Upper Forest Line Research Articles

Contributions of climate, vegetation and soil to the alpine sediment carbon accumulation rate in central China since the Middle Holocene

Large amounts of carbon in alpine sediments have been expected to be sensitive to climate change, but how carbon accumulation responds to climate change remains unclear. Thus, we explored the impact of different factors on the carbon accumulation rate (CAR) of alpine sediments by combining a variety of climatic variables, vegetation data and erosion indicators based on two alpine sediment successions on Taibai Mountain, the highest peak in central and eastern mainland China. One succession is near the modern treeline (Paomaliang Swamp, PML) and the other is located at the upper forest line (Sanqing Chi, SQC, a small lake). We used our previously published organic carbon content data and for the first time calculated the CAR, and further used pollen and physicochemical indicators to quantify the contributions from climate, vegetation and soil. We found that their contributions varied during different periods and between the two sediment successions. For the PML succession, from 5850 to 4000 calendar years before present (cal. a BP), the CAR was low, which was related to low annual temperatures, low vegetation cover and strong soil erosion. From 4000 to 2400 cal. a BP, a high CAR coincided with high annual temperatures, high vegetation cover and weak soil erosion. From 2400 to 200 cal. a BP, the CAR decreased, mainly attributed to low vegetation cover. Local vegetation cover had major impacts on the CAR in the SQC succession during the Middle–Late Holocene. In general, the local factor interpretation rate in SQC (83%) was higher than that of PML (47%), related to the vegetation stability of continuous forest and the treeline. This study highlights the important role of the local environment in determining carbon accumulation in the alpine region.

Metals in Plant Functional Types of Ombrotrophic Peatlands in the Sudetes (SW Poland).

The Sudetes are remarkable for the variety and number of peat bogs which receive nutrients via precipitation from atmospheric deposition as the only source of minerals. As this type of peat bogs with a very low buffering capacity is affected in the Sudetes by long-range exhausts from the former Black Triangle, strong response to atmospheric contamination may be expected. Therefore these peat bogs are highly suitable for bioindication purposes. As a result, metal levels in peat and plants should be controlled to evaluate potential ecological damage and to devise treatment strategies. The aim of this study was to evaluate the concentration of Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn in species from different plant functional types (PFTs): shrubs, evergreen dwarf shrubs, deciduous dwarf shrubs, tussock sedges, non-tussock sedges, forbs, Sphagnum mosses, brown mosses, liverworts, and algae collected from peat bogs of the Izera, Karkonosze, and Bystrzyckie Mountains. PFTs of the Karkonosze peat bogs situated above the upper forest line contained higher metal concentrations than those of the Izera and Bystrzyckie peat bogs from lower altitudes and surrounded by forests. Of all PFTs, the algae Zygogonium ericetorum accumulated the highest levels of Fe, Pb, and Zn. The PFTs of Sphagnum mosses were also very effective bioindicators of Cd, Cr, Fe, Hg, and Pb deposition to peat bog ecosystems. Pb, Fe, and Cr found in the examined vascular PFTs originated from atmospheric deposition. The results showed that airborne contaminants, including the ones connected with long-range transport, can make a significant contribution to a load of trace metals in peat bogs located above the upper forest line. These airborne depositions facilitate better recognition of the transport of contaminants carried over great distances and should be taken into account in monitoring and environmental protection programs. In particular, the results, first of all, show the differences in the bioaccumulation of metals in PFTs and their response to trace metal levels in such habitats. Of all PFTs, algae and Sphagnum mosses were the best choices for bioindication of trace metal pollution in ombrotrophic mountain mires. PFTs have not been used so far for investigating ombrotrophic mountain mires in Europe. Thus results of this investigation could be extended to this type of peat bogs in the mountains of Central Europe for better selection of PFTs for bioindication purposes.

