Annual Shoot Growth Research Articles

Conjunct use of organic manures, bio-fertilizers and inorganic fertilizers for improving plant health of plum cv. Santa Rosa

A field trial was conducted on plum orchards during 2011 and 2012 under north Indian conditions. The treatments involved the application of inorganic fertilizers (urea, SSP and MOP), FYM, vermi-compost, bio-fertilizers and green manure in different combinations. The results showed highest annual shoot growth (55.27 cm), tree height (4.98 m), tree volume (18.62 m3), leaf N (2.98%), K (3.44%) and Ca (2.86%) content with the treatment ‘T5’ - 75% NPK + bio-fertilizers (60 g each/tree basin) + green manuring (sunhemp @ 25 g seeds/tree basin). Whereas, the highest trunk girth (71.47 cm), leaf area (13.12 cm2), leaf Fe (265.16 ppm) and Zn (28.04 ppm) were observed with ‘T7’ = 50% NPK + bio-fertilizers (60 g each/tree basin) + green manuring (sunhemp @ 25 g seeds/tree basin) + FYM (40 kg) + vermicompost (11.5 kg). Thus, the combined application of nutrients in treatments T5 and T7 were found to be superior as compared to other treatments for enhancing the tree growth and leaf nutrients, which in turn lead to increase in fruit yield and quality.

Selection in a provenance trial of Norway spruce (Picea abies L. Karst) produced a land race with desirable properties

ABSTRACTSelections were made within East European Norway spruce provenances in a provenance trial in northern Sweden and the selected clones were grafted in a Norwegian seed orchard mixed with plus trees of local origin. Full-sib families were generated by controlled crosses, producing sets of both inter- and intraprovenance families, which were planted in two short-term and in long-term trials. Measurements were made of frost damage, tree height, annual shoot growth rhythm and lammas shoots, and genetic parameters were estimated. The intraprovenance families from selected trees of East European origin showed the least variation in all traits and had the lowest heritability values. The variation among the intraprovenance families of local origin was large and with the highest estimates of heritability. The means of the provenance hybrid families were intermediate between those of the intraprovenance families. Strong genetic correlations were present between the growth rhythm traits measured, and in the family group of local origin also between these traits and frost damage, as well as for lammas shoots and height. The progenies of the selected parents of East European origin seem to be a desirable land race with less damage, lower percentage of lammas shoots and less variability in growth capacity.

Habitat‐specific responses of shoot growth and distribution of alpine dwarf‐pine (Pinus pumila) to climate variation

AbstractAlpine dwarf‐pine (Pinus pumila) in dominant in the alpine regions of Japan, and often forms the krummholz zone of stunted alpine forest. The distribution of P. pumila is strongly related to the distribution of snow, and shoot growth is also sensitive to weather conditions. Changes in temperature and snowmelt regimes may well affect the distribution patterns of the krummholz zone. P. pumila usually occupies the habitat between the fellfield and snowbed communities, and responses to climate change may differ depending on whether plants are close to the fellfield or the snowbed. We compared the distribution and shoot growth patterns of P. pumila close to both surrounding ecosystems in the Taisetsu Mountains, northern Japan. P. pumila has expanded its distribution area by 14 % toward both edges over the last 32 years. Annual shoot growth was positively affected by summer temperature and sunshine duration, but negatively related to spring temperature toward the fellfield side. Shoot growth was greater at the southeastern edge of patches, where snowdrifts were formed. The results indicated that shoot growth and distribution area increased in warm summers. However, warm springs might have a negative influence on shoot growth, probably because the earlier reduction in cold‐resistance enhances the risk of frost damage in spring close to the fellfield side. This study suggests the importance of understanding the site‐specific responses of shrubs to predict the impacts of climate change on alpine ecosystems.

