Projecto Sobreiro: Seeding more ‘balotas’ in the São Jacinto dune reserve

Yesterday my two companions and I went for a big walk through the São Jacinto dune reserve. With us we carried two big bags full with balotas (acorns), which we seeded at the moister and shaded areas in the woods of the reserve. 2015 is the fourth year in which acorns are seeded there by us. This activity is undertaken to increase diversity of the woods, to reduce the chance of forest fires and to help fight invasive acacia species (see some earlier posts about this subject). Thankfully, now the wardens of the reserve also see the point of this and already seeded a large amount of acorns there earlier this fall. Very nice!




Over time this little oak will outgrow the acacia and attract a lot more wildlife.




Not all of the young oaks survive. Again, this summer a number of them died due to the scorching temperatures and draught that occur on the peninsula during summer. Most of the oaks that grow there now are English oaks (Quercus robur). Cork oaks (Q. suber) have also been seeded during the past four years, but this species appears to have more difficulties surviving its first years. I suspect that over time the oaks themselves will create better growing conditions for both types by changing the soil structure and chemistry, and by preserving moist.




At least three of the oldest English oaks in the reserve that have been planted there in the past, produced acorns this year (one more than last year). Although there were not many yet, the acorns that have been seeded thus far will certainly speed up the process. We’ll have to be patient, but in some decades from now the São Jacinto dune reserve can host the largest mixed forest of the Aveiro region, which once was dominated by oak (instead of monotomous Eucalyptus plantations…)!

The São Jacinto dune reserve: Projecto Sobreiro update (fall 2014)

One-year old Cork oak Quercus suber seedling.

Around this time last year I posted a blog entry about my idea to fight invasive Acacia Acacia longifolia in the forested parts of the São Jacinto dune reserve by sowing acorns, in particular those from Quercus suber (the Cork oak; Sobreiro in Portuguese) and Quercus robur (the Pedunculate oak) (http://www.timvannus.blogspot.nl/2013/09/projecto-sobreiro-planting-some-seeds.html). Besides these oaks (as well as some other species of native deciduous trees) would reduce chances for invasive acacia to grow in the reserve, there were several other reasons for this activity:

• The presence of oaks will increase the diversity of the reserve considerably.
• These oaks will reduce the chances of (large) forest fires to occur.
• More variation in tree species in the reserve would make it a lot more attractive to the public.

This blog entry gives an update on “Projecto Sobreiro", which is supposed to do just that, and provides some recommendations for future years.

Last winter hundreds of additional acorns were planted in the reserve. Many of these had no problem germinating, which resulted in many new seedlings. The summer of 2014 was also relatively moist, so most of this new generation of seedlings survived the hottest months fairly well.

The reserve's own acorns 
Before I started sowing acorns there in 2012, there were already about 15 - 20 oaks of various species growing in the reserve. These were all planted as young trees of a few years old. The oldest tree currently is probably around 20 years and about 5 meters in height. An employee of the reserve complained to me that it takes very long before these trees would reach a maturity. That’s true, on the reserve's sandy soil oaks can be expected to develop much slower than elsewhere, so this project takes time. Many of these trees will not grow up straight with a single trunk, but due to the low amount of nutrients they'll branch out lower to the ground, developing into more of a bushy shape (which is normal for oaks growing on sand dunes).
I figured it would take quite some time until the first trees would produce their first acorns. Unexpectedly, this year two of these oaks produced acorns themselves! This event coincides with what seems to be a mast year for oaks in the surrounding region.

Acorns on presumably a Pyrenean oak Quercus pyrenaica (or a hybrid?) in the São Jacinto dune reserve. Note the undeveloped and empty cupule in the back.

These two trees produced a total of only about 10 – 15 acorns. It seemed that a number of seeds never developed properly, as there were numerous empty cupules visible. These apparently never contained acorns, possibly because these never had been pollinated(?). I suspect this happened due to the lack of other flowering oaks or oak pollen in or around the park (even though oaks can pollenite themselves). The nearest oaks grow about five kilometers away from the reserve.

Besides the two species of oaks (Q. suber and Q. robur), as in 2012, last winter I also planted seeds of another native deciduous tree species: the Sweet chestnut Castanea sativa. There currently are at least 10 of these growing in the reserve. Most of these are doing well, especially around the more moist parts of the reserve.

A one-year old Sweet chestnut Castanea sativa seedling in the São Jacinto dune reserve.

