these results for species survival and pasture composition are discussed.     

The roles of exotic grasses and forbs when restoring native species to highly invaded southern California annual grassland

Many semi-arid shrublands in the western US have experienced invasion by a suite of exotic grasses and forbs that have altered community structure and function. The effect of the exotic grasses in this area has been studied, but little is known about how exotic forbs influence the plant community. A 3-year experiment in southern California coastal sage scrub (CSS) now dominated by exotic grasses was done to investigate the influence of both exotic grasses (mainly Bromus spp.) and exotic forbs (mainly Erodium spp.) on a restoration seeding (9 species, including grasses, forbs, and shrubs). Experimental plots were weeded to remove one, both, or neither group of exotic species and seeded at a high rate with a mix of native species. Abundance of all species varied with precipitation levels, but seeded species established best when both groups of exotic species were removed. The removal of exotic grasses resulted in an increase in exotic and native forb cover, while removal of exotic forbs led to an increase in exotic grass cover and, at least in one year, a decrease in native forb cover. In former CSS now converted to exotic annual grassland, a competitive hierarchy between exotic grasses and forbs may prevent native forbs from more fully occupying the habitat when either group of exotics is removed. This apparent competitive hierarchy may interact with yearly variation in precipitation levels to limit restoration seedings of CSS/exotic grassland communities. Therefore, management of CSS and exotic grassland in southern California and similar areas must consider control of both exotic grasses and forbs when restoration is attempted.     

Management intensity affects the relationship between non‐native and native species in subtropical wetlands

Question: Does management intensity affect the association between non‐native and native species and between non‐native species and soil nutrients in wetlands? Location: MacArthur Agro‐Ecology Research Center, Florida, USA. Methods: We evaluated native and non‐native plant richness and relative frequency in 15 1‐m² plots in 40 wetlands across two types of pastures, highly managed (fertilized, ditched, planted, heavily grazed by cattle) and semi‐natural (unfertilized, lightly seasonally grazed). Plant biomass was collected in five 0.25‐m² plots per wetland and sorted to species. Soil cores were collected to analyse soil total nitrogen (N) and phosphorus (P). An information‐theoretic approach was used to compare mixed effects models considering the association of non‐native richness, relative frequency, and biomass with native richness, relative frequency, biomass, C₃ grass relative frequency (a dominant native group), N, P and wetland‐type. Results: Non‐native richness was negatively correlated with native richness in semi‐natural wetlands, but there was no evidence of an association between these variables in highly managed wetlands. Non‐native richness increased with increasing soil N in semi‐natural wetlands, but not in the highly managed wetlands. Soil P was positively related to non‐native frequency in semi‐natural wetlands but negatively related in highly managed wetlands. Non‐native frequency and biomass were negatively related to relative frequency of C₃ grasses in both management types. Conclusions: Our results indicate that management intensity influences relationships between native and non‐native richness. Management intensity interacts with abiotic or biotic factors, such as soil nutrients and composition, in predicting where non‐native species will most likely need control.     

Reintroduction of Nassella pulchra to California coastal grasslands: Effects of topsoil removal,plant neighbour removal and grazing

Question: What is the most appropriate combination of treatments to reintroduce Nassella pulchra, a perennial bunchgrass, into degraded mediterranean coastal grasslands? Location: Central coast of California, USA. Methods: N. pulchra was sown from seeds and transplanted into a degraded grassland in a multi‐factorial experiment testing the effects of (1) two grazing intensities (lightly grazed by native mammal species or ungrazed); (2) topsoil removal and (3) reduction of plant neighbours. The experiment was carried out on two types of surrounding vegetation (exotic annual grasses and exotic forbs). Results: Topsoil removal greatly enhanced establishment from seeds and transplant survival, mainly because it reduced the exotic vegetation and thus reduced competition. While removing neighbours was essential when topsoil was left intact, it had a negative effect on N. pulchra when surrounding species included exotic forbs (Brassica spec, and Asteraceae) at low density (after topsoil removal). Moderate grazing by native mammals (deer, rabbits and gophers) did not affect N. pulchra. Conclusion: Our results suggest that seeding after topsoil has been removed is a promising method to reintroduce N. pulchra to highly degraded sites where there is little to no native seed bank.     

