Knowledge of tree growth and maintenance to maximize tree health and prevent unnecessary
tree mortality (e.g. avoiding certain herbicides, proper mowing procedures, and providing suitablemoisture levels) is required. Many land
management professionals typically have expertise
in trees/forestry or in farm systems but rarely
expertise in both (Schaefer 1989). Such situations
have led to on-farm failures of tree systems.
There are also time requirements for maintenance
that may include: mowing, spraying, irrigation,
and occasional tree replacement—5% to
10% tree mortality is common over the first
10 years for many otherwise healthy shelterbelts
(G. Horvath pers. comm. 2002). Some concern
has been expressed regarding the notion that
shelterbelts may provide habitat for on-farm pests
such as rats and other mammals as well as undesirable
insects. Research on this topic is limited.
But there has been very little evidence that this
has been a serious problem with crop field shelterbelts.
Undoubtedly more research is needed to
fully answer this question.
Because empirical evidence is lacking it is difficult
to assess the effectiveness of this technology
at this point. However it is likely that there is a
continuum of effectiveness. The lower the overall
level of odorous emissions emanating from a production site, the more effectual shelterbelts
are likely to be. It is likely that there is a threshold
at which shelterbelts (and other technologies) are
simply overwhelmed and a nuisance situation
may continue to exist. Field and laboratory tests
are needed for a better understanding of this
threshold.