San Carlos de Bariloche, Argentinia. The road to the airport is flanked by massive pine trees, blocking the view on the surrounding dry Patagonian steppe. They seem to flourish in this environment, although they are far from home. The new environment does not seem to stop them from growing tall and strong, and –most importantly – producing large amounts of seeds.
Those huge pinecones might have given it away, but pine plantations of every species can produce an enormous mass of seeds that dramatically accelerates the invasion process.
Pine seedling, the beginning of invasion
The impact of this seed rain is obvious as soon as one steps through the first row of planted trees. All through the Patagonian steppe, a mosaic of big, small and smaller pine trees is developping, turning the open steppe landscape into a conifer forest. The correlation with the planted seed source is obvious, with many and tall trees close to the roadside, from where they gradually decline in number and size over the next ten to hundreds of meters.
Pines invading the Patagonian steppe
This potential for spread outside the plantations and the massive impact of conifers on the native open steppe vegetation has sparked the attention of ecologists. Although many conifer species were introduced in South-America in the 19th century or earlier, the true large-scale introductions by means of commercial plantations only started throughout the 20th century. This makes conifer invasion a fairly recent phenomenon in South-America.
Invasion front, where pines are far from each other and limited in size.
This last fact might be an important key towards the management of the invasion. The introduction of conifers to South-America lags behind to several other important cases of pine invasion elsewhere on the Southern Hemisphere, like New Zealand, South Africa and Australia. With current conservation measures fairly weak in South America, it is really important to learn lessons from the successes and failures concerning past introductions elsewhere.
Experimental removal of pines to investigate regeneration of the natural vegetation.
Current investigations focus on the impact of these rapid changes on native ecosystems all over South-America. Changes in fire frequencies in the steppe, diversity losses in plants and animals, it all occurs in the shade of the spreading pines. Other important questions involve the abilities of the original vegetation to regrow after removal of the pines. More recently, we raised the question how this ongoing invasion might facilitate – or limit – invasion of other nonnative plant species. On that I surely hope to report in the future.
Pine invasion might replace the beautiful planes of the Patagonian steppe.
We will certainly hear more from these South-American pines, as they will more and more define the landscape all over the continent as they do in so many places all over the world.
Examples of literature:
Langdon B, Pauchard A, Aguayo M (2010). Pinus contorta invasion in the Chilean Patagonia: local patterns in a global context. Biological Invasions 12:3961-3971.
Simberloff D, Nunez MA, Ledgard NJ, Pauchard A, Richardson DM, Sarasola M, Van Wilgen BW, Zalba SM, Zenni RD, Bustamante R, Pena E, Ziller SR (2009). Spread and impact of introduced conifers in South America: lessons from other southern hemisphere regions. Austral Ecology doi:10.1111/j.1442-9993.2009.02058.x
So pines are real survivors but will their growth be slow on the Steppes. We plan to remove some of ours for firewood when grown up a bit but also we are watching the pine processionary moth get closer. It doesn’t bother seem interested in the umbrella pines which grow and are planted 50 miles south of us on more sandy soils.
I don’t think their growth will necessary be slow on the Steppes. I think the good thing in open landscape is that there is not much competition with other plants, so those pines that are growing there can use all the nutrients and water. Of course, that only works if there is enough water for the trees and if there are no humans cutting them down :).
So could be good source of fuel and help save the Steppes?
That sounds like good reasoning to me :)!
I guess I don’t understand or sympathize with the concern here. If the development of a pine forest ecosystem would crowd out and completely destroy native vegetation that might be a concern. However, if the pine trees simply become an ADDITION to native plants that could very well be a positive development.
Ponderosa pine (pinus ponderosa) can adapt itself to rather dry environments where they can help check erosion among other things. Also, fuel was mentioned for native inhabitants along with the possibility of a future lumber supply.
There are many semi-arid areas in the American Southwest that are similar to Argentina where these kinds of forests can do well.
Fred M. Cain,
Indiana
Thanks for your comment! I agree that there is plenty of benefits of pine trees, and every case study of invasive species, one should balance out the pro’s and con’s (and be ready to change that balance as new information occurs).
The invasion by pine trees in the Southern Hemisphere has however been shown to have high impacts on native diversity, as in: it would not be an addition to native plants, but fully replace them. They grow so well that they create dense forests of intertangled branches where one cannot even walk through, and where nothing grows underneath. This is a serious impact on a landscape that by its very nature is an open grassland. In addition, these pines have been shown to have several ecological and economical negative side effects. They increase fire risks, for example, and have been shown to consume far more wather in dry regions than the native regions, significantly drying out the soil.
It is thus a multi-faceted problem, with many down- ànd upsides, yet experiences in other countries like South Africa and New Zealand have convinced ecologists that management of these invasions is important.
Herr Lembrecht,
I still tend to lean in the direction that the addition of pines in some areas would have more benefits that downsides *BUT* it’s obvious that you have studied this more extensively than I so I want to take your comments seriously.
By the way, where did the railway crossing sign come from in the photos in the sideba
By the way, where did the railway crossing sign come from in the photos in the sideba