Structural response of Caribbean dry forests to hurricane winds: a case study from Guanica Forest, Puerto Rico

Tropical dry forests in the Caribbean have an uniquely short, shrubby structure with a high proportion of multiple-stemmed trees compared to dry forests elsewhere in the Neotropics. Previous studies have shown that this structure can arise without the loss of main stems from cutting, grazing, or other human intervention. The Caribbean has a high frequency of hurricanes, so wind may also influence forest stature. Furthermore, these forests also tend to grow on soils with low amounts of available phosphorus, which may also influence structure. The objective of this study was to assess the role of high winds in structuring dry forest, and to determine whether soil nutrient pools influence forest response following hurricane disturbance. Methods: Over 2000 stems in five plots were sampled for hurricane effects within 1 week after Hurricane Georges impacted field sites in 1998. Sprout initiation, growth, and mortality were analysed for 1407 stems for 2 years after the hurricane. Soil nutrient pools were measured at the base of 456 stems to assess association between nutrients and sprout dynamics. Results: Direct effects of the hurricane were minimal, with stem mortality at \u3c 2% and structural damage to stems at 13%, although damage was biased toward stems of larger diameter. Sprouting response was high . over 10 times as many trees had sprouts after the hurricane as before. The number of sprouts on a stem also increased significantly. Sprouting was common on stems that only suffered defoliation or had no visible effects from the hurricane. Sprout survival after 2 years was also high (\u3e 86%). Soil nutrient pools had little effect on forest response as a whole, but phosphorus supply did influence sprout dynamics on four of the more common tree species. Main Conclusions: Hurricanes are able to influence Caribbean tropical dry forest structure by reducing average stem diameter and basal area and generating significant sprouting responses. New sprouts, with ongoing survival, will maintain the high frequency of multi-stemmed trees found in this region. Sprouting is not limited to damaged stems, indicating that trees are responding to other aspects of high winds, such as short-term gravitational displacement or sway. Soil nutrients play a secondary role in sprouting dynamics of a subset of species. The short, shrubby forest structure common to the Caribbean can arise naturally as a response to hurricane winds

Growth-climate relationships of Pinus strobusin the floodway versus terrace forest along the banks of the Red Cedar River, Michigan

We examined the effects of climate (i.e. temperature, precipitation, moisture index, river discharge) on the radial growth of eastern white pine (Pinus strobus) in two contrasting microhabitats (floodway versus terrace) in relation to an elevational and moisture gradient along the banks of the Red Cedar River, Michigan. We hypothesized that trees growing on the terrace sites would have a greater sensitivity to climatic factors than trees growing in the floodway. Increment cores were sampled and crossdated from dominant and co-dominant trees in the floodway and terrace sites and standardized growth chronologies were developed. Mean sensitivity, standard deviation, percentage of absent rings, and intertree correlation were generally greater for eastern white pine on the terrace compared to the floodway forests. Dendroclimatic relationships were examined with bootstrapped correlation analysis, which indicated that radial growth of eastern white pine in both floodway and terrace sites was negatively associated with summer temperature (i.e. June and July) of the current growing season. Radial growth in both floodway and terrace sites were positively related to current May precipitation, moisture index, and river discharge. Dendroclimatic response of eastern white pine in floodway and terrace sites differed in that the effect of summer moisture stress was more persistent in the terrace sites into later summer (i.e. current July ) whereas floodway sites showed a negative response to prior-year May precipitation and moisture index. Although precipitation and hydrological conditions of the river were generally favorable during the summer months, which appeared to have promoted soil moisture recharge, flooding in early winter (i.e. prior November) had a negative impact on growth in both microhabitats. The effect of winter river discharge was significantly negative in January (t) in the floodway sites compared to the terrace sites.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]

Primary data

The search and selection of suitable regions, sites, species, and trees are fundamentally important in dendrochronological studies. Practically every dendrochronological study states the locality from which the material is taken and the number of tree rings contained in the samples and the chronologies. However, only in dendroecological papers are the principles of site and specimen selection described (e.g., Mueller-Stoll, 1951; Jazewitsch, 1961; Fritts, 1965; Shiyatov, 1973, 1986; Bitvinskas, 1974; Lovelius, 1979). LaMarche et al. (1982) point out the potentials and limits of dendrochronological studies in historical and ecological fields. These depend primarily on the aims and the tasks of the investigator, and their accuracy determines the quality of the tree-ring chronologies obtained. This section focuses on the importance of the sampling strategies for various applications of dendrochronology

Effects of adventitious roots on age determination in Balsam fir ( Abies balsamea

The age structure of balsam fir (Abies balsamea (L.) Mill.) regeneration is frequently used to investigate boreal forest dynamics of North America. Tree ages are usually estimated by counting annual growth rings at the shoot-root interface located above or close to the root system. Inaccurately locating the shoot-root interface could lead to imprecise age determination. In this study, balsam fir seedlings (<2 m height) were harvested in whole from closed forest stands located in the province of Quebec, Canada. Seedling age was determined by (i) counting the number of annual growth rings at the presumed shoot-root interface, and (ii) counting all terminal bud scars from the apex to the base of the hypocotyl (true collar). For all seedlings with adventitious roots, the number of terminal bud scars on the entire trunk was higher than the number of growth rings at the shoot-root interface. The formation of adventitious roots on the belowground trunk was accompanied by a reverse taper phenomenon, i.e., the number of annual growth rings decreased from the presumed shoot-root interface to the true collar. Counting annual growth rings at any level on the trunk of balsam fir seedlings that form adventitious root systems would not be reliable, underestimation's exceeding 20 years are possible and the resulting age structures could lead to erroneous interpretations of regeneration dynamics