The global extent and distribution of forest trees is central to our understanding of the terrestrial biosphere. We provide the first spatially continuous map of forest tree density at a global ...scale. This map reveals that the global number of trees is approximately 3.04 trillion, an order of magnitude higher than the previous estimate. Of these trees, approximately 1.39 trillion exist in tropical and subtropical forests, with 0.74 trillion in boreal regions and 0.61 trillion in temperate regions. Biome-level trends in tree density demonstrate the importance of climate and topography in controlling local tree densities at finer scales, as well as the overwhelming effect of humans across most of the world. Based on our projected tree densities, we estimate that over 15 billion trees are cut down each year, and the global number of trees has fallen by approximately 46% since the start of human civilization.
This dataset provides growth form classifications for 67,413 vascular plant species from North, Central, and South America. The data used to determine growth form were compiled from five major ...integrated sources and two original publications: the Botanical Information and Ecology Network (BIEN), the Plant Trait Database (TRY), the SALVIAS database, the USDA PLANTS database, Missouri Botanical Garden's Tropicos database, Wright (2010), and Boyle (1996). We defined nine plant growth forms based on woodiness (woody or non-woody), shoot structure (self-supporting or not self-supporting), and root traits (rooted in soil, not rooted in soil, parasitic or aquatic): Epiphyte, Liana, Vine, Herb, Shrub, Tree, Parasite, or Aquatic. Species with multiple growth form classifications were assigned the growth form classification agreed upon by the majority (>2/3) of sources. Species with ambiguous or otherwise not interpretable growth form assignments were excluded from the final dataset but are made available with the original data. Comparisons with independent estimates of species richness for the Western hemisphere suggest that our final dataset includes the majority of New World vascular plant species. Coverage is likely more complete for temperate than for tropical species. In addition, aquatic species are likely under-represented. Nonetheless, this dataset represents the largest compilation of plant growth forms published to date, and should contribute to new insights across a broad range of research in systematics, ecology, biogeography, conservation, and global change science.
Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations. Our ability to understand and predict changes in the forest ...carbon cycle--particularly net primary productivity and carbon storage--increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation) decrease, remain constant, or increase as trees increase in size and age. Here we present a global analysis of 403 tropical and temperate tree species, showing that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree. The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained, respectively, by increases in a tree's total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density. Our results resolve conflicting assumptions about the nature of tree growth, inform efforts to undertand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence.
The composition of ectomycorrhizal (EcM) fungal communities in Nothofagus rainforests and the responses of the fungal communities to timber harvesting have been unknown. We investigated EcM ...communities in two sites, 9 to 11 years after timber harvesting, and tested whether changes in the communities were driven by soil chemistry. The fungal communities in both sites were highly diverse, yet 53 out of 140 distinct terminal restriction fragment length polymorphism (T-RFLP) patterns were shared between the sites. At both sites, timber harvesting reduced the presence of EcM roots and caused shifts in the fungal community in the organic soil horizons. At one site, Laccaria spp. increased in harvested areas, which partially correlated with an increase in soil mineralizable nitrogen. The other site showed a decreased abundance of Russula sp. (cf. R. purpureotincta, R. roseostipitata) in harvested areas, which correlated with declines in soil carbon and organic horizon depth, and a decline in the abundance of rare species at the edge of harvested areas, which was related to inorganic phosphorus. The results show that EcM fungal communities in Nothofagus temperate rainforest are highly diverse at the local scale, yet have a high degree of similarity across sites. These communities are directly affected by timber harvesting and by shifts in soil chemistry following timber harvesting.
