Fire and vegetation history during the last 3800 years in northwestern Montana

Foy Lake in northwestern Montana provides a record of annual-to-decadal-scale landscape change. Sedimentary charcoal and pollen analyses were used to document fire and vegetation changes over the last 3800 years, which were then compared to similar records from AD 1880 to 2000. The long-term record at Foy Lake suggests shifts between forest and steppe as well as changes in fire regime that are likely the result of climate change. Fire activity (inferred from the frequency of charcoal peaks) averaged 18 fire episodes/1000 years from 3800 to 2125 cal year BP, and increased from 16 fire episodes/1000 years at 2125 cal year BP to 22 episodes/1000 years at 750 cal year BP, a period when the pollen data suggest that steppe vegetation yielded to increasing patches of forest cover. Between 2125 and 750 cal year BP, increased forest cover produced more background charcoal than before and after this period, when vegetation was dominated by steppe. Between 750 and 75 cal year BP steppe has expanded and fire episode frequency averaged 33 episodes/1000 years, increasing to a maximum of 40 episodes/1000 years at ca. 300 cal year BP and then decreasing to present levels. Since AD 1880, the pollen record indicates an increase in shrubs and grasses from AD 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing. No fires have been documented in the Foy Lake watershed since AD 1880. Charcoal from the extralocal fires of AD 1910, burning over 4,111,249 ha in Idaho, Montana, and Wyoming, however, is present in Foy Lake. Between AD 1970 and 2000, increased arboreal pollen in the record is consistent with observations that the forest has become more closed. The activities of Euro–Americans have led to a decline in forest cover between AD 1880 and 1970, followed by a recent increase as trees are now growing in areas previously occupied by steppe. Euro–Americans are likely the cause of a reduction in fire activity in watershed since AD 1880.     

Late glacial and Holocene vegetation history at Poets hill lake,western Tasmania

Pollen analysis of 3.25 m of late glacial and Holocene sediments gives a mid‐altitude (600 m) record of vegetation development after the last or Margaret Glaciation. Alpine herbfield, coniferous heath and Nothofagus gunnli scrub developed on the moraines until 11,400 BP. Wet montane forest and heath then developed with Phyllocladus aspleniifolius, Nothofagus cunninghamii and Eucalyptus until c. 10,000 BP. After 10,000 BP a mosaic of N. cunninghamii rainforest, Myrtaceae and Proteaceae scrub and Sprengelia incarnata heath occurred. The development of the vegetation from alpine communities to temperate rainforest, which is near its limit at 600 m, occurred under the influence of improving climatic conditions with rapid upslope migration or local expansion of taxa during the late glacial. Temperatures were warm enough for the development of rainforest at 600 m by 10,000 BP, if not earlier. The development of a mosaic of rainforest, scrub and heath vegetation rather than extensive rainforest after 10,000 BP reflects the influence of poor soils, bad drainage and fires. Comparison with similar pollen diagrams from western Tasmania suggests that the development of pollen/vegetation associations was time transgressive with altitude during the late glacial when climatic influences and migration rates were important, and that the mosaic of vegetation communities became more complex during the Holocene because of adjustment to or control by local ecological factors.     

A 140-year record of recent changes in aquatic productivity in a remote,tropical alpine lake in the Rwenzori Mountain National Park,Uganda

Environmental change in many tropical, alpine habitats remains poorly resolved due to an absence of proximate and sustained observations. In the Rwenzori Mountains of East Africa, glaciers have receded rapidly over the last century, and here we assess the impact of this recession through palaeolimnological analyses of a 45 cm sediment core (Buju3) from Lake Bujuku which is closest to the ice-fields and partly supplied by melt water in-flows. ²¹⁰Pb and ¹³⁷Cs suggest that Buju3 has an average sedimentation rate of 2.9 mm year⁻¹ and the base of the core can be dated to 1864 ± 20 years. Contemporary diatom taxa found in the lake are dominated by Tabellaria flocculosa and Synedra spp., but also include Achnanthes minutissima and Fragilaria pinnata. However, the diatom flora for Buju3 is less diverse and dominated by small, tychoplanktonic species of Fragilaria. Over the period associated with glacial recession, organic carbon isotope analysis (δ¹³C) suggests a small but distinct increase in within-lake productivity, which increases in rate since the mid 1970s up to the present day, in line with a shift towards increased algal productivity (as highlighted by C/N ratios). However, the diatom and pollen records appear rather insensitive to changes in glacier recession since the late 19th century.     

