Daniel Mailly

Modelling forest ecosystem net primary production: the hybrid simulation approach used in forecast

Abstract In order to evaluate the impacts of alternative stand-level management scenarios on long-term site productivity, forest resource managers need ecologically based forest growth models. The forecast forest ecosystem management simulation model combines the traditional bioassay modelling approach with process-based simulation modelling to provide a method of projecting future forest biomass yield as well as a variety of other ecosystem variables and social values under a range of management conditions. A review of the hybrid simulation approach to modelling forest ecosystems is provided, and the representation of stand-level net primary production and nutrient cycling in forecast is described. The major driving function in the model (shade-corrected foliage nitrogen efficiency), the concept of site quality, and the simulation of site quality change are discussed. The value of an accurate definition of the state of the simulated ecosystem at the start of a run is emphasized, and the use of the ecostate ( state of the eco system, as generated by forecast ) file in this process is described. Limitations of the forecast modelling approach are reviewed.

Advances in spatial, individual-based modelling of forest dynamics

Abstract Many individual-based models of forest dynamics lack spatial complexity. Although, in certain cases, spatially simple models may not be substantially inferior to spatially complex models, advances in vegetation science indicate potential weaknesses, particularly the lack of consideration of propagule availability in horizontal space, and varying patch (or canopy gap) dimensions. Models with vertical and horizontal spatial complexity can address these issues, but, thus far, evidence that they outperform patch (or gap) models is limited. Comparison of projections from models that differ only in their spatial complexity is needed to address the effects of propagule availability in space, spatial pattern of canopy tree mortality, and spatial resolution.

“Without bamboo, the land dies”: Biomass, litterfall, and soil organic matter dynamics of a Javanese bamboo talun-kebun system

Abstract The biomass, litterfall, and soil organic matter dynamics during a complete bamboo talun-kebun rotation cycle were studied in West Java, Indonesia. This cycle consisted of 1 year of mixed species vegetable cropping (kebun) after the removal of bamboo, followed by 1 year of cassava, and 4 years of bamboo fallow (talun): a total cycle length of 6 years. In general, fruit and pod biomass constituted the highest percentage (38–68%) of the total crop biomass of 8.4 Mg ha −1 accumulated during the first year cropping. Cassava yielded a total of 4.6 Mg ha −1 of roots and tubers during the second year cropping from a total biomass accumulation of 6.7 Mg ha −1 . An experimental second year of cassava cropping without any fertilization caused a decline in the yield of roots and tubers to 60% less than the comparable value for the first year of cassava. Weeds, which reached a maximum biomass value of 1.8 Mg ha −1 at the end of the first year cropping, were all but eliminated from the later stages of the bamboo talun. The total biomass of bamboo increased with increasing age and reached 76.6 Mg ha −1 after 6 years. The distribution of total bamboo biomass between above- and below-ground components also varied with age. At 16 months after bamboo harvest, above-ground biomass accounted for 6% of the bamboo total mass. By the end of the 4-year bamboo fallow, 6 years after the bamboo harvest, 59% of the bamboo biomass was above-ground. In the final year of the bamboo talun stage, total above-ground litterfall was estimated at 4.7 Mg ha −1 , while the forest floor mass was 13.5 Mg ha −1 . There was an increase of approximately 7 Mg ha −1 of soil organic matter in the surface 25 cm of soil during the 4-year fallow. The historical, sustained success of the system with minimal external inputs of fertilizer appears to be closely related to the growth habit and biogeochemical characteristics of the bamboo, i.e. its rapid biomass accumulation, the accumulation of its litter, and the extremely high biomass of fine roots. This study provides scientific support for the traditional saying of the local farmers: “without bamboo, the land dies”.

