Recipient Organization
UNIVERSITY OF NEVADA
(N/A)
RENO,NV 89557
Performing Department
Natural Resources & Environmental Sciences
Non Technical Summary
Mountain mahogany can be found on Nevada mountains, in areas occupied by sagebrush and pinyon-juniper woodlands as well as higher up. Information on the ecology of mountain mahogany is not as deep and comprehensive as for other woody species in the Great Basin. We know, for example, that mule deer uses mahogany as a food source and also for cover. We also know that mahogany trees can be quite old, and that they are often in competition with pinyon-juniper trees, but we need more accurate data on how mahogany trees grow to evaluate their overall contribution to Nevada's rangelands. The age distribution of mahogany stands, the rate at which they grow, the years when most individuals become established, and the relationship between size and age are not well documented. Having reliable data on those processes could change our understanding of how to maintain and improve rangelands on Nevada's mountain ranges. For example, public and private landowners planning pinyon and juniper removal projects may be able to prioritize projects not just for greater sage-grouse, but also for releasing mountain mahogany, which in turn may improve soil fertility and provide food for mule deer populations. Therefore, our project is directly related to the research priorities identified this year by the Nevada Agricultural Experiment Station (NAES). In particular, we will contribute information that is relevant to animal (mule deer) nutrition and health, and we will generate data from mahogany tree rings that are directly related to the impact of climate variability and change on Nevada's vegetation.This interdisciplinary project will be conducted by three faculty members from two CABNR departments, together with two research scientists also from two CABNR departments. The research collaboration will be 3 years in duration and will allow training a graduate student as well as a few undergraduate students.
Animal Health Component
40%
Research Effort Categories
Basic
60%
Applied
40%
Developmental
0%
Goals / Objectives
The overarching goal of this project is to expand our understanding of the ecology of curl-leaf mountain mahogany, including herbivory, in the context of pinyon and juniper encroachment. Objectives in support of this goal include:Identify and characterize vegetation and soil of current stands of mahogany in the Desatoya Mountains.Determine if mahogany tree rings are truly annual increments, and then use dendrochronological methods to quantify age structure, population dynamics, and climate impacts.Quantify mahogany tree and understory response to removal of pinyon and juniper.Clarify if wildlife browse of mountain mahogany differs under pinyon and juniper canopy vs. open stands.Use project results to verify and improve state and transition models in Major Land Resource Area 28B as well as other MLRAs with mahogany sites in central and northern Nevada.Develop a technical guide for land managers and stakeholders on mountain mahogany ecology and management.
Project Methods
Mahogany health and understory dynamicsCut/uncut study locations will be limited to areas in the Desatoya mountain range that have had recent (within 10 years) pinyon and juniper removal treatments. Field reconnaissance of treated areas will be used to finalize site selection. Three cut/uncut paired sites will be selected at first, with the possibility of adding more sites based on initial results and availability of funding. Selected sites shall include live, mature mountain mahogany trees, and should be at least 50 x 50 m in size. We will select sites to capture a spectrum of stand ages, creating a chronosequence.Multiple plots may be established at random locations within the perimeter of the site. At each plot, the following data will be collected:Site and soil characteristics. One soil pit will be dug at each site to a depth of 50 cm or until a hardpan or lithic contact is struck. Soils horizons will be described using the following characteristics and others as needed: texture, rock fragments, pH, depth, soil structure. Slope and aspect will also be recorded.Understory vegetation. At each plot, three 30-m transects will be established, each 10 m apart. The line point intercept method (at 0.5m spacing) will be employed to characterize vegetation by species. Vegetation height and litter depth will be measured at each point. We will use a GRS densitometer to identify overhead tree canopy by species.Woody plant density and age structure. Along each transect, a 2-m belt transect will be used to count individual woody plants rooted within the transect by species and height class and/or maturity class. Depending on vegetation density, the width of the belt transect may be altered. Smaller quadrats (1 m2) will be used along the transect lines to count mahogany seedlings; the number of quadrats per plot will be determined using a sample size equation. At least 5 mahogany stems that cover the full range of sizes present at the site will be cut in each transect for tree-ring analysis. Sections will be taken both at the root crown and at breast height.Mahogany health. Methods for mahogany health are adapted from the USDA Forest Inventory Analysis (FIA) program. In the belt transects, the