Tree Genetics

Influences on plant development genotype the exact genetic makeup of an individual environment climate, parent health, soil fertility Phenotype = influence of BOTH genotype and environment + Heritability = strength of genetic control Vg / (Vg + Ve) = Vg / Vt or, the ability of a character (e.g., height) to be passed on to the next generation or, the extent to which an attribute is under genetic control Given genotype may exhibit different phenotypes in different environments (plasticity of phenotype) - We never see the genotype! High heritability: stem straightness, stemwood specific gravity, susceptibility to leaf rusts, and date of bud burst in spring Low heritability: height (soil water & fertility), diameter (stand density) Non-genetic variation is caused by (1) external physical environment and (2) internal environment of plant (e.g., juvenile vs. adult [phase] in flowering).

The effect of environment on genetics Northern Red Oak Notice how much effect environment can have on the leaves of a Northern Red Oak, while the Shingle Oak is less affected. Shingle Oak

The effect of environment on genetics Figure 4.2 - Sitka Spruce Photoperiodism – largely controls entrance into dormancy of many woody plants, particularly species with northern ranges. They are genetically adapted for the photoperiodism. This is the same species with similar climate. There is a dramatic change of 50+ days in cessation of growth from the southern to the northern latitudes. (May not see such a strong relationship if different climate/soils/etc.) 1 degree of latitude north = 100m upward in altitude for Rockies (Wiersma, 1962). [83m in eastern NA, 110 continent-wide] Population at high elevation may have same length of gs as pop at lower elevation that occurs several degrees north => similar photoperiodic adaptation mechanisms If interchanged, may show only negligible differences in growth rates.

Plasticity of phenotype Plasticity  degree to which a character of a given genotype can be modified by environmental conditions Plastic Size of vegetative parts Number of shoots, leaves, flowers Stem elongation rate Rooting Depth Photoperiodism Non-plastic Leaf shape Serration of leaf margin Floral characteristics A genotype may assume one set of characters in one environment & exhibit a different phenotype in another environment. In general, those characteristics created over a long period of time tend to be more plastic than those created Rapidly because they are more subject to environmental influences. Why is plasticity so important to trees [substantial value]? Trees are rooted in environment Trees have life spans typically longer than annuals or herbaceous species. Can have wide-ranging species Ponderosa pine is found in both the Rockies & the Coast Range [2 varieties] Douglas fir is found thoughout the Pacific Northwest and in the Rockies from Mexico to Alberta & BC, Canada [2 geographic varieties]

Variations in genotype Mutation & recombination of genes Selection Gene flow between/within populations Geographic isolation Random drift Inability to adapt to changes = death Mutation – changes from breaks in DNA, errors in copying, or changes in sequence. ultimate source of all variation Selection – reduces an individual’s ability to reproduce severe drought my cause some individuals to die while others survive/reproduce Flow between/within populations migration – pollen/seeds blowing in from a source otherwise considered to be a separate population nonrandom mating – some individuals are more likely to mate than others because of location Geographic isolation – gene pool becomes less and less diverse Random drift – chance event unconnected with genetics that affects ability to reproduce. “Dumb luck”; e.g., a lightning strike or animal damage that kills tree. Genetic variation of any type is important for species survival & is a major advantage of sexual reproduction.

Niche Where? When? How? Spatial component Temporal component “a habitat supplying the factors necessary for existence” or “the ecological role of an organism in a community” Where? Spatial component When? Temporal component How? Functional component Definition is from M-W. Where…Where is this species able to exist? Is this species largely found in the Southern U.S. (Loblolly pine) or the northern U.S. (Douglas fir)? Does it exist only in floodplains (e.g., cottonwoods) or in drier areas (Juniper)? How dependent is this species on a given set of conditions? When…When does this species dominate at a given site? Is it found at the site early in succession (birch, lodgepole pine) , or is it a species which is only found after a site has been under development for some time (hemlock)? How….How do they reproduce? What is their growth rate? What is the tolerance of this species to disturbance (fire, flood, shade, drought, etc.)? Specialists vs. generalists

Niche Where? When? How? Spatial component Temporal component “a habitat supplying the factors necessary for existence” or “the ecological role of an organism in a community” Where? Spatial component When? Temporal component How? Functional component Fitness-flexibility compromise (Mather, 1943) fitness for environment as it exists; flexibility that will permit further change Fitness – inbreeding; low rate of recombination Flexibility – favored by variability-promoting mechanisms (cross-pollination, high rate of recombination) with further adaptive change

Tree Regeneration Regeneration includes production and maturation of seeds. It includes both sexual and asexual reproduction. It ensures the development of successive generations of plants of a given landscape ecosystem. Established plants either (1) die or (2) undergo recruitment into the lower layers of the forest. Even fewer reach the overstory or canopy layer. Regeneration is not just property of plants. It also includes the physical environment (light, temperature, moisture, nutrients, wind, disturbance).

