Stanley R. Herwitz

Interception storage capacities of tropical rainforest canopy trees

Abstract The rainwater interception storage capacities of mature canopy trees in a tropical rainforest site in northeast Queensland, Australia, were approximated using a combination of field and laboratory measurements. The above-ground vegetative surfaces of five selected species (three flaky-barked; two smooth-barked) were saturated under laboratory conditions in order to establish their maximum interception storage capacities. Average leaf surface interception storages ranged from 112 to 161 ml m−2. The interception storages of bark ranged from 0.51 to 0.97 ml cm−3. These standardized interception storages were applied to estimates of leaf surface area and bark volume for 51 mature canopy trees representing the selected species in the field site. The average whole tree interception storage capacities of the five species ranged from 110 to 5281 per tree and 2.2 to 8.3 mm per unit projected crown area. The highly significant interspecific differences in interception storage capacity suggest that both floristic and demographic data are needed in order to accurately calculate a forest-wide interception storage capacity for species-rich tropical rainforest vegetation. Species with large woody surface areas and small projected crown areas are capable of storing the greatest depth equivalents of rainwater under heavy rainfall conditions. In the case of both the flaky-barked and the smooth-barked species, bark accounted for > 50% of the total interception storage capacity under still-air conditions, and > 80% under turbulent air conditions. The emphasis in past interception studies on the role of leaf surfaces in determining the interception storage capacity of a vegetative cover must be modified for tropical rainforests to include the storage capacity provided by the bark tissue on canopy trees.

Mid-winter stemflow drainage from bigtooth aspen (Populus grandidentata Michx.) in central Massachusetts

Under winter conditions, stemflow drainage in forested ecosystems is often assumed to be a negligible component of the hydrological cycle. This paper reports on mid-winter stemflow drainage from the broadleaved deciduous tree species Populus grandidentata. Stemflow volumes from this species at air temperatures of < 0°C were found to be comparable to rainfall-generated stemflow during summer. Over the three-month period January–March 1993, stemflow ranged from 5.4 to 9.9% of the incident gross precipitation. Expressed as depth equivalents per unit trunk basal area, these stemflow inputs ranged from 1.8 to 4.9 m. These concentrated mid-winter inputs of liquid water to the bases of canopy trees were attributable to: (1) snow interception by the leafless woody frame of each tree; (2) snow retention by glazed ice precipitation associated with the snowfall event; (3) increased temperature at the bark/snow interface caused by the low albedo of the bark tissue; and (4) convergence of snowmelt drainage from steeply inclined upthrust primary branches. The hydrological and ecological significance of liquid water inputs to the forest floor under sub-zero conditions are discussed.

Mortality, Recruitment, and Growth Rates of Montane Tropical Rain Forest Canopy Trees on Mount Bellenden-Ker, Northeast Queensland, Australia

To better understand the physiognomy and dynamics of tropical forest canopy trees, the mortality, recruitment, and growth rates of trees -30 cm DBH were quantified on a montane tropical rain forest hilislope over the 10-yr period 1982-1992. The results indicate that the smaller stature of canopy trees growing on or near ridge-crests of montane rain forests is a consequence of higher turnover rates, not slower growth rates. The annual canopy tree turnover rate of approximately 1.7 percent in the upslope section of the sample area was two times greater than in the downslope section. The DBH growth increments in the upslope and downslope sections also were significantly different (P < 0.05), but it was the upslope trees that grew at the faster rate (upslope = 3.1 mm yr-1; downslope = 2.4 mm yr -). The mean DBH growth increment of 2.7 mm yr-1 for the entire plot is relatively high compared to other montane tropical rain forests. Interspecific variation among the 23 tree species also was notable, with mean DBH increments ranging from 0.4 to 7.8 mm yr-1. Ceratopetalum virchowii and Elaeocarpus ferruginiflorus were the most dominant species in 1982: C. virchowii increased its dominance over the 10-year period with a higher rate of recruitment than mortality and a change in relative importance from 22.7 percent in 1982 to 28.4 percent in 1992; E. ferruginiflorus, in contrast, experienced the most significant change of all the species examined, with a decrease in relative importance from 14.1 percent in 1982 to 5.3 percent in 1992 as a result of its high mortality, its slow growth rates, and its failure to recruit any individuals into the -30 cm DBH size-class; the local demise of this species may be part of a shifting floristic mosaic associated with natural disturbance events or perhaps part of an irreversible trend. It is recommended that more attention be directed to the growth patterns of co-occurring species and the life histories of individual trees to obtain a clearer sense for the long-term dynamics of montane tropical rain forest canopy tree populations.

