Contemporary Forest Structure Research Articles

Coupled archaeological and ecological analyses reveal ancient cultivation and land use in Nuchatlaht (Nuu-chah-nulth) territories, Pacific Northwest

Indigenous peoples’ legacies of plant cultivation and management can have profound effects on contemporary forest structure and species composition long after cultivation has ceased. Despite rich ethnographic accounts of practices like orcharding and fruit tree management in the Pacific Northwest, archaeological and ecological research documenting these practises have been lacking. To investigate ancient and historical land-use and cultivation in Nuchatlaht (Nuu-chah-nulth) territory, we undertook a multidisciplinary study combining archaeological surveys on Nootka Island and ecological analyses of seven anomalous plant communities found adjacent to former village sites. Fifty-seven archaeological sites were inventoried, and 16 previously recorded sites were updated, including six notable village sites. Intensive botanical surveys were subject to indicator species analysis, NMDS, and ANOSIM analysis, which suggest that three putative orchard sites were highly enriched for culturally important and edible fruit and root plants, such as Pacific crabapple (Malus fusca), saskatoon berry (Amelanchier alnifolia), salmonberry (Rubus spectabilis), and wild rice root (Fritillaria camschatcensis), and are highly distinctive compared to nearby sites and regional floristic patterns. Four shell midden sites were characterized by plant communities distinct from both orchard sites and control sites. Our archaeological and ecological analyses, alongside ethnohistorical data, strongly suggest a pattern of ancient and/or historical cultural landscape modification by Nuchatlaht peoples to produce food-bearing plant communities in their territories. This compliments findings in other literature, and what Indigenous peoples have long told researchers, that plant resources were routinely encouraged and harvested across their inhabited landscapes.

Long-term influence of early human occupations on current forests of the Guiana Shield.

To decipher the long-term influences of pre-Columbian land occupations on contemporary forest structure, diversity, and functioning in Amazonia, most of the previous research focused on the alluvial plains of the major rivers of the Amazon basin. Terra firme, that is, nonflooded forests, particularly from the Guiana Shield, are yet to be explored. In this study, we aim to give new insights into the subtle traces of pre-Columbian influences on present-day forests given the archaeological context of terra firme forests of the Guiana Shield. Following archaeological prospects on 13 sites in French Guiana, we carried out forest inventories inside and outside archaeological sites and assessed the potential pre-Columbian use of the sampled tree species using an original ethnobotanical database of the Guiana Shield region. Aboveground biomass (320 and 380 T/ha, respectively), basal area (25-30 and 30-35m2 /ha, respectively), and tree density (550 and 700 stem/ha, respectively) were all significantly lower on anthropized plots (As) than on nonanthropized plots (NAs). Ancient human presence shaped the species composition of the sampled forests with Arecaceae, Burseraceae, and Lauraceae significantly more frequent in As and Annonaceae and Lecythidaceae more frequent in NAs. Although alpha diversity was not different between As and NAs, the presence of pre-Columbian sites enhances significantly the forest beta diversity at the landscape level. Finally, trees with edible fruits are positively associated with pre-Columbian sites, whereas trees used for construction or for their bark are negatively associated with pre-Columbian sites. Half a millennium after their abandonment, former occupied places from the inner Guiana Shield still bear noticeable differences with nonanthropized places. Considering the lack of data concerning archaeology of terra firme Amazonian forests, our results suggest that pre-Columbian influences on the structure (lower current biomass), diversity (higher beta diversity), and composition (linked to the past human tree uses) of current Amazonian forests might be more important than previously thought.

Structure and Composition of a Dry Mixed-Conifer Forest in Absence of Contemporary Treatments, Southwest, USA

Dry mixed-conifer forests in the Southwest occupy an important ecological and hydrological role in upper watersheds. In the absence of reoccurring fire and silvicultural treatments over the last 50 years, we quantified forest structure and composition on prevailing north and south aspects of a dry mixed-conifer forest in southcentral New Mexico using mixed models and ordination analysis in preparation for an experiment in ecological restoration. Results indicated overstory and midstory were dominated by Douglas-fir (Pseudotsuga menziesii) and shade tolerant/fire intolerant white fir (Abies concolor) with interspersed mature aspen on north aspects, and Douglas-fir and Southwestern white pine (Pinus strobiformis) on south aspects. Ponderosa pine (Pinus ponderosa), which was historically co-dominant with Douglas-fir on north and south aspects, was subdominant on south aspects and almost entirely absent on north aspects. Regeneration was dominated by white fir saplings and seedlings on north aspects while ponderosa pine was completely absent. South aspect saplings and seedlings were characterized by Douglas-fir and Southwestern white pine, but almost no ponderosa pine. Ordination analysis characterized the effect of aspect on species composition. Understanding contemporary forest structure and composition is important when planning for desired future conditions that are to be achieved through ecological restoration using silvicultural techniques designed to foster resilience.

