[obol] blackberry

[Dan Gleason]

I have posted much of this information in years past but since this  
discussion has come up again, and there are more people on OBOL now,  
I thought I would resend some of my thoughts about blackberry and  
what they do or do not provide for birds.

I have often found myself disagreeing with other birders about the  
value of blackberry. Its value for food and shelter is often touted  
but I believe that both of these are of minimal value and then only  
to a few species. I strongly encourage removing blackberry wherever  
and whenever possible AND replacing it with a diversity of brushy  
natives, not simply leaving a void in a grassy field (most likely of  
non-native grasses as well.) Here are some points to consider about  
this invader.

Himalayan Blackberry is now better known as Armenian Blackberry  
(Rubus armeniacus). It is not native to North America and is a very  
invasive species that can easily dominate open fields and, once  
established, can be very difficult to eradicate. It does provide some  
food and cover for birds, so many birders believe that removal  
efforts should often be minimized in the best interest of the birds.  
It is nice to see the birds but the overall health of the local  
ecosystem should take precedence. A healthy, native ecosystem also  
provides the best diversity of native birds, unlike blackberry where  
only a few species are routinely found. Birds found in blackberry are  
found mostly around its periphery as the dense cover deep within a  
blackberry thicket offers little that is attractive to birds.

If you examine Internet sites about birds and blackberries, you will  
mostly find simple statements like: "birds use blackberry thickets in  
this area" or something similar but containing very little real data.  
One report on Yellow-breasted Chat (California Partners in Flight  
Riparian Bird Conservation Plan) indicates that, at least in parts of  
California, chats use blackberry thickets for food. In late summer,  
up to 1/2 of the diet may consist of a variety of berries, including  
Armenian blackberry. There is also limited use of blackberry for  
nesting by chats and the report gives some cautions about disrupting  
nests. The report also indicates that there is a lack of extensive  
nest data so it is difficult to make statements about strict habitat  
requirements. They suggest as an action to "Include native, thicket- 
forming shrub species (i.e., California blackberry, wild grape) in  
restoration plantings, while retaining existing tall, mature trees  
for song perches." The use of blackberry is documented in other parts  
of the country as well, but again, these are mostly in disturbed  
habitats that lack native brushy thickets attracting a greater  
variety of birds.

On the negative side, the list is very long. Blackberry thickets can  
produce 7,000-13,000 seeds per square meter! Seeds require 90 days of  
warm temperatures, followed by 90 days of cold (perfect conditions in  
the Willamette Valley) and seeds can remain viable for several years.  
The main method of seed dispersal is via birds and some mammals that  
eat the seeds and pass them through their digestive tracts.  
Apparently, this also greatly improves the germination rate. Young  
seedlings require strong sunlight to grow but the developing stalks  
cannot spread into areas with much less than 50% full sunlight. Once  
established, the stalks can grow as much as 7 meters in a single  
growing season. Over 95% of these stalks will have daughter plants  
growing at the apices, ready to begin growing as the stalks bend over  
and touch the ground. Most lateral branches also form daughter  
plants. An individual stalk may only live 2-3 years but the density  
of stalks is often over 500 per square meter. Even short pieces of  
stalk or root will readily propagate, so the reproductive potential  
of these plants is enormous.

In addition to choking out native vegetation (including some native  
blackberries), these plants often form a barrier along stream  
corridors that prevent some mammals from getting to sources of water.  
One mammal that does do well in blackberries is the black rat (Rattus  
rattus) also known as roof rat. This is a non-native, and often  
rather destructive animal that, in large populations, can serve as a  
vector for diseases including some human diseases. (See note below).

While I do enjoy its fruit, I can't really think of any good reason  
not to eradicate Armenian blackberries. Unfortunately, they are here  
to stay, despite our best efforts. I think that we should control  
these plants wherever they grow as best we can. They do not belong in  
native grasslands, wetlands or other fields and I advocate their  
removal. In riparian corridors, we should encourage their removal  
along with replacement of native plants that can provide the food and  
shelter needed by native fauna (from invertebrates, to birds and  
mammals).

---

As a side issue:  There is much misunderstanding about rodents and  
disease. In this country, Norway rat and black rat, both introduced,  
do not carry plague. Many native rodents do carry plague but their  
fleas tend to be very host specific, rarely biting humans, and so  
cases of plague are quite rare. (Fleas found on cats and dogs are  
generalists and do bite humans.) Also, contrary to popular belief,  
rodents do not carry rabies and no human cases of rabies have ever  
been linked to bites by any rodent species. Because of misinformation  
and ignorance, some people needlessly are given rabies shots after  
being bitten by a rodent (of any kind). Typhus and other diseases  
have been attributed to introduced rats.


Dan Gleason

-------------
Dan Gleason
dan-gleason at comcast.net
541 345-0450


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