Trees In Control Plots Research Articles

Comparing the Structure, Function, Value, and Risk of Managed and Unmanaged Trees along Rights-of-Way and Streets in Massachusetts

Trees provide numerous benefits in urban areas, including improving stormwater retention and filtration, removing gaseous and particulate pollutants from the air, sequestering atmospheric carbon, and reducing ambient temperature. However, trees also pose risks in urban areas. Trees growing near overhead electrical utility lines cause a large proportion of electrical power outages. To mitigate this risk, arborists frequently and sometimes severely prune trees near overhead utilities for clearance and to reduce the likelihood of failure. Ostensibly, urban trees distant from utility lines are not pruned as frequently or severely. This study aimed to (i) assess factors related to both individual trees and the sample populations of trees growing near and away from overhead utility lines, and (ii) determine whether those factors differed between the two groups. In total, 200 utility easement plots and 200 non-utility control plots were distributed in Eversource Energy’s distribution territories, encompassing 2361 trees in total. Diameter at breast height (DBH), crown height and spread, percent crown missing, percent twig dieback, and likelihood of failure were gathered for each tree in the study. These variables were compared individually among study groups, and used as inputs to calculate estimated ecosystem service delivery using USFS iTree Eco v6. Overall, trees in control plots were larger and delivered more ecosystem services, per tree, than trees in utility plots. However, on a population level, trees in utility plots were more populous and delivered more aggregate ecosystem services than those in control plots. Although the aesthetics of utility tree pruning is often debated, there were no differences in likelihood of failure ratings between trees in control and utility plots. These findings may help to frame trees near overhead utility lines, commonly seen as risks or eyesores, as valuable green infrastructure and community assets.

Effects of dry-season irrigation on leaf physiology and biomass allocation in tropical lianas and trees.

Lianas are more abundant in seasonal forests than in wetter forests and are thought to perform better than trees when light is abundant and water is limited. We tested the hypothesis that lianas perform better than trees during seasonal drought using a common garden experiment with 12 taxonomically diverse species (six liana and six tree species) in 12 replicated plots. We irrigated six of the plots during the dry season for four years, while the remaining six control plots received only ambient rainfall. In year 5, we measured stem diameters for all individuals and harvested above- and belowground biomass for a subset of individuals to quantify absolute growth and biomass allocation to roots, stems, and leaves, as well as total root length and maximum rooting depth. We also measured rate of photosynthesis, intrinsic water use efficiency (iWUE), pre-dawn and midday water potential, and a set of functional and hydraulic traits. During the peak of the dry season, lianas in control plots had 54% higher predawn leaf water potentials (ΨPD ), and 45% higher photosynthetic rates than trees in control plots. By contrast, during the peak of the wet season, these physiological differences between lianas and trees become less pronounced and, in some cases, even disappeared. Trees had higher specific leaf area (SLA) than lianas; however, no other functional trait differed between growth forms. Trees responded to the irrigation treatment with 15% larger diameters and 119% greater biomass than trees in control plots. Liana growth, however, did not respond to irrigation; liana diameter and biomass were similar in control and irrigation plots, suggesting that lianas were far less limited by soil moisture than were trees. Contrary to previous hypotheses, lianas did not have deeper roots than trees; however, lianas had longer roots per stem diameter than did trees. Our results support the hypothesis that lianas perform better and experience less physiological stress than trees during seasonal drought, suggesting clear differences between growth forms in response to altered rainfall regimes. Ultimately, better dry-season performance may explain why liana abundance peaks in seasonal forests compared to trees, which peak in abundance in less seasonal, wetter forests.

