Blog text by Petri Nummi, Eeva-Maria Suontakanen, Sari Holopainen and Veli-Matti Väänänen “Beavers facilitate Teals at different scales” is now available on the Ibis website.
In a remote country lived a rich mire species community. But that was once upon a time, when Finland was a land of mires. Nowadays, only fragmented pieces are left in the southern region, while large natural mires can still be found in Lapland. Nevertheless, only one third of historical levels remain. Most mireswere dried due to farming and forestry. Ditches were dug to gather water from ca. 6 million hectares of mires. This affected the hydrology and further the ecology of these wet ecosystems. Several plant and animal species are adapted to mires, and have thus suffered from habitat loss and fragmentation. For example, forest grouse and bean geese (Anser fabalis) utilize mires during their breeding period. Due to ditching, mires stop producing their ecosystem services, because berry production and game bird populations (these are cultural and provisioning ecosystem services), decrease, and thus the recreational values of the areas lessen.
Finland has about 10 million hectares of dried mires, more than half of which have been utilized by forestry. However, about a fifth of this area does not produce wood well enough for it to be profitable. After several centuries of mire destruction, a change is now in the air. Finnish mires are being restored with increasing effort. For example, in 2017 Metsähallitus (the Park and Forest Service) began an EU-funded project called Hydrology LIFE. The project aims to safeguard not just mires, but also small water bodies and important bird lakes in 103 Natura 2000 areas. The project restores and protects mires.
Hydrology is the most important issue to consider when restoring a mire. Blocking ditches leads to changes in water balance, and eventually to active peat formation, which is basically the definition of a mire. After the ditches are blocked, water levels normally rise rapidly to correspond with the natural situation. However, actual peatland processes return at a much slower speed. Forest vegetation is slowly replaced by mire vegetation, starting from the ditches. The processes take a long time, so whether or not the original mire ecosystem returns is yet to be seen. It is also possible that we are actually just creating new mire types.
Helping forest grouse
Peatland-forest ecotones are key environments for forest grouse, but unfortunately these areas are becoming very rare. The willow ptarmigan (Lagopus lagopus) has suffered from mire fragmentation in Finland. Ptarmigan habitats are fragmented especially in Southern Finland, and thus there are small populations living far from each other. Luckily, local people are usually interested in peatland restoration that helps species such as the willow ptarmigan. Several good examples exist of how ptarmigans have accepted restored peatlands. The Finnish Association for Nature Conservation has a project “SuoMaa”, which began in 2016, and targets protecting and restoring taiga nature. One of the aims is to restore peatlands to support and enlarge a ptarmigan breeding peatland network and create connections between strong and threatened populations.
A few decades ago the whoopers swan (Cygnus cygnus) was an endangered and rare species in Finland. It only bred in remote lakes and people rarely saw them. The population increase of whooper swans after protection is one of the success stories in Finnish nature conservation. Nowadays the swans can be heard gaggling all around Finland. The whooper swan is a large bird, and it thus consumes a lot of vegetation. Water horsetail (Equisetum fluviatile) is one of its favourites.
Certain other species also prefer water horsetails. For example, wigeon (Mareca penelope) broods forage within the horsetail growths searching for emerging invertebrates. A study published earlier this year showed that the water horsetail is disappearing from Finnish and Swedish lakes. The reasons for this pattern are unknown, but one possible explanation could be increased grazing pressure. Whooper swans effectively utilize horsetails, and swan grazing was therefore suspected to be influencing the disappearance of the horsetail. Wigeon populations have concurrently shown a worrying decrease.
A recently published study conducted of 60 Finnish and Swedish lakes utilized vegetation and waterbird data gathered in the early 1990s and in 2016. The study area widely covers the boreal, reaching from southern Sweden to Finnish Lapland. The whooper swan population increased strongly during the study period. Researchers studied whether whooper swans’ grazing on water horsetail is causing the negative trend in the wigeon population. Pair counts were used to indicate waterbird communities, and thus any changes caused during the brood time were not shown.
The study showed that whooper swans strongly preferred lakes with horsetails during the 1990s, but this connections is not seen anymore. While the number of swan-occupied lakes has increased, the number of horsetail lakes has decreased dramatically. However, it appears that swans and disappearing horsetails do not associate, because the horsetail has also been from lakes where swans don’t occur. The horsetail has increased in some swan-occupied lakes.
