Close Relatives, Different Niches: Urban Ecology of Two Range-Expanding Thrushes Recently Meeting in the Argentinian Pampas

One question about historical grassland ecosystems in the Great Plains region of central North America is the percentage of tree cover overall and near major rivers, compared to current tree cover. Here, I assessed tree cover in reconstructions of historical grasslands in the eastern Great Plains, isolating tree cover adjacent to major rivers, and then compared historical land cover to current (year 2019) land cover. As an extension to supply information for the entire Great Plains region, I modeled historical cover. For the 28 million ha extent of the eastern Great Plains, historical land cover was 86% grasslands and 14% trees, but 57% grasslands and 43% trees within 100 m of rivers. Tree cover near rivers ranged from 5.4% to 90% for 15 large river watersheds, indicating that any amount of tree cover could occur near rivers at landscape scales. Currently, the overall extent was 3.6% herbaceous vegetation and 6.6% forested, with 82% crops and pasture and 8% development. Within 100 m of rivers, crop and pasture decreased to 44% of cover, resulting in 14% herbaceous cover and 38% forested cover. Current tree cover ranged from 6.2% to 66% near rivers in 15 watersheds, which was relatively comparable to historical tree cover (ratios of 0.6 to 1.5). Results generally were similar for combined tree and shrub cover modeled for the entire Great Plains. Variability, even at landscape scales of large watersheds, was the normal condition for tree cover in grasslands and riparian ecosystems of the Great Plains. In answer to the question about tree cover in historical grassland ecosystems in the eastern Great Plains, tree cover typically was about three-fold greater near rivers than tree cover throughout grasslands. Combined tree and shrub cover near rivers was more than two-fold greater than tree and shrub cover throughout the Great Plains. Riparian forest restoration, as a management practice to reduce streambank erosion, overall has been effective, as indicated by current tree cover (38% near rivers in the eastern Great Plains) comparable to historical tree cover (43% near rivers in the eastern Great Plains), albeit as measured at coarse landscape scales with dynamics in vegetation and river locations. As a next step, restoration of grassland vegetation and non-riparian wetlands likely will help reestablish infiltrative watersheds, augmenting riparian forest restoration.

The flock formation of bird species is a crucial behavioral process that enables them to colonize urban areas. However, the factors influencing the structure and composition of ground-feeding bird flocks have not yet been analyzed. This study aimed to relate flock characteristics, including size, number, species richness, and composition, to local and landscape factors in the urban parks of Buenos Aires City, Argentina. Surveys of flocks were conducted in 16 parks during the breeding season, covering both mono-specific and mixed-species flocks. Flock numbers were positively correlated with tree, lawn, and bare ground cover but negatively associated with raptor presence in the parks. Flock species richness declined with increased noise and pedestrian traffic but rose in parks where raptors were present. The composition of species in flocks was linked to tree cover, noise, and the presence of raptors. While the Rock Dove (Columba livia) and the Rufous-bellied Thrush (Turdus rufiventris) were more abundant in parks with greater tree cover, the Eared Dove (Zenaida auriculata) and the Monk Parakeet (Myiopsitta monachus) showed increased abundance in more open parks. Zenaida auriculata and Columba livia experienced a decline in abundance in parks where raptors were present. Our findings indicate that resource availability and predation risk are crucial factors shaping flock formation in urban parks.

Types and spatial contexts of neighborhood greenery matter in associations with weight status in women across 28 U.S. communities

Towards an operational MODIS continuous field of percent tree cover algorithm: examples using AVHRR and MODIS data

Street-level neighborhood greenery linked to active transportation: A case study in Milwaukee and Green Bay, WI, USA

Effects of anthropogenic fire history on savanna vegetation in northeastern Namibia

