Effects Of Site Quality Research Articles

The Effects of Site Quality on Breeding-Site Fidelity in Bobolinks

Grâce a une experience de manipulation du succes de producteur, les effets de ce dernier sur la fidelite au site de reproduction sont examines. De plus l'importance relative de la mortalite et de la dispersion est evaluee en ce qui concerne les patterns de la fidelite au note chez Dolichonyx oryzivorus

Allometries, biomass stocks and biomass allocation in the thermophilic Spanish juniper woodlands of Southern Spain

The principal objective of this study was to investigate the variations of allometric relationships, biomass stocks and biomass allocation in a Spanish juniper thermophilic community (Juniperus thurifera var. hispanica Mill.) in response to two levels of woodland maturity: mature woodlands, which are situated in shallow stony soils with trees over 140years old and low tree density, and young woodlands, with trees under 100years old growing in deeper soils (generally, abandoned farmland). Branch- and tree-level allometric models were fit from measurements carried out on branches, stems and roots in 42 felled trees. Although age and site are confounded for this juniper community, it is expedient to utilize site-specific equations because the two woodlands showed distinct growth patterns as a result of their very different soil qualities and ages. At the branch level, the relationship was matched for foliage biomass depending on the site. At the tree level, site location significantly affected variables in allometric relationships that were not strictly cumulative (i.e., leaves, branch wood and fine-root biomass). Goodness of fit was improved by including the relative height of the first live whorl (pruning effect) as an additional predictor of crown and coarse root biomass. The young woodland supported more biomass stock across all components due to better soil. Biomass allocation measured in stems, coarse roots and fine roots was significantly higher in the mature woodland, although the young woodland did accumulate more dry mass in the crown. Differences in biomass allocation may be explained by both the age and strategies of J. thurifera to maximize nutrient and water capture for survival in poor soils (site quality effects). Our results also showed that, in mature woodlands, this species accumulates one of the smallest biomass stocks cited for temperate mature conifer stands (7.6Mgha−1) but has a high root to shoot ratio (0.43) as a consequence of growing in poor soil conditions.

Patterns and monitoring of Sesia apiformis infestations in poplar plantations at different spatial scales

Poplar plantations are expanding worldwide but little is known about the hornet clearwing moth, Sesia apiformis, one of their most severe pests. Thirty-two poplar plantations of 1-214 clone were sampled in Spain, according to a factorial design combining stand age, site condition and understorey management to investigate the main drivers of S. apiformis habitat selection at both tree and stand level. In each plantation, one pheromone trap was activated during the flight season to test the correlation between captures and percentage of attacked trees. The proportion of other poplar forests in surrounding landscapes was calculated and used as a covariate in predictive models of trap catches. There were significantly more attacked trees in older stands. In young stands, the percentage of infested trees increased with the percentage cover of understorey vegetation. There was no significant effect of site quality on the rate of infestation and no difference in tree height, diameter or crown condition between attacked and un-attacked trees within each stand, suggesting that S. apiformis could behave as primary pest. We hypothesized that the critical stage in the life cycle of the moth was the first instar larvae, which may benefit from protection of deep bark cracks in older stands and understorey vegetation in younger stands. We observed a positive correlation between trap capture and percentage of attacked trees in a radius of 100 m around the trap. The regression of trap catches against percentage of attacked trees was improved when the area of other poplar plantations within a distance of 600 m was incorporated in the model. This suggests that surrounding poplar stands may act as sources of immigrating moths in monitored stands. Our findings confirm that S. apiformis should be considered as a potential threat to poplar plantations and that pheromone trapping provides a suitable monitoring tool.

Thinning and site quality influence aboveground tree carbon stocks in yellow-poplar forests of the southern Appalachians

Little information exists regarding the effects of intermediate stand management activities (e.g., thinning) on C storage. This lack of information has created uncertainty regarding trade-offs between the benefits observed following thinning and C storage. Using long-term growth data, this study examines the effect of thinning on C storage while controlling for the effects of site quality in yellow-poplar ( Liriodendron tulipifera L.) forests throughout the southern Appalachian Mountains. In 1960, one hundred and eighteen 0.1 ha plots were established in yellow-poplar forests throughout the southern Appalachians and subsequently thinned to a randomly assigned residual basal area (RBA) (square metres per hectare). Carbon storage increased through time across all levels of RBA. RBA had a long-term effect on C storage with greater C storage occurring at greater RBA. On average-quality sites, thinning to 30 m2·ha–1 stored 84% more C than thinning to 10 m2·ha–1. At no time did plots with progressively lower RBA store more C than plots with progressively higher RBA. The results from this study provide information about the effects of intermediate silvicultural disturbance on C dynamics of the aboveground live tree pool in a complex landscape and may be used to inform decisions regarding trade-offs between active management and C storage.

