There are number of known and well-publicised issues with the use of monoculture Eucalyptus plantations across Galicia and other regions of Spain.
As someone that lives in Galicia I can only speak on behalf of what I've seen here - but I can imagine the same issues persist regardless of where exactly in Spain you are living - if you happen to be surrounded by lots of Eucalyptus too.
Loss of Biodiversity and Important Wildlife Habitats
Eucalyptus are largely existing in monoculture plantations - so they only consist of one species of tree. This type of factory farming, where hundreds of trees are grown in a close proximity, having been planted using very precise, expensive and large marchinery, has devastating affects on the local biodiversity.
Native forests on the other hand - which Galicia largely had, if we go back a few hundred years, support a wide variety of plant and animal species.
What happens to the valuable natural wildlife which made use of these native woodlands prior to them being cut down and replaced with this monoculture plantation? As you can imagine, they had to leave and try to find habitat elsewhere.
Why do you think Galicia is struggling with an influx of wild boar, turning up in our towns and cities, much to the dismay of the locals? Maybe if they had some native woodland to roam there would be less need for them to venture towards our streets, which is not something that would come naturally to them.
When eucalyptus plantations grow in such dense, crowded spaces, they drown out the light that would have reached the woodland floor and thus prevent the native flowers and plants from flourishing. Most plantations only contain Gorse and Brambles - which although being better than nothing, is far from ideal - they often prevent anything else from thriving.
Water Resource Depletion
Eucalyptus trees are thirsty plants - they have very high water requirements. Because of their quick-growing nature, and their dense root systems, they deplete soils of any moisture and lower surrounding water tables. At a time when water usage around the world is under more scrutiny, and will need to be carefully managed (even in rainy Galicia), we shouldn't forget the impact of eucalyptus.
Degradation of the Soil
One of the worst factors here is the nutrient depletion that occurs from the planting of eucalyptus - because of their fast growth rates, they consume a lot of goodness from the soil. And because they are rapidly harvested, and then almost instantly re-planted, the soil has no time at all to recover. We are in essence removing all of the goodness from the soil, just to allow a few owners to make money selling the timer for wood and pulp production.
Soil erosion also becomes a factor here as the trees aren't as good at preventing soil erosion, especially due to the leaf litter being less effective when compared to native trees. This issue is more apparent on slopes where eucalyptus plantations often exist - and will result in more erosion.
High Risk of Fire
Being a tree with such high oil content, these plantations are an extreme fire risk. With the number of forest fires in Galicia on the rise, and only likely to get worse as we see dryer and hotter summers as a result of climate change, we have to ask about the risk they have of impacting both the lives of wildlife and of humans.
When a eucalyptus tree catches fire it rapidly spreads to the surrounding trees, and when these trees are planted so densely across such broad areas it would be no surprise to hear of the huge damage that takes place in these forests from fires.
Invasive Species - and Risks of Spreading
Walking through any eucalyptus plantations you'll probably notice many escapees - trees that are growing outside of the plantation, and have self-seeded.
This is because eucalyptus can easily spread from their seeds, and will happily displace other important native species, with the result of impacting local ecosystems which can lead to further biodiversity loss.
Land Access Issues
When land is owned by corporations, or even individuals, and is used for huge eucalyptus plantations as often is the case, that land then becomes redundant - people can't access it, and it's as such "dead space".
Imagine if this was native woodland, where many important species could roam freely - and people could potentially access it too - as opposed to the private, protective nature of these plantations.
Previously this land might had a traditional use from natives, including traditional, low-impact agricultural and land uses. Imagine if these plantations were to revert to being used to grow crops to be consumed by local people, with small-scale or regenerative agriculture being practised?
The Use of Chemicals - Pesticides, Herbicides & Fertilisers
When you repeatedly grow a resource-intensive crop like Eucalyptus on the same patch of land year-after-year, it's inevitable that fertilisers need to be applied to the land to help with growth - but only because of the destructive practises of growing this species of tree.
