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Publications - Dendroecology
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Bruno
Vila, Frank Torre, Fréderic Guibal, Jean-Louis Martin, 2005, Can we reconstruct deer browsing history and
how? Lessons from Gaultheria shallon Pursh, Ann. For. Sci. 62
(2005) 153–162 – PDF
Abstract: We
identified and analysed browsing signatures left by Sitka black-tailed deer (Odocoileus hemionus sitkensis) on Salal (Gaultheria shallon) to reconstruct deer browsing history. Radial
growth analyses showed negative abrupt growth changes on islands with deer
probably linked to defoliation. Deer browsing pressure was best assessed by the
incidence of morphological changes caused by browsing in section form, lobes,
pith form, pith position or the presence of decaying wood and by changes in
stem age structures. Salal stems were twice older (30 years) on islands with
deer than on islands without deer (16 years). On islands with deer deficit of
stems in the youngest age classes suggested that deer impact has been strong on
these shrubs for at least 20 years in the northern sites and for about 10 years
in the southern ones.
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Bruno
Vila, Frank Torre, Fréderic Guibal, Jean-Louis Martin, 2004, Can we reconstruct browsing history and how far
back? Lessons from Vaccinium parvifolium Smith in Rees, Forest Ecology and Management 201 (2004)
171–185 – PDF
Abstract: We assessed
the impact of browsing by black-tailed deer (Odocoileus hemionus sitkensis) on a common long-lived shrub (the red huckleberry, Vaccinium parvifolium) on Haida Gwaii (British Columbia, Canada). We studied how deer impact can be
used as a marker of deer abundance and fluctuation and a means to reconstruct
the recent history of deer browsing over a significant section of the
archipelago. We compared islands with and without deer to understand
processes involved in these changes. We compared shrub features such as number
of stems and regenerating sprouts, age and height of stems and stem age-structures
between deer-free and deer-affected islands and analysed their spatial and
temporal variation. Deer, by
browsing
regenerating sprouts, stopped stem replacement. On deer-affected islands the number
of stems per individual shrub was 2–4 times lower than on deer-free islands. The
number of regenerating sprouts was 8–15 times higher. Stems were, on average, 2–3
times older. There was no variation in these characteristics among deer-free
islands. They varied both spatially and temporally among deer-affected islands
revealing spatial and temporal variation in deer impact. Deer impact has been prevalent
for at least 40–50 years before this study in all sites with deer but one. In
the latter, the most distant from the point of introduction, severe impact
seemed to date to less than 10 years before this study. On Reef Island, Ramsay Island and Burnaby Island, deer impact was prevalent 10–20
years earlier than on Louise and Haswell Islands, although the two latter were much closer and
more easily accessible from the point of introduction. Using independent information,
we interpreted this pattern as the result of differences in climate and habitat
rather than of a delay in colonisation. Effects of isolation on dispersal,
pattern of land use or access to alpine summer range are all likely to affect
delay between colonisation and severe impact.
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Bruno
Vila, Frank Torre, Fréderic Guibal, Jean-Louis Martin, 2004, Assessing spatial variation in browsing history
by means of fraying scars, Journal of Biogeography (J. biogeogr.) (2004) 31,
987–995 – PDF
Abstract:
Methods
We searched
for sites where trees with fraying scars were clustered. We studied the trees
that deer selected (species, size) and the characteristics of scars (number,
position, size). Using a cross-dating procedure, we dated fraying scars with
dendrochronology, obtaining an accurate estimate of the year the scar was formed.
Results
On Reef Island, Thuja plicata was
the tree species chosen for fraying. On South-Skedans Island, where Thuja plicata is
missing, deer chose Salix sp. And Alnus rubra.
Deer chose only trees with a circumference of less than 50 cm. About two to
three fraying scars were recorded per tree. All of them extended between 30–40
and 70–80 cm from the ground and were between 5 and 6 cm in width. On Reef Island, 95% of the scars were formed
during the last 50 years. On South-Skedans Island, 95% were formed over the last 10
years. Age distribution of scars showed a constant increase of the number of
scars over time. It indicated that deer had colonized Reef Island 53 years prior to this study but
were absent or rare on South-Skedans Island until 13 years prior to this study.
Main conclusions
These
results indicate different colonization dates and thus different length of
browsing histories for the islands studied and provide the historical
background necessary to analyse the involvement of deer in the current differences
in the flora and fauna observed between islands.
