Addenda to the Special Issue: The Science and Practice of Managing Forests in Cities

In these addenda to our first special issue, The Science and Practice of Managing Forests in Cities, we present five new case studies documenting approaches to conserving, managing, and building an equitable workforce for Forested Natural Areas in cities across the U.S. These case studies were presented at the third annual gathering of the Forests in Cities network which took place in Seattle, Washington in November, 2022

The Science and Practice of Managing Forests in Cities: Introduction to the Special Issue

The following special issue includes a practitioner note that provides context about Forested Natural Areas in cities and introduces eight themes that are explored in the 25 practitioner case studies. This publication is the product of a fruitful workshop that brought together leaders in the field of Forested Natural Areas management. The case studies document both widespread approaches that are being used in cities across the U.S., as well as innovation that is taking place in individual cities. The goals of both the workshop and this publication are to raise national awareness of urban forested natural areas, improve their management, and contribute to a community of practice

Realizing the Potential of Urban Forests: Forests in Cities Workshop Themes and City Case Study Descriptions

Like all forests, forests in cities require resources, science, management, protection, and programming in order to achieve desired conditions. Yet, achieving the desired condition in an urban environment may require new approaches that account for the dynamic and complex nature of the urban setting. These decisions and actions are occurring at the city, park, or site scale. Unlike national parks, or wilderness areas that have a national or state budget, staffing structures, and regulations; forests in cities are regulated and managed primarily at the local municipal scale. This also makes the approaches to forest management planning and policy regulations tailored to individual city governance structures, despite many similar challenges arising at the national level. As part of our Forest in Cities Workshop, we partnered with 12 cities across the United States to create case studies around common themes related to achieving healthy forests as a part of sustainable and healthy cities. Our goal was to provide examples of work on the ground but also provide a lens upon which the work of individual cities could be contextualized as part of common themes and solutions that could be applied broadly. Below we describe the themes of the workshop and the case studies developed by the cities that are included in this special issue

Comparison of fundamental positive-sequence detectors for highly distorted and unbalanced systems

This paper presents a performance comparison between a PLL and an Adaptive Filter for detecting the positive sequence at the fundamental frequency of any given voltage or current signals of a three-phase system. The comparative analysis was based on the evaluation of a series of steady state performance parameters (phase and amplitude errors, THD and unbalance) and on the response time. The tests were made to study the behaviour of both approaches when working with highly distorted and unbalanced signals. This work was carried out using the computer simulation tool PSCAD/EMTDC.The authors are grateful to FCT (Fundação para a Ciência e a Tecnologia), project funding POCTI/ESE/41170/2001

Nitrogen forms affect root structure and water uptake in the hybrid poplar

The study analyses the effects of two different forms of nitrogen fertilisation (nitrate and ammonium) on root structure and water uptake of two hybrid poplar (Populus maximowiczii x P. balsamifera) clones in a field experiment. Water uptake was studied using sap flow gauges on individual proximal roots and coarse root structure was examined by excavating 18 whole-root systems. Finer roots were scanned and analyzed for architecture. Nitrogen forms did not affect coarse-root system development, but had a significant effect on fine-root development. Nitrate-treated trees presented higher fine:coarse root ratios and higher specific root lengths than control or ammonium treated trees. These allocation differences affected the water uptake capacity of the plants as reflected by the higher sapflow rate in the nitrate treatment. The diameter of proximal roots at the tree base predicted well the total root biomass and length. The diameter of smaller lateral roots also predicted the lateral root mass, length, surface area and the number of tips. The effect of nitrogen fertilisation on the fine root structure translated into an effect on the functioning of the fine roots forming a link between form (architecture) and function (water uptake)

Effects of CO 2 and nutrient availability on mineral weathering in controlled tree growth experiments

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94968/1/gbc911.pd

Does the age of fine root carbon indicate the age of fine roots in boreal forests?

To test the reliability of the radiocarbon method for determining root age, we analyzed fine roots (originating from the years 1985 to 1993) from ingrowth cores with known maximum root age (1 to 6 years old). For this purpose, three Scots pine (Pinus sylvestris L.) stands were selected from boreal forests in Finland. We analyzed root 14C age by the radiocarbon method and compared it with the above-mentioned known maximum fine root age. In general, ages determined by the two methods (root 14C age and ingrowth core root maximum age) were in agreement with each other for roots of small diameter (<0.5mm). By contrast, in most of the samples of fine roots of larger diameter (1.5-2mm), the 14C age of root samples of 1987-89 exceeded the ingrowth core root maximum age by 1-10 years. This shows that these roots had received a large amount of older stored carbon from unknown sources in addition to atmospheric CO2 directly from photosynthesis. We conclude that the 14C signature of fine roots, especially those of larger diameter, may not always be indicative of root age, and that further studies are needed concerning the extent of possible root uptake of older carbon and its residence time in roots. Keywords: fine root age, Pinus sylvestris, radiocarbon, root carbon, ingrowth cores, tree ringPeer reviewe

First assessment of the comparative toxicity of ivermectin and moxidectin in adult dung beetles: Sub-lethal symptoms and pre-lethal consequences

