Summary
Germination and recruitment of ancient forest ground flora species may be problematic in post-agricultural forest. We hypothesised that tree species can influence these processes in acidification sensitive soils through their differential acidification effects. This effect could be helpful to facilitate recolonisation of characteristic ground flora species from natural or introduced sources. In this study pot trial experiments were undertaken using soils taken from underneath four deciduous tree species in Mortagne forest (a 27 year old post-agricultural forest) in northern Belgium.
The experiment was set up using soil (Luvisols) collected under four different tree species: sycamore Acer pseudoplatanus, alder Alnus glutinosa, beech Fagus sylvatica and poplar Populus x euramericana.
In Septemeber 1999, seed of sevenancient forest species (bluebell Scilla (Hyacynthoides) non-scripta, wood anemone Anemone nemorosa, herb paris Paris quadrifolia, oxslip Primula elatior, honeysuckle Lonicera periclymenum, greater stitchwortStellaria holostea and yellow archangel Lamiastrum galeobdolon) was sown. The experiment comprised 256 flowerpots: eight replicates for each combination of tree species (including non-sown controls to assess the seed bank).
Germination (emerging seedlings) was monitored up to April 2001.
Germination of four species was affected by tree species, while only S. non-scripta was indifferent. Germination of A. nemorosa and P. quadrifolia was unsuccessful in all cases. The acid intolerant P. elatior only germinated in soil taken from under P. x euramericana. The acid tolerant L. periclymenum and S. holostea also performed best in this soil, but least in the soil under A. glutinosa. L. galeobdolon preferred A. pseudoplatanus soil. Therefore germination in general followed the soil pH gradient created by the different tree species.
Germination of seed bank species (mainly Betula spp., Poaceae, Juncaceae, Lamiaceae, Cirsium and Taraxacum spp.) was much more successful in P. x euramericana soil than that of other tree species.
We conclude that tree species can affect germination of herb species characteristic of ancient forests; a pH related effect is assumed to explain this. Forest managers should be aware of the rapid acidification within a few decades after planting under certain trees such as Alnus and Fagus on acidification sensitive soils. This has potential negative effect on the colonisation chances of desired ground flora. Mull humus producing trees like Populus spp. favour germination of ancient forest herbs but also competitive seed bank species. The latter needs to be considered as it might limit establishment of desired species by competitive exclusion (if not constrained by shade). We suggest that mull humus producing trees should be at least intermixed in newly planted forests when aiming to facilitate colonisation of ancient forest herbs especially on acidification sensitive soils.