Introduced deer reduce native plant cover and facilitate invasion of non-native tree species: evidence for invasional meltdown

Invasive species are a major threat to native communities and ecosystems worldwide. One factor frequently invoked to explain the invasiveness of exotic species is their release in the new habitat from control by natural enemies (enemy-release hypothesis). More recently, interactions between exotic species have been proposed as a potential mechanism to facilitate invasions (invasional meltdown hypothesis). We studied the effects of introduced deer on native plant communities and exotic plant species on an island in Patagonia, Argentina using five 400 m² exclosures paired with control areas in an Austrocedrus chilensis native forest stand. We hypothesized that introduced deer modify native understory composition and abundance and facilitate invasion of introduced tree species that have been widely planted in the region. After 4 years of deer exclusion, native Austrocedrus and exotic Pseudotsuga menziesii tree sapling abundances are not different inside and outside exclosures. However, deer browsing has strongly inhibited growth of native tree saplings (relative height growth is 77% lower with deer present), while exotic tree sapling growth is less affected (relative height growth is 3.3% lower). Deer significantly change abundance and composition of native understory plants. Cover of native plants in exclosures increased while cover in controls remained constant. Understory composition in exclosures after only 4 years differs greatly from that in controls, mainly owing to the abundance of highly-browsed native species. This study shows that introduced deer can aid the invasion of non-native tree species through negatively affecting native plant species.     

Rescue tree monocultures! A phylogenetic ecology approach to guide the choice of seedlings for enrichment planting in tropical monoculture plantations

Monoculture tree plantations have been preferred by farmers and companies because they maximize the production of specific products and are easier to manage, while multispecies plantations can provide multiple ecosystem services but have still been adopted at very limited scales. One potential midway to enhance the ecological contribution of monoculture plantations is to introduce native tree species in the plantation understory. We conducted phylogenetically explicit enrichment planting experiments beneath the monocultures of two tree species native to the Brazilian Atlantic Forest to assess if the evolutionary distance of each seedling species to the overstory tree explained variations in seedling performance. We planted in the understory of two replicate plantations of species Esenbeckia leiocarpa Engl. (Rutaceae; 38 and 25 years old) and Zeyheria tuberculosa (Vell) (Bignoniaceae; both replicates were 30 years old) six native tree species, ranging in their evolutionary distances to these overstory species. We assessed individual seedling survival and height at 1, 7, and 19 months after planting. We found a weak yet significant, positive correlation between seedling performance (growth and survival) and the phylogenetic distance of the planted seedling to the overstory species, which was driven by the poor performance of conspecifics. Seedlings of the same order and class as the overstory trees showed a significantly lower risk of death compared to conspecifics and to the furthest relative, Cryptocarya aschersoniana. These findings highlight that very close relatives to the overstories should be avoided when planting beneath monoculture plantations, but that knowledge on species‐specific requirements is still the most important for a successful planting.     

Planting of different-sized tree transplants on arable soil

On the arable land of the Rosovka Stream alluvium in the Czech Republic, a windbreak containing native woody species, was planted within a restoration project. This study evaluates the effect of that planting of three different tree sizes, on the rate of growth. The sizes of transplants employed in this study included small (1.0–1.5 meters tall), medium-sized (2.0–2.5 meters tall) and large (with a trunk circumference of 0.1–0.12 meters). The following native tree species, from the Eurosiberian region, were used: Quercus robur L., Carpinus betulus L., Fraxinus excelsior L., Acer campestre L., Acer pseudoplatanus L., Tilia cordata Mill., and Prunus avium L. Growth rates were monitored over a five-year period. Small transplants had the highest growth; they grew approximately 0.4 meters more than transplants from the other size categories. Our results show that the selection of the size of transplant has a significant impact on development and growth. However, differences in the post-transplant responses of individual species were found.     

