DOI: 10.5061/dryad.69p8cz92g
title: Twenty-five years of tree demography in a frequently burned oak woodland

description: Due to decades of fire suppression, much of the Upper Midwest savanna
 habitat has converted to oak woodland.  In efforts to restore oak
 savanna habitat, fire has been re-introduced in many of these
 woodlands.  A primary purpose of these burns is to kill the
 fire-sensitive mesophytic tree species, which had established themselves
 during the decades of fire suppression, reduce the number of understory
 trees, and preserve the larger more widely spaced oaks.  It is
 clear from ongoing efforts that restoring oak savannas will require
 frequent fires over decades.  But frequent fires over the long
 term can also threaten the desirable oaks.  Long-term demographic
 studies at savanna restoration sites experiencing frequent fires are
 necessary to determine the extent to the frequent burns are supporting
 and/or confounding restoration goals.  Results presented here are
 from a twenty-five-year demographic study of an Upper Midwest bur oak
 (Quercus macrocarpa) savanna/woodland experiencing frequent fire, during
 which both the survival and growth of more than 9,000 trees were
 documented.  Survival was assessed annually and growth every five
 years.  In the face of frequent fires, stem survival was found to
 be strongly associated with tree species, stem size, and stem
 growth.  In turn, stem growth was found to be related to tree
 species and stem size.  Decades of frequent burning in this oak
 woodland have substantially reduced the abundance of unwanted trees,
 specifically mesophytic species and Q. ellipsoidalis, the latter which
 outcompetes Q. macrocarpa in the absence of fire.  While Q.
 macrocarpa mid-sized (10-25 cm dbh) and large (&gt; 25 cm dbh) trees
 are quite resistant to fire and now dominate the savanna landscape, they
 are not immune from fire-induced mortality.  It is recommended
 that the number and density of these trees should be re-evaluated every
 few years to ensure that desirable numbers remain.  If necessary,
 fires should be suspended for a period of time.  This will give
 smaller Q. macrocarpa trees time to grow larger and become more
 fire-resistant, thereby ensuring successive generations of Q.
 macrocarpa. 
description: Field observations were conducted at the Cedar Creek Ecosystem
 Science Reserve (CCESR) located in east-central Minnesota (Latitude:
 45.401, Longitude -93.201).  During 1988, I initiated the GLADES
 (<b>G</b>rid for <b>L</b>andscape
 <b>A</b>nalysis and <b>DE</b>mographic
 <b>S</b>tudy) project with the establishment of a square 16 ha
 grid (consisting of 1600 10 x 10 m cells) in a portion of Cedar Creek’s
 oak woodland/savanna habitat.  This grid was set up in a north-south
 configuration, using 1.5 m x 0.95 cm diam iron rebars to mark the grid
 nodes. A Cartesian coordinate system was used to map tree stems in the
 grid.  Each cell was identified by the x-y coordinates in the southwest
 corner of the cell.   In 1995, numbered aluminum tags
 were nailed into stems &gt; 10 cm.  In 1996, the
 tags were nailed into stems 5-9.9 cm dbh and attached with wire to stems
 2-4.9 cm dbh.  The dbh of these stems was measured and recorded when
 initially tagged.  In addition, the cell in which the stem was located was
 documented, as well as the stem’s x-y location within the cell (determined
 visually).  A burn program was instituted in the grid area in 1987, and
 the study grid contains three different burn units. Burn unit 1 (6.17 ha)
 was burned four times between 1987 and 1995 (prior to this study) and
 eleven times during the twenty-five-year study (1995-2020).  Burn unit 2
 (5.98 ha) was burned once prior to the study (1992) and nine times between
 1995-2020; burn unit 3 (3.25 ha) was burned for the first time in 2000 and
 eight times after that. All stems were visited annually
 and their statuses (live, dead standing (snag), or dead fallen) recorded.
 The dbh of live stems was measured every five years.  To facilitate some
 analyses involving stem size (dbh), <i>Quercus</i> stems were
 grouped into three size categories based on their dbh in 1995 or 1996
 (2-9.9 cm dbh, 10-24.9 cm, and &gt;25 cm). 
 Survival and growth rates of the two Quercus species and eight mesophytic
 species were analyzed using JMP Pro 15.1 (SAS Institute, Inc.).
description: <strong>Number of
 variable (columns): 39</strong> <strong>Number of tree
 stems (rows): 9314</strong>
 <strong>Variable Name; Variable
 Description</strong>
 <strong>ID_</strong> ; unique ID number for each
 stem <strong>SP</strong>, Species (B=bur
 oak (<i>Quercus macrocarpa</i>), P=pin oak (<i>Quercus
 ellipsoidalis</i>), AE=American elm           
    (<i>Ulmus americana</i>), BC= black cherry (<i>Prunus
 serotina</i>), BE=boxelder (<i>Acer negundo</i>),
 GA=green               ash (<i>Fraxinus
 pennsylvanica</i>), H=hawthorn (<i>Craetagus</i> sp.),
 QA=quaking aspen (<i>Populus</i>
 <i>              tremuloides</i>), PB=paper birch
 (<i>Betula papyrifera</i>), RM=red maple (<i>Acer
 rubrum</i>)) <strong>X</strong>; x
 coordinate of the 10 x 10 meter cell in which the stem is located, e.g.,
 X=20 means the southwest               corner of the
 cell is 200 meters to the right of the y axis 
 <strong>Y</strong>; y coordinate of the 10 x 10 meter
 cell in which the stem is located, e.g., Y=32 means the
 southwest               corner of the cell is 320
 meters above the x axis
 <strong>XX</strong>; x coordinate within the 10 x 10
 m cell, meters <strong>YY</strong>; y
 coordinate within the 10 x 10 m cell, meters
 <strong>DBH9596</strong>; stem diameter at breast
 height (cm); stems with dbh &gt; 10 cm were
 measured in 1995; stems                 with dbh
 between 2 and 9.9 cm were measured in 1996
 <strong>DBH GROUP</strong>; stems were assigned to
 one of three groups based on their 1995/1996 dbh:
 SMALL (includes                  stems with a 1996 dbh
 2 to 9.9 cm), MEDIUM (includes stems with a 1995 dbh 10-24.9 cm),
 LARGE                  (includes stems with a 1995 dbh
 greater or equal to 25 cm).