Tree species in the Pinaceae are some of the most widely introduced non-native tree species globally, especially in the southern hemisphere. In New Zealand, plantations of radiata pine (
Pinus ...radiata
D. Don) occupy
c
. 1.6 million ha and form 90% of planted forests. Although radiata pine has naturalized since 1904, there is a general view in New Zealand that this species has not invaded widely. We comprehensively review where radiata pine has invaded throughout New Zealand. We used a combination of observational data and climate niche modelling to reveal that invasion has occurred nationally. Climate niche modelling demonstrates that while current occurrences are patchy, up to 76% of the land area (i.e. 211,388 km
2
) is climatically capable of supporting populations. Radiata pine has mainly invaded grasslands and shrublands, but also some forests. Notably, it has invaded lower-statured vegetation, including three classes of naturally uncommon ecosystems, primary successions and secondary successions. Overall, our findings demonstrate pervasive and ongoing invasion of radiata pine outside plantations. The relatively high growth rates and per individual effects of radiata pine may result in strong effects on naturally uncommon ecosystems and may alter successional trajectories. Local and central government currently manage radiata pine invasions while propagule pressure from existing and new plantations grows, hence greater emphasis is warranted both on managing current invasions and proactively preventing future radiata pine invasions. We therefore recommend a levy on new non-native conifer plantations to offset costs of managing invasions, and stricter regulations to protect vulnerable ecosystems. A levy on economic uses of invasive species to offset costs of managing invasions alongside stricter regulations to protect vulnerable ecosystems could be a widely adopted measure to avert future negative impacts.
Many remote islands are degraded as a result of deforestation and browsing of vegetation by introduced goats. Goat eradication is therefore a focus for island restoration, but there are few long-term ...records of change on islands after eradications. In 1946, three permanent plots were established immediately after goats were eradicated from Great Island (Manawa Tawhi), 60
km from northern New Zealand, and provide a 57-year record of change across a sequence of forest succession. Since 1946, the native and non-native bird communities that disperse 75% of the woody flora have increased from six to eight species and bird-dispersed woody plants in plots have increased from 7 to 11 species. After 1946, palatable trees were recruited in the plots. Unpalatable understorey sedges, present when goats were abundant, have persisted and may impede tree seedling establishment. Of the bird-dispersed woody plant species, 41% occur in the plots compared with 67% of the non-bird-dispersed species. Large-seeded species were unable to germinate away from parents until native pigeons
Hemiphaga novaeseelandiae were present during the last decade. Forest succession is a consequence of interactions between the legacy of goat grazing and current disperser communities. Survival of seed-limited rare plants is not guaranteed in these circumstances. Although non-native goats no longer influence succession directly, non-native birds have been and remain important components of the disperser community. Our study supports the view that a whole-ecosystem understanding of the interactions between native and non-native species is needed to predict the consequences of eradications on islands worldwide.
We studied the invasion of a New Zealand mountain beech (Nothofagus solandri var. cliffortioides) forest by the exotic perennial herb, Hieracium lepidulum. We used data from 250 randomly located ...permanent plots (400 m2) established in 1970 that sampled 9000 ha of forest. Frequency of H. lepidulum was 11%, 43%, and 57% in 1970, 1985, and 1993, respectively. For each year of measurement, invasion patterns were related to (a) distance to the forest margin as a measure of dispersal limitation, (b) community structure, (c) stem biomass dynamics indicating disturbance history, and (b) environmental characteristics. In 1970, invaded plots had more species and lower potential solar radiation, and they were closer to the forest margin; however, invaded plots were only weakly predicted by these site variables. H. lepidulum also invaded relatively species-rich subplots (0.75 m2) showing that community structure was also significant at a microsite scale. Using the same sets of variables, the ability to predict which plots were invaded in any year increased from 1970 to 1993. This supports our hypothesis that in early invasion stages, with dispersal limitation, an invader may occur in only a subset of suitable sites giving a weak relationship with site variables. By 1993, distance to the forest margin was no longer related to which plots were invaded, and invaded plots had more species, occurred at lower elevations on more sheltered topographic positions, and had more fertile soils than uninvaded plots. Even though site variables were not independent (e.g., plots on fertile soils tend to have more species), multiple logistic regression showed that, all else being equal, invaded plots still tended to have more species than those not invaded. Our study therefore questions the hypothesis that, all else being equal, species-poor habitats are more prone to invasion by exotic species.