The effect of site quality on economically optimal stand management

This paper proposes a discrete-time type timber harvesting model for simultaneously determining (i) the optimal quantity of seedlings to be planted, (ii) the optimal quantities of timber harvested by thinnings, and (iii) the optimal rotation age. With the help of Microsoft Excel Solver, a generalized reduced gradient algorithm, numerical examples are developed to evaluate the impact of the variations in the quality level of a forest site on the optimal harvest strategy. It is shown that the level of optimal rotation age and optimal quantity of seedlings to be planted can individually exhibit non-monotonicity to the increase in site quality.

The effect of site quality on growth efficiency of upper crown class Picea rubens and Abies balsamea in Maine, USAPublication 3046 of the Maine Agricultural and Forestry Experiment Station.

The influence of site index on growth efficiency was studied for 411 dominant and codominant Abies balsamea (L.) Mill. and Picea rubens Sarg. from 10 sites across Maine, USA. Young A. balsamea (n = 204) were from stands precommercially thinned 15–20 years ago and ranged in site index from 18.4 to 24.3, while the older P. rubens (n = 207) were from stands that were not precommercially thinned and ranged in site index from 13.1 to 17.8. We hypothesized that site index positively influences growth efficiency. The results showed that volume increment – leaf area relationships and growth efficiency increased significantly with site index for A. balsamea but were unaffected by site index for P. rubens. A monotonic decreasing pattern of growth efficiency over increasing leaf area was found for both species. When standardized per unit site index, growth efficiency behaved nonlinearly for both species.

Short- and long-term consequences of individual and territory quality in a long-lived bird

Site-quality is a major determinant of fitness but its effect can be confounded by individual quality, a relationship that has been little studied in large, long-lived vertebrates. The fitness effects of quality estimates depend on the assumption of co-variation between individual and territory quality and can be framed as five working hypotheses: no effect on fitness, exclusive effect of individual quality, exclusive effect of site quality, and independent or interactive effects of the two. We explored such a framework using a medium-sized raptor, the black kite Milvus migrans, as a model species. Individual and territory quality co-varied, but the strength of the relationship varied across different estimates of individual quality (age, body size, or mass residuals). Short-term production of fledglings was related to the independent effects of both individual and territory quality. However, longer-term production of recruits was related solely to territory quality. The disappearance of individual quality effects over the long-term may be caused by antagonistic selective pressures acting during different stages of the life cycle. Our results contribute to a growing appreciation of the long-term fitness-benefits of advantages experienced in early life and highlight the importance of a long-term perspective in studies assessing the effects of individual and territory quality. In our case study, prioritizing sites for conservation on the basis of territory quality may be a feasible pathway to maintain the viability of the population. However, scenarios where such a method could be inefficient have been previously reported, suggesting caution in its application. More studies are needed to understand the generality of the efficiency of priority-setting approaches based on site quality.

Making good choices with variable information: a stochastic model for nest-site selection by honeybees

A density-dependent Markov process model is constructed for information transfer among scouts during nest-site selection by honeybees (Apis mellifera). The effects of site quality, competition between sites and delays in site discovery are investigated. The model predicts that bees choose the better of two sites more reliably when both sites are of low quality than when both sites are of high quality and that delay in finding a second site has most effect on the final choice when both sites are of high quality. The model suggests that stochastic effects in honeybee nest-site selection confer no advantage on the swarm.

Wetland plant decomposition under different nutrient conditions: what is more important, litter quality or site quality?