Among macrocyclic lactones (ML), ivermectin (IVM) and moxidectin (MOX) potentially affect all Ecdysozoan species, with dung beetles being particularly sensitive. The comparative effects of IVM and MOX on adult dung beetles were assessed for the first time to determine both the physiological sub-lethal symptoms and pre-lethal consequences. Inhibition of antennal response and ataxia were tested as two intuitive and ecologically relevant parameters by obtaining the lowest observed effect concentration (LOEC) values and interpolating other relevant toxicity thresholds derived from concentration-response curves (IC50, as the concentration of each ML where the antennal response is inhibited by half; and pLC50, as the quantity of ingested ML where partial paralysis was observed by half of treated individuals) from concentration-response curves. Both sub-lethal and pre-lethal symptoms obtained in this study coincided in that IVM was six times more toxic than MOX for adult dung beetles. Values of LOEC, IC50 and pLC50 obtained for IVM and MOX evaluated in an environmental context indicate that MOX, despite needing more time for its elimination in the faeces, would be half as harmful to dung beetles as IVM. This approach will be valuable to clarify the real impact of MLs on dung beetle health and to avoid the subsequent environmental consequences

Soil respiration in northern forests exposed to elevated atmospheric carbon dioxide and ozone

The aspen free-air CO 2 and O 3 enrichment (FACTS II–FACE) study in Rhinelander, Wisconsin, USA, is designed to understand the mechanisms by which young northern deciduous forest ecosystems respond to elevated atmospheric carbon dioxide (CO 2 ) and elevated tropospheric ozone (O 3 ) in a replicated, factorial, field experiment. Soil respiration is the second largest flux of carbon (C) in these ecosystems, and the objective of this study was to understand how soil respiration responded to the experimental treatments as these fast-growing stands of pure aspen and birch + aspen approached maximum leaf area. Rates of soil respiration were typically lowest in the elevated O 3 treatment. Elevated CO 2 significantly stimulated soil respiration (8–26%) compared to the control treatment in both community types over all three growing seasons. In years 6–7 of the experiment, the greatest rates of soil respiration occurred in the interaction treatment (CO 2  + O 3 ), and rates of soil respiration were 15–25% greater in this treatment than in the elevated CO 2 treatment, depending on year and community type. Two of the treatments, elevated CO 2 and elevated CO 2  + O 3 , were fumigated with 13 C-depleted CO 2 , and in these two treatments we used standard isotope mixing models to understand the proportions of new and old C in soil respiration. During the peak of the growing season, C fixed since the initiation of the experiment in 1998 (new C) accounted for 60–80% of total soil respiration. The isotope measurements independently confirmed that more new C was respired from the interaction treatment compared to the elevated CO 2 treatment. A period of low soil moisture late in the 2003 growing season resulted in soil respiration with an isotopic signature 4–6‰ enriched in 13 C compared to sample dates when the percentage soil moisture was higher. In 2004, an extended period of low soil moisture during August and early September, punctuated by a significant rainfall event, resulted in soil respiration that was temporarily 4–6‰ more depleted in 13 C. Up to 50% of the Earth’s forests will see elevated concentrations of both CO 2 and O 3 in the coming decades and these interacting atmospheric trace gases stimulated soil respiration in this study.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45867/1/442_2006_Article_381.pd

A dynamic leaf gas-exchange strategy is conserved in woody plants under changing ambient CO2: evidence from carbon isotope discrimination in paleo and CO2 enrichment studies

Rising atmospheric [CO2 ], ca , is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO2 ], ci , a constant drawdown in CO2 (ca - ci ), and a constant ci /ca . These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying ca . The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to ca . To assess leaf gas-exchange regulation strategies, we analyzed patterns in ci inferred from studies reporting C stable isotope ratios (δ(13) C) or photosynthetic discrimination (∆) in woody angiosperms and gymnosperms that grew across a range of ca spanning at least 100 ppm. Our results suggest that much of the ca -induced changes in ci /ca occurred across ca spanning 200 to 400 ppm. These patterns imply that ca - ci will eventually approach a constant level at high ca because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization towards any single strategy, particularly maintaining a constant ci . Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low ca , when additional water loss is small for each unit of C gain, and increasingly water-conservative at high ca , when photosystems are saturated and water loss is large for each unit C gain. This article is protected by copyright. All rights reserved.Rising atmospheric [CO2], c(a), is expected to affect stomatal regulation of leaf gas-exchange of woody plants, thus influencing energy fluxes as well as carbon (C), water, and nutrient cycling of forests. Researchers have proposed various strategies for stomatal regulation of leaf gas-exchange that include maintaining a constant leaf internal [CO2], c(i), a constant drawdown in CO2 (c(a)-c(i)), and a constant c(i)/c(a). These strategies can result in drastically different consequences for leaf gas-exchange. The accuracy of Earth systems models depends in part on assumptions about generalizable patterns in leaf gas-exchange responses to varying c(a). The concept of optimal stomatal behavior, exemplified by woody plants shifting along a continuum of these strategies, provides a unifying framework for understanding leaf gas-exchange responses to c(a). To assess leaf gas-exchange regulation strategies, we analyzed patterns in c(i) inferred from studies reporting C stable isotope ratios (C-13) or photosynthetic discrimination () in woody angiosperms and gymnosperms that grew across a range of c(a) spanning at least 100ppm. Our results suggest that much of the c(a)-induced changes in c(i)/c(a) occurred across c(a) spanning 200 to 400ppm. These patterns imply that c(a)-c(i) will eventually approach a constant level at high c(a) because assimilation rates will reach a maximum and stomatal conductance of each species should be constrained to some minimum level. These analyses are not consistent with canalization toward any single strategy, particularly maintaining a constant c(i). Rather, the results are consistent with the existence of a broadly conserved pattern of stomatal optimization in woody angiosperms and gymnosperms. This results in trees being profligate water users at low c(a), when additional water loss is small for each unit of C gain, and increasingly water-conservative at high c(a), when photosystems are saturated and water loss is large for each unit C gain