Tag Archives: ecosystems

Sowing density effects and patterns of colonization

That’s plant colonization, in case you were wondering what kind of colonization I am talking about. This study has a fairly simple premise – that in restoration you can sow the seeds that have the most trouble establishing at the highest densities, and seeds of plants that germinate and spread easily at lower densities, or even not at all.

Sowing density effects and patterns of colonization in a prairie restoration

A cost-effective approach in plant restorations could be to increase sowing density for species known to be challenging to establish, while reducing sowing density for species that easily colonize on their own. Sowing need not occur evenly across the site for rapidly dispersing species. We explored these issues using a prairie restoration experiment on a high-school campus with three treatments: plots sown only to grasses (G plots), to grasses and forbs (GF1), and to grasses and forbs with forbs sown at twice the density (GF2). In year 2, GF1 and GF2 plots had higher diversity than G plots, as expected, but GF2 treatments did not have twice the sown forb cover. However, high forb sowing density increased forb richness, probably by reducing stochastic factors in establishment. Cover of nonsown species was highest in G plots and lowest in GF2 plots, suggesting suppressive effects of native forbs on weedy species. Colonization of G plots by two sown forbs (Coreopsis tinctoria and Rudbeckia hirta) was apparent after 2.5 years, providing evidence that these species are self-sustaining. Colonization was greater in edges than in the central areas of G plots. Through construction of establishment kernels, we infer that the mean establishment distance was shorter for R. hirta (6.7 m) compared to C. tinctoria (21.1 m). Our results lead us to advocate for restoration practices that consider not only seed sowing but also subsequent dispersal of sown species. Furthermore, we conclude that restoration research is particularly amenable for outdoor education and university-high school collaborations.

tipping points and ecosystem collapse

This research presents seagrass meadows as an example of an ecosystem that seems to disappear suddenly, but actually reached a tipping point caused by chronic pollution.

Testing for thresholds of ecosystem collapse in seagrass meadows?

Ecological systems can be dynamic and unpredictable, with shifts from one ecosystem state to another often considered ‘surprising’. This unpredictability is often thought to be due to ecological thresholds, where small cumulative increases in an environmental stressor drives a much greater consequence than would be predicted from linear effects, suggesting an unforeseen tipping point is crossed. In coastal waters, broad-scale seagrass loss often occurs as a sudden event which is associated with human-driven nutrient enrichment (eutrophication). We tested whether the response of seagrass ecosystems to coastal nutrient enrichment represents a threshold effect. Seagrass response did follow a threshold pattern when nutrient enrichment (dissolved inorganic nitrogen) exceeded moderate levels, with a switch from positive to negative net leaf production. Epiphyte load also increased with nutrient enrichment, potentially driving this shift. Inadvertently crossing such thresholds, as can occur through ineffective management of land-derived inputs such as wastewater and stormwater on urbanised coasts, may help account for the widely observed ‘sudden’ loss of seagrass meadows. By identifying tipping points we may not only improve monitoring for adaptive management that seeks to avoid threshold effects, but also the restoration of systems that have crossed them.

cheetahs: going…going…gone?

In today’s depressing conservation news, cheetahs are in serious trouble.

Led by Zoological Society of London (ZSL), Panthera and Wildlife Conservation Society (WCS), the study reveals that just 7,100 cheetahs remain globally, representing the best available estimate for the species to date. Furthermore, the cheetah has been driven out of 91% of its historic range. Asiatic cheetah populations have been hit hardest, with fewer than 50 individuals remaining in one isolated pocket of Iran…

To make matters worse, as one of the world’s most wide-ranging carnivores, 77% of the cheetah’s habitat falls outside of protected areas. Unrestricted by boundaries, the species’ wide-ranging movements weaken law enforcement protection and greatly amplify its vulnerability to human pressures. Indeed, largely due to pressures on wildlife and their habitat outside of protected areas, Zimbabwe’s cheetah population has plummeted from 1,200 to a maximum of 170 animals in just 16 years – representing an astonishing loss of 85% of the country’s cheetahs.

Scientists are now calling for an urgent paradigm shift in cheetah conservation, towards landscape-level efforts that transcend national borders and are coordinated by existing regional conservation strategies for the species. A holistic conservation approach, which incentivises protection of cheetahs by local communities and trans-national governments, alongside sustainable human-wildlife coexistence is paramount to the survival of the species.

So it’s habitat loss and the relentless expansion of the human footprint, again. Are Africans just particularly callous toward the loss of the natural world? No, Africa is just one of the last places a lot of the large, charismatic animals are left. We had them elsewhere, but we have long forgotten them. Solutions exist. But I am in a pessimistic mood right now so I don’t think this time will be different, the declines and collapses will just continue to come faster and be more obvious until maybe some things will be done, but most likely they will be too little, too late. Too little, too late, but better than nothing. How is that for a silver lining?

 

clean water is not enough

This article presents evidence for the expected trend in biodiversity of riparian areas (whether lake, river, stream, etc. I can’t tell from the abstract) in response to urbanization. Large water features might be the one piece of the landscape that urban development has trouble erasing. But by changing the nature of the shoreline and adjacent habitat, you would expect a degradation in ecosystem quality, even if the water quality itself is perfectly fine (which it often is not, of course). The question is, could you design a shoreline and adjacent city that would support a significant fraction of the biodiversity and ecosystem function that was once there? In other words, a smaller nature that is still healthy? Or should we write off the idea of a high-functioning urban ecosystem and focus on protecting more wild areas? Well, I don’t know but I can guarantee that not making a serious attempt at either one will not lead to a good outcome.