Rove beetle (Coleoptera: Staphylinidae) communities of the upper forest line of the Ukrainian Carpathians: structure and biotopic distribution (on the example of the Polonynskyi ridge)

The results of studies of species diversity, community structure, and biotopic distribution of rove beetles (Insecta: Coleoptera: Staphylinidae) at the upper forest line on the Yavirnyk and Stinka mountain ridges (Polonynskyi massif, Ukrainian Carpathians) are presented. As a result, 91 species of Staphylinidae belonging to 53 genera and 10 subfamilies were found. In particular, 71 species were found on Yavirnyk, and 69 species on Stinka. The largest number of species was noticed on meadows of both ridges: 48 species on Yavirnyk and 51 on Stinka. The lowest number of species was recorded in in ecotones: 39 species on Yavirnyk and 40 on Stinka. The rove beetle dominant complex of the Yavirnyk ridge includes four species, including two eudominants—Eusphalerum alpinum and Philonthus politus, and two dominants—Eusphalerum anale and Philonthus decorus. The dominant complex of the Stinka ridge includes six species: three eudominants—Eusphalerum alpinum, Ocypus macrocephalus, and Staphylinus erythroptery, and three dominants in almost equal proportions—Anotylus mutator, Dinothenarus fossor, and Philonthus decorus. All indices of species richness and diversity of the rove beetle communities have higher values on the Stinka ridge, and they are the highest in forest biotopes of both mountain ridges, which indicates their high ecological quality and stability. This is also confirmed by the highest rate of originality of the species composition of Staphylinidae in these areas. The most similar in species composition are the rove beetle communities of meadows. The original fauna of rove beetles of Yavirnyk is represented by 25 species, and of Stinka by 19 species. Among the species of Staphylinidae, 18 occurred in all biotopes of the upper forest line, which is 19.8% of the total number of species found here. In terms of trophic specialization, predators that live in the forest floor, among remains of organic origin and in fungi predominate in all biotopes of the upper forest line (UFL). In terms of biotopic distribution, eurytopic species predominate.

Climate-human-landscape interaction in the eastern foothills of Mt. Kilimanjaro (equatorial East Africa) during the last two millennia

The Mt. Kilimanjaro region is known for its long history of intensive agriculture, but the temporal extent of human activity and its impact on the regional ecosystem are not well known. In this study, climate-human-landscape interactions during the past ~2200 years were examined using climate and vegetation proxies extracted from the continuous and high-resolution sediment record of Lake Chala. Ancient-to-modern regional human activity is documented against a backdrop of long-term vegetation dynamics in the low-elevation savanna woodland southeast of Mt. Kilimanjaro and riparian forest within Chala crater. During prolonged dry periods (~1170–1300 CE), succulent dry crater forest expanded relative to the moist lakeshore forest. The savanna landscape surrounding Chala crater was relatively stable through time, except that savanna grasses were stimulated by higher precipitation, consistent with the fuel-limited fire regime evidenced in the charcoal record. Expansion of subalpine ericaceous vegetation and a general decline in Afromontane forest taxa on Mt. Kilimanjaro after 550 CE may reflect a lowering of its upper forest line. The earliest robust signature of human influence on regional vegetation involves an increase in ruderal (weedy) plant taxa around 1100 CE, possibly associated with the development of Chagga homegardens and associated agroforestry in the submontane forest zone. A first hint of cereal agriculture (likely sorghum) is observed around 1550 CE, followed by a more robust signature from 1780 CE onwards which likely reflects the start of lowland irrigation agriculture. From 1780 CE we also find the first undisputed appearance of maize, introduced to East Africa about a century earlier.

Earlywood structure of evergreen conifers near forest line is habitat driven but latewood depends on species and seasons

Near upper forest line, values of conifer wood anatomical traits are species-specific, but relationships among traits are common. Growing season temperature significantly impacts wood anatomy only in its extremes. Quantitative wood anatomy can provide detailed insight into adaptation of trees to changing environment, especially on the borders of species distribution ranges. This study investigated wood anatomy of Pinus sylvestris L., Pinus sibirica Du Tour, and Picea obovata Ledeb. near the forest line in the Western Sayan Mountains, where local climate changes rapidly. Anatomical traits reflecting three developmental stages of conifer tracheids (division = cell number, cell enlargement = radial diameter, and secondary wall deposition = cell wall thickness) were calculated for earlywood, latewood and total tree ring over 50 years. Similar earlywood anatomical structure and low between-trait correlations (r = 0.21…67) were observed in all species, which supports prevalence of external impact on its formation, i.e. that shared habitat, climate, and similar habitus provide common trade-off between hydraulic efficiency and safety. Also, stronger nonlinearity of relationship between cell number and radial diameter in earlywood decreased correlations between them. In latewood, anatomical traits are strongly interconnected (r = 0.63…93) for all species. However, Siberian pine has significantly less pronounced latewood; later switch from earlywood and different strategy of carbon allocation are proposed as possible reasons. Length of vegetative season and sum of temperatures above thresholds 5 °C and 8 °C have no significant correlations with anatomical traits, but extremes of these temperature variables led to forming more pronounced latewood (higher proportion of latewood cells with thicker walls) during warm/long vegetative seasons than during short/cool ones.