Forest tree growth response to hydroclimate variability in the southern Appalachians

Climate change will affect tree species growth and distribution; however, under the same climatic conditions species may differ in their response according to site conditions. We evaluated the climate‐driven patterns of growth for six dominant deciduous tree species in the southern Appalachians. We categorized species into two functional groups based on their stomatal regulation and xylem architecture: isohydric, diffuse porous and anisohydric, ring porous. We hypothesized that within the same climatic regime: (i) species‐specific differences in growth will be conditional on topographically mediated soil moisture availability; (ii) in extreme drought years, functional groups will have markedly different growth responses; and (iii) multiple hydroclimate variables will have direct and indirect effects on growth for each functional group. We used standardized tree‐ring chronologies to examine growth of diffuse‐porous (Acer, Liriodendron, and Betula) and ring‐porous (Quercus) species vs. on‐site climatic data from 1935 to 2003. Quercus species growing on upslope sites had higher basal area increment (BAI) than Quercus species growing on mesic, cove sites; whereas, Acer and Liriodendron had lower BAI on upslope compared to cove sites. Diffuse‐porous species were more sensitive to climate than ring porous, especially during extreme drought years. Across functional groups, radial growth was more sensitive to precipitation distribution, such as small storms and dry spell length (DSL), rather than the total amount of precipitation. Based on structural equation modeling, diffuse‐porous species on upslope sites were the most sensitive to multiple hydroclimate variables (r² = 0.46), while ring‐porous species on upslope sites were the least sensitive (r² = 0.32). Spring precipitation, vapor pressure deficit, and summer storms had direct effects on summer AET/P, and summer AET/P, growing season small storms and DSL partially explained growth. Decreasing numbers of small storms and extending the days between rainfall events will result in significant growth reduction, even in regions with relatively high total annual rainfall.     

Nonannual tree rings in a climate‐sensitive Prioria copaifera chronology in the Atrato River,Colombia

In temperate climates, tree growth dormancy usually ensures the annual nature of tree rings, but in tropical environments, determination of annual periodicity can be more complex. The purposes of the work are as follows: (1) to generate a reliable tree‐ring width chronology for Prioria copaifera Griseb. (Leguminoceae), a tropical tree species dwelling in the Atrato River floodplains, Colombia; (2) to assess the climate signal recorded by the tree‐ring records; and (3) to validate the annual periodicity of the tree rings using independent methods. We used standard dendrochronological procedures to generate the P. copaifera tree‐ring chronology. We used Pearson correlations to evaluate the relationship of the chronology with the meteorological records, climate regional indices, and gridded precipitation/sea surface temperature products. We also evaluated 24 high‐precision ¹⁴C measurements spread over a range of preselected tree rings, with assigned calendar years by dendrochronological techniques, before and after the bomb spike in order to validate the annual nature of the tree rings. The tree‐ring width chronology was statistically reliable, and it correlated significantly with local records of annual and October–December (OND) streamflow and precipitation across the upper river watershed (positive), and OND temperature (negative). It was also significantly related to the Oceanic Niño Index, Pacific Decadal Oscillation, and the Southern Oscillation Index, as well as sea surface temperatures over the Caribbean and the Pacific region. However, ¹⁴C high‐precision measurements over the tree rings demonstrated offsets of up to 40 years that indicate that P. copaifera can produce more than one ring in certain years. Results derived from the strongest climate–growth relationship during the most recent years of the record suggest that the climatic signal reported may be due to the presence of annual rings in some of those trees in recent years. Our study alerts about the risk of applying dendrochronology in species with challenging anatomical features defining tree rings, commonly found in the tropics, without an independent validation of annual periodicity of tree rings. High‐precision ¹⁴C measurements in multiple trees are a useful method to validate the identification of annual tree rings.     

