Mature Mixed Stands Research Articles

Effects of Drought, Phosphorus Fertilization and Provenance on the Growth of Common Beech and Sessile Oak

The negative impact of drought on plant growth may be modified by the different availability of mineral nutrients and by their adaptation to different local habitat conditions. In this study, we examine the impact of drought, fertilization with phosphorus and provenance, as well as their interactions, on the growth and allometric growth relationships between the belowground and aboveground organs of common beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl.). The research was conducted on saplings originating from two mature mixed stands (dry and wet provenances) dominated by these species. In the common garden experiment, saplings were exposed to regular watering and drought in interaction with moderate and high phosphorus concentrations in the growing substrate (achieved by phosphorus fertilization). The obtained results indicate the negative impact of drought and phosphorus fertilization on the growth of both species. In common beech, a negative impact of phosphorus fertilization on the adaptive capacity to drought was demonstrated by unfavorable ratios between fine root mass and the mass of other organs. The sessile oak provenances under the impact of drought showed a different root collar diameter/stem height increment ratio, which indicates their different phenotypic plasticity as a consequence of adaptation to different frequencies of dry periods in their natural habitats.

Tree size drives growth interactions in mixed mature stands of black spruce (Picea mariana) and tamarack (Larix laricina)

Little is known about the growth interactions of black spruce (Picea mariana) and tamarack (Larix laricina), two important commercial tree species of the Canadian boreal forest. We investigated growth relations between black spruce and tamarack in mature mixed stands. We sampled tree-rings of 223 black spruce and 103 tamaracks to analyze their basal area increment over 10 years. We mapped, identified the species, and measured the diameter at breast height of each neighbouring tree in 112 circular plots of 400 m2 to analyze basal area increments through spatially explicit models. The model estimating crowding effect of neighbouring tree was adjusted with 4 parameters expressing the effect of distance, size of neighbours, size of target tree and species. Our models suggested that the size of neighbouring trees was the main parameter influencing competition between the studied species. Black spruce basal area increments over 10 years declined up to 22 cm2 when surrounded by large neighbours. Tamarack basal area increments declined by 48 cm2 due to competition by large neighbours. However, the overall crowding effect showed that tamarack was more sensitive to competition than black spruce and the intraspecific and interspecific competition had similar effect. Our research provides insight on growth relations between two important commercial species of the Canadian boreal forest.

Impact of climate change on tree-ring growth of Scots pine, common beech and pedunculate oak in northeastern Germany

Tree growth depends, among other factors, largely on the prevailing climatic conditions. Therefore, changes to tree growth patterns are to be expected under climate change. Here, we analyze the tree-ring growth response of three major European tree species to projected future climate across a climatic (mostly precipitation) gradient in northeastern Germany. We used monthly data for temperature, precipitation, and the standardized precipitation evapotranspiration index (SPEI) over multiple time scales (1, 3, 6, 12, and 24 months) to construct models of tree-ring growth for Scots pine (Pinus sylvestris L.) at three pure stands, and for common beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) at three mature mixed stands. The regression models were derived using a two-step approach based on partial least squares regression (PLSR) to extract potentially well explaining variables followed by ordinary least squares regression (OLSR) to consolidate the models to the least number of variables while retaining high explanatory power. The stability of the models was tested through a comprehensive calibration-verification scheme. All models were successfully verified with R²s ranging from 0.21 for the western pine stand to 0.62 for the beech stand in the east. For growth prediction, climate data forecasted until 2100 by the regional climate model WETTREG2010 based on the A1B Intergovernmental Panel on Climate Change (IPCC) emission scenario was used. For beech and oak, growth rates will likely decrease until the end of the 21st century. For pine, modeled growth trends vary and range from a slight growth increase to a weak decrease in growth rates. The climatic gradient across the study area will possibly affect the future growth of oak with larger growth reductions towards the drier east. For beech, site-specific adaptations seem to override the influence of the climatic gradient. We conclude that Scots pine has great potential to remain resilient to projected climate change without any greater impairment, whereas common beech and pedunculate oak will likely face lesser growth under the expected warmer and dryer climate conditions. The results call for an adaptation of forest management to mitigate the negative effects of climate change for beech and oak.

Age structure, growth performance and composition of native and invasive Salicaceae in Patagonia

In northern Patagonia, riparian ecosystems are highly modified due to alien plant invasions. The establishment of non-native willows and poplars has unknown effects for Salix humboldtiana, the only native floodplain tree species in this region. To clarify establishment processes and to assess whether interspecific competition among the Salicaceae taxa may occur and therefore whether the native species can coexist in the long term, we analysed age structure and growth performances of the dominant four taxa within mixed adult forest stands along the Rio Negro, Argentina. Low mean ages of <15 years for all four taxa within 20 stands could be detected and suggest frequent and severe disturbances resulting in the removal of existing vegetation and subsequent creation of sites for establishment. Trees of the same stand showed the same age structure indicating joint establishment events with all taxa involved. A significant better growth performance (basal area, crown diameter) could be proved for the invasive willows. Considering the upper and middle river separately in a total of 88 studied plots, S. humboldtiana was more frequent at the middle river stretch, while invasive willows showed an opposing pattern suggesting a downstream directed invasion process. The results showed that competition pressure in mature mixed stands could affect S. humboldtiana. However, these stands are usually removed by river dynamics creating new sediment bars and islands. These processes enable S. humboldtiana seeds to germinate frequently which may compensate for its inferior growth performance and potential impacts by the invasive willows and poplars.