Drawback
Unfortunately, there’s not only good news. I noticed that some seedlings disappeared or got stepped on, presumably by people that were clearing acacia near the trails. Around the duck pond, the area that I considered relatively save from the influence of human activity, the situation was worse. There numerous seedlings were either trampled upon or these had disappeared under piles of acacia cuttings that had been dumped there by students that cleared the trails around the pond (even though these had been informed about the presence of precious seedlings...).

Two-year old Quercus suber seedling after being stepped upon, even though it was marked with a stick.

Two-year old Castanea sativa seedling, saved from underneath a pile of acacia cuttings.

Currently the large majority of seedlings grow along the main trails of the reserve. Some time ago an employee of the reserve told me it would be better to sow them further away from the trails. The reason for me not to do this (yet) has been the following. After having visited the reserve for a few years I noticed that acacia gets cleared over larger areas in different ways. Until last year a company got paid to do this with the use of some very heavy machinery that would have destroyed any oak seedling in the area.

Last year I noticed that a number of private individuals were allowed to enter the reserve with chainsaws to cut whole patches of acacia for firewood. They were supposed to leave native flora intact. I was rather shocked to see the result of this. Not only was there the constant sound of multiple chainsaws over a large area in the reserve, each individual burned a fire to get rid of the smaller cuttings, as well as some garbage it seemed (at inspection the ashes contained the remains of several plastic bottles, bags and other waste). Besides this it was rather predictable that their activity would open the layer of leaf litter and would create new possibilities for acacia seeds to germinate.

A forest patch after it was cleared from acacia by private people. Not a single oak seedling would have survived here.

As expected, the following summer in the same area acacia seedlings are thriving.

Additionally, I heard that some people were allowed to enter the reserve to collect pine needles, presumably to be put in stables to suit the needs of livestock. Some oak seedlings apparently were destroyed by them in the process. The head of the reserve believes that the São Jacinto dune reserve (the only fully protected nature reserve in the whole region of Aveiro!) is there for the people. Now what people are we talking about here?

Development of the Cork oaks
I also got informed that there are some concerns about whether the Cork oaks would eventually reach reasonable height. The few that have been previously planted there thus far remained small, giving the impression of a bonsai tree. Therefore it would not be of any use continuing sowing Cork oak acorns (and this project should change its name into "Projecto Carvalho"?).

Demonstration “bonsai” Cork oak

However, I still believe that the Cork oak is of importance to the reserve. There are several reasons why the older ones thus far remained small. One of these would be the availability of nutrients. Oaks that were planted in sandy soil of which the layer of leaf litter is absent or consists primarily of moss or pine needles (which take a very long time to decompose) will have a hard time finding enough nutrients. Oaks growing in areas containing even a thin layer of leaf litter have better access to nutrients that have infiltrated in the soil.

Furthermore the amount of sunlight and drought influences the rate in which these trees grow. Another thing that counts is the amount of cover around these trees (competition for light). When planted out in the open the oaks have no need to grow up high in search for light. The bonsai shown above grows almost in full sunlight on bare dune sand with no existing leaf litter layer (just moss that dries up in summer) and no competitors around. Probably not the best place.

The circa 6 year old Cork oak shown below demonstrates that it is indeed possible for them to grow up normally. This tree grows on a very dry artificial sandy dune wall. I must admit that the key to its rapid success is the fact that it gets watered occasionally during summer with water from the duck pond. This water contains small particles of mud (containing also some organic matter) that infiltrate into the soil easily, providing nutrients and keeping the soil relatively moist. Besides this the tree grows up in the cover of other plants, forcing it to grow up in height.

Circa 6 year old Cork oak, watered.

With this I am not saying that all oaks should be watered during summer, but that the cork oaks will grow faster at locations with a decomposing layer of (deciduous) leaf litter, out of the sun and amongst other trees that will stimulate upward growth. I suspect that even amidst acacia stands these would grow, when the layer of leaves is not too thick for seedlings to develop.

I suspect that, when canopy cover and a leaf litter layer develops (and nutrients subsequently infiltrate), even the ‘bonsai’s’ growing elsewhere in the reserve over time will grow up to become normal mature trees.

Re-open the open dune reserve!
As mentioned before there is more to see in the São Jacinto dune reserve than just trees and I’m not aiming to turn the whole reserve into oak woodland. It is regarded an open dune reserve and much of its natural values still occur in the open areas. After the fire that took place there in 1995, the acacia also rapidly took over parts of the open dune habitat. Although in the past much of it has been removed, currently efforts to eradicate acacia focus primarily on areas around the most popular trails in the forested parts of the reserve. Obviously, this is done not only to keep the trails accessible and leave something for the public to see, but also to give them the idea that the acacia is being kept under control.

