Preadaptation leads to foreign conquest

“While most people have a negative view of spontaneous urban plants, they are actually performing many of the same ecological functions that native species perform in nonurban areas. ..absorbing excess nutrients that accumulate in wetlands; reducing heat buildup in heavily paved areas; controlling erosion along rivers and streams; mitigating soil, water, and air pollution; providing food and habitat for wildlife; and converting the carbon dioxide produced by the burning of fossil fuels into biomass.

The typical urban plant is well adapted to soils that are relatively fertile, dry, unshaded, and alkaline. Through a twist of evolutionary fate, many of these species have evolved life-history traits in their native habitats that are ‘pre-adapted’ them to flourish in cities.

Marble or brick buildings, for example, are analogous to naturally occurring limestone cliffs. Similarly, the increased use of deicing salts along walkways and highways has resulted in the development of high-pH microhabitats that are often colonized by either grassland species adapted to limestone soils or salt-loving plants from coastal habitats. Finally, the hotter, drier conditions one finds in cities favor species that come from exposed, sunny habitats in nature.

Preadaptation is a useful idea for understanding the emergent ecology of cities because it helps to explain that some plants and not others grow on piles of construction rubble, chain-link fence lines, highway median strips, pavement cracks, and compacted turf.

While most biologists view invasive plants as a serious biological problem, the fact remains that their initial introduction and distribution were usually the result of deliberate decisions that reflected the economic, ornamental, or conservation values of the day. Between the 1930s and the 1960s, various federal, state, and local agencies encouraged— and often subsidized— the cultivation of plants such as kudzu, multiflora rose, and autumn olive for erosion control and wildlife habitat purposes. It should come as no surprise that they became major problems forty years later, after millions of them had been planted. Indeed, the spread of nonnative species across the landscape is as much a cultural as a biological phenomenon, a fact often overlooked by advocates of strict ecological restoration.”  

--Peter Del Tredici

Bring Conservation Home

“The St. Louis Audubon Society envisions an ever-growing mosaic of native plant and animal landscapes across the St. Louis region, including even the smallest urban yard.  

Our Bring Conservation Home Program provides on-site assistance to small, private landowners in the greater St. Louis area for the restoration of native plant and animal habitat on their grounds. The Bring Conservation Home Program will offer advice in landscaping with environmentally healthy and sustainable native plant species, the removal of invasive plant species such as bush honeysuckle, water conservation on the urban landscape, and other stewardship practices that promote healthy habitat for birds, native wildlife and people.”

For more information visit http://www.stlouisaudubon.org/conservation/BCH/index.php

Yay Atlanta!!

In May 2018, the City of Atlanta launched its first urban ecology study. This effort will evaluate and inventory the City’s natural environs, including rivers and creeks, forest and tree canopy, ridges and watersheds, public and private green spaces, and other features that encompass and define the City’s existing landscape. The Urban Ecology Framework will identify what natural features are unique to the City of Atlanta, how ecosystems or habitats can be restored, and which policies promote development aligned with those features and systems. This inventory will be used to define a better future condition for the natural environment, including high-level recommendations about future green spaces, green connections, and green policies. This work represents the implementation of the Atlanta City Design value Nature, which aims to improve and accentuate Atlanta’s authentic character in a way that can accommodate a much larger population.

The Urban Ecology Framework (UEF) is being led by the Department of City Planning with involvement and cross-collaboration from other City Departments, such as Departments of Watershed Management and Parks and Recreation, as well as Partner organizations like Trees Atlanta and Park Pride. The consultant team, led by Biohabitats, Inc, is facilitating an ecological assessment to be followed by an evaluation of the Tree Preservation Ordinance (TPO).

Diversity increases ecosystem stability

Freiburg’s forestry scientists prove that forests that are more diverse are also more productive and more resilient

Freiburg, Sep 05, 2019

Forests with a large variety of species are more productive and stable under stress than monocultures: scientists from the University of Freiburg have confirmed this with data from the world’s oldest field trial on the diversity of tropical tree species. The team around PhD student Florian Schnabel has published its results in the journal Global Change Biology.

As the researchers state, there is increasing scientific evidence of positive relationships between the diversity of tree species and ecosystem functioning. However most studies on this relationship to date have used either data from forests where the influence of biodiversity cannot be separated from other factors, or from young planted experiments, which do not provide data on longer periods of time. Therefore, the Freiburg research team analyzed data from the Sardinilla experiment which was planted in Panama in 2001. This experiment covers 22 plots planted with one, two, three or five native tree species. Since these grow at different rates, the plots with a greater variety of species also have a greater structural diversity with regard to the height and diameter of the trees. Annual data on the size and height of the trees, which are seen as indicators of the productivity and stability of the ecosystem, come from the period 2006 to 2016.

The study concludes that mixtures of two and three tree species have on average a 25 to 30 per cent higher productivity than monocultures, and those with five species even 50 percent higher. The differences during a severe dry period caused by the tropical climate phenomenon El Niño were especially pronounced. This indicates that forests with a greater diversity of tree species are not only more productive, but also more stable and resilient under drought stress – the researchers believe this is a particularly important finding in view of global climate change. In the context of initiatives that aim to reduce atmospheric CO2 with extensive reforestation, these results indicate that to store the same amount of CO2 in biomass, far less space is needed with mixed-species forests.

According to the team, these results offer new insights into the dynamics of tropical plantation forests and emphasize the importance of analyses that cover a longer development period, since they contribute to a better understanding of the connections between the diversity, productivity and stability of ecosystems. The study is based on Florian Schnabel’s master thesis, for which he will be receiving the Hansjürg-Steinlin prize, a University of Freiburg award for new talent, in October at the start of the 2019/20 academic year. Florian Schnabel is now a PhD student involved in the TreeDì project at the German Centre for Integrative Biodiversity Research (iDiv) in Leipzig.

Plant recruitment in urban landscapes

Piana et al write in Frontiers in Ecology and the Environment (Aug 2019) that multiple drivers affect plant recruitment in the urban environment. From their analysis of available research--climate, biotic invasion, pollution, land cover change, and human activity all play pivotal roles. Their article is available at https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/fee.2098