Canopy Gap Dynamics Research Articles

Inferred causes of tree mortality in fragmented and intact Amazonian forests

In fragmented tropical landscapes, among the most pervasive causes of ecological change are edge effects – diverse ecological alterations associated with the abrupt, artificial boundaries of forest fragments (Laurance & Bierregaard 1997, Lovejoy et al. 1986, Turner 1996). A striking edge effect in fragmented Amazonian forests is chronically elevated tree mortality (Ferreira & Laurance 1997, Laurance et al. 1998a). Large (> 60 cm diameter) trees are especially vulnerable to fragmentation, dying three times faster within 300 m of edges than in forest interiors (Laurance et al. 2000). Elevated tree mortality alters canopy-gap dynamics, promotes a proliferation of disturbance-adapted successional species (Laurance et al. 1998b), reduces above-ground biomass (Laurance et al. 1997), and accelerates litter production (Didham & Lawton 1999, Sizer et al. 2000) and carbon cycling (Nascimento & Laurance, in press).

Canopy gap characteristics and their implications for management in the temperate rainforests of southeast Alaska

In the coastal temperate rainforests of southeast Alaska, much progress has been made in describing landscape-level natural disturbances and formulating management systems that emulate those disturbances. Little is known, however, concerning canopy gaps, the dominant form of natural disturbance in the region. During June–August, 1991–1993, we characterized canopy gap patterns and dynamics at three sites in the western hemlock/blueberry/shield fern plant association in the northern portion of the Tongass National Forest. Forest area in canopy gaps ranged from 5.8 to 12.6% and averaged 8.7%. The proportion of forest area in expanded gaps ranged from 18.1 to 43.9% and averaged 27.4%. Gap and gapmaker (tree whose death or crown displacement results in the creation or expansion of a canopy gap) characteristics were generally similar among sites. The majority of canopy gaps were <50 m 2 in area, had a D/ H ratio <0.50, were created from the death of one or two gapmakers, and had experienced gap expansion. The majority of expanded gap areas were <200 m 2. Gapmakers were usually snapped, had recently died (<20 years ago), and tended to be larger in diameter than surrounding overstory trees. Species composition of gapmakers was similar to surrounding overstory trees. A substantial amount of gap infilling takes place between 20 and 80 years following tree death, but gaps, or portions of gaps, can persist for >80 years. Forest turnover time was estimated to range from 230 to 920 years, and average 575 years. Canopy residence time was estimated to range between 210 and 840 years, and averaged 525 years. To emulate canopy gap dynamics in the plant association studied, forest managers should: (1) maintain a small proportion of a stand in openings within an otherwise undisturbed canopy; (2) use a combination of single tree selection and small group selection systems; (3) re-enter stands every 20–80 years; (4) select larger than average diameter crop trees in proportion to the species composition of the stand; (5) minimize soil disturbance and (6) select crop trees during re-entry so that the creation of new gaps and the expansion of old gaps is accomplished in approximately equal proportions.

Forest canopy and community dynamics in a temperate old‐growth evergreen broad‐leaved forest, south‐western Japan: a 7‐year study of a 4‐ha plot

Summary Forest canopy gap and community dynamics were studied in a 4‐ha permanent plot of an old‐growth evergreen broad‐leaved forest dominated by Castanopsis cuspidata var. sieboldii and Distylium racemosum in the Tatera Forest Reserve, Tsushima Islands, south‐western Japan. The forest was affected by a powerful typhoon in 1987 and was monitored from 1990 to 1997. In 1990, all woody stems ≥ 5 cm diameter at breast height (d.b.h.) in the plot were identified, mapped and marked, and the state of 1600 5 m × 5 m contiguous quadrats used to locate canopy gaps. Gaps occupied 17.1% of the plot, which contained 4494 tree and shrub stems (total basal area 63.48 m2 ha−1). Gaps were re‐censused in 1997 and both marked and newly recruited (≥ 5 cm d.b.h.) stems were recorded in 1992 and 1997. Over 7 years the rates of canopy gap formation and closure were 0.72% year−1 and 1.61% year−1, respectively, mortality and recruitment rates were 0.97% year−1 and 0.99% year−1, and the rates of loss and gain in basal area were 0.95% year−1 and 0.83% year−1. The mortality of stems was size‐dependent, with those in middle size classes having the lowest rates. Mortality of stems was lower in canopy and higher in the understorey, while the proportion of stems killed by disturbances increased with height. Stems that died during the 7 years were predominantly located in newly created gaps, whereas stems were recruited into both established and new gaps. Deciduous broad‐leaved species were largely restricted to gaps that remained open throughout the study. Both composition and structure of the forest changed in response to disturbance‐related effects on canopy dynamics.