The dynamics of stiff clubmoss Lycopodium annotinum L. patches in clumps of trees left on the clear-cutting in pine forest Leucobryo-Pinetum

Abstract Clumps of trees left on the clear-cuttings have an important role in protecting populations of endangered plant species against destruction during silviculture activities. The aim of this study is to describe the changes in the area of the Lycopodium annotinum patches. The area of L. annotinum patch in clump of trees, have been significantly reduced during 5 years after clear-cut. In the first year of the observations, the studied population occupied an area of 69.8 m2 whereas in 2012, it was only 37.5 m2. Most of the shoots were withered away on the south side of the clump. The probable reason was too strong insolation. Shoots that survived were located in the north part of the clump – shielded by young trees and shrubs layer. At this time, the control patch of L. annotinum located inside the forest increased its area. Before the clear-cuttings, the annual growth of vertical shoots of clubmoss was higher in the patch located in future tree clump. After the clear-cutting, growth of shoots in this patch was shorter than in patch located all the time inside the forests. The most effective growth was observed in the third studied patch located in the clear-cutting border. The explanation for this phenomenon could be the higher humidity of habitat on this site. Clumps of trees left after the clear-cutting contribute to the protection of endangered populations, but do not eliminate the significant microhabitat changes. The clubmoss patches located in moist habitats are more likely to survive even if they are partially exposed to the sunlight.

Structure and Alpha Biodiversity of Major Plant Communities in South Africa, a Close Biogeographical Relation with Australia

During the short season of annual shoot growth, Foliage Projective Covers (FPCs) in both overstorey and understorey strata, coupled with leaf attributes (Leaf Specific Weight, Leaf Area), are determined by aerodynamic fluxes flowing over and through the plant community. These parameters determined the Evaporative Coefficient — the monthly ratio of actual to potential evapotranspiration per mm of available soil moisture. Maximal FPC is produced in habitats supplied with optimal soil moisture during this short season of shoot growth. Vertical growth of foliage shoots — the number of leaves per shoot and internode lengths — is determined in relation with available soil water and soil nutrients (especially phosphorus and nitrogen ions) during this seasonal growth. Ambient temperature is similarly concerned. The Leaf Area Index (area of all leaves per hectare) determines the interception of solar radiation — and hence net photosynthesis per hectare per annum. This energy-fixation by overstorey foliage determines the yearly growth of the producer, consumer and decomposer sections of the ecosystem. In turn, the biodiversity (number of species per hectare) of producers and resident consumers is determined. Wherever optimal soil water occurred in median-nutrient soils in the coastal subtropical region, closed-forests/scrubs developed containing 131 ± 11 species compared with 80-90 species per hectare in nearby open-forests. Wherever optimal soil water occurred in nutrient-poor soils in the warm temperate region, closed-heathland (± tall proteoid shrubs) vegetation developed containing 90-135 species per hectare, compared with about 60 species per hectare in nearby open-heathlands.

Growth and phenology of three dwarf shrub species in a six-year soil warming experiment at the alpine treeline.

Global warming can have substantial impacts on the phenological and growth patterns of alpine and Arctic species, resulting in shifts in plant community composition and ecosystem dynamics. We evaluated the effects of a six-year experimental soil warming treatment (+4°C, 2007–2012) on the phenology and growth of three co-dominant dwarf shrub species growing in the understory of Larix decidua and Pinus uncinata at treeline in the Swiss Alps. We monitored vegetative and reproductive phenology of Vaccinium myrtillus, Vaccinium gaultherioides and Empetrum hermaphroditum throughout the early growing season of 2012 and, following a major harvest at peak season, we measured the biomass of above-ground ramet fractions. For all six years of soil warming we measured annual shoot growth of the three species and analyzed ramet age and xylem ring width of V. myrtillus. Our results show that phenology of the three species was more influenced by snowmelt timing, and also by plot tree species (Larix or Pinus) in the case of V. myrtillus, than by soil warming. However, the warming treatment led to increased V. myrtillus total above-ground ramet biomass (+36% in 2012), especially new shoot biomass (+63% in 2012), as well as increased new shoot increment length and xylem ring width (+22% and +41%, respectively; average for 2007–2012). These results indicate enhanced overall growth of V. myrtillus under soil warming that was sustained over six years and was not caused by an extended growing period in early summer. In contrast, E. hermaphroditum only showed a positive shoot growth response to warming in 2011 (+21%), and V. gaultherioides showed no significant growth response. Our results indicate that V. myrtillus might have a competitive advantage over the less responsive co-occurring dwarf shrub species under future global warming.

