Lichen Growth and Cities: A Study on Long Island, New York

The detrimental influence of New York City on the Long Island lichen flora extends as a "city effect" up to 40 miles from the center of industrial Brooklyn. The results of transplant experiments with Parmelia caperata, transect studies of corticolous lichens in red-oak stands, and distribution analyses of various Long Island lichen species all lead to the same general conclusions. City-induced drought is regarded as acting on pollution-tolerant lichens close to a city center with air pollution acting over much greater distances in decreasing lichen diversity and cover. It is immediately apparent to any observer of the Long Island lichen vegetation that one of the most obvious and far-reaching influences on the distribution of lichens is the proximity of New York City. Considering that the city itself (including Brooklyn and Queens as well as Manhattan, Staten Island, and the Bronx) has a population of well over eight million people and that it is heavily industrialized as well, this influence is not surprising. The growth of a city can have a detrimental influence on lichen populations in two ways: direct and indirect (Barkman 1961). The former involves the large-scale removal of available substrates on which lichens grow, i.e., by draining swamps, deforestation, and replacing soil with concrete and asphalt. It is the less conspicious indirect influence, the local and long-distance effects of city-induced atmospheric changes, which warrants discussion in greater detail. Lichenologists have known of the "city effect"-i.e., the detrimental influence of cities on lichen growth for almost a century, and within the past 30 years, detailed studies of some of the major European cities have appeared. Barkman (1958) and Skye (1958) have presented excellent reviews of the work up to 1958. Since then additional contributions to this field have been made by Beschel (1958) working in and around Innsbruck, Brightman (1959) studying an area near London, Fenton (1960, 1964) working around Belfast, Migdefrau (1960) studying in Munich, LeBlanc (1961) studying around Montreal, and Gilbert (1965) studying the Newcastle area. In general, previous workers, studying only corticolous lichens, mapped the presence of various species around the town or factory in question by marking the boundaries of lichen tolerances (sometimes also indicating the limits at which the species are normally developed) (Beschel 1958). Most studies differentiate between presence 1 This paper is part of a thesis submitted to the Department of Botany and Plant Pathology, Michigan State University, in partial fulfillment of the requirements for the Ph.D degree. 2 National Museum of Canada, Ottawa, Ontario. This content downloaded from 157.55. 39.141 on Sun, 11 Dec 2016 04:53:41 UTC All use subject to http://about.jstor. org/terms 428 THE BRYOLOGIST [Volume 69 at base and breast height, and almost all present a summary listing the species encountered in order of their tolerance. Certain basic trends, as one approaches a town, were observed by almost all the workers: 1. Fruticose lichens are the first to disappear, followed by foliose, then smooth-crustose, and finally leprose-crustose lichens. Thus, leprose lichens are apparently most tolerant of cities. 2. There are definite geographic gradients along which lichens disappear; some are steeper than others, depending on the size and extent of industrialization in the cities or towns involved. 3. The closer to a city, the poorer the condition of the lichens and the less surface area they cover. 4. The so-called "nitrophilous" lichens (on neutral or alkaline and often highly nitrogenous substrates) are by far the most citytolerant. 5. As one approaches a city, there is a gradual restriction of lichens to tree bases, parks, and bodies of water. 6. The disappearance of lichens and the appearance of industrialization are highly correlated, the effects being greatest where fuel consumption and population size are greatest. 7. A decrease in atmospheric humidity and an increase in atmospheric pollution can be detected towards the center of a town or industrial center. LICHEN STUDIES ON LONG ISLAND On Long Island, three approaches were taken in the study of the city effect: 1) a transect study of lichens in red-oak stands along the north shore at varying distances from the city, 2) the partial reconstruction of past distributions of some common lichens for comparison with their present distributions, and 3) transplant experiments with corticolous lichens. 1. Transect Studies. The methods used in the transect study will be published in detail (Brodo 1966), but a general description of the work is given here. Twelve red-oak forest stands were studied along the north shore in a generally east-west direction from central New