Human disturbance impacts the integrity of sacred church forests, Ethiopia
Human disturbance impacts the integrity of sacred church forests, Ethiopia
Catherine L. Cardelu? sID 0 1 2
Carrie L. WoodsID 1 2
Amare Bitew MekonnenID 1 2
Sonya Dexter 0 1 2
Peter Scull 1 2
Berhanu Abraha Tsegay 1 2
0 Department of Biology, Colgate University , Hamilton, NY , United States of America, 2 Department of Biology, University of Puget Sound, Puget Sound, WA, United States of America, 3 Department of Biology, Bahir Dar University , Bahir Dar , Ethiopia , 4 Department of Geography, Colgate University , Hamilton, NY , United States of America
1 Editor: Ben Bond-Lamberty, Pacific Northwest National Laboratory , UNITED STATES
2 Funding: The Dynamics of Coupled Natural Human Ecosystems Program of the National Science Foundation funded this research: https://
Land-use change can have profound effects on forest communities, compromising seedling recruitment and growth, and long-term persistence of forests on the landscape. Continued forest conversion to agriculture causes forest fragmentation which decreases forest size, increases edge effects and forest isolation, all of which negatively impact forest health. These fragmentation effects are magnified by human use of forests, which can compromise the continued persistence of species in these forests and the ability of the forests to support the communities that depend on them. We examined the extent and influence of human disturbance (e.g. weedy taxa, native and exotic tree plantations, clearings, buildings) on the ecological status of sacred church forests in the northern highlands of South Gondar, Ethiopia and hypothesized that disturbance would have a negative effect. We found that disturbance was high across all forests (56%) and was negatively associated with tree species richness, density, and biomass and seedling richness and density. Contrary to expectation, we found that forests < 15.5 ha show no difference in disturbance level with distance from population center. Based on our findings, we recommend that local conservation strategies not only protect large forests, but also the small and highly used forests in South Gondar which are critical to the needs of local people, including preserving large trees for seed sources, removing exotic and weedy species from forests, and reducing clearings and trails within forests.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Isolation and degradation can be the silent demise of forests as towering canopy trees give the
impression of a healthy forest ecosystem, while understory species composition can be
dominated solely by pioneer species, completely void of seedlings from old growth species. This
phenomenon has been written about in numerous ways, most famously by Janzen [
characterized latent extinction as single, majestic, long-lived trees stranded in vast agrospace
or a forest of trees that can no longer reproduce, but survive as living dead. Deforestation and
degradation, still rampant in tropical regions [
], are not the only form of forest loss. The
relentless destruction of buffer zones around forests increases forest isolation and edge effects,
such as increased wind and decreased humidity [
], and can be devastating to overall forest
integrity and ecology as they can magnify the disturbance within the forest. Disturbances
within forests, for example grazing animals that trample seedlings and compact the soil, can
also lead to forest decline, through forces such as reduced species richness and density, both of
which compromise regeneration potential [
]. A recent metanalysis on forest isolation
and edge effects indicates that 70% of the world?s remaining forests are within 1000 m of the
edge, with 20% of those within 100 m of an edge .
Land use change (LUC) continues in tropical countries, with a conservative estimate from
the Food and Agricultural Organization of 8 million ha deforested annually from 2000?2010
]. The human influence on this is clear as 6 million ha of these forests were converted to
agricultural land [
]. Smaller scale human impacts on forests such as timber and non-timber
product harvesting [
], planting of exotic species (e.g. Eucalyptus; [
]), and live-stock grazing,
and clearings or gathering areas [
] can have pervasive impacts on forests. The myriad impacts
of LUC on the local, regional and global scales are well documented such as the loss of
], decreased carbon storage, varying weather patterns , increased fire
frequency and intensity [
], and loss of other ecosystem services [
]. Land use change also
impacts the communities that use forest resources; as resources diminish, cultural traditions
can be compromised or lost . These effects can be felt more acutely in regions that rely on
the land and are socioeconomically disadvantaged.