Phytosociological analysis of European larch forests in the Southeastern Alps

Abstract Using the (unweighted) average linkage clustering (UPGMA) method we classified 458 phytosociological relevés of Larix decidua forests in the Southeastern Alps into 25 clusters. Based on their analysis we described the following new subassociations: Rhodothamno-Laricetum deciduae geetosum rivalis, sorbetosum chamaemespili, piceetosum abietis, adoxetosum moschatellinae, cystopteridetosum fragilis, cyclaminetosum purpurascentis, dryadetosum octopetalae and sorbetosum ariae. The selected method proved adequate in identifying the differences between larch stands on potential subalpine spruce and beech sites, and larch forests on the upper forest line, as well as the differences between initial larch stages on the upper forest line and more stable development stages on better developed soils on promontories and ledges above the upper beech forest line. Larch forests occur mainly in the altitudinal belt between (1,500) 1,600 and 1,800 (1,900) m, on shady aspects and slopes that are steeper than 30°. They are some of the best preserved forest types in the Southeastern Alps, on smaller surface areas (Macesnje above the Beli Potok valley in the Julian Alps) even virgin forests, and their role as biotopes is exceptional.

Biodiversity and climate change: consequences for upper tree line in Slovakia

Abstract Study of the effects of climate change on upper tree limit has mainly focused on the diversity of tree species as a result of the ability of species to tolerate temperature and moisture changes as well as some effects of disturbance regime changes. The tree species diversity changes due to climate change has been analysed via gap model and biodiversity indices. Gap models are individually based on simulations of establishment, growth, and mortality of each tree on the forest plot. Input ecological data for model calculations have been taken from the permanent research plots located in primeval forests in mountainous regions in Slovakia. The results of regional scenarios of the climatic change for the territory of Slovakia have been used, from which the values according to the CGCM3.1 (global) model, KNMI and MPI (regional) models. Model results for conditions of the climate change scenarios suggest a shift of the upper forest limit to the region of the present subalpine zone, in supramontane zone. The most significant tree species diversity changes have been identified for the upper tree line and current belt of dwarf pine (Pinus mugo) occurrence. Hill’s index of biodiversity in the upper forest line increased by 30 – 35% for horizon of 2050, resp. by 45 – 50% modeled for the horizon of 2075. Calculated values of Shannon’s index show an even higher increase due to climate change. For horizon 2050 is a roughly of three fold increase and horizon for 2075 by almost fivefold increase in the value of the index. Results from the gap model indicate the increase of tree species diversity 2 – 2,5 times.

Millennial-scale vegetation changes in the tropical Andes using ecological grouping and ordination methods

Abstract. We compare eight pollen records reflecting climatic and environmental change from northern and southern sites in the tropical Andes. Our analysis focuses on the last 30 000 years, with particular emphasis on the Pleistocene to Holocene transition. We explore ecological grouping and downcore ordination results as two approaches for extracting environmental variability from pollen records. We also use the records of aquatic and shoreline vegetation as markers for lake level fluctuations and moisture availability. Our analysis focuses on the signature of millennial-scale climate variability in the tropical Andes, in particular Heinrich stadials (HS) and Greenland interstadials (GI). The pollen records show an overall warming trend during the Pleistocene–Holocene transition, but the onset of post-glacial warming differs in timing among records. We identify rapid responses of the tropical vegetation to millennial-scale climate variability. The signatures of HS and the Younger Dryas are generally recorded as downslope upper forest line (UFL) migrations in our transect, and are likely linked to air temperature cooling. The GI1 signal is overall comparable between northern and southern records and indicates upslope UFL migrations and warming in the tropical Andes. Our marker for lake level changes indicated a north-to-south difference that could be related to moisture availability. The air temperature signature recorded by the Andean vegetation was consistent with millennial-scale cryosphere and sea surface temperature changes but suggests a potential difference between the magnitude of temperature change in the ocean and the atmosphere. We also show that arboreal pollen percentage (AP %) and detrended correspondence analysis (DCA) scores are two complementary approaches to extract environmental variability from pollen records.

