10.5061/DRYAD.V41NS1RW1
Zhou, Yong
0000-0003-2546-8462
Yale University
Tingley, Morgan
University of California Los Angeles
Case, Madelon
University of Oregon
Coetsee, Corli
Scientific Services, Kruger National Park
Kiker, Gregory
University of Florida
Scholtz, Rheinhardt
University of Nebraska-Lincoln
Venter, Freek
Balule Nature Reserve
Staver, Carla
Yale University
Woody encroachment happens via intensification, not extensification, of
species ranges in an African savanna
Dryad
dataset
2021
woody encroachment, species distribution modelling, community assemblages,
fire, rainfall, African savanna, Kruger National Park
Yale University
https://ror.org/03v76x132
2021-04-22T00:00:00Z
2021-04-22T00:00:00Z
en
5148603 bytes
4
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Widespread woody encroachment is a prominent concern for savanna systems
as it is often accompanied by losses in productivity and biodiversity.
Extensive ecosystem-level work has advanced our understanding of its
causes and consequences. However, there is still debate over whether local
management can override regional and global drivers of woody encroachment,
and it remains largely unknown how encroachment influences woody community
assemblages. Here, we examined species-level changes in woody plant
distributions and size structure from the late 1980s to the late 2000s
based on spatially intensive ground-based surveys across Kruger National
Park, South Africa. This study region spans broad gradients in rainfall,
soil texture, fire frequency, elephant density, and other topographic
variables. Species-level changes in frequency of occurrence and size class
proportion reflected widespread woody encroachment primarily by
Dichrostachys cinerea and Combretum apiculatum, and a loss of large trees
mostly of Sclerocarya birrea and Acacia nigrescens. Environmental
variables determining woody species distributions across Kruger varied
among species but did not change substantially between two sampling times,
indicating that woody encroachers were thickening within their existing
ranges. Overall, more areas across Kruger were found to have an increased
number of common woody species through time, which indicated an increase
in stem density. These areas were generally associated with decreasing
fire frequency and rainfall but increasing elephant density. Our results
suggest that woody encroachment is a widespread but highly variable trend
across landscapes in Kruger National Park and potentially reflects an
erosion of local heterogeneity in woody community assemblages. Many
savanna managers, including in Kruger, aim to manage for heterogeneity in
order to promote biodiversity, where homogenization of vegetation
structure counters this specific goal. Increasing fire frequency has some
potential as a local intervention. However, many common species increased
in commonness even under near-constant disturbance conditions, which
likely limits the potential for managing woody encroachment in the face of
drivers beyond the scope of local control. Regular field sampling coupled
with targeted fire management will enable more accurate monitoring of the
rate of encroachment intensification.
This data was collected from Kruger National Park (22° 20' to 25°
30' S; 31° 10' to 32° 00' E). Woody species distribution
data for 1989 was collected using a rapid Braun-Blanquet method.
Briefly, 1794 sites were selected across the park. At each site, woody
vegetation cover and species were examined in a 20 m × 20 m plot according
to three height classes: small (0.75–2.5 m), medium (2.5–5 m), and large
(> 5 m). These records were stored as presence and absence for each
woody species in each size class at each site. Woody species distribution
data for 2008 were collected from 342 sites across the park. At each site,
a 50 m × 60 m plot was established and four 50-m transects running at 0,
20, 40, and 60 m along the length of the plot were laid out. Woody plant
data was collected from eight sampling points located along the transects:
30 m and 50 m along the first and third transects, and 20 m and 40 m along
the second and fourth transects. At each sampling point, woody plants were
sampled according to their height classes (≤ 1 m, > 1 and ≤ 3 m,
and > 3 m) within three corresponding circles with a radius of 1 m,
2 m, and 5 m, respectively. In other words, woody plants with a height of
1 m or less that were found within a 1-m radius of each sampling point
were counted and identified to species; woody plants within a 2-m radius
with a height of > 1 m up to 3 m were measured in height and
identified to species; and woody plants within a 5-m radius and taller
than 3 m were measured in height and identified to species.
This data is comprised of four components: (1) data and code for species
occurrence and size distribution analysis; (2) data and code for species
distribution modeling; (3) data and code for linear regression modeling;
and (4) predicted maps of species distribution. Please refer to the paper
for more details.