Episodic stemflow inputs of magnesium and potassium to a tropical forest floor during heavy rainfall events

SummaryStemflow inputs of magnesium and potassium were measured from 57 canopy trees representing eight species under heavy rainfall conditions in two tropical forest sites in northeast Queensland, Australia. In the premontane tropical moist forest site on the Atherton Tableland, the stemflow input per unit trunk basal area of 51 canopy trees was found to be 0.46 g m-2 of Mg2+ and 4.22 g m-2 of K+ for an average wet season rainday of 99 mm. In the wetter montane tropical rainforest site on Mount Bellenden Ker, the stemflow input per unit trunk basal area of six canopy trees was 5.55 g m-2 of Mg2+ and 9.12 g m-2 of K+ for a wet season rainday of 38 mm. These stemflow inputs from single raindays are greater than the mean annual rainfall input and are almost of the same order of magnitude as the mean annual throughfall input of these cations to areas equal to the trunk basal area from which the stemflow was collected. Stemflow cation fluxes of this magnitude are mainly attributable to the funnelling of large quantities of rainwater down the trunks of these canopy trees by their thoroughly wetted, upwardly inclined branches.

Feasibility of Monitoring Coffee Field Ripeness with Airborne Multispectral Imagery

Multispectral images were collected by an unmanned aerial vehicle over a commercial coffee plantation during the 2002 harvest season. Selected scenes were georegistered to a base map and a mosaic of the study area was created. Image segmentation was performed to identify and mask soil, shadow, and cloud pixels. The remaining pixels, representing sunlit canopy, were assumed to be a mixture of four components: green leaf, underripe fruit, ripe fruit, and overripe fruit. Field and laboratory instruments were used to measure the reflectance spectrum of each component. Based on these spectra, a ripeness index was developed for the airborne imagery that involved computing the per-pixel ratio of digital counts in spectral channels centered at 580 and 660 nm. Results were aggregated on a per-field basis. Mean ripeness index per field was significantly correlated with ground-based counts recorded by the grower, and to eventual harvest date. The results suggest that remote sensing methods may provide an alternative, more spatially comprehensive method for monitoring ripeness status and evaluating harvest readiness of this high-value agricultural commodity.

Thematic mapper detection of changes in the leaf area of closed canopy pine plantations in Central Massachusetts

Abstract Remote sensing studies of conifer forests have previously reported that the Thematic Mapper Band 4/Band 3 ratio is positively correlated with regional differences in leaf area index (LAI). Our study was an attempt to determine whether Landsat Thematic Mapper data can be used to detect differences and changes in the LAI of closed canopy pine plantations on a local scale in central Massachusetts. Field measurements of LAI were obtained using locally-derived allometric relationships between leaf area and trunk diameter (DBH). A thinning treatment, which reduced the LAI of one of the larger plantations by more than 25%, resulted in a significant decrease ( P Such a reduction in LAI would demonstrate the limitations of allometric equations for evaluating LAI under conditions in which the relationship between leaf area and DBH may be changing from year to year. It also would explain why no significant relationship ( P > 0.1) was found between the 4/3 ratio and the LAI of the different unthinned plantations which had LAI values ranging from 3.96 to 7.01. We conclude that the TM sensor may be a better guide to moderate changes and differences in the LAI of closed canopy pine plantations at local scales than field measurements involving allometric equations.

LONG-TERM SURVIVORSHIP AND CROWN AREA DYNAMICS OF TROPICAL RAIN FOREST CANOPY TREES

Lateral shading of direct-beam irradiation among neighboring canopy tree crowns in a nonequatorial tropical rain forest canopy was modeled as a function of solar position using a photogrammetric database derived from large-scale color aerial stereopairs (1:1500–1:3000 scale) acquired in 1976. The interception of direct-beam irradiation by the orthogonally projected crown area of each tree was computed at hourly intervals over a full calendar year using a Parameterization model of cloud-attenuated direct-beam availability. The annual totals of intercepted direct-beam irradiation (Ib) ranged from 1.81 to 4.13 GJ·m−2·yr−1. Expressed as a percentage of the available incident direct-beam irradiation, these values ranged from 44% to 100%. Approximately 20% of the sample population intercepted <70% of the available annual direct-beam irradiation. The long-term effects of lateral shading and the intertree differences in Ib were assessed using repeat aerial stereophotography of the same section of forest 18 yr later in 1994 for the determination of the mortality, survivorship, and crown growth of the canopy trees delimited in the 1976 stereopairs. Mortality over the 18-yr period amounted to 27.2%. Based on the lateral shading simulations, the mean annual Ib totals of the survivors and those that died were significantly different (P < 0.001). Approximately 40% of the survivors experienced crown area reductions. Although there was no significant difference in the Ib of survivors with crown growth and those with crown reductions, a relationship was established between Ib and the extent of crown area change. Canopy trees that intercept the most direct-beam irradiation and experience the least lateral shading have higher probabilities of survivorship and significant crown area changes that may be in the form of crown growth or crown reduction. Their laterally shaded neighbors have a lower survivorship probability, and those that survive persist in an inhibited state with limited crown area change. We conclude that the effects of lateral shading are not limited to the margins of treefall gaps and that lateral shading determined by crown position in the uneven upper canopies of nonequatorial tropical rain forests has a detectable effect on the long-term fates of neighboring canopy trees.