Plants in nutrient poor environments are often characterized by high nutrient resorption resulting in poor litter quality and, consequently, slow decomposition. We used oligotrophic, P-limited herbaceous wetlands of northern Belize as a model system, on which to document and explain how changes in nutrient content along a salinity gradient affect decomposition rates of macrophytes. In 2001 we established a nutrient addition experiment (P, N, and N&P) in 15 marshes of a wide range of water conductivities (200–6000 μS), dominated by Eleocharis spp. To determine what is more important for decomposition, the initial litter quality, or site differences, we used reciprocal litter placement and cellulose decomposition assay in a combined “site quality” and “litter quality” experiment. Our prediction of the positive effects of P-enrichment on decomposition rate due to both the quality of litter and the site was confirmed. The site effect was stronger than the litter quality although both were highly significant. Strong site quality effect was apparently the result of more active decomposer community in P-enriched plots as supported by finding of higher microbial biomass in litter decomposing there. The strong effect of site quality on decomposition was further confirmed by the cellulose assay. The cellulose decomposition was significantly slower at high salinity sites indicating lower decomposer microbial activity. Litter nutrient N and P content and nutrient ratios were well correlated with decomposition with the best fit found for log C/P. At C/P mass ratio of >4000 decomposition processes were extremely slow. We hypothesize that in a long run, the increased decomposition will compensate the increase in primary production resulting from increased nutrient loading and there will be no differences in accumulation of organic material between the controls and nutrient enriched plots.

Sawfly (Hym., Diprionidae) outbreaks on Scots pine: effect of stand structure, site quality and relative tree position on defoliation intensity

From 1997 to 2001, Finland has experienced its largest-ever documented outbreak of Diprion pini L. (500 000 ha). We investigated—in four affected areas—the effects of site quality, stand structure and relative tree position on outbreak dynamics during two consecutive years (1999–2000). Most of the variation in outbreak intensity, as measured by defoliation intensity, was accounted for by variables pertaining to tree size, indicating a preference for more mature trees. However, we also found elevated and systematic defoliation of younger stands. Tree species composition, age difference with surrounding stands, stand area, stand openness and soil characteristics are secondary to the tree size variables in explaining the defoliation intensity, and often had ambiguous effects. As for the common assumption linking outbreaks to shallow, well-drained and unproductive soils, our data only suggest such a link on the level of pine forest vulnerability on a landscape level. As for the various tree canopy strata, we found only in young stands significant differences in defoliation intensity between them, with the dominant trees most affected. This has implications for forest management, because these trees, now undergoing the highest growth losses due to defoliation, normally benefit as trees of the future from thinning activities.

Sawfly (Hym., Diprionidae) outbreaks on Scots pine: effect of stand structure, site quality and relative tree position on defoliation intensity

From 1997 to 2001, Finland has experienced its largest-ever documented outbreak of Diprion pini L. (500 000 ha). We investigated—in four affected areas—the effects of site quality, stand structure and relative tree position on outbreak dynamics during two consecutive years (1999–2000). Most of the variation in outbreak intensity, as measured by defoliation intensity, was accounted for by variables pertaining to tree size, indicating a preference for more mature trees. However, we also found elevated and systematic defoliation of younger stands. Tree species composition, age difference with surrounding stands, stand area, stand openness and soil characteristics are secondary to the tree size variables in explaining the defoliation intensity, and often had ambiguous effects. As for the common assumption linking outbreaks to shallow, well-drained and unproductive soils, our data only suggest such a link on the level of pine forest vulnerability on a landscape level. As for the various tree canopy strata, we found only in young stands significant differences in defoliation intensity between them, with the dominant trees most affected. This has implications for forest management, because these trees, now undergoing the highest growth losses due to defoliation, normally benefit as trees of the future from thinning activities.

Effect of site quality and shading on sprouting patterns of holm oak coppices

Sprouting is its main regeneration mechanism of holm oak ( Quercus ilex) forests after disturbance. This study analyzes the variability of the sprouting ability of holm oak in plots located in the lower and upper parts of the slope (as a factor determining site quality in the study area), and with or without shading (two different shade conditions produced by cutting and removal (or not) of burned stems after a fire). Results obtained in this study show that position in the slope (which indicates, at least partially, site quality) is a key factor on size differentiation of sprouting holm oak individuals. Thus, individuals of lower-position plots are higher and larger than those of upper-position plots, and these differences between plots increase through time. Shading of sprouting stools has no effect on stool height growth, but affects crown surface, with a significant increase in full-light stools compared to shaded ones. Although initial rapid growth in height has been considered a key factor determining competitive advantages after disturbance, our results suggest that the pattern of horizontal occupation of space is also a fundamental trait to explain medium- and long-term holm oak coppice structure. Although in holm oak, the persistence of the root system after disturbance has been used to explain the vigorous growth rates of sprouting individuals, in this study, pre-fire size of individuals correlated poorly with the size of the stool after disturbance. This result suggests that some variables considered in this study, such as stool height, are more dependent on other factors which are variable at the stand level.

