Invasive non-native trees can cause structural and functional changes in plant communities, but how do their impact change over time? Michele de Sá Dechoum and colleagues explore this in their latest research on a coastal ecosystems in southern Brazil.

We learn, since growing up, that we should plant trees. There is no doubt that trees have very important environmental and social roles, especially in the current context of the climate crisis we now face. But such benefits may be compromised depending on the tree species and the areas where they are planted.

Some non-native trees can generate high-magnitude negative impacts in natural areas. Pine species introduced from the northern hemisphere negatively impact native plants and animals, change cultural landscapes, reduce the availability of resources such as water and food, and may also impact human wellbeing.

When this happens, eliminating such trees (defined as invasive alien species) reduces impacts on native plants and helps restore the functions of natural systems. These findings were part of the main results obtained from our study conducted in a coastal scrub ecosystem in the Dunas da Lagoa da Conceição Municipal Park, in Florianópolis (southern Brazil).

In our study, we show that, over time, native plants that are adapted to direct sunlight were gradually replaced by other plants adapted to shade in the areas invaded by pines. Small plants that require direct sunlight practically disappear as pines grow and produce shade, completely changing the composition of native flora and the landscape.

We also show that eliminating pines is not enough to ensure that native species are able to grow back – least not in the short term. A consequence of pine invasion is reduced plant diversity even after pine control efforts take place when compared with areas that were never invaded. Therefore, planting or sowing native herbs, shrubs and trees can help increase the diversity of native plants such as aroeira-brava (Lithraea brasiliensis) and caúna (Ilex dumosa).

Behind the research

The study was conducted to assess the results of an invasive pine control program in place since 2010 led by The Horus Institute for Environmental Conservation and Development and the Invasion Biology, Management and Conservation Lab of the Federal University in Santa Catarina state, Brazil.

Volunteers in the program gather once a month to cut down or pull out pines. To date, nearly 400,000 pines have been eliminated, sparing the city some USD 40,000 in expenses. Had the work not started in 2010, modelling projections estimated that about 1/3 of the park, which covers 700 hectares, would be dominated by pines by 2028.

Pine trees were introduced in Florianópolis in 1963 for commercial forestry, then locally disseminated in the 1970s. After that, pines were also planted for ornamental purposes or shade, as well as for dune stabilization in private properties around the municipal park where the study took place. These trees planted long ago are most likely the seed sources that caused the invasion in the park as pine seeds are adapted to wind dispersal and can be carried for dozens or, more seldom, hundreds of meters from the source.

The good news is that the invasive plant control program is thriving on our coastal areas. With support from the European Outdoor Conservation Association (EOCA), our work has been extended to new areas to restore coastal ecosystems and create opportunities to discuss issues on climate change and biological invasions with local communities.

It is important that residents understand the role and the relevance of coastal ecosystems as protection barriers against extreme weather events. New partnerships are being established with associations, residents, and the municipality in order to plant and sow native species in areas of high biological and cultural importance to society.

Read the full research: “Effects of time since invasion and control actions on a coastal ecosystem invaded by non-native pine trees” in Issue 3:1 of Ecological Solutions and Evidence.