Influence of rainfall and grazing on herbage dynamics in a seasonally dry tropical savanna

Species composition and herbage dynamics in relation to rainfall variability and cattle grazing were studied in permanently protected, grazed, and temporarily fenced treatments on three sites in a seasonally dry tropical savanna. Permanently protected sites, established between 1979 and 1984, were 55–79% similar with each other in species composition, and 14–25% similar with grazed sites during the period 1986–1988. Similarity among grazed sites was only 36–43%. Number of species was greater in the grazed treatment than in the permanently protected treatment. The percentages of annual grasses and non-leguminous forbs were greater in grazed savanna than in permanently protected savanna. Species diversity was higher in grazed savanna than in the corresponding permanently protected savanna. Species the two annual cycles studied, peak live shoot biomass was 614 g m^-2 in permanently protected savanna, 109 g m^-2 in grazed savanna, and 724 g m^-2 in temporarily fenced savanna. Live shoot biomass in temporarily fenced savanna was 18 to 44% greater than in permanently protected savanna. Peak canopy biomass ranged from 342 to 700 g m^-2 in permanently protected savanna. It was related with total rainy season rainfall, and was particularly sensitive to late rainy season rainfall. On the other hand, peak canopy biomass in grazed savanna ranged from 59 to 169 g m^-2 and was related to grazing intensity rather than either total rainy season rainfall or late rainy season rainfall. Coefficient of variation of green biomass in permanently protected savanna was related with rainfall variability indicating it to be a pulsed system which responds quickly to rainfall events. Biomass of woody species ranged from 2466 to 5298 g m^-2 in permanently protected savanna and from 744 to 1433 g m^–2 in the grazed savanna. Green foliage biomass was 3.7 to 6.4% of the woody biomass in permanently protected and 5.6 to 5.9% in grazed savanna, and supplements substantially the fodder resource during the dry periods of the year.     

Effects of Established Perennial Grasses on Introduction of Native Forbs in California

Prairie restoration is not complete without the establishment of both grasses and forbs. However, if desirable forbs and grasses are seeded simultaneously, control of broadleaf weeds is problematic. If possible, a two‐step process of introducing forbs after establishing grasses would allow use of broadleaf‐specific herbicides at the critical early stages of grass growth. We conducted experiments to investigate methods for introducing forbs into previously restored native perennial grasslands on rural roadsides in the Sacramento Valley of California. In one experiment, we studied the effects of background vegetation (established perennial grasses or tilled ground) on seven native forb species planted from seed. In a second experiment, we evaluated the effects of background vegetation (existing perennial grasses or tilled ground) and container size (36 ml or 105 ml) with excavation technique (excavation by core removal [core] or by creating an impression [dibble]) on the growth of transplants of the native perennial forbs Asclepias fascicularis and Sisyrinchium bellum. The presence of established perennial grasses reduced the growth of seeded forbs, but did not affect transplants, indicating the vulnerability of seedling forbs to interference. When compared to control plots that had been tilled in the autumn, weed canopy cover was significantly lower in the presence of perennial grasses if seeded with forbs, but not in the presence of perennial grasses alone. Both transplanted species grew better in the large container/core treatment than the small container/dibble treatment; however, existing grasses eliminated these positive effects. Asclepias fascicularis performed better when grown in large containers than in small containers, but its growth was not affected by excavation method; S. bellum performed better when planted with the core method than the dibble method of excavation, but container size made no difference. We attribute differences in the responses of the species to interactions between phenological differences and expansive clay soils that naturally de‐compact upon drying.     

Plant response to disturbance in a Mediterranean grassland: How many functional groups?

Abstract. Data referring to changes in vegetation composition resulting from cattle exclosure and ploughing in a Portuguese pasture dominated by annuals were used to test hypotheses regarding the biology of species favoured or eliminated by disturbance in semi-natural herbaceous communities. These hypotheses were tested in two ways. First we compared the distribution of six a priori groups – grasses, small rosettes, large rosettes, small species with leafy stems, large species with leafy stems, legumes – across grazed, ploughed and undisturbed plots. In a second set of analyses we examined changes in the frequencies of individual biological attributes in response to grazing and ploughing. These analyses were carried out separately for grasses and dicot forbs. Overall, the species composition showed little response to either grazing or ploughing, though species dominance changed. This lack of responsiveness of species composition was attributed to the long history of intensive land use which has resulted in the loss of disturbance-intolerant species over entire landscapes. When considering a priori groups, small rosettes were indifferent to disturbance. grazing and ploughing showed that dominated. Large rosettes, large species with leafy stems and legumes were generally intolerant to both grazing and ploughing, though individual species may increase in response to disturbance. Small species with leafy stems were the only group favoured by grazing whereas ploughing favoured grasses. As to individual traits, grazing excluded large grass species with heavy seeds and promoted a flat rosette canopy structure and a small size, along with a moderate dormancy and protected inflorescences. In forbs, grazing favoured small species, as expected, while it excluded tall species, and, in contrast to earlier results, a rosette canopy. These attributes were consistent with responses of the a priori groups, though it would not have been possible to reconstruct groups directly from the attribute list. Ploughing had no effect on any of the forb traits. As to grass traits, flat- and short-statured species increased and heavy-seeded species decreased. Our analysis revealed two advantages of establishing plant functional classifications within life forms. Subgroups within forbs had contrasting types of behaviour. For the same trait patterns could differ within the grass group from within the forb group. Finally, this analysis emphasizes the need for plant functional classifications aiming at the identification of syndromes of co-occurring attributes rather than of lists of isolated traits of which actual combinations are not specified.