Slashing Phragmites (Phragmites australis) prior to planting does not promote native vegetation establishment

Phragmites or Common Reed (Phragmites australis) is a tall rhizomatous cosmopolitan grass. While native to Australia, it can be invasive in wetlands, forming dense monocultures and reducing their ecological integrity. We assessed the potential for the cutting of Phragmites reeds prior to planting to promote the establishment of indigenous shrubs that might ultimately outcompete Phragmites. We established ten 5 m × 5 m quadrats in an area dominated by Phragmites, brush‐cut the reeds to ground level in five of them and left five uncut as controls. Within each quadrat, we planted 20 plants (~40 cm tall) of each of five indigenous shrub species, unguarded (4 plants/m²). We surveyed the plants one month after planting and annually for the following four years for survival, height and browsing damage. Browsing damage to plants was common (>50%) and unaffected by cutting. After four years, overall plant survival rates were ~25% and mean plant heights for the five shrub species ranged between 120 and 174 cm. Cutting of Phragmites had no positive effect on plant survival or height. In fact, two Melaleuca species grew taller in the uncut quadrats. Cutting of Phragmites reed beds prior to planting is unlikely to promote the establishment of woody plantings. However, planting within established Phragmites with or without prior brush‐cutting is worthy of further trialling as a potential tool for reinstating native diversity at Phragmites‐dominated sites.     

Growing the urban forest: tree performance in response to biotic and abiotic land management

Forests are vital components of the urban landscape because they provide ecosystem services such as carbon sequestration, storm‐water mitigation, and air‐quality improvement. To enhance these services, cities are investing in programs to create urban forests. A major unknown, however, is whether planted trees will grow into the mature, closed‐canopied forest on which ecosystem service provision depends. We assessed the influence of biotic and abiotic land management on planted tree performance as part of urban forest restoration in New York City, U.S.A. Biotic treatments were designed to improve tree growth, with the expectation that higher tree species composition (six vs. two) and greater stand complexity (with shrubs vs. without) would facilitate tree performance. Similarly, the abiotic treatment (compost amendment vs. without) was expected to increase tree performance by improving soil conditions. Growth and survival was measured for approximately 1,300 native saplings across three growing seasons. The biotic and abiotic treatments significantly improved tree performance, where shrub presence increased tree height for five of the six tree species, and compost increased basal area and stem volume of all species. Species‐specific responses, however, highlighted the difficulty of achieving rapid growth with limited mortality. Pioneer species had the highest growth in stem volume over 3 years (up to 3,500%), but also the highest mortality (up to 40%). Mid‐successional species had lower mortality (<16%), but also the slowest growth in volume (approximately 500% in volume). Our results suggest that there will be trade‐offs between optimizing tree growth versus survival when implementing urban tree planting initiatives.     

Everglades tree island restoration: testing a simple tree planting technique patterned after a natural process

Tree islands in the Everglades are critical landscape features, but anthropogenic modification of the Everglades during the past century has led to the degradation and loss of many of the tree islands that originally dotted the Everglades landscape. Many of the tree islands have lost elevation and the majority of their woody species such that they are now covered with emergent plants such as sawgrass (Cladium jamaicense). A simple, cost‐effective tree planting technique is needed for restoring degraded Everglades tree islands. We patterned our design after a natural Everglades process that creates floating islands, which promotes tree survival and growth in both flooded and dry conditions and may lead to the development of fixed islands. Commercial peat bags were tested as a means to provide the medium for the growth and establishment of potted tree saplings native to Everglades tree islands. Three tree species (Annona glabra, Ficus aurea, and Acer rubrum) and five treatments were evaluated. The results indicate that the preferred deployed peat‐bag configuration should provide the greatest additional elevation to minimize inundation and be planted with a single Everglades tree island species sapling, with a single commercial tree fertilizer spike inserted for nutrients. Although most plants survived and many thrived for the two‐year period of this study, determining whether the trees planted using this technique can become established will require longer‐term studies and extensive field tests.     

