THE TRUTH ABOUT NEVADA'S PINYON-JUNIPER FOREST
The following is an abstract of the article THE HISTORICAL STABILITY OF NEVADA'S PINYON-JUNIPER FOREST by Ronald M. Lanner and Penny Frazier which can be linked at http://www.phytologia.org/93(3)360-387LannerPinyonJuniperNevada.pdf
It appeared in the journal Phytologia, Dec. 2011, vol. 93, pp. 360-387. This article should lay to rest the extravagant claims of range ecologists that the forest is an illegitimate invader in the Great Basin.
The singleleaf pinyon-Utah juniper forests of Nevada have long been depicted as invasive communities that have expanded from sparse populations on rough terrain to overwhelm large areas of shrubland, reducing their forage value. This paradigm has led to deforestation programs to restore a cover condition thought by range managers to have characterized these lands at the time of settlement in the mid-19th century. We examine contemporary descriptions of the forest, mainly germane to the immense wood resources needed to support the mining and smelting industry. The early descriptions indicate that the pinyon-juniper forest was widespread, continuous over many mountain ranges throughout much of the state, and frequently dense. A comparison of lower forest border elevations reported in the 19th century with those currently mapped show no evidence of downward expansion. Three case studies of areas documented to have been deforested in the 19th century, have naturally re-forested, showing the resilience of the forest. Deforestation for restoration reasons is not justified in the absence of site-specific evidence that shrubland invasion has occurred in historic times.
FINALLY A CREDIBLE EXPLANATION OF SPIRAL GRAIN
As anybody who has studied tree structure or wood anatomy knows, there have been many explanations offered as to why many trees' wood fibers spiral up the trunk instead of being perfectly vertical. As I wrote in my new book, "The Bristlecone Book", "The cause of spiral grain has long been a subject of speculation, including theories about the direction of cambial cell divisions, influence of the earth's rotation, vague genetic characteristics, wind torque, growth rate, asymmetry in the root system.... but unfortunately none of this work has managed to explain just how a tree goes about laying down tilted tracheids."
Well, I spoke too soon. In early December 2007 I became aware of a paper by K. Schulgasser and A. Witztum:
THE MECHANISM OF SPIRAL GRAIN FORMATION IN TREES, in Wood Sci Technol (2007) 41: 133-156. The authors, a mechanical engineer and a biologist at Ben-Gurion University of the Negev must have benefited from that mind-clearing desert air, and have put together a convincing analysis that utilizes microscopic anatomy of cell walls, phenomenology of cambial cell division, and mechanical principles. Further, they show that formation of spiral grain and growth stresses are "...aspects of the same process occurring throughout the cambial zone during cell maturation."
Anybody interested in these wood features must now consult this most important scientific contribution.
THE MYTH OF THE DRIPLINE
Talk to nurserymen, horticulturists, growers of tree cultivars, and gardeners and you'll soon hear mention of the "dripline". This is the imagined line that could be drawn around a tree by projecting to the ground from the edge of the crown. The dripline is understood to mark the furthest extent of the tree's roots, and this knowledge is used to inform growers how to water a tree, fertilize it, and even safely dig near it without harm to the roots. Well, unfortunately, nobody ever informed trees that they were to grow their roots only as far as their branches reach out. Thus we have scads of undisciplined trees of all kinds -- gymnosperms as well as angiosperms -- growing their roots as freely as conditions permit. In other words, roots tend to grow out wherever they are not kept out. Forest trees growing along a meadow edge will put roots much farther into the meadow than into the forest, because the forest soil is filled with competing tree roots while the meadow is not. Roots can grow long distances along streambanks because they follow favorable moisture gradients. They grow into and through animal burrows, following a path of least resistance. They grow beneath boulders that block their path and then rise up to their preferred depth when clear of the boulder. They do all sorts of things, but they never know when they have reached the edge of a tree's crown and must STOP! I have traced easily recognizable pine roots at least a hundred yards from a forest edge into a meadow, where the root was at least half an inch thick and continued across a gully for who knows how much further.
Like lots of misinformation, the myth of the dripline is probably basically pretty harmless. Nobody goes broke believing in its existence and nobody kills for it. But it is a false doctrine, and as such we should root it out of our thinking.
A SCHEME TO MARKET AMERICA'S GREAT TREES
A couple of non-profits called the CHAMPION TREE PROJECT and the NATIONAL TREE TRUST have come up with a clever scheme for marketing so-called champion trees (they have even trademarked them ChampTrees (TM) to safeguard profits). In the last few years they have established a heroes' gallery of champions, supposedly the "hardiest, sturdiest, most resistant and best bred....of their species....the gold medalists of their kind". Then they take cuttings in order to clone those trees with the purpose of selling them as cultivars to people who can be convinced they are getting something of special genetic quality. Of course they claim all sorts of motherhood and patriotic virtues in prolonging these particular genotypes into the future.
But is there necessarily anything in a tree's genes that kept it from being cut down for a shopping mall, or left standing in front of an Italian restaurant? Of course there is not. The huge old trees of any species are huge and old because of many circumstances -- they have not been logged yet; they were not logged because an owner wanted to keep them; they do not grow in the paths of hurricanes; they have avoided infection by their species' more serious diseases; fire suppression policies have kept them from burning up -- and so on. Very little of that is influenced by genetic endowment. In addition, as any plant geneticist knows, you cannot judge the genetic character of a tree by eyeballing it or measuring it in its maturity. You can only do so by testing its progeny -- in other words, the offspring carry the clues to the parent's hereditary characteristics. Foresters learned this the hard way in the early history of forest genetics, and summarize it by saying the phenotype does not indicate the genotype.
