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Global Decline in Large Old Trees

Authors:
David Lindenmayer at Australian National University
David Lindenmayer
William F. Laurance at James Cook University Brisbane
William F. Laurance
Jerry F. Franklin at University of Washington
Jerry F. Franklin
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Abstract

The loss of large old trees in many ecosystems around the world poses a threat to ecosystem integrity.
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DOI: 10.1126/science.1231070
, 1305 (2012);338 Science et al.David B. Lindenmayer
Global Decline in Large Old Trees
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PERSPECTIVES
Large old trees are among the biggest
organisms on Earth. They are keystone
structures in forests, woodlands, savan-
nas, agricultural landscapes, and urban areas,
playing unique ecological roles not provided
by younger, smaller trees. However, popula-
tions of large old trees are rapidly declining in
many parts of the world, with serious implica-
tions for ecosystem integrity and biodiversity.
The definition of “large and old” trees
depends on the ecosystem, tree species, and
environmental conditions under consid-
eration. Both the size and the age of a tree
affect characteristics such as the large inter-
nal cavities, complex branching patterns,
and idiosyncratic canopy architectures that
distinguish large old trees from younger and
smaller trees ( 1).
Large old trees (see the fi gure, panels A to
C) play critical ecological roles. They provide
nesting or sheltering cavities for up to 30%
of all vertebrate species in some ecosystems
( 2). Large old trees also store large quantities
of carbon, create distinct microenvironments
characterized by high levels of soil nutri-
ents and plant species richness, play crucial
roles in local hydrological regimes, and pro-
vide abundant food for numerous animals in
the form of fruits, fl owers, foliage, and nec-
tar. In agricultural landscapes, large old trees
can be focal points for vegetation restoration,
facilitate ecosystem connectivity by attracting
mobile seed dispersers and pollinators, and
act as stepping stones for many animals.
Younger and smaller trees cannot provide
most of the distinctive ecological roles played
by large old trees ( 3). For instance, large old
trees in Mountain Ash (Eucalyptus regnans)
forests of mainland Australia provide irre-
placeable shelter and nesting sites for more
Global Decline in Large Old Trees
ECOLOGY
David B. Lindenmayer,
1
William F. Laurance ,2 Jerry F. Franklin
3
The loss of large old trees in many ecosystems
around the world poses a threat to ecosystem
integrity.
1Fenner School of Environment and Society, The Austra-
lian National University, Canberra, ACT 0200, Australia.
2Centre for Tropical Environmental and Sustainability Sci-
ence, and School of Marine and Tropical Biology, James
Cook University, Cairns, Queensland 4878, Australia.
3School of Environmental and Forest Science, University
of Washington, Seattle, WA 98195, USA. E-mail: david.
lindenmayer@anu.edu.au
cal regions of the world, but is rare in large
areas of central and western Africa where
many individuals lack Duffy-antigen recep-
tor expression on red blood cells. Thus, this
“Duffy-negative” phenotype appears to have
evolved as an innate resistance mechanism to
P. vivax infection.
McMorran et al. extend previous work that
demonstrated an important role for platelets in
resistance to malaria ( 8) by identifying plate-
let factor 4 (PF4) as a key molecule in plate-
let-mediated killing of P. falciparum. PF4 is
released from α granules in activated plate-
lets to promote blood coagulation ( 9). It binds
the Duffy-antigen receptor, along with sev-
eral other chemokines ( 10). McMorran et al.
found that a functional Duffy-antigen receptor
is required for the antiparasitic activity of PF4.
The implications of lacking this antipara-
sitic mechanism for Duffy-negative individ-
uals living in P. falciparum malaria endemic
regions are not yet clear. One might predict
that these individuals will be more prone to
episodes of severe malaria. Indeed, mortality
among African children with malaria-induced
coma is higher than in children with the same
condition from Papua New Guinea, where
Duffy-negative individuals are less common
( 11). However, further evidence is required
to support this proposition. Alternatively,
compensatory antiparasitic mechanisms may
have evolved in Duffy-negative individuals
to help control parasite growth and/or reduce
pathology following infection. The identifi ca-
tion of other such mechanisms will offer fur-
ther insights into innate immune responses to
infection, and potentially identify vulnerable
aspects of parasite biology.