Tree planting in organic soils does not result in net carbon sequestration on decadal timescales

Tree planting is increasingly being proposed as a strategy to combat climate change through carbon (C) sequestration in tree biomass. However, total ecosystem C storage that includes soil organic C (SOC) must be considered to determine whether planting trees for climate change mitigation results in increased C storage. We show that planting two native tree species (Betula pubescens and Pinus sylvestris), of widespread Eurasian distribution, onto heather (Calluna vulgaris) moorland with podzolic and peaty podzolic soils in Scotland, did not lead to an increase in net ecosystem C stock 12 or 39 years after planting. Plots with trees had greater soil respiration and lower SOC in organic soil horizons than heather control plots. The decline in SOC cancelled out the increment in C stocks in tree biomass on decadal timescales. At all four experimental sites sampled, there was no net gain in ecosystem C stocks 12–39 years after afforestation—indeed we found a net ecosystem C loss in one of four sites with deciduous B. pubescens stands; no net gain in ecosystem C at three sites planted with B. pubescens; and no net gain at additional stands of P. sylvestris. We hypothesize that altered mycorrhizal communities and autotrophic C inputs have led to positive ‘priming’ of soil organic matter, resulting in SOC loss, constraining the benefits of tree planting for ecosystem C sequestration. The results are of direct relevance to current policies, which promote tree planting on the assumption that this will increase net ecosystem C storage and contribute to climate change mitigation. Ecosystem‐level biogeochemistry and C fluxes must be better quantified and understood before we can be assured that large‐scale tree planting in regions with considerable pre‐existing SOC stocks will have the intended policy and climate change mitigation outcomes.     

Management implications for the reintroduction of the endangered Hawaiian state flower Hibiscus brackenridgei

Dry forests of Hawai'i are one of the most endangered forest types worldwide with 45% of all native tree and shrub species listed as federally threatened or endangered. Supplementation and reintroduction of endangered dry forest species are necessary to maintain viable population sizes. The goal of this research was to reintroduce Hibiscus brackenridgei mokuleianus, the state flower of Hawai'i and a federally endangered species, into its historical range on O'ahu. We determined the environmental variables contributing to plant survival and growth, assessed the effectiveness of a reintroduction program with minimal management, and evaluated the potential for habitat suitability models to assist in selection of optimal sites for reintroduction. Forty‐five individuals were grown from cuttings and transplanted in two regions: Ka'ena Point (2 sites, 10 individuals each site) and along Kealia Trail (5 sites, 5 individuals each site). Survival and height measurements were taken four times over the course of 25 months. There was 35% survival at Ka'ena Point and 76% survival at Kealia Trail and an average plant growth of 70.5 cm (±30.1 cm) and 121.6 cm (±61.7 cm), respectively. Ka'ena Point had significantly lower survival (p > 0.001) and growth rates (p > 0.001) than Kealia Trail. Plants survived best at sites with steep slopes and high soil moisture and grew the most in sites with steeper slopes, higher soil moisture, and lower soil bulk density. These findings provide insight into environmental variables which should be considered prior to planting as well as the intensity of site management.     

Effect of initial soil properties on six‐year growth of 15 tree species in tropical restoration plantings

In restoration plantings in degraded pastures, initial soil nutrient status may lead to differential growth of tropical tree species with diverse life history attributes and capacity for N₂ fixation. In 2006, we planted 1,440 seedlings of 15 native tree species in 16 fenced plots (30 × 30 m) in a 60‐year‐old pasture in Los Tuxtlas, Veracruz, Mexico, in two planting combinations. In the first year, we evaluated bulk density, pH, the concentration of organic carbon (C), total nitrogen (N), ammonia (), nitrate (), and total phosphorus (P) in the upper soil profile (0–20 cm in depth) of all plots. The first two axes of two principal component analyses explained more than 60% of the variation in soil variables: The axes were related to increasing bulk density, , , total N concentration, and pH. Average relative growth rates in diameter at the stem base of the juvenile trees after 6 years were higher for pioneer (45.7%) and N₂‐fixing species (47.6%) than for nonpioneer (34.7%) and nonfixing species (36.2%). Most N₂‐fixing species and those with the slowest growth rates did not respond to soil attributes. Tree species benefited from higher pH levels and existing litter biomass. The pioneers Ficus yoponensis, Cecropia obtusifolia, and Heliocarpus appendiculatus, and the N₂‐fixing nonpioneers Cojoba arborea, Inga sinacae, and Platymiscium dimorphandrum were promising for forest restoration on our site, given their high growth rates.     

