Growth Resource Availability Research Articles

Height-to-diameter ratios with temporal and dendro/morphometric variables for Brazilian pine in south Brazil

Height-to-diameter ratios (HD) are an important measure of the stability, density and competition of forest stands. It reflects the vertical growth of the trees, the vulnerability of the forest canopy structure and influences volumetric production. HD ratios vary according to tree size, availability of resources for growth, stand density and species composition. Data were taken from 210 trees and a regression technique of generalized linear models for the HD ratio applicable for forest structure conservation was developed. The objective of this study was to model the HD ratios of dominant and co-dominant trees of Araucaria angustifolia according to morphometric, dendrometric, annual diameter increment, stand density, and age variables in three sites in southern Brazil. The results show that the HD ratio decreases with increasing age, crown area and basal area, and increases with stand density and annual diameter increment. Accuracy of the developed equations was demonstrated by the values of deviation, Bayesian and Akaike criteria. The results are of interest to forest managers since they make decisions about silvicultural operations. Growth continuity and forest production indicate that any intervention should be directed at younger trees of smaller sizes, and that one of the main management factors for stand stability and growth is the formation of the stand and its capture of light.

Trends in growing space efficiency of four boreal forest species based on yield table data

Yield tables are used to identify trends in growing space efficiency (GSE) and to relate GSE to self-tolerance and intraspecific competition. The method is useful when data specifically collected for this purpose are not available. Plonski’s normal yield tables for jack pine (Pinus banksiana Lamb.), paper birch (Betula papyrifera Marshall), trembling aspen (Populus tremuloides Michx.), and black spruce (Picea mariana (Mill.) B.S.P.) are used. An exponential volume–age function was partitioned into volume–area and area–age functions. The exponents of these two components form the B/D ratio, which is used to determine the mode of the stand at a given time, e.g., if B/D is <3/2, then the stand is in area occupation mode, and if B/D is >3/2, then the stand is in area exploitation mode. The dominant mode is the one most responsive to availability of growth resources, showing greater acceleration when resources are plentiful and more rapid deceleration when resources are scarce. Jack pine and paper birch are identified as area occupiers, whereas trembling aspen and black spruce are area exploiters and are therfore self-tolerant. Asymmetric competition was deemed to be present for paper birch throughout the life of the stand on site class I and for trembling aspen on all sites prior to senescence.

Time vs. light: a potentially useable light sum hybrid model to represent the juvenile growth of Douglas-fir subject to varying levels of competition

Substitution of potential useable light sum for time in a commonly used mensurational equation resulted in a better fit to data from a complex vegetation management experiment. The experiment involved Douglas-fir ( Pseudotsuga menzeisii (Mirb.) Franco) as a crop species and a variety of competing species. Site occupancy by competing vegetation varied with time because control operations were intermittently either included or excluded from treatments over a period of 4 years. There were four randomized complete blocks of eight competition control treatments. Potentially useable light sum was estimated using measurements of radiation from a meteorological station that were modified by coefficients representing the ability of the crop plants to use light with varying soil water, vapour pressure deficit, and temperature. Light sums were further reduced by estimated competition for light from competing vegetation. Fits of the model to individual plots within the experiment yielded coefficients that did not differ significantly between competition control treatments, suggesting that the model accounted for significant variations in growth resource availability between treatments. Potentially useable light sum equations provide an integrated link between traditional mensurational modeling and ecophysiological modeling.

Fertile temperate grassland under elevated atmospheric CO 2—role of feed-back mechanisms and availability of growth resources

Human activities are responsible for the strong and very fast increase in the concentration of atmospheric CO 2 over the past 100 years; this trend will continue. An increase in CO 2 is expected to affect significantly grassland vegetation, which covers approximately 70% of agricultural land world-wide and undoubtedly plays an important role in the global C cycle. This review summarises the information about the response of temperate, intensively managed grassland to elevated atmospheric CO 2 under field conditions. 1. The yield response of grassland to elevated CO 2 under field conditions was weaker than expected from short-term laboratory experiments. 2. Different functional types of plant species responded differently to elevated CO 2, leading to changes in the proportion of plant species in grassland. 3. Adapted management of grassland was able to counteract—at least partly—CO 2-induced changes in species proportion. 4. The availability of growth resources other than CO 2 (e.g., N and P) strongly affected the plant’s response to elevated CO 2. 5. Symbiotic N 2 fixation and a strong sink for additionally fixed C (high growth rate, tillering, storage organs) were the functional traits that played a key role in the strong increase in yield under elevated CO 2. 6. An increased input of N through symbiotic N 2 fixation under elevated CO 2 played an important role in maintaining the C/N balance of the legume plant and of entire fertile grassland ecosystems. 7. The yield response to elevated CO 2 changed in the long-term indicating that processes in the soil that responded slowly (e.g., nutrient cycling and sequestration, activity and mass of micro-organisms) gradually adapted to the new environmental conditions. These results demonstrate that the response of ecosystems to elevated CO 2 cannot be deduced from measurements based on individual plants in controlled environments. Long-term experiments in the field where the availability of growth resources is varied, the plants interact with each other and the soil interacts with the plants (feed-back mechanisms) are necessary for predicting the effect of elevated CO 2.

