US Forest Service Research and Development Long-term Patterns of Seed Production in Ponderosa Pine Forests  - Rocky Mountain Research Station - RMRS - US Forest Service

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Long-term Patterns of Seed Production in Ponderosa Pine Forests

Regeneration of ponderosa pine is of crucial interest in all areas of the west, especially in light of recent large wildfires. Understanding the regeneration dynamics of ponderosa pine is important not only in re-establishing forests that have been destroyed by fire, but is also essential in planning fuel treatments in fire-susceptiable forests. Knowing how quickly and under what circumstances ponderosa pine will naturally regenerate and grow is critical in prescribing fuel reduction and forest restoration activities and in estimating how long they will be effective. This is especially true in the urban interfaces of the Colorado Front Range and Southwest, where climates are dry and ponderosa pine regeneration has been historically sporadic.

This 20-year study conducted at the Manitou Experimental Forest provided a unique opportunity to observe the long-term pattern of ponderosa pine seed production, as well as to follow the establishment, growth, and survival of natural and planted ponderosa pine seedlings in the harsh environment of the Colorado Front Range. In 1981, this study was initiated to compare the effects of two different vegetation management treatments (seedtree, shelterwood) on the establishment and growth of natural and planted ponderosa pine seedlings. The study also explored the benefits of scarification of the soil surface on seedling success. Scarification involved rototilling the polots with asmall rubber-tired tractor. Seedlings were planted on one-half of the experimental plots. Each year measurements were taken in terms of the number of live seedlings that were present in the fall, their height, and the production of seeds as capture by seed traps.

Ponderosa pine seed production is quite variable. Good seed crops are produced only every 4 to 6 years, with almost no viable seed producing in the intervening years. Seed viability is nominally less than one-half of the total seed production.

Planted seedlings survived much better than naturals. Overall, 62 percent of the seedlings planted in 1982 were still alive in 2001, compared with 8 percent of the natural seedlings that germinated in 1982. More seedlings survived under shelterwood overstories and on the scarified seedbeds for the seed producing years of 1982, 1989, and 1995. These data suggest that denser overstories and scarified seedbeds help promote seedling survival in years with abundant seed germination.

Shelterwood overstories containing between 6 and 14 m2 ha-1 stem basal area over scarified seedbeds provide optimal conditions for natural seedling establishment and growth. However, fickle climatic conditions and the intermittent occurrence of good seed crops may require many years to establish a fully stocked forest of natural seedlings. Planting seedlings appears to be a much more reliable method of quickly e-establishing new ponderosa pine forests.

Research continues on this study site with the unexpected wildfire treatment of the Hayman Fire. Recovery of understory vegation, and pine seedlings, as well as the pattern of seed production after this wildfire are among the many research topics being explored.

Citation

Shepperd, W.D.; Edminster, C.B.; Mata, S.A. 2006. Long-term seedfall, establishment, survival and growth of natural and planted ponderosa pine in the Colorado Front Range. Western Journal of Applied Forestry. 21(1):19-26.

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Last Modified: Monday, 28 April 2008 at 17:17:18 EDT (Version 1.0.5)