Aim To determine if elevational variation in the proportion of lianas in woody floras parallels the variation observed on latitudinal gradients. This is to be expected if the poleward decrease in the ...importance of lianas is related to the vulnerability of their wide vessels to freeze embolism. Location Coastal ranges of south-central Chile (latitude$37\textdegree-40\textdegree$S) and western South Island of New Zealand ($41\textdegree-43\textdegree S$). Methods The presence of all woody species was recorded in plots of 2500 m2 (Chile) or 100-400 m2(New Zealand) on four elevational gradients in temperate rain forest. Each species was classified as a tree, shrub or liana. Original data were obtained from 22 plots at two sites in Chile. In New Zealand, two surveys comprising a total of 296 plots were extracted from the National Vegetation Survey data base. Results Liana species richness declined more or less monotonically on all four gradients, whereas richness of trees and shrubs showed more varied elevational patterns. The proportion of woody species contributed by the liana life-form was negatively correlated with elevation on all four gradients, falling from 15 to 35% of the woody flora at c. 200 m a.s.l. to nil well below the tree line. The elevational and latitudinal limits of liana species were marginally significantly correlated in Chile, but not in New Zealand. Main conclusions The elevational parallel of the well-documented decline in liana representation with increasing latitude is consistent with the hypothesis that cold intolerance is a strong control on the global distribution of the liana life-form.
Testate amoebae analysis is used to provide the first quantitative reconstruction of Holocene surface wetness changes from a Southern Hemisphere ombrogenous bog. Water-table depth and surface ...moisture are the dominant environmental factors influencing testate amoebae species composition in a modern training set of 62 surface samples from 19 bogs in New Zealand. A transfer function based on partial least squares (PLS) performed well in cross-validation of modern samples, but produced unrealistic predictions of water-table depth and moisture for fossil samples. This resulted from poor overlap of species composition between modern and fossil samples. Peat humification data is used to examine decay-related species diversity trends and ordination is used to explore the differences between modern and fossil assemblages. Poor overlap can be explained by differential preservation in the fossil assemblages of those taxa with more robust tests. This enhances their abundance and reduces the overall diversity of the fossil assemblages. Human activities over the last 150 years have also influenced the surface environments and hydrology of the sampled bogs. In this situation, weighted average (WA) and tolerance downweighted weighted average (WA-Tol) models were more robust than PLS, and were applied, along with semi-quantitative scoring, to reconstruct more realistic Holocene surface wetness changes. Selection of the best model for reconstruction of surface wetness changes should be based on the characteristics of the fossil data rather than the predictive power of the model in cross-validation of the modern data alone.
We quantified the immediate impact of an earthquake (magnitude index Mw 6.7 in 1994) on a mountain beech (Nothofagus solandri var. cliffortioides) forest in the Southern Alps, New Zealand. Data from ...randomly located permanent plots (20 × 20 m) established in 1970 were used to determine the patterns and causes of damage. These plots were located 10 km southeast of the epicenter (Basin Creek, 28 plots in 920 ha) and 30 km southeast of the epicenter (Broken River, 34 plots in 2060 ha). Assessments of earthquake-induced damage in 1995 showed 24.0 ± 5.9% tree mortality and 22.5 ± 4.0% tree injury on Basin Creek plots (all values mean ± 1 SE), but only 0.6 ± 0.2% tree mortality and 3.3 ± 1.1% tree injury on Broken River plots. As a result, stem biomass declined from 149 ± 13.8 Mg/ha in 1993 to 114 ± 15.3 Mg/ha in 1995 on Basin Creek plots. On average, earthquake-induced landslides caused 74% of the total stem biomass mortality, and such mortality was greatest on steep slopes. Low-intensity stem biomass mortality was common in Basin Creek, with 25% of plots losing 1% to <20% of their live stem biomass. Damage intensity in that catchment depended on the scale of observation: 100% mortality occurred on 7% of the 20 × 20 m plots, 15% of the 10 × 10 m subplots, and 21% of the 5 × 5 m subplots. In contrast to previous studies, our results show that much of an earthquake's immediate impact is widespread, low-intensity damage to forests.
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