A phenological timetable of oak growth under experimental drought and air warming.

Climate change is expected to increase temperature and decrease summer precipitation in Central Europe. Little is known about how warming and drought will affect phenological patterns of oaks, which are considered to possess excellent adaptability to these climatic changes. Here, we investigated bud burst and intra-annual shoot growth of Quercus robur, Q. petraea and Q. pubescens grown on two different forest soils and exposed to air warming and drought. Phenological development was assessed over the course of three growing seasons. Warming advanced bud burst by 1–3 days °C−1 and led to an earlier start of intra-annual shoot growth. Despite this phenological shift, total time span of annual growth and shoot biomass were not affected. Drought changed the frequency and intensity of intra-annual shoot growth and advanced bud burst in the subsequent spring of a severe summer drought by 1–2 days. After re-wetting, shoot growth recovered within a few days, demonstrating the superior drought tolerance of this tree genus. Our findings show that phenological patterns of oaks are modified by warming and drought but also suggest that ontogenetic factors and/or limitations of water and nutrients counteract warming effects on the biomass and the entire span of annual shoot growth.

Effect of Transplanting Date and Harvest Method on Growth and Survival of Three Urban Tree Species in an Arid Climate

The major challenges for transplanting trees in arid regions compared to temperate regions are higher mortality and slower rate of establishment. As such, date and method of transplanting can potentially improve survival and establishment as well as subsequent landscape performance of transplanted trees in arid climate. In the present study, three urban species commonly used in the Isfahan, Iran, landscape including eldarica pine (Pinus eldarica Medw.), white mulberry (Morus alba L.), and smoothleaf elm (Ulmus carpinifolia Gled.), were transplanted from January to June 2010, when mean air temperature was less than 10°C (early winter), between 10°C and 20°C (early spring), or more than 20°C (late spring). Half of the trees were bare root (BR) and half balled and burlapped (B&B). White mulberry and smoothleaf elm trees transplanted early in winter had the highest survival percentage over two years. The best survival for eldarica pine was observed in early spring transplanted trees. For all species, survival rate and trunk diameter increase of B&B trees were significantly greater than BR trees during the first year. Also, the first year’s shoot growth and shoot number of pine trees, and dieback on elm trees, were significantly affected by transplanting method. During the second year, tree growth and survival for all species were similar for B&B and BR trees. Annual shoot growth of eldarica pine and smoothleaf elm trees, but not white mulberry, equaled to nontransplanted trees by the end of third year after transplanting, suggesting a species-specific response for post-transplant establishment in arid climate.

Direct and Indirect Effects of Climate on Demography and Early Growth of Pinus sylvestris at the Rear Edge: Changing Roles of Biotic and Abiotic Factors

Global change triggers shifts in forest composition, with warming and aridification being particularly threatening for the populations located at the rear edge of the species distributions. This is the case of Scots pine (Pinus sylvestris) in the Mediterranean Basin where uncertainties in relation to its dynamics under these changing scenarios are still high. We analysed the relative effect of climate on the recruitment patterns of Scots pine and its interactions with local biotic and abiotic variables at different spatial scales. Number of seedlings and saplings was surveyed, and their annual shoot growth measured in 96 plots located across altitudinal gradients in three different regions in the Iberian Peninsula. We found a significant influence of climate on demography and performance of recruits, with a non-linear effect of temperature on the presence of juveniles, and a positive effect of precipitation on their survival. Abundance of juveniles of P. sylvestris that underwent their first summer drought was skewed towards higher altitudes than the altitudinal mean range of the conspecific adults and the optimum elevation for seedlings' emergence. At local level, light availability did not influence juveniles' density, but it enhanced their growth. Biotic interactions were found between juveniles and the herb cover (competition) and between the number of newly emerged seedlings and shrubs (facilitation). Results also highlighted the indirect effect that climate exerts over the local factors, modulating the interactions with the pre-existing vegetation that were more evident at more stressful sites. This multiscale approach improves our understanding of the dynamics of these marginal populations and some management criteria can be inferred to boost their conservation under the current global warming.

