14 NEBRASKAland • MAY 2018
Tree Diversity
By Steve Brey, Horticulturalist
With emerald ash borer about to ravage our state and
eliminate one of our most widespread and common native
trees, the green ash, tree diversity is imperative.
Dutch elm disease took the American elm out of our
pallet of plantable trees starting in the 1960s. Every village,
town and city used this iconic tree as a street and park tree.
Because of our love for this tree, we couldn't get enough
of it, and that was a big mistake. Along came Dutch elm
disease, which for the most part, wiped out the entire
American elm population. We learned a valuable lesson:
diversify, diversify, and diversify.
The problem is we did not heed our own advice, and
because of this we are now facing another monumental
problem of removing ash trees. Entire neighborhoods, or in
the case of our state parks, entire campgrounds were planted
back to ash after we lost our elms. That was understandable,
as ash is a native tree; this species is very tough and able to
withstand harsh growing conditions. But there was no excuse
for over-planting.
A useful guideline for tree planting is the 10-20-30 rule,
proposed by Dr. Frank Santamour at the U.S. National
Arboretum. The 10-20-30 rule, also called the 10 percent
rule, basically states that in any one area the tree population
should not contain more than 10 percent of one species, 20
percent of one genus and 30 percent of one family.
If we follow this guideline now and in the future, we
may not be faced with catastrophic losses when another insect
or disease problem occurs. As an example, if you have 100 trees
growing in one of your campgrounds you should have no more
than 20 different kinds of oaks or 20 maples.
Reducing trees to 30 percent of any given family becomes
a little more difficult. Some experts have proposed the idea of
no more than 5 percent of one species planted in any
given area. Many of our campgrounds have cottonwoods that
pre-date the campgrounds themselves, and these old giants
are coming to the ends of their lives. This turnover will give
us a chance to diversify these areas so we do not repeat
history.
Therefore, no more than 20 percent of any one genus
should be planted in a given area. This concept is far from
perfect, but it is a start to diversifying our campgrounds. ■
Tree diversity throughout the state will be key in the coming
years to prevent disease outbreaks.
PHOTO
BY
ERIC
FOWLER
