Variation in Leaf Morphological Traits of European Beech and Norway Spruce Over Two Decades in Switzerland

Leaf morphological traits (LMTs) of forest trees have been observed to vary across space and species. However, long-term records of LMTs are scarce, due to a lack of measurements and systematic leaf archives. This leaves a large gap in our understanding of the temporal dynamics and drivers of LMT variations, which may help us understand tree acclimation strategies. In our study, we used long-term LMT measurements from foliar material collections of European beech (Fagus sylvatica) and Norway spruce (Picea abies), performed every second year from 1995 to 2019 on the same trees within the Swiss Long-term Forest Ecosystem Research Program LWF. The 11 study plots (6 beech, 4 spruce, and 1 mixed) are distributed along gradients of elevation (485–1,650 m a.s.l.), mean annual precipitation (935–2142 mm), and mean annual temperature (3.2–9.8°C). The investigated LMTs were (i) leaf or needle mass, (ii) leaf area or needle length, and (iii) leaf mass per area or needle mass per length. We combined this unique data set with plot variables and long-term data on potential temporal drivers of LMT variations, including meteorological and tree trait data. We used univariate linear regressions and linear mixed-effects models to identify the main spatial and temporal drivers of LMT variations, respectively. For beech LMTs, our temporal analysis revealed effects of mast year and crown defoliation, and legacy effects of vapor pressure deficit and temperature in summer and autumn of the preceding year, but no clear long-term trend was observed. In contrast, spruce LMTs were mainly driven by current-year spring conditions, and only needle mass per length showed a decreasing long-term trend over the study period. In temporal models, we observed that LMTs of both species were influenced by elevation and foliar nutrient concentrations, and this finding was partly confirmed by our spatial analyses. Our results demonstrate the importance of temporal analysis for determining less recognized drivers and legacy effects that influence LMTs, which are difficult to determine across space and species. The observed differences in the temporal drivers of beech and spruce LMTs suggest differences in the adaptation and acclimation potential of the two species.

Stoichiometry of needle litterfall of Pinus hartwegii Lindl. in two alpine forests of central Mexico

Introduction: It is essential to have baselines on nutrient dynamics in forests, due to disturbances that climate change may cause.Objective: To quantify the annual production of needles of Pinus hartwegii Lindl. and the proportion of nutrients in the alpine forests of Jocotitlán (JO) and Tláloc (TL) mountains, Estado de México.Materials and methods: A total of 12 circular needle litter traps (30 cm diameter) were placed at ground level, in each forest, distributed in four topographically contrasting sites. For one year, 228 leaf mass measurements and 1 140 chemical determinations were made to determine needle stoichiometry. Measurements were subjected to a longitudinal analysis of variance, by testing trends over time (P < 0.05).Results and discussion: Needle production in JO were 67 % higher (11.2 Mg∙ha-1∙year-1) than in TL (6.7 Mg∙ha-1∙year-1); needle litterfall was higher during summer (June and July, months with higher precipitation). For JO, nutrient flux was 98.0, 5.2, 8.7, 24.6, and 5.6 kg∙ha-1∙year-1 for N, P, K, Ca, and Mg, respectively; for TL it was 55.3, 3.4, 7.8, 14.4, and 4.7 kg∙ha-1∙year-1 in the same order of nutrients. Nutrient concentrations were lower from March to May. Except for K, nutrient concentrations and needle production showed quadratic and cubic seasonal trends. Mg dynamics and N:Mg and N:K ratios in TL were more positive for tree growth.Conclusions: Jocotitlán and Tláloc forests produce significant needle mass (compared to other ecosystems) with high dynamic in nutrient transfers.

Mountain Norway spruce forests: Needle supply and its nutrient content

Soon after bark-beetle attack as well as after clear cutting, grown-up mountain Norway spruce forest cast the following mass of needles: 50&ndash;60 kg of dry matter per tree, or 18&ndash;20 tons per hectare, containing 8,800&ndash;10,000 kg/ha of carbon, 190 to 250 kg/ha of nitrogen, 13&ndash;16 kg/ha of phosphorus, 65&ndash;91 kg/ha of calcium, 9&ndash;13 kg/ha of magnesium and 56&ndash;67 kg/ha of potassium. These values were obtained by application of equations assessing needle mass from measured tree and plot parameters, and from chemical analyses of two types of needle material (from living and dead trees).

Crown condition, needle mass, and sapwood area relationships of Norway spruce (Picea abies)

Crown-condition assessment, hypothesized to estimate needle losses following damage from several sources, one of which might be air pollution, suffers from the subjective notion of a standard "healthy" tree. On the other hand, the foliage biomass - sapwood area ratios are reported to depend on a number of factors, e.g., site quality, stand density, crown class, and tree ring width conductivity. The authors hypothesize that early sapwood area might help to even better estimate needle biomass of Norway spruce (Picea abies (L.) Karst.) and to help standardize crown-condition assessment. Thirty-six Norway spruce trees at two Austrian sites, from three age-classes, three crown classes, and two crown-condition classes were felled. Needle mass, cross-sectional area, sapwood area, and early sapwood area (i.e., sapwood area excluding latewood) were measured. The results of this study indicate that indeed early sapwood area is a good estimator of foliage, independent of site, age, crown class, and crown condition. The ratio between early sapwood area and cross-sectional area could be a good estimator for crown condition and thus help to standardize crown-condition assessments by different surveyors.

Contrasting patterns of biomass allocation in dominant and suppressed loblolly pine

We investigated above- and below-ground biomass allocation and allometric relationships of canopy dominant and suppressed loblolly pine (Pinus taedaL.) trees from a range of diameters at breast height (DBH = 3.5-35.6cm) to determine if shifts in allocation may influence the growth and persistence of suppressed trees in the understory. Using mass and volume conversions from harvested trees (15 dominant and 15 suppressed), we developed regressions to predict total and component biomass from DBH. Bole, branch, needle, and total mass differed between dominance categories (ANCOVA, P < 0.10). For a representative size (15cm DBH), dominant trees allocated 63.4, 13.2, 11.3, and 12.0% of biomass to bole, branch, needle, and root tissue compared with 75.9, 6.7, 5.6, and 11.7% for suppressed trees. At any given DBH, suppressed trees were also taller than dominant trees and had a greater porportion of heterotrophic (bole plus branch plus root mass) to autotrophic (needle mass) tissue. Percent carbon and nitrogen of tissues did not differ between dominance categories. Unlike the increased investment in leaf area observed for seedlings and saplings of shade-tolerant species, suppressed loblolly pine increased allocation to bole mass and height growth. An increase in height for this shade-intolerant species may enable some suppressed individuals to escape competition for light. However, increased allocation to heterotrophic versus autotrophic tissue in suppressed trees may confer a cumulative disadvantage over time because of increased respiratory load.