Perennial flower strips for pest control in organic apple orchards - A pan-European study

In many crops, the intensive use of pesticides causes major problems both for the environment and for natural ecosystem services. Apple is Europe's most frequently produced orchard fruit, requiring high pesticide input to combat the most important apple insect pests, Dysaphis plantaginea (Passerini) and Cydia pomonella (L.). Here we sought to control these pests by promoting natural enemies using sown perennial flower strips. We trialled these in the alleyways of organic apple orchards in seven European countries. Visual assessments over two years revealed a higher number of natural enemies on plant parts, and specifically in D. plantaginea colonies on trees, in flower strip plots than on trees in control plots with standard orchard vegetation. Trees in the flower strip plots recorded a slower D. plantaginea population increase as compared with control plots, resulting in reduced fruit damage after the second fruit drop. Likewise, from 2016–2017, the number of preadult codling moths decreased more in the flower strip plots as compared to the control plots resulting in reduced fruit damage. Our study shows on a wide continental scale that the implementation of perennial flower strips in the alleyways between apple tree rows boosts natural enemies and reduces key apple pests and the associated fruit damage. This supports the role of functional agrobiodiversity as a way to potentially reduce insecticide use in orchards and thus further promote conservation of agrobiodiversity. We also provide suggested plant composition for flower strips adapted to different European countries and recommendations for implementation and management in practice.

Effects of thinning on stand structure and tree stability in an afforested oriental beech (Fagus orientalis Lipsky) stand in northeast Turkey

We studied relationships between stand structure and stand stability according to thinning intensity in an afforested oriental beech stand. Various thinning intensities were applied in sample stands. We sampled eight plots in stands that were lightly thinned, eight plots in heavily thinned stands and eight plots in unthinned stands as a control. Height and diameter distributions of the stands were measured to assess stand structure. We quantified individual tree stability and collective stability. Heavy thinning during the first thinning operation damaged the storied structure of the stand in thicket stage and affected collective structuring ability. While most control plots had multi-storied stands, after light and heavy thinning two-storied structure became more common. Large gaps occurred in the canopy after heavy thinning. On average, nine tree collectives were formed per sampling plot in the untreated stand, seven collectives after thinning in 2008 and four collectives after thinning in 2009. Stable trees accounted for 17 % of trees in control plots, 24 % in lightly thinned plots, and 15 % in heavily thinned plots. Collective stability values were 83 % in control plots, 82 % in lightly thinned plots and 36 % in heavily thinned plots. We conclude that it is necessary to retain collective structuring capacity during thinning operations for sustaining stand stability.

A self-perpetuating bamboo disturbance cycle in a neotropical forest

We investigate a hypothesis for explaining maintenance of forest canopy dominance: bamboo (Guadua weberbaueri and Guadua sarcocarpa) loads and crushes trees, resulting in a self-perpetuating disturbance cycle. Forest inventory data revealed a peculiar pattern of tree form and size class distribution in bamboo-dominated plots within the Tambopata River watershed, Madre de Dios, Peru. Bamboo disproportionately loaded trees 5–29 cm in diameter, and this size class had over seven times more canopy damage than trees in control plots without bamboo. These differences were accompanied by reduced tree basal area and tree density in the 5–29-cm-diameter size class in the presence of bamboo. Elevated tree canopy damage was not apparent for trees ≥30 cm dbh, which are beyond the reach of bamboo. Additional evidence for the impact of bamboo was revealed by an experiment using artificial metal trees. Artificial trees in bamboo-dominated forest plots had nine times higher frequency of physical damage and nine times more plant mass loading as compared with control plots. Our results support the hypothesis that bamboo loading causes elevated physical damage to trees and suppresses tree recruitment, particularly for trees 5–29 cm in diameter.

Decadal-scale fates of [formula omitted] tracers added to oak and pine stands under ambient and elevated N inputs at the Harvard Forest (USA)

