Dr Margaret A. Brock
Botany, Rural Science and Natural Resources, University of New England
Environment Australia, 2000
Comparison of plant communities developing and reproducing from Spring and Autumn planted donor seed banks in the UNE Experimental Wetlands.
Methods - Data analyses
Species richness of plant communities in each water regime was compared between January 1998 and May 1998, two months after the planting dates of the two seed bank strips (Spring 1997 - November - and Autumn 1998 - March).
Species richness was also broken down into species richness of different functional groups, where the functional groups were:
|S||Obligate submerged species|
|AR||Amphibious: fluctuation responder species|
|AT||Amphibious: fluctuation tolerator species|
|TDA||Terrestrial: damp species|
|TDR||Terrestrial: dry species|
A list of species present under different water regimes at the two dates was compiled. Species richness was compared for both species present and species reproducing.
Total species richness and reproductive species richness
The number of species present on the two seed bank strips did not vary with time of planting. At the Jan98 and May98 vegetation scores, the spring and autumn seed bank strips were respectively two months old. At these times there was no consistent pattern showing that the autumn or spring planting produced a more species rich community (Fig 14a). In the AF, M and SF water regimes, the spring planted seed bank strip was more species rich than the autumn planted seed bank strip two months after planting. This contrasted with the P and TF water regimes, in which the autumn planted seed bank strip was more species rich than the spring planted one.
These results contrasted with the number of species which had reached reproductive maturity (Fig 14b). More species were reproducing on the spring planted seed bank than the autumn seed bank strip two months after planting in all water regimes. This difference was not great in some regimes (AF and M), but was large in the P, SF and TF regimes. Also, in May98 more species on the spring planted seed bank strip (now six months since planting) were reproducing than either the same communities in Jan98 at two months old (except for the SF regime), and the autumn planted seed bank strip in May98 at two months old.
Functional group species richness (species presence and species reproduction)
Species from most of the five functional groups were present under all water regimes on the spring and autumn planted seed bank strips and at the two times (Jan98 and May98). The exception was the submerged species which were not present when the wetlands were empty or just beginning to fill (AF and M in May98).
In contrast, reproductive species did not cover a wide range of functional groups. As a general rule, the spring planted seed bank strip in May98 (ie the six month old strip) had the broadest range of species reproducing, but the two month old seed bank strips (spring-planted in Jan98 and autumn planted in May98) were limited to Terrestrial and Amphibious species. Submerged species were only reproductive two months after planting on the autumn strip in the SF and P water regimes.
In the initial stages of plant community establishment, season and length of time since planting did not affect the number or diversity of species present. Conversely, the number of species and diversity of plant types which had reached reproductive maturity was influenced by season and length of time since planting. Thus the timing of planting donor seed banks in wetlands potentially influences which species add seeds to the soil seed bank in the first year of establishment. To maximise the number of species being added to the seed bank within the first year of revegetating a wetland, donor seed banks should be planted in spring time so that most species have reached reproductive maturity by summer and autumn, and have seeded before winter.
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