NZ-3: Beech-fire dynamics
Title: Recent post-fire vegetation transitions
Investigators: Veblen, Perry, Tepley
Student: Nacify (CU Phd)
Objectives: This research primarily addresses the Post-fire Dynamics/Disturbance Interactions theme in the PIRE Science Plan by studying vegetation dynamics following the burning of Nothofagus forests during the 19th century European settlement and modern eras. The research will examine potential feedbacks from initial burning of tall Nothofagus forest that may enhance the fire hazard associated with post-fire vegetation. We will quantify fuel characteristics, vegetation structures, and microclimate conditions in post-fire shrublands and second-growth forests for comparison with adjacent unburned (> 150 years) Nothofagus forests.
Work Plan: We will conduct studies of 1) post-fire vegetation transitions at burned forest edges (hereafter the ecotone study) to characterize the effects of burning on Nothofagus forest vegetation; and 2) landscape-scale post-fire dynamics of Nothofagus forests based on stand-origin mapping of post-fire cohorts (hereafter the landscape fire study).
This ecotone study will focus on red and silver beech forests located in the northern one-third of the South Island (mostly in the Nelson Lakes and northern Canterbury districts), east of the crest of the Southern Alps. Approximately 15 ecotone sites were visited and selected for sampling in Jan-March 2012.
Initially, the landscape fire study will focus on silver beech forests in the Blue Mountains of Otago. In March 2011, A. Tepley and T. Veblen conducted initial reconnaissance with Glenn Stewart (Lincoln University) who has a study underway that has documented the existence of extensive areas of post-fire cohorts in the Blue Mountains and who will collaborate in this research. Potentially, the study will include other sample areas if we can locate other extensive areas of post-fire beech cohorts.
Sampling protocols are currently being developed for both studies and will be available by May 2.
Research will complement efforts by Perry and others to model post-fire vegetation dynamics during the IBP. Dating of 19th and early 20th century fires from tree-ring data (cohorts) will be used to calibrate charcoal records from nearby lakes either already sampled or to be sampled by McWethy and others (PIRE NZ-2).
There is no associated funding.
Additional NZ researchers are welcome to participate in this research. G Perry will coordinate conversations with Landcare scientists about collaborating on the role of mycorrhizae in post-fire tree establishment as well as any other potential collaborative topics. Tepley has begun and will continue discussions with Norm Mason of Landcare regarding the possibility of integrating our field-based work on feedbacks of post-fire vegetation structure and microclimate on subsequent fire hazard with his on-going, lab-based work on flammability attributes of individual species.
The results will be published with Tepley as lead author (probably in two separate papers with Perry, Veblen and Stewart as co-authors), and the data and findings will be available to other projects and synthetic activities.
Year 2 Update
The objective of this research is to characterize post-fire vegetation development trajectories and evaluate how the vegetation structure/fuel loading and microclimatic conditions/fuel moisture at each stage of the trajectory feed back on susceptibility to additional fire. Field work was led in New Zealand by CU postdoc Alan Tepley with the assistance of Naficy, Fernandez, and Veblen. Field sampling was conducted in 13 pairs of recently burned, former beech forests and adjacent unburned beech forests, plus two additional sites that help to illustrate the pattern of vegetation development following fire on the northern half of the South Island of New Zealand. In each pair of sites, vegetation composition and structure (stem densities, diameters, heights, and crown base heights), tree ages, and fuel characteristics were measured in one 20 x 30-m plot within the recently burned, former beech forest and one 20 x 30-m plot in the adjacent beech forest that shows no sign of fire within the last 150 years. These data help to determine the time since fire and post-fire establishment patterns by species at each site, which can be compiled across sites as a chronosequence illustrating stand development patterns over time. Microclimate data (temperature and relative humidity) were recorded over a 10-week period in the four of the site pairs.
In addition to the pair of plots, a transect consisting of a series of contiguous 20 x 20-m plots was sampled along the transition from unburned forest into the recently burned vegetation. In each transect, data were collected on vegetation structure, tree ages, and evidence of fire (e.g., charred tree stumps). The transect data help to characterize whether the sites have been burned a single time or multiple times and how the fire or fires have affected the forest. In addition, the transect data help to illustrate the spatial pattern and rate of recovery of beech forest following the fires.
The paired plots encompass sites ranging from 30 to 150 years since the most recent fire. All recently burned sites were dominated by manuka and kanuka, with stem densities ranging from 23,000 stems/ha and an average height of 2.65 m in the youngest site to 3,000 stems/ha and an average height of 16 m in the oldest site. Most sites showed evidence of burning multiple times, and this observation was supported by evidence from historical photos at three of the sites. There was very little beech regeneration in most of the recently burned stands, and only two of the burned plots had beech seedlings present at a density > 400 trees/ha. Beech regeneration was abundant, however, along the edges of the unburned forests. In these areas, beech trees commonly formed a dense, even-aged cohort dating to the most recent fire or one of the earlier fires. The abundant beech regeneration covered an area ranging in width from 20 m to more than 150 m from the unburned forest edge, depending largely on the distribution of trees that survived the fires.
Field sampling was initiated in the Blue Mountains of central Otago in an effort to reconstruct the spatial patterns of fire over the last 2-4 centuries and its effects on beech forests across a ca. 5,000-ha area in the Blue Mountains. This work was conducted in collaboration with Dr. Glenn Stewart of Lincoln University, who has previous research experience in this study area. Aerial photos reveal a mosaic of alternating patches of relatively smooth-textured forest canopy that appeared to be young, post-disturbance stands alternating with areas of rough-textured canopy that have likely remained free of large-scale disturbances for several centuries. Prior to initiating field work, stands with different textured canopies were delineated on the aerial photos. Sampling of forest structure and tree-age distributions was conducted in nine of the stands.
The tree-age data support a pattern of relatively young, even-aged stands, probably of fire origin, alternating with uneven-aged, older stands. Uneven-aged stands support trees up to 500 years old and establishment dates are nearly continuous from the time these trees established to the present. By contrast, in the younger, even-aged stands, most trees established within a window of 60–80 years and older trees are absent. In the data analyzed so far, one of these relatively even-aged stands was initiated in the 1740s and another in the 1780s, both of which predate the period when European settlers were likely to have substantial impact in this region. Thus, most of the stands were probably initiated by fires associated with Maori activities or by lightning-ignited fires; influences of disturbances other than fire (e.g., wind) cannot be excluded. The presence of these > 200-year-old beech stands of probable fire origin illustrates the potential for relatively rapid recovery of beech forest following fire, in contrast to much of the work in the northern half of the South Island, where stands probably burned multiple times and show little sign of recovery over the 150 years since the last fire.