Greater Litter Cover Research Articles

Influence of pipelines and environmental factors on the endangered plant, Halimolobos virgata (Nutt.) O.E. Schultz over a 10 year period

We investigated the effects of pipeline construction and environmental factors on the occurrence and characteristics of the endangered plant Halimolobos virgata (Nutt.) O.E. Schultz. The plants were surveyed from 2007 to 2016 at three sites along the Keystone Pipeline in southern Alberta, Canada. Plant height, number of flowers and siliques, as well as microhabitat and climate data were collected up to 300 m away from the pipeline. Pipeline construction and distance had no effect on plant numbers or physical characteristics, with occurrences increasing markedly over time. Greater litter cover and depth and spring precipitation were associated with plant height and number of flowers and siliques. Vegetation cover was negatively correlated with H. virgata cover; however, plant height and number of flowers and seed pods were positively influenced by graminoid cover. The highest occurrences of H. virgata coincided with the driest and wettest years, and higher winter and spring temperatures. Some of this pattern can be attributed to the plant’s annual, biennial, and short perennial life forms, which may overlap and create a temporary exponential growth rate for an annual plant under ideal conditions. This research highlights the importance of understanding a species’ life history for the development of effective conservation and recovery strategies.

Excavations of giant armadillos alter environmental conditions and provide new resources for a range of animals

AbstractBurrowing species can be considered important ecosystem engineers that increase landscape heterogeneity, create subterranean shelters and provide foraging opportunities. We measured and described different aspects of giant armadillo (Priodontes maximus) excavations (size, age), and differences generated in relation to the surrounding environment (vegetation, humidity, temperature) in three sites of the Argentine Chaco Region. We used camera‐traps in two protected areas to monitor the use of burrows by other species and tested two primary and non‐mutually exclusive hypotheses: Giant armadillo burrows are used as thermal protection from temperature extremes and provide new foraging opportunities for other species. Greater litter cover and depth were recorded in giant armadillo burrows, and more bare ground in spoil piles, producing habitat heterogeneity. Burrows had higher humidity and more moderate temperatures, with lower temperatures during hot months and higher temperatures during cold months. Out of 48 vertebrate species recorded by camera‐traps, 27 taxa (17 mammals, 9 birds and one reptile) were recorded using burrows. White‐lipped peccaries (Tayassu peccari) and collared peccaries (Pecari tajacu) used burrows more frequently than other mammals. Medium‐sized carnivores such as Pampas fox (Lycalopex gymnocercus) and Geoffroy´s cat (Leopardus geoffroyii) tended to only investigate burrows, probably searching for prey. In no instances, animals other than giant armadillos were recorded staying inside burrows for more than a few seconds. Medium‐sized species interacted more frequently than large‐sized species, and smaller species used giant armadillo burrows less than larger ones, suggesting that the benefits provided by excavations to other species depend on their body weight. The probability of use of burrows decreases with time, suggesting that burrows provide a finite resource used opportunistically. Further reduction in the distribution of the giant armadillo is therefore likely to have effects on habitat heterogeneity and biodiversity, probably impacting the fitness of species that use their burrows as foraging sources.

Microhabitat Selection for Nesting and Brood-Rearing by the Greater Sage-Grouse in Xeric Big Sagebrush

Understanding selection of breeding habitat is critical to conserving and restoring habitats for the Greater Sage-Grouse (Centrocercus urophasianus), particularly in xeric landscapes (≤25 cm annual precipitation). We monitored radio-marked female sage-grouse in south-central Wyoming in 2008 and 2009 to assess microhabitat use during nesting and brood rearing. For each model we grouped variables into three hypothesis sets on the basis of the weight of support from previous research (a priori information). We used binary logistic regression to compare habitat used by grouse to that at random locations and used an information-theoretic approach to identify the best-supported models. Selection of microhabitat for nests was more positively correlated with mountain big sagebrush (Artemisia tridentata vaseyana) than with Wyoming big sagebrush (A. t. wyomingensis) and negatively correlated with cheatgrass. Nesting hens also selected microhabitats with greater litter cover. Microhabitat for brood-rearing had more perennial grass and sagebrush cover than did random locations. Microhabitat variables most supported in the literature, such as forb cover and perennial grass cover, accounted for only 8% and 16% of the pure variation in our models for early and late brood rearing, respectively. Our findings suggest sage-grouse inhabiting xeric sagebrush habitats rely on sagebrush cover and grass structure for nesting as well as brood-rearing and that at the microhabitat scale these structural characteristics may be more important than forb availability. Therefore, in xeric sagebrush, practices designed to increase forb production by markedly reducing sagebrush cover, as a means to increase sage-grouse productivity, may not be justified.

