Individual study: Rapid response of cowslip Primula veris to habitat restoration by clear-cutting of a former Norway spruce Picea abies plantation in Voeren municipality, Limburg, Belgium
Endels P., Jacquemyn H., Brys R. & Martin Hermy M. (2005) Rapid response to habitat restoration by the perennial Primula veris as revealed by demographic monitoring. Plant Ecology, 176, 143-156
In recent decades, species-rich calcareous grasslands in Western Europe have decreased dramatically both in number and size mainly due to agricultural intensification, and have also in many areas become degraded due to a reduction in traditional grazing. In Voeren municipality, eastern Belgium, several relic grasslands have been afforested in fairly recent years. This study focused on the effects of management on population dynamics and life history traits of cowslip Primula veris, a long-lived perennial herb, typical of calcareous grasslands. Two contrasting habitats were examined: a grassland restoration site after clear-cutting of a former Norway spruce Picea abies plantation, and an ash Fraxinus excelsior plantation on former calacareous grassland characterized by a slowly closing tree canopy.
Study area: The study was conducted at two sites in Voeren (unofficially Fourons in French) (50º45'N, 5º49'E), a municipality in the province of Limburg, eastern Belgium. At one site, 'Altenbroek', Norway spruce trees were planted in 1990 on formerly intact calcareous grassland. These were felled and removed in early spring 1999 in an attempt to restore the original species-rich ground flora. The second site, 'Vrouwenbos', comprised an ash Fraxinus excelsior plantation planted in 1980 (again on former calcareous grassland) and characterized by a closing tree canopy.
Experimental design and monitoring: Just after clear-felling in 1999, eight 2 x 2 m permanent plots were positioned in areas with high cowslip density at both sites; this may have led to slight overestimates of recruitment but allowed for comparison between sites.
Each May, all individuals within the plots were mapped and a life stage assigned to each: seedling (individuals with cotyledons still present); juvenile (immature plants with only one leaf rosette, leaf size smaller than vegetative adults); vegetative adult (non-flowering with one or more leaf rosettes); generative adult (one or more flowering stalks, one or more leaf rosettes; for each flowering adult, the number of rosettes and flower stalks was counted). Mortality was determined.
In late spring 2000, at each site, 30 flowering adults in total were randomly selected within the plots and the following were recorded: length and width of the three biggest leaves, total number of leaves, number of rosettes, number and length of the flowering stalks, and total number of flowers.
Adult cowslips at the restoration site (cleared in 1999) showed high performance in 2000; average leaf length and leaf number (17) were significantly higher compared to the ash plantation (average leaf number 6). Likewise, reproductive parameters (number of flowers and number of flowers per inflorescence stalk) were also much higher e.g. 34.3 flowers/reproductive plant at the restoration site, compared to 5.7 in the ash plantation.
Over the three survey years (1999-2001), in the ash plantation plots there was a shift towards relatively more non-flowering adults (compared to flowering ones), although numbers were stable (45 in 1999; 44 in 2000; 43 in 2001), but with declines in flowering individuals (49 in 1999; 44 in 2000; 31 in 2001) and fewer seedlings (223 in 1999; 171 in 2000; 101 in 2001). Rosette and flowering stalks losses also increased in every year.
In contrast at the restoration site, seedlings rapidly increased, especially in the second year after clearing (23 in 1999; 172 in 2000; 277 in 2001); juveniles showed a slight lag but then rapidly increased in number as the seedlings matured (17 in 1999; 16 in 2000; 63 in 2001). Flowering adults increased steadily (50 in 1999; 95 in 2000; 111 in 2001), and there was also a major increase in the number of inflorescence stalks the first year after clear-felling.
Conclusions: In the Fraxinus plantation there was a decrease in number of flowers, inflorescence stalks and plant size in the plots between 1999 and 2001 under the closing tree canopy. The first signs of decline included lower proportions of flowering individuals, after which there was an increase in mortality; there was a slow population decline over the three years but the decrease was larger in the final year when higher mortality affected the number of reproductive individuals. In contrast, tree felling and removal, resulted in an immediate flowering response and, increased growth and seedling recruitment. The number of seedlings, juveniles and reproductive adults gradually increased over the 3 years subsequent to tree removal.
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