Unfortunately, during recent years little or no effort has been put into eradicating acacia from the open dune areas anymore. At the same time there seems to be another problem arising there. The pine trees that were once planted (they’re just as naturally occurring there as the oaks) are expanding rapidly. Together with the acacia they are now covering large areas of what once were largely open dunes.

Besides acacia, the open dune areas have rapidly become overgrown with pine trees, both purposely planted (left) as well as by natural regeneration (right). A loss of flora and fauna characteristic for the dune reserve.

The aerial photo below (partly taken in 2011 and 2012) gives the impression that the São Jacinto dune reserve is still a largely open dune reserve. Closer inspection of this photo and visits to the reserve reveal that in the open dune areas Pine trees have been planted on a large scale. At the same time natural regeneration occurred and those young pine trees are now covering large areas that were previously open. Why it was recently decided to start new Pine plantation remains unknown to me. The reserve does not produce timber for the market and 'protection' of the dunes from wind erosion is at those locations not applicable. These pine trees are of little value to the reserve's wildlife. Underneath them there is nothing more than a thick layer of very slowly decomposing pine needles, leaving no place for any other native plants. This leads to not only loss of flora, but also of other wildlife, like lizards, insects and birds that are characteristic for the dune habitat.

This aerial photo gives the illusion of the São Jacinto dune reserve is still containing open dune habitat. Closer inspection reveals that most of the open areas are currently overgrown with either Spruce trees or acacia (source: Google Earth).

Recommendations

• Stop the reckless clearing of whole patches of acacia and do not allow private people to start clearing acacia for firewood the way that is currently taking place. This does more harm to the reserve than it does any good.
• Continue to clear acacia around the main trails by hand, but be aware of the oak seedlings growing there. In the future these will function as a buffer for the acacia.
• As long as the present oaks do not produce significant numbers of acorns themselves, continue to sow oaks in the forested parts of the reserve wherever this seems possible. Aim for a mixed forest of pine and oak.
• For diversity, add other tree species that are native to the area such as Sweet chestnut Castanea sativa, Prunus avium and Tilia sp.. Concentrate these around the moist parts of the reserve.
• Re-open parts of the overgrown dunes as soon as possible. The São Jacinto dune reserve should not become primarily a closed forest and should certainly not contain large areas of monotonous pine plantations. Locally, allow clear-cuttings, but leave some individual trees as well as groups, scattered over the open dune areas. Avoid cutting trees in the birds' breeding season (February - September).

“Projecto Sobreiro”: planting some seeds in the São Jacinto dune reserve

Cork oak Quercus suber sapling in the São Jacinto dune reserve

Reserva Natural das Dunas de São Jacinto (the São Jacinto dune reserve) is a 666 ha dry and sandy dune reserve, located on the long peninsula along the north-central coast of Portugal, in between the Atlantic Ocean and the northern part of the Ria de Aveiro (a large intertidal lagoon). It is one of the 30 areas which are officially under protection in the country (a Natura 2000 area, I believe). In the early 20th century, Acacia longifolia, a fast growing invasive leguminous tree originating from Australia, was introduced in order to contain the sandy soil and protect the peninsula from the ocean. After its introduction it formed extensive stands, particularly enhanced by fire events. The most recent fire took place during the summer of 1995, in which about 200 ha of the reserve burned down to the ground. During the years following this fire, A. longifolia completely took over the burned areas and beyond, resulting in a dense monotonous Acacia jungle and some mixed stands, covering around 350 ha. Before this fire took place São Jacinto contained a mosaic of sparse native vegetation including herbs and few shrubs and Pine tree Pinus pinaster(?) plantations. The understory of these plantations included a few scattered individuals of A. longifolia (according to Silva & Merchante, in Moreira et al. 2012).

A. longifolia jungle

Seven years after the fire a study was conducted aiming to evaluate the impacts of the A. longifolia invasion and several techniques for eradication have been implied until now. These have cost a lot of money and none of these appeared to have been successful. A. longifolia continues to be dominating the São Jacinto dune reserve. Eradication of A. longifolia, the most abundant of six invasive species that grow in the area, has been pointed out as being complex and it requires persistence and patience (and a lot of money that could have been used for other matters) (http://www.publico.pt/sociedade/noticia/reserva-natural-das-dunas-de-sao-jacinto-combate-crescimento-descontrolado-de-acacias-83352). I want to present a partial solution here: plant oak seeds.