Litter of an alien tree, Casuarina equisetifolia, inhibits seed germination and initial growth of a native tree on the Ogasawara Islands (subtropical oceanic islands)

We investigated the effects of the accumulation of litter of an alien tree, Casuarina equisetifolia, on the initial establishment of Schima mertensiana, a tree native to the Ogasawara (Bonin) Islands, in the northwestern Pacific Ocean, in field and greenhouse experiments. The field experiment compared emergence of seedlings in forests dominated by C. equisetifolia with those in native forests, with and without litter removal. The greenhouse experiment compared seedling germination and biomass among 12 treatments that included two soil types (collected from the C. equisetifolia and native forests), two litter types (C. equisetifolia and native litter), and three amounts of litter (5, 15, or 45 g/pot). Significantly fewer S. mertensiana seedlings emerged at sites dominated by C. equisetifolia than at sites of native species in the field experiment. Litter removal tended to increase seedling emergence. Fewer and smaller S. mertensiana seedlings germinated with greater litter cover regardless of soil type or litter type in the greenhouse experiment. Our results demonstrate that C. equisetifolia litter suppresses germination and initial growth of S. mertensiana, and that the main cause of the suppression is the greater amount of litter accumulated under C. equisetifolia forest floor rather than factors such as the nature of the soil or litter between native and alien species.

URban Biotopes of Aotearoa New Zealand (URBANZ) II: Floristics, biodiversity and conservation values of urban residential and public woodlands, Christchurch

Urban forests are increasingly valued for multiple benefits such as amenity, cultural values, native biodiversity, ecosystem services, and carbon sequestration. Urban biodiversity in particular, is the new focus although global homogenisation is undermining regional differentiation. In the northern hemisphere (e.g., Canada and USA) and in the southern hemisphere, particularly in countries like South Africa, Australia, South America and New Zealand, local biodiversity is further impacted by historical colonisation from Europe. After several centuries, urban forests are now composed of synthetic and spontaneous mixtures of native species, and exotic species from around the temperate world (e.g., Europe, North and South America, South Africa, Asia). As far as we are aware no-one has carried out in-depth study of these synthetic forests in any Southern Hemisphere city. Here we describe the composition, structure, and biodiversity conservation imperatives of urban temperate forests at 90 random locations in Christchurch city, New Zealand. We document considerable plant diversity; the total number of species encountered in the 253 sampled urban forest patches was 486. Despite this incredibly variable data set, our ability to explain variation in species richness was surprisingly good and clearly indicates that total species richness was higher in larger patches with greater litter and vegetation cover, and taller canopy height. Species richness was also higher in patches surrounded by higher population densities and closer to very large native forest patches. Native species richness was higher in patches with higher soil pH, lower canopy height, and greater litter cover and in patches closer to very large native forest patches indicating dispersal out of native areas and into gardens. Eight distinct forest communities were identified by Two-Way INdicator SPecies ANalysis (TWINSPAN) using the occurrence of 241 species that occurred in more than two out of all 253 forest patches. Christchurch urban forest canopies were dominated by exotic tree species in parklands and in street tree plantings (linear parkland). Native tree and shrub species were not as common in public spaces but their overall density high in residential gardens. There was some explanatory power in our data, since less deprivation resulted in greater diversity and density, and more native species, which in turn is associated with private ownership. We hypothesise that a number of other factors, which were not well reflected in our measured environmental variables, are responsible for much of the remaining variation in the plant community structure, e.g., advertising, peoples choice. For a more sustainable asset base of native trees in New Zealand cities we need more, longer-lived native species, in large public spaces, including a greater proportion of species that bear fruit and nectar suitable for native wildlife. We may then achieve cities with ecological integrity that present multiple historical dimensions, and sequester carbon in legible landscapes.

Plant Interspaces Resulting From Contrasting Grazing Management in Northern Mixed-Grass Prairie: Implications for Ecosystem Function

