Recipient Organization
HUMBOLDT STATE UNIV
(N/A)
ARCATA,CA 95521
Performing Department
Forestry
Non Technical Summary
Given the sharp increase in the frequency of severe wildfire in California in the last few decades, there is a great deal of interest in post-fire regeneration. In particular, one asks if our non-serotinous species can persist in an era of short return times. Unfortunately, we have only a handful of case studies of post-fire regeneration, not a general theory of the regeneration process. This project will develop a theoretical framework based on the three recruitment mechanisms: dispersal from the edge, dispersal from old closed cones (serotiny), and dispersal in situ from current seeds surviving passage of the flaming front (facultative serotiny). The latter mechanism requires a late summer fire during a good seed crop. Additionally, we will conduct a novel experiment where the water receipt for germinants of several commercially valuable conifer species is varied in absolute amount and in the timing over the summer. We seek to know the critical absolute summer rain amount and critical between-event interval for germinants to survive in this Mediterranean climate.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Goals / Objectives
There are two main goals. The first is to examine the three mechanisms by which conifer seed is made available after fire: dispersal from living trees at the edge, serotiny, and what we are calling facultative serotiny. The second objective is to determine the how the summer precipitation amount and its intra-summer temporal variation govern the survivorship of conifer germinants in burns.
Project Methods
Precipitation experiment. (2000-2002)We will establish common gardens in a severely burned area at three 2018 fires: the Carr fire in the Klamath region, the Camp fire in the northern Sierras, and a third fire in the central Sierras. We will use seeds of the commercial species Ponderosa pine, gray pine, Douglas fir, incense cedar, and white fir. All plots will have the same soil, a well-mixed layer of three parts sand, three parts clay, and one part humus. This "A horizon" will be placed above the native mineral soil exposed by smoldering combustion, and will be 10 cm thick. Seeds will be sown off-site in flats, and transplanted into the experimental plots as they begin to germinate. The first watering will occur during the transplantation. To retard lateral diffusion from the plot, it will be sited on flat ground, and water will be added, not just to the plot 1 m2 area of germinants, but also to the adjacent area extending 1 m in all directions.There will be a transparent plastic canopy 40 cm above each plot except for the control. Only the control will receive the actual rainfall registered in the summer of the experiment. Netting to keep out vertebrate herbivores will be placed around each plot. At each site the watering regime will consist of the mean annual local summer precipitation amount (x) divided over the summer (May 1 to September 30) into 2, 4, or 8 events (n). Thus, the watering amount becomes x/n, and so a plot can have a few large amounts or many smaller ones, more equitably distributed. Additionally, two other arrays of plots at each garden will have either x/2n (half the total expected amount) or 2x/n (double the normal precipitation amount). Altogether then, there will be 12 plots (including the controls) at each garden. The final proportion of germinants surviving will be tallied in late September. This procedure will be repeated each summer from 2020 to 2022. There will be 100 germinants annually of each species at each garden for each rainfall regime.Facultative serotiny in Ponderosa pine and Douglas fir. (2000)As part of my ARI grant (continuing into the 2000 field season) we have examined regeneration of Ponderosa pine at the 2017 Helena fire and the 2018 Carr fire. The latter occurred in late July. We intend to extend that analysis to other 2018 fires that burned at other dates: Klamathon (July 5), Natchez (July 15), Hirz (Aug 9), Stone (Aug 15), Delta (Sept 5) and Camp (Nov 8). We expect no seeds to have been germinable in early July. Subsequently the ratio of seedlings to cones should increase with fire date as more seeds mature. (However, the Camp fire is expected to provide no recruits as the cones would have already been open by that fire date and thus the seeds should have been consumed.) Given an extra assistant hired using M-S funds, we can extend this analysis at multiple 2018 fires to Douglas fir.At each fire for each species, we select 10 m radius circular plots that contained at least one burnt pine canopy tree. Plots must be at least 100 m from any living conspecific source tree. Within each plot we enumerate fallen cones and recruits. A positive correlation among plots at a fire between cone number and recruit number will demonstrate that the seed source must be local. We will also collect data on scorch height on the burnt trees. Finally, these data allow us to see if these two species have, on average across the landscape, replaced themselves.Immaturity Risk and Facultative Serotiny. (2000-2002)An older (about 100 years) forest in Kootenay National Park burned in 2002 (Shanks fire) and 2007 (Tokum fire). The early August 2018 Wardle fire then burned through both the older fire and much of the two newer fires. We predict that spruce in the post-2006 burn and post-2007 fire will be extirpated, despite 2018 being a mast year, because they were still a few years too early to produce their first crop. Meanwhile, pine will be reduced to very low levels (especially in the 2007 fire) because they had only begun to produce a few cones. Finally, it is predicted that facultative serotiny will be observed (Engelmann spruce, subalpine fir, and Douglas-fir; all three had good crops in 2018) where the older forest was burned in 2018.Methods will be similar to the ponderosa pine study with 10 m radius circular plots for enumerating cone and recruit density in the burned older forest. At the two younger, recently burned areas however we will use transects. Along each 200 m long, 1 m wide transect we will tally all recruits, cones (no spruce cones are expected), and burnt stems.