CRYPTIC DENSITY DEPENDENCE: EFFECTS OF COVARIATION BETWEEN DENSITY AND SITE QUALITY IN REEF FISH

The importance and strength of density dependence continues to engender debate because of its central importance to population dynamics and regulation. Here, we show how confounding effects of site quality can mask strong effects of density dependence. In particular, we explore spatiotemporal variation and covariation among (1) densities of newly settled coral reef fish (Thalassoma hardwicke), (2) environmental characteristics, and (3) the strength of density-dependent mortality. Environmental features of patch reefs were spatially and temporally variable and influenced density-dependent survival. Higher-quality sites (i.e., reefs possessing features that yield greater numbers of recruits at any given settlement level) received greater settlement, and this relationship masked the operation of density dependence when variation in quality among sites (or times) was not distinguished (a common approach in many observational studies of density dependence). Our work illustrates how spatiotemporal covariation in settlement density and site quality can obscure patterns of density dependence at larger scales, contributing to a phenomenon we call “cryptic density dependence.” Acknowledging patterns and consequences of covariance may alter the way we study population dynamics, especially of marine organisms, where the link between processes that affect settlement and post-settlement survival remains relatively poorly understood. Corresponding Editor: J. R. Bence.

Effects of site quality and season of clearcutting on upland hardwood forest composition 38 years after harvest

This study is an examination of the effects of site quality and season (summer and winter) of clearcutting 38 years after harvest in upland central hardwood stands at a location in Ohio. Comparisons are made with data collected 18–20 years after harvest. Mesophytic stands dominated by mixed hardwoods and red maple developed on good sites (black oak ( Quercus velutina Lam.) site index >23 m at reference age 50) regardless of harvest season. On medium sites (black oak site index 18–23 m) summer clearcutting produced oak-hickory dominated stands while winter clearcutting produced a more equal mixture of oak-hickory, mixed hardwoods, and red maple. The oak-hickory composition in the overstory of these stands could be predicted from potential crop trees identified at age 18–20 years. Red maple continued to represent a major component of the overstory in all treatment combinations, but is decreasing in diameter growth and crown dominance. It is unlikely that red maple will dominate the overstory of the stands studied unless released.

Conditioning a distance-dependent competition index to indicate the onset of inter-tree competition

Data from a loblolly pine ( Pinus taeda L.) spacing trial were used to investigate relationships between a distance-dependent competition index (CI) and the inflection age of sigmoidal single-tree cumulative basal area curves. Inflection ages increased with increasing initial growing space (GS), consistent with the hypothesis of maximum usable GS. Competition intensity as measured by the CI was generally smallest at a given point in time for trees with large inflection ages, but the trend varied by planting density. CI values at the inflection age also varied with planting density. The CI was modified so that it gave a constant CI value at the inflection age, on average, across all planting densities. Effects of site quality were accounted for to a limited degree, but the range of sites was narrow in the spacing trial. The modified CI should be useful as an absolute measure of competition independent of spacing.

Site quality effects on post‐fire regeneration of Pinus brutia forest on a Greek island

Abstract. Natural stands of Pinus brutia were compared to burned areas after a great fire in 1985 on the island of Thasos, North Greece, in relation to site quality effects on the success of natural regeneration and understorey vegetation. The number of seedlings in the natural stands of P. brutia was 1124/ha against 3188/ha in the burned area. In both cases natural regeneration was successful. Under the canopy of P. brutia forests the predominant shrubs were Quercus coccifera and vPhillyrea latifolia. A high percentage (up to 40%) of the total area was covered by these species. In the burned areas, 12 yr after the wildfire of 1985, Cistus incanus and C. salvifolius played a significant role in the survival of P. brutia seedlings. These species had covered the burned area long before the pine seed germination.