Storm rainfall conditions for floods and debris flows from recently burned areas in southwestern Colorado and southern California

Debris flows generated during rain storms on recently burned areas have destroyed lives and property throughout the Western U.S. Field evidence indicate that unlike landslide-triggered debris flows, these events have no identifiable initiation source and can occur with little or no antecedent moisture. Using rain gage and response data from five fires in Colorado and southern California, we document the rainfall conditions that have triggered post-fire debris flows and develop empirical rainfall intensity–duration thresholds for the occurrence of debris flows and floods following wildfires in these settings. This information can provide guidance for warning systems and planning for emergency response in similar settings.Debris flows were produced from 25 recently burned basins in Colorado in response to 13 short-duration, high-intensity convective storms. Debris flows were triggered after as little as six to 10 min of storm rainfall. About 80% of the storms that generated debris flows lasted less than 3 h, with most of the rain falling in less than 1 h. The storms triggering debris flows ranged in average intensity between 1.0 and 32.0 mm/h, and had recurrence intervals of two years or less. Threshold rainfall conditions for floods and debris flows sufficiently large to pose threats to life and property from recently burned areas in south-central, and southwestern, Colorado are defined by: I = 6.5D^− 0.7 and I = 9.5D^− 0.7, respectively, where I = rainfall intensity (in mm/h) and D = duration (in hours).Debris flows were generated from 68 recently burned areas in southern California in response to long-duration frontal storms. The flows occurred after as little as two hours, and up to 16 h, of low-intensity (2–10 mm/h) rainfall. The storms lasted between 5.5 and 33 h, with average intensities between 1.3 and 20.4 mm/h, and had recurrence intervals of two years or less. Threshold rainfall conditions for life- and property-threatening floods and debris flows during the first winter season following fires in Ventura County, and in the San Bernardino, San Gabriel and San Jacinto Mountains of southern California are defined by I = 12.5D^−0.4, and I = 7.2D^−0.4, respectively. A threshold defined for flood and debris-flow conditions following a year of vegetative recovery and sediment removal for the San Bernardino, San Gabriel and San Jacinto Mountains of I = 14.0D^−0.5 is approximately 25 mm/h higher than that developed for the first year following fires.The thresholds defined here are significantly lower than most identified for unburned settings, perhaps because of the difference between extremely rapid, runoff-dominated processes acting in burned areas and longer-term, infiltration-dominated processes on unburned hillslopes.     

鲁西北地区土地现实生产力调查与估算

以鲁西北地区县级1∶5万土壤类型图图斑作为基础评价单元,根据农户现有的投入水平,采用“调查法”模拟分析农业土地资源的现实生产力,并与统计资料和“机制法”模型模拟结果进行对比分析。研究结果表明,现实投入水平下鲁西北地区夏玉米单产略高于冬小麦单产,对冬小麦的投入从整体上来看相当于中等投入,但又存在着区域差异。对夏玉米的投入具有南北向的差异,由南到北投入水平逐渐降低。鲁西北地区土地现实生产力以宁津县最高,庆云县最低,与“机制法”模型模拟结果比较,各县市之间土地生产潜力差距较大。由此可以说明,各县市土壤质量本身对土地年生产力的大小起着重要作用,进一步证明“调查法”能充分反映土壤在土地综合性质中的主要作用。     

Estimating the short-term impact of fire on rangeland productivity in a semi-arid climate of South Africa

The short-term (2 years) influence of fire burning with the wind (head fire) and against the wind (back fire) on the productivity (above-ground phytomass and litter) and fire behaviour were determined over seven growing seasons (1995/96–2001/02) in a semi-arid rangeland. The results showed that head fires had significantly greater flame height and rate of spread than back fires. Fire caused a decrease of 40.5% and 22.5% in basal cover for the first and second seasons after burning respectively. The seasonal above-ground phytomass production and litter were significantly decreased by fire over all growing seasons. Seasonal production losses due to fire varied between 225 and 430 kg ha⁻¹. The relation between above-ground phytomass production loss due to fire, and two independent variables namely seasonal rainfall and fuel load (above-ground phytomass plus litter) before burning, were investigated. The multiple linear regression equations obtained for one (r=0.89) and 2 years (r=0.86) after a fire, can be used with great success in estimating seasonal production losses due to fire in semi-arid rangeland.     