North Andean environmental and climatic change at orbital to submillennial time-scales: Vegetation, water-levels and sedimentary regimes from Lake Fúquene between 284 and 130 ka

We present a record of environmental and climatic changes in the northern Andes during the penultimate interglacial–glacial cycle based on integrated information from pollen and grain size distributions (GSDs). The record reflects the 58.33–26.21m interval of a new sediment core from Lake Fúquene (2540m elevation; 5°N) in the Colombian Andes. The age model is mainly based on cyclostyratigraphy and shows that this core interval reflects the period from 284 to 130ka. The 1cm sample increments yield a resolution of ~60yr. In 2553 samples we analyzed 66 selected pollen and spore taxa with the best known ecological ranges. We reconstructed upper forest line (UFL) positions between ~2000 and ~3400m elevation and the most abrupt temperature shifts ranged up to 10°C/100yr at Terminations II and III. Regional vegetation change is mainly driven by eccentricity (100kyr) and obliquity (41kyr) cycles, while changes in local aquatic vegetation show variability in the obliquity and precession (21kyr) bands. Millennial-scale climate variability reflecting Dansgaard–Oeschger (DO) climate cycles in the upper part of the record, continues in this penultimate intergalcial–glacial cycle strongly suggesting that this variability has a persistent character in Pleistocene vegetation and climate dynamics. Short-lived upslope excursions of the UFL reflect 20 DO-style cycles during marine isotope stages (MIS) 7 and 6. Changes in species composition of montane forest are evident, and trees with most pioneer qualities (Alnus, Morella, Quercus and Weinmannia) migrated at the forefront. Other arboreal taxa like Podocarpus, Miconia, and Hedyosmum mostly followed later. Changes in regional vegetation distribution and forest composition, as well as in local aquatic vegetation and GSD of sediments supplied to the lake, allowed the development of an integrated reconstruction of the biotic and abiotic environments in the drainage basin.

Extreme climatic events in the Republic of Tuva according to tree-ring analysis

This paper presents results of the spatial distribution of anomalies (disturbances) in the anatomical structure of the annual and missing rings of Siberian larch at the upper forest line in the Republic of Tuva. The spatial analysis of tree-ring chronologies that was conducted on six sites (Mongun, Kolchan, Tan, Derzik, Kungur, and Taris) has made it possible to identify the extreme events of local (1662, 1699, 1792, 1804, 1814, 1821, 1847, 1867, and 1993), regional (1698, 1754, 1775, 1779, 1785, 1788, 1789, 1797, 1813, 1819, 1843, 1854, 1869, 1870, 1882, 1911, and 1923), and interregional (1783, 1784, 1812, and 1884) importance; the latter are in good agreement with the data on large volcanic eruptions (the Grimsvotn, Lakagigar, Soufriere St. Vincent, and Krakatau volcanoes) and data from historical sources.

Facilitation and edge effects influence vegetation regeneration in old‐fields at the tropical Andean forest line

AbstractQuestionsDo local plant–plant interactions and facilitation play an important role in vegetation dynamics after disturbance in the high tropical Andes? In particular, does the dominant shrub Baccharis prunifolia have an effect on microclimate and local vegetation structure within old‐fields at the upper forest line? Does distance from the border of the surrounding forests also influence community structure within fallow plots? Is there an interaction between facilitation and edge effects on vegetation regeneration?LocationGavidia Valley, Sierra Nevada de Mérida, Venezuela.MethodsPlant cover, species richness and community structure were compared in circular micro‐plots placed under the canopy of B. prunifolia shrubs and in open areas (12 micro‐plots in each case) both near and far from the forest border within two 10–12 yr successional plots at 3400 m a.s.l. (a total of 96 micro‐plots). Additionally, topsoil temperature was monitored for 1 mo in the four situations under study.ResultsAverage and maximum temperature and temperature amplitudes were lower under the canopy of B. prunifolia shrubs than in open areas; this effect being more marked far from the forest edge. Species richness, vegetation cover and the density of dominant forest trees were higher under the shrubs’ canopy than in the inter‐shrub spaces. The proximity to the edge of the surrounding forest also had a positive effect on species richness, with no significant interaction with the local sampling situation (under shrub vs outside).ConclusionsOur results suggest that both facilitation and edge effects influence the effectiveness of vegetation regeneration within old‐fields in the high tropical Andes. Consequently, these processes should be considered for interpreting vegetation dynamics in environmental change scenarios at the tropical mountain tree line and for the design of ecological restoration strategies in these high‐diversity ecotones, which have been subjected to large‐scale anthropogenic transformations in recent decades.