Summary Large mammalian herbivores (LMH) exert strong effects on plants in tropical savannas, and many wild LMH populations are declining. However, predicting the impacts of these declines on vegetation structure remains challenging. Experiments suggest that tree cover can increase rapidly following LMH exclusion. Yet it is unclear whether these results scale up to predict ecosystem‐level impacts of LMH declines, which often alter fire regimes, trigger compensatory responses of other herbivores and accompany anthropogenic land‐use changes. Moreover, theory predicts that grazers and browsers should have opposing effects on tree cover, further complicating efforts to forecast the outcomes of community‐wide declines. We used the near‐extirpation of grazing and browsing LMH from Gorongosa National Park during the Mozambican Civil War (1977–1992) as a natural experiment to test whether megafaunal collapse increased tree cover. We classified herbaceous and tree cover in satellite images taken (a) at the onset of war in 1977 and (b) in 2012, two decades after hostilities ceased. Throughout the 3620‐km2 park, proportional tree cover increased by 34% (from 0.29 to 0.39) – an addition of 362 km2. Four of the park's five major habitat zones (including miombo woodland, Acacia–Combretum–palm savanna, and floodplain grassland) showed even greater increases in tree cover (51–134%), with an average increase of 94% in ecologically critical Rift Valley habitats. Only in the eastern Cheringoma Plateau, which had historically low wildlife densities, did tree cover decrease (by 5%). The most parsimonious explanation for these results is that reduced browsing pressure enhanced tree growth, survival and/or recruitment; we found no directional trends in rainfall or fire that could explain increased tree cover. Synthesis. Catastrophic large‐herbivore die‐offs in Mozambique's flagship national park were followed by 35 years of woodland expansion, most severely in areas where pre‐war wildlife biomass was greatest. These findings suggest that browsing release supersedes grazer–grass–fire feedbacks in governing ecosystem‐level tree cover, consistent with smaller‐scale experimental results, although the potentially complementary effect of CO2 fertilization cannot be definitively ruled out. Future work in Gorongosa will reveal whether recovering LMH populations reverse this trend, or alternatively whether woody encroachment hinders ongoing restoration efforts.

Optimal dates for assessing long-term changes in tree-cover in the semi-arid biomes of South Africa using MODIS NDVI time series (2001–2018)

The expansion of Juniperus occidentalis (western juniper) has been extensive in the last century, and increases in density and cover have been linked with the indirect effects of domestic livestock grazing (i.e. cessation of periodic fires, increases of nurse‐plant sites), and more favourable climatic conditions. In this study, we document changes in vegetation (including J. occidentalis) in central Oregon over a 23‐year period and relate these changes to their probable causes. In June 1995 we returned to the Horse Ridge Research Natural Area (HRRNA), a site that has a history of minimal anthropogenic impacts, to replicate a 1972 vegetation survey. Using the canopy‐intercept method, line intercept method, and aerial photography analysis to measure herbaceous cover, shrub cover and tree cover, respectively, we found significant changes had occurred in the 23‐year period between studies. Relative changes of tree, shrub, and perennial herbaceous cover were 59%, 7%, and – 38%, respectively. Relative increases in J. occidentalis density, as measured by the number of clumps and the number of stems, were 37% and 53%, respectively. Mean maximum height of J. occidentalis had increased by 10%. We examined the role of potentially confounding influences (e.g. fire, grazing, pathogens, climatic variability) and found that none of the traditional mechanisms implicated in J. occidentalis expansion adequately explained the observed changes. We suggest that the role of biological inertia of both anthropogenic and natural means may have had a profound effect on the J. occidentalis ecology of HRRNA.

Amenity trees and green space structure in urban settlements of Kigali, Rwanda

ABSTRACTMonitoring crop net primary productivity (NPP) and its proportion returned to soil in the form of carbon (C) input is vital to better understand the ecological responses to environmental and anthropogenic changes. However, quantification of NPP and C inputs from cropping systems at a regional scale is challenging due to the temporal and spatial variability of soils, climate, and management practices. The aim of this study was to estimate (i) the NPP from soybean crop [Glycine max (L.) Merr.] and (ii) the C inputs from soybean residues into soils of the Pampas and Extra-Pampas regions of Argentina between 1993 and 2005 using a simple approach based on the crop yield census records, a C budget equation, and crop-specific conversion factors at regional scale. Soybean NPP (t ha−1 year−1) at a regional scale was estimated by grain yields and harvested areas reported in the long-term (1993–2005) National database for several districts within each province. The mean annual soybean NPP in the Pampas was 0.3 t ha−1 higher (P < 0.05) than in the Extra-Pampas, resulting in a higher C input from soybean residues of 0.4 t ha−1 year−1 in the Pampas region. Due to improved cultivars and higher nutrient inputs in the Pampas region, the mean NPP and C inputs increased by about 25% from 1999 to 2005. Crop NPP and C inputs from residues into soils play a major role in C dynamics and should be considered for further studies at different scales to understand soil organic C modifications through agricultural changes.