 <strong>DBH0001</strong>; stem diameter (cm) measured
 at breast height in 2000 or 2001; stems with dbh
 &gt; 10 cm were                 
 measured in 2000; stems with dbh between 2 and 9.9 cm were measured in
 2001 <strong>DBH05</strong>; stem diameter
 (cm) measured at breast height in 2005
 <strong>DBH10</strong>; stem diameter (cm) measured
 at breast height in 2010
 <strong>DBH15</strong>; stem diameter (cm) measured
 at breast height in 2015
 <strong>DBH20</strong>; stem diameter (cm) measured
 at breast height in 2020
 <strong>Y95</strong>; status of stem in 1995 (since
 only live stems were tagged in 1995 all stems were listed as live,
 L) <strong>Y96</strong>; status of stem in
 1996, L=live, D=dead standing, DR=dead stem that is resprouting, DF=dead
 fallen) <strong>Y97</strong>; status of
 stem in 1997, L=live, D=dead standing, DR=dead stem that is resprouting,
 DF=dead fallen) <strong>Y98</strong>;
 status of stem in 1998, L=live, D=dead standing, DR=dead stem that is
 resprouting, DF=dead fallen)
 <strong>Y99</strong>; status of stem in 1999, L=live,
 D=dead standing, DR=dead stem that is resprouting, DF=dead
 fallen) <strong>Y00</strong>; status of
 stem in 2000, L=live, D=dead standing, DR=dead stem that is resprouting,
 DF=dead fallen) <strong>Y01</strong>;
 status of stem in 2001, L=live, D=dead standing, DR=dead stem that is
 resprouting, DF=dead fallen)
 <strong>Y02</strong>; status of stem in 2002, L=live,
 D=dead standing, DR=dead stem that is resprouting, DF=dead
 fallen) <strong>Y03</strong>; status of
 stem in 2003, L=live, D=dead standing, DR=dead stem that is resprouting,
 DF=dead fallen) <strong>Y04</strong>;
 status of stem in 2004, L=live, D=dead standing, DR=dead stem that is
 resprouting, DF=dead fallen)
 <strong>Y05</strong>; status of stem in 2005, L=live,
 D=dead standing, DR=dead stem that is resprouting, DF=dead
 fallen) <strong>Y06</strong>; status of
 stem in 2006, L=live, D=dead standing, DR=dead stem that is resprouting,
 DF=dead fallen) <strong>Y07</strong>;
 status of stem in 2007, L=live, D=dead standing, DR=dead stem that is
 resprouting, DF=dead fallen)
 <strong>Y08</strong>; status of stem in 2008, L=live,
 D=dead standing, DR=dead stem that is resprouting, DF=dead
 fallen) <strong>Y09</strong>; status of
 stem in 2009, L=live, D=dead standing, DR=dead stem that is resprouting,
 DF=dead fallen) <strong>Y10</strong>;
 status of stem in 2010, L=live, D=dead standing, DR=dead stem that is
 resprouting, DF=dead fallen)
 <strong>Y11</strong>; status of stem in 2011, L=live,
 D=dead standing, DR=dead stem that is resprouting, DF=dead
 fallen) <strong>Y12</strong>; status of
 stem in 2012, L=live, D=dead standing, DR=dead stem that is resprouting,
 DF=dead fallen) <strong>Y13</strong>;
 status of stem in 2013, L=live, D=dead standing, DR=dead stem that is
 resprouting, DF=dead fallen)
 <strong>Y14</strong>; status of stem in 2014, L=live,
 D=dead standing, DR=dead stem that is resprouting, DF=dead
 fallen) <strong>Y15</strong>; status of
 stem in 2015, L=live, D=dead standing, DR=dead stem that is resprouting,
 DF=dead fallen) <strong>Y16</strong>;
 status of stem in 2016, L=live, D=dead standing, DR=dead stem that is
 resprouting, DF=dead fallen)
 <strong>Y17</strong>; status of stem in 2017, L=live,
 D=dead standing, DR=dead stem that is resprouting, DF=dead
 fallen) <strong>Y18</strong>; status of
 stem in 2018, L=live, D=dead standing, DR=dead stem that is resprouting,
 DF=dead fallen) <strong>Y19</strong>;
 status of stem in 2019, L=live, D=dead standing, DR=dead stem that is
 resprouting, DF=dead fallen)
 <strong>Y20</strong>; status of stem in 2020, L=live,
 D=dead standing, DR=dead stem that is resprouting, DF=dead
 fallen)