Wind and topography influence the crown growth of Picea jezoensis in a subalpine forest on Mt. Deogyu, Korea

Tree growth in subalpine ecosystems is sensitive to wind due to their wide exposure to strong winds and sparsely wooded short surroundings. This study was conducted to understand the effects of wind and topographic wind barriers on the tree growth in a subalpine ecosystem. The annual shoot growth, bud mortality and needle moisture content of Jezo spruce (Picea jezoensis (Siebold et Zucc.) Carrière) were compared between a wind-exposed site and a wind-protected site. The wind-exposed site was located in a windward position and was exposed directly to the prevailing winds from W and WSW. The wind-protected site was located on leeward slopes with topographic barriers that blocked the prevailing winds. The wind-exposed site had higher air temperature, lower soil water content and shallower snow depth than the wind-protected site in late winter and spring. The annual mean shoot growth on the wind-exposed site was 4cm – significantly lower than that of 6.1cm on the wind-protected site (P<0.01). The bud mortality was highest at 32.9% in the western sectors of the upper crowns in the wind-exposed site, which was the crown sector that was most exposed to the prevailing winds. The needle moisture content decreased by 8–60% from January 2009 to April 2009, and the decrease was significantly higher in the wind-exposed site than in the wind-protected site (P<0.01), indicating the potential for drought stress in trees in the wind-exposed site. Topographic wind barriers play a decisive role on the tree growth in subalpine areas by changing temperature and moisture regimes, lowering needle moisture loss and bud mortality, and reducing the potential for drought stress.

Variation of Maximum Tree Height and Annual Shoot Growth of Smith Fir at Various Elevations in the Sygera Mountains, Southeastern Tibetan Plateau

Little is known about tree height and height growth (as annual shoot elongation of the apical part of vertical stems) of coniferous trees growing at various altitudes on the Tibetan Plateau, which provides a high-elevation natural platform for assessing tree growth performance in relation to future climate change. We here investigated the variation of maximum tree height and annual height increment of Smith fir (Abies georgei var. smithii) in seven forest plots (30 m×40 m) along two altitudinal transects between 3,800 m and 4,200/4,390 m above sea level (a.s.l.) in the Sygera Mountains, southeastern Tibetan Plateau. Four plots were located on north-facing slopes and three plots on southeast-facing slopes. At each site, annual shoot growth was obtained by measuring the distance between successive terminal bud scars along the main stem of 25 trees that were between 2 and 4 m high. Maximum/mean tree height and mean annual height increment of Smith fir decreased with increasing altitude up to the tree line, indicative of a stress gradient (the dominant temperature gradient) along the altitudinal transect. Above-average mean minimum summer (particularly July) temperatures affected height increment positively, whereas precipitation had no significant effect on shoot growth. The time series of annual height increments of Smith fir can be used for the reconstruction of past climate on the southeastern Tibetan Plateau. In addition, it can be expected that the rising summer temperatures observed in the recent past and anticipated for the future will enhance Smith fir's growth throughout its altitudinal distribution range.