Platelets decrease in number (thrombocy-
topenia) during acute malaria. McMorran et
al. suggest that this is not to the host’s advan-
tage, limiting this innate form of resistance.
However, other data show that platelets can
contribute to cerebral malaria, a major cause
of mortality. Platelets at normal physiologi-
cal concentrations cause clumping of para-
sitized red blood cells from African chil-
dren, a phenomenon associated with cerebral
malaria ( 12). Thrombocytopenia may there-
fore reduce pathology by protecting the host
against cerebral malaria, which may explain
in part why there has been less pressure to
maintain platelet-associated parasite killing
mechanisms in Africans. The Duffy-negative
phenotype to prevent P. vivax invasion of red
blood cells seems to have been under stron-
ger selective pressure than the maintenance
of a PF4-dependent antiparasitic mechanism
in central and western Africa. However, given
the potentially different origins and timelines
of P. falciparum and P. vivax adaptations to
humans ( 13, 14), another possibility is that
the Duffy-negative phenotype has simply
been under selective pressure in this part of
Africa for longer. In addition, nonmalaria
pressures may also have infl uenced this selec-
tion over time.
Cells of the innate immune system—mac-
rophages, natural killer cells, dendritic cells,
and γδ T cells—play an important role in
defending against parasites, often providing a
fi rst line of defense and augmenting acquired
(adaptive) immunity. By understanding how
innate mechanisms of protection against
malaria have been under strong selective pres-
sure during evolution, we may better under-
stand how to protect people from malaria. For
example, how PF4 kills P. falciparum is not
yet clear, but when this knowledge is avail-
able, vulnerable features of parasites will be
identifi ed that could be targeted with appro-
priate drugs. Understanding new antiparasitic
mechanisms selected by evolution will enable
us not only to complement existing cellular
and molecular approaches to identifying drug
targets to kill parasites, but also to select safer
targets that have less effect on the host.
References
1. World Health Organization, “World Malaria Report” WHO
Press, Geneva, 2011.
2. B. McMorran et al., Science 338, 1348 (2008).
3. A. A. Escalante, F. J. Ayala, Proc. Natl. Acad. Sci. U.S.A. 92,
5793 (1995).
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6. J. D. Haynes et al., J. Exp. Med. 167, 1873 (1988).
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N. Engl. J. Med. 295, 302 (1976).
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14. R. Culleton, R. Carter, Int. J. Parasitol. 42, 1091 (2012).
15. D. I. Baruch et al., Blood 90, 3766 (1997).
10.1126/science.1232439
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7 DECEMBER 2012 VOL 338 SCIENCE www.sciencemag.org
1306
PERSPECTIVES
than 40 species of cavity-using vertebrates
( 4). For many dependent species, the keystone
roles of large old trees continue for decades
or even centuries after tree death, when they
become standing dead trees or large logs ( 1).
The loss of large old trees is a recognized
concern in many ecosystems worldwide.
For example, populations of large old trees
are plummeting in intensively grazed land-
scapes in California, Costa Rica, and Spain,
where such trees are predicted to disappear
within 90 to 180 years ( 5). In southeastern
Australia, millions of hectares of grazing
lands are projected to support less than 1.3%
of the historical densities of large old trees
within 50 to 100 years ( 6).
Large old trees are declining in forests at
all latitudes. Larger trees (>45 cm in diameter)
throughout southern Sweden have declined
from historical densities of ~19 per hectare
to 1 per hectare ( 7). In California’s Yosemite
National Park, the density of the largest trees
(see the figure, panel A) declined by 24%
between the 1930s and 1990s ( 8). Large old E.
regnans trees—Earth’s tallest fl owering plants
(see the figure, panel B)—are predicted to
decline from 5.1 in 1997 to 0.6 trees per hect-
are by 2070 ( 4). Fragmented Brazilian rain-
forests are likely to lose half of their original
large trees (≥60 cm diameter) in the fi rst three
decades after isolation ( 9).
