Lab 3 - Seed Cone Production-1
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Dec 6, 2023
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Lab 3: Climate and Ponderosa Pine Seed Cone Production
Introduction to Ponderosa Pine and Mast Seeding
Ponderosa pine (
Pinus ponderosa var. scopulorum
) is a widely distributed
conifer species in the western United
States. This species provides a range of
ecosystem services to humans and
critical habitat to a variety of wildlife
species. Ponderosa pine has
experienced extensive mortality due to
abnormally large high severity
wildfires over the past several decades,
raising concern about the potential
bottlenecks to ponderosa pine
regeneration, such as seed availability,
with increasing temperatures.
Ponderosa pine is a mast seeding species, which means that this species has high annual variability and also high synchronicity in seed production among trees within a stand. In other words, every few years ponderosa pine populations produce very high amounts of seeds (or bumper crops) and then in other years ponderosa pine populations produce very few seeds. Similar to other pine species, it takes multiple months for cones to mature. First, cones are initiated in early summer, which is when pollen and
ovule meiosis occurs. Fertilization then occurs in
early summer of the following year, at which time
little cones or conelets develop and then over
winter. The following fall is when the mature seed
cones have formed (~26 months after those cones
were initiated). In this lab, you will develop
hypotheses of how ponderosa pine cone production
is associated with climate, how climate-cone
relationships may vary in relation to landscape
position, and then use data collected through the
cone abscission scar method to assess relationships
between climate and ponderosa pine cone
production at four sites in the Colorado Front
Range. Part 1: Hypotheses and Predictions
Photo 1. Image of ponderosa pine tree (left) and cone (right). Photo credit: Colorado State Forest Service.
Photo 2. Image of an Abert’s squirrel (
Sciurus aberti
) a species found in montane (8,000-10,000 foot) forest ecosystems of Colorado that rely on ponderosa pine cones. Photo Credit: CSU Extension
1.) Use information from the following paper that was presented in class on ponderosa pine cone production (see Figure 1 at the end of this document from the article, and the full article is available on bCourses), please answer the following questions to answer the following questions about which climate variables were associated with ponderosa pine cone production. Be sure to pay attention to not only the month/season of the climate variables but also whether it was during
the year of cone initiation (two years prior to mature cone formation), fertilization (one year prior
to cone maturation), or the year of seed maturation. Article: Mooney, K. A., Y. B. Linhart, and M. A. Snyder. 2011. Masting in ponderosa pine: comparisons of pollen and seed over space and time. Oecologia 165:651–661.
A. List the climate variable(s) that were associated with ponderosa pine cone production. Be sure
to state the month/season and during which year of the reproductive process and the direction of the effect (i.e. was there a negative or positive association between that climate variable and ponderosa pine cone production or did it vary).
B. Likely explanation for each climate variable associated with ponderosa pine cone production.
2.) Develop hypotheses and predictions of:
A.
How you expect mean ponderosa pine cone production to vary at the different landscape positions (specifically differences in elevation and aspect (N, E, S, W). In other words, which landscape positions do you expect ponderosa pine to produce the most cones.
B.
How you expect the relationship between ponderosa pine cone production and temperature during cone initiation and one other annual climate variable identified in #1 to vary at different landscape positions, specifically differences in elevation and aspect (N,
E, S, W). In other words, which landscape positions do you expect ponderosa pine to be more sensitive to annual climate?
Part 2: Results
1.)
Graphically show the relationship between ponderosa pine cone production and June maximum vapor pressure deficit during cone initiation (2 years prior to mature cone formation) as well as June precipitation during cone initiation.
Which variable(s) are most strongly associated with ponderosa pine cone production? Are these consistent with the previous study you had read? *
Note: temperature and vapor pressure deficit are very strongly positively correlated, so if you read a study about temperature and see a similar (or different) pattern with VPD than that should be discussed.
Graphing tips: You can use the “Average Cones” data for creating these graphs (rather than using each individual site data. Remember, independent variables should be on the x-axis whereas dependent variables should be on the y-axis. Don’t forget to add axis titles and units too, such as: “Precipitation (mm.)” and to show the trendline and R
2
value.
2.)
Graphically show how the relationship between maximum vapor pressure deficit during cone initiation and cone production differ depending upon landscape position. Are these data consistent with your hypotheses? Why or why not? What might explain these findings.
Graphing Tips: For these graphs, you will most likely need to make three separate graphs, one for each site (i.e Low Elevation South, Low Elevation North, and High Elevation). Don’t forget to
label the axes and show the trendline and provide the R
2 value.
3.)
Now create a graph to examine how mean cone production differs in relation to landscape position (High Elevation, Low Elevation – North, Low Elevation – South). Are these data consistent with your hypotheses? Why or Why not? What might explain these findings. 4.)
What are the limitations of this study? Describe at least two limitations.
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Part 3: Future of Ponderosa Pine Forests
As part of the US Forest Service Climate Change Strategy that began in 2011, each national forest is responsible for assessing the vulnerability of ecosystem elements to the impacts of climate change. The Arapaho and Roosevelt National Forest District of the US Forest Service has been tasked with assessing how predicted changes in climate may affect future ponderosa pine regeneration. As a silviculturist working in the ponderosa pine forests in this region, you have been asked by the forest to make predictions about how future climate may affect ponderosa pine cone production and what steps might be taken to reduce any adverse negative impacts. High emission global climate model scenarios predict temperature increases of about 5 ˚C by the end of the century, but precipitation predictions are much more variable, with some models showing declines in winter precipitation and others showing increases. Your short summary report should include the following information: 1.) A prediction of how and why ponderosa pine cone production will change across the forest at different landscape positions (i.e. different aspects and elevations) with increasing temperatures; 2.) A discussion of how increases or decreases in precipitation would affect those predictions; 3.) A recommendation of how these forests could be managed to increase cone production (see your results plus Fig. 2 below to guide this). In writing this report, please draw on the findings of this study (to the extent that you think that they are accurate) as well as findings from previous work (focus on work that is done on ponderosa pine in
the Rocky Mountains [i.e. exclude studies in California, Oregon, Washington, and British Colombia]). It’s okay if you discuss studies that we reference in Figures 1 and 2. This short report should be between ½ page and 1 page, single spaced and will be graded based on content (85%) and writing quality (15%).
Figure 1. Correlation coefficients between monthly climatic variables and seed cone or seed production (solid lines seed cones and seeds counted in fall of year x) and pollen production (dashed line pollen cones
counted in spring of year x-1) in the years prior to seed cone and pollen production at a, b Boulder Canyon
and c, d Manitou. Thresholds for significance based on the sample size at each site are indicated with horizontal solid lines for seed cones and seeds and horizontal dashed lines for pollen production.
Figure 2. Figure from a recent paper on ponderosa pine cone production that shows how tree age, size (diameter at breast height [DBH]), and stand basal area affects average cone production (
top panel), the interannual variability in cone production (CVi, middle panel)
, and synchrony in cone production (
bottom
panel
). Interannual variability in cone production describes how whether cone production tended to be consistent overtime among that tree or more sporadic (i.e. huge cone crop one year, with very small cone crops other years), with a higher CVi showing more interannual variability and a lower CVi showing less. Synchrony describes how synchronous the trees were at producing seed crops, with greater synchrony indicating that all the trees in the stand produced large seed crops the same year. Figure from: Wion, A. P, Pearse, I.S., Rodman, K., Veblen, T.T., and M.D. Redmond. (2023). Masting is shaped by tree-level attributes and stand structure, more than climate, in a Rocky Mountain conifer species. Forest Ecology and Management
531, 120794.
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