We used isotope mass balances to track the fates of ecosystem-scale 15 N tracer additions to control non-fertilized and nitrogen (N)-fertilized plots in oak-dominated hardwood and red pine-dominated pine over nine growing seasons. The plots used in our tracer study are the same as of those used in the Chronic Nitrogen Amendment study (see Magill et al., this volume) at the Harvard Forest in central Massachusetts, USA. Nitrogen tracers were added monthly during growing seasons (April–October) of fertilization years 4 and 5 (1991 and 1992) as either 15 NH 4 or 15 NO 3 to control and to N-fertilized plots (low N treatment, receiving additions of 5 g N m −2 per year as NH 4NO 3). Seven years after the end of 15 N additions (1999), tracer recoveries were highest in organic soil, ranging from 34 to 83% of additions across 15 N ion form, N loading rate and forest type. Mineral soil (0–20 cm depth) was the second largest sink, with tracer recoveries ranging from 15 to 34% of additions. Tree biomass (foliage, woody tissue, plus fine roots) accumulated 7–16% of tracer additions. Patterns of 15 N recoveries after 7 years differed from recovery patterns at the end of the 2-year labeling period. At the end of labeling in 1992, recoveries in tree biomass were higher under chronic N fertilization than under ambient atmospheric N loading (control plots), higher with 15 NO 3 than 15 NH 4 additions, and higher in hardwoods than in pines. Seven years after the end of labeling, recoveries in trees were still higher with 15 NO 3 than with 15 NH 4 labeling, and trees in control plots continued to accumulate 15 N tracers. In contrast, tracer recoveries in trees on the chronically fertilized plots were lower after 7 years than at the end of the labeling period. This was due mainly to transfers of 15 N tracer from leaf and root tissue to other ecosystem pools during the years since labeling. Wood produced during the 2-year labeling period and the 7-year post-labeling interval continued to accumulate 15 N tracers in control and chronically fertilized plots in both forest types. However, recoveries were low in woody tissues (wood formed from 1990 through 1999 plus bark), ranging from 1.1 to 6.1% of 15 N additions across forest types and treatments. Our comparisons of 15 N tracer recoveries at the end of a 2-year labeling period and at 7 years following the end of labeling suggest that soils are the dominant sinks for N deposition on temperate forests and that N does not contribute substantially to enhanced carbon uptake into tree biomass.

Whole-tree biomass and carbon allocation of juvenile trees of loblolly pine (Pinustaeda): influence of genetics and fertilization

To assess the contribution of belowground biomass allocation towards total carbon (C) allocation of two provenances of loblolly pine (Pinus taeda L.), we examined the total biomass allocation of a fast- and slow-growing family from each provenance. Since planting on a xeric, infertile site in Scotland County, N.C., U.S.A., trees in this study have been subjected to one of two nutrient treatments: optimal nutrition or control (no fertilization). Total biomass of 24 (1 tree/family plot × 2 families × 2 provenances × 2 treatments × 3 blocks) 5-year-old (juvenile) trees was harvested in January 1998. Fertilization increased total root, total shoot, and total tree biomass in all families as compared with harvested trees in control plots. Fertilization also increased biomass of coarse-root, woody-root, taproot, stem, branch, and foliar components of families as compared with trees in control plots. Although there were treatment and family differences in standing-crop biomass of the total root, total shoot, total tree, and various individual root and shoot components, the percent biomass (whole-tree) allocation to these tissues remained similar across treatments. Total nonstructural carbohydrate (TNC) analysis indicated some treatment, family, and provenance differences in TNC concentrations and partitioning to starch and soluble sugars. At the time of harvest, TNC concentrations of belowground tissues were much higher than those of aboveground tissues, and enhanced partitioning towards starch in root tissues indicates an important C storage role for belowground tissues at this time. Indeed, more than 90% of the trees starch content was present in root tissue in January. Although constrained by a sample size of three harvested trees per family, this study suggests that biomass allocation on a whole-tree level was similar between fast- and slow-growing families of different provenances of juvenile loblolly pine and was not affected by fertilizer treatment.

Evaluation of Methyl Iodide for Control of Peach Replant Disorder.

Peach replant soils were fumigated with methyl bromide (MB) or methyl iodide (MI) at rates of 392 to 448 kg/ha. In two trials, peach tree growth in fumigated soil or in untreated soil was evaluated by measuring trunk diameter and weight of branches removed by pruning. In both trials, trunk diameter of trees grown in MB- and MI-fumigated plots was greater than trees in control plots (P ≤ 0.01). In both trials, weight of branches pruned from trees grown in fumigated plots was greater than branch weights from trees grown in control plots (P ≤ 0.01). Plots fumigated with MI did not differ from plots fumigated with MB in trunk growth, weight of branch prunings, or reductions in population densities of the nematode Paratylenchus. MI and MB appeared to be equally effective in controlling replant disorder.

Relaxation of an induced defense after exclusion of herbivores: spines on Acacia drepanolobium.