Large old trees are exceptionally vulnera-
ble to intentional removal, elevated mortality,
reduced recruitment, or combinations of these
drivers (see the figure, panel C). They are
removed during logging, land clearing, agri-
cultural intensifi cation, fi re management, and
for human safety. Droughts, repeated wild-
fi res, competition with invasive plants, edge
effects, air pollution, disease, and insect attack
( 10) can all increase tree mortality. The likeli-
hood of new trees growing into large old trees
can be diminished by overgrazing or browsing
by native herbivores ( 11) and domestic live-
stock ( 6), by competition with exotic plants,
and by altered fi re regimes.
Drivers of large old tree loss often inter-
act to create ecosystem-specifi c threats ( 12).
In agricultural landscapes, chronic livestock
overgrazing, excessive nutrients from fertil-
izers, and deliberate removal for firewood
and land clearing combine to severely reduce
large old trees ( 6). Populations of large old
pines in the dry forests of western North
America declined dramatically in the last cen-
tury because of selective logging, uncharac-
teristically severe wildfi res, and other causes,
although efforts are now made to reduce the
density of the stands so that high-severity fi res
do not occur and large trees are saved (see the
fi gure, panel D). Salvage logging is equally
damaging, whereby natural disturbances,
such as fi re or insect attack, are followed by
removal of all remaining live and dead trees
(see the fi gure, panel E). In certain tropical
savannas and temperate forests, interactions
among drivers occur over vast areas and result
in entire landscapes supporting few large old
trees ( 13). Modeling suggests that even mod-
est increases in adult mortality can seriously
erode populations of long-lived organisms
such as large old trees ( 14).
Although large old trees are declining
across much of the planet, not all ecosystems
are losing such trees. Elevated plant-growth
rates in tropical forests, possibly in response
to rising concentrations of atmospheric car-
bon dioxide, might result in larger numbers
of large old trees, at least where such forests
escape other human disturbances.
Large old trees are more likely to per-
sist in particular parts of landscapes such
as disturbance refugia. Research is needed
to determine the locations and causes of
such refugia and to devise strategies to pro-
tect them ( 15). For example, timber or other
commodity extraction (e.g., cropping) in
managed landscapes might be concentrated
where large old trees are least likely to per-
sist or develop. Maintenance of appropriate
population age structures can help to ensure
the perpetual supply of large old trees. This
requires policies and management practices
that intentionally grow such trees and reduce
their mortality rates ( 5).
Just as large-bodied animals such as ele-
phants, tigers, and cetaceans have declined
drastically in many parts of the world, a grow-
ing body of evidence suggests that large old
trees could be equally imperiled. Targeted
research is needed to better understand their
key threats and devise strategies to counter
them. Without such initiatives, these iconic
organisms and the many species dependent on
them could be lost or greatly diminished.
References
1. R. van Pelt, Identifying Mature and Old Forests in Western
Washington (Washington State Department of Natural
Resources, Olympia, WA, 2007).
2. J. Remm, A. Lohmus, For. Ecol. Manage. 262, 579 (2011).
3. D. B. Lindenmayer, Forest Pattern and Ecological Process:
A Synthesis of 25 Years of Research (CSIRO Publishing,
Melbourne, 2009).
4. W. F. Laurance, New Sci. 213, 39 (2012).
5. P. Gibbons et al., Conserv. Biol. 22, 1309 (2008).
6. J. Fischer et al., Proc. Natl. Acad. Sci. U.S.A. 107, 19597
(2010).
7. M. T. Jönsson et al., J. Veg. Sci. 20, 91 (2009).
8. J. A. Lutz, J. W. van Wagtendonk, J. F. Franklin, For. Ecol.
Manage. 257, 2296 (2009).
9. W. F. Laurance et al., Nature 404, 836 (2000).
10. W. R. Anderegg et al., Nat. Climate Change, 10.1038/
nclimate1635 (2012).