Quantifying the effects of drought on abrupt growth decreases of major tree species in Switzerland

Drought entails important effects on tree physiology, which may result in short‐ to long‐term radial growth decreases. While the majority of studies have focused on annual drought‐related variability of growth, relatively little is known about sustained growth decreases following drought years. We apply a statistical framework to identify climatic factors that induce abrupt growth decreases and may eventually result in tree mortality. We used tree‐ring data from almost 500 standing dead trees and 200 living trees in eight sites of the Swiss network of strict forest reserves, including four of the most important Central European tree species (Abies alba, Picea abies, Fagus sylvatica and Quercus spp.). First, to assess short‐term growth responses to drought under various climate and site conditions, we calculated correlations and linear mixed‐effects models between ring‐width indices (RWIs) and drought based on the Standardized Precipitation Evapotranspiration Index (SPEI). Second, to quantify drought effects on abrupt growth decreases, we applied distributed lag nonlinear models (DLNMs), which account for both delayed effects and the nonlinear relationship between the SPEI and the occurrence of abrupt growth decreases. Positive correlations between RWIs and the SPEI indicated short‐term growth responses of all species, particularly at arid sites. Results of the DLNMs revealed species‐specific growth responses to drought. For Quercus spp., abrupt growth decreases were more likely to occur several years following severe drought, whereas for P. abies, A. alba, and F. sylvatica abrupt growth decreases started frequently immediately in the drought year. We conclude that the statistical framework allows for quantifying the effects of drought intensity on the probability of abrupt growth decreases, which ultimately contributes to an improved understanding of climate impacts on forest community dynamics.     

Invasion by native tree species prevents biotic homogenization in novel forests of Puerto Rico

There is concern that secondary forests dominated by introduced species, known as novel forests, increase taxonomical similarity between localities and lead to biotic homogenization in human-dominated landscapes. In Puerto Rico, agricultural abandonment has given way to novel forests dominated by the introduced African tulip tree Spathodea campanulata Beauv. (Bignoniaceae). In this study, I characterized the tree species composition of S. campanulata forests in Puerto Rico as means to evaluate if biotic homogenization is occurring. Non-metric multidimensional scaling was used to examine what variables were related to the large (≥10 cm diameter at breast height [DBH]), small (≥2.5 to <10 cm DBH), and juvenile (<2.5 cm DBH) tree species composition of 20 sites. Species composition was strongly related to substrate properties, less related to land use history, and unrelated to spatial attributes. The introduced species component was low (mean = 17%, S.E. = 1.8) and compositional differences were mostly due to native tree species of secondary to old growth forests on equivalent substrates. Animals appear to disperse most species (86%) into these forests yet because of this some introduced species will persist. Although uncommon species were largely absent, recent species establishment is shaped by substrate properties making biotic homogenization in these forests unlikely. The S. campanulata forests of Puerto Rico facilitate native tree species establishment in lands where poor management practices extirpated the original forest. These results highlight the importance of remnant old growth forests or trees that act as seed dispersal sources and facilitate native species recovery in novel forests.     

Effects of Tree Guards and Weed Mats on the Establishment of Native Tree Seedlings: Implications for Forest Restoration in Hong Kong, China

The effects of tree guards and weed mats on establishment and growth of native tree seedlings, Thick‐leaved oak (Cyclobalanopsis edithiae (Skan) Schott., Fagaceae), planted in an exposed hillside grassland in Hong Kong, were investigated. The natural regeneration of C. edithiae is poor due to a lack of seed dispersal agents and high seed predation, and therefore, this species is often targeted for forest restoration. The experiment lasted for 3.5 years during which the height, basal diameter, and crown diameter of individual seedlings were measured and survivorship recorded. The use of weed mats alone did not have a significant effect, but a combination of tree guards and weed mats led to a significant improvement in establishment, survivorship, and growth of the seedlings during the experimental period. Initially, the guards promoted rapid height growth of the seedlings, although lateral growth and secondary stem thickening were compromised. After the seedlings grew over the tree guards, the basal diameter and crown diameter increased at a notably faster rate. The combined effect of the tree guard and weed mat on the seedling growth pattern was found to be beneficial and contributed to the high survivorship of the seedlings. Comparing the survivorship data and the costs of various treatments, the use of tree guards in combination with the weed mats was demonstrated to be more cost‐effective than planting the seedlings without tree guards or weed mats. The potential for applying the technique in afforestation programs with native tree species for forest restoration in Hong Kong and other tropical regions is discussed.     