Silva & Merchante noted introduction (sown or transplanted) of desirable species to accelerate recovery, as this has successfully been implied in some restoration projects (Hartman & McCarthy 2004). Development of A. longifolia requires sunlight, so it doesn’t develop well under a shady forest canopy. At least that’s the idea. Transplanting of saplings would in this case, according to Silva & Merchante, probably be most successful as these will have a height advantage over the invasive seedlings (Galatowitsch and Richardson 2005). Thus far at the reserve, saplings of primarily the Pine trees have been introduced and only few saplings of other (deciduous) species were planted, including a few oaks.

During the last two years I have visited the São Jacinto dune reserve regularly and have noticed the rapid development of A. longifolia. I also noticed that there is no place in the reserve where these Pine trees give enough shade preventing A. longifolia seeds from germinating (and there is a very extensive seed bank of A. longifolia present throughout the reserve). Pine trees may form dense stands when they’re young, but at some point, as their roots don’t go very deep into the soil, storm damage will create large gaps in the canopy, allowing A. longifolia to germinate. Oaks (and other deciduous trees) will root deeper and I am expecting storm damage to be not so much of an issue. This allows for a more closed forest canopy, preventing future germination of A. longifolia much more successfully.

Open Pine tree canopy allowing regeneration of A. longifolia

In the winter of 2012/2013 I collected a few hundred seeds elsewhere in the region of two species of oaks: Quercus suber (the Cork oak; Sobreiro in Portuguese) and Quercus robur (the Pedunculate oak). I planted these at two main locations in the reserve, where their development could easily be monitored and young trees will (hopefully) not easily get destroyed during the clearing of A. longifolia. At a recent inspection I was surprised by the results: probably well over 80% of the seeds had germinated, was alive and in good condition (now who would have guessed that, after such a dry summer!?). A number of saplings that were present, however, were dead. It was obvious that the lack of shade was the cause of this. Surprisingly, even the seeds that were planted amidst dens stands of A. longifolia had germinated and these appeared to be in good condition. I suspect that in the future, regardless of the dense cover of A. longifolia, most of these will grow and eventually develop into mature trees. A. longifolia does not grow very tall at this location and storm damage eventually creates enough open space and light for the oaks to further develop their crown. At least that is what I suspect will happen.

Quercus robur, one of the survivors

Quercus suber, sowed in full sunlight

Why oaks? Oaks do not naturally occur in the São Jacinto dune reserve!?

So what! Neither do the Pine trees. Both species of oaks are native to the region of Portugal and I suspect that due to the relatively isolated location of the peninsula, oak seeds have not managed to find their way to the relatively young reserve yet. Oak seeds can disperse up to several kilometers, especially when these are picked up by Jays Garrulus glandarius or Red squirrels Sciurus vulgaris and buried by them for winter supply. However, considering the distance of the reserve from the nearest oak (largely due to the popularity of extensive monospecific Eucalyptus plantations in the surrounding regions, allowing barely any other native deciduous tree species to grow in the region (there’s barely a single native deciduous forest remaining!)) natural arrival is not to be expected in the near future. Besides these oaks, several other deciduous tree species could be introduced that are native to the region, i.e. Castanea sativa, Fraxinus angustifolia and Tilia spp. (and possibly also another oak species; Quercus faginea (Portuguese oak)?). The oaks however, in particular the Cork oak, will probably come with the most advantages.

In my opinion there are numerous advantages to gain when introducing these species in the São Jacinto dune reserve by seeding them. To summarize:

• Oaks will over time (yes, it will take quite some time, I realize!) provide a more closed canopy, preventing A. longifolia to develop and also killing its long lasting seed bank. This will eventually be a lot cheaper than the manual eradication of this species.
• Introduction of oaks and other deciduous trees will increase chances for wildlife dramatically, as the current diversity of the wooded parts of the reserve are limited (primarily existing of Pine trees, about one native shrub that rarely produces berries due to the drought, and invasive Acacia).
• The presence of deciduous trees, in particular Quercus suber, will decrease chances of forest fires to occur and to spread (and knowing the Portuguese a little you can be sure that fires will continue to occur there in the future!).
• In summer, deciduous trees provide more shade, which will make a walk through the São Jacinto dune reserve a very pleasurable experience for visitors, especially on those ridiculously hot days, as I have experienced there regularly. Additionally, with an increase in wildlife diversity these woods would become a much more exciting place to be.
• Seeding is, compared to planting saplings, a much easier, more effective and cheaper way of introducing these species than planting saplings, as has been done up till now.