11. A. T. Vanak et al., Ecography 35, 315 (2012).
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13. B. J. Palik et al., For. Ecol. Manage. 261, 128 (2011).
14. S. L. Lewis et al., Nature 457, 1003 (2009).
15. B. Mackey et al., Ecol. Appl. 22, 1852 (2012).
A B C
DE
Global decline. (A) Over 95% of California’s majestic coastal redwoods have been lost to logging and for-
est clearing ( 8). (B) Large old Mountain Ash (E. regnans) trees in mainland southern Australia are critical
habitats for many elements of the biota but are also readily killed and often consumed by wildfi res ( 4). (C)
Baobab trees, like this giant in Tanzania, are under threat from land clearing, droughts, fungal pathogens,
and overharvesting of their bark for mat-weaving ( 3). (D) Efforts to conserve large old Ponderosa Pine (Pinus
ponderosa) trees include reducing the risk of stand-replacing fi re by removing small trees and applying low-
severity prescribed fi re. (E) During post-insect attack salvage logging operations in British Columbia, Canada,
all large trees are removed.
10.1126/science.1231070
PHOTO CREDITS: (A) R. BUTLER; (B) W. INCOLL; (C) W. LAURANCE; (D) R. NOSS; (E) K. HODGES
Published by AAAS
on December 6, 2012www.sciencemag.orgDownloaded from
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Impacts of forest restoration on multifaceted bird diversity and community assembly in the Loess Plateau of China
Article
  • Oct 2024
  • FOREST ECOL MANAG
Restoring forests is crucial for safeguarding biodiversity and providing ecosystem functions on degraded lands globally. Despite significant restoration efforts over a half-century in the Loess Plateau of China ’s prominent dryland region, the impact of restored forests on biodiversity remains less understood. Unlike the abundant studies in the tropics, such understanding is urgently needed for dryland regions given that forest restoration is being scaled up. Here, we assessed the alpha- and beta-diversity of birds from taxonomic and functional dimensions in restored forests, and compared them to that of relatively undisturbed primary forests. We conducted rigorous point-count surveys and acoustic recordings during the avian breeding season in 2021 and 2023. We found that plantations have limited support for bird taxonomic and functional diversity compared to secondary and primary forests. Notably, the biodiversity inference drawn from our acoustic recordings generally supported similar conclusion of bird diversity across studied forest types. Additionally, secondary forests exhibited greater functional richness compared to plantations and contributed complementary functional trait space relative to primary forests. While nestedness dominated functional beta-diversity, spatial turnover dominated the taxonomic beta-diversity between the bird communities of restored forests and primary forests. Importantly, spatial proximity positively influenced the nestedness component of taxonomic beta-diversity, indicating that the distance of plantations to local primary forests (i.e., dispersal limitation) influenced bird community assembly during forest recovery. Overall, our findings provide insights on preserving intact primary forests, delivering biodiversity benefits of forest restoration in dryland regions, and prioritizing restoration locations only when tree planting is necessary.
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Consequences of widespread tree Mortality triggered by drought and temperature stress
Article
Full-text available
  • Sep 2012
Forests provide innumerable ecological, societal and climatological benefits, yet they are vulnerable to drought and temperature extremes. Climate-driven forest die-off from drought and heat stress has occurred around the world, is expected to increase with climate change and probably has distinct consequences from those of other forest disturbances. We examine the consequences of drought- and climate-driven widespread forest loss on ecological communities, ecosystem functions, ecosystem services and land–climate interactions. Furthermore, we highlight research gaps that warrant study. As the global climate continues to warm, understanding the implications of forest loss triggered by these events will be of increasing importance.