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Bruno Vila, Frank Torre, Fréderic Guibal, Jean-Louis
Martin, 2003,
Growth
change of young Picea sitchensis in response to deer browsing, Forest Ecology and Management 180 (2003) 413–424 – PDF
Abstract: Taking
advantage of the introduction of the black-tailed deer to the Queen Charlotte Islands (British Columbia, Canada), we used dendrochronological
analyses to understand the consequences of deer browsing on Sitka spruce growth. We compared shape,
radial growth, height growth and age of young spruce in three sites.We
identified two types of trees growing side by side: (1) stunted and heavily
browsed spruce, smaller than the browsing limit and (2) escaped spruce that
were taller than the browsing limit but still browsed in their lower part. The
compact and heavily ramified shape in stunted spruce was the result of repeated
and intense browsing. In escaped spruce this was also the case below the
browsing limit (1:16m _ 0:07 m), in sharp contrast with the normal shape that escaped spruce
resumed above the browsing limit. We show that the release of browsing
pressure, once the tree reaches the browsing limit, is characterised by an
abrupt increase in radial growth. Before release, trees show a growth stagnation
characterized by narrow rings (0.5 mm per year) and small annual height
increments (<5 cm per year). After release, trees show a growth
stabilisation characterised by wider rings (3 mm per year) and larger annual
height increments (20 cm per year). We use this pattern to estimate frequency
and age at release and their possible variation over time. Age differences
between stunted and escaped spruce are highly significant and indicate that,
despite of browsing, most if not all trees will ultimately reach the browsing
limit and escape. Heavy deer pressure (30 deer per km2) delays spruce sapling recruitment by about 8
years. This delay varies in relation to site quality and seems to have
increased over time, suggesting an increase in browsing pressure.
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Bruno
Vila, Franck Torre, Jean-Louis Martin, Frédéric Guibal, 2003, Response of young Tsuga
heterophylla to deer browsing: developing tools to assess deer impact on forest
dynamics, Trees (2003) 17:547–553 – PDF
Abstract: We used
dendroecology to describe and understand the consequences of deer browsing on
regenerating western hemlock (Tsuga heterophylla). We compared tree shape, growth
rate, height and age at four different sites in Haida Gwaii (British Columbia, Canada) that had trees
representative
of the range of deer impact on trees: (1) trees showing no sign of browsing,
(2) escaped trees which were still browsed below the browse line and (3) stunted
and heavily browsed trees. Repeated and intense browsing resulted in the small
size, compact heavily
ramified
shape of stunted trees and in the short compact and ramified lower branches of
escaped trees. These contrasted with the shape of non-browsed trees, a shape that
was also found in escaped trees above the browse line. Before release, all
browsed trees experienced stagnation in growth characterised by narrow rings (0.3
mm/year) and a small annual height increment (2.5 cm/year). At release, growth
rate increased and stabilised: rings were wider (1.3 mm/year) and annual height
increments were greater (10.5 cm/year). Nonbrowsed
trees had a
mean ring-width of 1.3 mm/year and an annual height increment of 22 cm/year. Delay
in tree recruitment caused by deer varied from site to site. It had been about
15 years for the escaped trees and is estimated at 30–40 years for the stunted
trees. Spatial variation in
deer impact
may reflect spatial variation of browsing pressure resulting from local
differences in the availability of preferred forage or to differences in tree
chemical defences/nutritional values.
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Bruno Vila, Fréderic Guibal, 2001, Assessing browsing influence in
forest understory using dendrochronology on Haida Gwaii archipelago (British Columbia,
Canada), Dendrochronologia 19 (1) - 2001: 139 –
151 – PDF
Abstract: The impact
of introduced deer (Odocoileus hemionus
sitchensis) on
understory vegetation is assessed by analyzing browsed and non browsed
individuals of a shrub (Gaultheria shallon) and a tree species (Picea sitchensis). Browsing is expressed in terms of morphology
change, diameter growth patterns differences and traumatic anatomical
characteristics occurrence on cross-sections.
At the
impacted site, an upper browsing limit at a height of 1.10 m is evidenced. Abrupt
growth change associated with scars are evidenced on shrubs but deer impact on
shrub growth is not directly assessed because of high inter-shrub variance among
ring-width series. Deer impact can be assessed taking into account particular
anatomical features as pith position, pith and stem form, wedging rings and
scar occurrence for which impacted and non impacted populations differ statistically.
Samples from the impacted population display non circular cross-sections with
altered wood areas, eccentric piths and several discontinuous or wedging rings.
As regards
with spruce, browsing pressure decreases apical growth and induces at severely
browsed individuals a shrubby port. Narrow ring patterns are caused by
browsing; these patterns are followed by a sudden growth change occurring when herbivore
pressure stops. That involves a lengthening of the recruitment period in
windthrows which results in a delay of the habitat closing processes.
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Bruno Vila, Thierry Keller, Frédéric Guibal, 2001, Influence of
browsing cessation on Picea sitchensis radial growth, Ann. For. Sci. 58 (2001) 853–859 – PDF
Abstract:
Picea sitchensis is an ecological and economical component of North
America north temperate rain forest. In Haida Gwaii which is one of the
most productive forest land of British Columbia archipelago (Canada),
it is an important and a valuable commercial species. The present study
aims at precising deer browsing consequences on growth regeneration of
Picea sitchensis. Using ring-width series, an empirical model is built
which describes browsing impact on radial growth and removal of these
pressure. Taking into account deer pressure and browsing upper limit
when building predictive height growth models proves valuable for
comparing growth pattern of different species under browsing pressure
and deducing changes in forest dynamics.
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