The number of lakes used by wigeon has decreased, but swans are apparently not causing this. Wigeon loss has not been stronger on lakes occupied by swans. Quite the opposite, as wigeons and swans appear to positively correlate. Even though wigeons prefer horsetail lakes, their disappearance is not associated with the horsetail loss occurring in the study lakes, which suggests that wigeons can also utilize other lake types. On the other hand, the researchers note that this study did not considered the critical brood time, when the foraging opportunities among the horsetail growths are especially important. Thus it may still be possible that wigeons are affected by horsetail loss, but this effect only appears during the brood time.
Many geese populations in Fennoscandia are increasing rapidly, and geese have become more visible in human-inhabited landscapes. Currently geese utilize agricultural lands and even urban lawns. High geese brood densities have a significant impact on their environments due to increasing grazing pressure.
Geese broods prefer pastures near shores
A newly published Swedish study revealed that greylag geese broods are rather picky when selecting farmland fields for grazing. The most used fields were pasturelands near water. Goslings preferred shorter vegetation, assumingly due to its higher quality and the open landscape views in case of predators. Grazing geese also keep the vegetation short.
Broods tend to prefer grazing areas near shores, from where they can easily reach the safety of water when threatened. Grazing geese broods are suggested to pose a fairly small risk of agricultural conflicts due to their preference for near-shore pastures (instead of crop fields for example). However, extremely high grazing pressure by geese can reduce plant biomass, thus affecting livestock grazing. In arctic areas, such as Greenland and Svalbard, geese grazing is observed to be the reason for decreased hay and decreased seed counts in soil.
In contrast to broods that prefer near-shore areas, non-breeding geese can cause conflicts with agriculture, due to their grazing in crop fields. Non-breeding birds that are able to fly can utilize areas further from water, and according to a Swedish study, they also graze also on crop and vegetable fields in addition to pastures. Large flocks preferred typically open and flat with no or few trees or shrubs.
The two differing patterns shown by broods and adults means that geese managers should consider the two behavioural strategies when planning geese management.
City geese have found Helsinki’s shore lawns
The barnacle goose is a fairly new species in Helsinki. The species tends to breed in remote arctic areas, but after geese were released from the local zoo in the late 1980s, geese began breeding on the islands and islets of the Helsinki archipelago. The released geese are assumed to have returned to breed, and brought their offspring and other geese with them. Since then the goose population has been growing and occupying shore areas from the islands and mainland. Grazing geese are nowadays a visible element in the city of Helsinki, competing over space with citizens.
Geese densities are rather high on Helsinki shore lawns, where non-flying broods gather to graze. In August juvenile birds can move further from the shoreline to feed. The best seashore lawns tempt dozens of broods. In urban areas lawns are usually a nice buffet table for the geese: they typically prefer plant species used in lawns, and mowing sustains fresh vegetation. Compared to natural lawns, urban lawns can be better for broods.
However, geese grazing is affecting plant diversity by decreasing it. Few plant species tend to dominate in the grazed areas, while the diversity and coverage of species is more balanced in areas with no geese grazing. Good quality lawns benefit broods, because they don’t need to move long distances while grazing. Geese population growth in the Helsinki area has been refracting after reaching ca. 1300 breeding pairs, and one reason is thought to be the limitation of good feeding habitats for broods. Geese already use almost all possible lawns in Helsinki. During dry summers with poor lawn growth geese may be greatly food-limited, which is reflected in the population size. Thus it seems that the barnacle goose population in Helsinki has reached its carrying capacity.
Methods for preventing geese grazing were measured in Helsinki. One possibility is to use plant species that geese don’t prefer, instead of the current species mix that seems to be especially tempting for geese. Another possibility is to fence off areas were geese are not welcome. Goslings cannot fly, and thus cannot reach fenced areas, and they also avoid areas where they have limited visual contact to water.
Beaver activity enhances the occurrence and diversity of pin lichens (Caliciales). Both the number of species and individuals is much higher in beaver-created wetlands than in other types of boreal forest landscapes. There are four reasons behind this:
1. High amounts of deadwood. Pin lichens grow on both living trees and deadwood. Decorticated deadwood in particular is preferred by pin lichens. Beaver-induced flooding kills trees in the riparian zone and produces high amounts of decorticated snags.
2. Diversity of deadwood types. Beaver activity produces snags, logs and stumps. Snags are created by the flood, whereas logs and stumps are also produced by beaver gnawing. The diversity of deadwood tree species is also wide, containing both deciduous and coniferous tree species. The diversity of deadwood types maintains a high diversity of pin lichen species.