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Forest Pattern and Ecological Process: A Synthesis of 25 Years of Research
Book
  • Jan 2009
Forest Pattern and Ecological Process is a major synthesis of 25 years of intensive research about the montane ash forests of Victoria, which support the world's tallest flowering plants and several of Australia's most high profile threatened and/or endangered species. It draws together major insights based on over 170 published scientific papers and books, offering a previously unrecognised set of perspectives of how forests function. The book combines key strands of research on wildfires, biodiversity conservation, logging, conservation management, climate change and basic forest ecology and management. It is divided into seven sections: introduction and background; forest cover and the composition of the forest; the structure of the forest; animal occurrence; disturbance regimes; forest management; and overview and future directions. Illustrated with more than 200 photographs and line drawings, Forest Pattern and Ecological Process is an essential reference for forest researchers, resource managers, conservation and wildlife biologists, ornithologists and mammalogists, policy makers, as well as general readers with interests in wildlife and forests. 2010 Whitley Certificate of Commendation for Zoological Text.
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Receptor-like specificity of a Plasmodium knowlesi malarial protein that binds to Duffy antigen ligands on erythrocytes
Article
  • Jun 1988
A 135-kD parasite protein, a minor component of the Plasmodium knowlesi malaria radiolabeled proteins released into culture supernatant at the time of merozoite release and reinvasion, specifically bound to human erythrocytes that are invaded and carry a Duffy blood group determinant (Fya or Fyb), but did not bind to human erythrocytes that are not invaded and do not carry a Duffy determinant (FyFy). Specific anti-Duffy antibodies blocked the binding of the 135-kD protein to erythrocytes carrying that specific Duffy determinant. Purified 135-kD protein bound specifically to the 35-45-kD Duffy glycoprotein on a blot of electrophoretically separated membrane proteins from Fya and Fyb erythrocytes but not from FyFy erythrocytes. Binding of the 135-kD protein was consistently greater to Fyb than to Fya both on the blot and on intact erythrocytes. The 135-kD protein also bound to rhesus erythrocytes that are Fyb and are invaded, but not to rabbit or guinea pig erythrocytes that are Duffy-negative and are not invaded. Cleavage of the Duffy determinant by pretreating Fyb human erythrocytes with chymotrypsin greatly reduced both invasion and binding of the 135-kD protein, whereas pretreating Fyb erythrocytes with trypsin had little effect on the Duffy antigen, the 135-kD protein binding, or on invasion. However, instances of invasion of other enzyme-treated erythrocytes that are Duffy-negative and do not bind the 135-kD protein suggest that alternative pathways for invasion do exist.
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Landscape‐scale effects of herbivores on treefall in African savannas
Article
  • Nov 2012
Herbivores cause treefalls in African savannas, but rates are unknown at large scales required to forecast changes in biodiversity and ecosystem processes. We combined landscape‐scale herbivore exclosures with repeat airborne Light Detection and Ranging of 58 429 trees in Kruger National Park, South Africa, to assess sources of savanna treefall across nested gradients of climate, topography, and soil fertility. Elephants were revealed as the primary agent of treefall across widely varying savanna conditions, and a large‐scale ‘elephant trap’ predominantly removes maturing savanna trees in the 5–9 m height range. Treefall rates averaged 6 times higher in areas accessible to elephants, but proportionally more treefall occurred on high‐nutrient basalts and in lowland catena areas. These patterns were superimposed on a climate‐mediated regime of increasing treefall with precipitation in the absence of herbivores. These landscape‐scale patterns reveal environmental controls underpinning herbivore‐mediated tree turnover, highlighting the need for context‐dependent science and management.
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Big trees: How the mighty are fallin'
Article
  • Jan 2012
  • NEW SCI
From the kings of the jungle to the boreal giants, the world's greatest trees are in big trouble
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Tree cavities in forests – The broad distribution pattern of a keystone structure for biodiversity
Article
  • Aug 2011
  • FOREST ECOL MANAG
We explored the main factors affecting the global distribution of tree cavities – a habitat component of mostly biotic origin that is crucial for many animal species. We considered the influence of eight environmental variables (ranging from the single-tree to the biogeographic-region scale) on cavity density in a meta-analysis of 103 published studies. The global median density of cavities was 16ha−1, with densities highest in Australasia and lowest in the Palaearctic region. Two major factors influencing density were identified: cavity density was positively related to the amount of precipitation, and was higher in natural than in managed forests. These effects suggest that the distribution of tree cavities largely reflects the incidence of fungal heart-rot in trees, and that forest management, by affecting wood decay processes, can have a broad-scale impact on tree microhabitat availability. Although air temperature, forest composition and wood hardness had suggestive univariate effects, neither these variables nor biogeographic region explained any additional variation in multifactor models. In regions where woodpeckers are present there was an upper limit to the density of woodpecker-excavated cavities (approximately 10–20cavitiesha−1) that was considerably lower than the highest total cavity densities encountered (up to 140ha−1). This indicates that primary cavity-nesters are particularly important keystone species in cavity-poor forests where wood decay processes are suppressed either climatically or by forest management.