Phenology and growth dynamics in Mediterranean evergreen oaks: Effects of environmental conditions and water relations

Budburst date and shoot elongation were measured in two mature Mediterranean evergreen oaks ( Quercus suber and Quercus ilex) and their relationships with meteorological and tree water status (predawn leaf water potential) data were analysed. Experimental work took place at two sites: Mitra 2 – Southern Portugal (2002–2003) and Lezirias – Central Portugal (2007–2010). Quercus suber phenology was studied at both sites whereas Q. ilex was only studied at Mitra 2. Quercus suber budburst date occurred at a photoperiod around 13.8 h (± 0.26) – late April/early May – and was highly related to the average daily temperature in the period 25 March – budburst date (ca. 1.5 months prior to budburst), irrespective of site location. In that period, budburst date was much more dependent on average maximum than average minimum daily temperature. Base temperature and thermal time for Q. suber were estimated as 6.2 °C (within the reported literature values) and 323 degree-days, respectively. Q. ilex budburst occurred about 6 weeks earlier than in Q. suber (photoperiod: 12.3 h (±0.3)). Relationships of Q. ilex budburst date and temperature were not studied since only 2 years of data were available for this species. Q. suber shoot elongation underlying mechanisms were quite different in the two sites. At Mitra 2 ( Q. suber and Q. ilex), there was a considerable tree water stress during the dry season which restricted shoot elongation. Shoot growth was resumed later in the wet autumn when tree water status recovered again. At the Lezirias site Q. suber water status was not restrictive. Therefore, shoot elongation was mainly dependent on nutrient availability in top soil, as suggested by the strong and positive relationships between annual shoot growth and long-term cumulative rainfall (2–4 months) and short-term average temperature (1 month) prior to budburst. Annual shoot elongation at this well-watered site was higher than in Mitra 2, and variability of growth between trees was enhanced after warm, wet springs when shoot elongation was higher. Results obtained are relevant to the carbon balance, productivity and management of evergreen Mediterranean oak woodlands, particularly under the foreseen climate change scenarios.

Growth and community responses of alpine dwarf shrubs to in situ CO2 enrichment and soil warming

• Rising CO₂ concentrations and the associated global warming are expected to have large impacts on high-elevation ecosystems, yet long-term multifactor experiments in these environments are rare. • We investigated how growth of dominant dwarf shrub species (Vaccinium myrtillus, Vaccinium gaultherioides and Empetrum hermaphroditum) and community composition in the understorey of larch and pine trees responded to 9 yr of CO₂ enrichment and 3 yr of soil warming at the treeline in the Swiss Alps. • Vaccinium myrtillus was the only species that showed a clear positive effect of CO₂ on growth, with no decline over time in the annual shoot growth response. Soil warming stimulated V. myrtillus growth even more than elevated CO₂ and was accompanied by increased plant-available soil nitrogen (N) and leaf N concentrations. Growth of Vaccinium gaultherioides and E. hermaphroditum was not influenced by warming. Vascular plant species richness declined in elevated CO₂ plots with larch, while the number of moss and lichen species decreased under warming. • Ongoing environmental change could lead to less diverse plant communities and increased dominance of the particularly responsive V. myrtillus in the studied alpine treeline. These changes are the consequence of independent CO₂ and soil warming effects, a result that should facilitate predictive modelling approaches.

Exploring local borders of distribution in the shrub Daphne laureola: Individual and populations traits

Biogeographic models predict that marginal populations should be more geographically isolated and smaller than central populations, linked to more stressful conditions and likely also to a reduction in density of individuals, individual growth, survival and reproductive output. This variation in population features could have important consequences for different aspects of plant ecology such as individual reproductive success, population genetic structure or plant-animal interactions. In this study, we analyze if individuals of the evergreen shrub Daphne laureola at disjunt populations in a local border of its distribution area in southern Iberian Peninsula differ in individual size, shoot growth, reproductive output and the pollination environment from central continuous populations within the area. Plants of central continuous populations were larger and produced more flowers and fruits than plants of marginal disjunct populations suggesting more optimal conditions, although they had lower annual shoot growth. In contrast, fruit set was higher in plants at the local border, suggesting a more efficient pollinator service in these populations where the main pollinator in central continuous populations, the pollen beetle Meligethes elongatus, was not present. Our results do not support strong differences in the ecological stress between marginal disjunct and central continuous populations of D. laureola in the south of the Iberian Peninsula but indicate some changes in plant-pollinator interactions that could be relevant for the sexual polymorphism in this gynodioecious species.