Descriptive and experimental evidence suggests that spine length is an inducible defense, with longer spines being produced by branches experiencing greater levels of herbivory. Here we present results from a replicated, controlled herbivore exclusion experiment in which cattle, wildlife (large mammalian herbivores), and megaherbivores (elephants and giraffes) were independently manipulated. Experimental wildlife barriers virtually eliminated herbivory on Acacia drepanolobium branches at all heights. Megaherbivore barriers reduced herbivory on branches more than 1.75 m from the ground by up to 80%, and reduced herbivory on lower branches by 40%. These patterns of herbivory were matched by patterns of relaxation of spine length that occurred in response to the treatments. After 22 months of herbivore exclusion, the lengths of newly produced spines were 19% shorter on branches protected from large mammal herbivory than on trees in control plots. On low branches, there was a steady increase in spine length from total exclusion plots (shortest spines) to plots with wildlife to plots with both megaherbivores and wildlife (longest spines). On higher branches, new spines were shorter in total exclusion plots and wildlife plots than in plots in which megaherbivores were allowed. This is the first replicated, controlled experimental demonstration that browsing by free-ranging herbivores is associated with greater spine lengths. Examination of trees incidentally protected from herbivory for several years suggests that reduction in spine length in the experimental plots will eventually exceed 70%. Initially slow relaxation of spine length may represent a cautious adaptive strategy in an environment where a given branch is likely to escape herbivory in a given growth season, even when herbivores are present.

Nutritional assessment of a forest fertilisation experiment in northern Sweden by root bioassays

Roots were excised from long-term nitrogen, phosphorus and potassium fertilisation experiments in a Pinus sylvestris plantation in northern Sweden, and tested for their ability to take up 15N, 32P or 86Rb from solutions of ammonium chloride, potassium dihydrogen phosphate and rubidium chloride. High levels of uptake in these tests indicate low nutrient status. At this site, lower uptake rates in the trees from the fertilised treatments showed they had responded to the addition of all three nutrients, although the nitrogen test could not detect a difference in root response between trees from the two higher nitrogen treatments, which, according to other criteria, were high enough to create nitrogen-saturated conditions. There was no evidence from the nitrogen uptake measured that this was affected by phosphorus or potassium fertiliser treatment, suggesting that correcting the supply of these elements did not induce further nitrogen demand. Conversely, trees receiving high nitrogen additions did not show any increased demand for phosphorus or potassium. This is in agreement with data on tree growth and nitrogen retention of the stands. Trees from plots treated with acid 16–21 years previously or lime 21 years previously did not respond differently from trees in control plots, unless nitrogen, phosphorus and potassium fertiliser were also added, when demand for the three nutrients was reduced. The results suggest that, in spite of difficulties in sampling tree roots in an area with a rich ground flora, the method is a useful test of the long-term nutrient status in forest fertilisation experiments.

Keystone species and mangrove forest dynamics: the influence of burrowing by crabs on soil nutrient status and forest productivity

The density of the burrowing crab fauna in a mangrove forest was reduced, using pitfall traps, to test the hypothesis that decreased burrowing would lead to: (1) increased soil sulphide concentrations; (2) altered nutrient concentrations; and (3) decreased forest productivity and growth. Experiments were conducted in Rhizophora-dominated forests in north Queensland, Australia, over a 12-month period. Crabs were trapped and removed from the experimental plots during 1 week each month for a year. Soil chemical and forest growth parameters were measured at monthly intervals in the experimental and appropriate control plots. Over the course of the experiment, soil sulphide and ammonium concentrations increased to levels which were significantly higher in plots from which crabs were being removed in comparison to controls. No differences were observed for either phosphate or nitrate plus nitrite. Cumulative forest growth, as measured by stipule fall, was significantly less in removal plots than in controls. Additionally, trees in the removal plots had significantly less reproductive output than did trees in control plots. These results support the hypothesis that burrowing by crabs is an important process in Australian Rhizophora forests. It appears that burrowing affects soil aeration which in turn affects the productivity and reproductive output of Rhizophora. Knowledge of the ecology of grapsid crabs from other continents, however, is very limited. It remains to be seen if the roles played by grapsid crabs are as important elsewhere as in Australia. This is particularly true for the Caribbean region from which many of our paradigms concerning mangrove forest ecology were developed.