The ecology of tree reproduction in an African medium altitude rain forest

The occurrence of flowering and fruiting in tropical trees will be affected by a variety of factors, linked to availability of resources and suitable climatic triggers, that may be affected by increasing global temperatures. Community‐wide flowering and fruiting of 2526 trees in 206 plots were monitored over 24 years in the Budongo Forest Reserve (BFR), Uganda. Factors that were assessed included the size of the tree, access to light, the impacts of liana load, effects of tree growth, and variation between guilds of trees. Most flowering occurs at the end of the long dry season from February to April. Trees that had access to more light flowered and fruited more frequently. Pioneer and non‐pioneer light‐demanding species tended to reproduce more frequently than shade‐bearing species. Trees that grew faster between 1993 and 2011 also fruited more frequently. When examining all factors, growth rate, tree size, and crown position were all important for fruiting, while liana load but not growth rate was important in reducing flowering. Trees in BFR show a large decline in fruiting over 24 years, particularly in non‐pioneer light demanders, shade‐bearers, and species that produce fleshy fruits eaten by primates. The decline in fruit production is of concern and is having impacts on primate diets and potential recruitment of mahogany trees. Whether climate change is responsible is unclear, but flowering of the guilds/dispersal types which show declines is correlated with months with the coolest maximum temperatures and we show temperature has been increasing in BFR since the early 1990s.     

Tree guards and weed mats in a dry shrubland restoration in New Zealand

Associated with restoration of 150 ha of native plant communities within a highly exposed low rainfall landscape, we evaluated whether the benefits of tree guards and weed mats justified a doubling of planting costs. One‐year‐old nursery‐grown specimens of Kānuka (Kunzea serotina) and Pomaderris (Pomaderris amoena) were planted with and without polythene and rigid plastic tree guards, and weed mats, then monitored for 12 months. Herbivory was reduced with both types of tree guard by 10–35%, but mortality was largely caused by desiccation. Polythene tree guards provided the best protection, buffering extremes of ambient and soil temperature in summer but with no effect on soil temperature in winter. Weed mat addition reduced soil temperature fluctuation further in winter; a moss turf mat was best. Both mulch and moss weed mats reduced soil temperature in summer and raised soil moisture in winter. We showed that tree guards could save at least NZ$ 70 k/ha, but this is likely to vary with plant species traits and site conditions.     

Native tree regeneration in native tree plantations: understanding the contribution of Araucaria angustifolia to biodiversity conservation in the threatened Atlantic Forest in Argentina

Deforestation is a global process that has strongly affected the Atlantic Forest in South America, which has been recognised as a threatened biodiversity hotspot. An important proportion of deforested areas were converted to forest plantations. Araucaria angustifolia is a native tree to the Atlantic Forest, which has been largely exploited for wood production and is currently cultivated in commercial plantations. An important question is to what extent such native tree plantations can be managed to reduce biodiversity loss in a highly diverse and vulnerable forest region . We evaluated the effect of stand age, stand basal area, as a measure of stand density, and time since last logging on the density and richness of native tree regeneration in planted araucaria stands that were successively logged over 60 years, as well as the differences between successional groups in the response of plant density to stand variables. We also compared native tree species richness in planted araucaria stands to neighbouring native forest. Species richness was 71 in the planted stands (27 ha sampled) and 82 in native forest (18 ha sampled) which approximate the range of variation in species richness found in the native forests of the study area. The total abundance and species richness of native trees increased with stand age and time since last logging, but ecological groups differed in their response to such variables. Early secondary trees increased in abundance with stand age 3–8 times faster than climax or late secondary trees. Thus, the change in species composition is expected to continue for a long term. The difference in species richness between native forest and planted stands might be mainly explained by the difference in plant density. Therefore, species richness in plantations can contribute to local native tree diversity if practices that increase native tree density are implemented.     

