Kesting, Stefan

In Europe, semi-natural grasslands are an important            resource of biodiversity and are, therefore, of high            conservation interest. They are often invaded by            shrubs, and they are threatened by under-utilization or            abandonment which leads to further shrub            encroachment.            A gradient analysis of shrub-invaded temperate            grasslands (from shrub-free to pioneer forest) in            Germany was carried out to study the effect of shrub            encroachment on plant biodiversity, herbage mass and            nutritive value of herbage, as well as the effect on            seed bank-vegetation similarity. The latter was driven            by the question of the role of the soil seed bank for            ecological restoration (Bossuyt & Honnay            2008).            Our hypotheses are: (1) An initial shrub invasion leads            to enhanced habitat diversity and according to the            habitat heterogeneity hypothesis (MacArthur &            Wilson 1967) thereby to higher species diversity. (2)            Shrub encroachment leads to a loss of similarity            between vegetation and soil seed bank. (3) Herbage mass            and variables describing nutritive value of herbage            decrease with increasing shrub encroachment.The selected 30 plots (10 m x 10 m) covered a wide            gradient of shrub encroachment. Canopy height of the            shrubs was between 15 and 500 (1000) cm, and the canopy            cover ranged from less than 1 % to nearly 100 %. We            recorded a total of 203 vascular plant species in the            vegetation. Number of species per plot ranged between            27 and 68 (mean = 44.5), maximum species number per            square meter was 41. Highest species diversity was            found at medium shrub invaded sites, which is in line            with our hypothesis of a hump-back relation between            shrub encroachment and plant biodiversity.            Similarity between seed bank and aboveground vegetation            (Jaccard s coefficient of community) ranged between 7.5            and 36.4 %. Highest similarity was found in            intermediate shrub invaded grasslands. We have to            reject our hypothesis of decreasing seed            bank-vegetation similarity with increasing shrub            encroachment, but we found evidence for decreasing            similarity with changing vegetation composition from            grassland to shrub and forest vegetation. The following            plant functional types were positively correlated with            Jaccard index: therophytes (life form), annual plants            (life span), and proportion of forbs.            We found a reduction of herbage mass of DM from 3570 to            210 kg ha-1 with increasing shrub            encroachment. Metabolizable energy concentration of            herbage ranged from 8.9 to 10.2 MJ kg-1 DM            and crude protein concentration from 72 to 171 g            kg-1 DM, both measures being positively            correlated with shrub occurrence. Increasing shrub            occurrence was associated with a decrease in            water-soluble carbohydrates concentration (from 151 to            31 g kg-1 DM) and a reduction in the            indicator  forage value . The results are in line with            our hypothesis of decreasing herbage mass, but are            contradictory to the hypothesis of decreasing nutritive            value of herbage with increasing shrub            encroachment.Our results emphasise the importance of semi-natural            grasslands as a resource of biodiversity. Conserving            these grasslands is closely connected to continuous            agricultural use. Our results indicate a potentially            large agronomic value for shrub-encroached temperate            grasslands and suggest its utilization for livestock            production

Georg-August-University Göttingen

Shrub encroachment of temperate grasslands: Effects on plant biodiversity and herbage production

https://ediss.uni-goettingen.de/bitstream/11858/00-1735-0000-0006-B044-0/1/kesting.pdf

Shrub encroachment of temperate grasslands: Effects on plant biodiversity and herbage production

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Georg-August-University Göttingen