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GRASSY RECONSTRUCTION: A Plant Competition Trial and insights into the relative competitiveness of two Cumberland Plain grass species Some Challenges in Reconstructing Grassy Habitats • Seed supply • Seed establishment knowledge • Weed control • Ecological approaches to weed control • Managing for diversity and weed resistance A Plant Competition Trial: -Trial Overview- Monocultures & Mixtures Species Selection & Location rationale for sites & species Bulking-up Seed for Trial Trial planting in 1996 Trail Measurements An Early Hypothesis Mixtures would be more productive (and therefore weed resistant) than monocultures; due to resource partitioning, mutualism, and diversity of growth habits and requirements Some Microlaena & Chloris Results % of total plot productivity Microlaena in Chloris mixtures as a % of total plot productivity over time 40 32.17 30 17.44 20 10 8.77 0 Sampling year: 1998, 1999 & 2004 % of total plot productivity Chloris in Microlaena mixtures as a % of total plot productivity over time 100 91.2 50 50 3.5 0 Sampling year: 1998, 1999 & 2004 Comparison of 1998 herbage mass for Microlaena and Chloris Herbage mass 160 141.36 140 134.06 120 100 80.06 80 60 40 20 0 Mic. mono, Chloris mono, & CM mixture Comparison of 1999 herbage mass for Microlaena and Chloris 45.61 Herbage mass 46 44 42 40.81 41.76 40 38 Mic. mono, Chloris mono, & CM mixture Comparison of 2004 % cover for Microlaena and Chloris % cover 60 50.62 50 36.92 40 30 27.4 20 10 0 Mic. mono, Chloris mono, CM mixture Observations: Mic. & Chloris • Mic. inferior competitor early and therefore more productive in monoculture than in mixture • Chloris stronger competitor early and performing well in mixture and monoculture • Chloris very productive early (good early cover) • By 2004 Mic. is the stronger competitor and is displacing Chloris • Mic. monocultures are the superior treatments with highest cover scores in 2004 • Chloris loosing productivity over time • Mic. gaining productivity over time Hypothesis Outcome • In many circumstances (time of sampling, species make-up in treatment, etc) monocultures were more productive (not expected) • A new observation: slower growing species better competitors in the longer term Consistent with Ecological Theory of Tillman: At moderate to low mortality rates, transient dominance is predicted whereby species may actually be replaced by slower growing species with lower resource requirements Strategies & Implications of Results • Seeding of monoculture mosaics may be more suitable than blended mixes in some circumstances (for some species) • Some species will perform better in blends • Inclusion of slower growing & longer lived species is important • Quick growing species such as Chloris may be a useful cover & nurse crop for slower growing species • Slower growing species may be best sown into alternative seed beds (not cultivated) such as into a native cover crop or into sprayed down exotic cover Herbicide & Sowing Rate Trials Application of trial results to seed production & rehab. areas Reconstruction can be successful; success requires… • Reliable seed supply from local or regional sources • Ongoing improvements in establishment knowledge, including weed control • Careful consideration of genetic & provenance policies in the context of fostering seed supply sufficient to meet the need