LATE GLACIAL AND HOLOCENE ENVIRONMENTAL CHANGE INFERRED FROM THE PÁRAMO OF CAJANUMA IN THE PODOCARPUS NATIONAL PARK, SOUTHERN ECUADOR

To reconstruct the environmental history including vegetation, fire and climate dynamics, from the Cajanuma valley area ( 3285 m elevation) in the Podocarpus National Park, southern Ecuador , we address the following major research question: (1) How did the mountain vegetation developed during the late Glacial and Holocene? (2) Did fire played an important control on the vegetation change and was it natural or of anthropogenic origin?. Palaeoenvironmental changes were investigated using multiple proxies such as pollen, spores, charcoal analyses and radiocarbon dating. Pollen data indicated that during the late Glacial and transition to the early Holocene (ca. 16 000–10 500 cal yr BP) herb paramo was the main vegetation type around the study area, while subparamo and mountain rainforest were scarcely represented. The early and mid-Holocene (ca. 10 500 to 5600 cal yr BP) is marked by high abundance of paramo during the early Holocene followed by a slight expansion of mountain forest during the mid-Holocene. During the mid- to late Holocene (ca. 5600–1200 cal yr BP) there is a significant presence of paramo and subparamo while Lower Mountain Forest decreased substantially, although, Upper Mountain Forest remained relatively stable during this period. The late Holocene, from ca. 1200 cal yr BP to present, was characterized by paramo; however, mountain forest and subparamo presented significantly abundance compared to the previous periods. Fires became frequent since the late Holocene. The marked increased local and regional fire intensity during the wetter late Holocene strongly suggests that were of anthropogenic origin. During the late Glacial and early Holocene, the upper forest line was located at low elevations; but shifted slightly upslope to higher elevations during the mid-Holocene.

An ecological paradox: high species diversity and low position of the upper forest line in the Andean Depression.

Systematic investigations of the upper forest line (UFL) primarily concentrate on mid and high latitudes of the Northern Hemisphere, whereas studies of Neotropical UFLs are still fragmentary. This article outlines the extraordinary high tree diversity at the UFL within the Andean Depression and unravels the links between the comparatively low position of the local UFL, high tree-species diversity, and climate. On the basis of Gentry′s rapid inventory methodology for the tropics, vegetation sampling was conducted at 12 UFL sites, and local climate (temperature, wind, precipitation, and soil moisture) was investigated at six sites. Monotypic forests dominated by Polylepis were only found at the higher located margins of the Andean Depression while the lower situated core areas were characterized by a species-rich forest, which lacked the elsewhere dominant tree-species Polylepis. In total, a remarkably high tree-species number of 255 tree species of 40 different plant families was found. Beta-diversity was also high with more than two complete species turnovers. A non-linear relationship between the floristic similarity of the investigated study sites and elevation was detected. Temperatures at the investigated study sites clearly exceeded 5.5°C, the postulated threshold value for the upper tree growth limit in the tropics. Instead, quasi-permanent trade winds, high precipitation amounts, and high soil water contents affect the local position of the UFL in a negative way. Interestingly, most of the above-mentioned factors are also contributing to the high species richness. The result is a combination of a clearly marked upper forest line depression combined with an extraordinary forest line complexity, which was an almost unknown paradox.

Spatial relations and population structure of a dominant tree along a treeline ecotone in the Tropical Andes: interactions at gradient and plant-neighbourhood scales

Background: Studies in temperate mountains suggest that plant–plant interactions modulate tree establishment above the forest line. In tropical mountains worldwide this issue remains largely unexplored. Aims: To analyse the population structure and local spatial relationships of a dominant tree at a species-rich tropical Andean forest line. Methods: We determined changes in the population structure of Diplostephium venezuelense along an elevation gradient between continuous forest and open páramo and analysed plant community structure and superficial rock cover in the neighbourhood of saplings and adults at the upper forest line. Results: Sapling and adult densities were highest in low-altitude páramos adjacent to the forest line and at the borders of small forest islands. Saplings showed local spatial aggregation, were positively associated with small boulders and low shrubs, and negatively associated with mosses and lichens. However, no spatial association was found between scattered adults in the páramo and saplings of other forest trees. Conclusions: Complex species-specific local spatial interactions, suggesting both facilitative and antagonistic effects, seem to modulate the establishment of the dominant tree D. venezuelense at and above the upper forest line. Nevertheless, the establishment of other tree species above continuous forests does not appear to be facilitated by the canopy cover offered by the isolated D. venezuelense individuals established in open páramo environments.

