Tree invasion of a montane meadow complex: temporal trends,spatial patterns,and biotic interactions

Questions: Do spatial and temporal patterns of encroachment of Pinus contorta and Abies grandis in a montane meadow suggest strong biotic controls on the invasion process? Location: Forest–meadow mosaic, 1350 m a.s.l., Cascade Range, Oregon, US. Methods: We combined spatial point pattern analysis, population age structures, and a time‐series of stem maps to quantify spatial and temporal patterns of conifer invasion over a 200‐yr period in three plots totaling 4 ha. Results: Trees established during two broad, but distinct periods (late 1800s, then at much greater density in the mid‐1900s). Recent invasion was not correlated with climatic variation. Abies grandis dominated both periods; P. contorta established at lower density, peaking before A. grandis. Spatially, older (≥90 yr) P. contorta were randomly distributed, but older A. grandis were strongly clumped (0.2‐20 m). Younger (<90 yr) stems were positively associated at small distances (both within and between species), but were spatially displaced from older A. grandis, suggesting a temporal shift from facilitation to competition. Establishment during the 1800s resulted in widely scattered P. contorta and clumps of A. grandis that placed most areas of meadow close to seed sources permitting more rapid invasion during the mid‐1900s. Rapid conversion to forest occurred via colonization of larger meadow openings – first by shade‐intolerant P. contorta, then by shade‐tolerant A. grandis– and by direct infilling of smaller openings by A. grandis. Conclusions: In combination, spatial and temporal patterns of establishment suggest an invasion process shaped by biotic interactions, with facilitation promoting expansion of trees into meadows and competition influencing subsequent forest development. Once invasion is initiated, tree species with different life histories and functional traits can interact synergistically to promote rapid conversion of meadow to forest under a broad range of climatic conditions.     

Variation in ecophysiological properties among conifers at an ecotonal boundary: comparison of establishing seedlings and established adults at timberline

Question: Environmental limitations on carbon acquisition and use can impact successful establishment and restrict a species range, such as for trees at timberline. How do ecophysiological properties associated with carbon uptake and allocation change along an elevation gradient for adult compared to seedling conifers in a timberline ecotone? Location: Teton Range in the Rocky Mountains, Wyoming, USA Methods: Photochemical efficiency (F_v/F_m), specific leaf area (SLA) and foliar nonstructural carbohydrates (NSC) were compared along an elevation gradient (2200‐3050 m) among two age classes (seedling and adult) and species (Abies lasiocarpa and Pseudotsuga menziesii) at timberline during mid‐summer. Results: F _v/F_m values were relatively high in both seedlings and adults across the elevation gradient, with the exception of a low F_v/F_m for seedlings in the site having the lowest soil temperatures. SLA was surprisingly constant within each age class and species across the timberline ecotone. Foliar NSCs did not increase or decrease consistently with elevation in either age class. Nonetheless, NSCs were highly variable among sites, but only in seedlings and not in adults. Conclusions: Elevation effects on these indicators of the efficiency of interception and use of sunlight in the timberline ecotone were minimal during the optimum period of the growing season. However, establishing seedlings had a tendency to exhibit greater responses to the timberline environment, particularly in their allocation of photosynthate to NSC, which may be a constraint to tree establishment at high elevations.     

Post-glacial migration of silver fir (Abies alba Mill.) in the south-western Alps

Aim  Previous studies have failed to reconstruct the regional post-glacial migration pattern of Abies alba in southern France. Based on the first exhaustive compilation of palaeoecological data in this region, we present the state-of-the-art and attempt to synthesize the available information concerning glacial refugia and post-glacial migration, and analyse the information with regard to climate and orography.
Location  South-western Alps and adjacent areas, southern France.
Methods  The work compiles the available palaeoecological data in the south-western Alps (52 sites, 290 radiocarbon dates). The post-glacial migration pattern of Abies alba is reconstructed based on 22 selected palynological analyses (11 well-dated reference sites and 11 supplementary ones).
Results  The geographical patterns of approaching area limit, immigration and expansion are reconstructed at the scale of the southern French Alps.
Main conclusions  Despite previous assertions, the evidence of refugia in southern France is non-existent. The late-glacial records of fir pollen, previously interpreted in French Mediterranean regions and on adjacent foot-hills as possibly reflecting regional refugia, most probably correspond to reworking phenomena or long-distance pollen transport. Fir migration, originating in the Apennine refugia and through the south-western extremity of the Alps, was extremely rapid in the southern French Alps, only spanning a few centuries between 10,100 and 9800 cal. yr bp . The subsequent spread of fir populations was controlled by local parameters, such as the aridity of the inner valleys, which resulted in a delayed expansion in comparison to other regions. Abies almost disappeared from the south-western Alps during the Roman era, around 2000 cal. yr bp .     