3. High humidity conditions. High humidity conditions are favorable for many pin lichen species. Old-growth forests are usually the only places in the boreal forest belt that contain high humidity conditions. There the shading of trees creates a beneficial microclimate for pin lichens. Lighting, on the other hand, becomes a limiting factor for pin lichens in old-growth forests. Most snags in beaver wetlands stand in water, where steady and continuously humid conditions are maintained on the deadwood surface.
4. Sufficient lighting conditions. Because most of the deadwood in beaver wetlands stands in water, it is concurrently in a very open and sunny environment. Many boreal pin lichens are believed to be cheimophotophytic (cheimoon=winter), meaning that they are able to maintain photosynthesis also during winter at very low temperatures. The algae member of pin lichens requires enough light for photosynthesis. Open beaver wetlands make photosynthesis possible for pin lichens during both summer and winter. Snow also enhances light availability during winter.
More information: Vehkaoja, M., Nummi, P., Rikkinen, J. 2016: Beavers promote calicioid diversity in boreal forest landscapes. Biodiversity and Conservation. 26 (3): 579-591.
This is a mallard (Anas platyrhynchos). It is your basic duck, familiar from park wetlands. A mallard quack is also the classic duck sound.
Age and season affect plumages
But mallards do not always look like those in the picture above. Males do not always have green heads, nor are females always brownish grey. Depending on the season, and the age and genes of an individual, mallards can look a little different. Downy ducklings resemble the ducklings of all other dabbling duck species. However, they rapidly develop species-specific characters, and young drakes for example develop a hint of green on their head even before all the down has disappeared. In the summertime males briefly change into summer (eclipse) plumage that looks like female plumage. Except that a male beak is still yellow.
Beak reveals sex
In addition to normal changes in plumages caused by seasons or growth, weird looking mallards can also be found. Their plumages might be different due to changes in their genes or hormones.
Various phenotypes are rather typical among animal species. These variations are common in mallards, and peculiar individuals can be found especially in cities. For example, females might be light due to mutations. Mutations can work in several ways causing changes in pigment production or in its appearance traits. Lightly coloured mallards produce pigments, but their colour appearance has changed. If an individual does not produce melanin pigments at all, it becomes a completely white albino.
Colour variations are thought to be typical in mallards in city environments, where predator pressure is lower and thus exceptional individuals survive better. On the other hand, mallard farming has potentially produced weird-looking individuals that have escaped and spread their genes to natural populations.
The beak has an important role in identifying mallard sexes because males have yellow beaks and females have orange-spotted beaks around the year. The beak can also reveal intersexual females. They are individuals that express both female and male outfit. This can be caused by disturbances in female hormone production, or then an individual has both female and male features. Hormones regulate the outfit, and if large quantities of testosterone are produced, male plumage may result. Beak colouration is not as sensitive to hormonal changes and even though a female displays male characteristics, it will still have a female beak.
Mallard flocks may also have hybrid individuals. Duck species are close relatives, and can thus mix rather easily. Various species mixes are known, for example mallards can mix with common teals, Eurasian wigeons, northern pintails and black ducks. However, hybrids are quite rare, because each duck species have specific behaviours and characteristics that prevent hybridization. But sometimes these barriers collapse, and hybrid individuals are born. Hybrid individuals express characteristics from both original species. Their habits and characteristics typically do not interest individuals from the original species and therefore might not breed successfully.
Hybridization can cause several problems, which in the worst-case scenario can lead to the extinction of the original species. The hybridizations of mallard and black ducks in North America is becoming more common after shifts in their distribution. Hybridization is now threating black duck populations. Alien mallards can also cause a serious risk for endemic duck species and to their gene pool. For example, the Hawaiian duck (Anas wyvilliana) is unfortunately going extinct because of non-native mallards. Survival of the species now depends on protection actions that target the extirpation of all mallards and hybrids from the islands
It looks like a duck
Mallards are commonly farmed, and several different colour variations exist among the domestic breeds. A white duck known by everyone is also a mallard variant. Farmed mallards have sometimes escaped, and now breed with natural mallards. Extraordinary ducks, resembling mallards more or less, are a fairly common sight in Southern and Central European parks. Alien genes in the natural mallard population become more rare in the northern parts of Europe.