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Ecosystem greenspots: Identifying potential drought, fire, and climate-change micro-refuges
Article
  • Sep 2012
In response to climate change and other threatening processes there is renewed interest in the role of refugia and refuges. In bioregions that experience drought and fire, micro-refuges can play a vital role in ensuring the persistence of species. We develop and apply an approach to identifying potential micro-refuges based on a time series of remotely sensed vegetation greenness (fraction of photosynthetically active radiation intercepted by the sunlit canopy; fPAR). The primary data for this analysis were NASA MODIS 16-day L3 Global 250 m (MOD13Q1) satellite imagery. This method draws upon relevant ecological theory (source sink habitats, habitat templet) to calculate a micro-refuge index, which is analyzed for each of the major vegetation ecosystems in the case-study region (the Great Eastern Ranges of New South Wales, Australia). Potential ecosystem greenspots were identified, at a range of thresholds, based on an index derived from: the mean and coefficient of variance (COV) of fPAR over the 10-year time series; the minimum mean annual fPAR; and the COV of the 12 values of mean monthly fPAR. These greenspots were mapped and compared with (1) an index of vascular plant species composition, (2) environmental variables, and (3) protected areas. Potential micro-refuges were found within all vegetation ecosystem types. The total area of ecosystem greenspots within the upper 25% threshold was 48 406 ha; around 0.2% of the total area of native vegetation (23.9 x 10(6) ha) in the study region. The total area affected by fire was 3.4 x 10(6) ha. The results of the environmental diagnostic analysis suggest deterministic controls on the geographical distribution of potential micro-refuges that may continue to function under climate change. The approach is relevant to other regions of the world where the role of micro-refuges in the persistence of species is recognized, including across the world's arid zones and, in particular, for the Australian, southern African, and South American continents. Micro-refuge networks may play an important role in maintaining beta-diversity at the bio-region scale and contribute to the stability, resilience, and adaptive capacity of ecosystems in the face of ever-growing pressures from human-forced climate change, land use, and other threatening processes.
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Forest history and the development of old-growth characteristics in Swedish spruce forests
Article
  • Feb 2009
  • J VEG SCI
Questions: Can small and isolated high-conservation value forests (e.g. designated woodland key habitats) maintain old-growth forest characteristics and functionality in fragmented landscapes? To what extent have past disturbances (natural and anthropogenic) influenced the development of old-growth characteristics of these forests? How long does it take for selectively cut stands to attain conditions resembling old-growth forests? Location: Southern boreal zone of central Sweden. Methods: We linked multiple lines of evidence from historical records, biological archives, and analyses of current forest structure to reconstruct the forest history of a boreal landscape, with special emphasis on six remaining core localities of high-conservation value forest stands. Results: Our reconstructions revealed that several of these stands experienced wildfires up to the 1890s; all had been selectively harvested in the late 1800s; and all underwent substantial structural and compositional reorganization over the following 100-150 years. This time interval was sufficient to recover considerable amounts of standing and downed dead wood (mean 60.3 m3 ha−1), a range of tree ages and sizes (mean basal area 32.6 m2 ha−1), and dominance of shade-tolerant spruce. It was insufficient to obtain clearly uneven tree age structures and large (>45 cm diameter) living and dead trees. Thus, these forests contain some, but not all, important compositional and structural attributes of old-growth forests, their abundance being dependent on the timing and magnitude of past natural and anthropogenic disturbances. Our landscape-level analysis showed marked compositional and structural differences between the historical forest landscape and the present landscape, with the latter having a greater proportion of young forests, introduction of non-native species, and lack of large trees and dead wood. Conclusions: The remnant high-conservation value stands were not true representatives of the pre-industrial forests, but represent the last vestige of forests that have regenerated naturally and maintained a continuous tree cover. These traits, coupled with their capacity for old-growth recovery, make them valuable focal areas for conservation.
