Canopy Gap Characteristics Research Articles

Spatial and temporal characteristics of canopy gaps caused by Armillaria root disease and their management implications in lowveld forests of South Africa

AbstractRoadside reconnaissance and aerial photo surveys were used to characterize the frequency and size of canopy gaps caused by Armillaria root disease in 1763 stands of Pinus spp. in the eastern Transvaal, South Africa. Root disease occurred in 290 stands, most of which grew at altitudes 1000 m. Pinus elliottii was the most commonly infected host, followed by P. kesiya, P. roxburghii, P. caribaea, P. taeda, and P. patula. Disease severity (proportion of stand area with gaps) increased rapidly to age 3, remained nearly constant between ages 6–17, increased rapidly again between 17–28, and then decreased abruptly between ages 28–40. Gap incidence (proportion of all stands with gaps) rapidly increased to age 10, after which it remained nearly constant. Host species present in previous stands influenced whether disease developed in current stands.

Canopy Gap Characteristics and Drought Influences in Oak Forests of the Coweeta Basin

Canopy gaps in southern Appalachian mixed—Quercus forest were characterized to assess the impact of the 1985—1988 record drought on patterns of tree mortality in relation to topographic variables and changes in overstory composition. Using permanent transects, we samples 68 canopy gaps within the Coweeta Basin. Among 1—5 yr old gaps, the most common gap type was the 1—yr—old single—tree snag, accounting for 49% of all gaps sampled; 65% of all gaps occurred within 2 yr of the drought peak. Gap area ranged from 40 to 850 m2, averaged 239 m2, with a median of 152 m2. Analysis of 1988 color infrared (IR) aerial imagery yielded a gap formation rate of 0.8 gaps°ha—1°yr—1 in mixed—Quercus stands affecting 2.0% of the area in this forest type in 1988. The most frequent gap—forming species were Quercus coccinea, Q. rubra, and Q. velutina, respectively. Evidence suggests that moisture stress brought on by severe drought increases the susceptibility of Quercus species of the shoe—string fungus Armillaria mellea, which may result in significant shifts in canopy composition in these forests.

Forest development in canopy gaps in old‐growth beech (Nothofagus) forests, New Zealand

Abstract. Tree size and age structures, treefall and canopy gap characteristics, and regeneration responses to treefalls were compared for three stands of old‐growth beech (Nothofagus) forest dominated by N. fusca and N. menziesii on the South Island, New Zealand. Treefall gaps (up to 1000 m2) were most often caused by standing trees killed by drought and/or insect attack, or by trees snapped by wind. The causes of gap formation and the size and age distributions of treefall gaps varied between localities because of spatial and temporal differences in the histories of disturbance. At Fergies Bush where drought‐related dieback had produced many large gaps with standing dead trees, gaps were generally young. Conversely, at Station Creek, small, old gaps formed by bolesnap dominated the disturbance regime. At Rough Creek, gaps of all ages and sizes were found along with an almost complete fern cover, and abundant shrubs and occasional subcanopy hardwood trees.Although overall patterns of regeneration were unrelated to differences in gap size, the relative abundance of N. fusca and N. menziesii varied between localities according to the seemingly minor differences in forest structure and disturbance history described above. Interpretations of regeneration response to gap parameters, therefore, need to account for differences in disturbance history between sites. Differences in the disturbance history between localities will also influence rates of gap closure, and because closure rates are used to estimate forest turnover times, meaningful comparisons of disturbance regimes for different forest types can only be made if this intersite variability is addressed.