zone are bumblebees and flies. Plants utilize different strategies to deal with these limits, including alternate flowering time and clonal propagation. Early flowering plants Some plants flower immediately after snow melting or soil thawing. These early flowering plants always form their flowers in the previous season, called preformation. This flower primordium is produced one to three years before flowering which ensures that flowering is not delayed after snowmelt and that with the right environmental conditions, there will be enough time for seed set. Consequently, they risk frost damage to the preformed inflorescence. In order to minimize frost damage, preformed flowers are often surrounded by tightly packed bracts that are densely covered in trichomes. This helps to keep the interior of a flower bud warm. Because of early-season pollinator limitation, plants that bloom early generally have a low rate of reproductive success. One advantage of flowering early is that seeds that are produced have a greater chance of developing to maturity before the next freeze. They also have a high outcrossing rate, which helps to increase genetic diversity. Speed and time of flowering is dependent on the time of snowmelt, temperature, and photoperiod, but usually occurs 10 to 20 days after snowmelt. Mid-season flowering Approximately half of all alpine species flower in mid-season. Flowering at the seasonal peak combines some of the advantages and risks of early flowering and late flowering plants. Some mid-season plants pre-form their inflorescences, but not all do. Late flowering Late flowering occurs after the main growing season ends. They have a high seed output but their seeds have a reduced rate of maturing because of time constraints. These plants tend towards self pollination, apomixis, and vivipary. Clonal propagation Because investment in flowers and seed production can be costly for alpine plants, they often use clonal propagation. This strategy becomes increasingly more frequent as elevation increases, and is most common among cryptogams and grasses. Some alpine plants use it as their predominant method of reproduction. In these plants, sexual reproduction is rare and does not contribute significantly to reproductive output. An example of such a plant is Carex curvula, which is estimated to have a clonal age of approximately 2000 years. After establishment, each year new shoot growth occurs rapidly from the perennating bud which is usually located close to the soil surface. This growth occurs after snowmelt when the soil temperature is above 0 °C. Some