Forest size, the degree of disturbance, the presence of roads and distance to population
center can also contribute to forest degradation. In tropical regions, roads are cited as the ?first of
a hundred cuts? that degrade intact forests, as they allow the initial penetration of the forests,
which is quickly followed by increased population density, logging, and minor road
]. As such, distance to population center can be used as a proxy for LUC; regions void
of significant road development are often characterized by more intact forest [
forests, fragments and patches, are well-studied and known to have strong abiotic and biotic
responses to decreasing forest size. Edge effects increase temperature, light, wind, and
disturbance, while decreasing humidity. These effects permeate up to 300 m into the forest  and
have been associated with negative effects on taxon abundance, diversity, carbon storage, and
ecosystem services in general .
While landscapes characterized by large, intact forests are best suited to sustain high levels
of biodiversity and provide a constant supply of multiple ecosystem services [
15, 24, 25
landscapes have been so heavily transformed that a mosaic of small forest patches is all that
remains to serve as an ecosystem refuge. These areas cannot immediately transition back to
large intact, mature forests and, thus, the overall health of the forest mosaic is critical to avoid
further declines in biodiversity. This is seen acutely in northern Ethiopia where the last
remaining forests are small patches that average 5 ha in size [26, 27]. However, while small in
size, in South Gondar alone (14,607 km2) there are 1022 of these forests that span elevations
and biomes making up ~ 5500 ha of tree cover (Scull, unpublished data). These forests have a
church at their center and are considered critical in protecting the sacredness of the church
and as such their association with the church protects them . This protection due to
sacredness is often referred to as shadow conservation [27, 29]. These church forests in
northern Ethiopia have shown remarkable persistence; 99% of forests have survived the past
halfcentury, with no forest found without a church . However, the density of scattered trees
and bushlands that surround these forests has declined over the past 80 y, which amplifies
forest isolation and edge effects [
]. As a result of declining woody biomass outside of the forests,
the demand on the forest for both material and non-material use has likely increased, which
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could compromise the integrity and persistence of these forests on the landscape. Previous
work in the region has found that over a 50 y time span, crown closure declined significantly
and 37% of the total forest area was characterized by some form of disturbance .
This study principally aimed to determine the impacts of human disturbance (e.g. human
structures, planted taxa, weedy taxa) on church forest integrity and regeneration potential. In
addition, we examined the factors of forest size, elevation, distance to population center, and
the presence of an exterior wall on species richness, density (ha-1), and biomass (ha-1) of
standing live trees, as well as the richness and density of tree seedlings in 44 church forests across
South Gondar, Ethiopia. Previous research indicates that the presence of a wall, established for
various reasons including demarcating land and blocking human and animal access, can have
a protective effect on forests as their presence increased seedling richness and density, but did
not affect tree species richness or density [
]. As such, we include the presence of walls in our
analysis of seedling richness. We hypothesized that human disturbance would negatively affect
tree species richness, density, biomass and seedling regeneration and have a greater impact in
smaller forests that were closer to a population center. This research is part of a long-term
study on the factors that contribute to the effective management of church forests in Ethiopia.
Materials and methods
Study area and site selection
We established long-term research sites in 44 church forests in the tropical, seasonally dry
montane region of South Gondar in northern Ethiopia. The average annual rainfall is 700?800
mm with most falling June?August (Nyssen et. al. 2005). The distribution and abundance of
the church forests in the region are detailed in another paper . In brief, there are ~1022
church forests in South Gondar, with no forest detected without a church. The forests are
scattered throughout the landscape separated by approximately 2.10 km (? 0.03) ha and are small
on average, 5.42 (? 0.34; range 0.02?148.86) ha  (Figs 1 & 2). To access church forests, we
secured permission from the office of Abune Aregawi, Bishop of South Gondar, which gave us
permission letters for entry to each church forest.
These forests are sacred as they surround a Christian Orthodox Tewahido Church [26, 28,
30]. The church itself is usually in the center of the forest within a walled clearing (Fig 3).