Assessing intra- and inter-regional climate effects on Douglas-fir biomass dynamics in Oregon and Washington, USA

While ecological succession shapes contemporary forest structure and dynamics, other factors like forest structure (dense vs. sparse canopies) and climate may alter structural trajectories. To assess potential sources of variation in structural trajectories, we examined proportional biomass change for a regionally dominant tree species, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), across vegetation zones representing broad gradients in precipitation and temperature with 3510 forest inventory plots in Oregon and Washington, USA. We found that P. menziesii biomass change decreased with P. menziesii biomass stocks and increased with P. menziesii density, remaining positive in older stands only in the wet and warm vegetation zone. Within two of the vegetation zones, biomass change was greatest in warm and wet environments. In dry vegetation zones, positive P. menziesii biomass change responses to initial canopy cover and canopy cover change (i.e., increases with cover loss and decreases with cover gain) indicated shifts in forest structure. Variation in P. menziesii biomass dynamics within and between vegetation zones imply multi-scale climatic controls on forest structural trajectories for P. menziesii and highlight the potential for continued atmospheric carbon sequestration in warm and wet forests of the Pacific Northwest for both young and old forests, given that future climatic conditions support similar forest dynamics.

Forest Structure and Fire History at Lake Arcadia, Oklahoma County, Oklahoma (1820–2014)

Evidence indicates that the structure of Oklahoma Cross Timbers forests are in transition due to changing climate, land-use patterns, and fire suppression efforts. However, only a handful of studies have addressed the history of fire across the Oklahoma Cross Timbers landscape. This research adds to the body of literature by studying the contemporary forest structure and fire history at Lake Arcadia in Oklahoma County, Oklahoma. Results demonstrate that post oak ( Quercus stellata Wangenh.) and blackjack oak ( Q. marilandica Munchh.), two common species in Oklahoma Cross Timbers, dominate the forest. However, several mesophytic tree species are found in the overstory as well as the sapling layer of the forest. A total of 25 fire events (mean fire interval = 4.14 years) were documented during the 20 th century using fire-scar analysis of Q. stellata trees and remnant wood (stumps, snags, recently dead trees). High fire frequencies in the early to mid-20 th century corresponded to the recruitment of Q. stellata and Q. marilandica . Wet conditions (PDSI > 0) during the late 20 th century and no fires after 1985 corresponded to the recruitment of non-oak, mesophytic species at the study site. The results of this study suggest that changes in fire frequency and moisture availability are contributing to changes in tree density and species composition at the study site.

Quantifying Ancient Maya Land Use Legacy Effects on Contemporary Rainforest Canopy Structure

Human land use legacies have significant and long-lasting ecological impacts across landscapes. Investigating ancient (>400 years) legacy effects can be problematic due to the difficulty in detecting specific, historic land uses, especially those hidden beneath dense canopies. Caracol, the largest (~200 km2) Maya archaeological site in Belize, was abandoned ca. A.D. 900, leaving behind myriad structures, causeways, and an extensive network of agricultural terraces that persist beneath the architecturally complex tropical forest canopy. Airborne LiDAR enables the detection of these below-canopy archaeological features while simultaneously providing a detailed record of the aboveground 3-dimensional canopy organization, which is indicative of a forest’s ecological function. Here, this remote sensing technology is used to determine the effects of ancient land use legacies on contemporary forest structure. Canopy morphology was assessed by extracting LiDAR point clouds (0.25 ha plots) from LiDAR-identified terraced (n = 150) and non-terraced (n = 150) areas on low (0°–10°), medium (10°–20°), and high (>20°) slopes. We calculated the average canopy height, canopy openness, and vertical diversity from the LiDAR returns, with topographic features (i.e., slope, elevation, and aspect) as covariates. Using a PerMANOVA procedure, we determined that forests growing on agricultural terraces exhibited significantly different canopy structure from those growing on non-terraced land. Terraces appear to mediate the effect of slope, resulting in less structural variation between slope and non-sloped land and yielding taller, more closed, more vertically diverse forests. These human land uses abandoned >1000 years ago continue to impact contemporary tropical rainforests having implications related to arboreal habitat and carbon storage.