‘Without bamboo, the land dies’: A conceptual model of the biogeochemical role of bamboo in an Indonesian agroforestry system

Abstract The ‘talun-kebun’ system consists of a 6–7 year management cycle in which a 4–5 year fallow period of perennial clump bamboo is alternated with 2 years of food crop production. Clearcutting, raking the forest floor and slash into piles for burning, and hoeing the soil to a depth of 25 cm reduces the vigour of the bamboo to the point at which it poses no competitive threat to the first year of planted food crops. These crops are (typically) cucumber, bitter solanum and hyacinth (pole) beans. Ash from the burned slash piles, plus some animal mamure and application of NPK fertiliser (only recently), are used to increase the production of these vegetables. In spite of these nutrient additions, the fertility of the upper soil layers declines during the first year, and the field is planted to cassava (a less nutrient-demanding root crop) the second year after clearcutting. After 2 years of cultivation, bamboo regrowth and declining soil fertility prevent continued food cropping. The field is abandoned and permitted to revert to an unmanaged stand of bamboo for 4–5 years. The historical success of the system appears to be based largely on the ‘nutrient pumping’ action of the bamboo, the slow decomposition of its silica-rich litter, and the extremely high biomass of bamboo fine roots. Studies reported earlier and in subsequent papers support the interpretation that the bamboo recovers much of the nutrients leached deeper into the soil profile during the 2 years of cropping and deposits them at or near the soil surface as above-ground litter and dead fine roots. The biogeochemical role of bamboo in sustaining the productivity of this agroforestry system reflects the rural farmers saying: ‘without bamboo, the land dies’.

'Without bamboo, the land dies': nutrient cycling and biogeochemistry of a Javanese bamboo talun-kebun system.

Abstract The accumulation and removal of biomass, and the inventory of five major nutrients (N, P, K, Ca, and Mg) in plants, litterfall, forest floor, and in the mineral soil were quantified at various stages of a bamboo talun-kebun agroforestry system (West Java, Indonesia). Data were collected in order to explain the biogeochemistry of the system over an entire rotation cycle. This cycle consisted of 1 year of mixed species vegetable cropping (kebun) after the removal of bamboo, followed by a year of cassava cropping, and 4 years of bamboo fallow (talun): a total cycle length of 6 years. The accumulation of five major nutrients in live plant biomass during a complete talun-kebun rotation cycle was 787, 134, 692, 218, and 248 kg ha−1 for N, P, K, Ca, and Mg, respectively. The overall nutrient removals accounted for approximately 51%, 48%, 55%, 52%, and 56% of N, P, K, Ca, and Mg accumlated in the live plant biomass, respectively. Accumulation of N, P, K, Ca, and Mg in the forest floor peaked at the end of the mature talun stage, i.e. when the forest floor mass accumulation reached its maximum. Fertilization was an important input during the first year of cropping: it accounted for 63%, 145%, 100%, 188%, and 225% of N, P, K, Ca, and Mg output, respectively, during this period. Cassava cultivation decreased the content of exchangeable K in the mineral soil during the second year of cropping. Available P in the surface 5 cm of mineral soil increased slightly after clearing and hoeing, but decreased to 92% and 75% of its original value in the first and second year cropping stages, respectively. About 220 kg N ha−1 was lost from the system over the 6-year rotation, a difference between input and output to and from the system which reflected changes in the soil N compartment. Soil data on P, Ca, and Mg did not suggest a current problem of declining availability of these elements on the site, although the use of an NPK fertilizer does suggest concern over the availability of K. Finally, soil leaching losses were very small in comparison to losses in harvest removals.

Disturbance and succession in a coniferous forest of northwestern North America: simulations with DRYADES ,a spatial gap model