Outside of the use of fertilisers (which require a lot of energy to create, and have huge associated carbon emissions, as well as negative impact on the local habitat), pesticides and herbicides are often applied either to control pests or weeds. And all to grow more timber that can be shipped out to far-flung lands like China, to be used as paper or pulp.
Issues with Carbon Sequestration and Climate Change
A positive about eucalyptus is that because they're fast growing, they can sequester carbon relatively quickly - but that is only if the trees are left to remain in the ground. Instead, they are harvested every 10-15 years, so the carbon gets released back into the atmosphere fairly quickly.
Compared to native woodlands and forests, carbon isn't sequestered over a long period of time. So these short-sighted plantations don't really work to prevent the impacts of climate change - simply because they're not kept in the ground long enough.
Impact from Machinery and the Harvesting of Eucalyptus
If you've ever seen eucalyptus trees being harvested you'll be surprised - usually there is just one or two people, operating a huge, very technologically advanced machine, which cuts the trees as well as splitting the timber, removing the bark, and just about anything else that is needed.
There's little to no human involvement - so very few people are employed in the harvest. So the economical benefits are tiny in comparison. The people who benefit from the plantations are the 1 or 2 people employed at the point of harvest (every 10 years or so), the owner of the land, and the companies that benefit from the buying and selling of the end products - the pre-processed timber and then the paper/pulp.
If you look around after the harvest has been completed, the entire woodland floor is decimated. Tracks are muddied up, soil is left heavily compacted from the use of the machinery, and it looks like a bomb has been dropped. And then there's the access to-and-from the site, often down quiet lanes that require access from tractors and other big machinery. There's a lasting visible and ecological impact of the harvesting of the trees which is clear for all to see.
Eucalyptus Monoculture Plantations Are Bad - So What's the Solution?
I understand that despite the above, there will be a need for eucalyptus plantations somewhere in Spain. I'm not proposing we just shift the problem elsewhere, to another region of Spain or a different country, to let them deal with the ecological issues we've discussed.
I think there are ways in which we can incorporate some Eucalyptus plantations, whilst not ignoring their heavy environmental impact.
1 - A Stronger Mixture of Native Trees Mixed in Existing Plantations
It's not natural to have a plantation of thousands of one species of tree, precisely planted in neat and tidy rows in a patch of land. So instead of having these ongoing plantations, why not mix this up with native trees - oak, hazle, beech, chestnut, silver birch, alder and willow - to name just a few.
Oak trees have been shown to be more protective when forest fires break out, which as mentioned is a huge risk of these plantations.
By having a healthier mix of trees - or designated "native" woodlands area that help to break up eucalyptus plantations, there's going to be more native wildlife which will help boost biodiversity.
2 - Restrictions on the Number of Eucalyptus Planted, and Harvesting Rates
If we could impose a limit on the number of trees that can be planted per area, and also to require that they stay in the ground for a minimum period of time, with a specified "cooling-off" period, this would have a big positive impact on the local environment.
By giving time for the land to recover inbetween harvesting a crop, we could request that the land is then turned over to native woodland for a set period of time, instead of the continual growing of eucalyptus which is shown to leach out any soil nutrients and water.
3 - Investment in Eco-Tourism and Agro-Tourism Initiatives
People who farm or grow eucalyptus are likely doing it for the money it gives - although this isn't a very profitable business, it's better than leaving the land bare (at least for them, financially).
What if the Galician government was instead to pay land owners to rewild it and to encourage native species to flourish? Whilst we understand this might be a bit idlyic, similar initiatives have been implemented in the UK and elsewhere, with the government encouraging farmers to sow wildflower meadows by paying them in essence "not to farm".
An alternative idea here would be to invest in eco-tourism initiatives or in agro-tourism. Imagine if native woodlands could be restored at scale across Galicia, and native species could be welcomed again - wolves, bears, lynx and bison.
By providing natural habitat for these animals, many people would be sure to flock to Galicia to try and spot one of these rare creatures - which is where eco and agro tourism could flourish.
This could become a great way to grow the local economy in a sustainable and eco-friendly way.