2202 Diamond Mountain Road
Calistoga, CA 94515
February 16, 2019
To the Napa County Planning Commission
RE: PROPOSED TREE PROTECTION ORDINANCE
OAK REPLACEMENT SPECIFICATIONS
Following are specifications on seedling oak replacements of harvested oaks in the county's oak woodlands which ought to be incorporated in the regulations under consideration.
The current consideration is only regarding the ratio of replacement proposed to be 3:1. However there are additional aspects which must be included in order to insure the survival of the replacement oaks.
In support of my recommendations, I attach the relevant sections - underlined sections for convenience - of several research papers (some repetitive) issued by the University of California, California Department of Forestry, USDA and others on which they are based:Oak planting data
1) Replacement planting layout
2) Cluster planting v. single planting
3) Microsite planting selection
4) Seedling source selection
5) Optimal season planting
6) Clearing of surrounding vegetation and maintenance
My conclusions and recommendations assume that:
The goal of seedling replacement is to adopt the best possible practices for replacing mature oaks with ones which eventually will have the best chances of becoming mature themselves.
Natural stands of oak seedlings serve dual ecological purposes:
Acorns fall or are transported by animals covering the entire area of oak woodlands. Some are close to the mother trees and some further away.
Acorns deposited close to the mother tree compete for nutrients from that tree and grow under its shade. Some of the eventual seedlings survive in a stunted mode, their ecological function being to insure the replacement of the mother tree when it dies.
Acorns deposited beyond other oaks' drip lines, are free of moisture, nutrient and sunshine competition which helps them grow to rapid maturity which is the assumed goal of the replanting program.
The root systems of mature oaks is overwhelmingly in a lateral direction and extend 2 to 6 times or 50 feet, beyond a mature oak's drip line. For practical purposes in this discussion, I assume a conservative 10' drip line and a root system extending 2 times or 10 ' beyond the drip line.
1) PLANTING LAYOUT:
Assuming a drip line of 10 feet, a minimum seedling's best chance of attaining full maturity is for it to be planted at a minimum 2x10' = 20' away from its next oak (or a replacement seedling) PLUS 2x10' = 20' to accommodate its own eventual root system, together totaling a 40 foot distance of one seedling to the next or from seedlings from existing oaks.
In restoration projects in riparian zones, denser clusters 15-20 feet apart are more desirable.
It is also recommended that site specific existing, naturally established oak growth patterns are best followed in determining planting layout of replacement oaks.
2) CLUSTER PLANTING V. SINGLE PLANTING:
Assuming all conditions are optimal (see above and below), the survival rate of seedlings is approximately 75% in 2 years and an additional 75% in 5 years. Given this survival rate, it seems that a replacement ratio of 3:1 is far more preferable to a 2:1.
Research suggests cluster plantings of 3-4 seedlings per any given location (counting as one) rather than single ones have a better chance of survival.
3) MICROSITE SELECTION:
Research suggests that since financial resources for replacement planting are limited, it is advisable to select the best sites to ensure survival to maturity. Soils which do not retain moisture (such a sandy ones)are to be avoided unless enhanced by irrigation. The same applies to exposed ridges and south facing slopes which are drier than north facing ones.
Other site selection considerations which are favorable include annual precipitation of more than 10 inches, deep soils, alluvial sites, swales, or other places with subsurface water.
In general, gentle to moderate slopes insure better survival rates than steep ones because the latter rarely meet these conditions. They are also typically heavily wooded requiring substantial clearing to insure that seedlings are free of competition for moisture, nutrients and light.
4) SEEDLING SOURCE SELECTION:
Since tree species have adopted to specific environments, it is important to plant oak species where they naturally occur. Even within species, one must be careful to only plant acorns or seedlings that come from the a parent tree growing in the same general environment.
Early planning for harvesting such acorns and nurturing them to seedlings ready for planting is required.
5) OPTIMAL SEASON PLANTING:
Acorns should be planted from early November (after the first rains have soaked the soil) until early March.
Seedlings should be planted between December and February, when the soil is wet but not frozen.
6) CLEARING OF SURROUNDING VEGETATION AND MAINTENANCE:
Adjacent plants, especially grasses can use up so much of the available sol moisture that little is left for the seedlings. It is recommended that a 2 -3 foot radius circle around the planting spots be cleared of other vegetation for at least 2 years after planting.
in addition, seedlings must be protected from animals in appropriate cages.
CONCLUSIONS AND RECOMMENDATIONS:
á In general, seedling oak replacement should be planted in similar areas from which the original oaks have been removed and with the same species of oaks (preferably originating from the same acorn seedlings).
á Spacing must be at a minimum 40 feet apart from each other and/or from existing oak stands unless they are replacing oaks removed from riparian areas in which case they should be 15 - 20 feet apart.
á Areas with poor soils or low water retention such as most steep slopes, south facing slopes, pooling water locations and exposed ridge areas must be avoided.
á Replacement seedlings counting as one, should be constituted of clusters of 3 - 4 rather than single ones.
á Seedling planting must be performed between December and February.
á Planting areas of 2-3 foot radius must be maintained weed free for a period of at least 2 years and seedlings must be planted in protective cages.
á The County must perform periodic annual inspections for a period of 5 years in order to ascertain the health of the replacement seedlings. If they are found to be in ill health, a certified arborist must evaluate the cause of failure (sub soil, dryness, sun exposure, faulty species etc) and insure that they are immediately replaced in a manner in which they will flourish.