A crown model for simulating long-term stand and gap dynamics in northern hardwood forests

Evaluation of ecosystem management alternatives in forests will require new or revised models capable of simulating the development of multi-aged stands managed on long rotations and with unconventional stand structures. In this paper we describe the development and testing of an individual tree, crown-based model (CANOPY) designed to simulate canopy gap dynamics and stand structural changes in mature and old-growth northern hardwood forests dominated by Acer saccharum. The model was calibrated with data from 63 plots in managed and unmanaged stands, with sample trees ranging in age from 17–311 years. For A. saccharum, R 2 values ranged from 0.76 to 0.81 for prediction of basal area increment, 0.45–0.50 for crown radial increment, and 0.63–0.79 for height increment. Equations using field-measured crown size and crown competition variables provided only slightly better predictions than conventional mensurational variables such as DBH and plot stocking level. Use of the model for long-term (250 year) projections of cumulative DBH and crown radius provided a good match to largely independent size-age trends in the data base, but total height appeared to be moderately overestimated for trees >100 years old. Both the field data and simulations suggest that basal area increment of individual trees does not decline with age in these species but actually increases up to the observed maximum of 300 years, which is consistent with nearly linear diameter-age trends often reported for shade-tolerant species. Lateral crown growth of trees with exposed crown margins, however, showed curvilinear decreasing trends with age. These findings suggest that the common assumption of constant radial closure of canopy gaps by border trees could potentially overestimate rates of gap closure and underestimate the probability of successful gap capture by saplings in multi-aged stands.

Spatial Ecology: Physical Approach to Biological Pattern Formation.

In animal and plant populations, local interactions between individuals generate some unique and global spatial patterns. For example, trees competing for light and nutrient with their neighbors in limited area show clumpy spatial distribution rather than random distribution. Here we introduce spatial patterns observed in forests and propose the models which describe their growing mechanisms. We focus on the wave regeneration patterns in subalpine forests, canopy-gap dynamics in a neotropical forest and fluctuating and synchronized reproduction in Beech forests. Theoretical analysis based on lattice models and CMLS was effective at describing characteristic interaction with neighbors and to reproduce observed spatial patterns.

Temporal variation in the woody understory of an old‐growth Fagus‐Acer forest and implications for overstory recruitment

Abstract. Changes in woody vegetation were examined over eight years, using a 1.05‐ha permanent plot in which the location of every shrub and tree &gt; 1m height was mapped. There was little change in the overstory vegetation, as expected for an old‐growth forest. Much greater change occurred in the understory, primarily related to a 40 % increase in density. Differences occurred among species in the under‐story, as Acer saccharum and Prunus serotina increased and Fraxinus americana and Fagus grandifolia decreased. Canopy gap dynamics are implicated in differences among species in the establishment and growth of individuals in the understory and their recruitment into the overstory. It is concluded that because understory is temporally variable, overstory recruitment from the understory may take different courses at different times in the same forest.

Stand Structure in Subalpine Forests of Yosemite National Park, California

Abstract Variation of seedling densities and diameter-class distributions with site condition is examined for 5 coniferous tree species sampled in 30 stands between 2400 and 3300 m elevation in Yosemite Park, California. There is an apparent tolerance ranking from mountain hemlock and red fir (high tolerance) through lodgepole pine (intermediate) to whitebark and western white pine (low tolerance). Diameter curves for each species vary in form across environmental gradients, from stable, persistent forms (reverse-J and multimodal) on optimal sites to random forms on marginal sites. Multimodal diameter structure is common among populations in Sierran subalpine forests. In this climatically rigorous setting, interannual variability of conditions affecting seedling survival and growth rates may combine with canopy gap dynamics to yield stable diameter curves punctuated by discrete episodes of establishment, release and growth. For. Sci. 34(4):1047-1058.

Light gaps and long-term seedling performance of a Neotropical canopy tree (Dipteryx panamensis, Leguminosae)

Tropical tree regeneration results from a complex interplay of biotic and abiotic factors: the actions of seed dispersers, seed predators, pathogens, and herbivores influence the distribution patterns of seedlings within an environment that is heterogeneous with respect to the light, water, and soil nutrients required for eventual growth to the canopy. In a study of the canopy tree Dipteryx panamensis (Pitt.) Rec. & Mell (Leguminosae) on Barro Colorado Island, Panama, De Steven & Putz (1984) found that seedling recruitment in most years was limited by mammalian predation on the large, 4-cm long seeds and that firstyear seedling growth and survival were strongly light-dependent. They hypothesized that Dipteryx regeneration required the establishment of a population of seedlings tolerant of understorey suppression while awaiting canopy gap formation and that high seed predation prevented such establishment on Barro Colorado Island. Continuation of observations for six years has now provided long-term data on differential seedling performance that suggests how canopy gap dynamics may influence Dipteryx regeneration. Methods. The tropical moist forest of Barro Colorado Island, Panama (90 09' N, 790 51' W) has been described extensively by Croat (1978). The area receives approximately 2600 mm of rainfall annually, with a distinct dry season during the 4-5 months from late December through April. Dipteryx panamensis is widely distributed on the island, but is more abundant in secondary forest areas that were extensively cleared about 100 years ago. De Steven & Putz (1984) provide a general description of its life history. Experimental microenvironments were selected to span a gradient in light availability. In the initial experimental design (described in De Steven & Putz 1984), seedlings germinated in three field sites in May 1981 were transplanted