Reconstruction of late Holocene forest dynamics in northern Ecuador from biomarkers and pollen in soil cores

Centuries of human interference have led to large scale reduction of montane forests in the northern Ecuadorian Andes. As a result the natural position of the upper forest line (UFL) in the area is now subject of scientific debate, which is hindering sustainable reforestation efforts. Uncertainty is fuelled by insufficient precision of fossil pollen spectra to reconstruct the natural UFL position. Here we tried to resolve this issue by using biomarkers, i.e. plant species specific patterns of n-alkanes and n-alcohols, preserved in soils in the northern Ecuadorian Andes as additional proxy to reconstruct the natural UFL position. To unravel preserved biomarker patterns we used the recently developed VERHIB model, and for the first time assessed its applicability in soil archives. Changes in Holocene biomarker-based vegetation composition were directly compared to changes in pollen-based vegetation composition from the same soil profiles. Both proxies proved to be complementary and a combined application allowed for a more accurate reconstruction of past vegetation than with pollen analysis alone. We found that the present-day UFL in the study area has not been significantly depressed by human interference and was at 3650m maximally during late Holocene times. For the moment of post-glacial forest development we found a migration lag between pollen (earlier) and biomarkers (later). This reflects the difference between the non-transported biomarker signal showing spot-dating (thus in paleoecological studies functionally equalling the information from plant macro-remains in peat bogs), and the upslope wind-blown pollen signal showing an upslope forest expansion up to over a millennium ahead. The combined pollen-biomarker approach in soil cores shows great potential for vegetation reconstruction. However, more research of biomarker consistency and preservation is needed before application in other environments.

North Andean environmental and climatic change at orbital to submillennial time-scales: Vegetation, water levels and sedimentary regimes from Lake Fúquene 130–27 ka

We present a record of environmental and climatic change in the northern Andes during the last interglacial–glacial cycle based on integrated information from pollen and grain size distributions (GSD). The record reflects the 26.21–1.64m interval of a new sediment core from Lake Fúquene (2540m elevation; 5°N) in the Colombian Andes. The age model was developed by Groot et al. (2011) and shows this core interval reflects the period from 130 to 27ka and the 1-cm sample increments yield an average resolution of 60years. We analyzed in 2032 samples 66 pollen and spore taxa with optimal ecological constraints. We reconstructed upper forest line (UFL) positions between ~2200 and ~3400m elevation. We found frequent temperature changes up to 2–3°C/100yr. Regional vegetation change is mainly driven by obliquity (41kyr), and eccentricity (100kyr). Important short-lived upslope excursions of the UFL reflect millennial-scale climate variability superimposed on orbital-scale variability. These cycles reflect Dansgaard–Oeschger (DO) climate cycles in time and signature. DO cycles 8, 12, 14, 19, 20, 26, 27 and 28 are most prominently documented. Cycles vary from ~1.5 to 3kyr with an average of 2.7kyr.Changes in species composition of montane forest are evident and trees with mostly pioneer qualities (Alnus, Myrica, Quercus and Weinmannia) migrate in the forefront. Other trees like Podocarpus, Miconia, and Hedyosmum mostly follow later. Changes in regional vegetation distribution and forest composition, changes in local aquatic vegetation, and changes in GSD of sediments supplied to the lake allow to develop an integrated reconstruction of the biotic and abiotic environments in the drainage basin.

Pollen-based 17-kyr forest dynamics and climate change from the Western Cordillera of Colombia; no-analogue associations and temporarily lost biomes