Periodicity of cambial activity in Abies balsamea. I. Effects of temperature and photoperiod on cambial dormancy and frost hardiness

The relationship between from hardiness and growth potential, and their dependence on temperature and photoperiod, was investigated in the one-year-old cambium of balsam fir [Abies balsamea (L.) Mill.]. Six-year-old trees were exposed for 9 weeks to either the natural environment or one of 4 controlled environments in the fall (18 September-18 November), spring (12 April–14 June) and summer (19 July – 19 September). The 4 controlled environments were (1) WS, warm temperature (24/20°C in day/night) + short day (8 h). (2) WL. warm temperature (24/20°C) + long day (8 h + 1 h night break), (3) CS. cold temperature (9/5°C) + short day (8 h) and (4) CL, cold temperature (9/5°C) + long day (8 h + 1 h night break). At the beginning and end of each exposure, cambial activity was measured by recording the number of xylem, cambium and phloem cells, frost hardiness was estimated from the cambium's ability to survive freezing to –40°C, and cambial growth potential was deduced from the duration of the cell cycle and the production of xylem, cambium and phloem cells in cuttings cultured for 4 weeks with exogenous indole-3-acetic acid (IAA) under environmental conditions favourable for cambial activity. In the natural environment, frost hardening began in September and was completed in November, while dehardening occurred when the cambium reactivated. CL, CS, and to a lesser extent WS, promoted hardening in the summer and fall, but did not prevent dehardening in the spring. The cambial growth potential in the natural environment declined from a maximum in April to a low level in June, reached a minimum in September, then increased to a high level in November. This potential was promoted by CL and CS on all dates by WL in the summer and fall. The ratio of xylem to phloem induced by IAA treatment was greatest in June and least in September in cuttings from trees exposed to the natural environment, and was increased by CL and CS in the fall. The cambium in intact branches of trees protected from chilling during the fall and winter resumed cell cycling after less than 9 weeks of dormancy, but produced mostly or only phloem in the subsequent growing period. It is concluded that the frost hardiness of the cambium, the IAA-induced cycling of cambial cells, and IAA-induced xylem to phloem ratio vary independently with season, temperature and photoperiod, and that the periodicity of these processes is regulated endogenously.     

Periodicity of cambial activity in Abies balsamea. II. Effects of temperature and photoperiod on the size of the nuclear genome in fusiform cambial cells

Previously, we showed that the size of the nuclear genome, measured cytophotometrically in Feulgen-stained fusiform cambial cells of Abies balsamea (L.) Mill., oscillates annually between a maximum in spring and a minimum in late summer, the labile, extra DNA being synthesized during the fall. To determine it the oscillation is induced by the concomitant seasonal changes in temperature and photoperiod, genome size was measured in cambial cells obtained from one-year-old branches of 6-year-old potted trees at the beginning and end of 9 weeks of exposure during the fall, spring and summer to either the natural environment or one of 4 controlled environments, viz. (1) WS, warm temperature (24/20°C in day/night) and short photoperiod (8 h). (2) WL, warm temperature (24/20°C) and long photoperiod (8 h + 1 h night break), (3) CS, cold temperature (9/5°C) and short photoperiod (8 h). and (4) CL, cold temperature (9/5°C) and long photoperiod (8 h + 1 h night break). Overall, genome size (2C) varied between 20 and 34 pg. In the fall, when the cambium was initially dormant, the genome size increased in the natural environment, did not change under short days (WS and CS), and decreased under long days (WL and CL). The cambium reactivated in both WS and WL conditions. In the spring, while the cambium reactivated, the size of the genome decreased in the natural, WS and WL conditions, but not in the CS environment. In the CL conditions, the genome size started to decrease at the end of the 9-week exposure period. The decrease apparently occurred between prophase and telophase, which suggests that the extra DNA is extrachromosomal. In the summer, while the cambium ceased activity, the genome size did not change in the WS, WL and natural environments, whereas it decreased in the CS and CL conditions. The results indicate that increasing temperature and lengthening photoperiod in the spring induce the loss of the extra DNA. However, the environmental conditions that promote DNA synthesis in the fall remain unknown. Genome size varied independently of cambial growth potential and frost hardiness measured previously in the same experimental trees, indicating that the regulation of these processes does not directly involve the extra DNA. However, the finding that cambial cells cycled in the CS and CL environments only in the spring, when their genome size was large, suggests that the extra DNA is important for cambial growth at low temperatures.     