following metrics will be collected for all live trees with diameter at root crown greater or equal to a minimum threshold (possibly 2.5 cm, but higher if stem density is high): crown density, uncompacted live crown ratio, crown light exposure, crown position (overstory, understory, open canopy), crown vigor class, crown dieback, and foliage transparency.DendrochronologySample preparation. Mahogany sections will be sanded using progressively finer sand paper until cell walls are visible under a 10-30x binocular microscope. Visual crossdating will be performed using ring-width patterns, starting with those in common to 4 radii on a section, and continuing with patterns in common amongst the wood samples, leading to the development of a tree-ring site (or master) chronology. Visual inspection of the ring anatomy will initially be used for discriminating false rings from true annual growth rings, and preliminary dates will be assigned.Radiocarbon dating. Rings that are tentatively dated as years 1955, 1962, 1964, 1966, and 1975, will be manually collected by carefully separating individual growth layers in the tangential direction. Seven radii, each on a different section, will be sampled, for a total of 35 specimens. Individual year collection will end after reaching about 1 g of material. Sample identification codes will be assigned without reference to the tentative calendar years or location in the cross-section. By doing so, the 14C analysis, to be performed at an off-campus laboratory, will not be influenced by prior knowledge on the chronological sequence of the samples.Ring-width measuring. Results obtained from 14C analyses will be used to evaluate the dendrochronological results. Ring-width measurements will then be obtained at 1-µm resolution using the MeasureJ2X software interfaced with a Velmex measuring stage and a videocamera mounted on a stereozoom binocular microscope with 10-70x magnification.Age-size relationship and stand structure. Accurate dates obtained from the previous methodological steps will be used to determine time needed to reach breast height, as well as age-diameter relationships at ground level and at breast height. Using both directly aged trees, and the size-age relationship, we will then determine stand age structure, lifetime growth patterns, and potential recent changes in mahogany productivity and health.Site chronology. A master chronology will be developed from standardized tree-ring indices as follows:Formula 1 (see figures and graphics file)where ?t = chronology value in year t = median annual index; nt = number of samples in year t, with nt≥5; w = crossdated ring width (mm, with 1000th digit resolution) of sample i in year t;y=value of sample i in year t computed by fitting a cubic smoothing spline with 50% frequency response at a period of 100 years to ring width series i; wt/yt = dimensionless index value of sample i in year t. The degree of synchronicity in tree growth patterns will be evaluated using commonly accepted, albeit empirical, parameters, such as the expressed population signal calculated for 30-year moving windows. Sensitivity will be estimated using the Gini coefficient, which considers all possible temporal lags in the tree-ring chronology rather than only the first one, as it is done with mean sensitivity.Dendroclimatic analysis. A comparison will first be conducted with other tree-ring chronologies developed in close proximity to the study area, especially the pinyon tree-ring chronology for the Desatoya Mtns. (1504-2001; Biondi unpublished data). Other chronologies are available from the International Tree-Ring Data Bank as well as from previous DendroLab projects. Growth-climate relationships will be quantified using monthly temperature and precipitation time series starting from Jan 1895, to be extracted from the public-domain, 4-km gridded, PRISM (Parameter-elevation Regressions on Independent Slopes Model) dataset. The temporal stability of statistical relationships will also be evaluated.WildlifeMahogany browse evaluation. An architecture-based browse use method will be used. In year one, quantitative browse history will be completed at all cut/uncut sites. Each sample unit must contain 20 mahogany plants for browse classification. Browse history and current-year browse will be completed during the growing season (June - August) along with other understory measurements.Mule deer demographics. We will use remote cameras to document presence of mule deer in mountain mahogany stands in areas of cut and uncut pinyon-juniper. A grid of cameras will be set up at about 200 m intervals to document mule deer use and movements. While mule deer are present, cameras will be continuously monitoring. Pictures will be collected from cameras every two weeks, and then cameras will be reset. We will use pictures to document sex and age distributions of mule deer and the presence of neonates when possible. Those data will provide information on mule deer demographics in the area. We will use occupancy modeling, and also capture-mark-recapture methods if individuals can be reliably identified.Mule deer diet. Every two weeks throughout the seasons when mule deer are present in the study area we will collect fecal pellets to identify primary forage plants in diet, and we will measure fecal nitrogen as an index of diet quality.