Individual study: Germination of bog plants in relation to depth of peat burial and their recolonization potential of milled peatlands: a greenhouse experiment, Québec, Canada
Campbell D.R. & Rochefort L. (2003) Germination and seedling growth of bog plants in relation to the recolonization of milled peatlands. Plant Ecology, 169, 71-84
After commercial peat extraction, restoration of vegetation is a desired objective, preferably using those native species occurring in peatlands prior to peat extraction. In this study conducted in Québec, Canada, two experiments were conducted to evaluate the potential of vascular plants (both those species occurring in undisturbed bogs and those, sometimes undesirable species, colonising milled bogs) to germinate and establish in abandoned milled peatlands and to assess whether easily measured plant traits can be used to predict their probable success. Study species included 20 frequently occurring perennial herbs, graminoids, shrubs and trees of undisturbed bogs or abandoned milled bogs. A glasshouse experiment was performed to test the effect of different burial depths under peat on germination and seedling emergence (summarised here), and a growth chamber experiment was conducted to measure relative growth parameters of seedlings (for a summary see: www.conservationevidence.com/ViewEntry.asp?ID=1169).
Study species: Study species were chosen as the most frequent vascular plants occurring in either natural bogs or abandoned milled bogs in Québec, Canada. Desirable species for restoration are those of natural bogs, while some species which recolonize milled bogs may include undesirable species not usually found in undisturbed bogs (e.g. birch Betula spp.). In total, 21 species were chosen, including perennial herbs, graminoids, shrubs and trees (Table 1, attached). Seeds was collected from milled and natural peatlands at three sites in Québec.
Seed burial and germination: The effects of burial on seedling emergence was first evaluated in spring 1998 from seed collected in 1997 and receiving stratification treatment, but germination for several species was poor, apparently due to fungal infestation during stratification. The experiment was repeated in spring 1999 using mostly seeds collected in 1998 with modifications to seed stratification techniques (see original paper for details). Germination was acceptable for all species, except Carex limosa, C. stricta and Scirpus cespitosus which had low seed viability. Consequently, the 1999 experiment is reported for all species except C.limosa and S.cespitosus, for which data from the 1998 experiment is presented, as both germinated well in 1998. Carex stricta never germinated well so is not reported.
In early May 1999, peat to be used as the growth medium was sieved dry, then wetted with distilled water. Square pots 8 cm wide x 9 cm deep with drainage holes were filled to 2 cm from the rim. Either 25 or 50 seeds were planted per pot, depending on species. Seeds were buried at one of four depths: 0, 5, 10 or 15 mm. The pots were refrigerated at 8ºC in the dark for 1-3 days and then placed in a glasshouse. Pots were watered with a mist of deionized water (pH 4.9) every 1 to 3 days from early May to mid-August to maintain surface moisture. Emerged seeds were recorded and removed. A sample of 100 stratified seeds of each species was used to determine seed viability .
For C.limosa and S.cespitosus, the experiment was conducted as in 1999 (except seeds were collected in 1997, and seed pre-treatment was different). Fifty seeds of each species were sown but only three burial treatments were used: 0, 5 and 10 mm. The experiment began in early May, and lasted for 43 days. Seed viability was not assessed.
Median germination times ranging from 6 days (Picea mariana) to 39 days (Vaccinium angustifolium). Buried seeds showed similar germination patterns as unburied seeds but generally emerging 2 to 7 days later depending on the species and burial depth. Two exceptions were V.angustifolium and V.oxycoccus which lagged by up to 26 and 14 days, respectively at 15 mm burial.
For most species, seedling emergence declined exponentially with burial depth. The decline in emergence with depth varied dramatically among species but was most marked in small-seeded species (average seed mass in mg in parentheses) Andromeda glaucophylla (0.179) Chamaedaphne calyculata (0.071), Drosera rotundifolia (0.008), Kalmia angustifolium (0.005), K.polifolia (0.006), Ledum groenlandicum (0.006) and Rhododendron canadense (0.018), most failing to germinate at just 5 mm burial depth. Overall, seeds less than about 0.1 mg in mass were most sensitive to burial (see Table 1 for seed masses of all study species).
Four species (Carex oligosperma, Eriophorum angustifolium, E.vaginatum and Scirpus cespitosus) did not show any significant effect of burial on germination, within the range of burial depths tested (0 to 15 mm).
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