Changes in the understory of Canadian southern boreal forest after fire

Abstract. We investigated changes in the composition and abundance of understory species after fire in the southern boreal forest around Lake Duparquet, Québec. Ten plots of 100 m² were sampled in each of eight sites varying in post-fire age from 26 to 230 yr, with 20 1-m² quadrats in each of these 80 plots. Variation in the understory was described by DCA ordination and interpreted as a regeneration succession series. Thickness of the organic layers, stand age and canopy composition were all correlated with vegetational change. This change was not constant throughout succession; some old sites showed an increase in the diversity and abundance of certain pioneer species. This was partly related to openings in the canopy resulting from a major outbreak of spruce budworm, which affected sites dominated by Abies balsamea. The ordinations were performed on both the 100-m² plots and the 1-m² quadrats. Heterogeneity within sites was larger at the 1-m² scale and there was a great deal of overlap in the position of the quadrats in ordination space. At the smaller scale of analysis, stand age and thickness of the organic layers were not correlated with the changes observed in the understory.     

Vesicular endophytes in roots of the Pinaceae

Vesicles and hyphae typical of vesicular-arbuscular mycorrhizae (VAM) were common in seedlings of Pseudotsuga menziesii, Abies lasiocarpa and Tsuga mertensiana growing in openings where herbaceous hosts of these fungi were common. Seedlings of A. lasiocarpa, Tsuga heterophylla, and T. mertensiana growing under closed forest canopies also had vesicles but at a much lower incidence than seedlings in the openings. The Pinaceae are generally assumed to be ectomycorrhizal, but Glomus-type colonizations occurred on the same seedlings as the ectomycorrhizae. The ecological significance of abundant VAM-type endophytes in otherwise ectomycorrhizal hosts deserves comprehensive study.     

Physical, immunological and kinetic properties of ribulose-1,5-bisphosphate carboxylase/oxygenase from fir (Abies alba) and spruce (Picea abies)

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) from fir ( Abies alba Mill.) and spruce ( Picea abies [L.] Karst.) needles was purified to homogeneity. The enzyme was isolated from crude extracts through quantitative precipitation in 40-55% and 40-60% (NH₄)₂SO₄ for fir and spruce. respectively, followed by linear sucrose gradient centrifugation. Using two dimensional gel electrophoresis, the isoelectric points were determined. For the large subunit (LSU) it was 6.7 for both species, and for the small subunit (SSU) it was 7.1 and 7.7 for fir and spruce, respectively. Very few differences in tryptic peptides and amino acid composition of Rubisco LSU were observed between fir and spruce. By contrast, marked differences characterized the same analyses for the Rubisco SSU of the two species. Moreover, substitution of residues was observed in the sequenced N-terminal region when comparing fir and spruce SSU. The Ouchterlony technique showed no immu-nochemical difference between Rubisco of fir and spruce when a rabbit antiserum to spinach Rubisco was used. The Eadie-Hofstee plots of carboxylase activity indicated that the apparent K_m(CO₂) were 31 and 36 μ M for the fir and spruce enzymes, respectively.     

The economic use of Abies wood as timber in central Europe during Roman times

Abies alba (Mill.) is native only to some parts of central Europe. The tree is indigenous to the Alps, the Black Forest, the Vosges, the Bayerischer Wald, and to some hilly and mountainous areas north of the Alps. A number of pollen diagrams from these regions demonstrate a clear Abies decline dating to the Roman period, and it appears that this Abies decline is a good time marker in central European pollen diagrams from the area mentioned. Firs were felled where they grew and their trunks were transported by the rivers Rhine and Danube to regions where Abies timber was needed for the construction of houses and bridges. During the excavation of sites situated far from indigenous fir stands, Abies needles and wood were found, indicating that the fir trunks were transported to these Roman towns by river. Fir timber is extremely valuable for the construction of large buildings, boats, and bridges. It is apparent that long distance transport on the central European rivers began in Roman times. Transport of timber was, of course, only a part of the new river commerce: building stone, wine, and crops were also transported for long distances.