Influence of tree composition upon epiphytic macrolichens and bryophytes in old forests of Acadia National Park, Maine

To better understand associations between epiphytes and old forests, lichens and bryophytes that grow on tree bark were quantified in relatively undisturbed stands of Acadia National Park (ACAD). Four plots were dominated by hardwoods and eight by spruce. To obtain data from upper boles, we climbed four maple trees per plot (eight plots) and four spruce trees per plot (four of the eight plots). We found 85 macrolichen species and 62 bryophyte taxa (60 species, two varieties). Eight macrolichens are newly documented from ACAD. At the state-level, Acadia NP plots were notably species-rich including 15 species not found in 50 other plots in Maine surveyed using the USDA FS Forest Inventory and Analysis Program (FIA) lichen protocol. At the plot-level, the epiphyte flora of spruce-dominated plots differed significantly from that of hardwood-dominated plots, although species richness was comparable. At the tree-level, the epiphyte flora of maple trees was significantly influenced by tree composition within the surrounding stand. Mixed composition of tree species in the stand correlated with higher epiphyte diversity. Cyanolichens were more likely to occur on large hardwood trees in hardwood-dominated plots. Fruticose lichen occurrence was influenced by interactions between tree size, plot and tree species. Using comprehensive tree tally searches in combination with climbing of four maples per plot, we found that we missed an average of 15% of the macrolichen flora in the search area using only the two-hour timed survey required by the FIA protocol. This study serves as an important baseline for detecting future changes in the epiphyte flora of ACAD and further highlights the importance of mature mixed stands to epiphyte conservation in northern forests of eastern North America.

Stand scale effects of partial harvesting and clearcutting on small mammals and forest structure

Documenting responses of small mammals to alternative forestry practices (e.g., clearcutting versus partial harvesting versus no management) facilitates inferences about effects on wildlife communities. We compared abundances of small mammals (voles, mice, and shrews) during four summers among partially harvested mixed coniferous–deciduous stands (52–59% basal area removal, 15 m 2/ha live-tree residual basal area), regenerating commercial clearcuts (11–20-year-old), mature (>12 m tree height) mixed stands, mature deciduous, and mature coniferous stands. Partially harvested stands had significantly greater overall abundance of deer mice ( Peromyscus maniculatus) than mature mixed stands, but abundances of red-backed voles ( Clethrionomys gapperi) and short-tailed shrews ( Blarina brevicauda) were not significantly different. Regenerating clearcut stands had significantly lower abundances of voles and mice relative to mature mixed stands, and ranked low in abundance of shrews. Mature coniferous stands also ranked low in relative abundance of shrews and had the lowest abundance of deer mice relative to other mature stand types. Mature deciduous stands ranked high in abundance of deer mice and had the greatest abundance of short-tailed shrews among all stand types. Despite reduced canopy closure, lower relative density of coniferous trees and saplings, and decreased basal area of deciduous trees and snags, partially harvested stands supported densities of mice and voles comparable to mature mixed-forest types. Forest harvesting practices that retain some structural attributes of mature forests may be beneficial to small mammals and associated predators that utilize mice, voles, and shrews as prey.

Root biomass and rooting profile of naturally regenerated beech in mid-elevation Scots pine woodlands

The natural establishment of shade-tolerant forest species such as beech (Fagus sylvatica L.) occurs in naturally regenerated Scots pine (Pinus sylvestris L.) woodlands that develop on former pastures and cultivated lands. To examine possible effects of underground competition in beech establishment, we studied the root biomass and the rooting profile of 53 mixed Scots pine-natural beech woodlands in French mid-elevation volcanic areas. Stands were arranged along a maturation gradient. Roots were sampled using the root-auger technique (0 to 75 cm depth every 15 cm). In addition, 23 young beeches were uprooted to study the entire root system. Total beech fine-root biomass was closely correlated with most beech aerial characteristics, (e.g., height, diameter and girth), and correlated moderately with tree age. However, it correlated poorly with basic competition indices such as stand density and basal area. Conversely, competition indices including vertical dimensions of competing trees were correlated with the underground biomass, probably as a result of redundancy with beech height. The rooting profile (fine roots, < 5 mm) of beech and pine were quite similar, and did not change significantly along the stand maturation gradient. Beech has a heart-shaped root system while pine is more plate-like and dimorphic. Beech fine-root biomass progressively surpassed pine biomass throughout the soil layers, thus confirming that it is dynamic and competitive in mature mixed stands. The coexistence of the root systems of beech and pine in the same soil layers presumably results in strong underground competition.