Effects of partial defoliation on carbon and nitrogen partitioning and photosynthetic carbon uptake by two-year-old cork oak (Quercus suber) saplings.

At the end of the growing season in late July, 20-month-old cork oak (Quercus suber L.) saplings were partially defoliated (63% of leaf area) to evaluate their ability to recover leaf area after defoliation. At 18 and 127 days after defoliation, changes in starch and nitrogen pools were determined in leaves and perennial organs, and variations in photosynthetic carbon uptake were investigated. To determine the role of stored nitrogen in regrowth after defoliation, plant nitrogen was labeled in the previous winter by enriching the nutrient solution with 15N. Plants recovered the lost leaf area in 127 days. Although there was remobilization of starch and nitrogen from leaves and perennial organs, the availability of resources for growth in the following spring was not decreased by defoliation. On the contrary, starch concentration in coarse roots was higher in defoliated saplings than in control saplings, presumably as a result of the higher net CO2 exchange rate in newly developed leaves compared with pre-existing leaves.

Effects of site management operations on the nutrient capital of a eucalypt plantation system in South Africa

Synopsis The Karklo of Project is a case study ofthe effects ofintensive site management operations during the interrotational period, on (a) the nutrient capital of the system, and (b) the availability of growth resources (nutrients and water) in a commercial Eucalyptus grandis stand in South Africa. This paper specifically focuses on the nutrient contents in various pools of the system, namely the soil, the forest floor, and the above- and below-ground biomass. The effects of nutrient removal through harvesting operations, slash management or slash burning were examined in relation to estimates of readily plant-available nutrient pools in the system. The removal of individual nutrient elements through harvesting plus slash burning was calculated for a regime ofone planted crop followed by two coppice crops. In this regime, slash burning (if used) and fertilization are normally only implemented immediately before replanting. The combined losses of harvesting and burning (averaged per crop cycle) amounted to 13,25, 11,5 and 3% of the readily available pools for N, P, K, Ca andMg, respectively. The system is thus well buffered against the depletion of most macronutrients over the short term. Despite this fact, the cumulative effect of nutrient removal through successive rotations could add up to substantial amounts over long periods of time. Nutrients removed from the system need to be replenished to ensure sustained productivity in perpetuity. The comparatively large percentage loss off is small in actual quantity (ca. 20 kg ha−1 per crop cycle) and is commonly mitigated to some degree by recommended fertilization practices. Losses ofMg are very small relative to available Mg pools. However, N, K and Ca losses are not replenished under current management regimes and management will need to deal with this to ensure long-term ecological sustainability. Strategies to ensure sustainable supplies of these nutrients are discussed.

Browsing by Moose on Scots Pine in Relation to Plant Resource Availability

The availability of resources for growth is believed to have a significant impact on the chemical defense of plants against herbivores. However, the means by which resource availability affects different plant traits, and the way in which these factors in turn affect diet selection, are not well understood. I addressed the relation between plant biomass, morphology, and tissue nutritional quality and browsing by moose (Alces alces (L.)) on Scots pine (Pinus sylvestris L.). In two experiments nutrient and light availability were manipulated and trees were subsequently exposed to free—ranging moose at feeding stations. Treatments included fertilization, shading, clipping, or root—cutting for 1—2 growing seasons. Treatments had a significant effect on tree height, twig biomass, shoot morphology, carbon/nitrogen ratio, and nitrogen concentration in current—year shoots. Twig biomass and shoot morphology explained most of the variation in per—tree twig biomass consumption by moose, whereas the carbon/nitrogen ratio had a significant impact only when between—treatment differences in biomass were removed. These findings show that variation in resource availability induces changes in a variety of plant traits other than tissue nutritional quality, to which moose respond by adjusting foraging behavior. This may have important implications for plant—animal interactions: the plants' chemical defense could be less effective against herbivores like moose that adjust foraging behavior at a variety of spatial and temporal scales.