For these reasons, the cloning program of the ChampTrees(TM) marketers is at best a feel-good publicity stunt and at worse appears to be a new way of parting a tree enthusiast from his money.
EPINASTY -- MYTH OR REALITY?
Epinasty is defined as the turning down of branches in order to stay out of the way of the tree's leading shoot. According to Mattheck (Trees, the Mechanical Design) it is the executive mechanism of apical dominance, and is accomplished by increased growth on the branch's upper surface. References to epinasty in Kozlowski, Kramer, and Pallardy (1991) all seem to relate to the effect of ethylene on leaves, not much help there. In many years of tracking tree-growth literature I have never run into evidence of greater growth on upper branch sides than on lower ones. This would require tracheids (in conifers) growing longer than normal, or dividing differently than is normal. As an explanation, this looks tenuous.
The required effect could come about from gravity continually pulling the branch down, and a lesser production of compression wood to offset gravitational effects. This happens constantly, for example on the big ponderosa pines outside my window. The tips keep arching upwards each year as a geotropic effect, but after a while gravity has its way with them too as new growth weighs in further out the axis.
So why do we need the term EPINASTY? Any ideas out there? email me at firstname.lastname@example.org
WHEN IS A RULE NOT A RULE?
I have on my shelf a copy of "The Urban Tree Book --an uncommon field guide for city and town" by Arthur Plotnik, published in 2000 by Three Rivers Press. In many ways a nice book, with good illustrations. But on page 317, discussing eastern white pine (Pinus strobus), we read:
"The white pine follows 'the rule of five'--- each year, five branches-to-be whorl out from the trunk at the same height. The baby branches (shoots) develop from five buds surrounding the leader bud, which is the trunk's growing tip."
Well, that was news to me, and I've spent years studying shoot growth in many species of pines. But I didn't have any white pines on hand to check this out. So I went to the Conifers Forum of Garden Web and asked any of its members who had white pines to go out and make some counts for me. The answers were most interesting. Here they are:
Respondent 1 checked 20 trees. There were 3 to 6 branches per whorl, with 4 most common, followed by 5.
Respondent 2 checked 10 trees. There were 5 to 15 branches per whorl, the average being 11.9.
Respondent 3 sent in a picture of one whorl from one tree. It had 5 branches.
Respondent 4 checked seven trees. There were 3 to 13 branches per whorl, the average being 6.8.
So instead of a consistent 5 branches per whorl, as promised by Arthur Plotnik, the range turned out to be 3 to 15 branches per whorl. One can only wonder where Mr. Plotnik got his information. Apparently the "rule of fives" was a rule meant to be broken.
(P.S.-- Shortly after the above was posted, I heard from the author. He was unable to recall where he had gotten the white pine misinformation. I believe he was probably misled by a "rule of five" statement in a field guide -- can't remember which -- that came out a few years ago.)
ABSTRACTS OF SOME RECENT ARTICLES
DOES BRISTLECONE PINE SENESCE? Abstract of article by R.M.Lanner and K.F.Connor in Experimental Gerontology 36(2001): 675-685.
We evaluated hypotheses of senescence in old trees by comparing putative biomarkers of aging in Great Basin bristlecone pine (Pinus longaeva) ranging in age from 23 to 4713 years. To test a hypothesis that water and nutrient conduction is impaired in old trees we examined cambial products in the xylem and phloem. We found no statistically significant age-related changes in tracheid diameter, or in several other parameters of xylem and phloem related to cambial function. The hypothesis of continuously declining annual shoot growth increments was tested by comparing trees of varying ages in regard to stem unit production and elongation. No statistically significant age-related differences were found. The hypothesis that aging results from an accumulation of deleterious mutations was addressed by comparing pollen viability, seed weight, seed germinability, seedling biomass accumulation, and frequency of putative mutations, in trees of varying ages. None of these parameters had a statistically significant relationship to tree age. Thus, we found no evidence of mutational aging. It appears that the great longevity attained by some Great Basin bristlecone pines is unaccompanied by deterioration of meristem function in embryos, seedlings, or mature trees, an intuitively necessary manifestation of senescence. We conclude that the concept of senescence does not apply to these trees.
WHY DO TREES LIVE SO LONG? Abstract of article by
Ronald M.Lanner in Ageing Research Reviews 1(2002):653-671.
A long life multiplies a tree's reproductive opportunities, thus increasing its fitness. Therefore, characteristics that prolong life should be naturally selected. Longevity in trees is achieved by means of numerous behaviors and characteristics, some of which are unique to trees. These include the retention of stem-cell-like meristematic cells after each growth cycle; the ability to replace non-vigorous, lost, or damaged organs, both above and below ground, in the presence or absence of trauma; a sectored vascular system that allows part of a tree to survive where a whole one cannot; formation of clones; a mechanical structure that can react to forces tending to de-optimize it; a hormonal control system that coordinates the above behaviors; and synthesis of defensive compounds.