Growth limitation of mountain birch caused by sheep browsing at the altitudinal treeline

Treelines are advancing on a global scale and encroaching upon alpine ecosystems. Browsing by vertebrate herbivores could affect treeline dynamics and forest expansion by limiting growth of trees. However, this has not been experimentally investigated, and due to a combination of herbivore behaviour and plant responses to herbivory, is unlikely to be a simple relationship. A long term (8 years of manipulation), large scale (0.3 km 2) sheep enclosure experiment, in the Scandes of Norway, was used to investigate the effect of three densities of sheep (no sheep, low and high densities with respectively 0, 25 and 80 sheep km −2) on tree growth within a mountain birch ( Betula pubescens tortuosa) treeline ecotone. Birch trees were most likely to be browsed at intermediate heights of around 100–130 cm and the likelihood of an individual being browsed did not differ between low and high sheep densities. However, when browsed, the intensity of browsing increased with sheep density. High densities of sheep reduced the net annual shoot growth of young mountain birch in comparison to growth in the absence of sheep. The long-term height growth of smaller mountain birch (stem diameter < 15 mm) was also reduced at high densities of sheep, but the height growth of larger birch was resistant to browsing, even though these trees were on average still within browsing height. This study shows that susceptibility to browsing in birch decreases with size, but by restraining the height growth of trees high densities of sheep can keep trees at heights at which they remain susceptible to browsing. Reductions in livestock density over a period as short as 8 years can thus facilitate altitudinal forest expansion.

An architectural approach to the growth forms of Nothofagus pumilio (Nothofagaceae) along an altitudinal gradient

Variations in the architecture and axis structure of different growth forms of Nothofagus pumilio (Poepp. et Endl.) Krasser (Nothofagaceae) were studied along an altitudinal gradient. We evaluated the primary growth and branching pattern of annual shoots belonging to the main axis categories (trunk, main branches, and secondary (short) branches) of four growth forms developed at different altitudes (1200–1600 m a.s.l.) in northern Patagonia: (i) low shrubs at the high-altitude timberline, (ii) high shrubs at high altitude, (iii) low trees at mid-altitude slopes, and (iv) high trees at low-altitude single-species forests. Shoot structure and branch distribution along shoots were similar for all axis categories and growth forms. Significant differences between axis categories were found regarding the sizes of shoots, which decreased from trunk to secondary/short branches. For each axis category, shoots of similar size differed between growth forms in stem slenderness and internode length. The extent of differentiation between axis categories is key in the structural distinction between growth forms of N. pumilio.

Variation in shoot elongation patterns in Pinus contorta and Pinus sylvestris in north-west Russia

A phenological study of six lodgepole pine populations from Swedish seed orchards and one local Scots pine population was performed in a field trial located in Komi Republic (northern Russia) (61°40′ N, 51°03′ E, 132 m a.s.l.) at the age of 5 years. The species differences in annual shoot elongation, growth onset and cessation were significant (p<0.05). The annual growth of undamaged leader shoots varied considerably among the populations and the mean shoot length was 315 mm (range 291–333 mm) for lodgepole pine and 215 mm for Scots pine seedlings. The growth rate was also higher for lodgepole pine but this difference was not statistically significant. Lodgepole pine generally had earlier onset and later cessation of shoot elongation than Scots pine. The northern lodgepole pine populations tended to initiate and cease growth earlier than southern ones but these differences were insignificant.