A height increment equation for young ponderosa pine plantations using precipitation and soil factors

A height increment equation was used to determine the effects of site quality and competing herbaceous vegetation on the development of ponderosa pine seedlings ( Pinus ponderosa var. scopulorum Engelm.). Study areas were established in 36 plantations across northwest and west-central Montana on Champion International Corporation’s timberland (currently owned by Plum Creek Timber Company). Site quality indices used in the equation were available water index (available water capacity multiplied by the natural logarithm of annual precipitation) and site index (SI) of the previous stand. Three-year height increment was modeled as a function of tree size, vigor, and competition by using available water index (AWI) and SI separately as site quality indicators in the same equation form. Comparison of the two equations suggest that soil factors in combination with precipitation data may be a useful alternative to traditional tree-based site quality indices in predicting height increment of young stands where site index is not known or is poorly estimated.

The process-based stand growth model Formix 3-Q applied in a GIS environment for growth and yield analysis in a tropical rain forest.

Managing tropical rain forests is difficult because few long-term field data on forest growth and the impact of harvesting disturbance are available. Growth models may provide a valuable tool for managers of tropical forests, particularly if applied to the extended forest areas of up to 100,000 ha that typically constitute the so-called forest management units (FMUs). We used a stand growth model in a geographic information system (GIS) environment to simulate tropical rain forest growth at the FMU level. We applied the process-based rain forest growth model Formix 3-Q to the 55,000 ha Deramakot Forest Reserve (DFR) in Sabah, Malaysia. The FMU was considered to be composed of single and independent small-scale stands differing in site conditions and forest structure. Field data, which were analyzed with a GIS, comprised a terrestrial forest inventory, site and soil analyses (water, nutrients, slope), the interpretation of aerial photographs of the present vegetation and topographic maps. Different stand types were determined based on a classification of site quality (three classes), slopes (four classes), and present forest structure (four strata). The effects of site quality on tree allometry (height-diameter curve, biomass allometry, leaf area) and growth (increment size) are incorporated into Formix 3-Q. We derived allometric relations and growth factors for different site conditions from the field data. Climax forest structure at the stand level was shown to depend strongly on site conditions. Simulated successional pattern and climax structure were compared with field observations. Based on the current management plan for the DFR, harvesting scenarios were simulated for stands on different sites. The effects of harvesting guidelines on forest structure and the implications for sustainable forest management at Deramakot were analyzed. Based on the stand types and GIS analysis, we also simulated undisturbed regeneration of the logged-over forest in the DFR at the FMU level. The simulations predict slow recovery rates, and regeneration times far exceeding 100 years.

Factors affecting site productivity of a Costa Rican secondary rain forest in relation to Vochysia ferruginea, a commercially valuable canopy tree species

We estimated site productivity and its variation in a 28-year-old secondary rain forest in Florencia, San Carlos, Costa Rica, in relation to the dominant tree species, the commercially important Vochysia ferruginea. Thirty-six sample plots (20×20m2) were installed in such a way as to cover the whole range of substrate variation at the site. The stand was assumed to be even-aged and of dominant height, estimated as the mean total height of the four tallest Vochysia trees in each plot, used as a measure of site productivity. Intra-plot coefficients of variation of total height of these four trees were <20%, indicating homogeneous conditions within plots in terms of site productivity and phytosanitary state. Of the dominant trees, however, 8% were found to have partially shaded crowns, which could lead to a subestimation of dominant height. For this reason, estimations of dominant height using two of the four trees per plot (these having fully illuminated crowns) were also developed. Dominant height of Vochysia was significantly correlated with mean plot canopy height and basal area of all species, and with its own basal area. Soil variables significantly correlated with dominant height were, at soil depth 0–12cm, clay(%), organic matter(%), P, Fe (all negatively correlated) and Cu (positively correlated). Adjusted multiple regression models of dominant height on soil variables were fitted by stepwise regression (Forward method). For four trees per plot, the best fit was obtained using P, Mn, percent organic matter and percent clay as independent variables (R2=79.5%, S.D. 1.8m). For two trees with fully illuminated crowns, best fit was obtained from a model using the same variables except P. R2 was lower for this latter model (74.4%), but the S.D. was also lower (1.2m). Dominant height appears to be a potentially useful indicator of site productivity in neotropical secondary forests of similar ages, although it appears important, in mixed forests, to use crown variables to aid in the definition of dominant trees. There may be an important effect of site quality on production of timber in such forests, and such effects should be taken into account in the development of models of stand dynamics, growth and yield.

The effect of site quality on soil respiration rates in a 30 year-old Japanese cedar (Cryptomeria japonica) plantation

The effect of site quality on soil respiration rates in a 30 year-old Japanese cedar (Cryptomeria japonica) plantation