These church forests are active with religious services and events throughout the week .
Along the edges of the forests are mahabirs, or gathering areas, which are maintained open
spaces that are used for meetings and other events . These mahabirs along with trails,
graves, and small huts contribute to the constant human presence within forests, which could
influence the integrity of the forest. In addition, often along the edges there are plantings of
both native and exotic taxa . Sometimes these forests have a wall surrounding the
perimeter of the forest that is made with local rocks; these walls all vary in height, age, and intactness.
The church forests of Ethiopia span elevations and biomes, with montane region (1800?
2050 m a.s.l.) characterized by evergreen broadleaf taxa Prunus (Rubiaceae) and Mimusops
(Sapotaceae) and the upper montane region (2400?2700 m a.s.l) characterized by Juniperus
(Cupressaceae) and Euphorbia (Euphorbiaceae) . To determine the effects of disturbance,
forest size, distance to population center, elevation, and the presence of a wall on forest status,
we selected 44 forests that ranged in size between 1.4?15.4 ha, both above and below the mean
size, but still representative (Table 1). Distance was categorized as either near (< 50 km) or far
(> 50 km) from two cities, Bahir Dar (population 243,330) for montane church forests or
Debre Tabor (population 87,100) for upper montane church forests . Sample church forest
number is not uniform for all categories, however; we have at least four forests within each
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Fig 1. Map of study area in the South Gondar region of northern Ethiopia. Description: Church forests are
scattered in the landscape and are separated by ~ 2 km with a matrix of agricultural land separating them. Named areas
are Woredas or Districts . Basemap images obtained form ESRI.
category. Forest properties assessed were: human disturbance, rarefied species richness, tree
density, and biomass ha-1; and seedling richness and density.
Transect Methods: Disturbance, species richness & density, biomass
Modified Gentry transects [27, 32] were established in each forest at three cardinal directions
(0?, 120?, and 240?) from the church center to the edge of the forest (Fig 3). Each transect was
Fig 2. Average size of church forests in the region is small, 5.42 (+/- 0.34 ha). There are 1022 church forests in South
Gondar, Ethiopia, an area of 14,059 km2. Forest range from <1?148.7 ha, 93% of these forests are < 15 ha .
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Fig 3. Transect design for the quantification of plant species richness, density, and biomass in 44 church forests in
northern Ethiopia. Modified Gentry transects were established in each forest at three cardinal directions (0?, 120?, and
240?) from the church center out towards the edge of the forest. Each transect was 2 m wide and the length depended on
the size of the forest. Within each transect every stem > 1 cm was measured and identified as well as any type of
2 m wide and the length depended on the size of the forest. Along each transect, all woody
species greater than 1 cm were identified, measured for diameter at breast height (dbh), and
recorded. Biomass of trees was calculated using the same allometric relationship because
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species-specific functions were not available (Eq 1).
Native taxa were noted along each transect in addition to the type and location of any form
of disturbance across four categories (Table 2). While our aim was to note disturbance, both
natural (e.g. gaps, tree falls) and human (e.g. clearings), we quickly discovered that there was
little to no natural disturbance and we were documenting human disturbance. The percent of
native taxa and each disturbance type along the transect was calculated (Eq 2).
area of human disturbance type
area of transect
Type of Human
Along each transect at three points (in the center, 10 m from the outer edge, and 10 m from
the internal wall around the church), we measured seedling richness and density in 1 m2
quadrats for a total of 3 seedling plots per transect and 9 seedling plots per site.
We used Model 1 Fixed Effects Analysis of Variance (ANOVA) to determine if size, distance to
population center, elevation, and the presence of a wall were significantly associated with each of
our dependent variables, namely: tree species richness, trees species density, tree biomass, seedling
density, seedling richness, and disturbance . We used regressions to determine if there were
causative linear relationships between our independent and dependent variables. Because
disturbance was pervasive across sites, we also examined the association of disturbance with the
dependent variables in ANOVA and Regression models. Normality of model residuals for both
regression and ANOVA were tested using the Shapiro-Wilk Normality Test, and all models
presented conform to normality assumptions for ANOVA and Regression analysis (p > 0.05).
