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Gill, Amy S.; Fehmi, Jeffrey S.; Gornish, Elise S.
<p>ABSTRACT:</p><p>Encroachment of <i>Eragrostis lehmanniana</i> (Lehmann lovegrass), a non-native perennial grass species, challenges land managers in the southwestern United States due to its tendency to increase fire frequency and displacement of natives. In areas characterized by disturbance, <i>E. lehmanniana</i> displaces <i>Agave palmeri</i> (Palmer's agave), an ecologically and socioculturally significant native plant species in the Sonoran Desert. We explored strategies to enhance short-term <i>A. palmeri</i> establishment using a greenhouse experiment. We assessed survival and growth responses of transplanted <i>A. palmeri</i> exposed to a variety of manipulated variables, including biotic (agave size at planting and <i>E. lehmanniana</i> competition) and abiotic (simulated precipitation and surface litter). We found a significant increase in <i>A. palmeri</i> biomass in the absence of <i>E. lehmanniana</i> in the high and medium watering treatments compared to agave in the presence of clipped <i>E. lehmanniana</i> neighbors. The presence of <i>E. lehmanniana</i> did not significantly affect <i>A. palmeri</i> biomass in the low water treatment. In the medium and low watering treatments, <i>A. palmeri</i> with litter had nearly twice the biomass as those without litter. The absence of <i>E. lehmanniana</i> with the high watering treatment and litter resulted in the largest agave biomass. For improved <i>A. palmeri</i> growth (and likely its survival) in restoration projects, we recommend supplemental watering and litter addition. Removal of <i>E. lehmanniana</i> is also suggested (by hand if possible); however, this species could operate as a nurse plant for agaves.</p>
Gowdy, Geron; Hernández, Fidel; Fulbright, Timothy; Grahmann, Eric; Wester, David; Vreugdenhil, Ellart; Henehan, Anthony; Smith, Forrest; Hehman, Michael
<p>ABSTRACT:</p><p>Non-native, invasive grasses can pose a threat to biodiversity in the southern U.S. <i>Pennisetum ciliare</i> (buffelgrass) is an example of an introduced invasive grass that has established in southwestern rangelands and negatively influenced biodiversity. Since its introduction, millions of hectares in the southwestern U.S. have been planted with, or invaded by, buffelgrass. Buffelgrass can form monocultures that not only reduce biodiversity but can also change ecosystem processes. Native-grassland restorations may be able to mitigate such negative impacts of non-native grasses. We conducted a study to document the response of herbaceous plants (grasses and forbs) and wildlife (grassland breeding birds, grassland wintering birds, and butterflies) to a 118-ha grassland restoration (involving prescribed fire, multiple discing and herbicide applications, and native-plant seeding) in La Salle County, Texas during 2013â2019. In general, we documented a numerical increase for all three taxa (native plants, birds, and butterflies) in species richness and relative abundance on the restoration site compared to a control. Our results suggest that native-grassland restoration is possible in a landscape dominated by buffelgrass. These restoration efforts can increase plant and wildlife diversity, although the time and expense required to achieve such responses are great.</p>
Chiquoine, Lindsay P.; Greenwood, Joshua L.; Abella, Scott R.; Weigand, James F.
<p>ABSTRACT:</p><p>Much plant recruitment in deserts occurs in shaded microsites below canopies of mature perennial plants. Absence of "nurse plants" from disturbed sites often hinders ecological recovery. Given uncertainty and expense of directly restoring live plants in deserts, we explored using abiotic structuresânurse rocksâas a restoration option for reestablishing <i>Opuntia basilaris</i> (beavertail pricklypear) on a disturbed site in the Sonoran Desert, of the U.S. Wild populations at this site were strictly associated with large varnished surface rocks. To examine whether rocks functioned similarly as nurses for <i>O. basilaris</i> recruitment in disturbed and undisturbed reference habitats, we transplanted 30 rooted individuals each into habitat in which large varnished surface rocks were removed and into nearby undisturbed habitat. Within habitats, half the individuals were transplanted into open (no rocks) or rock (rocks surrounding transplants) microsites. In the first 15 months after planting, which had average precipitation, transplant survival did not differ between microsite types in either habitat but functional measures were influenced positively by nurse rocks. Nurse rocks sharply increased vegetative growth in 91.7% of transplants in undisturbed habitat and in flowering occurrence in 28.6% of transplants in disturbed habitat. Nurse rocks became even more important during extreme drought as the experiment progressed. By 27 months after planting, 2Ã (disturbed habitat) and 8Ã (undisturbed habitat) more transplants survived with nurse rocks compared to without. As a low-cost technique utilizing on-site material, nurse rocks show promise for enhancing revegetation success on disturbed desert sites, especially during drought.</p>
<p>ABSTRACT:</p><p>The appropriate collection zone for seeds and transplants is a key concern for plant restoration ecology, with local sourcing thought to be the "gold standard." Local sourcing is based on the premise that most plant species are genetically adapted to the local environment through the action of natural selection, and that non-local ecotypes will disrupt this adaptation. However, a number of factors may allow practitioners to expand sourcing. These include genetic variation that is non-adaptive, phenotypic plasticity, climate change, disturbance, and a host of practical issues. These factors are reflected in the range of collection zone protocols that have been developed by practitioners, ranging from local sourcing to bypassing species identity in favor of function. In addition, phenotypic plasticity, because it allows a single genotype to produce different phenotypes in response to environmental variation, may also allow for a broadened collection zone. Little is known about the degree of genetic variation and local adaptation for most plant species. More evidence-based sourcing could result from collaboration between researchers and practitioners, including tracking seed and plant sources, their performance at restoration sites, and conducting reciprocal transplant studies. Inferring the degree of gene flow based on morphological characters has also shown some promise for inferring genetic variation among populations. Research that includes more robust sampling of populations within species would lead to more precise estimates of gene flow in relation to plant traits.</p>