Effects of the COVID-19 pandemic on noise pollution in three protected areas in metropolitan Boston (USA).

Noise pollution can reduce the ability of urban protected areas to provide a refuge for people and habitat for wildlife. Amidst an unprecedented global pandemic, it is unknown if the changes in human activity have significantly impacted noise pollution in metropolitan parks. We tested the hypothesis that reduced human activity associated with the COVID-19 pandemic lockdowns would lead to reduced sound levels in protected areas compared with non-pandemic times. We measured sound levels in three urban protected areas in metropolitan Boston, MA (USA) at three time periods: in the fall and summer before the pandemic, immediately after the government-imposed lockdown in March 2020 when the trees were leafless, and during the beginning of reopening in early June 2020 when the trees had leaves. At all time periods, sound levels were highest near major roads and demonstrated a logarithmic decrease further from roads. At the two protected areas closest to the city center, sound levels averaged 1-3 dB lower during the time of the pandemic lockdown. In contrast, at the third protected area, which is transected by a major highway, sound levels were 4-6 dB higher during the time of the pandemic, likely because reduced traffic allowed vehicles to travel faster and create more noise. This study demonstrates that altered human levels of activity, in this case associated with the COVID-19 pandemic, can have major, and in some cases unexpected, effects on the levels of noise pollution in protected areas.

Leaf longevity in temperate evergreen species is related to phylogeny and leaf size.

Leaf longevity (LL), the amount of time a photosynthetically active leaf remains on a plant, is an important trait of evergreen species, affecting physiological ecology and ecosystem processes. A long LL gives leaves more time to fix carbon but carries higher construction costs, while a short LL allows plants to respond more rapidly to changing environmental conditions. For many evergreen taxa, LL data are not readily available, and it is not known if LL is phylogenetically conserved. To address this gap, we measured LL for 169 temperate and boreal evergreen woody species at the Arnold Arboretum, a botanical garden in Boston, Massachusetts, along with metrics of leaf size and number known to be related to LL. We hypothesized that LL is phylogenetically conserved, and that longer LL is associated with a greater numbers of leaves, smaller leaves, and a colder hardiness zone of the species' native range. We found that average LL ranged from 1.4 years in Rhododendron tomentosum to 10.5 years in Abies cilicia. LL was phylogenetically conserved, with some genera, such as Abies and Picea, exhibiting long LL (> 3 years) and others, such as Ilex and Rhododendron, exhibiting short LL (< 3 years). Leaf length was negatively correlated with LL in conifers, due to differences between Pinus and other genera; however, there was no correlation between LL and number of leaves. This study highlights the considerable variation and phylogenetic pattern in LL among temperate evergreen species, which has implications for carbon budgets and ecosystem models.

Humidity does not appear to trigger leaf out in woody plants.

In order to anticipate the ecological impacts of climate change and model changes to forests, it is important to understand the factors controlling spring leaf out. Leaf out phenology in woody trees and shrubs is generally considered to be strongly controlled by a combination of spring warming, winter chilling requirement, and photoperiod. However, researchers have recently suggested that temperature-related air humidity, rather than temperature itself, might be the main trigger of the spring leaf-out of woody plants. Here, we sought to examine the relationship between air humidity and leaf-out across a range of humidities and plant functional groups. We did not find any consistent, measurable effect of high humidity advancing leaf-out in the 15 woody shrubs and trees examined in this study, and we did not see progressive patterns of earlier leaf-out in successively higher humidities. Our results indicate that more work must be done on this topic before researchers can properly determine the effect of humidity on the leafing out process for woody species.

Citizen scientists and university students monitor noise pollution in cities and protected areas with smartphones.

Noise pollution can cause increased stress, cognitive impairment and illness in humans and decreased fitness and altered behavior in wildlife. Maps of noise pollution are used to visualize the distribution of noise across a landscape. These maps are typically created by taking a relatively small number of sound measurements or simulated on the basis of theoretical models. However, smartphones with inexpensive sound measuring apps can be used to monitor noise and create dense maps of real-world noise measurements. Public concern with noise can make monitoring noise pollution with smartphones an engaging and educational citizen science activity. We demonstrate a method utilizing single-day citizen science noise mapping events and a university lab to collect noise data in urban environments and protected areas. Using this approach, we collected hundreds of noise measurements with participants that we used to create noise maps. We found this method was successful in engaging volunteers and students and producing usable noise data. The described methodology has potential applications for biological research, citizen science engagement, and teaching.

Low-cost observations and experiments return a high value in plant phenology research.

Plant ecologists in the Anthropocene are tasked with documenting, interpreting, and predicting how plants respond to environmental change. Phenology, the timing of seasonal biological events including leaf-out, flowering, fruiting, and leaf senescence, is among the most visible and oft-recorded facets of plant ecology. Climate-driven shifts in plant phenology can alter reproductive success, interspecific competition, and trophic interactions. Low-cost phenology research, including observational records and experimental manipulations, is fundamental to our understanding of both the mechanisms and effects of phenological change in plant populations, species, and communities. Traditions of local-scale botanical phenology observations and data leveraged from written records and natural history collections provide the historical context for recent observations of changing phenologies. New technology facilitates expanding the spatial, taxonomic, and human interest in this research by combining contemporary field observations by researchers and open access community science (e.g., USA National Phenology Network) and available climate data. Established experimental techniques, such as twig cutting and common garden experiments, are low-cost methods for studying the mechanisms and drivers of plant phenology, enabling researchers to observe phenological responses under novel environmental conditions. We discuss the strengths, limitations, potential hidden costs (i.e., volunteer and student labor), and promise of each of these methods for addressing emerging questions in plant phenology research. Applied thoughtfully, economically, and creatively, many low-cost approaches offer novel opportunities to fill gaps in our geographic, taxonomic, and mechanistic understanding of plant phenology worldwide.