Thanks to those that helped refine this sample protocol!
Comments appreciated, especially as they pertain to clarifying this protocol or proposing new measurements for a later time.
Isotope page set up for methodologies to analyze d13C of NSC's as well as add connections to other isotope campaigns.
MS Word version of draft methods (rev 6/7)
Datasheet (rev 6/7)
We recognize that many plots will occur at already-existing research sites to leverage pre-existing measurements, datasets, and logistics of measurement. If you will be making measurements at these already-selected sites, we ask that you provide some quick ancillary site information on the Datasheet Coversheet of what the site was selected for, how it was selected, known disturbance history, and any notable hydrological components (e.g. “a stream runs 5 m from plot on South/downhill side”).
If you will be selecting new sites to make measurements, we recommend the following guidelines for selecting plots. In general, avoid recent major stand disturbance (fire, windthrow, timber harvest, other human disturbance) and stand edges in selecting plots. We recommend a buffer (>30 m) from improved roads. Finally, within a given region that you are interested in, random selection of a plot center is ideal. This can quickly determined with a random number generator to generate a random compass bearing and random distance from a starting point to a plot center.
Naturally, drought timing and peak severity will differ greatly across the US. We are working with the NLDAS2 modeling group to see about the possibility of generating “drought tracks” or weekly/monthly drought forecasts for US regions. We will be in touch as to whether this is possible or not. In the absence of these guiding forecasts, individual participants should use their best knowledge of their field system to pick sampling dates for each of the sampling period.
To best capture pre-drought conditions and physiology, drought stress, and post-drought effects, three sampling periods are needed. These are:
Only a partial protocol (Step 2, below) is necessary in Sampling Period 3 (2013).
Drought-induced tree mortality is an important but poorly understood process in the terrestrial carbon cycle. We currently do not have a predictive model of drought-driven tree death across species or ecosystems, leading to substantial uncertainties the impacts of climate change on biodiversity, ecological communities, forestry, and the carbon cycle. In part, this is because drought research is typically carried out on individual sites and a handful of species. And in part, this is also because major regional droughts are, by nature, relatively rare, hard to anticipate, and hard to study during peak drought stress. Our goal in this research is to develop a broader perspective across sites and species and to step back and examine the broad view of what determines the vulnerability of a given tree to drought, with a goal of modeling mortality at larger spatial scales.
We want to acknowledge up front that there are many challenges in an effort like this. As the wealth of site-level drought physiology research shows, much of tree’s response to drought is context-dependent, depending on site and soil characteristics, biotic community attributes, drought characteristics, and antecedent conditions. This makes cross-species and cross-system comparisons difficult. Second, capturing this context-influenced and dynamic drought response in spot measurements at single points in time is often hard. Nonetheless, cross-site comparisons have been done successfully across sub-continental regions and the potential to draw upon the expertise and wealth of ongoing research on US forests during drought holds great promise.
Our guiding question in this research is: How do species identity and individual tree attributes, community and edaphic context, and drought characteristics affect the vulnerability of a tree to drought? More specifically, within a plot or region with similar drought conditions, is a given tree’s probability of death influenced by species identity, species traits associated with drought response such as wood density, community characteristics such as stand density, and soil characteristics such as soil texture? Across regions, how does mortality vary with drought duration, intensity, and order (e.g. spring drought followed by summer drought)? How do drought characteristics interact with individual, trait, species, community, and edaphic elements (e.g. is a short but intense drought hardest on species with lowest evidence of stomatal control or individuals on fine-textured soils)?
Thus, we have designed a short protocol to measure tree mortality, individual characteristics, some drought-relevant species traits, and soil characteristics. The first and most important component of measurement is determining who lived and who died – mortality for each species before, during, and after drought to compare with the USFS Forest Inventory and Analysis background mortality rate. Individual tree metrics indicate stress, biotic attack, and microclimate and competitive context. Soil gravimetric water content provides a snapshot of soil moisture and surface soil texture give a coarse indication of the water holding capacity of a site’s soils. While not perfect drought-response traits, wood density (correlate of embolism resistance). 13C of leaf sugars and starches (correlate of recent stomatal closure) are easy to sample species drought traits. A few other physiology measurements – notably pre-dawn and mid-day water potential – are highly encouraged but not included in the core protocol (see below).
Aims: Simple and clear methods that are 1) comparable across observers and systems, 2) can be done by a single trained person in less than a day, 3) require minimal specialized equipment, and 4) drawn from and standardized with national monitoring protocols for forest health (Forest Health and Management (FHM) protocol).
NOTE: The measurement protocol below is written for establishing a new plot for these measurements. If you will instead be making measurements in an already-established plot, skip Step 1a and 1c in “Methods.”
NOTE: Steps 3-7 (physiology measurements) are needed only for 2012 sampling periods. The 2013 sampling period should consist only of Step 2 (stand health and mortality).
Bill Anderegg 11611 Rd. 22 Cortez, CO 81321
These measurements can provide greater physiological insight and power, especially across systems, but often require specialized equipment or training and more time. If you are interested in measuring any these variables, we highly encourage doing so. Include these measurements in the “Notes” column (or add additional columns) in the datasheet so that measurements can be associated with the specific trees from which they came.