Growth of Slender Banksia from seedling planting,with and without fertiliser

Slender Banksia (Banksia attenuata) is a primary component of declining Banksia woodlands around Perth, south‐western Australia. It is important that its re‐establishment be promoted, but there are little data on its growth rates and response to applied nutrients. To quantify longer‐term growth rate, I periodically measured heights of Slender Banksia planted mid‐2005 over 7½ years. Without fertiliser, these seedlings grew slowly to about 1½ m. In mid‐2009, I planted Slender Banksia on the same site, with and without fertiliser tablets, and evaluated survival, growth and root development over 1½ years. First‐summer Slender Banksia seedling survival of around 30% was not unusual for this species. Low‐phosphorus native plant fertiliser tablets increased growth significantly.     

Neogene origins and implied warmth tolerance of Amazon tree species

Tropical rain forest has been a persistent feature in South America for at least 55 million years. The future of the contemporary Amazon forest is uncertain, however, as the region is entering conditions with no past analogue, combining rapidly increasing air temperatures, high atmospheric carbon dioxide concentrations, possible extreme droughts, and extensive removal and modification by humans. Given the long‐term Cenozoic cooling trend, it is unknown whether Amazon forests can tolerate air temperature increases, with suggestions that lowland forests lack warm‐adapted taxa, leading to inevitable species losses. In response to this uncertainty, we posit a simple hypothesis: the older the age of a species prior to the Pleistocene, the warmer the climate it has previously survived, with Pliocene (2.6–5 Ma) and late‐Miocene (8–10 Ma) air temperature across Amazonia being similar to 2100 temperature projections under low and high carbon emission scenarios, respectively. Using comparative phylogeographic analyses, we show that 9 of 12 widespread Amazon tree species have Pliocene or earlier lineages (>2.6 Ma), with seven dating from the Miocene (>5.6 Ma) and three >8 Ma. The remarkably old age of these species suggest that Amazon forests passed through warmth similar to 2100 levels and that, in the absence of other major environmental changes, near‐term high temperature‐induced mass species extinction is unlikely.     

Light acclimation of four native tree species in felling gaps within a tropical mountain rainforest

Ecuadorian mountain rainforests are declining dramatically due to deforestation. Exploitation of remaining forests has led to low abundances of native, valuable timber species. Enrichment planting of selected native tree species into forest gaps is a strategy that may increase their abundance and maintain biodiversity. However, the development of successful planting strategies requires knowledge of environmental demands on, and ecological requirements of, native species during their establishment. This knowledge is currently lacking for mid- and late-successional species in Central American forests. Two deciduous, mid-successional (Cedrela montana, Tabebuia chrysantha) and two evergreen, late-successional native tree species (Nectandra membranacea, Podocarpus sprucei) were planted into felling gaps. Photosynthetic performance and growth in height of these species were assessed along light gradients during seedling establishment to test whether species-specific light responses were related to plant successional traits. Both mid-successional species benefited from higher light levels in gaps up to 30% canopy openness_60°. In larger gaps, C. montana exhibited a significant decline in growth. As expected, growth of the late-successional species was only marginally increased at higher light levels. Nevertheless, the photosynthetic apparatus of N. membranacea displayed rapid acclimation to higher light conditions in gaps. Plant response to felling gaps may not always be predicted based on successional status. Our results suggest that the four investigated species may coexist in the same gap by occupying different niches along light gradients. This arrangement may offer an ecological basis to increase the abundance of valuable timber species through enrichment planting in Ecuador mountain rainforests.