There is however one thing that I must point out: the São Jacinto reserve is a DUNE reserve and not a forest. Especially the open dune areas contain unique vegetation and I must therefore make clear that my idea is certainly not to turn the whole reserve into primarily closed woodland!

I therefore want to make the following recommendations for future management of the park:

• Decide what parts of the reserve are designated open dune areas and what parts can be turned in closed broad-leaved or mixed woodland. Of course, in the management of a natural forest it’s never good to create such strong boundaries. Concentrate eradication activities of A. longifolia in and around the more open dune areas and in a few locations inside the woodland areas (but these must be surrounded by oaks).
• Collect and plant as much oak seeds as possible annually from nearby areas, up to the point where the first saplings in the reserve are old enough to produce seeds themselves. Plant the seeds in shaded and partly shaded locations. Crawl through the A. longifolia jungle to plant them if necessary. The few oaks that are currently there are between 2 and 9 years old, I believe, and will start to produce a ‘workable’ number of seeds in about 10 - 15 years from now (a very rough estimation). From then on Jays will do the rest of the work for you.
• Stop the introduction of Pine tree saplings. The Pine trees regenerate successfully by themselves, but have proven to be unsuccessful in the battle against A. longifolia. Pine trees have some advantages (i.e. wood production) and these will probably manage to remain present in the wooded areas. Eventually a mixed broad-leaved forest will develop; interesting for humans as well as for wildlife.
• Sow a high density of oaks in a 50 – 100 meter wide boundary around the park as soon as possible. This will prevent, or at least reduce, the speed in which future fires will spread into the reserve. This boundary will also work as a buffer for A. longifolia seeds from around the reserve to enter. A. longifolia seeds do not disperse very far, usually up to several meters at the most.
• Try out some other native deciduous tree and shrub species that could grow in the wooded parts of the reserve, species that would survive the bare sandy soil and the drought. Try to grow them from seeds straight in the soil, not from saplings. Don’t go crazy over it, try to keep the reserve natural, but keep in mind that for a visitor a single Castanheira can be just as exciting as one hundred Pine trees.

Good luck!

Quercus suber, along the blue trail.

Catry FX, Rego F, Moreira F, Fernandes PM, Pausas, JG (2010). Post-fire tree mortality in mixed forests of central Portugal. Forest Ecology and Management 206, 1184-1192. (see: http://www.uv.es/jgpausas/papers/Catry-2010-FEM_Postfire-tree-mortality-Portugal.pdf )

Fidalgo, B., R. Salas, J. Gaspar and P. Morais (2009). Assessing biodiversity at landscape level starting from forest inventory data (see: http://skog.for.msu.edu/meeting/proc2/Fidalgo_Salas_Gaspar_Morais.pdf )

Galatowitsch, S.M., Richardson, D.M., 2005. Riparian scrub recovery after clearing of invasive alien trees in headwater streams of the Western Cape. Biological Conservation 122: 509 – 521

Hartman, K. M. and B. C. McCarthy. 2004. Restoration of a forest understory after the removal of an invasive shrub, Amur Honeysuckle (Lonicera maackii). Restoration Ecol 12: 154 – 165.

Marchante H, Marchante E, Freitas H (2003) Invasion of the Portuguese dune ecosystems by the exotic species Acacia longifolia (Andrews) Willd.: effects at the community level. In: Child LE, Brock JH, Brundu G et al (eds) Plant invasions: Ecological threats and management solutions. Backhuys, Leiden, pp 75 – 85

Marchante H, Marchante E, Buscardo E, Maia J, Freitas H (2004) Recovery potential of dune ecosystems invaded by an exotic Acacia species (Acacia longifolia). Weed Technol 18: 1427 – 1433

Moreira, F., Arianoutsou, M., Corona, P., De lasHeras, J., (Eds.) 2012. Post-fire management and restoration of European forests. Managing Forest Ecosystems, Vol. 24, Springer, Dordrecht (see: http://books.google.pt/books?id=GXWYBvfIP8sC&pg=PA243&lpg=PA243&dq=sao+jacinto+fire&source=bl&ots=4mNKFlQYjx&sig=NBascBFhVRKGyDFdeZP_SbEqeZg&hl=en&sa=X&ei=u20zUuqKDaKr7Ab_uIH4DQ&ved=0CHwQ6AEwCQ#v=onepage&q=sao%20jacinto%20fire&f=false)