We assessed plant interspaces in July 2007 using continuous line intercepts in twice-replicated pastures of northern mixed-grass prairie with contrasting grazing treatments: 1) long-term (25 yr) heavily grazed, dominated by the bunchgrass blue grama (Bouteloua gracilis), and 2) ungrazed, dominated by the rhizomatous grass western wheatgrass (Pascopyrum smithii). The number of plant interspaces was 26% higher in pastures heavily grazed, but the amount of soil surface occupied by plant interspaces was 27% greater without grazing. Plant interspaces were larger without grazing (14.8 6 1.2 cm, mean 6 1 SE) than heavily grazed (8.9 6 0.4 cm). Plant interspaces represented 87% and 68% of the total soil surface in the ungrazed and heavily grazed communities, respectively. The percentage of soil surface covered by plant interspaces , 20 cm was higher for the heavily grazed (94%) compared to the ungrazed (79%). Litter cover in the plant interspaces was higher without grazing (80 6 1%) compared to the heavily grazed (57 6 3%). Grazing-induced structural changes from a rhizomatous- to a bunchgrass-dominated vegetation community were manifest in the size and distribution of plant interspaces. Ecological consequences for erosion from raindrop impacts in larger plant interspaces in the ungrazed community are likely offset by greater litter cover in these communities; conversely, lower litter cover in heavily grazed pastures may increase erosion potential despite occurrence of smaller plant interspaces and less proportion of the soil surface covered by interspaces. Management practices that increase the cover of litter in plant interspaces should reduce the potential of erosion from water and wind in this semiarid rangeland.

Tree-grass relationships in open eucalypt woodlands of northeastern Australia: influence of trees on pasture productivity, forage quality and species distribution

Pasture yield, quality and species distributions were compared between zones around live and killed eucalypt trees at two woodland sites in northeast Queensland which differed markedly in soil fertility. Trees affected pasture quality and yield on an individual tree basis: N concentration and dry matter digestibility tended to be higher under trees than in inter-tree areas at both sites and pasture yields declined with distance from killed trees at the lower fertility site. However, the distribution of individual species did not vary markedly with distance from trees. Trees also affected pasture yield on a woodland basis: yields were greater where the trees were killed than under intact woodland. Soil under trees had higher levels of organic carbon and greater litter cover than soil in inter-tree areas. However, pasture yields did not generally reflect this fertility gradient since growth was limited by moisture availability due to drought conditions during the study period. Pasture N concentration was higher under trees that in inter-tree areas since plants under trees produced a similar amount of biomass as plants in inter-tree areas, but had access to higher nutrient levels. Trees appeared to have a greater effect on soil nutrient availability at the low fertility site. Live trees depressed pasture yields to a lesser degree at the low fertility site, demonstrating that the effects of trees on soil water availability (on a woodland scale) are less important when soil nutrients are more limiting to growth. These results indicate that, while removing trees may enhance pasture productivity, this benefit may be offset by a reduction in pasture quality. Given the beneficial effect of trees on soil nutrients, tree removal may also have longer term implications for soil nutrient dynamics.

A Study of the Ecological Bases of Cooperative Breeding in the Harris' Hawk

We compared ecological variables of pairs and larger groups of Harris' Hawks (Parabuteo unicinctus) in southeastern New Mexico in an effort to test several ecologically based hypotheses proposed to explain cooperative breeding. Univariate and multivariate analyses of 21 habitat variables revealed no differences (P > .1) between the nest areas of pairs and groups. Habitats not occupied by hawks had significantly (P < .05) fewer and smaller mesquite trees and greater litter cover than occupied areas. Densities of lagomorph fecal pellets (an index of abundance of the primary prey species) was slightly greater (P > .1) in group areas than pair areas in summer, but the pattern was reversed in winter. Pair ranges had significantly (P < .05) fewer woodrat (Neotoma, an alternate prey) nests than group areas in all seasons. Rabbit femurs from prey remains of groups were slightly, but not significantly, longer than those from pair remains. Although general hypotheses cannot be fully evaluated in studies of single species, the data we obtained do not provide clear support for any of several current hypotheses concerning cooperative breeding in the Harris' Hawk. Instead, group living in this hawk appears to be related to dependence on large, elusive prey in a manner analogous to the social system of wolves (Canis lupus) and wild hunting dogs (Lycaon pictus). We conclude that this species' social system is based on (1) extended parental care, where young birds remain with older group members during their first year or years, and (2) cooperation, where group hunting and prey—sharing provide a critical advantage to each individual.

Ecological Relationships of Two Species of Akodon in Central Chile

Analyses of habitat selection and diet showed significant ecological separation between Akodon longipilis and A. olivaceus (Cricetidae) in Mediterranean-climate areas of Chile. Comparing five sites with different climates and vegetation, A. longipilis was more common than A. olivaceus at those localities with higher rainfall and shrub cover. At two coastal scrub sites A. longipilis was strongly associated with trap stations having greater shrub cover, greater litter cover, taller shrubs, less herbaceous cover, and lower herb heights than stations selected by A. olivaceous. A discriminant analysis found measures of herbaceous and litter cover to be the strongest variables differentiating microhabitats of the two species. Analyses of stomach contents showed both species to be omnivorous, but A. longipilis consumed higher proportions of arthropods than A. olivaceus at most sites. Habitat use and diet may be correlated with adaptations in skull morphology and body size in these two species.