F. Noble fir (pollen cones) Douglas fir (pollen & seed cones) Eastern hemlock Slash pine (pollen cones) Bald cypress (seed cones) Noble fir (seed cone) F. Noble fir (pollen cones) A. http://www.botanik.uni-bonn.de/conifers/pi/ps/menziesii4.jpg B. http://www.ohiodnr.com/forestry/Education/ohiotrees/hemlock.htm C. http://www.cnr.vt.edu/dendro/dendrology/syllabus/pelliottii.htm D. http://www.cas.vanderbilt.edu/bioimages/pages/cones.htm E. (http://www.cnr.vt.edu/dendro/dendrology/syllabus/Aprocera.htm) E. & F. http://plants.usda.gov/cgi_bin/topics.cgi?earl=plant_profile.cgi&symbol=ABPR Trees can have both male and female flowers on a single tree (monoecious) or on different trees (dioecious). Self-pollination usually leads to reduced growth, and these seedlings are often eliminated through competition – but quite important after fires. Angiosperms rarely produce viable self- pollinated seeds, while conifers (esp. pines) often do. Photos from the U.S. Forest Service

(Pseudotsuga menziesii ) Douglas fir (Pseudotsuga menziesii ) Closeup of the underside of a sun foliage shoot of P. menziesii, showing pollen cone buds and the manner of leaf attachment to the twig [C.J. Earle]. Immature seed cone and active pollen cones [C.J. Earle, 4-May-2002]. Pollination occurs via wind and insects. Wind-pollinated species flower in early spring before leaves flush out. Insect-pollinated species will flower as leaves are flushing. Conifers are exclusively wind pollinated; female cones are found in top third of the crown, increasing chances of cross-pollination. Avoiding cross-pollination: spatial separation plant has both male and female flowers, which can be in different locations on branch or plant. Ratio is not necessarily 50-50. temporal separation pollen released & several days later, stigma will open (or vice versa). Each flower in this case contains both stamen and pistils; without temporal separation, self-pollination would likely occur. self-incompatibility some plants recognize self-pollination has occurred and abort the process. Mature cones [C.J. Earle]. http://www.botanik.uni-bonn.de/conifers/pi/ps/menziesii.htm

Pinus species Immature Seed Cone Immature Pollen Cones Pollen Cones (yellow) & Seed Cone (green) Human & climate effects on pollination: windy, rainy – no pollination bees and other pollinating insects are decreasing due to pesticides, etc. Mature Seed Cone http://www.botany.hawaii.edu/faculty/webb/BOT201/Conifers/conifer_lecture.htm

seed production establishment dispersal germination Sexual reproduction is the basic mode by which plants maintain their populations, adapt to changing environments, and thus persist in time and space. The zygote (seed) is genetically different from either parent and other offspring. The full seed reproduction cycle depends upon a number of factors. There must be resources available to support seed production. There is actual pollination & seed development. Seed dispersal Seed bank – active or dormant Germination Seedling bank (persistent juveniles) Established plant Seed bank -> remain dormant in soil until conditions (light, wide temperature fluctuations, and/or high soil nitrate) trigger germination Seedling bank -> large-seeded species, show negligible growth beneath the dense shade of the forest canopy, but grow rapidly in treefall gaps.

Asexual reproduction (cloning) also occurs [genetically identical] Asexual reproduction (cloning) also occurs [genetically identical]. Almost all woody plants are capable of some form of cloning. As far as we know, a plant’s asexual reproduction doesn’t prevent sexual ability. Vegetative shoots can arise from: basal stem – where the stem joins the roots (oak, hickory, alder, birch) roots (aspen, beech, sweetgum) rhizome (horizontal underground stems (many shrubs, dogwood, striped maple) lignotuber – a buried mass of stem tissue (eucalypts) stolons – arching branches that take root after coming in contact with soil surface (dogwood) fragmentation – branch breaks off, is buried and becomes established (willow, cottonwood) layering – lower branches are pressed into soil by weight of snow or woody debris and take root (boreal and northern conifers among others) Established plant: Juvenile – no flowering & adult – flowering not just whole tree, but even parts of trees – meristems of branches near trunk and near bottom of mature trees. ***Attainment of flowering is more closely related to tree size than age.

