In hybrid aspen plantations aged a dozen years plus, ground vegetation rather resembles a field – not a forest – as explained by Tea Tullus, in her Doctoral thesis. However, as early as six-seven years back, the ground was rich in red boleti.
Professor surprised by boleti on aspen fields
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Hardi Tullus, a professor at Estonian University of Life Sciences and supervisor for Doctoral thesis by Tea Tullus – his daughter-in-law – the appearance of red aspen boleti (Leccinum aurantiacum) comes as the greatest surprise related to the project. Keeping in mind that, already six years after being planted, the mushrooms formed a mycorrhiza with the aspen roots.
«This led to the welcome conclusion that nature will arrive, in all its diversity, as soon as it gets a chance,» explains Hardi Tullus.
Grass plants still there
In the 24 hybrid aspen fields observed, Tea Tullus has discovered numerous orchids: early march orchids, commons potted-orchids, lesser butterfly-orchids. Of trees, birch, willow, elm, ash, spruce and others have found a place in between the aspens.
No alien species has accompanied the hybrid aspen sets, brought from Finland. The aspens themselves, like in the 13 years old plantation at Nõgiaru, Nõo Commune, have grown to be twenty centimetres stout at breast height, being over 15 metres tall.
«As I first described the test areas, six-seven years ago, I assumed there would be greater tendencies towards forest in the following six-seven years, in the ground vegetation,» said Tea Tullus. «Not so. Grassland species still dominate: dandelions, common bent, redtop, rough bluegrass, cock’s-foot and others.»
An important part of the thesis by Tea Tullus was comparison with white birch stands, planted in way similar to hybrid aspen stands: as a monospecific tree plantation, unto fallow farmland.
As it appeared, species-specific differences are negligible – the main differing feature being in lushness of vegetation. Birch being thicker in its crown, and planted with greater density, casting darker shadows and causing the vegetation to be more peaky.
«There are more similarities than differences in ground vegetation,» added Tea Tullus.
Pursuant to a 9 years old decree by Minister of the Environment, hybrid aspen – a cross between Common aspen and American aspen, is named as one of thirteen alien tree species permitted to be grown in Estonia as forest trees.
Hardi Tullus, having also supervised other research work related to hybrid aspen, desired to underline that Estonian University of Life Sciences still will not propagate replacement of indigenous forest trees with hybrid aspen.
«We only view it as an alternative for fallow farmland,» stressed Prof Tullus.
Soil fertility improved
Hardi Tullus also pointed out that, in hybrid aspen plantations, soil fertility will in no case deteriorate. Rather, nitrogen, phosphor, and potassium content will increase, little by little. After the first clear cutting, best performed after 25 years, deforestation may be opted for – should it be deemed imprudent to continue timber production.
«It was the green movement that, disparagingly, launched the term tree fields,» recalls Hardi Tullus. «True: this is, indeed, a tree field. However, it has more in common with a forest than a rye field with a wooded meadow.»