Fire history and tree recruitment in the Colorado Front Range upper montane zone: implications for forest restoration

Forests experiencing moderate- or mixed-severity fire regimes are presumed to be widespread across the western United States, but few studies have characterized these complex disturbance regimes and their effects on contemporary forest structure. Restoration of pre-fire-suppression open-forest structure to reduce the risk of uncharacteristic stand-replacing fires is a guiding principle in forest management policy, but identifying which forests are clear candidates for restoration remains a challenge. We conducted dendroecological reconstructions of fire history and stand structure at 40 sites in the upper montane zone of the Colorado Front Range (2400-2800 m), sampled in proportion to the distribution of forest types in that zone (50% dominated by ponderosa pine, 28% by lodgepole pine, 12% by aspen, 10% by Douglas-fir). We characterized past fire severity based on remnant criteria at each site in order to assess the effect of fire history on tree establishment patterns, and we also evaluated the influence of fire suppression and climate. We found that 62% of the sites experienced predominantly moderate-severity fire, 38% burned at high severity, and no sites burned exclusively at low severity. The proportion of total tree and sapling establishment was significantly different among equal time periods based on a chi-square test, with highest tree and sapling establishment during the pre-fire-suppression period (1835-1919). Superposed epoch analysis revealed that fires burned during years of extreme drought (95% CI). The major pulse of tree establishment in the upper montane zone occurred during a multidecadal period of extreme drought conditions in the Colorado Front Range (1850-1889), during which 53% of the fires from the 1750-1989 period burned. In the upper montane zone of the Colorado Front Range, historical evidence suggests that these forests are resilient to prolonged periods of severe drought and associated severe fires.

Assessing the Representativeness of the Oldest Permanent Inventory Plots in Northern Arizona Ponderosa Pine Forests

Abstract A network of permanent plots established between 1909 and 1913 (the Woolsey plots) contains the oldest measured data in northern Arizona ponderosa pine forests. These forest inventory data offer a unique opportunity to reconstruct pre‐settlement reference conditions, as well as detect and quantify changes in southwestern forest structure and composition. However, the selection of plot locations in the early 1900s followed a subjective nonrandom approach. To assess the applicability, or inference space, of results obtained from these historical plots, we compared their environmental characteristics (terrestrial ecosystem unit [TEU, based on a U.S. Forest Service (USFS) ecological classification system], site index, elevation, insolation index, and soil parent material) as well as contemporary forest structure (trees per hectare, basal area, and quadratic mean diameter) with two large inventory samples: USFS Forest Inventory and Analysis (FSFIA) and Arizona State Land Department Continuous Forest Inventory (AZCFI). Analytical methods included multivariate permutation tests, ratios of variance, and Kolmogorov–Smirnov two‐sample tests. Results indicated that the Woolsey plots (1) were neither historically nor contemporarily representative of the entire study area because of environmental and current forest structural differences with respect to the FSFIA and AZCFI and (2) may be considered historically representative of their corresponding TEUs. Our study supports the use of TEUs for defining the applicability of information obtained from the Woolsey plots.

Comparison of Historical and Contemporary Forest Structure and Composition on Permanent Plots in Southwestern Ponderosa Pine Forests

Abstract We compared historical (1909–1913) and contemporary (1997–1999) forest structure and composition on 15 permanent plots in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests of Arizona and New Mexico. We used the same sampling methods as in the early 1900s and compared stand density, diameter distributions, species composition, and broad age classes from the two periods. Stand density (trees ≥9.14 cm dbh) significantly (P < 0.001) increased on plots from an average of 77.4 trees per plot (s = 49.9) at plot establishment in 1909–1913 to 519.1 trees per plot (s = 252.3) at remeasurement in 1997–1999. Basal area significantly (P < 0.001) increased from 8.0 m2 per plot (s = 3.5) to 28.5 m2 per plot (s = 10.1). Contemporary tree diameter distribution shifted toward smaller size classes as demonstrated by a significant (P = 0.001) decrease in quadratic mean diameter from 38.5 cm (s = 7.5) in 1909–1913 to 28.6 cm (s = 7.1) in 1997–1999. Broad age classes yielded an average of 61.5 (s = 49.5) residual live trees classified as “blackjack” ponderosa pine (P. ponderosa <150 years) and 13.3 (s = 11.9) “yellow pine” (P. ponderosa ≥150 years) in 1909–1913. In 1997–1999, 416 live trees (s = 229.6) were “blackjack” and 57.2 (s = 28.5) trees on average were “yellow pine.” Twelve of the 15 plots were not invaded by other tree species (remained pure ponderosa pine type), while composition shifted slightly on three plots toward more shade-tolerant and fire-intolerant species. Ninety-one percent of the historically (1909–1913 or older) mapped tree structures (live trees, snags, logs, stumps, etc.) were relocated, which suggested that the forest reconstruction field techniques are reliable within 10%. Dramatic increases in tree densities may represent an increased potential for bark beetle epidemics and stand replacing wildfire over large areas in the Southwest. FOR. SCI. 50(2):162–176.