Rainfall variability,rainfed agriculture and degree of human marginality in North Guanajuato,Mexico

Mexico has a heterogeneous climate due to its geographical location. Half of the Mexican territory is dryland, mostly in the centre and north of the country, within which agriculture is the main activity in the primary production sector. At present, climate variability has a strong impact on Mexican agriculture. This study analysed rainfall variability, its impact on the agricultural productivity in terms of harvested quantity and productivity of 1996‐2014, and in parallel, the role that socioeconomic development plays on the well‐being of the population who live in areas with rainfed agriculture and a semi‐dry climate. The data obtained were analysed with the Statistical Analysis System. A positive correlation was found between rainfall and productivity (r = 0.76 for maize; r = 0.711 for beans). Rainfall variations therefore have a great impact on agricultural productivity, on food security and on the economy. Besides production losses, a parallel consequence is marginalization of the population because producers' income is increasingly reduced due to smaller crop volumes.     

Water relations and the effects of clearing invasive Prosopis trees on groundwater in an arid environment in the Northern Cape,South Africa

Several Prosopis species have been introduced into South Africa in the last century and many of them have become invasive. This study investigates the water relations, effects of clearing, and the seasonal dynamics of groundwater use by invasive Prosopis trees. The trees were growing on deep sandy soils in the floodplain of an episodic river in the arid Northern Cape Province of South Africa. Data were collected on tree water uptake, evapotranspiration and water table depth over different seasons. Effects of tree clearing on groundwater were quantified by comparing data from a Prosopis invaded and an adjacent cleared area. Transpiration rates were less than 1.0 mm/d throughout the year and the trees showed structural and physiological adaptations to the combined low rainfall and low water holding capacity of the soils by developing very narrow sapwood areas and by closing their stomata. The trees abstracted groundwater as evidenced by the decline in borehole water levels in the Prosopis stand before the rainy season. Groundwater savings of up to 70 m³/month could be achieved in spring for each hectare of Prosopis cleared. The study suggests that clearing of invasive Prosopis would conserve groundwater in the arid parts of South Africa.     

Holocene Vegetation Dynamics, Fire History, Lake Level and Climate Change in the Kootenay Valley, Southeastern British Columbia, Canada

The environmental history of the Kootenay Valley in the southern Canadian Rockies was reconstructed using lake sediment from Dog Lake, British Columbia, and compared to other paleoenvironmental studies in the region to understand how vegetation dynamics and fire regimes responded to climate change during the Holocene. A pollen-based vegetation reconstruction indicates five periods of vegetation change. At 10,300 cal yr B.P. Pinus-Juniperus parkland colonized the valley and by 7600 cal yr B.P. was replaced by mixed stands of Pinus, Picea and Pseudotsuga/Larix. Fire frequencies increased to their Holocene maximums during the 8200–4000 cal yr B.P. period. From 5500–4500 cal yr B.P. Pseudotsuga/Larix reached its maximum extent in the Kootenay Valley under a more frequent fire regime. At 5000 cal yr B.P. Picea and Abies began to expand in the area and by 4500 cal yr B.P. the forest shifted to a closed montane spruce forest type with dramatically reduced fire frequency. The shift to less frequent forest fires after 4500 cal yr B.P., along with a moisterPicea – dominated closed forest, corresponds to Neoglacial advances in the Canadian Rockies and Coast Mountains. Fire intervals after 4000 cal yr B.P. are significantly longer than the shorter fire intervals of the early to mid Holocene. A return to drier, more open forest condition occurs between 2400–1200 cal yr B.P. with a slight increase in fire activity and summer drought events. Lower lake levels inferred by charophyte accumulation rates during the 2400–1200 cal yr B.P. interval support this moisture regime shift. An abrupt shift toPicea dominated forest occurred from 1200–1000 cal yr B.P. and a final period of wet-closed forest cover reaches its maximum extent from 700–150 cal yr B.P. that appears to be a response to Little Ice Age cooling. Present forests are within their natural range of variability but are predicted to shift again to a drier more open structure with increased Pseudotsuga/Larix cover. More frequent stand replacing fires and increased area burned likely will accompany this change due to continued global warming.     

Nest dynamics of Constrictotermes cyphergaster (Termitidae,Nasutitermitinae) and its association with the supporting vegetation in a semiarid area,northeast, Brazil

We evaluated growth, abandonment, decay and emergence of new nests of the Neotropical termite Constrictotermes cyphergaster (Termitidae) and its association with the supporting vegetation in an area of caatinga (arid thorn scrub in the state of Paraíba, northeastern Brazil). In an area of 1 ha, a total of 272 nests were observed monthly, from March 2005 to March 2007. Of these, 245 nests were small, 9 were of medium size, and 18 were large nests. During the rainy season (from June to February), nests grew 94.2 L, whereas during the dry season (March–May), their total growth was 23 L. The number of abandoned nests was positively correlated with rainfall. Decomposition of nests was greater during the rainy season. The pattern of nest distribution was associated with the distribution of the primary supporting plants. Rainfall appears to be one of the most important factors in the dynamics of growth of nests of C. cyphergaster in the caatinga.     