A 17kyr long pollen record from the unexplored Western Cordillera of Colombia (Páramo de Frontino; 3460m elevation) shows vegetation change and inferred climate dynamics at ~125yr resolution. The cold and wet Lateglacial showed well-defined stadials and interstadials. At the transition to the Holocene the upper forest line (UFL) shifted within 200years 700–800m upslope reflecting a temperature increase of ~4.5°C. Dead wood in the forests may have caused frequent fires. Individual taxa show clear and discrete successive expansion events, such as Podocarpus around 15calka, Quercus, Melastomataceae, Myrsine, Weinmannia, and Hesperomeles around 11.5calka, and Alnus around 9calka showing the floristic composition of the montane forest changed during its upslope migration. After forest had reached around 9calka a quasi-stable altitudinal interval forest taxa continued to change proportions showing that upslope forest migration caused significant internal forest dynamics. Forest stability is not found suggesting that an equilibrium between forest composition and environmental variables was not reached. We hypothesize trees migrated faster upslope than the shrubs causing a temporarily loss of this shrub biome. During most of the Holocene the UFL varied between 3500 and 3700m indicating warmer temperatures than today. High upper limits of subandean forest suggest that the lowermost level of significant night frost was at higher elevations than today. Driest pulses were registered ~9170 and ~8200calka since 620calka deforestation of Quercus, Podocarpus and Weinmannia in particular shows anthropogenic impact. Comparisons with other Andean climate records show a climatic asymmetry mainly related to migrations of the ITCZ. An implication of the present benchmark records of vegetation and climate variability and modeling is that new records should be analyzed at better than century resolution.

Pollen–vegetation relationships at a tropical cloud forest's upper limit and accuracy of vegetation inference

Palaeoecological records are increasingly needed from tropical montane systems. To infer past tropical vegetation dynamics, understanding modern pollen–vegetation relationships is required, but understanding effects of different sampling media between calibration datasets and palaeorecords is also needed. This is especially true when palaeorecords are derived from bogs or lakes with boggy shores and common wetland plants share the same pollen taxon with important upland plants that distinguish tropical vegetation types (e.g., Poaceae and Plantago). We assessed modern pollen–vegetation relationships around an upper cloud forest line in the Hawaiian Islands and tested the utility of a modern pollen calibration dataset derived from 88 surface soil samples when applied in 10 test wetland sites more typical of palaeorecords. We assessed over- and under-representation of pollen/spore taxa with a direct comparison to plant abundance and derived several metrics from the pollen/spore assemblages — analogs, ordinations, relative abundance of life forms, and ratios of life forms. We used the Receiver Operator Characteristic (ROC) to (1) compare metric performance at distinguishing vegetation around the upper forest line, (2) assess whether excluding wetland taxa significantly affected metric performance, and (3) test the accuracy of vegetation inference. Pollen–vegetation relationships were influenced by great ecological breadth and over- or under-representation of pollen and spores, which could be explained by pollination syndrome (wind vs. animal), grain/spore mass and upslope transport in winds. However, we found no evidence that upslope transport significantly blurred the upper-forest-line signal here, likely because winds are predominantly perpendicular to slope, and vertically constrained by the trade-wind inversion. Pollen from Poaceae and Plantago characterizes vegetation around this Hawaiian upper forest line and dominates wetland assemblages. Removing wetland taxa from the modern pollen calibration dataset levied no cost on a metric's performance, and greatly reduced the incidence of inaccurate vegetation inference in test sites. Minor error rates remained when rare, over-represented, or ecologically broad types were used in isolation. Overall, this study demonstrates that inferring forest line position from fossil pollen/spore assemblages requires careful consideration because (1) differences in sampling media between the modern calibration dataset and palaeorecords create opportunity for inaccurate vegetation inference and (2) some metrics perform better than others.

Commentary: Is climate change making plants go up mountains?