aspen, cottonwood, many pines, alder almost all woody plants are capable of some form of cloning, especially aspen, willow, sumac, and dogwood aspen, cottonwood, many pines, alder most conifers (except hard pines), hardwoods (upland oak, hickory, basswood, white ash, black cherry) lodgepole pine, jack pine, Virginia pine, Monterey pine cottonwoods, willows, aspen Reproductive cycle is closely adapted to complex of environmental factors where it grows. Many river flloodplain and wetland species will flower in early spring and disperse seeds 4-6 weeks later – into moist seedbeds [recently flooded]. => millions of small seeds rather than large seeds Other North Temperate Zone trees – fruits & seeds develop throughout growing season [2-4 mos], are disseminated in the fall/winter, typically lie dormant over winter, germinate in moist forest floor the following spring. Larger seeds containing more food for seedling to help it establish root system in anticipation of soil-water stress to come. upland oaks, hickories, walnuts, chestnuts, conifers, firs shade-tolerant species, Sugar maple, American beech, Hemlock, true firs, western red cedar, Engelmann spruce

Primordium = group of cells representing the initial stages in the development of a plant organ Primordium is the undifferentiated group of cells Initiated the growing season of the year before the opening of the flowers. 5 possible pathways of primordium development. Overall number of primordia may be the same from year to year, but the ratio may change. In initial stages of development. If a primordium is aborted, there is no trace left. If latent, forms bud scales and stops may develop into vegetative shoot later if plant is damaged. Seed, Vegetative, Pollen ratio of these may change annually depending on internal nutrition and hormonal relations in shoot and tree (e.g., periodicity of cone crop). Lateral buds at the base of a young shoot tend to become pollen cones, while those towards the tip tend to become seed cones or vegetative shoots.

Pollen cones Seed cones or vegetative shoots Seed, Vegetative, Pollen So, primordia located at the base of a shoot tends to become a pollen cone Near the end of the shoot, it tends to become a seed cone or vegetative shoot. Seed, Vegetative, Pollen ratio changes from year-to-year based on hormone relations & internal nutrition. Lateral buds at the base of a shoot tend to become pollen cones. Lateral buds at the ends of a shoot tend to become seed cones or vegetative shoots.

Fig. 5.3 - Reproductive cycle of Douglas fir 18-month cycle to cone development. Most seeds develop through the growing season of 2-4 months and are disseminated in fall or winter. Primordial development Following year, pollen development, flowering fertilization 2-4 months of maturation, then disseminated This is typical of most conifers and many hardwoods. In contrast – Pinus genus, red oaks fertilization occurs 12 months AFTER pollination. cycle is one full year longer.

Fig. 5.6 Sound seed deposited (m2) Distance from forest edge (m) -20 50 100 150 Sound seed deposited (m2) 1000 2000 3000 4000 Gene flow is not only function of how widely pollen and seeds are dispersed. range of seed dispersal tends to be limited. Exception: small-seeded trees such as birch, hemlock, poplar, willow. bird dispersal, etc. Several other factors: (1) limited number of breeding trees (2) differences in flowering time of individuals pollen can be transported long distances (20-km or more) most occurs close to source, so most are pollinated & fertilized by their neighbors timing of pollen release and female receptivity is closely related to air temperature, humidity [usually favors local trees] (3) biological and ecological factors that control zygote viability and seedling establishment (genetic incompatibility, frost, drought, shade, herbivory, etc.) Hybridization – crossing between individuals of populations with different adaptive gene complexes (races, subspecies, species).

Fig. 5.5 - Cone Crop Periodicity Western white pine, northern Idaho 240 120 180 60 51 1950 1967 52 53 54 55 56 57 58 59 61 62 63 64 65 66 Year Mature Cones Tree 19 Tree 58 Tree 22 Tree 17 After Rehfeldt et al., 1971 Good cone crops every 3-4 years Marked drop off after peak production (1952, 1960, 1963) Individual trees tend to be on a similar cycle – why?? Considerable variation in inherent productive ability Tree must mature before able to produce first seeds. Maturation time varies with species. A lodgepole pine may produce its first seeds in 10-20 years, while a Douglas fir typically takes 20-40 years. Ponderosa pines, spruces, and many firs take 40-60 years to produce their first seeds.

Cone Crop Periodicity 1-2 years - Lodgepole pine, willows, poplars 2-3 years – Engelmann spruce, Western hemlock, oak 3-5 years – western larch 3-10 years – Ponderosa pine, Douglas fir What are the best seed producers? dominant trees with large exposed crowns, vigorous growth, and of medium age.