Abstract In this paper we describe a model of forest development that has been adapted for use in a coniferous forest of northwestern North America. The simulator, dryades , is a spatial gap model used to examine the effects of disturbances of different types, sizes, and frequencies in mature Douglas fir dominated forests on zonal sites of the Coastal Western Hemlock drier maritime (CWHdm) subzone of British Columbia. Simulation exercises were carried out to test the following (not mutually exclusive) hypotheses in relation to forest compositional variations observed within the study area today: (1) disturbance-mediated succession can accelerate the conversion of early successional forest communities dominated by pioneer tree species (e.g. Douglas fir) to later successional associations; (2) when present in the canopy, long-lived, tall, pioneer species such as Douglas fir strongly influence stand dynamics, regardless of the type of canopy disturbance; (3) silvicultural practices that emulate the autogenic natural disturbance regime of small canopy gaps will maintain a late-successional character at the stand level. Model simulations of forest successional dynamics suggested that: (1) repeated, small-scale disturbances such as light windstorms or small patch harvesting can accelerate the rate of tree species replacement by accelerating forest succession; (2) large-scale disturbances such as infrequent severe fires set back succession to an earlier seral stage dominated by Douglas fir; (3) clear-cutting without Douglas fir planting accelerates forest succession towards a western hemlock/western redcedar forest; (4) on mesic sites in the CWHdm subzone, Douglas fir will not dominate stand dynamics, unless there are infrequent, severe fire disturbances; (5) the creation of small openings through partial harvesting did not allow shade intolerant species to re-establish naturally and dominate the forest stand dynamics. It was concluded that modelled successional dynamics and composition of these forests are largely a function of the initial competitive interactions and the relative shade tolerance of species involved.

Forest floor and mineral soil development in Casuarina equisetifolia plantations on the coastal sand dunes of Senegal

Abstract Forest floor and mineral soil samples were collected from the interdune depressions of 6-, 8-, 17-, and 34-year old Casuarina equisetifolia Forst. & Forst. plantations growing on the coastal sand dunes of Senegal. The accumulation of organic matter as well as all mineral elements in the forest floor except sodium followed a linear pattern. The thickness of the litter layer increased from 4.2 to 8.0 cm. Forest floor biomass increased up to 120.3 Mg ha−1; an average increase of 3.3 Mg ha−1 year−1. Nitrogen in the forest floor accumulated up to 1567 kg ha−1; an average increase of 45 kg ha−1 year−1. Calcium, aluminum, magnesium, iron, potassium and phosphorus in the forest floor accumulated at 6.8, 3.7, 1.8, 1.3, 0.49 and 0.25 kg ha−1 year−1, respectively. In the mineral soil, total phosphorus and exchangeable calcium decreased with plantation age. Nitrogen in the mineral soil increased by 30 kg ha−1 year−1 while organic matter in the mineral soil increased by 61.5 kg ha−1 year−1. The pH of the mineral soil decreased from 7.3 to 6.5. As a result of a particular combination of species characteristics and ecological conditions, C. equisetifolia plantations on these coastal sand dunes appear to accumulate forest floor organic matter at rates comparable to those found in boreal and subalpine forests. A nitrogen to phosphorus ratio in the litter layer of 164:1 indicates that decomposition processes are strongly limited by phosphorus. This suggests that introducing strains of nitrogen-fixing bacteria capable of fixing even greater amounts of nitrogen would do little to improve soil fertility. Since there was no sign that accumulation of either organic matter or mineral nutrients had reached steady-state, a minimum of a 34 year rotation would seem justified if soil improvement is the primary management objective. Since the overwhelming majority of the organic matter and nutrient capital is located in the forest floor and upper 2 cm of mineral soil, proper management of this fragile layer following harvest will be extremely important if the benefits realized in the first rotation are to be capitalized on during subsequent rotations.

An analytical framework to assist decision makers in the use of forest ecosystem model predictions

The predictions from most forest ecosystem models originate from deterministic simulations. However, few evaluation exercises for model outputs are performed by either model developers or users. This issue has important consequences for decision makers using these models to develop natural resource management policies, as they cannot evaluate the extent to which predictions stemming from the simulation of alternative management scenarios may result in significant environmental or economic differences. Various numerical methods, such as sensitivity/uncertainty analyses, or bootstrap methods, may be used to evaluate models and the errors associated with their outputs. However, the application of each of these methods carries unique challenges which decision makers do not necessarily understand; guidance is required when interpreting the output generated from each model. This paper proposes a decision flow chart in the form of an analytical framework to help decision makers apply, in an orderly fashion, different steps involved in examining the model outputs. The analytical framework is discussed with regard to the definition of problems and objectives and includes the following topics: model selection, identification of alternatives, modelling tasks and selecting alternatives for developing policy or implementing management scenarios. Its application is illustrated using an on-going exercise in developing silvicultural guidelines for a forest management enterprise in Ontario, Canada.

