Monthly Archives: July 2016

Summer Tree Failure

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A failed Norway Maple on SE 49th. This picture was taken June 28th, five days after a big rain event. You can see that this tree has been struggling for some time as evidenced by the dead branches still in its crown and the stressed flagging leaves up there. The girth of the trunk is greater than the width of its planting space. It is pinched beneath the overhead lines and the requirements for street trees regarding road clearance. It’s height has been ‘controlled’ and limited over the years.

Trees fail all of the time and when they are older, this can be quite spectacular, or devastating, if your car, home or an individual have the misfortune of being in the its path.  Like most people I used to believe that most such failures happened as the result of storms, and many do, but it is relatively common for trees, or major limbs, to come crashing down with calm conditions in the Spring. The new flush of growth brings with it a great deal more tissue and water weight than a tree in active growth has previously supported or, for a tree struggling, compromised by the burden of significant rot in its core and/or limbs.  Look at any tree and look at its girth, its canopy spread and on many species, its long, often horizontal limbs and try to imagine their weight.  To help with this fill a couple of buckets with water, lift them and try to hold them horizontal away from your body.  Trees are static structures, comprised of countless overlapping fibrous layers, much of it hard and rigid with a great deal of compression and torsional strength.  The were ‘born’ for this.  Few of us would last for more than a few seconds trying to support so much of our own weight on extended arms.  We shouldn’t be surprised when they fail, even as elegant and as well ‘engineered’ as they are. Continue reading

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Agaves, Hybrids and Our Role as Gardeners & Stewards

 

Sharkskin bracketed by its parents, A. scabra left and A. victorian-reginae on the right

Hybridizing is always a bit of a crap shoot!  Cross two species and the progeny will range all across the morphological map!  Hybridizers grow on their seedlings and select those that share the characteristics that they’re looking for or individuals with startling and unusual features.  They toss the rest.  They in effect are giving their selections an advantage, an advantage they would never receive in nature on their own.  In nature hybrids can only occur when the natural ranges of the two parent species overlap and their proclivities align with the possibilities.  Plant breeders are not limited by this.  Pollen can be collected and stored from anywhere and used to pollinate selected plants.  In nature, survival is a numbers game.  Seedlings must be competitive in an existing plant community with limited available niches.  They have to possess a certain robustness.  Those that survive, grow on and perpetuate themselves, possessing survival characteristics that allow them to do so and have been blessed with the conditions that favor them.  Hybrid creations of nursery people and breeding programs may be lacking in these survival features.  They are pampered, lined out in nursery rows and flats. The result of their intentions may actually put their selections at a competitive disadvantage if they were to be left on their own in nature. Continue reading