Fire has historically played an important role in shaping the structure and composition of Sonoran semi-desert grassland vegetation. Yet, human use and land management activities have significantly altered arid grassland ecosystems over the last century, often producing novel fuel conditions. The variety of continuously updated satellite remote sensing systems provide opportunities for efficiently mapping combustible fine-fuels and fuel-types (e.g., grass, shrub, or tree cover) over large landscapes that are helpful for evaluating fire hazard and risk. For this study, we compared field ceptometer leaf area index (LAI) measurements to conventional means for estimating fine-fuel biomass on 20, 50 m × 20 m plots and 431, 0.5 m × 0.5 m quadrats on the Buenos Aires National Wildlife Refuge (BANWR) in southern Arizona. LAI explained 65% of the variance in fine-fuel biomass using simple linear regression. An additional 19% of variance was explained from Random Forest regression tree models that included herbaceous plant height and cover as predictors. Field biomass and vegetation measurements were used to map fine-fuel and vegetation cover (fuel-type) from plots on BANWR comparing outcomes from multi-date (peak green and dormant period) Worldview-3 (WV3) and Landsat Operational Land Imager (OLI) imagery. Fine-fuel biomass predicted from WV3 imagery combined with terrain information from a digital elevation model explained greater variance using regression tree models (65%) as compared to OLI models (58%). Vegetation indices developed using red-edge bands as well as modeled bare ground and herbaceous cover were important to improve WV3 biomass estimates. Land cover classification for 11 cover categories with high spatial resolution WV3 imagery showed 80% overall accuracy and highlighted areas dominated by non-native grasses with 87% user’s class accuracy. Mixed native and non-native grass and shrublands showed 59% accuracy and less common areas dominated by native grasses on plots showed low class accuracy (23%). Digital data layers from WV3 models showed a significantly positive relationship (r2 = 0.68, F = 119.2, p &lt; 0.001) between non-native grass cover (e.g., Eragrostis lehmanniana) and average fine-fuel biomass within refuge fire management units. Overall, both WV3 and OLI produced similar fine-fuel biomass estimates although WV3 showed better model performance and helped characterized fine-scale changes in fuel-type and continuity across the study area.

Climate-induced shifts in the composition and structure of alpine vegetation cover, both expansion and reduction, are altering alpine ecosystem functions. However, accurately quantifying variations over large-scale regions requires a detailed characterization of the fine-scale mosaic vegetation covers. In this study, we employed a regression-based unmixing model using synthetic data to develop a multi-temporal machine learning model aimed to estimate the fractions of alpine plant functional types (PFTs) from 1984 to 2024 in the Yarlung Zangbo River Basin (YZRB), China. The estimated cover fractions for tree cover, shrub cover and herbaceous cover had mean absolute errors of 10.36%, 14.06% and 13.38%, respectively. The variations in the fractions of each alpine PFT revealed a slight increase in tree cover and shrub cover, alongside a contraction in herbaceous cover. Specifically, tree cover and shrub cover expanded by +1.54% and +1.83% per decade, respectively, while herbaceous cover declined at a rate of 1.98% per decade. These variations were predominantly observed at higher elevations (4000–6000 m), on shaded aspects, and on lower slopes. The variations in these fractions are also positively correlated with air temperature and soil moisture in most regions. This study provides new insights into vegetation cover shifts in this ecologically sensitive region.

Characterizing the Response of Piñon-Juniper Woodlands to Mechanical Restoration Using High-Resolution Satellite Imagery

Reviewers Urban Forestry & Urban Greening, Vol. 7 (2008)