Individual study: The effect of soil disturbance and fertilizer application on growth and seed production of goldenseal Hydrastis canadensis in Essex County, Ontario, Canada
Sinclair A. & Catling P.M. (2004) Restoration of Hydrastis canadensis: experimental test of a disturbance hypothesis after two growing seasons. Restoration Ecology, 12, 184-189
Goldenseal Hydrastis canadensis is an endangered perennial woodland herb of north eastern USA and Canada (where it occurs chiefly in Ontario). An experiment was undertaken to evaluate the effects of soil disturbance and fertilizer on goldenseal, including effects on seed production and germination.
Study site: The study was carried out at five deciduous woodland sites (four near the town of Arner, one near Amhertsburg) in Essex County, Ontario, Canada.
Experimental design: Twenty 3 × 3 m blocks at each of the five sites for transplants and 10, 3 × 3 m blocks at each of four of these sites for seed sowing were randomly established in apparent goldenseal habitat within 30 m of existing colonies. Only sites with large populations (>700 stems) were chosen. Four treatments were randomly applied to each block a day before sowing seeds or transplanting. Each treatment covered 1 m², and was 1 m apart to avoid effects of neighbouring plots. Treatments were:
1) substrate turnover - topsoil overturned to 4 cm depth with a shovel, mimicking mammal disturbance or uprooted trees;
2) fertilizer application - 7 g of slow-release granular bone meal (2 : 14 : 0 NPK) sprinkled over the ground, mimicking fertilization by massive defaecation events of formerly present fauna, e.g. flocks of passenger pigeons Ectopistes migratorius (now extinct) or fertilization via flooding;
3) substrate turnover and fertilization;
4) control (no manipulation).
Seed sowing: From 11 to 15 July 1999, ripe fruit was picked from nearby patches and the seeds removed. In the 10 blocks for seeds, 25 seeds were planted just below the soil surface following a 12 cm grid (based on cultivation literature in order to maximize the number of seeds per plot). The total number of planted seeds was 4,000 (25/treatment plot, 100/block, 1,000/site).
Transplanting: From 24 to 27 August 1999 (start of senescence) using a trowel, a rhizome from a stem that had flowered or lost fruit was transplanted from a nearby patch into each 1 m² treatment plot. A total of 400 rhizomes were transplanted (1 per treatment plot, 4 per block, and 80 per site). Stems that had flowered and/or fruited were chosen to eliminate life stage as a factor and to ensure rhizomes of approximately equal size.
Data collection: From 4 to 6 May, 19 to 21 June, and 21 to 23 August 2000 and from 7 to 9 May and 9 to 12 July 2001, transplant stem height and leaf width were measured. Presence or absence of flowers and fruit were noted in 2000, and the number of pericarp divisions per fruit were counted as an estimate of seed production in 2001 (to avoid squashing fruit and interfering with dispersal). Seedlings were visible in 2001, and the number in each plot was recorded from 9 to 12 May.
Effects of treatment on stem production and seedlings: Treatment did not have a significant effect on lack of stem production (rhizome death or dormancy), in either the first or second year, or on lack of germination. This supports the assumption that there was no differential effect of treatment on absence of stem and seedling development.
Cover: Disturbance increased plant cover in both years. After 1 year, there was significantly more cover in soil turnover plots (turnover only c.300 cm²; turnover + fertilizer c. 280 cm²) compared with the control (c.224 cm²). Differences between turnover treatments and the control although not statistically significant in the second year, may have been biologically significant.
Flower and fruit production: In the second year, plants in soil turnover (c.0.28) and soil turnover + fertilization (c.0.3) plots had significantly more flowers compared with the control (c.0.14) after 2 years. Soil turnover + fertilization also gave significantly more fruit compared with the control after 2 years, but the disturbance treatments did not differ significantly from each other.
Seeds: More seeds were produced in the soil turnover + fertilization plots (2.5 seeds/fruit) compared with the control (c.0.6/fruit) after 2 years. Germination and number of seedlings were slightly greater in the control, but standard errors overlapped extensively among treatments. These germination and seedling number differences were not significant in contrast to the significant increase in production of seeds associated with disturbance.
Conclusions: Substrate turnover alone, and in combination with fertilizer, promoted goldenseal growth and recruitment potential (flower, fruit and seed production). Beneficial results of disturbance after 2 years lend support for the idea that goldenseal benefits from certain kinds of natural disturbance currently absent or less frequent than would have formerly occured, and that if disturbance events are accompanied by fertilization (e.g. from bird/mammal droppings), this further benefits the plant.
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