Decadal declines in bird abundance and diversity in urban riparian zones, Landscape and Urban Planning, Volume 159, March 2017, Pages 48–61

Urbanization is frequently cited as a major driver of species losses worldwide; however, most studies in urban areas use a space-for-time substitution approach to document effects of urbanization through time. Ultimately, understanding the effects of urbanization on biodiversity requires long-term datasets. We examined long-term changes in bird assemblages at 12 riparian sites in the greater Phoenix metropolitan area and nearby Sonoran Desert region, featuring a range of human modifications and levels of water flow. Riparian areas in arid cities represent a key habitat type that is sensitive to human modification and supports high levels of species diversity. We used long-term data to: (1) explore variation in bird communities as a function of water permanence and degree of human-modification; (2) identify which environmental variables best describe differences found across riparian site types; and (3) assess how riparian bird communities, abundance, and species richness have changed through time. Engineered riparian sites supported more broadly distributed generalists; whereas, natural riparian sites supported more specialists. Sites with perennial flows had more vegetation and water compared to ephemeral sites and engineered sites had more impervious surface compared to natural sites. In nearly all comparisons, bird species richness, diversity, and abundance declined across riparian types during the period of study, even for common species. Bird communities in natural settings have changed more than communities at engineered sites. Overall, the riparian bird community is shifting toward urban dwelling, resident species that are characteristic of riparian sites with less water and more impervious surface.

drought in the U.S. SOUTHeast

We are hearing a lot about drought in the U.S. Southwest. It is severe and a big deal. The climate situation may not be as severe in the Southeast, and yet the consequences may be severe because the population is unprepared and the development and forest management practices are putting people in harm’s way.

Although wildfires may draw more attention in the western U.S., the Southeast is no stranger to them. The U.S. Geological Survey and the Federal Emergency Management Agency mapped wildfire frequency from 1994 to 2013 and showed that while most hot spots are across large swaths of the West, there are a few key hazardous areas in the Southern Appalachians and parts of Alabama and Georgia. To researchers such as Costanza, another devastating wildfire in the Southeast was a long time coming. “But seeing pictures of Gatlinburg — that is scary, and anything like that is surprising,” she said…

Wildfires present such danger in the region partly because a significant amount of the population — more than in any other region — lives in wildland-urban interfaces, where development meets natural areas. Asheville, North Carolina, and Atlanta are among the cities near forests, national and state parks and other public lands and have been under high alert during this season’s fires. Officials are monitoring how close the fires come to city limits. About 80 million people live in the Southeast, according to 2015 estimates from the U.S. Census Bureau. And urban sprawl is expected to increase dramatically in the region, potentially putting people even closer to forested areas…

If more droughts and a population that continues to come into contact with wild areas are in the region’s future, funding for prevention steps such as creating healthier ecosystems, promoting community preparedness and fire education, and managing prescribed burns is crucial, experts said. Although scientists and climatologists don’t yet know whether this season of fires represents the start of a long-term pattern, conditions suggest that the Southeast might start seeing more intense fires like the one in Gatlinburg — and if so, the region will have to adapt.

“artificial rainforest” in Dubai

I continue to think that places like Dubai and Singapore with extremely inhospitable climates are preparing humanity for its future in space. They are creating cities that consist of climate-controlled high rise apartments, office buildings, malls, and indoor parks, all connected by subway lines, so there is really no reason to go outside. It’s not too hard to imagine transferring one of these cities to Mars.

30% of African elephants gone in 7 years

A project called The Great Elephant Census has this shocking statistic.

Continent-wide survey reveals massive decline in African savannah elephants

African elephants (Loxodonta africana) are imperiled by poaching and habitat loss. Despite global attention to the plight of elephants, their population sizes and trends are uncertain or unknown over much of Africa. To conserve this iconic species, conservationists need timely, accurate data on elephant populations. Here, we report the results of the Great Elephant Census (GEC), the first continent-wide, standardized survey of African savannah elephants. We also provide the first quantitative model of elephant population trends across Africa. We estimated a population of 352,271 savannah elephants on study sites in 18 countries, representing approximately 93% of all savannah elephants in those countries. Elephant populations in survey areas with historical data decreased by an estimated 144,000 from 2007 to 2014, and populations are currently shrinking by 8% per year continent-wide, primarily due to poaching. Though 84% of elephants occurred in protected areas, many protected areas had carcass ratios that indicated high levels of elephant mortality. Results of the GEC show the necessity of action to end the African elephants’ downward trajectory by preventing poaching and protecting habitat.

It’s heartbreaking for at least two reasons. The obvious one is the elephants themselves because they are such a charismatic, iconic species. The African savannah ecosystem more broadly is iconic and its loss is also deeply disturbing. This is an example of a problem that probably almost everyone can understand and agree on, and yet our species is not solving it. It’s hard to have hope that we can solve the more complex and controversial problems if we can’t solve this one. It’s going to be a sad day when we realize the wild elephants are gone, possibly a sort of psychological tipping point for our civilization’s relationship with nature.

global human footprint mapping

This article in Nature Communications is about detailed global mapping of human impacts on the Earth’s ecosystems.

Sixteen years of change in the global terrestrial human footprint and implications for biodiversity conservation

Human pressures on the environment are changing spatially and temporally, with profound implications for the planet’s biodiversity and human economies. Here we use recently available data on infrastructure, land cover and human access into natural areas to construct a globally standardized measure of the cumulative human footprint on the terrestrial environment at 1 km2 resolution from 1993 to 2009. We note that while the human population has increased by 23% and the world economy has grown 153%, the human footprint has increased by just 9%. Still, 75% the planet’s land surface is experiencing measurable human pressures. Moreover, pressures are perversely intense, widespread and rapidly intensifying in places with high biodiversity. Encouragingly, we discover decreases in environmental pressures in the wealthiest countries and those with strong control of corruption. Clearly the human footprint on Earth is changing, yet there are still opportunities for conservation gains.