Ducks Unlimited: Waterfowl Hybrids
Bark beetles (Scolytinae) are small beetles a few millimeters in size. Their larva develop under tree bark eating the phloem, xylem, and cambium layers. Certain species cause extensive forest damage by killing healthy trees, while others only impact weakened individuals. The eating patterns (called galleries) and the trees’ defensive reactions cause disturbances in the nutrient and water cycling within the trunks. The trees literally dry to death.
Bark beetles can be detected by the gallery patterns they leave on tree trunks. These patterns are species-specific, and often very beautiful. The patterns can be used to recognize infestations and begin warding off the worst damage. Then again, the gallery patterns cannot be seen until the tree bark falls off.
Bark beetles also have a secret weapon: wood-staining fungi. This group of fungi includes several species that damage wood or cause serious diseases to trees. Bark beetles and wood-staining fungi have developed various relationships such as the ambrosia beetles that spread certain fungi species into their galleries to farm them for food. Wood-staining fungi benefit from the bark beetles transporting them to new trees, and have developed exceptionally sticky spores that attach to adult beetles as they are preparing to disperse. Bark beetles also benefit: the fungi weaken new tree individuals, giving adult bark beetles the opportunity to infest and lay their eggs in these trees.
It’s hard to believe that tiny beetles and even more minuscule fungi can kill gigantic trees. Situations where a bark beetle or fungi spreads to a new geographical region among lumber are particularly devastating. The new host trees have no immunity or defense mechanisms against this new organism and the alien species spreads like wildfire.
Dutch elm disease is a prime example of this. Ophiostoma ulmi, a fungus killing elm shoots spread from Asia initially to Europe and then, fueled by the post-World War I reconstruction boom, from Europe to North America in lumber. European elm species coped with the disease slightly better than their North American cousins. European elms also died, but the spread of the disease around Europe took several decades and finally the outbreak waned. 10–40% of the elms died, depending on the country in question. The situation was very different in North America. The American elm (Ulmus americana), a very popular urban and ornamental tree, formed large forests in the eastern areas of the continent. It narrowly escaped extinction through active eradication and education measures such as campaigns forbidding the transportation of firewood outside infected states. Unfortunately, a new, much more virulent fungus (Ophiostoma nova-ulmi) causing Dutch elm disease spread to Europe and North America during the 1940s. This fungus has caused the near annihilation of elms from several European countries. As of yet Finland has mostly been spared by the disease, but this may change with a warming climate that allows beetles belonging to the Scolytus genus that carry Dutch elm disease to overwinter in more northern regions. These beetles are already found on the northern coast of Estonia and in the Stockholm area of Sweden. The birch bark beetle (Scolytus ratzeburgi), commonly found in Finland, does not spread Dutch elm disease as it has specialized in solely utilizing birch trees.
However, the birch bark beetle spreads the Ophiostoma karelicum -fungus. Trappings
conducted during 2008 and 2009 for a study carried out in Norway, Finland, and Russia revealed the prevalence of O. karelicum: every single birch bark beetle individual carried the fungus, which was also found in each of the beetle’s galleries that were searched. The life cycle and ecology of O. karelicum is very similar to the fungi spreading Dutch elm disease, and the commonness of the fungus and the birch bark beetle means a very high risk of the disease spreading to e.g. North America. The birch species native to North America would most probably have no resistance to the disease.
On the other hand, pitch canker (Gibberella circinata) is a fungus spread by bark beetles, originating in North America, which has now spread to Europe where it causes pine mortality. The Scots pine (Pinus sylvestris), native to e.g. Finland, is especially susceptible, but the disease has not spread as far north as Scandinavia yet.
To make these dynamics even more complicated, several mite species have also been shown to transport or act as the primary hosts of wood-staining fungi. These mites are in turn spread by bark beetles. The relationships and interactions between these three organisms are still poorly understood.
The disease resistance of tree species can be increased through cultivation. American elm cultivars more resistant to Dutch elm disease have been found, and their disease resistance has been further enhanced through cultivation. These cultivars are most probably the reason that elm forests still exist today in North America, although the age and size composition of these forests has changed considerably with the death of the old and large trees. Biological and chemical disease control is also a possibility: fungicides can be injected into live trees to stop the spread of specific diseases. Six fungicides combating Dutch elm disease are currently on the market in the US.
Similar control measures can most probably be developed against O. karelicum. However, widespread injection campaigns are difficult to implement. In the US, Dutch elm disease is mainly controlled by injecting individual ornamental or urban trees. Injection control as an effective eradication measure requires more development before it becomes a feasible tool for preventing damage caused by alien species.