The Species Richness of Vascular Plants and Amphibia in Major Plant Communities in Temperate to Tropical Australia: Relationship with Annual Biomass Production

Aerodynamic fluxes (frictional, thermal, evaporative) in the atmosphere as it flows over and through a plant community determine the Foliage Projective Covers and eco-morphological attributes of new leaves developed annually in overstorey and understorey strata. The number of leaves produced on vertical foliage shoots depends on available soil water and nutrients, also ambient temperature, during this short growth season. Stem density (number of stems per hectare) and species richness (number of species per hectare) in the overstorey of major Floristic Groups are correlated with annual shoot growth (ASG, t ) in that stratum. Species richness in the overstorey increases in the climatic gradient from the arid to the humid zone as well as with increasing air temperatures (about C) from temperate to tropical Australia. Species richness in the understorey is highest in plant communities in temperate Australia, decreasing in the temperature gradient towards the tropics. As with other major plant and animal groups within an ecosystem, the species richness of Amphibia is correlated with the amount of solar energy fixed (per annum) by the major plant formation in the region—a photosynthetic potential determined by the foliage shoots (ASG, t ) produced annually in the overstorey.

Limited plasticity of shoot preformation in response to light by understorey saplings of common walnut (Juglans regia)

Background and aims Analysis of the variability of organogenesis and extension (two basic processes of primary growth) is needed to improve our understanding of architectural plasticity in trees. An example of such plasticity is the difference in size between fully grown shoots found at different positions on the tree. The contribution of preformation processes to these differences was explored by determining the intraspecific variability of shoot preformation of main stems of understorey saplings of Juglans regia. Methodology In 2007, two samples of annual shoots that differentiated in 2006 were taken from saplings growing in a Mediterranean mixed forest in the south of France. At the first sampling, the terminal winter bud of each parent shoot was dissected and the nodes of these buds were counted. For the second sampling, annual shoot growth was measured after the 2008 growing season. The percentage of light transmitted through the understorey was determined by hemispherical photographs. Principal results The effect of plant development (ontogeny) on the number of preformed leaves and the annual shoot extension was strong. Light availability also contributed to explaining differences in the length of annual shoots. The impact of light on the number of preformed leaves was minimal. Conclusions Ontogeny (onset of branching) and reduced irradiance both affected leaf preformation in buds of annual shoots, with ontogeny being the more influential. The results suggest that the shoot preformation did not contribute to the plasticity of morphology of annual shoots. Light availability was more influential and promoted annual shoot extension.

Effect of ecosystem warming on boreal black spruce bud burst and shoot growth

AbstractThe boreal forest is predicted to experience the greatest warming of any forest biome during the next 50–100 years, but the effects of warming on vegetation phenology are not well known. The objectives of this study were to (1) examine the effects of whole ecosystem warming on bud burst and annual shoot growth of black spruce trees in northern Manitoba, Canada and (2) correlate bud burst to cumulative degree‐days (CDD). The experimental design was a complete randomized block design that consisted of four replicated blocks. Each replicate block contained four treatments: soil warming only (heated outside, HO), soil and air warming (heated inside, HI), control outside (no chamber, no heating, CO), and inside a chamber maintained at ambient conditions (no soil or air warming, control inside, CI). Bud burst was measured during the first and second years of the experiment, starting in 2004, and annual shoot growth was measured for the first 3 years (2004–2006) of the study. On average, shoot bud burst occurred 11 and 9 days earlier in 2004 and 2005, respectively, for HI than for other treatments. However, mean CDD required for bud burst for HI was within the standard deviation of CO for both years. In year 1 of the treatments, shoot bud burst occurred earlier for HI than other treatments (CI, CO, HO), but final shoot length of HI trees was less than in CO trees. In the second year of warming, final shoot length was not different for HI than CO. By the third year of warming final shoot length was significantly greater for HI than all other treatments. Empirical results from this study suggest that soil and air warming causes an earlier bud burst for all years of observation and greater shoot lengths by the third season of warming. A longer growing season and greater annual shoot growth should increase carbon uptake by boreal black spruce trees in a warmer climate.