To compare tree species richness among church forests, we used rarefied species richness to
control for the variation in the number of individual trees found among our sites. We used the
rarefy function in the vegan package (v. 2.5?3, ) in R (v. 2.51, ) to generate rarefied tree
Across 44 church forests, we identified and measured 11,310 trees > 1 cm and identified 139
species (excluding unknowns) in 105 genera and 69 families and found an average species
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richness, excluding exotic and planted taxa, of 10.8 (? 0.5). The most species rich plant families
were: Fabaceae, Asteraceae, Rubiaceae, Celastraceae, Euphorbiaceae, Lamiaceae and Malvaceae.
Human disturbance was pervasive across sites, with an average total disturbance of 56.2% (?
3.2; Fig 4). When broken down by disturbance types, human-induced disturbance due to
buildings and clearings was significantly higher than human disturbance due to the
introduction of weeds and the planting of exotic or native species (ANOVA: F3,180 = 33.02, p < 0.001;
Fig 4). We found that disturbance was not significantly associated with forest size, distance
to population center, elevation, or the presence of a wall (ANOVA: F4,39 = 1.888, p = 1.34).
However, disturbance had a weak but significant, negative linear relationship with forest area
(F1,42 = 4.32, R2 = 0.10, p = 0.047).
Species richness. We found that species richness was significantly associated with forest
size and disturbance, but not elevation, distance to population center or the presence of a wall
(Table 3). Species richness had a significant, negative relationship with disturbance across all
sites (Fig 5).
Density. Tree density (ha-1) was significantly associated with forest size, disturbance, and
elevation, but was not associated with distance to population center or the presence of a wall
(Table 3). Tree density (ha-1) was significantly higher in the montane region (65.5 ? 9.2) than
the upper montane region (40.03 ? 4.45; t = 2.52, p = 0.017). While disturbance did not vary
significantly between elevations (t = 1.26, p = 0.214), tree density in montane forests did not
vary with disturbance whereas upper montane forest tree density varied significantly with
disturbance (Fig 6).
Biomass. Disturbance was the only factor that significantly explained biomass (ha-1) in
the full ANOVA model (Table 3). As with other variables, there was a significant, negative
relationship of biomass with disturbance (F1,42 = 19.72, R2 = 0.30, p < 0.001).
Seedlings. Seedling density (2.1 ? 0.33) and richness (0.66 ? 0.09) were low across all sites.
We found that there was a significant effect of a wall, forest size, and a significant wall size
interaction on seedling richness (Model: F3,40 = 5.35, p = 0.034; wall F1 = 7.15, p = 0.018; forest
size: F1 = 5.01, p = 0.031; wall size, F1 = 5.66, p = 0.022) and a marginally significant effect of
wall and wall size interation, but no effect of forest size, on seedling density (Model: F3,40 =
3.06, p = 0.039; wall F1 = 3.82, p = 0.058; forest size: F1 = 2.27, p = 0.139; wall size, F1 = 3.99,
p = 0.052). In church forests with a wall, we found a significant positive relationship between
seedling richness and density with forest size (seedling richness: F1,20 = 9.98, R2 = 0.30,
p = 0.005; seedling density: F1,20 = 5.35, R2 = 0.17, p = 0.032), but no significant effect of either
without a wall (F1,20 = 0.01, R2 = 0.05, p = 0.920; F1,20 = 0.12, R2 = 0.04, p = 0.714).
Our research on 44 sacred Ethiopian church forests across elevations and distances from
population center indicate that more than half of the forest area showed human disturbance, which
was the key factor, followed by size, influencing species richness, biomass (ha-1) and density
(ha-1) of species. The forest clearings are important for human gatherings and other activities
, however; this use can further increase disturbance and decreases the opportunity for
seedling establishment and regrowth. The dominance of weedy species is also problematic for
forest regeneration as weedy species, such as Justica and Acanthus (Acanthaceae), have been
shown to outcompete tree species hindering regeneration [36, 37].