Phytoplankton composition and dynamics in three shallow temporary salt lakes (Monegros, Spain)

The present study deals with phytoplankton composition and dynamics of three ephemeral saline lakes (La Muerte, Piñol and Sulfúrica) situated in one of the most arid inland zone in Europe (Los Monegros). The lakes show marked differences among one another, although they are all temporary, shallow and saline systems (>30 g l⁻¹). La Muerte is dominated by microbial mats that are absent from the other two. Piñol is more exposed to strong winds than the other two lakes and exhibits higher turbidity. Sulfúrica appears to be the most extreme system, with the highest salinity, which leads to a complete absence of macrozooplankton. Phytoplankton composition in these lakes varies as a consequence of the different physico-chemical conditions; it is fundamentally composed of typical hypersaline species such as Dunaliella sp., Aphanothece sp., and soil benthic species (e.g. Hantzschia amphyoxis) that appear to play an important role in these systems. Comparative analysis of the microbial component (phytoplankton diversity and temporal evolution) under in situ conditions and the presence of various abiotic and biotic factors, including the impact of macrozooplankton grazing, shows that it is easy to overlook large differences in the community structure of apparently similar ecosystems. The present study is a contribution to the understanding of the often-neglected microbial ecology of ephemeral shallow lakes.     

Constraints to smallholders production of frankincense in Metema district, North-western Ethiopia

Frankincense, an aromatic exudate obtained from several Boswellia species, is an important commodity with the potential to invigorate economic development of the drylands of Ethiopia. Local people have been producing and trading frankincense for centuries to diversify their income sources. However, local people's involvement in the production of frankincense varies considerably among the producing dryland regions of the country. The objectives of this study were to investigate: (i) the potential of frankincense production, (ii) socio-cultural, economic and policy factors affecting the involvement of local people in the production of frankincense, and (iii) the current status of Boswellia woodlands in Metema district, which is one of the major frankincense producing areas in Ethiopia. The results showed that Boswellia papyrifera comprised 51% of the species composition of the vegetation of the district with 253.5 kg/ha/year production potential. The total annual frankincense production potential of the district was estimated to be 79,168 tons. However, almost all inhabitants do not benefit economically from the species due to: (i) cultural influence (67%), (ii) unattractiveness of income from frankincense compared to other economic activities in the area (38%), property tenure (27%), government policy on incense production (20%), poor knowledge on frankincense production (19%) and unawareness of the potential of frankincense as a source of income (5%). The absence of direct economic benefits for the local people from the woodlands is triggering their widespread degradation mostly from human induced fire, improper forest use and agricultural land expansion.     

A ~30,000-year record of environmental changes inferred from Lake Chen Co,Southern Tibet

Climatic and environmental changes since the last glacial period are important to our understanding of global environmental change. There are few records from Southern Tibet, one of the most climatically sensitive areas on earth. Here we present a study of the lake sediments (TC1 core) from Lake Chen Co, Southern Tibet. Two sediment cores were drilled using a hydraulic borer in Terrace 1 of Lake Chen Co. AMS ¹⁴C dating of the sediments showed that the sequence spanned >30,000 years. Analyses of present lake hydrology indicated that glacier melt water is very important to maintaining the lake level. Sediment variables such as grain size, TOC, TN, C/N, Fe/Mn, CaCO₃, and pollen were analyzed. Warm and moderately humid conditions dominated during the interval 30,000–26,500 cal year BP. From 26,500 to 20,000 cal year BP, chemical variables and pollen assemblages indicate a cold/dry environment, and pollen amounts and assemblages suggest a decline in vegetation. From 20,000 to 18,000 cal year BP, the environment shifted from cold/dry to warm/humid and vegetation rebounded. The environment transitioned to cold/humid during 16,500–10,500 cal year BP, with a cold/dry event around 14,500 cal year BP. After 10,500 cal year BP, the environment in this region tended to be warm/dry, but exhibited three stages. From 10,500 to 9,000 cal year BP, there was a short warm/humid period, but a shift to cold/dry conditions occurred around 9,000 cal year BP. Thereafter, from 9,000 to 6,000 cal year BP, there was a change from cold/dry to warm/humid conditions, with the warmest period around 6,000 cal year BP. After 6,000 cal year BP, the environment cooled rapidly, but then displayed a warming trend. Chemical variables indicate that a relatively warm/dry event occurred around 5,500–5,000 cal year BP, which is supported by time-lagged pollen assemblages around 4,800 cal year BP. Our lake sediment sequence exhibits environmental changes since 30,000 cal year BP, and most features agree with records from the Greenland GISP2 ice core and with other sequences from the Tibetan Plateau. This indicates that environmental changes inferred from Lake Chen Co, Southern Tibet were globally significant.     