ISSN 1948-6596 news and update commentary Is climate change making plants go up mountains? Paleontological evidence indicates that about 2.5 million years ago the world climate entered a pe- riod of instability. Climatic fluctuations, probably forced by cyclical changes in the earth’s orbit around the sun, resulted in a series of ice ages and today we are in a period between glacial ad- vances. Alterations in solar radiation are also thought to cause climatic variation such as the Medieval Warm Period (~950-1200 AD) and Little Ice Age (~1650-1850 AD); and major volcanic eruptions lead to short-term changes by changing atmospheric reflectance. In addition to these natural factors, climate is also increasingly thought to be influenced by human activities, an issue that is the topic of intense international dis- cussion under the United Nations Framework Con- vention on Climate Change (UNFCCC) and where the scientific indicators of climate change have been under a media spotlight. During the last century almost all environ- mentally important atmospheric trace gases have increased dramatically, and the consensus opinion of the Intergovernmental Panel on Climate Change (IPCC) is that there is correlation between changes in atmospheric composition and ob- served changes in the global climate. Major rea- sons are increasing use of fossil fuel energy, to- gether with land use changes such as for food and energy production. These human activities lead to the mobilisation and volatilisation of soil and plant carbon and nitrogen stocks, increasing the flux of CO 2 , CH 4 and N 2 O into the atmosphere (IPCC 2007). During the last century, global mean sur- face temperature has increased with unprece- dented speed since records began and CO 2 levels range beyond any of those of the last 650,000 years (IPCC 2007). In a study of the altitudinal distribution of 171 western European mountain forest plant spe- cies based on an impressive database, Lenior et al. (2008) have provided some evidence that ob- served increases in regional temperature are be- ing translated into upward shifts of plant species. They compared the altitudinal distribution of their sample between two time periods: 1905-1985 and 1986-2005, over an elevational range of 0-2600 m, and calculated an aggregate upwards shift of 64 meters from 1971 (mean year of the first interval) and 1993 (mean year of the second interval) in the core ranges of the plants investigated. As might be expected with such rapid changes in climate, trees showed less response than herbaceous species. In an additional study to investigate whether or not woody plants were also upwardly mobile, Lenoir et al. (2009) tried to demonstrate that, even if adult trees did not show a climate change signal, their seedlings were indeed responding. Both studies made attempts to eliminate confounding variables, but in doing so included some bias. They investigated the spatial core of the species’ ranges, rather than the edges of distributions, where the effects of climate change are likely to be most apparent, but where there is also likely to be greater natural fluctuation. In addition they only included forest communities, which are buff- ered by the micro-climate created by the forest canopy and so are less likely to show short-term responses. Moreover they ruled out the effects of increasing nitrogen deposition, land-use change, invasive species and CO 2 fertilisation. On the other hand they excluded trees with a high risk of hu- man introduction such as spruce, and in so doing lost one of the most important trees of the upper forest line. How important is this evidence in the con- text of policy making? It shows that, in western European mountains at least, regional tempera- ture increases are partly being translated into up- ward shifts of plant communities. However, as one would expect from an individualistic response to environmental change, the species did not be- have uniformly. Mountain plants showed greater shifts than elevation generalists, as did plants with faster life history traits. Of the 171 species in the first paper (Lenoir et al. 2008) two-thirds went up but a third went down. Similarly of the tree spe- cies analysed in detail (Lenoir et al. 2009), the seedlings of 10 species showed an upward trend frontiers of biogeography 2.1, 2010 — © 2010 the authors; journal compilation © 2010 The International Biogeography Society

Three millennia upper forest line changes in northern Ecuador: Pollen records and altitudinal vegetation distributions

New pollen records from a peat bog and a soil profile in the Guandera Reserve (0°36′N, 77°42′E) document the altitudinal position and dynamics of the natural upper forest line (UFL) in the deforested landscape of northern Ecuador during the last ~ 3000 yr. We tested the hypothesis that páramo vegetation between 3600 and 4100 m developed during the last centuries as a consequence of anthropogenic deforestation. Analysis of pollen and non-pollen palynomorphs in 170 cm long peat core G8 at 3810 m, some 200 m above the current UFL, shows five periods of forest dynamics: (1) from 2880 to 1370 cal yr BP the UFL was at ~ 3500 m and patches with asteraceous trees and shrub in the páramo were close to the site; (2) from 1370 to ~ 500 cal yr BP the UFL lowered to ~ 3350 m; (3) from ~ 500 to ~ 300 cal yr BP upper montane rainforest (UMRF) expanded rapidly and the UFL shifted to ~ 3550 m while relatively wet climatic conditions prevailed; (4) from ~ 300 to ~ 150 cal yr the UFL reached ~ 3600 m and (5) from ~ 150 cal yr BP to present high proportions of Rumex indicate an increase of agricultural fields. The UFL continued at ~ 3600 m. Pollen analysis of the 70 cm deep soil monolith G7 shows during the last three millennia a continuous presence of páramo at 3820 m elevation but did not allow to estimate altitudinal shifts of the UFL. We conclude that during the last three millennia the natural UFL was maximally at 3700 m elevation. This is in support of previous palynological studies by Wille et al. (2002) and Bakker et al. (2008). The hypothesis assuming an UFL around 4000 m is rejected which implicates páramo vegetation above 3650 m reflects a natural ecosystem. There is now compelling evidence that planting forest in the frame of the Kyoto Protocol is unjustified above 3650 m elevation.