Redefining the ecological niche of a tropical rain forest canopy tree species using airborne imagery: long-term crown dynamics of Toona ciliata

Past controlled growth experiments indicate that the seedling and sapling responses of the tropical rainforest canopy tree species Toona ciliata are most consistent with a light-demanding, early successional pioneer. This ecological niche assignment was tested in the mature stage of its life cycle after it achieves a position in the upper canopy. Mortality, survivorship and crown growth rates over the 18-y period 1976-1994 were measured using co-registered repeat airborne stereophotographic coverage of a representative forest stand in northeast Queensland, Australia, where T. ciliata had the fourth highest relative importance in a population of 46 co-occurring canopy tree species. The airborne re-inventory was conducted in a 3.6-ha sample area and limited to only canopy trees. The results were compared with a ground-based inventory of both canopy and subcan- opy trees l10 cm dbh in a 0.5-ha permanent plot. Over the period 1976-1994, there was no mortality and no evidence of decline among T. ciliata conspecifics having crown areas >60 m2 and trunk diameters >30 cm. In the 3.6-ha airborne sample area, more than 85% of T. ciliata survivors experienced positive crown growth, in contrast to only 57% of the other co-occurring canopy trees. Toona ciliatas crown growth rates were highest in the 60-80-m2 crown size class. Upon reaching an upper canopy position, T. ciliata not only persisted as a dominant canopy tree species, but it also achieved some of the largest crown areas (> 100 m2). Toona ciliata mortality in the ground-based plot involved mainly subcanopy trees of 10-30 cm dbh that had not yet assumed a canopy position and were not detectable in the aerial stereopairs. Both the crown and dbh growth rates of T. ciliata indicate enhanced vigour in the later stage of its life cycle. Its long-term survivorship and growth patterns are indicative of a persistent canopy tree species

Floristic diversity and co-occurrences in a subtropical broad-leaved forest and two contrasting regrowth stands in central-west Yunnan Province, China

Many of the natural forested ecosystems that still remain in mainland China are being cleared with potentially detrimental effects on woody plant species diversity on both local and regional scales. The most extensive stand of subtropical broad-leaved forest remaining in China is located in Yunnan Province. In an effort to document the influence of human-induced disturbance on Yunnans woody flora, floristic inventories were conducted in a stand of primary forest and in regrowth stands located in its interior and along its outer margin in the Xujiaba Nature Sanctuary in the Ailao Mountain Range. Of particular interest was the location of the disturbance relative to the primary forest source area. A total of 134 woody plant species representing 74 genera and 43 families were recorded. The floristics of the two regrowth stands were significantly different from each other, with < 10% of their respective floras comprised of co-occurring species. The interior regrowth stand had a higher number of co-occurring species with the primary forest; however, > 40% were still non-co-occurring. The principal families represented in the primary forest and the interior regrowth stand were Aquifoliaceae, Berberidaceae, Fagaceae, Lauraceae, Rosaceae, Smilacaceae, Symplocaceae, Theaceae, and Vacciniaceae. The three dominant species with relative importance values ranging from > 5% to 18% in both the primary forest and the interior regrowth stand were Castanopsis wattii, Lithocarpus jingdongensis, and Symplocos sumuntia. The edge regrowth stands had the lowest species diversity and were dominated by the native pine Pinus yunnanensis, with a relative importance of 24%. The principal families represented in the edge regrowth stand were Betulaceae, Ericaceae, Fagaceae, Myricaceae, Pinaceae, and Theaceae. Only the Fagaceae and Theaceae were well-represented in all three stands. The results of the study document the low species diversity in post-cutting regrowth on the margins of the primary forest as compared with post-cutting regrowth in the forest interior.

Neural Network Algorithm for Coffee Ripeness Evaluation Using Airborne Images

A NASA unmanned aerial vehicle (UAV) was deployed over a commercial coffee plantation during the 2002 harvest season. An on-board digital camera system collected a set of high-resolution surface reflectance images in three spectral bands (580, 660, and 790 nm). An intelligent and robust algorithm operated on the multispectral images to estimate absolute percentages of under-ripe (green), ripe (yellow), and over-ripe (brown) coffee cherries displayed on the canopy surface. The procedure was based on a coupled leaf/canopy radiative transfer model (LCM2), modified to include fruiting bodies as photon scattering and absorbing elements. A neural network (NN) set was trained on simulated data, and then used to invert LCM2 for retrieval of fruit and leaf percentages from empirical canopy reflectance data. A projection technique was implemented to systematically mitigate situations where the observed reflectance data fell outside the NN training set domain and the inversion thus initially rendered non-physical solutions (fruit percentages outside of range 0 to 100%). The algorithm was applied to three study fields representing a broad gradient of mature (ripe plus over-ripe) fruit ranging from 28% to 61%. Correlation between predictions and yield data across all ripeness levels was 0.78, with a mean absolute error of 11% (range 1% to 26%). By comparison, a standard ground-based harvest readiness assessment produced a correlation 0.64 with yield, mean absolute error of 13% (range 5% to 23%). The procedure was designed to operate on a reasonably modest set of a priori specifications and, by coupling with remote sensing, potentially represents an efficient method for monitoring ripeness progression or other agricultural phenomena that alter visible and near-infrared crop canopy reflectance.