Tectonics of the Xining Basin in NW China and its implications for the evolution of the NE Qinghai‐Tibetan Plateau

The continuous Cenozoic strata in the Xining Basin record the growth and evolution of the northeastern Qinghai–Tibetan Plateau. Here, the mechanisms and evolution of the Xining Basin during the Cenozoic were investigated by studying the sedimentary facies of 22 Cenozoic sections across the basin and detrital zircon U‐Pb ages of three Cenozoic sections located in the eastern, central and western basin, respectively. In the Eocene (ca. 50–44 Ma), the India‐Eurasia Collision affected the northeastern Qinghai–Tibetan Plateau. The Central Qilian Block rotated clockwise by ca. 24° to form the Xining Basin. The Triassic flysch sediments surrounding the basin were the primary sources of sediment. Between ca. 44–40 Ma, the basin enlarged and deepened, and sedimentation was dominated by saline lake sediments. Between ca. 40–25.5 Ma, the Xining Basin began to shrink and dry, resulting in the deposition of saline pan and saline mudflat sediments in the basin. After ca. 20 Ma, the Laji Shan to the south of the Xining Basin was uplifted due to the northward compression of the Guide Basin to the south. Clasts that eroded from this range dominated the sediments as the basin evolved from a lacustrine environment into a fluvial system. The Xining Basin was an extensional basin in the Early Cenozoic, but changed into a compressive one during the Late Cenozoic, it was not a foreland basin either to the Kunlun Shan or to the western Qinling Shan in the whole Cenozoic. The formation and deformation of the Xining Basin are the direct responses of the India‐Eurasia Collision and the growth of the Qinghai‐Tibetan Plateau.     

Carbon exchange rates in Polytrichum juniperinum moss of burned black spruce forest in interior Alaska

The Boreal black spruce forest is highly susceptible to wildfire, and postfire changes in soil temperature and substrates have the potential to shift large areas of such an ecosystem from a net sink to a net source of carbon. In this paper, we examine CO₂ exchange rates (e.g., NPP and Re) in juniper haircap moss (Polytrichum juniperinum) and microbial respiration in no-vegetation conditions using an automated chamber system in a five-year burned black spruce forest in interior Alaska during the fall season of 2009. Mean ± standard deviation microbial respiration and NEP (net ecosystem productivity) of juniper haircap moss were 0.27 ± 0.13 and 0.28 ± 0.38 gCO₂/m²/hr, respectively. CO₂ exchange rates and microbial respiration showed temporal variations following fluctuation in air temperature during the fall season, suggesting the temperature sensitivity of juniper haircap moss and soil microbes after fire. During the 45-day fall period, mean NEP of P. juniperinum moss was 0.49 ± 0.28 MgC/ha following the five-year-old forest fire. On the other hand, simulated microbial respiration normalized to a 10 °C temperature might be stimulated by as much as 0.40 ± 0.23 MgC/ha. These findings demonstrate that the fire-pioneer species juniper haircap moss is a net C sink in the burned black spruce forest of interior Alaska.     

Rainfall variability may modify the effects of long-term exclosure on vegetation in Mandalgobi,Mongolia

Starting in 2005, we examined differences in vegetation for three consecutive years across an airport fence that separated heavily grazed areas from areas in which grazing had been excluded for 24 years in Mandalgobi, Mongolia. We performed repeated-measures analysis separately on two community types (dominated by Allium polyrrhizum and Achnatherum splendens, respectively) to compare the effects of fencing and year on the cover of different plant functional types. There was a significant fence × year interaction for grass cover in the Allium type (but not the Achnatherum type), due to greater cover of grasses inside the fence only when rainfall was sufficient during the growing season. The effect of grazing exclusion on perennial forb cover was confounded by a significant fence × year interaction in both types. In 2007, perennial forbs were found outside the fence, but had almost disappeared inside the fence, resulting in this interaction. Annual forbs only had much greater cover values inside the fence than outside in 2006, also resulting in a significant fence × year interaction in both community types. This study thus suggests that the high rainfall variability in arid and semi-arid rangelands may modify the effects of long-term exclosure on vegetation.     