When a disturbance occurs in a small forest every disturbance becomes a higher percentage
of the whole. Small forests are more susceptible to edge effects and tree mortality than larger
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Fig 4. Human disturbance is pervasive across church forests. A. Box-and-whiskers plots of percent no disturbance
and human disturbance across 44 church forests in northern Ethiopia. Asterisk indicates significant difference using a
student?s t-test (t = 3.18, p = 0.002). B. Human disturbance types across church forests. Box-and-whisker plots of
disturbance types in church forests. Lower case letters indicate significant differences among categories using a Tukey
HSD, p < 0.05. The majority of disturbance in church forests is from direct human impacts followed by the
proliferation of weedy species.
forests and these effects can have a large, negative impact on their resilience and long-term
persistence [38, 39]. With increasing disturbance, species richness, biomass (ha-1) and tree
density (ha-1) decreased significantly and this was exacerbated by decreasing forest size. In a
survey of 78 church forests in the northern highlands of Ethiopia, the average size was even
smaller than found in our study (~2 ha, [40, 41]), and they found that their forests had > 50%
of the tree species richness found in tropical northeastern Africa. In tropical lowland forests in
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Church forest disturbance and size were the factors that were most strongly associated with species richness (ha-1), density (ha-1), and biomass (ha-1).
central Amazonia, rates of mortality of large canopy trees (dbh > 60 cm) were significantly
higher in edges (up to 300 m) than in interior forest (> 300 m into the forest) (Laurance et al.
2000). Thus, in small church forests where edge effects likely influence the entire forest, large
canopy trees, which are often the seed sources for forest regeneration, are compromised.
Tree density (ha-1) was the only variable influenced by elevation, with upper montane forest
density decreasing with increasing disturbance while montane forest density did not vary
significantly (Fig 5). The montane church forests had more variable disturbance than the upper
montane forest which may reflect differential use by local people. These differences may also
reflect the different plant life zones within each elevation, as the montane forests are
represented by more dense evergreen broadleaf plant taxa such as Teclea (Rutaceae) and Mimusops
(Sapotaceae), whereas the upper montane region has more sparcely dispersed taxa such as
Juniperus (Cupressaceae) and Euphorbia (Euphorbiaceae).
Consistent with previous research, the presence of a wall had a significant effect on seedling
number and richness across sites [
], however; the differences in these numbers was small.
These findings suggest that while a wall may have a positive influence on seedling
communities, the regeneration potential of these forests is compromised by the magnified effects of
Fig 5. Species richness decreases significantly with increasing percent disturbance. The relationship between tree
species richness and percent forest disturbance in 44 church forests in northern Ethiopia.
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Fig 6. Tree density decreases with increasing percent disturbance in upper montane forests. Description: Tree
density (ha-1) decreased significantly with increasing percent disturbance in the upper montane forest sites, however;
density did not vary significantly with disturbance in the montane sites.
disturbances on the adult trees in these small forests. Lower species richness could reduce the
ability of these forests to recover from disturbance and lower density could compromise the
cultural services provided by the forest to the community, such as shade and cover for the
Our data do not support research indicating that increasing isolation, as measured by
distance from population centers, is associated with decreased human disturbance . In fact,
our data indicate that forests < 15.5 ha show no difference in disturbance with distance. One
reason for the lack of difference between forests close to population centers vs. those > 50 km
from a population center may be related to the high rural population in Ethiopia, 80% ,
that may be reliant on forests for their basic needs (e.g. firewood, honey, etc.) compared to
their city-dwelling counterparts. Thus, demand may be similar in both areas, in the city
because of high population numbers and in the rural areas because of need. It could also be
that urban timber needs are being met by Eucalyptus, which is more readily available in church
forests near population centers .