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Biocomplexity in large tree mortality: Interactions between elephant, fire and landscape in an African savanna
Article
The vegetation dynamics of the savanna ecosystem are driven by complex interactions between biotic and abiotic factors, and thus are expected to exhibit emergent properties of biocomplexity. We explore the relative importance of static and dynamic drivers in explaining the patterns of mortality of large trees in the Kruger National Park, South Africa. Data on large trees were collected from 22 transects in April 2006, and these transects were re-sampled in November 2008. Of the 2546 individually-identified trees that were re-sampled, 290 (11.4%) died in the interim. We tested several competing hypotheses with varying levels of complexity, and found that mortality of large trees was affected mainly by both static (geophysical and landscape characteristics) and dynamic (elephant damage and fire) factors that were either additive or interactive in their effects. Elephant damage was the main predictor of tree mortality, but fire also played an important role depending on the landscape type. Other static variables such as position-on-slope, height below canopy, and altitude had weak effects in explaining tree mortality. These results indicate that keystone features such as large trees, show differential vulnerability to mortality that is landscape-specific. For conservation managers, this implies that the dynamic drivers (elephant and fire) of tree mortality have to be managed at the specific landscape-level. We suggest that this emergent biocomplexity in the spatial and temporal patterns of large tree mortality is not unique to the African savannas, but is likely widespread across heterogeneous landscapes.
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Twentieth-century decline of large-diameter trees in Yosemite National Park, California, USA
Article
  • May 2009
  • FOREST ECOL MANAG
Studies of forest change in western North America often focus on increased densities of small-diameter trees rather than on changes in the large tree component. Large trees generally have lower rates of mortality than small trees and are more resilient to climate change, but these assumptions have rarely been examined in long-term studies. We combined data from 655 historical (1932–1936) and 210 modern (1988–1999) vegetation plots to examine changes in density of large-diameter trees in Yosemite National Park (3027 km2). We tested the assumption of stability for large-diameter trees, as both individual species and communities of large-diameter trees. Between the 1930s and 1990s, large-diameter tree density in Yosemite declined 24%. Although the decrease was apparent in all forest types, declines were greatest in subalpine and upper montane forests (57.0% of park area), and least in lower montane forests (15.3% of park area). Large-diameter tree densities of 11 species declined while only 3 species increased. Four general patterns emerged: (1) Pinus albicaulis, Quercus chrysolepis, and Quercus kelloggii had increases in density of large-diameter trees occur throughout their ranges; (2) Pinus jeffreyi, Pinus lambertiana, and Pinus ponderosa, had disproportionately larger decreases in large-diameter tree densities in lower-elevation portions of their ranges; (3) Abies concolor and Pinus contorta, had approximately uniform decreases in large-diameter trees throughout their elevational ranges; and (4) Abies magnifica, Calocedrus decurrens, Juniperus occidentalis, Pinus monticola, Pseudotsuga menziesii, and Tsuga mertensiana displayed little or no change in large-diameter tree densities. In Pinus ponderosa–Calocedrus decurrens forests, modern large-diameter tree densities were equivalent whether or not plots had burned since 1936. However, in unburned plots, the large-diameter trees were predominantly A. concolor, C. decurrens, and Q. chrysolepis, whereas P. ponderosa dominated the large-diameter component of burned plots. Densities of large-diameter P. ponderosa were 8.1 trees ha−1 in plots that had experienced fire, but only 0.5 trees ha−1 in plots that remained unburned.
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