Diatom habitats,species diversity and water-depth inference models across surface-sediment transects in Worth Lake,northwest Ontario,Canada

We analyzed surface-sediment samples collected along transects from three sub-basins of a relatively large (~115 ha), bathymetrically complex lake, in northwest Ontario, Canada, to assess the reproducibility of diatom species habitats and diversity along a water-depth gradient. Transects displayed different orientations with respect to prevailing wind direction and varied in complexity and degree of slope along the lake bottom. Each transect consisted of three replicate samples at a resolution of ~1 m water depth from ~1 to 30 m for the two deep-basin transects and from ~1 to 18 m in the shallower basin. Distinct diatom assemblages were identified in all transects: (1) a near-shore community composed largely of attached life-forms and some motile benthic taxa, (2) a mid-depth community composed largely of motile life-forms and other benthic taxa that are adapted to lower light conditions (e.g. Staurosirella pinnata), and (3) a deep-water community dominated by planktonic taxa. Species richness was highest in the benthic zones (<9 m), with greatest species evenness in the mid-depth zone (~3–9 m). Species richness and evenness were highly correlated across the three transects (r = 0.89–0.93, p < 0.01). Diatom-inferred depth models were developed from the individual transects to assess reproducibility and applicability for down-core analyses using modern analog (MAT) and weighted-averaging (WA-PLS) approaches. Coefficients of determination (r ²) for these models ranged from 0.80 to 0.98, and RMSEP ranged from 1.2 to 4.2 m. The models developed from the transect with the highest resolution sampling, gentlest non-complex slope and shallowest maximum depth were the strongest ( r_\textMAT² = 0.97 r_{\text{MAT}}^{2} = 0.97 ; r_{\textWA - PLS}² = 0.98 r_{\text{WA - PLS}}^{2} = 0.98 ) and had the lowest RMSEP (MAT = 1.2 m, WA-PLS = 1.3 m). These inference models can be used to infer past fluctuations in the depth of the benthic/planktonic boundary from cores retrieved near this ecotone and provide a sensitive record of the past change in location of the benthic zone. These types of data can be used to assess past variability in droughts and lake levels to better plan for potential future extremes. Such records incorporate more realistic estimates of natural variability than the ~100-year instrumental records currently used by water resource managers.     

The influence of Holocene tree-line advance and retreat on an arctic lake ecosystem: a multi-proxy study from Kharinei Lake,North Eastern European Russia

A consequence of predicted climate warming will be tree-line advance over large areas of the Russian tundra. Palaeolimnological techniques can be used to provide analogues of how such changes in tree-line advance and subsequent retreat affected lake ecosystems in the past. A Holocene sediment core taken from Kharinei Lake (Russia) was dated radiometrically and used for multi-proxy analyses with the aim of determining how climate and tree-line dynamics affected the productivity, community structure, carbon cycling and light regime in the lake. Pollen and macrofossil analyses were used to determine the dates of the arrival and retreat of birch and spruce forest. C:N ratios and percent loss-on-ignition were used to infer past changes in sediment organic matter. Visible-near-infrared spectroscopy and diatom analysis were used to infer past changes in lake-water carbon. Algal pigments and aquatic macrophytes were used to determine changes in lake productivity and light. Chironomids together with remains of the aquatic flora and fauna were used to provide information on past July temperature and continentality. Lake sedimentation was initiated shortly before 11,000 cal. years BP, when both chironomid- and pollen-inferred temperature reconstructions suggest higher summer temperatures than present, between 1 and 2°C warmer, and lake productivity was relatively high. A few trees were already present at this time. The spruce forest expanded at 8,000 cal. year BP remaining in the vicinity of the lake until 3,500 cal. year BP. This period coincided with a high concentration of organic material in the water column, and relatively high benthic productivity, as indicated by a high benthic: planktonic diatom ratio. After tree-line retreat, the optical transparency of the lake increased, and it became more open and exposed, and was thus subject to greater water-column mixing resulting in a higher abundance of diatom phytoplankton, especially heavily silicified Aulocoseira species. The colder climate resulted in a shorter ice-free period, the lake was less productive and there was a loss of aquatic macrophytes. Increased wind-induced mixing following forest retreat had a greater influence on the lake ecosystem than the effects of decreasing organic matter concentration and increased light penetration.