A comparison of mortality rates between top height trees and average site trees

Abstract• Although comparisons between methods of selecting trees for site index estimates are well documented in the literature, little is known on mortality rates of different canopy tree cohorts used for that purpose.• This study was initiated to test the hypothesis that the mortality rates of top height trees are lower than those of codominants only or a combination of codominant and dominant trees. To test this hypothesis, we used records from a network of permanent sample plots in Québec and studied the fate of different cohorts of site trees for five different species.• Our results did not show clear evidence of lower mortality rates for top height trees. Instead we found that depending on the species, top height trees have lower (Populus tremuloides, Pinus banksiana), higher (Picea mariana, Abies balsamea) or equal mortality rates (Betula papyrifera) than codominant trees or codominant and dominant trees combined.• These results suggest a tendency for shade intolerant species to maintain lower top height tree mortality rates over time when compared to shade tolerant species. In the latter case, it is also shown that spruce budworm epidemics (Choristoneura fumiferana) did not change the pattern of mortality rates of site trees of A. balsamea.Résumé• Bien que des études comparatives sur les méthodes servant à déterminer l’indice de qualité de station sont disponibles dans la littérature, on connaît peu de choses sur les taux de mortalité de différentes cohortes d’arbres utilisées à cette fin.• Cette étude a été initiée dans le but de tester l’hypothèse selon laquelle les taux de mortalité de arbres dominants sont plus faibles que ceux des arbres codominants ou de ceux d’une combinaiso d’arbres codominants et dominants. Afin de tester cette hypothèse, nous avons utilisé la base de don nées des placettes-échantillons permanentes du Québec et nous avons suivi la destinée de différente cohortes d’arbres indicateurs de la station pour cinq espèces différentes.• Nos résultats n’ont pas montré de façon tranchée que les arbres dominants ont un taux de mortalit inférieur à celui des autres cohortes à l’étude. Nos résultats démontrent plutôt que selon les espèces, les arbres dominants ont un taux de mortalité inférieur (Populus tremuloides, Pinus banksiana), suérieur (Picea mariana, Abies balsamea) ou égal (Betula papyrifera) au taux de mortalité des arbre codominants ou à une combinaison d’arbres codominants ou dominants.• Ces résultats suggèrent que les taux de mortalité des espèces classées intolérantes à l’ombre ont ten dance à demeurer plus faibles dans le temps lorsqu’on les compare aux taux de mortalité des espèce tolérantes à l’ombre. Pour ces dernières, les résultats démontrent de plus que l’effet des épidémie de la tordeuse des bourgeons de l’épinette (Choristoneura fumiferana) n’ont eu aucun effet sur le patrons de mortalité des différentes cohortes d’arbres indicateurs de la station en ce qui concern A. balsamea.

Spatial and temporal heterogeneity of forest site productivity drivers: a case study within the eastern boreal forests of Canada

Forest productivity is driven by a suite of direct climatic and non-climatic factors that are transient or permanent. The kind of productivity driver and the nature of their effects vary by species, and scale dependencies potentially complicate these relationships. This study explored productivity-driver relations in eastern Boreal Canada and determined spatial effects in productivity control when expressed with stand dominant height at a reference age (site index). Data from 4,217 temporary sample plots obtained from boreal mixedwood and conifer bioclimatic domains, and with varied species composition, were used in this study. A single-level global model that assumes equal sensitivities across spatial scales was calibrated and compared with three alternative models reflecting different hypotheses on possible spatial heterogeneities. Alternative models were calibrated by plot-level soil deposit types (microscale), landscape dominant deposits (mesoscale) and bioclimatic domains (macroscale). A marked difference between the global and alternative models was observed, suggesting that a single global model does not sufficiently reflect existing heterogeneity in productivity-driver relationships. A combination of macro- and microscale models provided the best explanation of site index. Results further showed that site index is mainly driven by species composition (complementarity effects of aspen and jack pine compositions) and stand diameter structural diversity effects. It is concluded that successional changes, more than direct climatic effects, drive productivity.