While these church forests have exhibited remarkable persistence over the last 50?80 years,
on average only 0.42 ha smaller 50 years ago [
], recent work on the matrix between forests
shows that the buffer, shrubs and trees, around forests has decreased significantly [
]. The loss
of a buffer increases edge effects, such as lower relative humidity, higher temperatures and
higher winds  and increases mortality rates of seedlings [
]. These church forests are at
risk of being Janzen?s [
] ecologically ?living dead? (i.e., forests that last only until the large
trees die as they do not have any regeneration) due to their increasing isolation combined with
high disturbance and low seedling recruitment [
6, 45, 46
While seemingly stagnant in recruitment of seedlings and high disturbance, these forests
are alive with human activity as they are gathering areas for meetings, worship, and schooling
for the local people [27, 28, 47]. Conservation initiatives usually prioritize biodiversity and
ecosystem function and not human use, however; if this approach is taken in South Gondar, few
forests would be protected as there are very few large forests, most notably there are only 9
forests > 50 ha (Fig 2), which is why we focused our study on forests that were the average
size. In fact, in the 14,059 km2 area of our study, there are 1022 forests with 93% of them < 15
10 / 14
ha (Fig 2; ). Unfortunately, continued deforestation around the world is increasing forest
fragmentation, increasing their proximity to edges [
], and highlighting the need for
conservation efforts directed toward forest fragments.
These church forests, even when small, are important refugia for trees and biodiversity in
general [41, 48], however; their continued persistence on the landscape is threatened without
active conservation efforts [
]. We recommend that conservation priorities not only protect
large forests, but also the small and highly used forests which are critical areas for local people.
Previous research and local initiatives have found that building a wall increases seedling
species richness and density, likely because it not only reduces access to the forest by grazing
cattle, but also because it directs people to use the trails rather than randomly entering and
walking through the forest [
]. However, as our findings and those of others show [40, 41],
seedling recruitment and diversity with walls is still not high and most species are not
represented . Thus, walls alone are not enough and solutions that protect and enhance forest
regeneration potential while also preserving cultural needs, such as active planting programs
both inside and between the forests, the removal of exotic and weedy species, discouraging the
creation of new paths and clearings, and maintaining large trees as they are important seed
sources, must be implemented. The interdependence between the forest and the church
community make conservation efforts essential.
S1 Appendix. Data on 44 sacred church forest study sites. Data on sacred church forests
include: Woreda, Kebele, size, distance to population center, elevation, the presence of a wall,
tree species richness, trees species density, tree biomass, seedling density, seedling richness,
and % of disturbance types.
We acknowledge the students of the Cardelu?s lab and Scull lab at Colgate University, the
Woods lab at the University of Puget Sound, and the Tsegay lab at the University of Bahir Dar,
Ethiopia, for their contributions to collection of field data in Ethiopia. We are also grateful to
the respected Ethiopian priests and monks for allowing us access to their sacred church
Conceptualization: Catherine L. Cardelu?s, Carrie L. Woods, Peter Scull.
Data curation: Catherine L. Cardelu?s, Carrie L. Woods, Amare Bitew Mekonnen, Sonya
Formal analysis: Catherine L. Cardelu?s, Carrie L. Woods, Sonya Dexter.
Funding acquisition: Catherine L. Cardelu?s, Carrie L. Woods, Peter Scull.
Investigation: Catherine L. Cardelu?s, Carrie L. Woods, Amare Bitew Mekonnen, Peter Scull.
Methodology: Catherine L. Cardelu?s, Carrie L. Woods, Peter Scull.
Project administration: Catherine L. Cardelu?s, Berhanu Abraha Tsegay.
Resources: Catherine L. Cardelu?s.
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Supervision: Catherine L. Cardelu?s, Carrie L. Woods, Amare Bitew Mekonnen, Berhanu
Visualization: Catherine L. Cardelu?s, Peter Scull.
Writing ? original draft: Catherine L. Cardelu?s, Sonya Dexter.
Writing ? review & editing: Catherine L. Cardelu?s, Carrie L. Woods, Amare Bitew
Mekonnen, Sonya Dexter, Peter Scull, Berhanu Abraha Tsegay.
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